Variations on a theme: diversification of cuticular hydrocarbons in a clade of cactophilic Drosophila

Abstract

BackgroundWe characterized variation and chemical composition of epicuticular hydrocarbons (CHCs) in the seven species of the Drosophila buzzatii cluster with gas chromatography/mass spectrometry. Despite the critical role of CHCs in providing resistance to desiccation and involvement in communication, such as courtship behavior, mating, and aggregation, few studies have investigated how CHC profiles evolve within and between species in a phylogenetic context. We analyzed quantitative differences in CHC profiles in populations of the D. buzzatii species cluster in order to assess the concordance of CHC differentiation with species divergence.ResultsThirty-six CHC components were scored in single fly extracts with carbon chain lengths ranging from C29 to C39, including methyl-branched alkanes, n-alkenes, and alkadienes. Multivariate analysis of variance revealed that CHC amounts were significantly different among all species and canonical discriminant function (CDF) analysis resolved all species into distinct, non-overlapping groups. Significant intraspecific variation was found in different populations of D. serido suggesting that this taxon is comprised of at least two species. We summarized CHC variation using CDF analysis and mapped the first five CHC canonical variates (CVs) onto an independently derived period (per) gene + chromosome inversion + mtDNA COI gene for each sex. We found that the COI sequences were not phylogenetically informative due to introgression between some species, so only per + inversion data were used. Positive phylogenetic signal was observed mainly for CV1 when parsimony methods and the test for serial independence (TFSI) were used. These results changed when no outgroup species were included in the analysis and phylogenetic signal was then observed for female CV3 and/or CV4 and male CV4 and CV5. Finally, removal of divergent populations of D. serido significantly increased the amount of phylogenetic signal as up to four out of five CVs then displayed positive phylogenetic signal.ConclusionsCHCs were conserved among species while quantitative differences in CHC profiles between populations and species were statistically significant. Most CHCs were species-, population-, and sex-specific. Mapping CHCs onto an independently derived phylogeny revealed that a significant portion of CHC variation was explained by species' systematic affinities indicating phylogenetic conservatism in the evolution of these hydrocarbon arrays, presumptive waterproofing compounds and courtship signals as in many other drosophilid species.

Hydrocarbon divergence and reproductive isolation in Timema stick insects

“…This pattern of speciational change has also been found for the macro evolution of Timema courtship behavior, but not for the macroevolution of male genitalic morphology, which has diversified in proportion to phyletic branch lengths, apparently under forces of sexual selection or sexual conflict [52]. Among other insect species, previous studies of macroevolutionary change in hydrocarbon profiles have reported rapid evolution in conjunction with species specificity and a notable degree of phylogenetic conservatism [50,53,54], patterns that are largely concordant with those described here for Timema , but have not been partitioned into speciational versus phyletic concentrations of change. If changes in cuticular hydrocarbon profile drive speciation, then directional selection due to mate choice with profile-based criteria should characterize processes of divergence or reinforcement, while stabilizing selection should predominate at other times.…”

Mito-nuclear discordance with evidence of shared ancestral polymorphism and selection in cactophilic species ofDrosophila

“…() and Oliveira et al . (): D. serido , [( D. gouveai , ( D. seriema , D. borborema )]. The geometric mean of the population mutation rate (θ = 4Nu) of the independent loci was used to estimate priors for population size and migration rate parameters, as suggested in the IMa2 manual.…”

Phylogeny, environment and sexual communication across the Drosophila genus

“…Although modelling abiotic conditions, such as temperature and precipitation, should be regional enough to make conclusions valid, we have not considered confounds from species that could have been sampled from microclimates. For instance, arid species, such as D. buzzatii, have been collected from arid corridors of otherwise tropical areas of Brazil (Oliveira et al, 2011); thus pressures concerning water and precipitation will be different than in arid areas adjacent to temperate regions. This highlights the difficulties in making generalizations, even within a species, and underscores the need to record where and under what conditions the samples are acquired in any study.…”