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Spatio-Temporal Distribution of the Cryptic Flies of the Drosophila willistoni (Diptera: Drosophilidae) Subgroup in a Neotropical Forest
Abstract
Identifying cryptic species is a challenging but critical task for conservation biology because such identifications improve the resolution of taxonomic inventories and increase our ability to precisely assess the biodiversity of environments as well as the conservation status of rare species. To understand the temporal and spatial distribution of the cryptic species contained in the Drosophila willistoni subgroup, we re-examined all of the individuals of this subgroup identified in a previous work that analyzed drosophilids associated with a forest patch in the Brazilian Cerrado from December 2007 to November 2008. Each collection consisted of banana-baited traps distributed in three vertical strata of the forest (0-, 4-, and 8-m heights) at three horizontal positions (edge, transition between edge and river, and river area). Our results revealed that the specimens originally identified as D. willistoni consisted of three cryptic species: D. willistoni (n=1,344), D. paulistorum (n=1,001), and D. tropicalis (one male). Most D. willistoni and D. paulistorum specimens were collected during the rainy season on the ground of the edge forest patch. However, D. paulistorum was more temporally and spatially restricted than D. willistoni. Our findings confirm that these three cryptic species of the subgroup D. willistoni differ not only in abundance but also in ecological tolerance. This study contributes to the improved understanding of the Brazilian savanna communities, whose high levels of species richness and endemism are well documented for plants but poorly known for insects.
... The drosophilid communities in the Brazilian Savanna have been studied since 1998 and support the name of the genus: "Drosophila" means "dew-loving". During the rainy summer, drosophilid populations typically expand through all vegetation types, whereas during the dry winter, they shrink and concentrate in the mild forest patches (Tidon 2006;Mata and Tidon 2013;Mata et al. 2015b;Roque et al. 2017). In this scenario, elongated wings would be adaptative for dispersing during the warm rainy season in the Brazilian Savanna. ...
Phenotypic plasticity has been described for morphological and life-history traits in many organisms. In Drosophila, temperature drives phenotypic change in several traits, but few neotropical species have been studied and whether the phenotypic variation associated with plasticity is adaptive remains unclear. Here, we studied the phenotypic response to temperature variation in the distant related neotropical species Drosophila mercatorum (Patterson and Wheeler, 1942) and Drosophila willistoni (Sturtevant, 1916). We evaluate if wing shape variation follows that observed in the neotropical species Drosophila cardini (Sturtevant, 1916): round wings at lower temperatures and narrower wings at higher temperatures. The variation in egg-adult development time and wing size, shape, and allometry was described using reaction norms and geometric morphometrics. In both species, development time and wing size decreased with increasing temperature and wing allometry showed that size explained ≈10% of the shape variation. Wing shape, however, exhibited contrasting responses. At higher temperatures, D. mercatorum developed slightly slender wings, following the pattern previously found for D. cardini, while D. willistoni developed plumper and shorter wings, supporting previous studies on Drosophila melanogaster (Meigen, 1830). We conclude that all traits studied here were influenced by temperature, and that wing shape seems also to be influenced by phylogeny.
... The species with the greatest resource breadth were: D. simulans (90 plant taxa), D. nebulosa (57), Z. indianus (44), D. willistoni (43), D. melanogaster, and D. polymorpha (both 42). Several studies did not completely discriminate between sibling species, particularly in the D. willistoni subgroup (D. willistoni, D. paulistorum, D. equinoxialis and D. tropicalis), but when identifications were made, D. willistoni was usually the most common (Spassky et al., 1971;Garcia et al., 2014;Roque et al., 2017). If D. willistoni is assumed to be present in all references where the identification was incomplete, the number of plant species used by this drosophilid would be 114, the broadest niche breadth of all species reported. ...
1. Species of Drosophilidae are frequently used as model organisms, but their relationships with the environment, particularly in immature stages, remain poorly known.
2. This is the most comprehensive survey to date of fruit‐breeding drosophilids and their hosts in the Neotropics. Drosophilid host‐utilisation patterns were analysed as to geographic origin (native versus exotic) and level of specialisation.
3. The 180 species of plants recorded as drosophilid hosts are distributed across the main Angiosperm lineages and fleshy‐fruited orders; plant families that hosted the greatest number of drosophilid species were Arecaceae, Moraceae, and Myrtaceae. The 100 nominal drosophilid species recorded breeding in fruits belong to just over one‐third of Neotropical genera; most species (91) belong to Drosophila. Drosophilid species with the greatest resource breadth were Drosophila simulans, Drosophila nebulosa, and Zaprionus indianus.
4. Exotic drosophilids breed in more plant species than Neotropical drosophilids and use exotic hosts more frequently, possibly because they are generalists that have survived the trial of introduction and establishment in the Neotropics. Native drosophilids are more variable in resource breadth and sometimes adopt exotic hosts.
5. Amongst the 49 drosophilids with enough records for analysis (> 4), 48 were categorised as generalists. One possible explanation for such overwhelming generalism is the high diversity of Neotropical habitat or hosts. A second, non‐exclusive explanation, suggested by recent studies and empirically supported by the absence of host specialisation found in this study, is that drosophilids could be selective of the dominant yeasts and bacteria in host tissue, and not of the hosts themselves.
