No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Breeding System and Habitat Effects on Fitness Components in Three Neotropical Costus (Zingiberaceae)
Abstract
All species are self-compatible, and require a treefall gap for germination and establishment. Self-pollination resulted in lower seed output in all species; this difference was significant for Costus allenii and C. laevis. Seedling growth of selfed, outcrossed and naturally-pollinated Costus allenii, C. laevis and C. guanaiensis in sun and shade habitats in the greenhouse was unaffected by breeding system, but significantly affected by habitat, with reduced growth in shade. Selfed progeny had the lowest biomass in all treatments, with inbreeding depression for growth ranging from 8-25% compared to out-crossed performance. Reduced growth and greater variation in growth for selfed, as compared to out-crossed, progeny are consistent with the hypothesis that inbreeding depression in these species results from homozygosity of rare, deleterious alleles which are not expressed in the heterozygous state. Relative biomass production varied more between sun and shade habitats for selfed, than outcrossed or naturally-pollinated progeny, suggesting that increased homozygosity following inbreeding reduces genotypic versatility.-from Author
... 8). An increasing number of studies have measured inbreeding depression for fitness traits expressed early in the life cycle, such as seed mass, seed set, abortion rate, and germination (Schemske 1983;Shykoff 1988;Stevens 1988;Stevens and Bougourd 1988;Jolls and Chenier 1989;Kalisz 1989;Karron 1989;Krebs and Hancock 1990;Fenster 1991). A smaller number of studies have measured the expression of inbreeding depression through a more extended course of the life cycle (Schoen 1983;Kesseli and Jain 1984;Sakai et al. 1989;Dudash 1990;Holtsford and Ellstrand 1990;Schmitt and Ehrhardt 1990;Agren and Schemske 1993;Willis 1993;Wolfe 1993). ...
... For many of the individual traits studied (seed mass, proportion of viable seeds, germination, gmax, flowering age and number of flowers in the high-fertilizer environment, and number of flowers and A max in the low-fertilizer environment), inbreeding depression was not expressed to the same degree in all maternal families. Similar variation among families was found in S. salicaria, S. globosa (Sakai et al 1989), and several other species (Schemske 1983;Kalisz 1989;Dudash 1990;Agren and Schemske 1993). Some of these differences among families may result from the field microhabitat of the maternal parents and the community environment of seedlings before transplanting.Sakai et al. (1989)suggested that hermaphroditic plants of S. salicaria may vary in the amount of selfing they typically undergo, possibly because of genetic differences in the degree of protandry. ...
... Inbreeding depression was greater in the field than the greenhouse or garden plot, where the field was considered the harshest environment, based on plant mortality and decreased water availability (Dudash 1990). Inbred progeny of three Costus species showed increased inbreeding depression (as reduced aboveground biomass) in shade, compared to progeny grown in the sun, where shade was considered poorer habitat (Schemske 1983). Inbreeding depression in Impatiens capensis was measured at different plant densities (leading to different levels of interspecific competition) and was greatest when plants from cleistogamous and chasmogamous seeds were grown at high density in competition with one another (Schmitt and Ehrhardt 1990). ...
We compared inbreeding depression in hermaphroditic Schiedea lydgatei and its gynodioecious sister species, S. salicaria, to infer the level of inbreeding depression in their common ancestor. With measurements of selfing rates, this information can be used to assess the importance of inbreeding depression in the evolution of breeding systems in S. lydgatei and S. salicaria. Morphological and physiological characters related to fitness were compared for inbred and outcrossed S. lydgatei in high- and low-fertilizer environments in the greenhouse. Seed mass, number of seeds per capsule, germination, survival, biomass, number of flowers, and age at first flowering were compared for inbred versus outcrossed progeny. We also measured inbreeding depression in maximal rates of photosynthetic carbon assimilation and stomatal conductance to water vapor, traits that affect fitness through their influence on plant carbon balance and water-use efficiency (ratio of carbon gain to water loss). All traits except number of seeds per capsule in parents and survival showed inbreeding depression, with the magnitude depending on family and environment. High inbreeding depression is likely in the ancestor of S. lydgatei and S. salicaria, indicating that, with sufficiently high selfing rates, females could spread in populations. Hermaphroditism in S. lydgatei is probably favored by low selfing rates. In contrast, the evolution of gynodioecy in S. salicaria apparently has been favored by relatively high selfing rates in combination with high inbreeding depression.
... Within Costaceae, the placement of Tapeinochilos with respect to other genera has been a source of debate in the taxonomic literature . Ants and birds are recognized as seed dispersers in Costaceae (Schemske 1983). There are no reports of seed dispersal in Hellenia speciosa so far. ...
... No dispersal syndrome was noticed in T. ananassae that show indehiscent capsular fruit. Earlier study by Schemske (1983) reported that birds were recognized for seed dispersal in C. laevis. ...
Exomorphic and anatomical characters of seeds of five species of Costaceae were examined using light
and scanning electron microscopy. Seed anatomy was investigated to observe seed structural diversity as a
taxonomic aid for the identification of taxa and to explain the adaptive characters for seed dispersal
syndromes. Morphometric and micromorphological traits of seeds revealed considerable variation in size,
shape and surface pattern. Among all the studied taxa, the taxonomic placement of Tapeinochilos ananassae
was uncertain. But the micromorphological characters such as striate round dotted seed surface with
tuberculate aril surface and areolate aril structure separate the Tapeinochilos ananassae from other taxa.
Micromorphological and anatomical characters support the taxonomical delimitation of five species within
the family Costaceae and are significant to analyze the aril structure in detail with implications on seed
dispersal syndrome.
... (table 3) although biomass and maternal fecundity were significantly reduced when plants were stressed with the lower level of irrigation. Allard and Hansche (1964) have suggested that the relative viability of inbred individuals is much lower under stressful conditions such as drought and disease than under more favorable conditions, and suboptimal environmental conditions have indeed been shown to enhance inbreeding depression in some species (Libby et al. 1981;Schemske 1983;Sobrevila 1988). Although Marshall (1988) did not control for the genetic relatedness of pollen donors and recipients, she found that components of reproduction in R. sativus were more strongly affected by paternity when maternal plants were subject to water stress. ...
... The effects of inbreeding on maternal fecundity and reproductive fitness were much greater than the fitness effects of inbreeding at earlier stages in the life cycle. Most studies, primarily of self-compatible species, have found artificial self-pollination to result in reduced seed set relative to artificial cross-pollination (Jain 1979;Price and Waser 1979;Schemske 1983;Jolls 1984;Kesseli and Jain 1984;Levin 1984;Schemske and Pautler 1984;Stevens and Bougourd 1988;Levin 1989;Sakai et al. 1989;Dudash 1990;Waser and Price 1991). The level of inbreeding resulting from selfing in self-compatible populations should be comperable to that associated with full-sib crosses in obligately outcrossing populations. ...
Studies of inbreeding depression in plant populations have focused primarily on comparisons of selfing versus outcrossing in self-compatible species. Here we examine the effect of five naturally occurring levels of inbreeding (f ranging from 0 to 0.25 by pedigree) on components of lifetime fitness in a field population of the self-incompatible annual, Raphanus sativus. Pre- and postgermination survival and reproductive success were examined for offspring resulting from compatible cross-pollinations. Multiple linear regression of inbreeding level on rates of fruit and seed abortion as well as seed weight and total seed weight per fruit were not significant. Inbreeding level was not found to affect seed germination, offspring survival in the field, date of first flowering, or plant biomass (dry weight minus fruit). The effect of inbreeding on seedling viability in the greenhouse and viability to flowering was significant but small and inconsistently correlated with inbreeding level. Maternal fecundity, however, a measure of seed yield, was reduced almost 60% in offspring from full-sib crosses (f = 0.25) relative to offspring resulting from experimental outcross pollinations (f = 0). Water availability, a form of physiological stress, affected plant biomass but did not affect maternal fecundity, nor did it interact with inbreeding level to influence these characters. The delayed expression of strong inbreeding depression suggests that highly deleterious recessive alleles were not a primary cause of fitness loss with inbreeding. Highly deleterious recessives may have been purged by bottlenecks in population size associated with the introduction of Raphanus and its recent range expansions. In general, reductions in total relative fitness of greater than 50% associated with full-sib crosses should be sufficient to prohibit the evolution of self-compatibility via transmission advantage in Raphanus.
... Survival of year-old plants over two summers in natural habitats and garden arrays indicated that inbreeding depression is expressed beyond the early life-history stages. As in other studies (Schemske 1983;Dudash 1990), harsher conditions in the field led to greater reductions in the relative survival of selfed offspring (5, field = 0.26, garden = 0.08). Moreover, there existed some indication that inbreeding was expressed more strongly in the uninhabited (5 = 0.36) compared with the inhabited site (5 = 0.16), but the contrast between sites was not significant (see Schemske 1983). ...
... Glasshouse studies may often underestimate the component of/j expressed during severe episodes ofselection that are likely to occur during seedling establishment and overwintering; especially in populations oflong-lived perennials (Harper 1977). The few studies that have examined early life-history stages in the field suggest that levels of mortality may be extremely high under natural conditions; thus large sample sizes are required to obtain a statistically robust estimate of/j (Schemske 1983;Kohn 1988;Ashman 1992). We addressed this problem by formulating an alternative measure of /j based on truncation selection rather than a linear relationship between offspring vigor and fitness. ...
Inbreeding depression is a major selective force favoring outcrossing in flowering plants. Some self-fertilization, however, should weaken the harmful effects of inbreeding by exposing genetic load to selection. This study examines the maintenance of inbreeding depression in partially self-fertilizing populations of the long-lived, herbaceous wetland plant, Decodon verticillatus (L.) Ell. (Lythraceae). Estimates from ten populations indicate that 30% of offspring are produced through self-fertilization. Population-genetic estimates of inbreeding depression (δ = 1 - relative mean fitness of selfed progeny) based on changes in the inbreeding coefficient for the same ten populations were uniformly high, ranging from 0.49 to 1.79 and averaging 1.11 ± 0.29 SE. Although confidence intervals of individual population estimates were large, estimates were significantly greater than 0 in six populations and greater than 0.5 in four. Inbreeding depression was also estimated by comparing growth, survival, and flowering of experimentally selfed and outcrossed offspring from two of these populations in a 1-yr glasshouse experiment involving three density regimes; after which offspring were transplanted into garden arrays and two field sites and monitored for two consecutive growing seasons. Overall δ^ for survival averaged 0.27 ± 0.01 in the glasshouse, 0.33 ± 0.04 in the garden, and 0.46 ± 0.04 in the field. The glasshouse experiment also revealed strong inbreeding depression for growth variables, especially above-soil dry weight (δ^ = 0.42 ± 0.03). The fitness consequences of inbreeding depression for these growth variables approximately doubles if survival to maturity is determined by severe truncation selection. Despite substantial selfing, inbreeding depression appears to be a major selective force favoring the maintenance of outcrossing in D. verticillatus.
