Maxi Polihronakis Richmond

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

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.

Deciphering the routes of invasion of Drosophila suzukii by means of ABC random forest

Abstract 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 role of aedeagus size and shape in failed mating interactions among recently diverged taxa in the Drosophila mojavensis species cluster

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.

Population genetics and phylogenetic relationships of beetles (Coleoptera: Histeridae and Staphylinidae) from the Sonoran Desert associated with rotting columnar cacti

Dozens of arthropod species are known to feed and breed in the necrotic tissues (rots) of columnar cacti in the Sonoran Desert. Because the necrotic patches are ephemeral, the associated arthropods must continually disperse to new cacti and therefore the populations of any given species are expected to show very little local genetic differentiation. While this has been found to be true for the cactophilic Drosophila, the evolutionary histories and characteristics of other arthropods inhabiting the same necrotic patches, especially the beetles, have yet to be examined. Here we used nucleotide sequence data from segments of the mitochondrial 16S rRNA and cytochrome c oxidase subunit I (COI) genes to examine population structure and demographic history of three sympatric beetle species (Coleoptera: Histeridae and Staphylinidae) collected on senita cactus (Lophocereus schottii) from six widely-separated localities on the Baja California peninsula of northwestern Mexico. Two histerids, Iliotona beyeri and Carcinops gilensis, and an unidentified staphylinid, Belonuchus sp., showed little or no population structure over a broad geographic area on the peninsula, consistent with the prediction that these beetles should show high dispersal ability. Demographic tests revealed varying levels of historical population expansion among the beetle species analyzed, which are discussed in light of their ecologies and concurrent biogeographic events. Additionally, phylogenetic analyses of COI sequences in Carcinops collected on a variety of columnar cacti from both peninsular and mainland Mexico localities revealed several species-level partitions, including a putative undescribed peninsular species that occurred sympatrically with C. gilensis on senita.

The challenges faced by living stock collections in the USA

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

On the Origins of the Insect Fauna of California's Channel Islands: A Comparative Phylogeographic Study of Island Beetles

Abstract. Californias 8 Channel Islands host a large diversity of insects, the vast majority of which are shared with mainland southern California. The existence of a small number of recognized endemic species, however, suggest that, for some lineages, the islands are isolated enough to have permitted significant differentiation. Here we investigate the phylogeographic relationships of 4 beetle species (Thinopinus pictus, Hadrotes crassus, Hypocaccus lucidulus, and Nyctoporis carinata): all occurring on the mainland and on multiple (up to 6) Channel Islands. Sequences of the cytochrome oxidase I mitochondrial gene (and, for one species, an intron in the nuclear guftagu gene) are analyzed by Bayesian, haplotype network, and population genetic methods to examine relationships and gene flow among island and mainland populations. In no instances were all island populations resolved to be monophyletic, and northern (Santa Cruz, Santa Rosa, San Miguel) and southern (San Nicolas, San Clemente, Santa Catalina) island groups generally showed separate relationships to the mainland. Northern island populations of Hy. lucidulus were also found to be closely related to those on the southern island of San Nicolas. Populations on San Clemente and Santa Catalina islands did not show close relationships to each other or to San Nicolas Island populations in any species. San Clemente and especially San Nicolas islands hosted disproportionately high levels of diversity in all species examined. This study suggests that the Channel Islands do not function as a biogeographical unit and that several of the islands exhibit levels of diversity comparable to, or even exceeding, similarly sampled populations on the mainland. Thus, as an insular refuge from southern Californian development, the Channel Islands constitute a center of high conservation importance.

Early events in speciation: Cryptic species of Drosophila aldrichi

Abstract Understanding the earliest events in speciation remains a major challenge in evolutionary biology. Thus identifying species whose populations are beginning to diverge can provide useful systems to study the process of speciation. Drosophila aldrichi, a cactophilic fruit fly species with a broad distribution in North America, has long been assumed to be a single species owing to its morphological uniformity. While previous reports either of genetic divergence or reproductive isolation among different D. aldrichi strains have hinted at the existence of cryptic species, the evolutionary relationships of this species across its range have not been thoroughly investigated. Here we show that D. aldrichi actually is paraphyletic with respect to its closest relative, Drosophila wheeleri, and that divergent D. aldrichi lineages show complete hybrid male sterility when crossed. Our data support the interpretation that there are at least two species of D. aldrichi, making these flies particularly attractive for studies of speciation in an ecological and geographical context.

Population Subdivision of Zarhipis integripennis (Coleoptera: Phengodidae), in Southern California

ABSTRACT The current study investigates phylogeographic structure of Zarhipis integripennis (LeConte) (Coleoptera: Phengodidae), a sexually dimorphic beetle with strongly asymmetrical dispersal abilities, to elucidate the spatial and temporal mechanisms of gene flow among populations in southern California. Using DNA sequences of a mitochondrial DNA marker and a nuclear intron in the krotzkopf verkehrt gene we compared the effect of differential dispersal on patterns of genetic structure among Z. integripennis populations across this area. Integrating these data with an ecological niche modeling analysis supported the hypothesis that dispersal between populations with fragmented niche availability was biased toward males and that female movement was limited and based on the availability of contiguous habitat. There was also evidence for historical restrictions to gene flow in the Sierra Pelona region of the Transverse Ranges based on a genetic break in both genes in this region.