Recent reviews of data on worldwide insect decline include almost no information on Brazil. We gathered evidence from literature searches and a survey sent to researchers, to which 96 replied and 56 provided information and publications. We present 75 instances of trends recorded over an average span of 11 years for aquatic and 22 years for terrestrial insects. These include time-replicated samples and expert opinion based on long-term local collections. Most terrestrial data are for butterflies, bees and scarab beetles. Aquatic studies include several insect orders, usually sorted to genus or family. Terrestrial insects showed significantly more cases of declines than increases, both in abundance (17 : 3) and in diversity (11 : 1). In aquatic cases, no tendency was detected in abundance (2 : 2) or diversity (3 : 4), not counting cases with no trend. Differences in these results among habitats may be due to the shorter span and less change in environmental conditions in the aquatic surveys, which included sites already degraded before sampling. We offer guidelines for future long-term assessments, including resampling of legacy collection sites.
Mealybugs damage a variety of crops worldwide, vectoring viruses and causing problems from sooty mould. The identification of the citrophilous mealybug (Pseudococcus calceolariae, CMB) female sex pheromone has created opportunities for its use as a pest management tool that could potentially result in a reduced reliance on insecticides. Mass trapping is a pest management technique that uses baited traps to decrease pest insect densities. To assess the efficacy of the P. calceolariae sex pheromone as a mass trapping tool, a field trial was conducted in citrus in South Australia. The vertical distribution of CMB within the citrus was examined. Male flight activity was monitored using red delta traps in the centre of six 1-ha ‘plots’, after which time half the plots had 306 tent traps containing synthetic CMB pheromone lures deployed (mass traps). Six weeks after the application of mass trapping we observed a 90% lower catch in treated plots compared to catches in control plots. There were strong spatial patterns in trap catch with the Edge to Centre ratio being 3.6:1. P. calceolariae male flight activity showed peaks in October and May. Mass trapping showed promise as an effective management technique for P. calceolariae. Challenges such as male multiple mating and mealybug airborne dispersal still need to be overcome before mass trapping can be used as a reliable management technique.
Thirteen exotic species of drosophilids are recorded in the Neotropical Region, and some of them are highly invasive and a significant threat to fruit cultures. We provide an illustrated key for identifying exotic drosophilid species in Brazil and briefly discuss their taxonomic status, distribution, and occurrence in the Neotropics. The key should support newcomers to the study of Drosophila and facilitate the identification of exotic drosophilids by illustrating their specificities.
Inserido no livro “Cerrado: caracterização e recuperação de Matas de Galeria”, este capítulo apresentou o mais recente check list da flora fanerogâmica das Matas de Galeria e Ciliares do bioma Cerrado. A compilação resultou em uma lista com 2.031 espécies, pertencentes a 686 gêneros e 134 famílias (sensu Cronquist 1988).
An intrinsic property of invaders that determines many of the effects they produce in the areas they colonize is their great abundance. However, a lack of data generally hampers the exploration of the complex interactions of factors that regulate the abundance of most invasive populations. This lack of data generally hinders the understanding of the invasion process and, more specifically, interferes with the management of these populations. This paper uses hierarchical complex models to investigate how temperature, humidity, competitive interactions and resource availability affect the growth rates of naturalized populations of two invaders in the Brazilian Savanna: the African Drosophila simulans and Zaprionus indianus. We also assess how morphological (life-history) and demographic traits mediate these effects. Our results suggest that the population growth rates of both species depend on complex interactions between several of the studied variables but are regulated primarily by rapid and direct responses to resource availability. We found evidence that resources determine immediate oviposition rates, inducing a very rapid regulation of population sizes (in one generation, i.e., approximately 1 month). Our study also demonstrates a lower predictability for Z. indianus and we suggest that this finding is a result of the shorter evolutionary history of Z. indianus in the Brazilian Savanna. These results, valid for the system we have investigated, if validated by other studies, will help to increase the mechanistic understanding of invasions and may contribute to the development of effective management strategies to mitigate their effects on natural and agro-ecosystems.
Cryptic species meet the biological definition of species, but are morphologically identical or quite similar. Several ecological studies underestimate richness and neglect important information on cryptic species, as they are rather difficult to identify. Among insects, drosophilids of the willistoni subgroup, which includes Drosophila willistoni Sturtevant, Drosophila paulistorum Dobzhansky & Pavan, Drosophila equinoxialis Dobzhansky, Drosophila tropicalis Burla & da Cunha, Drosophila insularis Dobzhansky, and Drosophila pavlovskiana Kastritsis & Dobzhansky, are good examples of cryptic species. Although several studies have shown that this subgroup is one of the most abundant in the Neotropical region, no identification to species level has been reported for areas where these individuals live in sympatry. This study evaluates the seasonal oscillations in abundance of this subgroup in biomes with contrasting vegetation and rainfall regimes: the Caatinga and the Atlantic Forest, in northeastern Brazil. Approximately 39,000 drosophilids were captured in 24 collections, of which 18,000 belonged to the willistoni subgroup. The most abundant were D. willistoni, D. paulistorum, and D. equinoxialis, in this order. D. equinoxialis was recorded in only one of the environments surveyed, represented by few individuals. In all environments, individuals of the willistoni subgroup were more abundant in the rainy season, when richness often was higher. The results underline the importance of humidity and of temperature for the subgroup willistoni and indicate the ecological versatility of some of its species.
