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Capitulum ofTolpis succulentaon Graciosa Island, visited by a small halictid bee (Halictus malachurus). Photo by H. Shaefer
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Genome-wide genotyping and Bayesian inference method (BORICE) were employed to estimate outcrossing rates and paternity in two small plant populations of Tolpis succulenta (Asteraceae) on Graciosa island in the Azores. These two known extant populations of T. succulenta on Graciosa have recently evolved self-compatibility. Despite the expectation t...
Citations
... Our prior genetic molecular studies were valuable for the conservation of genetic diversity in Juan Fernández endemics; however, the prior markers were limited because they resolved a relatively small number of loci, with a percentage of the loci being invariant [81]. These two factors reduce the utility of the markers for studies of island plants where genetic variation is typically lower than in continental taxa [82]. ...
The human footprint on marine and terrestrial ecosystems of the planet has been substantial, largely due to the increase in the human population with associated activities and resource utilization. Oceanic islands have been particularly susceptible to such pressures, resulting in high levels of loss of biodiversity and reductions in the numbers and sizes of wild populations. One archipelago that has suffered from human impact has been the Juan Fernández (Robinson Crusoe) Archipelago, a Chilean national park located 667 km west of Valparaíso at 33° S. latitude. The park consists of three principal islands: Robinson Crusoe Island (48 km2); Santa Clara Island (2.2 km2); and Alejandro Selkirk Island (50 km2). The latter island lies 181 kms further west into the Pacific Ocean. No indigenous peoples ever visited or lived on any of these islands; they were first discovered by the Spanish navigator, Juan Fernández, in 1574. From that point onward, a series of European visitors arrived, especially to Robinson Crusoe Island. They began to cut the forests, and such activity increased with the establishment of a permanent colony in 1750 that has persisted to the present day. Pressures on the native and endemic flora increased due to the introduction of animals, such as goats, rats, dogs, cats, pigs, and rabbits. Numerous invasive plants also arrived, some deliberately introduced and others arriving inadvertently. At present, more than three-quarters of the endemic and native vascular species of the flora are either threatened or endangered. The loss of vegetation has also resulted in a loss of genetic variability in some species as populations are reduced in size or go extinct. It is critical that the remaining genetic diversity be conserved, and genomic markers would provide guidelines for the conservation of the diversity of the endemic flora. To preserve the unique flora of these islands, further conservation measures are needed, especially in education and phytosanitary monitoring.
... For example, in the annual Hypochaeris salzmanniana DC. (Asteraceae), the proportion of selfing depends on pollinators availability (Arista & al. 2017), maintaining a mixed mating system over time. The paucity of pollinators might also be related with a partial shift to selfing in two isolated populations of the Madeiran endemism Tolpis succulenta (Aiton) Lowe (Asteraceae) (Crawford & al. 2019;Kerbs & al. 2020). The shift to self-compatibility may be associated with the floral biology, life cycle, and ecology of the species (Barrett 2014;Arista & al. 2017;Barrett & Harder 2017). ...
The breeding system of Anacyclus linearilobus, an annual and endemic species restricted to dune ecosystems of the Algerian coast were assessed through the effect of self-fertilization and intra- and inter-population artificial crosses on the probability of producing viable seeds in 20 individuals from two populations in a common garden. The breeding system was determined for each individual by the self-incompatibility index (ISI). These results were compared with those published for other species of the genus, A. clavatus, A. homogamos and A. valentinus. Results of experimental crosses showed that there was high variation in the female reproductive success between individuals of A. linearilobus, like that found in its sister species, A. valentinus. Unlike the other species in the genus that are self-incompatible, A. linearilobus showed a mixed mating system, with a majority of self-incompatible individuals, others partially self-incompatible and some self-compatible. We argue that this strategy may be related to reproductive assurance in this endemic, annual species whose effective population size has been reduced probably due to individual mating incompatibilities.
