Testing for biogeographic mechanisms promoting divergence in Caribbean crickets (genus Amphiacusta )

This work examines whether the history of diversification of Amphiacusta (Orthoptera, Gryllidae) in the Caribbean corresponds to a vicariant or a dispersalist model.The Greater Antillean islands of the Caribbean region.The phylogenetic relationships among species were estimated using a procedure that directly estimates the underlying species tree from independent loci (in this case, one mitochondrial and one nuclear locus). This tree was then used to test for topological congruence with a vicariant model, and to estimate divergence times.The analyses based on the expected pattern of species divergence (i.e. species-tree topology) support a vicariant model. With the notable exception of a dispersal event marking the colonization of Jamaica, the timing of the events are generally consistent with a vicariant scenario, given the current taxon sampling and potential errors with dating the divergence events.The tendency of species to co-segregate by island suggests that intra-island diversification is common. Despite their flightlessness, species of Amphiacusta are apparently capable of long-distance dispersal, such as colonization from the Puerto Rican/Virgin Island bank to Jamaica. The topology of the species tree is consistent with a vicariant model of divergence, and the dates of divergence between island groups are generally consistent with an island–island vicariance model. A strict island–island vicariance scenario can, however, be rejected because of inferred dispersal events such as the colonization of Jamaica. Nevertheless, the biogeographic tests suggest that most of the diversity was generated under a combination of intra-island diversification and island–island vicariance. Additional sampling of taxa will be needed to verify this hypothesized scenario. Our findings indicate that Amphiacusta presents an ideal opportunity for examining the role of sexual selection in promoting diversification, which would complement the large number of studies focused on adaptive divergence of Caribbean taxa.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79301/1/j.1365-2699.2009.02231.x.pd

Biogeographic and Evolutionary Mechanisms Driving Diversification in Caribbean Ground Crickets (genus Amphiacusta).

Amphiacusta is a species-rich genus of flightless ground crickets distributed throughout the Caribbean which exhibits substantial variation habitat use and male reproductive traits. This ecological and sexual diversity displayed by Amphiacusta furnishes a natural experiment to investigate driving population and species divergence because geographic isolation on islands can lead to the reduction or elimination of gene flow This research addresses three questions. First, what biogeographic mechanisms have influenced the pattern of species diversification of Amphiacusta? Estimates of the phylogenetic relationships among Amphiacusta are used to test the predictions of two biogeographic models for the Caribbean: island-island vicariance and overwater dispersal. Both topological evidence and estimates of the timing of divergence events provide little evidence for a strict interpretation of the island-island vicariance model, suggesting rather that both vicariance and overwater dispersal, followed by intra-island diversification, have played a role in the history of this genus. Second, is morphological divergence in the Virgin Islands species Amphiacusta sanctaecrucis the result of neutral or selective divergence? A comparison of phenotypic differentiation in three morphological traits (body size and shape, mandible shape, and genitalia shape) with neutral gene differentiation, indicates that all three exhibit significant variation between populations and have diverged by natural or sexual selection. Finally, are these traits evolving solely through local selection in isolation, or do extrinsic factors, such as the geographic configuration of islands and the ocean currents between them, influence morphological divergence between populations? An analysis of microsatellite loci finds that gene flow is very limited between islands, and furthermore, that there is no association between distance or gene flow and morphological divergence. This confirms that morphological divergence is the result of local adaptation and suggests that even weak selection over the course of their recent isolation could result in significant morphological divergence between populations. Overall, these results demonstrates that both the geological history of the Caribbean, as well as the evolutionary mechanisms operating within isolated populations are involved in the diversification of Amphiacusta.Ph.D.Ecology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/62315/1/eoneal_1.pd

Data from: Ecological selection as the cause and sexual differentiation as the consequence of species divergence?

Key conceptual issues about speciation go unanswered without consideration of non-mutually exclusive factors. With tests based on speciation theory, we exploit the island distribution and habitat differences exhibited by the Caribbean cricket Amphiacusta sanctaecrucis, and with an analysis of divergent ecological selection, sexually selected differentiation, and geographic isolation, address how these different factors interact. After testing for divergent selection by comparing neutral genetic and morphological divergence in one ecological (mandible shape) and one sexual (male genitalia shape) trait, we examine whether ecological or sexual selection is the primary mechanism driving population divergence. We find that while all three factors—isolation, ecological, and sexual selection—contribute to divergence, and that their interaction determines the stage of completeness achieved during the speciation process, as measured by patterns of genetic differentiation. Moreover, despite the striking diversity in genitalic shapes across the genus Amphiacusta which suggests that sexual selection drives speciation, the significant differences in genitalia shape between forest habitats revealed here implies that ecological divergence may be the primary axis of divergence. Our work highlights critical unstudied aspects in speciation – differentiating the cause from the consequence of divergence—and suggests avenues for further disentangling the roles of natural and sexual selection in driving divergence in Amphiacusta