The Brazilian Pampa (the southernmost end of the country) is currently a highly modified environment because of increasing agricultural activities. In many places, only small parts of grasslands remain inside an agricultural landscape. Drosophilidae (Diptera) have been widely used as a potential bioindicators to monitor the effects of anthropogenic changes in natural environments. However, the fauna of Drosophilidae in the Pampa Biome from natural and disturbed environments, still remains largely unknown. The present study represents one of the first attempts to fill this gap, showing results from monthly collections in the municipality of São Luiz Gonzaga (28º24'28"S, 54º57'39"W), in the Brazilian Pampa. A species inventory was carried out in two contrasting environments, an urban zone and a forest remnant (rural zone). In both areas banana-baited traps were used to capture adult drosophilids. The identification was made using external morphology and male terminalia. In total, 13,379 drosophilids were analyzed (rural zone: N = 8,812 and Sobs = 25; urban zone: N = 4,567 and Sobs = 16). In the present study, 16 (60%) out of 26 species were found exclusively or preferentially in the forest. The period of highest richness was between the months of June to November (roughly winter and spring), and the period of lowest richness was from December to May (roughly summer and autumn). An analysis of cluster by the Coefficient of Jaccard showed that species composition slightly changes when the period of the year with higher temperatures (from January to May) is compared with the period with lower temperatures (from June to October). The species abundances were also highly affected by seasonality, as revealed by the Morisita Index, since the samples clustered into similar groups in consecutive periods and in the same season, showing the seasonal preference of some species. The time component was a determinant in the diversity of the assemblage, surpassing the spatial effect. The strong reduction in diversity in the urban area when compared to a small forest patch is evidence of the importance of the natural environments in maintaining the diversity in the Pampa biome, currently a highly disturbed landscape.
A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
The Paranã Valley, located in the Central Brazil Plateau, within the domain of the Cerrado biome, is frequently cited as a center of endemism and diversity. Nonetheless, this region is poorly known, mainly considering its invertebrate fauna. Here, drosophilid flies were used as biological tools to contribute to a broader inventory, whose goals were mapping the Cerrado biodiversity and identifying areas to be conserved. Three previously unsampled areas in the Paranã Valley were sampled. Amongst the 12,297 specimens collected 45 species were identified, which represents 50% of the drosophilid species previously recorded in the Cerrado. Moreover, this sampling presented eight new occurrences for the biome (Drosophila annulosa, D. calloptera, D. papei, D. neomorpha, D. roehrae, Gitona bivisualis, Rhinoleucophenga lopesi, and the genus Diathoneura) and three species that had only one record for the biome, or that were recorded only in a specific area. Therefore, this study confirms the importance of the Paranã Valley as a center of biodiversity in the Cerrado biome, and recommends the establishment of conservation units in this region.
Habitat fragmentation is the main cause of biodiversity loss, as remnant fragments are exposed to negative influences that include edge effects, prevention of migration, declines in effective population sizes, loss of genetic variability and invasion of exotic species. The Drosophilidae (Diptera), especially species of the genus Drosophila, which are highly sensitive to environmental variation, have been used as bioindicators. A twelve-month field study was conducted to evaluate the abundance and richness of drosophilids in an edge-interior transect in a fragment of semideciduous forest in São Paulo State, Brazil. One objective of the study was to evaluate the applied methodology with respect to its potential use in future studies addressing the monitoring and conservation of threatened areas. The species abundance along the transect showed a clear gradient, with species associated with disturbed environments, such as Drosophila simulans, Scaptodrosophila latifasciaeformis and Zaprionus indianus, being collected at the fragment edge and the species D. willistoni and D. mediostriata being found in the fragment's interior. Replacement of these species occurred at approximately 60 meters from the edge, which may be a reflection of edge effects on species abundance and richness because the species found within the habitat fragment are more sensitive to variations in temperature and humidity than those sampled near the edge. The results support the use of this methodology in studies on environmental impacts.
The drosophilids of a gallery forest in the Brazilian savanna were investigated
to identify the temporal and vertical patterns in the community structure of these insects.
Twelve monthly collections were performed (December 2007 to November 2008) in three
vertical strata of the forest (0, 4 and 8 m heights) using 30 traps baited with fermented
banana. The drosophilid assemblage was composed of 61 species (7,623 individuals),
experienced temporal fluctuations and was vertically stratified. Both the diversity and
abundance of the flies were very low during the dry season, a time when the assemblages
were dominated by the exotic species Drosophila simulans, whereas the community
showed an increased abundance and richness of neotropical species and showed vertical
stratification in the wet season. Rare species were found primarily at the ground level (flies
usually associated with neotropical forests) or in the canopy, which harbors species currently
associated with open vegetation, little-studied neotropical species and most likely
several new species. These changes, which reflect drosophilid adaptations to different
environments, involve a shifting of the ecological niches occupied by the flies in the forest
over time. This process of change is termed niche construction. Thus, we conclude that this
complex and dynamic community structure, which is related to the interaction of several
environmental factors associated with different forest environments, contributes to the high
diversity of gallery forests in the Brazilian savanna.