... obs.). Schemske (1983) reported seeds surrounded by waxy arils and dispersal by birds in Costus laevis Ruiz & Pav. ...
The monocot family Costaceae Nakai consists of seven genera but their mutual relationships have not been satisfactorily resolved in previous studies employing classical molecular markers. Phylogenomic analyses of 365 nuclear genes and nearly-complete plastome data provides almost fully resolved insights into their diversification. Paracostus is identified as sister to all other taxa, followed by several very short branches leading to discrete lineages, suggesting an ancient rapid radiation of these early lineages and leaving the exact relationships among them unresolved. Relationships among Chamaecostus, Dimerocostus and Monocostus confirmed earlier findings that these genera form a monophyletic group. The Afro-American Costus is also monophyletic. By contrast, Tapeinochilos appeared as a well-supported crown lineage of Cheilocostus rendering it paraphyletic. As these two genera differ morphologically from one another owing to a shift from insect- to bird-pollination, we propose to keep both names. The divergence time within Costaceae was estimated using penalized likelihood utilizing two fossils within Zingiberales, †Spirematospermum chandlerae and †Ensete oregonense, indicated a relatively recent diversification of Costaceae, between 18–9 Mya. Based on these data, the current pantropical distribution of the family is hypothesized to be the result of several long-distance intercontinental dispersal events, which do not correlate with global geoclimatic changes.
... However, it contrasts with many other studies that either found the opposite (Galen et al. 1985;Navarro & Guiti an 2002) or no differences in seed weight between selfed and crossed flowers (Eckert & Barrett 1994;Abdelgadir et al. 2009). Regarding germination, crossed and lighter seeds of E. simplex germinated more and faster than selfed seeds; moreover, within the control seeds, heavier seeds performed better than lighter ones, in agreement with findings from other studies (Schemske 1983;Navarro & Guiti an 2002). The thicker coat of the seeds from selfed flowers is probably the reason for slower germination (Crocker 1906;Miyoshi & Mii 1988). ...
Background and Aims
Oceanic island ecosystems favor the appearance of novel interactions as a consequence of their depauperate and disharmonic flora and fauna. Echium simplex, endemic to the Anaga Biosphere Reserve in NE Tenerife, Canary Islands, belongs to the Canarian bird–flower element.
Methods
Along two flowering seasons, we studied its breeding system, identified the floral visitors, and compared the pollination effectiveness of different animal guilds (insects vs. vertebrates) by means of selective exclosures.
Key Results
The plant showed to be self‐compatible but selfing significantly reduced fruit set. The flowers were visited by five bird species (mostly Phylloscopus canariensis and Serinus canarius, but also Cyanistes teneriffae, Sylvia atricapilla and Sylvia melanocephala), a lizard species (Gallotia galloti), and over a hundred insect species (mainly hymenopterans and coleopterans). Flying insects increased fruit set whereas small flower dwellers (mostly beetles) decreased both fruit and seed set; by contrast, vertebrates had a negligible effect on reproductive success.
Conclusions
We conclude that despite the floral resources provided by E. simplex may be important to some vertebrate species, these do not appear to notably contribute to increase the fitness of the plant, which show to be more dependent upon flying insects to set fruits and seeds. We additionally found that plant reproductive structures are heavily damaged by feral goats, which threaten the maintenance of this Canarian endemic species.
This article is protected by copyright. All rights reserved.
... Seeds were checked daily until all reached emergence of the radicle. While some studies on seed germination consider only a set of seeds (Schemske, 1983;Gil and López, 2015;Raphael et al., 2017;Farooq et al., 2018), we took into account all of the collected seeds for the analysis. ...
The domestication syndrome of many plants includes changes in their mating systems. The evolution of the latter is shaped by ecological and genetic factors that are particular to an area. Thus, the reproductive biology of wild relatives must be studied in their natural distribution to understand the mating system of a crop species as a whole. Gossypium hirsutum (upland cotton) includes both domesticated varieties and wild populations of the same species. Most studies on mating systems describe cultivated cotton as self-pollinated, while studies on pollen dispersal report outcrossing; however, the mating system of upland cotton has not been described as mixed and little is known about its wild relatives. In this study we selected two wild metapopulations for comparison with domesticated plants and one metapopulation with evidence of recent gene flow between wild relatives and the crop to evaluate the mating system of cotton’s wild-to-domesticated complex. Using classic reproductive biology methods, our data demonstrate that upland cotton presents a mixed mating system throughout the complex. Given cotton’s capacity for outcrossing, differences caused by the domestication process in cultivated individuals can have consequences for its wild relatives. This characterization of the diversity of the wild relatives in their natural distribution, as well as their interactions with the crop, will be useful to design and implement adequate strategies for conservation and biosecurity.
... B). Hummingbird syndrome flowers have evolved seven or eight times in Costus from bee-adapted flowers (Kay et al. 2005;Salzman et al. 2015), a genus that is SC (Schemske 1983;Kay and Schemske 2008). Aquilegia and Mimulus are two predominantly SC genera that have each experienced two evolu- ...
Pollinator-mediated selection on plants can favor transitions to a new pollinator depending on the relative abundances and efficiencies of pollinators present in the community. A frequently observed example is the transition from bee pollination to hummingbird pollination. We present a population genetic model that examines whether the ability to inbreed can influence evolutionary change in traits that underlie pollinator attraction. We find that a transition to a more efficient but less abundant pollinator is favored under a broadened set of ecological conditions if plants are capable of delayed selfing rather than obligately outcrossing. Delayed selfing allows plants carrying an allele that attracts the novel pollinator to reproduce even when this pollinator is rare, providing reproductive assurance. In addition, delayed selfing weakens the effects of Haldane’s sieve by increasing the fixation probability for recessive alleles that confer adaptation to the new pollinator. Our model provides novel insight into the paradoxical abundance of recessive mutations in adaptation to hummingbird attraction. It further predicts that transitions to efficient but less abundant pollinators (such as hummingbirds in certain communities) should disproportionately occur in self-compatible lineages. Currently available mating system data sets are consistent with this prediction, and we suggest future areas of research that will enable a rigorous test of this theory.
... Geralmente, espécies do gênero Costus crescem em baixa densidade populacional. A maioria tem ramos espirais com inflorescências terminais que produzem apenas uma flor por dia (raramente duas) e apresenta um período de floração estendido (Schemske, 1980;1981;1982;1983;Kay e Schemske, 2003). ...
Costus spiralis (Jacq.) Roscoe (Costaceae) ou Cana-do-brejo ou Cana-de-macaco é uma espécie amplamente encontrada no Brasil. Quais valores médicos e/ou potenciais terapêuticos? O objetivo desta revisão foi destacar a pluralidade da planta Costus spiralis para curar ou melhorar o sofrimento da população contra doenças e suas comorbidades. A partir dos vários artigos utilizados, destacamos a forte preocupação com a melhora da comunicação entre profissionais e usuários, mais especificamente sobre o Costus spiralis, devido a sua pluralidade em propriedades medicinais, a fim de evitar maiores complicações à saúde. Ressaltamos que, apesar da pouca literatura, os dados quantitativos e qualitativos sobre a dose e terapêutica de C. spiralis na medicina popular e/ou científica (extrato aquoso ou droga vegetal), as pesquisas revisadas neste artigo, sugerem, de forma indireta, a possibilidade de utilização desta planta para o tratamento da síndrome metabólica e suas comorbidades. Estudos multidisciplinares ainda são necessários e ampliados para verificar como agem nas comorbidades da síndrome metabólica, quais são os seus efeitos tóxicos e colaterais, como seriam suas interações com novos medicamentos alopatas, quais as estratégias mais adequadas para o controle de qualidade e produção de fitoterápicos, para atender às normas das agências reguladoras, como as resoluções da ANVISA.
... Geralmente, espécies do gênero Costus crescem em baixa densidade populacional. A maioria tem ramos espirais com inflorescências terminais que produzem apenas uma flor por dia (raramente duas) e apresenta um período de floração estendido (Schemske, 1980;1981;1982;1983;Kay e Schemske, 2003). ...
Espécies do gênero Piper são utilizadas na medicina popular e carecem de validação farmacológica. Estudos científicos com a espécie Piper amplum são concentrados principalmente nos efeitos antimicrobianos e pouco se sabe sobre suas ações sobre o sistema nervoso central (SNC), apesar da planta ser utilizada de forma etnofarmacológica em processos neurológicos. Portanto, para avaliar os efeitos sobre o SNC, o óleo essencial obtido de Piper amplum (OEPA) (50, 100 150 mg/kg, v.o.) foi administrado em camundongos fêmeas Swiss (25-30 g/ n=8-10 animais e 60 minutos após os mesmos foram submetidos a testes de: depressão (teste do nado forçado, TNF), deambulação motora (campo aberto, TCA e Rotarod), convulsão e hipnose. Grupos controle-positivo (fármacos usados na terapêutica) e negativo (veículo no qual o OEPA foi dissolvido) foram utilizados nas mesmas condições experimentais. Os resultados demonstraram que o tratamento com OEPA não afetou a deambulação e atividade exploratória dos animais no TCA, assim como não afetou o sistema motor no Rotarod. Não foram detectados efeitos anticonvulsivante, hipnótico e ansiolítico do OEPA; entretanto, verificou-se atividade antidepressiva no TNF nas doses testadas. Diante dos efeitos do OEPA sobre o SNC, pode-se considerar o mesmo como alvo potencial para maiores estudos relacionados a atividade antidepressiva
... However, no such relationship is apparent in these Mimulus populations (fig. 2d). The expression ofinbreeding depression is also influenced by the environment in which plants are grown (Antonovics 1968;Schemske 1983). In general, inbreeding depression is more severe in stressful environments (Dudash 1990), under competition (Wolfe 1993), or in environments to which the plants are not adapted (Schmitt and Gamble 1990). ...
When recessive mutations are the primary cause of inbreeding depression, a negative relationship between the levels of prior inbreeding and inbreeding depression is expected. We tested this prediction using 15 populations chosen a priori to represent a wide range of prior inbreeding among four closely related taxa of the Mimulus guttatus species complex. Artificially selfed and outcrossed progeny were grown under controlled growth-chamber conditions, and inbreeding depression was estimated for each population as one minus the ratio of the fitness of selfed to outcrossed progeny. Estimates of inbreeding depression varied from 0% to 68% among populations. Inbreeding coefficients, estimated from electrophoretic assay of field-collected progenies, ranged from 0.02 to 0.76. All five fitness traits displayed a negative association between inbreeding depression and the inbreeding coefficient, but only height showed a statistically significant correlation. Inbreeding depression was also not correlated with the level of genetic variability. In addition, populations with similar levels of prior inbreeding showed significant differences of inbreeding depression, whereas populations with different levels of prior inbreeding showed similar inbreeding depression. Within populations, inbreeding depression did not differ between progeny selfed one versus two generations. Our results are weakly consistent with the recessive mutation model of inbreeding depression, but suggest that additional factors, including genotype-by-environment interaction and complex modes of inheritance, may influence the expression of inbreeding depression.