Data from: Paternity analyses in wild-caught and lab-reared Caribbean cricket females reveal the influence of mating environment on post-copulatory sexual selection

Polyandry is ubiquitous in insects and provides the conditions necessary for male- and female-driven forms of post-copulatory sexual selection to arise. Populations of Amphiacusta sanctaecrucis exhibit significant divergence in portions of the male genitalia that are inserted directly into the female reproductive tract, suggesting that males may exercise some post-copulatory control over fertilization success. We examine the potential for male-male and male-female post-copulatory interactions to influence paternity in wild-caught females of A. sanctaecrucis and contrast our findings with those obtained from females reared in a high-density laboratory environment. We find that female A. sanctaecrucis exercise control by mating multiple times (females mount males), but that male-male post-copulatory interactions may influence paternity success. Moreover, post-copulatory interactions that affect reproductive success of males are not independent of mating environment: clutches of wild-caught females exhibit higher sire diversity and lower paternity skew than clutches of lab-reared females. There was no strong evidence for last-male precedence in either case. Most attempts at disentangling the contributions of male-male and male-female interactions toward post-copulatory sexual selection have been undertaken in a laboratory setting and may not capture the full context in which they take place —such as the relationship between pre-mating and post-mating interactions. Our results reinforce the importance of designing studies that can capture the multifaceted nature of sexual selection for elucidating the role of post-copulatory sexual selection in driving the evolution of male and female reproductive traits, especially when different components (e.g., pre-copulatory and post-copulatory interactions) do not exert independent effects on reproductive outcomes

PaternityDryad

File is in the GENEPOP format. Data is microsatellite genotypes from one female, the last male to be mated with her, and up to 24 of her offspring. VGB = Virgin Gorda Baths; VGP = Virgin Gorda Peak; LAB = lab population sourced from Virgin Gorda Baths; LMMale=last mated male. Missing data is represented by "?"

Inversion and noninversion marker data

Data from 16 markers, 8 located within the DIV1 inversion on linkage group 8, and 8 distributed throughout the Mimulus genome, formatted for Genalex

Amphiacusta sanctaecrucis morphological and microsatellite data

Amphiacusta sanctaecrucis morphological and microsatellite dat

Data from: Disruption of endosperm development is a major cause of hybrid seed inviability between Mimulus guttatus and Mimulus nudatus

Divergence of developmental mechanisms within populations could lead to hybrid developmental failure, and might be a factor driving speciation in angiosperms. We investigate patterns of endosperm and embryo development in Mimulus guttatus and the closely related, serpentine endemic Mimulus nudatus, and compare them to those of reciprocal hybrid seed. We address whether disruption in hybrid seed development is the primary source of reproductive isolation between these sympatric taxa. M. guttatus and M. nudatus differ in the pattern and timing of endosperm and embryo development. Some hybrid seeds exhibit early disruption of endosperm development and are completely inviable, while others develop relatively normally at first, but later exhibit impaired endosperm proliferation and low germination success. These developmental patterns are reflected in mature hybrid seeds, which are either small and flat (indicating little to no endosperm) or shriveled (indicating reduced endosperm volume). Hybrid seed inviability forms a potent reproductive barrier between M. guttatus and M. nudatus. We shed light on the extent of developmental variation between closely related species within the M. guttatus species complex, an important ecological model system, and provide a partial mechanism for the hybrid barrier between M. guttatus and M. nudatus

Seed set and proportion seed type from self-pollinations and reciprocal M. guttatus x M. nudatus crosses

This file contains seed count data from self-pollinations of Mimulus guttatus and M. nudatus and sympatric, reciprocal M. guttatus x M. nudatus hybrids. In addition to total seed set, proportions of round, shriveled and flat seeds are given. M. guttatus accessions are CSS4 and DHR14; M. nudatus accessions are CSH10 and DHRo22. CSS4 and CSH10 are sympatric; DHR14 and DHRo22 are sympatric

Growth from 1-5 days after pollination of immature seeds

This is a text file with size data from immature seeds derived self-pollination of Mimulus guttatus and M. nudatus accession and sympatric, reciprocal M. guttatus x M. nudatus hybrids. M. guttatus accessions are CSS4 and DHR14; M. nudatus accessions are CSH10 and DHRo22. CSS4 and CSH10 are sympatric; DHR14 and DHRo22 are sympatric. Hybrid seeds either exhibit endopserm development from 2-5 days after pollination ('Hybrid Developing') or exhibit arrested developing starting at 2 days after pollination ('Hybrid Arrested'). CSS4x = self-pollinated CSS4, etc.; DAP = days after pollination; UO = unfertilized ovule. Size is measured from the chalazal to micropylar end and is given in mm. All crosses are female x male