Natural populations of Drosophila willistoni collected every three months over banana baits between September, 1978 and May, 1982 at Parque de Itapuã and Parque do Turvo, Rio Grande do Sul, Brazil, localised in different regions in terms of climate, flora and fauna, were studied with respect to the variation of their chromosomal polymorphism associated with meteorological variables and population fluctuations.
3. Fellow from FAPESP. ABSTRACT. A reanalysis, based on museum specimens, of our previously published data on the geographical distribution of the species of Drosophila belonging to the cardini group in Brazil is presented and discussed. As previously recorded in several papers, including ours, the following four species were recognized: D. cardini, D. cardinoides, D. neocardini, and D. polymorpha. However, it was realized that most of the flies we have previously identified as Drosophila cardinoides belong in fact to Drosophila cardini. To facilitate the proper identification of these four near-sibling species, their holotypes were analyzed and their terminalia were described and illustrated. A key to the four species is also provided.
How many species are there is a question receiving more attention from biologists and reasons for this are suggested. Different methods of answering this question are examined and include: counting all species; extrapolations from known faunas and regions; extrapolations from samples; methods using ecological models; censusing taxonomists' views. Most of these methods indicate that global totals of 5 to 15 million species are reasonable. The implications of much higher estimates of 30 million species or more are examined, particularly the question of where these millions of species might be found.
ABSTRACT: In this study, drosophilids that bred in fruits of three common plant species of the Brazilian Savanna were investigated: Emmotum nitens, Hancornia speciosa and Anacardium humile, along with the temporal and spatial distribution of these insects among fruits obtained from six individuals of E. nitens. Fallen fruits were collected in natural environments, placed on moist sand in individual containers and all drosophilids that emerged from these resources during 15 days were collected, counted and identified. From 3,651 fruits collected (3,435 of E. nitens, 179 of A. humile and 37 of H. speciosa) 4,541 flies emerged and were classified into 19 species of Drosophilidae. Their distribution was unequal among the three resources, also over time, and among the six individuals of E. nitens. Such fluctuations probably reflect the availability of resources in time and space and probably the action of selective factors such as larval competition. _______________________________________________________________________________ RESUMO Neste estudo, são investigados os drosofilídeos que se criam em frutos de três espécies de plantas comuns do Cerrado brasileiro: Emmotum nitens, Hancornia speciosa e Anacardium humile, juntamente com a distribuição temporal e espacial desses insetos entre os frutos obtidos de seis indivíduos de E. nitens. Frutos recolhidos sobre a serrapilheira, em ambientes naturais, foram mantidos no laboratório e os drosofilídeos que deles emergiram foram contados e identificados. Dos 3.651 frutos coletados (3.435 de E. nitens, 179 de A. humile e 37 de H. speciosa) emergiram 4.541 drosofilídeos, classificados em 19 espécies. A distribuição dessas espécies foi desigual entre os três tipos de recursos, ao longo do tempo, e também entre os seis indivíduos de E. nitens. Essas flutuações refletem a disponibilidade dos recursos no tempo e no espaço, e provavelmente a ação de forças seletivas como a competição entre as larvas.
Seasonality can cause severe bottlenecks in natural populations, even leading to local extinction. Large variation in resource availability may explain the bottlenecks, but the role of these variations is still poorly understood. The goal of this study was to analyze if temporal variations in the guild of drosophilids breeding in fruits of Mauritia flexuosa (Arecaceae) can be explained by the shortage of this resource during the dry season. Fruits of M. flexuosa were collected over one year in a gallery forest located in the Central Brazilian Savanna. The drosophilid assemblage varied over time, with a lower density of species and of individuals in the dry season, when the percentage of colonized fruits was also smaller. These findings suggest that although the fruits were available during the dry season, they were underused. This way, the resource availability does not seem to regulate the community in the dry season.
Two decades of research have not established whether tropical insect herbivores are dominated by specialists or generalists. This impedes our understanding of species coexistence in diverse rainforest communities. Host specificity and species richness of tropical insects are also key parameters in mapping global patterns of biodiversity. Here we analyse data for over 900 herbivorous species feeding on 51 plant species in New Guinea and show that most herbivorous species feed on several closely related plant species. Because species-rich genera are dominant in tropical floras, monophagous herbivores are probably rare in tropical forests. Furthermore, even between phylogenetically distant hosts, herbivore communities typically shared a third of their species. These results do not support the classical view that the coexistence of herbivorous species in the tropics is a consequence of finely divided plant resources; non-equilibrium models of tropical diversity should instead be considered. Low host specificity of tropical herbivores reduces global estimates of arthropod diversity from 31 million (ref. 1) to 4 6 million species. This finding agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global diversity based on ecological samples of tropical communities with those based on sampling regional faunas.
Forest canopies represent the functional interface between 90% of the Earth's terrestrial biomass and the atmosphere and include some of the most threatened of all terrestrial ecosystems. However, we lack even a basic understanding of how the biomass of plants and animals is distributed throughout forest canopies, even though this information is vital for estimating energy flow, carbon cycling, resource use and the transfer of materials within this ecosystem. Here we measure the biomass of invertebrates living in a common rainforest epiphyte, describe a striking relationship between fern size and the biomass of animals within the ferns, and reveal that one large epiphyte may contain an invertebrate biomass similar to that found in the whole of the rest of the tree crown on which it is growing. Using these data, we show that including the fauna of these epiphytes--a neglected component in rainforest ecosystems--can more than double our estimate of the total invertebrate biomass in an entire rainforest canopy.