... However, these results should be interpreted with caution. Studies of inbreeding depression have shown that differences in offspring fitness that are expressed in the field need not be detectable in the benign greenhouse environment (Schemske 1983;Dudash 1990). We are currently studying the performance of naturally produced progeny from several Skeppsvik populations in a long-term field experiment. ...
In tristylous plant populations, style-morph frequencies are governed by an interaction between frequency-dependent selection due to disassortative mating and stochastic processes. Provided that there are no inherent fitness differences among morphs, frequency-dependent selection should result in equal morph frequencies at equilibrium. Stochastic models indicate that the short-styled morph has the highest and the long-styled morph the lowest probability of being lost from local populations as a result of random processes. We surveyed the morph composition of 82 populations of the tristylous, self-incompatible herb Lythrum salicaria in two archipelagos, one in central and one in northern Sweden, located close to the range-margin of the species. To examine whether deviations from even morph frequencies can be explained by among-morph differences in reproductive success, we quantified flower and seed production in six and three populations in the northern and southern archipelago, respectively, and we recorded segregation ratios in offspring produced in six trimorphic populations in the northern area. Seed germination and offspring growth were studied in the greenhouse.
... The ability to calculate such a confidence interval should facilitate comparisons of inbreeding depression among populations or species (Schemske 1983;Levin 1984;Stevens and Bougourd 1988;Karron 1989;Johnston 1992). Nonparametric confidence intervals are provided by Hollander and Wolfe (1973, chap. ...
... If so, an important consequence would be that when comparing inbreeding load among populations, for example, to check for genome purging effects of selfing rates in a common environment (Holtsford and Ellstrand 1990) conclusions may be different from those when measurements are conducted within the natural site ofeach population. The effect of environment on the expression of inbreeding depression in natural populations has been investigated in several studies (Schemske 1983;Schoen 1983;Dudash 1991). In general, more severe inbreeding depression is found in the natural environment (Dudash 1991). ...
If, because of genetic erosion, the level of homozygosity in small populations is high, additional selfing will result in small reductions of fitness. In addition, in small populations with a long inbreeding history selection may have purged the population of its genetic load. Therefore, a positive relationship between population size (or level of genetic variation) and level of additional inbreeding depression, here referred to as inbreeding load, may be expected. In a previous study on the rare and threatened perennial Salvia pratensis, a positive correlation between population size and level of allozyme variation has been demonstrated. In the present study, the inbreeding load in six populations of varying size and allozyme variation was investigated. In the greenhouse, significant inbreeding load in mean seed weight, proportion of germination, plant size, regenerative capacity, and survival was demonstrated. In a field experiment with the two largest and the two smallest populations, survival of selfed progeny was 16% to 63% lower than survival of outcrossed progeny. In addition, survival of outcrossed progeny was, with the exception of the largest population, lower (16% to 37%) than of hybrid progeny, resulting from crosses between populations. Effects on plant size were qualitatively similar to the effects on survival, but these effects were variable in time because of differential survival of larger individuals. In all populations the total inbreeding load, that is, the effects on size and survival multiplicated, increased in time. It was demonstrated that inbreeding load in different characters may be independent. At no time and for no character was inbreeding load or the heterosis effect correlated to the mean number of alleles per locus, indicating that allozyme variation is not representative for variation at fitness loci in these populations. Combined with results of previous investigations, these results suggest that the small populations are in an early phase of the genetic erosion process. In this phase, allozyme variation, which is supposed to be (nearly) neutral, has been affected by genetic erosion but the selectively nonneutral variation is only slightly affected. These results stress the need for detailed information about the inbreeding history of small populations. The relative performance of selfed progeny was lowest in all populations, in the greenhouse as well as in the field, and inbreeding depression could still influence the extinction probabilities of the small populations.
... A relationship between pollen tube growth rate and zygotic genetic quality was suggested as a plausible explanation. Additionally, since self pollen may differ from foreign pollen in quality (Darwin, 1876;Maynard Smith, 1978;Schemske, 1983;Schoen, 1983), it is interesting to note that self-fertilized seeds have been shown to be smaller in size in Impatiens capensis (cleistogamous versus chasmogamous flowers; Waller, 1984) and in Mertensia ciliata (Geber, 1985). The idea that detectable genetic variation can influence variation in seed size, however, needs further empirical investigation. ...
... Hedychium spicatum (Giri and Tamta, 2012), Elettaria cardamomum (Dahanayake, 2014) and Amomum subulatum (Bhowmick and Chattopadhyay, 1960). In some species, seeds germinated within about 1 month and were considered to be non-dormant (Schemske, 1983), while seeds of other species require many months to germinate and presumably have physiological dormancy (PD) (Chanchula et al., 2013;Dahanayake, 2014;Rivai et al., 2015). In the case of Alpinia malaccensis (Rivai et al., 2015) and Globba spp. ...
Little information is available on seed dormancy of members of the Zingiberales and especially the Zingiberaceae. Our aim was to investigate the dormancy breaking and germination requirements of Alpinia galanga in vitro with a minimum number of seeds, using the move-along experiment. The mass of imbibed seeds increased by 17.5% in 1 d, showing that seeds were water permeable. The best germination in the move-along experiment (86.7%) was obtained when seeds were exposed to the sequence of temperature regimes that began with winter (20/10°C), and seeds began to germinate after 6 weeks at this temperature regime. Seeds dry stored for 4 months and then incubated at the sequence of temperature regimes that began with summer (30/20°C) started germinating in the sixth week at this temperature regime and had germinated to 93.3% after 18 weeks. Seeds kept dry for 4 months and then treated with 50 mg l−1 gibberellic acid (GA3) began to germinate at 30/20°C after 2 weeks. Control seeds incubated continuously at 20/10, 25/15 or 30/20°C germinated to 80.6, 77.8 and 60.0%, respectively. When incubated at 15, 20, 25 or 30°C, the ideal temperature for embryo growth was 20°C. Since GA3 and dry storage can break non-deep physiological dormancy and embryos grew during warm stratification, seeds of A. galanga have non-deep simple morphophysiological dormancy (MPD). This is the first report of non-deep simple MPD in the Zingiberaceae.
Geitonogamy, the transfer of pollen from one flower to another on the same plant, is often the primary means of self-pollination in flowering plants. For self-compatible plants, self-fertilization may lead to greatly reduced offspring fitness via inbreeding depression. For self-incompatible plants, geitonogamous pollen transfer can result in low seed set, even when stigmatic pollen loads are substantial. For multiple self-compatible, native California plants, we found that honey bees visited more flowers per plant than native insects, and that offspring resulting from pollination by honey bees had reduced fitness relative to those resulting from native insect pollination. Here we investigate whether honey bees generally make more geitonogamous visits than other pollinators using data from a global survey of 41 manuscripts that reported floral visitation data. Compared to the average of all non-honey bee visitors in a plants pollinator assemblage, honey bees visit significantly more flowers per plant, though they do not differ from the non-honey bee visitor with the highest rate of geitonogamous visitation. However, the disparity between rates of geitonogamous visitation by honey bees and non-honey bee visitors is a function of the frequency of honey bees relative to non-honey bee visitors. As honey bees become increasingly numerically dominant, there is a trend for their rates of geitonogamous visitation to increase, accompanied by a significant decline in flowers visited per plant by non-honey bee visitors. While we found that honey bees visited more flowers per plant compared to the average of other visitors, large or eusocial pollinators were as likely as honey bees to be the most geitonogamous visitor.
The spiral gingers (Costus L.) are a pantropical genus of herbaceous perennial monocots; the Neotropical clade of Costus radiated rapidly in the past few million years into over 60 species. The Neotropical spiral gingers have a rich history of evolutionary and ecological research that can motivate and inform modern genetic investigations. Here, we present the first two chromosome-level genome assemblies in the genus, for C. pulverulentus and C. lasius, and briefly compare their synteny. We assembled the C. pulverulentus genome from a combination of short-read data, Chicago and Dovetail Hi-C chromatin-proximity sequencing, and alignment with a linkage map. We annotated the genome by mapping a C. pulverulentus transcriptome and querying mapped transcripts against a protein database. We assembled the C. lasius genome with Pacific Biosciences HiFi long reads and alignment to the C. pulverulentus genome. These two assemblies are the first published genomes for non-cultivated tropical plants. These genomes solidify the spiral gingers as a model system and will facilitate research on the poorly understood genetic basis of tropical plant diversification.
The evolution of hummingbird pollination is common across angiosperms throughout the Americas, presenting an opportunity to examine convergence in both traits and environments to better understand how complex phenotypes arise. Here we examine independent shifts from bee to hummingbird pollination in the Neotropical spiral gingers (Costus) and address common explanations for the prevalence of transitions from bee to hummingbird pollination.
We use floral traits of species with observed pollinators to predict pollinators of unobserved species and reconstruct ancestral pollination states on a well‐resolved phylogeny. We examine whether independent transitions evolve towards the same phenotypic optimum and whether shifts to hummingbird pollination correlate with elevation or climate.
Traits predicting hummingbird pollination include small flower size, brightly colored floral bracts and the absence of nectar guides. We find many shifts to hummingbird pollination and no reversals, a single shared phenotypic optimum across hummingbird flowers, and no association between pollination and elevation or climate.
Evolutionary shifts to hummingbird pollination in Costus are highly convergent and directional, involve a surprising set of traits when compared with other plants with analogous transitions and refute the generality of several common explanations for the prevalence of transitions from bee to hummingbird pollination.
en Seasonal drought has been shown to greatly influence the distributions and species composition of plants in tropical rain forests. By conducting a series of field, greenhouse, and growth chamber experiments, we examined how Costus villosissimus, a forest edge species, has adapted to drought and differentiated from C. allenii, its closely related species in the understory. We hypothesize that delayed seed germination and high drought tolerance may lead to habitat differentiation and thus reproductive isolation between closely related plant species in the tropics.
Abstract in Spanish is available with online material.
Resumen
es Se ha demostrado que la sequía estacional influye de manera importante en la distribución y composición de las especies de plantas en las selvas tropicales. Mediante una serie de experimentos de campo, invernadero y cámara de crecimiento, examinamos cómo Costus villosissimus, una especie del margen selvático, se ha adaptado a la sequía y se ha diferenciado de C. allenii, una especie del sotobosque con la que está estrechamente relacionada. Nuestra hipótesis es que la germinación tardía de las semillas y la alta tolerancia a la sequía pueden conducir a la diferenciación del hábitat y, por lo tanto, al aislamiento reproductivo entre especies de plantas estrechamente relacionadas en los trópicos.