... For example, in the annual Hypochaeris salzmanniana DC. (Asteraceae), the proportion of selfing depends on pollinators availability (Arista & al. 2017), maintaining a mixed mating system over time. The paucity of pollinators might also be related with a partial shift to selfing in two isolated populations of the Madeiran endemism Tolpis succulenta (Aiton) Lowe (Asteraceae) (Crawford & al. 2019;Kerbs & al. 2020). The shift to self-compatibility may be associated with the floral biology, life cycle, and ecology of the species (Barrett 2014;Arista & al. 2017;Barrett & Harder 2017). ...
The breeding system of Anacyclus linearilobus, an annual and endemic species restricted to dune ecosystems of the Algerian coast were assessed through the effect of self-fertilization and intra- and inter-population artificial crosses on the probability of producing viable seeds in 20 individuals from two populations in a common garden. The breeding system was determined for each individual by the self-incompatibility index (ISI). These results were compared with those published for other species of the genus, A. clavatus, A. homogamos and A. valentinus. Results of experimental crosses showed that there was high variation in the female reproductive success between individuals of A. linearilobus, like that found in its sister species, A. valentinus. Unlike the other species in the genus that are self-incompatible, A. linearilobus showed a mixed mating system, with a majority of self-incompatible individuals, others partially self-incompatible and some self-compatible. We argue that this strategy may be related to reproductive assurance in this endemic, annual species whose effective population size has been reduced probably due to individual mating incompatibilities.
... Before our study, we expected that individuals of the self-compatible S-morph preferentially mates using selfing (Kerbs et al. 2020). Surprisingly, the elongation dynamics of pollen tubes highlighted another process susceptible to favour allogamy in Lgh, even in the self-compatible S-morph. ...
Breeding system influences local population genetic structure, effective size, offspring fitness and functional variation. Determining the respective importance of self- and cross-fertilization in hermaphroditic flowering plants is thus important to understand their ecology and evolution. The worldwide invasive species, Ludwigia grandiflora subsp. hexapetala (Lgh) presents two floral morphs: one self-compatible short-styled morph (S-morph) and one self-incompatible long-styled morph (L-morph). In this study, we identified the breeding systems of western European experimental and natural populations of Lgh by comparing structural characteristics of pollen and style, by studying self- and cross-pollen tube elongations and the viability of the resulting seeds and seedlings in both floral morphs. Our results showed no differences in pollen shape and stigma surfaces no matter the floral morph. In the self-incompatible L-morph flowers, self-pollen tubes were stopped tardily, in the ovarian area, and were unable to fertilize the ovules. This first formal identification of a late-acting, prezygotic self-incompatible system (LSI) in Ludwigia genus contributes a case of LSI in an additional family within the Myrtales order. In the self-compatible S-morph flowers, self-pollen always succeeded to self-fertilize the ovules that nearly all developed into viable seedlings. However, cross-pollen tubes always elongated faster than self-pollen tubes in both morphs. S-morph individuals may thus advantage preferential allogamy over selfing when cross-pollen is available despite its self-compatibility. As expected in late-acting self-incompatible systems, L-morph flowers authorised 0.2‰ of selfed seeds during the uppermost flowering season, that increased to 1‰ at the end of the flowering season. Such delayed selfing resulted in a significant quantity of viable floating seeds. They may contribute to the local regeneration, seed bank and propagation of the L-morph, which may contribute to explain its invasion success worldwide. Management plans of Lgh would gain to consider the breeding systems we identified.
... Genetic drift can directly affect the mating system by reducing the number of S-alleles that segregate within selfincompatible (SI) or pseudo-self-compatible (PSC) species, thus reducing mate availability (Wagenius, Lonsdorf & Neuhauser, 2007). Despite its clear importance in the island setting, there are few mating system studies of island endemic species (Sun & Ganders, 1988;Nielsen et al., 2000;Crawford et al., 2010;Gibson et al., 2020;Kerbs et al., 2020). ...