Biodiversity hotspots have a prominent role in conservation biology, but it remains controversial to what extent different types of hotspot are congruent. Previous studies were unable to provide a general answer because they used a single biodiversity index, were geographically restricted, compared areas of unequal size or did not quantitatively compare hotspot types. Here we use a new global database on the breeding distribution of all known extant bird species to test for congruence across three types of hotspot. We demonstrate that hotspots of species richness, threat and endemism do not show the same geographical distribution. Only 2.5% of hotspot areas are common to all three aspects of diversity, with over 80% of hotspots being idiosyncratic. More generally, there is a surprisingly low overall congruence of biodiversity indices, with any one index explaining less than 24% of variation in the other indices. These results suggest that, even within a single taxonomic class, different mechanisms are responsible for the origin and maintenance of different aspects of diversity. Consequently, the different types of hotspots also vary greatly in their utility as conservation tools.
The arctic flora is considered to be impoverished, but estimates of species diversity are based on morphological assessments, which may not provide accurate counts of biological species. Here we report on crossing relationships within three diploid circumpolar plant species in the genus Draba (Brassicaceae). Although 99% of parental individuals were fully fertile, the fertility of intraspecific crosses was surprisingly low. Hybrids from crosses within populations were mostly fertile (63%), but only 8% of the hybrids from crosses within and among geographic regions (Alaska, Greenland, Svalbard, and Norway) were fertile. The frequent occurrence of intraspecific crossing barriers is not accompanied by significant morphological or ecological differentiation, indicating that numerous cryptic biological species have arisen within each taxonomic species despite their recent (Pleistocene) origin.
• crossing relationships
• cryptic species
• Draba
• speciation
• postmating isolation
The phylogenetic relationships among nine entities of Drosophila belonging to the D. willistoni subgroup were investigated by establishing the homologous chromosomal segments of IIR chromosome, Muller's element B (equivalent to chromosome 2L of D. melanogaster). The sibling species of the D. willistoni group investigated include D. willistoni, D. tropicalis tropicalis, D. tropicalis cubana, D. equinoxialis, D. insularis and four semispecies of the D. paulistorum complex. The phylogenetic relationships were based on the existence of segments in different triads of species, which could only be produced by overlapping inversions. Polytene banding similarity maps and break points of inversions between species are presented. The implications of the chromosomal data for the phylogeny of the species and comparisons with molecular data are discussed. The aim of this study is to produce phylogenetic trees depicting accurately the sequence of natural events that have occurred in the evolution of these sibling species.
The dog, Cams familiaris, is the oldest domesticated animal. The actual time when domestication first occurred will probably never be known, but the oldest known remains, obtained from a cave in the Beaverhead Mountains of Idaho, have been carbon dated to be from the period 8300–9500 B.C., which means that they may be as much as 11,500 years old. Assuming, as Lawrence (1967) does, that the first dogs were domesticated approximately 12,000 years ago, they could have gone through as many as 6000 generations in domestication, based on an average generation span of 2 years, or, more conservatively, 4000 generations at a rate of one generation per 3 years. Since dogs associated with primitive human cultures were usually kept in small semi-isolated populations, the opportunities for rapid evolutionary change have been great. As Scott (1968) has pointed out, domestication presents a situation similar to a species entering into a new environment. We would expect the phenomenon of adaptive radiation to have taken place, particularly since dogs spread to all parts of the world and were kept not only in a great variety of human cultural environments, but also exposed to almost every climatic condition, from tropical to arctic. At the time of the historical exploration of the world, dogs were found associated with people on all continents, and most islands as well.
Biologists are still trying to grasp the global dimensions of the phylum Arthropoda and its major class the Insecta, in spite of the fact that over a million species of arthropods have been described. The canopy of rain forest trees is believed by many to hold the key to the immense diversity of insects. In recent years the use of knock-down insecticides to sample insects from rain forest canopy has revealed information on the canopy's arthropod inhabitants and community structure. The sampling techniques involved are outlined and data reviewed on taxonomic and guild structure, species abundance, body size and biomass of insects, and the faunal similarity of trees. Calculations by Erwin 1982, based on knock-down insecticide studies of the beetle fauna of one species of Central American tree, suggest there may be 30 million species of tropical forest arthropods. Reanalysis of these calculations, using additional data, produces a range of possible estimates from about 10 to 80 million. The unknown range of plant host-specificities of tropical insects is the main weakness of this method of calculation. Assessment of the faunal importance of the canopy in relation to that of other rain forest biotopes requires comparative quantitative studies. The preliminary results of one such simple study suggest that over 42 million arthropods may be found in a hectare of Seram rain forest (at the time of study), and that 70% occur in the soil and leaf litter and 14% in the canopy. They also suggest that Collembola and Acarina are the dominant groups in this hectare, and that there are as many ants as all the other insects (excluding Collembola).
A new species, Drosophila pavlovskiana Kastritsis and Dobzhansky, is described. It was encountered in two localities in British Guiana and originally considered as a Guianan race of Drosophila paulistorum Dobzhansky and Pavan. A more detailed study has shown that it must be considered specifically distinct.