The purpose of this study was to determine the incompatibility relationships among the three different morphs of the tristylous plant Lythrum salicaria, and to assess whether there are fitness consequences to breakdown in incompatibility. Twenty-four different types of pollinations were performed using all possible combinations of anthers and stigmas. These can be grouped as legitimate pollinations (pollinations from the appropriate anther level of a compatible morph), illegitimate intermorph pollinations (pollinations from the inappropriate anther level of a compatible morph), intramorph pollinations (pollinations between individuals of the same morph), and self pollinations. Legitimate pollinations produced significantly more seed than illegitimate intermorph pollinations, intramorph pollinations, and self pollinations. The difference between legitimate and illegitimate intermorph pollination success is particularly interesting because pollen for these crosses came from the same genetic individual. Pollination types also differed in offspring quality. In the rare examples where progeny were produced by illegitimate intermorph pollinations, the progeny did not have significantly lower values for seedling growth traits compared to legitimate progeny. Seedlings produced by self pollinations had significantly lower values for four out of six seedling growth traits measured. Comparisons of legitimate and self progeny traits indicate that inbreeding depression for most traits is close to or above 0.5. The finding that some seed were produced from illegitimate pollinations suggests that there is variation among individuals in incompatibility. There was a significant effect of parental morph type on the probability of breakdown in incompatibility with the midstyled maternal parents setting more seed from illegitimate pollinations.
We experimentally examined the effects of pollen composition on progeny fitness in the self-compatible, annual plant Chamaecrista fasciculata. Plants were hand-pollinated with single- and mixed-donor pollen loads and with various combinations of self- and outcross pollen. For outcrosses, pollen was obtained from two plants at each of two different distances within the same subpopulation as the female parent. Seedlings from all crosses were planted back into the maternal site. For single-donor crosses, seed weight, progeny fruit production, and overall relative fitness were significantly higher for outcross, as compared to self-treatments, but we found no significant differences among outcross sources. For all fitness components, the value observed for crosses derived from mixed loads was intermediate between the values for the singledonor crosses that comprised the mixed load. In a parallel experiment, an analysis of seed paternity of progeny which resulted from pollen mixtures of self- and outcross pollen showed random paternity in two maternal families, and significant excess of outcross in one family. Our results demonstrate that mixed pollen loads do not confer a fitness advantage to the maternal plant in this species, and that the fitness observed for progeny derived from mixed loads is generally consistent with a hypothesis of random paternity.
The prevalence of nonrandom fertilization due to postpollination events has rarely been studied in natural populations, despite important implications for outcrossing rates, mate choice, and plant fitness. Nonrandom paternity within fruits can be caused by both unequal fertilization and unequal embryo abortion. Using self-compatible Hibiscus moscheutos, we studied the potential for nonrandom fertilization by comparing growth rates of pollen-tubes from different donors. The branched style of Hibiscus allowed within-flower comparisons between pollen donors. Relative pollen-tube growth rates were determined by applying pollen from pairs of donors to different stigmas on adjacent stylar branches. We then measured the number of callose plugs per tube in cross-sectional transects across the style after 3 hr. We demonstrate that rates of callose plug formation can be used as a sensitive indicator of relative pollen-tube growth rate. Differences between pollen donors were common and repeatable. Self-pollen-tubes grew slower than outcross pollen-tubes in some crosses and faster in others. Allozyme variation in glucose phosphate isomerase was used to show that individuals with fast-growing pollen-tubes sired a disproportionate number of seeds following mixed pollinations (up to 72%). Since seed abortion was negligible, we conclude that variation in pollen-tube growth rates leads to nonrandom paternity within fruits.
Populations of Leavenworthia crassa (Cruciferae) studied for 3 years exhibited among- and within-population genetic variation for a suite of floral and reproductive traits (flower width, petal length, anther position, ability to set seeds in the absence of pollinators, time to first flowering) associated with breeding system. We used electrophoretic markers to show that a population with small, monomorphically colored flowers with introrse anthers had a significantly lower outcrossing rate (t = 0.03) than did a population with larger, polymorphically colored flowers with extrorse anthers (t = 0.33). In the more-outcrossing population the correlation between higher maternal plant outcrossing rate and the suite of six traits approached significance (P < 0.067), with greater petal size, greater flower width, and reduced ability to set seeds in the absence of pollinators contributing significantly. Plants in selfing populations had a generally higher reproductive success, with a higher number of flowers per plant, a smaller proportion of unfertilized ovules, a smaller proportion of fertilized ovules aborted, a higher rate of fruit set, and overall a larger number of seeds matured than did plants from the more outcrossing populations. Pollen limitation did not appear to account for lower reproductive success in outcrossing populations. Resource limitation did not differ substantially between populations. However, within-ovary patterns of fertilization, abortion, and seed weight were significantly less random in outcrossing populations than in selfing populations, suggesting that differential gamete and embryo success may be responsible for lower reproductive success in outcrossing populations.
Drimys brasiliensis Miers, locally known as "cataia" or "casca-de-anta", is a native tree of "Floresta Ombrófila Mista", in Brazil. Its bark has been used for medicine, through the exploitation of plants of natural populations. The present work aimed to study aspects of reproductive biology of Drimys brasiliensis in order to establish strategies for sustainable management and conservation, in order to generate alternative income from the exploitation of this non-timber forest product. Studies about reproductive phenology (296 plants during 2 years and a half), pollination and dispersal ecology, and floral biology were realized. The flowering season occurred the summer, with its peak in January. There are unripe fruits throughout the year, becoming ripe fruits as the temperature increases. There is a superposition of unripe and ripe fruit phenology from different flowering seasons. Ripe fruits are then, available for animals throughout the year. Hymenopteras are flower visitors with major potential for gene flow via pollen, but their frequency is low, like others flowers visitors, despite the high flowers production and pollen viability. Therefore, the highest fruit production which was seen comes from self-fecundation. The primary fruit dispersers are rare, birds being observed. However, the secondary dispersal of seeds that reach the ground by barocory is high.
The role of gene establishment in gene flow was investigated in a population of the annual legume Chamaecrista fasciculata by determining the effect of interparent distance on progeny fitness throughout the entire life history. A decelerating gain in progeny fitness with increasing interparent distance was observed. Selfed progeny suffered a 2-fold fitness disadvantage compared to progeny derived from mating events between individuals in the same neighborhood. Progeny derived from within neighborhood crosses had lower fitness than progeny from crosses between neighborhoods. Coupling the effect of interparent distance on gene establishment with information on gene dispersal resulted in a considerable increase in estimated gene flow. However, gene flow was still limited, as the average neighborhood area corresponded to a circle with radius of approximately 3.0 m. Yearly fluctuations in population size and variation in reproductive output lowered the estimate of Ne below the census estimate to approximately 100 individuals. The role of a seed bank in increasing the estimate of Ne was found to be insignificant. It is likely that genetic drift plays a major role in determining the distribution of genetic variation in this population.
Like many angiosperms, Crinum erubescens is partially self-compatible, producing fewer seeds upon selfing than after outcrossing. In this paper we test the relative magnitude of the prefertilization and postfertilization effects of self-incompatibility, inbreeding depression, or both in a natural population of this hermaphroditic tropical herb. We characterize prefertilization effects by examining pollen tube growth, while postfertilization effects are characterized by examination of embryo abortion and seed maturation. Statistical methods are developed to test the magnitude of these effects from one life-cycle stage to the next. We find that although pollen performance in selfed flowers is lower than that in outcrossed flowers, pollen performance is low overall. Postfertilization effects attributable to inbreeding depression account for a larger proportion of the reduction in fecundity in selfed compared to outcrossed flowers. Among naturally pollinated plants, despite ample pollen deposition, the numbers of fruits and seeds set are intermediate to selfed and outcrossed treatments.
If pollen donors are equally effective at siring seeds, the presence of equal proportions of pollen from two pollen donors on a stigma will lead to equal proportions of seeds sired by each pollen donor. Variation in germination rates, pollen-tube growth, and embryo viability may cause one donor to sire more seed than another. We looked for differential donor success in the field by simultaneously applying equal amounts of pollen from two pollen donors. We simultaneously applied equal amounts of self and outcross pollen to receptive stigmas and simultaneously applied pollen from two donors at different physical distances from the recipient. Following simultaneous application of self and outcross pollen, significantly more of the seeds were sired by outcross pollen donors. Seed set following simultaneous application of two outcross donors was also nonrandom. Pollen donors from 100 m were more likely to sire seeds when competing with pollen from plants nearby (1 m). To determine whether pollen-tube growth rates were responsible for these patterns of paternity, we varied the timing of deposition of outcross pollen allowing self pollen tubes a head start on the stigma. Outcross pollen was applied 3 or 24 h after self pollen. In spite of this time delay, the majority of the seeds were again sired by outcross pollen. There was no significant difference in the amount of seeds sired by self pollen between the two delay treatments. This result suggests that mechanisms operating after ovule fertilization may contribute to the discordance between the proportions of the pollen present and the proportions of seeds sired.
The focus of this study was to examine the consequences of five sequential generations of enforced selfing and outcrossing in two annual populations of the mixed-mating Mimulus guttatus. Our primary goal was to determine whether purging of deleterious recessive alleles occurs uniformly between populations and among families, and thus gain insights into the mode of gene action (dominance, overdominance, and/or epistasis) governing the expression of inbreeding depression at both the population and family levels across the life cycle.
Outcrossing rates varied from 0% to 69% among Jamaican populations of Turnera ulmifolia. A correlation between increasing herkogamy and outcrossing rate occurred among populations. Predictions from sex-allocation theory were tested by estimating allocation to reproductive functions. Significant differences in allocation patterns occurred among populations, but they were not correlated with outcrossing rates. The fitness consequences of inbreeding were assessed in high- and low-density greenhouse experiments for nine populations with variable outcrossing rates. No evidence for inbreeding depression occurred in early portions of the life history, but multiplicative fitness functions provide evidence for inbreeding depression. We tested the prediction that selfing populations have lower levels of inbreeding depression than outcrossing populations but found no significant correlation.
