Chromosomal rearrangement polymorphisms are common and increasingly found to be associated with adaptive ecological divergence and speciation. Rearrangements, such as inversions, reduce recombination in heterozygous individuals and thus can protect favourable allelic combinations at linked loci, facilitating their spread in the presence of gene flow. Recently, we identified a chromosomal inversion polymorphism that contributes to ecological adaptation and reproductive isolation between annual and perennial ecotypes of the yellow monkeyflower, Mimulus guttatus. Here we evaluate the population genetic structure of this inverted region in comparison with the collinear regions of the genome across the M. guttatus species complex. We tested whether annual and perennial M. guttatus exhibit different patterns of divergence for loci in the inverted and noninverted regions of the genome. We then evaluated whether there are contrasting climate associations with these genomic regions through redundancy analysis. We found that the inversion exhibits broadly different patterns of divergence among annual and perennial M. guttatus and is associated with environmental variation across population accessions. This study is the first widespread population genetic survey of the diversity of the M. guttatus species complex. Our findings contribute to a greater understanding of morphological, ecological, and genetic evolutionary divergence across this highly diverse group of closely related ecotypes and species. Finally, understanding species relationships among M. guttatus sp. has hitherto been stymied by accumulated evidence of substantial gene flow among populations as well as designated species. Nevertheless, our results shed light on these relationships and provide insight into adaptation in life history traits within the complex.

Summary Divergence of developmental mechanisms within populations may lead to hybrid developmental failure, and may be a factor driving speciation in angiosperms. We investigate patterns of endosperm and embryo development in Mimulus guttatus and the closely related, serpentine endemic M. 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 seed 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 seed, 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.

The apparently rapid and ancient diversification of many avian orders complicates the resolution of their relationships using molecular data. Recent studies based on complete mitochondrial DNA (mtDNA) sequences or shorter lengths of nuclear sequence have helped corroborate the basic structure of the avian tree (e.g., a basal split between Paleognathae and Neognathae) but have made relatively little progress in resolving relationships among the many orders within Neoaves. We explored the potential of a moderately sized mtDNA data set ( approximately 5000 bp for each of 41 taxa), supplemented with data from a nuclear intron ( approximately 700 bp per taxon), to resolve relationships among avian orders. Our sampling of taxa addresses two issues: (1). the sister relationship and monophyly, respectively, of Anseriformes and Galliformes and (2). relationships of the enigmatic hoatzin Opisthocomus hoazin. Our analyses support a basal split between Galloanserae and Neoaves within Neognathae and monophyly of both Galliformes and Anseriformes. Within Galliformes, megapodes and then cracids branch basally. Within Anseriformes, mitochondrial data support a screamer (Anhimidae) plus magpie goose (Anseranatidae) clade. This result, however, may be an artifact of divergent base composition in one of the two anatids we sampled. With deletion of the latter taxon, Anseranas is sister to anatids as in traditional arrangements and recent morphological studies. Although our data provide limited resolution of relationships within Neoaves, we find no support for a sister relationship between either cuckoos (Cuculiformes) or turacos (Musophagiformes) and hoatzin. Both mitochondrial and nuclear data are consistent with a relationship between hoatzin and doves (Columbiformes), although this result is weakly supported. We also show that mtDNA sequences reported in another recent study included pervasive errors that biased the analysis towards finding a sister relationship between hoatzin and turacos.

The Caribbean is characterized by a rich and diverse fauna that exhibits high levels of endemism. Numerous attempts have been made over the past several decades to elucidate the means by which this unique fauna emerged (Barbour

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 geographical 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 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 speciationdifferentiating 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.

Identifying the factors that contribute to the adaptive significance of mating preferences is one major goal of evolutionary research and is largely unresolved. Both direct and indirect benefits can contribute to mate choice evolution. Failure to consider the interaction between individual consequences of mate choice may obscure the opposing effects of individual costs and benefits. We investigate direct and indirect fitness effects of female choice in a desert fly (Drosophila mojavensis), a species where mating confers resistance to desiccation stress. Females prefer males that provide a direct benefit: greater resistance to desiccation stress. Mating preferences also appear to have indirect consequences: daughters of preferred males have lower reproductive success than daughters of unpreferred males, although additional experimentation will be needed to determine if the indirect consequences of female preferences actually arise from 'sexually antagonistic' variation. Nevertheless, the results are intriguing and are consistent with the hypothesis that an interaction between direct and indirect benefits maintains sexually antagonistic variation in these desert flies: increased desiccation resistance conferred by mating might offset the cost of producing low-fecundity daughters.

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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 laboratory-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 towards 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 premating 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. precopulatory and post-copulatory interactions) do not exert independent effects on reproductive outcomes.