Biologists generally agree that species are to be delimited on the basis of genetic discontinuities. The two species concepts that depend on such discontinuities to delimit species are the biological and the evolutionary species concepts. A biological species is a group of interfertile populations that is reproductively isolated from other such groups and that occupies a specific niche in nature (following Mayr, 1982). An evolutionary species is a single lineage of ancestor-descendant populations that maintains its own identity from other such lineages, that fits into its own ecological niche, and that has a unique evolutionary history (Simpson, 1961; Grant, 1981; Wiley, 1981). It thus differs from the biological species concept in that it is equally applicable to both sexually and asexually reproducing organisms. Under both the biological and the evolutionary species concepts, genetic discontinuities between sister species are thought to arise stochastically following speciation. It is assumed that as time passes, the two diverge progressively in a suite of morphological, physiological, and ecological attributes. Although most botanists espouse an evolutionary species concept in their theoretical writings, in their classifications they often recognize only species that have distinctive structural characters by which the taxa can be identified. In so doing, they are employing the morphological species concept of their
Data are given on the quality and quantity of the chromosomal polymorphism in certain populations of Central and South America which have not been previously studied. The over-all picture that emerges is summarized in figures 1 and 2. Some of the populations are highly polymorphic and other predominantly monomorphic. Populations of the central part of the geographic distribution area of the species tend to be more polymorphic than those of the peripheral parts and distributional pockets; populations which occupy rich and diversified environments are more polymorphic than those of submarginal and marginal environments; and populations which face the competition of closely related species are more monomorphic than those enjoying a near-monopolistic status. These regularities suggest that the chromosomal polymorphism is, in Drosophila willistoni, a method whereby populations may achieve a mastery of their environments. Using this working hypothesis, we have attempted to predict the extent of the polymorphism expected in populations of certain hitherto not studied localities. Such predictions have been verified by observation. Nevertheless, the populations of a part of coastal Brazil constitute an exception, being less polymorphic than they might have been expected to be.
The genetic polymorphism, as manifested in heterozygosis for chromosomal inversions, has been studied in populations of Drosophila willistoni from the West Indies and Central America, and compared with the situation in South American populations. The genetic variability is depauperate in island and marginal populations compared to continental and central ones. The reduction of the genetic variability is especially pronounced on the Lesser Antilles, except for Trinidad which has a population not very different from some continental ones. The island of St. Kitts has the most nearly monomorphic population known in the species D. willistoni. The populations of the different islands differ from each other rather more strikingly than do continental populations living at comparable distances. Larger islands tend to have more polymorphism than smaller islands. This agrees with the more general rule, that the amount of adaptive polymorphism in a population tends to be proportional to the diversity of environmental opportunities which this population exploits.
Molecular sequences now overwhelm morphology in phylogenetic inference. Nonetheless, most molecular studies are conducted on a limited number of taxa, as DNA rarely can be analysed from old museum types or fossils. During the last 20 years, more than 150 molecular studies have challenged the current phylogenetic classification of the family Drosophilidae Rondani based on morphological characters. Most studies concerned a single genus, Drosophila Fallén, and included only few representative species from 17 out of the 78 genera of the family. Therefore, these molecular studies were unable to provide an alternative classification scheme. A supermatrix analysis of seven nuclear and one mitochondrial genes (8248 bp) for 33 genera was conducted using outgroups from one calyptrate and four ephydroid families. The Bayesian phylogeny was consistent with previous molecular studies including whole genome sequences and divided the Drosophilidae into four monophyletic clades. Morphological characters, mostly male genitalia, then were compared thoroughly between the four clades and homologous character states were identified. These states were then checked for 70 genera and a revised phylogenetic, family-group classification for the Drosophilidae is proposed. Two genera –Cladochaeta Coquillett and Diathoneura Duda – of the tribe Cladochaetini Grimaldi are transferred to the family Ephydridae. The Drosophilidae is divided into two subfamilies: Steganinae Hendel (30 genera) and Drosophilinae Rondani (43 genera). A further two genera, Apacrochaeta Duda and Sphyrnoceps de Meijere, are incertae sedis, and Palmophila Grimaldi, is synonymized with Drosophilasyn.n. The Drosophilinae is subdivided into two tribes: the re-elevated Colocasiomyini Okada (nine genera) and Drosophilini Okada. The paraphyly of the genus Drosophila was not resolved to avoid affecting the binomina of important laboratory model species; however, its subgeneric classification was revised in light of molecular and morphological data. Three subgenera, namely Chusqueophila Brncic, Phloridosa Sturtevant and Psilodorha Okada, were synonymized with the subgenus Drosophila (Drosophila) Fallén syns.n. Among the 45 species groups and 5 species complexes of Drosophila (Drosophila), 22 groups and 1 complex were transferred to the subgenus Drosophila (Siphlodora) Patterson & Mainland and 6 groups, 2 species subgroups and 3 complexes are considered incertae sedis within the genus Drosophila. Different morphological characters provide different signals at different phylogenetic scales: thoracic characters (wing venation and presternal shape) discriminate families; grasping and erection-related characters discriminate subfamilies to tribes; whereas phallic paraphyses, i.e. auxiliary intromittent organs, discriminate genera and Drosophila subgenera. The study shows the necessity of analysing morphological characters within a molecular phylogenetic framework to translate molecular phylogenies into taxonomically-comprehensive classifications.