Inbreeding depression is commonly observed in natural populations. The deleterious effects of forced inbreeding are often thought to be less pronounced in populations with self-pollinating mating systems than in primarily outcrossing populations. We tested this hypothesis by comparing the performance of plants produced by artificial self- and cross-pollination from three populations whose outcrossing rate estimates were 0.03, 0.26, and 0.58. Outcrossing rates and inbreeding coefficients were estimated using isozyme polymorphisms as genetic markers. Analysis of F statistics suggests that biparental inbreeding as well as self-fertilization contribute to the level of homozygosity in the seed crop. Biparental inbreeding will reduce the heterozygosity of progeny produced by outcrossing, relative to random outcrossing expectations, and hence will reduce the effects of outcrossing versus self-fertilization. Heterotic selection may increase the average heterozygosity during the life history. Selfed and outcrossed seeds from all three populations were equally likely to germinate and survive to reproduce. However, inbreeding depression was observed in fecundity traits of plants surviving to reproduction in all three populations. Even in the population whose natural self-fertilization rate was 97%, plants grown from seed produced by self-pollination produced fewer fruits and less total seed weight than plants grown from outcrossed seed. There was no detectable inbreeding depression in estimated lifetime fitness. Inbreeding effects for all reproductive yield characters were most severe in the accession from the most outcrossing population and least severe in the accession from the most self-fertilizing population.
Selfed and outcrossed progeny of 60 maternal parents were produced to investigate the joint and individual effects of mating system, seed weight, and emergence date on the expression of characters related to fitness and adult fecundity. A series of analyses of variance investigated these effects through time and indicated that 1) mating system explained 56% of the variance in seed weight, 2) seed weight explained 51% and mating system explained 38% of the variance in emergence date, and 3) mating system explained 71% and seed weight explained 15% of the variance in fecundity. Outcrossed-seed means differed significantly from selfed-seed means for all traits measured. On average, outcrossed seeds were larger, germinated earlier, had higher percentage emergence, and produced plants that were more fecund than selfed seeds. The coefficient of inbreeding depression increased through time in this study, from 0.05 for seed weight to 0.23 for fecundity. Seed weight and emergence date were positively correlated, both phenotypically and genetically, for both mating systems. Genetically, this indicates that genes that increase the value of seed weight also increase the value of emergence date and vice versa. Phenotypically, the positive correlation indicates that larger seeds germinate later. Outcrossed seeds were significantly larger but germinated earlier than selfed seeds, suggesting that mating system has an overriding effect in influencing fitness. In light of the selection on emergence date quantified in a previous study, seed weight, emergence date, and mating system may be functioning as a cluster of characters on which selection acts jointly in this species.
Progeny from chasmogamous (CH) and cleistogamous (CL) flowers of the grass Danthonia spicata were raised in their native habitat and in the greenhouse in order to determine how genetic variation was distributed among families and between CH and CL progeny within families. Twelve quantitative characters were measured on clones from individuals known to have arisen from either CH or CL flowers on a particular plant. Significant genetic variation existed for all characters measured. Most genetic variation was between families and two morphologically similar groups of families were identified. Relatively little genetic variation was found within families (approximately 5% of the total phenotypic variance). In field-raised plants, variance component analysis suggested that CL progeny were genetically more similar to each other than were CH progeny from the same plant. Levene's test of the average deviation of CH and CL progenies from their group means was nonsignificant but suggested there was a trend (0.05 < P < 0.10) for CH progeny to be more variable than CL progeny in the field but less variable in the greenhouse. The amount and distribution of genetic variation in the study population indicates that selective differentials would be larger among families than within families.
If microgeographic variation in selection within a natural plant population has resulted in local adaptation, then offspring fitness should decline with distance from the parental site. If outcrossed progeny are less well-adapted to the parental environment than inbred progeny, but perform better in environments different from that of the parent, then the fitness of inbred progeny relative to outcrossed progeny should decrease with dispersal distance from the parent. To test these predictions, we collected seedlings at 10-m intervals from a 40 times 40-m permanent grid in a natural population of Impatiens capensis, grew them in a greenhouse, and crossed them to produce outcrossed chasmogamous seeds. Seedlings from outcrossed chasmogamous and self-fertilized cleistogamous seeds were planted back into the source population in the original site of their maternal parents and in arcs 3 and 12 m from the parental location and censused weekly for survival and reproduction. The fitness of inbred offspring declined significantly and the magnitude of observed inbreeding depression increased with distance from the parental site, supporting the local adaptation hypothesis.
We investigated the effect of intraspecific competition on the magnitude of inbreeding depression in Impatiens capensis by planting seeds from chasmogamous (CH) and cleistogamous (CL) flowers in three experimental greenhouse treatments: in individual pots, in flats in dense pure stands according to seed type, and in flats with the two seed types intermixed in a checkerboard array. The size distributions of plants grown in flats were significantly more hierarchical than those of plants grown individually, indicating that larger plants competitively suppressed smaller plants in the high-density treatments. The magnitude of inbreeding depression at high density depended upon the planting arrangement of CL and CH seeds. CH advantage was greatest when CH and CL seedlings were grown in competition with one another, suggesting that fitness differences between outcrossed and inbred individuals were intensified by dominance and suppression. For plants grown individually, the effects of maternal parent, seed weight, and emergence date on seedling size disappeared with plant age, whereas at high density these effects remained at the final harvest. Thus, plant density may influence patterns of natural selection both on mating system and on juvenile traits in natural Impatiens populations.
This study compares survival and growth of progeny derived from chasmogamous (CH) and cleistogamous (CL) flowers in Impatiens capensis, a forest annual. When progeny were grown in the field, CH seeds had significantly higher survival rates over winter (64% versus 56%), and the survival advantage of outcrossed progeny was not attributable to seed weight differences. No differences in seedling growth were detected. Greenhouse comparisons revealed no difference in seed survival but a 30% growth advantage to CH seedlings. We found no changes in developmental homeostasis of three leaf shape characters between inbred and outbred progeny, nor was there any difference in variability within CH and CL families. The outcrossing advantage observed in these experiments could not have been caused by avoidance of sib competition. Theory predicts that self-pollinated progenies may be more variable than outcrossed progenies if rare, recessive alleles are important contributors to genetic variances. Electrophoretic markers indicate that progeny derived from CH flowers are predominantly outcrossed (at least 54-97%).
A bimodal distribution of outcrossing rates was observed for natural plant populations, with more primarily selfing and primarily outcrossing species, and fewer species with intermediate outcrossing rate than expected by chance. We suggest that this distribution results from selection for the maintenance of outcrossing in historically large, outcrossing populations with substantial inbreeding depression, and from selection for selfing when increased inbreeding, due to pollinator failure or population bottlenecks, reduces the level of inbreeding depression. Few species or populations are fixed at complete selfing or complete outcrossing. A low level of selfing in primarily outcrossing species is unlikely to be selectively advantageous, but will not reduce inbreeding depression to the level where selfing is selectively favored, particularly if accompanied by reproductive compensation. Similarly, occasional outcrossing in primarily selfing species is unlikely to regularly provide sufficient heterosis to maintain selection for outcrossing through individual selection. Genetic, morphological and ecological constraints may limit the potential for outcrossing rates in selfers to be reduced below some minimum level.
The amounts of inbreeding depression upon selfing and of heterosis upon outcrossing determine the strength of selection on the selfing rate in a population when this evolves polygenically by small steps. Genetic models are constructed which allow inbreeding depression to change with the mean selfing rate in a population by incorporating both mutation to recessive and partially dominant lethal and sublethal alleles at many loci and mutation in quantitative characters under stabilizing selection. The models help to explain observations of high inbreeding depression (> 50%) upon selfing in primarily outcrossing populations, as well as considerable heterosis upon outcrossing in primarily selfing populations. Predominant selfing and predominant outcrossing are found to be alternative stable states of the mating system in most plant populations. Which of these stable states a species approaches depends on the history of its population structure and the magnitude of effect of genes influencing the selfing rate.
One of the potential selective mechanisms invoked in discussions of breeding-system evolution is that competition within sibships increases the fitness of outcrossed progeny relative to selfed progeny. We tested this sib-competition hypothesis using cleistogamous (CL) and chasmogamous (CH) seeds of Impatiens capensis in a large greenhouse experiment. The experimental design was a double replacement series which also allowed us to test for inbreeding depression and overall resource partitioning among sibships. We found no evidence for strong inbreeding depression in the study population; although plants from CH seeds had a slight advantage over plants from CL seeds in total flower and pod production, CL plants had slightly higher growth. We also could not detect significant resource partitioning among sibships nor any evidence to support the sib-competition hypothesis for outcrossing advantage. CH sibships were not significantly more variable than CL sibships in any of the phenotypic traits measured. These results suggest that sibling competition may have little importance in the evolution of Impatiens breeding systems.
The effect of biparental inbreeding on the conditions governing the evolution of selfing is examined using recursions in mating-type frequencies. Sibmating in combination with random outcrossing influences two key determinants of the adaptive value of selfing: 1) the meiotic cost of biparental reproduction and 2) the level of inbreeding depression due to deleterious mutations. Biparental inbreeding serves to maintain biparental reproduction by increasing relatedness between parents and their biparentally derived offspring and introduces the possibility of an optimal mating system that incorporates both modes of reproduction. Biparental inbreeding serves to promote uniparental reproduction by reducing the relative inbreeding depression suffered by uniparental offspring. The net effect of these two antagonistic trends depends upon the extent to which mutational load accounts for differences in the numbers of the two types of offspring. A brief summary of the empirical literature suggests that: 1) biparental inbreeding may occur in populations exhibiting mixed mating systems; 2) while inbreeding depression represents an important factor, it does not account entirely for differences in offspring number between the two modes of reproduction.
Introduction Floral Adaptive Mechanisms Sterility Gamete Competition and Resource Allocation Self-Incompatibility (SI) Incongruity Inbreeding Depression Apomixis Polyploidy Differentiation Between Reproductive Barriers Concluding Remarks Literature Cited
Einer der Eckpfeiler der genetischen Evolutionstheorie, das Hardy-Weinberg-Gesetz, geht von einer unendlich großen Population mit Zufallspaarung aus, in der also jedes Individuum zufällig einen Paarungspartner wählt. Reale Populationen sind jedoch in der Größe endlich, und die Wahl des Paarungspartners kann auf verschiedene Weise nichtzufällig strukturiert sein. Zum Beispiel kann die Paarungswahrscheinlichkeit zweier Individuen von ihren phänotypischen Merkmalen abhängen. Auf diesen Punkt und die damit verbundenen Folgen werden wir am Ende dieses Kapitels und nochmals in Kapitel 8 zurückkommen.
The success of an individual plant is determined by the ability to leave progeny that are themselves successful in reproducing. The determinants of fitness are highly complex in plants and have both genetic and ecological constraints. Fitness is a function of both the genotype of the plant and its interaction with the local micro-habitat. We will consider adaptive evolution here as the process by which populations become better suited to their environment. This includes adaptation to the physical environment, where physiological processes become more closely atuned to such specific habitat features as temperature, moisture, or nutrients. Such evolution also includes adaptation to the biological environment. Among the governing factors here are species-species interaction such as competition, predation, and mutualistic plant-pollinator interactions. Many processes and phenomena constrain or strongly influence adaptive evolution. Factors such as breeding system or genetic covariance among fitness parameters, can limit the range and possibilities of adaptive evolution.
