Evolution of reproductive morphology among recently diverged taxa in the Drosophila mojavensis species cluster.

Division of Biological Sciences, Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093.
Ecology and Evolution (Impact Factor: 1.66). 02/2012; 2(2):397-408. DOI: 10.1002/ece3.93
Source: PubMed

ABSTRACT The morphological evolution of sexual traits informs studies of speciation due to the potential role of these characters in reproductive isolation. In the current study, we quantified and compared genitalic variation within the Drosophila mojavensis species cluster to infer the mode of evolution of the male aedeagus. This system is ideal for such studies due to the opportunity to test and compare levels of variation along a divergence continuum at various taxonomic levels within the group. Shape variation was quantified using elliptic Fourier descriptors and compared among the four D. mojavensis host races, and between D. mojavensis and its sister species Drosophila arizonae. Aedeagus shape was diagnostic for D. arizonae, and among three of the four D. mojavensis subspecies. In each of these cases, there was less variation within subspecies than among subspecies, which is consistent with the pattern predicted if genitalia are evolving according to a punctuated change model, and are involved with mate recognition. However, aedeagus shape in Drosophila mojavensis sonorensis was highly variable and broadly overlapping with the other three subspecies, suggesting aedeagus evolution in this subspecies is more complex and subject to additional evolutionary factors. These results are interpreted and discussed in the context of selection on mate recognition systems and the potential for failed copulation.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Male genitalia show patterns of divergent evolution, and sexual selection is recognised as being responsible for this taxonomically widespread phenomenon. Much of the empirical support for the sexual selection hypothesis comes from studies of insects. Here, I synthesise the literature on insect genital evolution, and use this synthesis to address the debate over the mechanisms of selection most likely to explain observed patterns of macroevolutionary divergence in genital morphology. Studies of seven insect orders provide evidence that non-intromittent genitalia are subject to sexual selection through their effects on mating success, while intromittent genitalia are subject to selection through their effects on fertilisation success. However, studies that use quantitative methods to analyse the form of selection are necessary to identify the mechanisms of sexual selection involved. Phylogenetic analyses from diverse taxonomic groups confirm that divergence in male genital morphology can be predicted from variation in the opportunity for sexual selection. Much debate revolves around the importance of female choice and sexual conflict in the evolution of male genitalia, the resolution of which lies in economic studies of mating interactions and in recognising sexual selection as a continuum between male competition, sexual conflict and female choice. The species isolating lock-and-key hypothesis is frequently dismissed as unimportant in genital evolution because in part of a perceived lack of variation in female genitalia across species. Increasingly, however, studies report species-specific variation in female genital morphology and its coevolutionary divergence with male genital morphology. Contemporary views recognise a continuum between female choice that enforces species isolation and female choice that targets variation in male quality within populations, placing lock-and-key processes into the realm of sexual selection. Distinguishing between species-isolating and directional forms of female choice will require studies that examine both the tempo and mode of divergence, both within and among species.
    Australian Journal of Entomology 10/2013; · 0.80 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Investigating the evolution of species-specific insect genitalia is central to understanding how morphological diversification contributes to reproductive isolation and lineage divergence. While many studies evoke some form of sexual selection to explain genitalia diversity, the basis of selection and the mechanism of heterospecific mate exclusion remains vague. I conducted reciprocal mate pair trials in the Drosophila mojavensis species cluster to quantify the frequency of failed insemination attempts, historically referred to as pseudocopulation, between lineages with discrete size and shape differences of the male aedeagus.ResultsIn cross-taxon matings aedeagus size had a significant effect on pseudocopulation frequencies, while aedeagus shape and genetic distance did not. The direction of the size difference was an important factor for successful mating. When females were mated to a cross-taxon male with a larger aedeagus than males from her own species, the pair could not establish a successful mating interaction. Females mated to cross-taxon males with a smaller aedeagus than conspecific males were able to establish the mating interaction but had issues disengaging at the end of the interaction.Conclusions The results of this study support a role for aedeagus size in the male-female mating interaction, with a secondary role for aedeagus shape. In natural populations, mating failure based on aedeagus size could serve as an important reproductive isolating mechanism resulting in failed insemination attempts after both the male and female show a willingness to mate.
    BMC Evolutionary Biology 12/2014; 14(1):255. · 3.41 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sperm competition (SC) is a major component of sexual selection that enhances intra- and intersexual conflicts and may trigger rapid adaptive evolution of sexual characters. The actual role of SC on rapid evolution, however, is poorly understood. Besides, the relative contribution of distinctive features of the mating system to among species variation in the strength of SC remains unclear. Here, we assessed the strength of SC and mating system factors that may account for it in the closely related species Drosophila buzzatii and Drosophila koepferae. Our analyses reveal higher incidence of multiple paternity and SC risk in D. buzzatii wild-inseminated females. The estimated number of fathers per brood was 3.57 in D. buzzatii and 1.95 in D. koepferae. In turn, the expected proportion of females inseminated by more than one male was 0.89 in D. buzzatii and 0.58 in D. koepferae. Laboratory experiments show that this pattern may be accounted for by the faster rate of stored sperm usage observed in D. koepferae and by the greater female remating rate exhibited by D. buzzatii. We also found that the male reproductive cost of SC is also higher in D. buzzatii. After a female mated with a second male, first-mating male fertility was reduced by 71.4% in D. buzzatii and only 33.3% in D. koepferae. Therefore, we may conclude that postmating sexual selection via SC is a stronger evolutionary force in D. buzzatii than in its sibling.
    Molecular Ecology 08/2013; · 5.84 Impact Factor

Full-text (2 Sources)

Available from
Jun 4, 2014