The Brazilian cerrado (savanna) biome covers 2 million km2representing 23% of the area of the country. It is an ancient biome with rich biodiversity, estimated at 160000 species of plants, fungi and animals. There are about 800 species of trees and large shrubs in the savanna vegetation and several times that number of ground species (herbs and subshrubs). When the flora of gallery forests, mesophytic forests and other habitats occurring in the biome are included, the total number of vascular plant species is estimated to reach about 10000. During the last 25 years modern agriculture has been developed in the cerrado to produce soya, maize, rice, etc and enormous numbers of cattle are raised in planted pastures. Charcoal production for the Brazilian steel industry also causes great destruction of the cerrado. By 1994 an estimated 695000 km2of cerrado (representing 35% of its area) had been converted to ‘anthropic landscape’. This compares to the destruction of about 400000 km2of Brazilian Amazonian forest representing 12 or 13% of the area of this biome. Conservation initiatives are now desperately needed. Only 1.5% of the cerrado biome is preserved as Federal Reserves and this area needs to be at least tripled. Surveys of the vascular flora aimed at discovering biogeographic patterns are now in progress with the objective of choosing representative areas and biodiversity ‘hot spots’ for conservation.
Morphologically cryptic species act as a wild card when it comes to biodiversity assessments and conservation, with the capacity to dramatically alter our understanding of the biological landscape at the taxonomic, ecological, biogeographic, evolutionary, and conservation levels. We discuss the potential effects that cryptic species may have on biodiversity assessments and conservation, as well as some of the current issues involving the treatment of cryptic species both at taxonomic and conservation levels. In addition, using a combination of advertisement call and morphological data, we describe a new species of the Leptodactylus marmoratus group from the upper Amazon basin, and we assess how cryptic species can affect conservation assessments of species in the Leptodactylus marmoratus group by examining how recent findings affect our understanding of the distribution of what is assumed to be a widespread Amazonian species, Leptodactylus andreae.
The Drosophila willistoni group consists of 23 species of which six are sibling species and belong to the D. willistoni subgroup: D. willistoni, Drosophila equinoxialis, Drosophila tropicalis, Drosophila insularis, Drosophila pavlovskiana and Drosophila paulistorum. These sibling species are abundant in the Neotropical region and can hardly be differentiated by the usual taxonomic traits. Four of them (D. willistoni, D. equinoxialis, D. tropicalis and D. paulistorum) cover extensive geographic distribution areas overlapping in places while two of them are endemic (D. insularis and D. pavlovskiana). In this study, we presented a method for the identification of five sibling species of the D. willistoni subgroup based on the allozyme variation of acid phosphatase-1 (Acph-1) in acrylamide gel electrophoresis. Our work showed that Acph-1 allozyme differences can be used for species-diagnostic characterization. This method was shown to be a more efficient tool for species identification than others because it is both quicker and produces reliable results.
Biologists are still trying to grasp the global dimensions of the phylum Arthropoda and its major class the Insecta, in spite of the fact that over a million species of arthropods have been described. The canopy of rain forest trees is believed by many to hold the key to the immense diversity of insects. In recent years the use of knock-down insecticides to sample insects from rain forest canopy has revealed information on the canopy's arthropod inhabitants and community structure. The sampling techniques involved are outlined and data reviewed on taxonomic and guild structure, species abundance, body size and biomass of insects, and the faunal similarity of trees. Calculations by Erwin (1982), based on knock-down insecticide studies of the beetle fauna of one species of Central American tree, suggest there may be 30 million species of tropical forest arthropods. Reanalysis of these calculations, using additional data, produces a range of possible estimates from about 10 to 80 million. The unknown range of plant host-specificities of tropical insects is the main weakness of this method of calculation. Assessment of the faunal importance of the canopy in relation to that of other rain forest biotopes requires comparative quantitative studies. The preliminary results of one such simple study suggest that over 42 million arthropods may be found in a hectare of Seram rain forest (at the time of study), and that 70% occur in the soil and leaf litter and 14% in the canopy. They also suggest that Collembola and Acarina are the dominant groups in this hectare, and that there are as many ants as all the other insects (excluding Collembola).
Although natural populations of drosophilid flies have been the subject of ecological studies, the population ecology of these insects in the tropics is still poorly known. This paper discusses aspects of the relationship between droso-philids and their environment, based on 28 monthly collections made in two contrasting vegetations of the Brazilian Cerrado biome: gallery forest and savanna. Exotic species were found in both types of environment; but 14 of the 30 captured Neotropical species occurred exclusively in the gallery forests, probably because of their climatic stability and greater environmental heterogeneity. Even though some endemic species were more abundant in the dry and cold months, most populations exhibited peaks of abundance in the wet season. The species diversity indexes (H ′ and D), higher in the dry season, were probably affected by increased evenness at this time of year, when the populations of practically all the species are greatly reduced. As species richness in the savanna vegetation clearly decreased in the dry season, increasing again in the wet season, it is suggested that some drosophilids migrate to the forests when climatic conditions are too stressful in the savannas.