The ability to self in the absence of pollinators, i.e. reproductive assurance, and the detrimental consequences of inbreeding, i.e. inbreeding depression, are central factors influencing plant mating system evolution. The purpose of this study was to quantify whether self-fertility and inbreeding depression are related to levels of inbreeding in four Cyclamen species, namely C. balearicum (mean F-is = 0.930), C. creticum (mean F-is = 0.748), C. repandum (mean F-is = 0.658) and C, hederifolium (mean F-is = 0.329). C. balearicum showed a markedly greater capacity to autonomously self-fertilize than the three other species, which may have favoured inbreeding in this species. Levels of inbreeding depression were highest in C. creticum and C. hederifolium at the fruit maturation (delta = 0.18 and 0.20, respectively) and seed number (delta = 0.32 and 0.30, respectively) stages, and for C. repandum at the seed weight stage (delta = 0.23). Although C. balearicum showed inbreeding depression on seed germination (delta = 0.45), this may be an artefact of the generally low levels of seed germination in the experiment. Overall, we observed only limited evidence for the predicted negative relation between inbreeding coefficients and levels of inbreeding since C. creticum had high levels of inbreeding and inbreeding depression. Other factors may thus influence the relationship between inbreeding and inbreeding depression in these species.
Fitness and rates of extinction were compared among populations of the housefly, Musca domestica L., kept either at constant effective sizes of 50, 500 or 1500 or passed through extreme founder events reducing effective size to 5. Populations were maintained for 24 generations, which for small to medium-sized mammals would be less than the 200 years suggested by Soule et al. (1986) as necessary for maintaining viable populations of endangered species. The results demonstrate that effective population sizes have to be greater than the 50 individuals suggested by Franklin (1980) to retain fitness and escape extinction, even in the short term. In contrast to populations of constant size that exhibited monotonic decreases in fitness through time, populations established with few founders rebounded from initial inbreeding depression. However, they were less adaptable to environmental stress than constant size populations, suggesting that populations founded with few numbers may do well within a single environment but may do far less well if they are reintroduced to natural environments or exposed to rapid environmental changes.
Few studies of inbreeding depression have focused on species producing both showy, chasmogamous (CH) flowers and self-pollinated, cleistogamous (CL) flowers. The goals of this investigation were to measure the level of inbreeding depression in the North American violet, Viola canadensis L., and to determine if any fitness differences were linked to floral type (CH versus CL) rather than to cross type (self versus outcross). Hand pollinations were carried out to produce self- and outcross-pollinated CH progeny, and CL seeds were also collected. In a greenhouse, selfed and outcrossed CH flowers produced similar numbers of seeds, and both types of progeny had similar survival rates and comparable numbers of CH flowers, although outcrossed CH progeny had 14% greater vegetative biomass than selfed CH progeny. The level of inbreeding depression in V. canadensis was low, indicating that there may be few drawbacks to selfing in this species. A comparison of CL and self-pollinated CH progeny showed that, although there were differences in CH flower number, overall fitness differences were minimal. The similar performance of selfed (CL and CH) and outcrossed progeny in early life-history stages of V. canadensis suggests a history of inbreeding in the population.
Flowers are not only “designed as organs for a plant’s sexual reproduction.” They are, as Sprengel [2] pointed out more than two centuries ago, also designed to attract pollinators. Because plants are sessile, outcrossing among them requires that an external agent be recruited to move pollen from one to another. The enormous variety of external agents available—wind, water, bees, flies, bats, butterflies, and moths, to name only a few—is complemented by an equally enormous variety of floral forms. Pollination biologists have explained this variety by following the grand tradition established by Darwin [3–5] and the encyclopedists [6,7], i.e, they have explained this diversity as a result of natural selection to ensure outcrossing.
To reveal inbreeding depression, the growth characters and some phenotypic traits of parents and self-crossed progenies (I1, I2 and I3) of Dendranthema morifolium 'rml-3' and D. morifolium '02-42-6' were comparatively analyzed. The results show that compared with each parents, number of seed setting per flower of I1 and I2 progenies of 'rm1-3' reduces 89.5% and 97.2% , that of I1 and I2 progenies of '024-2-6' reduces 91.2% and 92.0% , respectively, the differences are highly significant (P <0.01). The average germination rate of self-crossed progenies of two cultivars gradually decreases with self-crossed generation increasing, in which that among progenies of 'rml-3' has highly significant difference and that of I3 progeny of '024-2-6' is very significantly lower than that of I1 and I2 progenies (P<0. 01). There is no significant difference of leaf length between self-crossed progenies and their parents of two cultivars, but survival rate, plant height, flowering rate and flower diameter of parents are significantly higher than those of self-crossed progenies. Survival rate, plant height, flowering rate and flower diameter of I1 progenies of two cultivars are higher than those of I2 and I3 progenies. The crown width and flower number per plant of self-crossed progenies of two cultivars are also lower than those of their parents, but those of I1 progenies have no significant differences with those of their parents. In addition, compared with their parents, the flowering time of I1, I2, I3 progenies of 'rm1-3' and of I1, I2 progenies of '024-2-6' postpones 9.4, 8.9, 5.9, 11.9 and 7. 6 d, respectively, and the postponed days shorten gradually with self-crossed generation increasing, but that of I3 progeny of '02-42-6' is ahead 10.7 d than its parent. It is suggested that the self-crossed progenies of Dendranthema morifolium have obvious inbreeding depression compared with their parents.
In the preservation of plant biodiversity, there are fundamental genetic and ecological similarities involved in: (1) predicting the fate of small, isolated populations, (2) ensuring the successful reintroduction of endangered species back into natural habitats, and (3) understanding the establishment of species beyond their native ranges. In all three cases, populations small in size may experience high levels of inbreeding and subsequently the expression of inbreeding depression. The ability of these populations to persist will depend, in part, on the magnitude of inbreeding depression and the ability of selection to remove (or purge) the genetic load that causes inbreeding depression. The loss of genetic variation caused by inbreeding or drift in these small populations will restrict their evolutionary potential, placing a high premium on the ability of plants to respond plastically to environmental variation. When plants make appropriate phenotypic adjustments in truly novel environments while maintaining high fitness, we suggest the use of a new term, "opportunistic plasticity," for this attribute. Opportunistic plasticity may be particularly critical and advantageous in the case of plant introductions in ecological restoration where habitats resemble but are not identical to seed collection sites, or in the initial establishment phase of exotic species in non-native locations where many aspects of the environment differ from the native range. Overall phenotypic plasticity may also be an important means of dealing with environmental heterogeneity in many small populations, but unfortunately we have limited data on the interaction between inbreeding and plasticity in plants. The science and practice of conservation biology has generally appreciated the importance of inbreeding, but we feel that it will benefit greatly by considering the potential interactions between inbreeding and phenotypic plasticity and their effects in the establishment and persistence of small populations.
Drimys brasiliensis Miers, locally known as “cataia” or “casca-de-anta”, is a native tree of “Floresta Ombrófila Mista”, in Brazil. Its bark has been used for medicine, through the exploitation of plants of natural populations. The present work aimed to study aspects of reproductive biology of Drimys brasiliensis in order to establish strategies for sustainable management and conservation, in order to generate alternative income from the exploitation of this non-timber forest product. Studies about reproductive phenology (296 plants during 2 years and a half), pollination and dispersal ecology, and floral biology were realized. The flowering season occurred the summer, with its peak in January. There are unripe fruits throughout the year, becoming ripe fruits as the temperature increases. There is a superposition of unripe and ripe fruit phenology from different flowering seasons. Ripe fruits are then, available for animals throughout the year. Hymenopteras are flower visitors with major potential for gene flow via pollen, but their frequency is low, like others flowers visitors, despite the high flowers production and pollen viability. Therefore, the highest fruit production which was seen comes from self-fecundation. The primary fruit dispersers are rare, birds being observed. However, the secondary dispersal of seeds that reach the ground by barocory is high. © 2014 Universidade Federal de Santa Maria. All rights reserved.
The reproductive biology of Impatiens pallida Nuttal and Impatiens biflora Walt (Balsaminaceae) was studied in relation to the evolutionary significance of cleistogamy and chasmogamy. Plant survivorship varied markedly between sites and was affected by abiotic agents such as drought and flooding, and occasional heavy damage from host-specific herbivores. Cleistogamy was the dominant mode of reproduction at all sites, but absolute and relative chasmogam production generally increased with total bud output. Extreme variability in seed production and reproductive mode was observed within and between sites. Cleistogams produced fewer seeds per ovary, matured faster and had a greater probability of surviving to produce seeds than chasmogams in all populations. The energetic investment in fertilization costs (i.e., sepals, petals, pollen and nectar) of chasmogams was >100 times that of cleistogams. Calculation of energetic expenditure per seed based on survivorship curves for each flower type and energy investment for major developmental stages indicated chasmogams were 2-3 times as costly as cleistogams. Greater chasmogam cost was also suggested by the earlier onset of senescence in greenhouse plants with high relative chasmogam output. Plants grown in the greenhouse under different light regimes displayed extreme plasticity in reproductive response as measured by absolute and relative output of cleistogams and chasmogams. The proportion of chasmogams produced per plant generally increased with light intensity. Plants collected from I. pallida populations where chasmogamy was rarely observed had significant chasmogam production when grown in the greenhouse. The tremendous differences observed in plant survivorship and reproductive output demonstrate a high degree of temporal and spatial variation in quality of Impatiens habitats. It is suggested that these conditions have exerted strong selective pressure for reproductive plasticity. Multipurpose genotypes capable of producing cleistogams and chasmogams, depending on habitat suitability, are highly adaptive in environments where genetic tracking is inefficient. The evolution of a dual reproductive mode in Impatiens provides seed production at minimal expense via cleistogamy and the opportunity for outcrossing and pollen donation through chasmogamy. The outcrossing potential of Impatiens chasmogams is enhanced by (1) functional monoecy and (2) a fivefold difference in relative lifespans (@M phase > @V), which results in strongly skewed intraplant sex ratios.
The hypothesis that the understory herbs Costus allenii and C. laevis (Zingiberaceae) have converged in floral characteristics to use the same pollinator was investigated in central Panama. Observations and experiments indicated that these species (1) occupy the same habitats, (2) flower synchronously, (3) are identical in flower color, morphology, and nectar secretion patterns, (4) share the same pollinator, the bee Euglossa imperialis, (5) are self-compatible, but not autogamous, and (6) have strong barriers to hybridization. Both grow in low density along streamsides and produce a single flower per day for an extended period (up to 4 mo). Flower density is depressed through extensive predation by the weevil Cholus cinctus, which damaged 31% of all C. allenii and 60% of all C. laevis inflorescences. Direct observation of foraging bees indicated that individuals regularly visit both plant species. An experimental analysis of interspecific pollen transfer using powered paint as a marker verified these results; 97% of the flowers checked had received heterospecific visits. The high probability of interspecific pollination did not affect fruiting success. I suggest that low flower density, exaggerated by extreme floral predation, has selected for floral similarity and pollinator sharing in these species. Floral convergence increases effective flower density and nectar supplies, and probably increases the regularity and rate of pollinator visitation.
