Deciphering invasion routes from molecular data is crucial to understanding biological invasions, including identifying bottlenecks in population size and admixture among distinct populations. Here, we unravel the invasion routes of the invasive pest Drosophila suzukii using a multi-locus microsatellite dataset (25 loci on 23 worldwide sampling locations). To do this, we use approximate Bayesian computation (ABC), which has improved the reconstruction of invasion routes, but can be computationally expensive. We use our study to illustrate the use of a new, more efficient, ABC method, ABC random forest (ABC-RF) and compare it to a standard ABC method (ABC-LDA). We find that Japan emerges as the most probable source of the earliest recorded invasion into Hawaii. Southeast China and Hawaii together are the most probable sources of populations in western North America, which then in turn served as sources for those in eastern North America. European populations are genetically more homogeneous than North American populations, and their most probable source is northeast China, with evidence of limited gene flow from the eastern US as well. All introduced populations passed through bottlenecks, and analyses reveal five distinct admixture events. These findings can inform hypotheses concerning how this species evolved between different and independent source and invasive populations. Methodological comparisons indicate that ABC-RF and ABC-LDA show concordant results if ABC-LDA is based on a large number of simulated datasets but that ABC-RF out-performs ABC-LDA when using a comparable and more manageable number of simulated datasets, especially when analyzing complex introduction scenarios.

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.

The Drosophila nannoptera species group, a taxon of Mexican cactophilic flies, is an excellent model system to study the influence of abiotic and biotic factors on speciation, the genetic causes of ecological specialization and the evolution of unusual reproductive characters. However, the phylogenetic relationships in the nannoptera species group and its position within the virilis-repleta phylogeny have not been thoroughly investigated. Using a multilocus data set of gene coding regions of eight nuclear and three mitochondrial genes, we found that the four described nannoptera group species diverged rapidly, with very short internodes between divergence events. Phylogenetic analysis of repleta group lineages revealed that D. inca and D. canalinea are sister to all other repleta group species, whereas the annulimana species D. aracataca and D. pseudotalamancana are sister to the nannoptera and bromeliae species groups. Our divergence time estimates suggest that the nannoptera species group radiated following important geological events in Central America. Our results indicate that a single evolutionary transition to asymmetric genitalia and to unusual sperm storage may have occurred during evolution of the nannoptera group.

BackgroundInvestigating 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0255-3) contains supplementary material, which is available to authorized users.

Many discoveries in the life sciences have been made using material from living stock collections. These collections provide a uniform and stable supply of living organisms and related materials that enhance the reproducibility of research and minimize the need for repetitive calibration. While collections differ in many ways, they all require expertise in maintaining living organisms and good logistical systems for keeping track of stocks and fulfilling requests for specimens. Here, we review some of the contributions made by living stock collections to research across all branches of the tree of life, and outline the challenges they face.DOI: http://dx.doi.org/10.7554/eLife.24611.001