Erwin's much debated estimate of 30 million species of arthropods is revised. The original estimate is based on the evaluation of host specificity of guilds in beetle samples, and subsequent hierarchical ratio extrapolations. The growing number of studies including mass sampling of arthropods have provided several data sets suitable for obtaining an empirical basis of this estimate. The structure in this modified version is somewhat changed compared to the original estimate in order to make each hierarchical step more easily testable. Plant species are separated into different growth forms, and host specificity measures are based only on phytophagous species. Effective specialization is applied as a measure of host specificity to correct for the fauna shared between plant species. A between community correction factor is applied to correct for differences in host specificity at different spatial scales. There are still great uncertainties attended with such estimates. The largest problems refer to the between community correction factor and the proportion of canopy species to total species. Further work on host specificity and the least known hyperdiverse groups are also needed. The revised version of the estimate does not support hyperestimates of 30 100 million species. Rather, it compares nicely with estimates derived from other estimation methods, indicating a global arthropod species richness of 5–10 million species.
The Cerrado is one of the world's biodiversity hotspots. In the last 35 years, more than 50% of its approximately 2 million km² has been transformed into pasture and agricultural lands planted in cash crops. The Cerrado has the richest flora among the world's savannas (>7000 species) and high levels of endemism. Species richness of birds, fishes, reptiles, amphibians, and insects is equally high, whereas mammal diversity is relatively low. Deforestation rates have been higher in the Cerrado than in the Amazon rainforest, and conservation efforts have been modest: only 2.2% of its area is under legal protection. Numerous animal and plant species are threatened with extinction, and an estimated 20% of threatened and endemic species do not occur in protected areas. Soil erosion, the degradation of the diverse Cerrado vegetation formations, and the spread of exotic grasses are widespread and major threats. The use of fire for clearing land and to encourage new growth for pasture has also caused damage, even though the Cerrado is a fire-adapted ecosystem. Ecosystem experiments and modeling show that change in land cover is altering the hydrology and affecting carbon stocks and fluxes. Cerrado agriculture is lucrative, and agricultural expansion is expected to continue, requiring improvements in and extension of the transportation infrastructure, which will affect not only the Cerrado but also the Amazon forest. Large-scale landscape modification and threats to numerous species have led to renewed interest from various sectors in promoting the conservation of the Cerrado, particularly through strengthening and enlarging the system of protected areas and improving farming practices and thus the livelihoods of local communities.
Focuses on tropical environments, examining how insects respond to seasonality in rainfall and in sunshine (in part related to diurnal rainfall distribution). Attention is paid not only to physiological and ecological constraints which affect seasonal timing of activity, but also responses to non-seasonal activity patterns. -P.J.Jarvis
Forest canopies contain a major proportion of the diversity of organisms on Earth and constitute the bulk of photosynthetically active foliage and biomass in forest ecosystems. For these reasons canopy research has become integral to the management of forest ecosystems, and to a better understanding of global change. Ecological research in forest canopies is relatively recent and has been primarily descriptive in scope. The development of new methods of canopy access has enabled scientists to conduct more quantified research in tree crowns. Studies of sessile organisms, mobile organisms, and canopy interactions and processes have emerged as subdisciplines of canopy biology, each requiring different methods for collecting data. Canopy biology is beginning to shift from a descriptive autecology of individuals to a more complex ecosystem approach, although some types of field work are still limited by access.
Questions currently addressed in canopy research are extremely diverse but emphasize comparisons with respect to sapatial and temporal variation. Spatial scales range from leaves (e.g. quantifying the number of mites on individual phylloplanes) to trees (e.g. measuring photosynthesis between sun and shade leaves), to forest stands (e.g.measuring turbulence above the canopy), and entire landscapes (e.g. comparing mammals between different forest types). Temporal variation is of particular significance in tropical forest canopies, where populations of organisms and their resources have diurnal, seasonal, or even annual periodicity. As the methods for canopy access improve, more rigorous hypotheses-driven field studies remain a priority of this newly coalesced discipline.
Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.
Examination of genetic and ecological relationships within sibling species complexes can provide insights into species diversity and speciation processes. Alpheus angulatus and A. armillatus, two snapping shrimp species with overlapping ranges in the north-western Atlantic, are similar in morphology, exploit similar ecological niches and appear to represent recently diverged sibling species. We examined phylogenetic and ecological relationships between these two species with: (i) sequence data from two mitochondrial genes (16S rRNA and COI); (ii) data on potential differences in microhabitat distribution for A. armillatus and A. angulatus; and (iii) data from laboratory experiments on the level of reproductive isolation between the two species. DNA sequence data suggest A. armillatus and A. angulatus are sister species that diverged subsequent to the close of the Isthmus of Panama, and that haplotype diversity is lower in A. armillatus than in A. angulatus. Both species are distantly related to A. heterochaelis and A. estuariensis, two species with which A. angulatus shares some similarities in coloration. Ecological data on the distribution of A. angulatus and A. armillatus from two locations revealed differences in distribution of the two species between habitat patches, with each patch dominated by one or the other species. However, there was no apparent difference in distribution of the two species within habitat patches with respect to microhabitat location. Ecological data also revealed that heterospecific individuals often occur in close proximity (i.e. within metres or centimetres) where sympatric. Behavioural data indicated that these species are reproductively isolated, which is consistent with speciation in transient allopatry followed by post-divergence secondary contact. Our data further resolve taxonomic confusion between the sibling species, A. armillatus and A. angulatus, and suggest that sympatry in areas of range overlap and exploitation of similar ecological niches by these two recently diverged species have selected for high levels of behavioural incompatibility.