To elucidate the causal factors responsible for diversity gradients in avian communities, avian populations were studied for 12 months in seven lowland tropical areas in the Republic of Panama and compared with populations in structurally similar habitats in Illinois. Resident (breeding) species made up 38-49% of the species on temperate areas but only 20-36% of the species in similar tropical habitats. There were significantly more species of irregular occurrence in mature tropical habitats. Tropical grassland avifaunas were no higher in diversity (number of species and information measures of diversity) than those of temperate grassland areas, but shrub and forest habitats in the tropics had higher diversity as measured by either diversity measure. The number of species was proportionately higher than the information measure because of the relatively small effect of the many rare species on the information measure. Determination of the biomass and energy relations for the bird populations showed that higher total population size in tropical areas is correlated with smaller bird size and reduced individual energy requirements. When only breeding seasons are compared, the reduced energy requirements are a result of the higher temperatures in tropical areas. Twenty-five to fifty per cent of the increased number of tropical breeding species when compared to similar temperate habitats results from the addition of a new food source, i.e., fruits. Additional species are primarily insectivores. The increase in insectivores seems to be due to additional subdivision of the resources and exploitation of a new kind of insect food, especially by species that depend on relatively large insects. Since energy requirements of tropical and temperate avifaunas are about the same, increased productivity is not related causally to the increased tropical diversity. The stratal distribution of species in several tropical (lowland and montane) and temperate avifaunas indicates that avian communities may subdivide the vegetation profile similarly throughout the world despite sharp differences in the number of species in the various areas. Bark species are about equally numerous in Panama and Illinois forest, but ground, low, medium, and high strata contain increased numbers of species in the tropics. The shift away from classical defended territories in mature tropical habitats seems to be correlated with patchy distribution of food resources in frugivores and ant-following species and reduced food abundances in other species. As a result of this food distribution, the frequency of flocking increased in shrub and forest habitats. In grassland habitats, which experience greater seasonal changes in precipitation, the spacing systems of birds are more similar to those in all temperate habitats studied. Degree of territorial defense against conspecifics and amount of interspecific flocking is inversely related to the distribution of food resources; more patchy or unpredictable food distributions, or both, result in fewer species defending exclusive territories. The major factor related to the increased diversity of tropical avifaunas seems to be the relative stability of food resources resulting from environments that are more or less @'equitable@' throughout the year. Both within- and between-habitat increases in diversity of avian communities are discussed. The stability-time hypothesis is discussed in light of available data on organization of avian communities.
Monthly mist-net censuses were conducted in central Panama to contrast the species richness and composition of the understory avifauna in treefall gaps to that of adjacent, intact forest. We compiled 826 captures of 73 species over a 9-mo period. Species richness was greater in gaps than forest (66 vs. 53 species), but capture rates were nearly identical (gap, 409; forest, 417). Of the 31 species with adequate sample sizes, 5 displayed significant habitat preference (P @? .05): 3 in gaps and 2 in forest. Ordination of all nets by Bray-Curtis analysis indicates that gap and forest bird assemblages are quite distinct. We suggest that treefall gaps contribute to the structural heterogeneity of the forest and influence the composition and richness of the bird community.
Plant populations are characterized by a wide variety of mating systems. The precise influence of the mating system on genetic transmission can be measured with marker genes and elementary statistical models. This paper shows that measurement of mating structure in natural and experimental plant populations can be a powerful aid in isolating the various phenomena influencing the transmission process.
The species richness and composition of ant assemblages at the extrafloral nectaries of four Costus spp. (Zingiberaceae) in Panama were quantified. Although inflorescences of Costus spp. commonly produce extrafloral nectar for several months, there was little turnover in ant-species composition on individual inflorescences. A total of 34 ant species in 5 subfamilies were observed, but plant species varied significantly in ant species richness. Number of ant species expected from equal sampling (40 inflorescences per Costus sp.) was 9 for C. pulverulentus, 13 for C. scaber, 15 for C. allenii and 20 for C. laevis. Among-species differences in ant species richness were not a function of plant distribution, the volume or composition of extrafloral nectar, or the duration of nectar flow. The number of ant species was positively correlated with inflorescence height, which varied from 0.6-2.0 m. The differences in ant species richness with inflorescence height were due primarily to the addition of arboreal ants, which increased from 3 species representing 3% of all ant species observations on the shortest plant, C. pulverulentus, to 12 species representing 62% of all ant observations on the tallest plant, C. laevis. The number of terrestrial ant species varied only from 6-8. High ant species richness and the similarity in nectar characteristics among Costus spp. suggest these are relatively generalized mutualisms with limited coevolution between the plants and their attendant ants. The brief period of extrafloral nectar production (mean 36-55 d), coupled with spatial variation in ant species distributions, probably limit the degree of specialization among mutualists.-from Author
This chapter discusses the effects of inbreeding in terms of genetic models of steadily increasing complexity. It correlates theoretical effects with observations and measurements that show that inbreeding populations contain large amounts of genetic variability and that this variability is organized into highly integrated and flexible systems. The observed structure of inbreeding populations results from an appropriate integration of inbreeding into the constellation of genetic and ecological factors that are involved in the regulation of variability and maintenance of flexibility. An understanding of the genetic structure of inbreeding species derives from the combining analyses of theoretical models with studies on experimental and natural populations. Inbreeding can arise in populations either as a result of various mechanisms that affect the mating system, or from restrictions in actual or effective population size. The theoretical effects of inbreeding are introduced in terms of single-locus population models in which population size is assumed sufficiently large to avoid sampling effects and in which it is assumed that selective values, mating system parameters, and other population parameters are constant in all environments. The effects on population structure of linkage and epistatic interactions among different polymorphisms are considered in terms of multilocus genetic models involving deviations from a fixed optimum, heterotic models, and mixed optimum-heterotic models.
The study of phenotypes and their variation often provides evidence for phylogenetic inferences in plant systematics. Therefore, it is critical that the phenotypes analyzed reflect as directly as possible the underlying genotypes. The equation between phenotype and genotype is simpler and better understood for evidence obtained by electrophoresis of plant enzymes than for most morphological characters. This article discusses the advantages and limitations of electrophoretic evidence to test hypotheses in plant systematics and evolution. It also summarizes the results of a large number of studies which have utilized this evidence. Three general observations from these studies are: (1). Conspecific plant populations are extremely similar genetically as documented by their very high mean genetic identities, 0.95 + 0.02. This result suggests that one or a few populations often constitute an adequate sample of a species. (2). Congeneric plant species have strikingly reduced mean genetic identities, 0.67 + 0.07. However, certain pairs of annual plant species have genetic identities similar to those of conspecific populations. In these cases, the species have been shown to be related as progenitor and derivative with the derivative being of recent origin. (3). The amount of genetic variability within plant populations appears closely correlated with their breeding system, with outcrossing populations substantially more variable than inbreeding ones. The article also describes a number of actual and potential applications of electrophoresis in plant systematics. Evidence obtained by electrophoresis of enzymes has not been widely utilized by plant systematists although it has dominated the research of many of their zoological counterparts and population geneticists (Manwell & Baker, 1970; Lewontin, 1974; Nei, 1975; Ayala, 1976). This has meant that the strengths and weaknesses of such evidence for solving systematic and evolutionary questions in plant biology have not been sufficiently discussed. The present article is designed to facilitate an efficient evaluation, and emphasizes the unique characteristics of electrophoretic evidence, the requirements for its analysis, and actual and potential applications in plant systematics and evolution.
1. Gradual build-up of the heteromorphic incompatibility system in the tribe Staticeae of the Plumbaginaceae probably took place in a series of stages. Beginning with the physiological incompatibility system, without morphological differentiation between the cross-compatible groups, pollen dimorphism was the first to be added. This was followed by stigma dimorphism and, finally, heterostyly. Various sections and subsections of Limonium, as the genus is currently recognized, occupy each stage of the presumed phylogenetic ladder, suggesting that it should be split into several genera. 2. Heterostyly occurs in the tribe Plumbaginaceae without morphological differentiation of the pollen and stigmas. 3. The dimorphic incompatibility system in Limonium (A/cob, B/papillate) has broken down several times in two kinds of way: through production of a self-compatible monomorphic recombinant (usually A/papillate); and by the onset of apomixis (agamospermy). 4. In Armeria, arctic and New World taxa show derived monomorphism (A/papillate) with consequent self-compatibility. However, while the pollen of the monomorphics will only produce successful pollen tubes in papillate stigmas of dimorphic taxa, the stigmas and styles of the monomorphics allow pollen tubes from both type A and type B grains to grow and effect fertilization. 5. Crosses within and between dimorphic and monomorphic taxa have revealed the supergene basis of the heteromorphic incompatibility system. In dimorphic taxa A/cob plants are heterozygous (AC/ac); B/papillate plants are homozygous recessive (ac/ac). A/papillate monomorphics are also homozygous (Ac'/Ac'). 6. At least in one population in the Shetland Islands (Hillswick Ness) self-incompatibility has been produced by loss of powers of inhibition of pollen tube growth in stigmas and styles without any morphological rearrangement. Such self-compatible plants are B/papillate (homozygous recessive, ac'/ac'). Usually, however, such loss of stylar inhibition follows a rearrangement within the supergene which has produced a "legitimately" self-compatible combination of pollen and stigmas. 7. Summaries of the evolutionary sequences apparently involved in the breakdown of the heteromorphic incompatibility systems in Armeria and Limonium are given. The sequence in the production of self-incompatible Armeria is markedly different from the sequence postulated as a general rule by Lewis and Crowe (where the first step is a mutation giving pollen the power to overcome any stylar inhibition). Such a step is not involved at all in Armeria. It is suggested, however, that the Armeria sequence may be general in the breakdown of heteromorphic incompatibility systems.
Eleven populations belonging to six species of Leavenworthia were analyzed to determine the pattern of variation of six enzyme systems. Three of the species are self-incompatible and thought to be autogamous. It was found that the self-compatible species show less variation in their isozyme pattern within a population and also less within and between family variation. The differences between populations of self-compatible species tended to be greater than the differences between populations of self-incompatible species. Since other species of autogamous plants that have been investigated show a greater deal of variation than the autogamous species of Leavenworthia, the differences cannot be attributed solely to the breeding system. Additional work is needed to explain the differences between Leavenworthia and other autogamous species.