... These limitations can be overcome by application of genomewide SNP scoring with which hundreds to thousands of markers may be resolved (Eaton & Ree, 2013;Colicchio et al., 2020). This is especially advantageous for endangered island plant species because precise estimates can be made from the few progeny available in the small populations (Gibson et al., 2020;Kerbs et al., 2020). ...
... Here, we extracted DNA from maternal plants and genotyping of these individuals greatly increased our estimation precision for both mothers and offspring. Based on previous results from Tolpis (Gibson et al., 2020;Kerbs et al., 2020) and many other plants (Scofield & Schultz, 2006), we had expected that progeny would show higher levels of homozygosity (inbreeding) than maternal plants (Ritland, 1990). However, we found a higher incidence of inbreeding in parents than in offspring. ...
There have been many studies of morphological and genetic variation in island plant radiations, but few have shown how the mating system has shaped the patterns of variation. In this study, outcrossing rates and paternity in eight populations of the Madeiran endemic Tolpis macrorhiza were estimated using genome-wide RADseq genotyping. The species is believed to have evolved early in the geological history of the island, and we here examine mating system evolution during colonization and establishment of populations across Madeira. The mating system is highly outcrossing in seven populations and mixed mating in one. Some maternal plants in highly outcrossing populations were inbred, suggesting that mating system varies temporally as well as spatially. This mating system may provide flexibility for establishment of new populations in the dynamic landscapes of oceanic islands while maintaining genetic diversity within populations. Multiple paternity is prevalent in populations, indicating that compatible mates are not limited to a few sires. Our analyses of T. macrorhiza were enabled by several methodological advances included in the v.3 release of the BORICE estimation program. These include SNP filtering programs to generate valid likelihoods and post-processing scripts to partition mating system variation among populations and among maternal plants within populations.
... However, a more in-depth assessment to determine the range expansion or contraction of these reintroduced species would be beneficial. Specifically, the T. succulenta plants growing on Praia, and found in low numbers in the Azores, may be a new species or subspecies, endemic to the Azores or even to Graciosa (Kerbs et al. 2020;Crawford et al. 2020). The plants found on Praia may be of considerable conservation importance, due to the threats of anthropogenic habitat degradation and competing exotic plants on inhabited Azorean islands, particularly on Graciosa (Borges Silva et al. 2015). ...
... However, a more in-depth assessment to determine the range expansion or contraction of these reintroduced species would be beneficial. Specifically, the T. succulenta plants growing on Praia, and found in low numbers in the Azores, may be a new species or subspecies, endemic to the Azores or even to Graciosa (Kerbs et al. 2020;Crawford et al. 2020). The plants found on Praia may be of considerable conservation importance, due to the threats of anthropogenic habitat degradation and competing exotic plants on inhabited Azorean islands, particularly on Graciosa (Borges Silva et al. 2015). ...
The removal of invasive species and mitigation of habitat loss are vital conservation tools for species such as seabirds. We surveyed habitats across the entirety of a small seabird islet reserve, Ilhéu da Praia, in the Azores, two decades on from mammalian eradication and floral restoration. Here, we present a fine-scale map, to a 12 metre resolution, representing the first full habitat survey of this islet. This resource can serve as a baseline for monitoring future habitat changes to this internationally important seabird islet. Following restoration efforts in the 1990s, the islet's dominant habitats are meadow, grassland dominated by Festuca petraea, or a combination of the two. We also report a novel observation of both Band-rumped Hydrobates castro and Monteiro's H. monteiroi Storm Petrels breeding in the cavities of Tamarix africana, an invasive tree species. Published in Seabird.
... Before our study, we expected that individuals of the self-compatible S-morph preferentially mates using selfing (Kerbs et al. 2020). Surprisingly, the elongation dynamics of pollen tubes highlighted another process susceptible to favour allogamy in Lgh, even in the self-compatible S-morph. ...