The interaction of divergent genomes as seen in the expression and stability of molecular, physiological and morphological characters may have a profound effect on the fitness of hybrids and bring forward new variations on which selection may act. The evolutionary implications of developmental interactions should prove to be a most rewarding area of inquiry for biosystematists.
The flowering phenology of Sanguinaria canadensis L. was quantified by censusing marked plots in 1974, 1975 and 1976. In all years, most flowering was restricted to a short period in early spring, but the period of peak flowering depended on spring temperatures. Experimental field analysis of the breeding system of Sanguinaria indicated that autogamy occurred within several hours of first flower opening. This adaptation retains the potential for outcrossing and ensures fertilization during early spring when temperatures are often too low for the flight of insect pollinators. Ovule number per flower was variable and positively correlated with anther and petal number, indicating tight developmental integration of floral organs. Significant differences in mean ovule number per ovary were observed for both spatial and temporal comparisons of populations, suggesting that growth conditions affect ovule development. The ovule production pathway suggested for Sanguinaria allows fecundity to track habitat quality, thus increasing plasticity in reproductive output.
An optimality model based on the tradeoffs between seed set efficiency and outbreeding is presented that predicts under what conditions selfing should be favored over outcrossing. The model predicts that local density and distributional pattern, degree of environmental predictability, and adult and seed longevity are the independent variables that determine the shape of the marginal benefit curves for seed set and offspring heterogeneity. Some data supporting the model are presented derived from a study of species of the genus Leavenworthia (Cruciferae).
Five varieties of the fern Pteridium aquilinum tested lack a genetic self-incompatibility system. Most of the sporophytes studied gave evidence indicating that they were heterozygous for recessive sporophytic lethals. The sporophytes with the highest frequencies of lethals came from areas where Pteridium is an aggressive weed. The sporophytes with the lowest levels of lethals came from the Galapagos Islands. The latter data indicated that these islands were initially colonized by homozygous sporophytes developing from self-compatible gametophytes.
A group of closely related taxa of the small genus Leavenworthia (Cruciferae) that grows in uniform cedar glade environments has been examined both experimentally and under field conditions to determine the genetic structure of populations, the pollinating mechanism, seed set efficiency, growth pattern, and size and distribution of populations. Between and within population comparisons were made between self-compatible and self-incompatible taxa. The data show that the breeding system, whether self-compatible or self-incompatible, is the single most important feature determining population structure. On the whole, a narrow range of variation is correlated with self-compatibility while a wider range of variation correlates with self-incompatibility. But in one species, L. exigua, the within population variability in fruit characteristics is greater than in two mostly self-incompatible species, L. alabamica and L. crassa which, however, are strictly limited in their geographical distributions. The self-compatible species are more efficient seed producers than the self-incompatible species but the latter tend to be more successful and persistent in favorable habitats where the full range of their greater variability comes into play. There is strong evidence for evolutionary shifts from self-incompatibility to self-compatibility both at the specific and intraspecific levels. It is believed the most potent selective force pushing in the direction of self-compatibility is the timing of potential pollinator emergence in relation to the drying of the glade habitat.
(1) Observations and experiments were carried out in central Panama to examine the hypothesis that ants increase the reproductive success of Costus woodsonii. (2) The plant secretes extrafloral nectar from bracts on the inflorescence and the nectar is harvested by ants. (3) The fly Euxesta sp., a specialist on Costus woodsonii, oviposits beneath the bracts on immature fruit, and its larvae destroy the seeds and arils. (4) In both the dry and wet seasons, plants with ants experimentally removed had a higher rate of fly-oviposition and produced only one-third as many seeds as control plants with ants. (5) The ant Camponotus planatus was dominant in the dry season, and had less influence on seed production than had Wasmannia auropunctata, the wet-season dominant. (6) Among dry-season control plants, the probability of fruit maturation was significantly correlated with an index of ant activity based on the consistency of ant occupation. (7) As a consequence of larval damage to the arils, seeds from plants with ants excluded had a lower probability of dispersal in both dry and wet seasons than those from plants with ants.
Several populations of two species of the genus Limnanthes, (L. alba, an outbreeder and L. floccosa, an inbreeder) were examined with respect to variability of fifteen quantitative characters, allozyme variation at 11 loci, and response to different pollination conditions and moisture stress. Nearly equal amounts of phenotypic variability were found in the two species. L. alba had higher within-family variability than L. floccosa, but this result was highly heterogeneous among characters. A study of between- and within-population variance estimates did not reject the null hypothesis that L. alba and L. floccosa are similar with regard to the partitioning and amount of variability for quantitative characters. However, allozyme variation at 11 loci in a large number of populations showed L. alba to be highly polymorphic in contrast to the virtual monomorphism within L. floccosa populations. The average number of alleles per locus in L. alba and L. floccosa was 1.97 and 1.02, respectively, and on an average, L. alba and L. floccosa populations had 63% and 3% loci with polymorphism, respectively. Three groups of allozyme allelic combinations emerged which correlated well with the taxonomic delineation of allogamous L. alba, three semi-autogamous L. floccosa forms and two autogamous L. floccosa forms.
All taxa showed a significant reduction in the seed output per plant due to moisture stress. L. alba suffered a further loss of fecundity under the paucity of pollinators, L. floccosa ssp. floccosa showed no significant effect from this factor, whereas L. floccosa ssp. grandiflora exhibited a curvilinear response which peaked at ‘partial pollination’ and decreased to a lower level at ‘full pollination.’
The geographic distribution of the two species with regard to the temperature and rainfall distribution did not suggest L. floccosa to be living in drier marginal areas. Patterns of variation in flowering time showed L. alba to be less variable than L. floccosa. Overall, there seemed to be little direct support for the thesis that inbreeding species originated from outcrossing taxa in marginal environments as a direct adaptation to a shortened growing season of xeric environments and to the lack of pollinators. Alternative hypotheses suggest that autogamy in L. floccosa might have evolved as a reproductive isolating barrier acting through either cleistogamy or divergence in flowering times.
The fitnesses of two phenotypes which differ in their frequency of self-fertilization are expressed exactly in terms of various parameters, including the relative fitness of progeny from selfing, i, and the proportion of available ovules fertilized with the aid of an external agent, e. Strategic models of natural selection find stationary conditions where the two phenotypes have the same fitness. Conditions when selfing is advantageous to populations and to individuals are not usually identical. Conditions favoring self-fertilization are more stringent when selfing competes with crossing (for individual selection, i > 1/2) and less stringent when selfing occurs prior to crossing (i > e/2). When selfing is delayed until after all opportunities for crossing, it is always advantageous if the parameters vary independently. Some functional interactions between parameters, as when an increase in selfing simultaneously reduces the efficiency of external pollinating agents, result in stationary conditions with mixed self- and cross-fertilization under certain conditions. Following a change in the level of self-fertilization, certain evolutionary adjustments increase the advantage of the acquired mode of fertilization. The models demonstrate that the evolution of various levels of self-fertilization in plants can be explained by individual selection without recourse to postulates of long-term advantages to populations.
Thirty-five coastal Douglas-fir trees were evaluated for embryonic genetic load from comparisons of sound seed set following self- and cross-pollinations, that is, from determinations of relative self-fertility. Estimates for the 35 trees ranged from about 3 to about 27 lethal equivalents per zygote active in the embryo stage, with the median tree carrying about 10 lethal equivalents per zygote. Relative self-fertility of Douglas-fir was compared with that reported for other coniferous species, and genetic load was compared with that reported for Drosophila, Tribolium, and man.
A model of the effect of density-independent optimizing selection on the distribution of a character is developed. Both the direct effect of the selection on the character and the secondary effect of the selection on a modifier allele which changes the distribution is analyzed. The results are that there would be selection for a lower variance in a constant environment and selection for a larger variance when the optimal value of the character is changing in time, only if the fluctuations in the optimum exceed a certain threshold amplitude. The application of the model to populations subject to different temporal patterns of fluctuating selection is discussed.
An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.
An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.
Samples of seven wild populations of the predominantly selfing species Triticum longissimum were compared with samples of five populations of the closely related, but predominantly outcrossing species, T. speltoides. For most of the 36 quantitative characters which were examined, the differences between populations, the total variances of the populations and the mean within-family variances, were greater in the selfer than in the outbreeder. Theoretical models were analysed in an attempt to explain these results, using concepts of classical population genetics.
This review encompasses a decade of studies of enzyme polymorphism in plant populations, in the light of both general theory and specific, simplified models. The patterns of the observed frequency of heterozygotes, compared with panmictic expectations adjusted only for inbreeding, are summarised for 23 outbreeding and 7 inbreeding plant species. There is a trend for outbreeders to show less heterozygosity than expected, and inbreeders to show more, despite the contrary evolutionary pressures on the mating system (the so-called heterozygosity paradox). An annual life cycle and pollination by animal vectors seem to increase the discrepancy in outbreeders. Of the several forces which might account for this paradox, the effects of intense microgeographic differentiation, of low gene flow, of self compatibility and of overdominance of linked segments are predominant. The evidence indicates that inbreeding plant species show more intense geographic and microgeographic differentiation, and more intense multilocus associations than outbreeders. Recent attempts to describe selection operating on variants by the analysis of life cycle components, of physiological processes, and of genetic demography are discussed. The fundamental importance of mating systems and their variation, as a distinctive feature of plant populations is already clear from the studies in hand. Therefore a closer integration of the joint microevolution of mating systems, and of genetic variation is required in both theoretical and experimental studies.
R. A. Fisher (1930) was perhaps the first to realize that the key to sex ratio evolution lay in the almost trivial fact that (under diploidy) everyone has one mother and one father; that in terms of autosomal genes males and females contribute equally to any zygote formed. This paper shows that his observations proves a useful key to a host of other sex related problems. It is for this intuitive reason that fitness measures for the alteration of sex function are often of the general form W = m̂/m + f̂/f. In such a measure male and female function are assigned equal weight. It is somewhat surprising that this notion continues to hold under haplodiploidy (at least from the mother's viewpoint). There is much that this paper has ignored--inbreeding, fluctuating or stochastic environments, etc. A treatment of many of these is much beyond me. It will be quite interesting to know how well the m̂/m + f̂/f notion holds up to alterations in the basic models proposed here.
An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.
It is commonly thought that sexual reproduction evolved and is maintained because the more rapid production of recombinant genotypes is of advantage to the species, but this advantage is long-term and is maintained by group selection while the individual committed to sexual reproduction is at an immediate disadvantage. However, Williams & Mitton (1973) and Williams (1975) have recently put forward models for the evolution of sexuality which derive it from individual and not group selection. These are reviewed below and certain limitations pointed out. An alternative, more general model is described. This accounts for the evolution and maintenance of sexual reproduction by processes of individual selection, but does not require to assume enormous fecundity, hyperintense selection, or special life-history features. It is suggested that the present model is sufficiently general to apply to most or all cases of the evolution of sexual reproduction.
An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.