Mating system influences local population genetic structure, effective size, offspring fitness and functional variation. Determining the respective importance of self- and cross-fertilization in hermaphroditic flowering plants is thus important to understand their ecology and evolution. The worldwide invasive species, Ludwigia grandiflora subsp. hexapetala (Lgh) presents two floral morphs: one self-compatible short-styled morph (S-morph) and one self-incompatible long-styled morph (L-morph). Most invasive populations worldwide are only composed of self-incompatible L-morphs, which questions the importance of sexual reproduction during the invasion. In this study, we identified the mating systems of western European experimental and natural populations of Lgh by comparing structural characteristics of pollen and style, by studying self- and cross-pollen tube elongations and the viability of the resulting seeds and seedlings in both morphs. Our results showed no differences in pollen shape and stigma surfaces among and between the two floral morphs. In the self-incompatible L-morph flowers, self-pollen tubes were stopped tardily, in the ovarian area, and were unable to fertilize the ovules. This first formal identification of a late-acting, prezygotic self-incompatible system in Ludwigia genus questions on the distribution of this mating system in the Myrtales order. In the self-compatible S-morph flowers, rarer in worldwide invasive populations, self-pollen always succeeded to self-fertilize the ovules that nearly all developed into viable seedlings. However, cross-pollen tubes always elongated faster than self-pollen tubes. S-morph individuals may thus advantage preferential allogamy over selfing when cross-pollen is available despite its self-compatibility. As expected in late-acting self-incompatible systems, L-morph flowers authorised 0.2‰ of selfed seeds during the uppermost flowering season, that increased to 1‰ at the end of the flowering season. Such delayed selfing resulting in a significant quantity of viable floating seeds may contribute to the local regeneration, seed bank and propagation of the L-morph, which may explain its invasion success worldwide. Management plans of Lgh would gain to consider the mixed mating system we identified.
Asteraceae are among the most abundant angiosperm families on oceanic islands. The reproductive biology of Asteraceae is reviewed and the attributes of the family contributing to their success on islands are discussed. Asteraceae are effective dispersers (the small, single-seeded fruits are moved great distances by wind and birds), and colonization is most likely limited by establishment. The pollinators of the colonizing ancestors rarely disperse with them to islands. Divorced from the pollinators of their ancestral habitats, the capitulum of aggregated small, shallow flowers typical of Asteraceae facilitates pollination of colonizers by various novel biotic visitors and by wind. Self-compatible (SC) colonizing ancestors are common, permitting establishment of sexual populations from one or few propagules. However, several large insular lineages of Asteraceae originated from functionally self-incompatible (SI) colonizers that may have also possessed the capacity to set some self-seed. Establishment may also be facilitated by dominance relationships among S-alleles in the sporophytic SI (SSI) system of Asteraceae, increasing cross-compatibility within small populations. Factors potentially promoting outcrossing in SC Asteraceae are: gynomonoecy, with temporal separation of receptive pistillate ray florets and pollen presentation in the hermaphroditic disc florets of a capitulum (interfloral protogyny); and intrafloral protandry where pollen presentation occurs before stigmata become receptive. Dioecy, gynodioecy, and monoecy are infrequent sexual systems in insular Asteraceae. Multiple paternity is similar in island composites to other Asteraceae, suggesting that neither compatible mates nor pollinators are typically limiting. Additional studies, particularly with genomic markers, are needed for more refined insights into mating systems and paternity in island Asteraceae as these results have important conservation implications.
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Lucy M. Slatter, Susanne Barth, Chloe Manzanares, Janaki Velmurugan, Iain Place and Daniel Thorogood A new genetic locus for self-compatibility in the outcrossing grass species perennial ryegrass (Lolium perenne), Annals of Botany, Volume 127, Issue 6, 7 May 2021, Pages 715–722, https://doi.org/10.1093/aob/mcaa140
