Does social context influence male mating tactics in Drosophila melanogaster?

Social context, such as mate availability and perceived competition, can influence a male’s mating tactics. In Drosophila melanogaster most research has investigated how physical interactions and the perceived levels of sperm competition alter mating behaviour. I wanted to know if males would respond to the perceived social environments without the presence of physical interaction. Using a unique apparatus, I altered focal males’ social context by separating them physically from a social environment using a screen. Focal males were either in: (i) the presence of rival males and mates, (ii) the presence of potential mates only, (iii) isolation, or (iv) the presence of rival males only. I also manipulated the period the focal male was conditioned to a social environment to assess if the timing of cues is important. My findings suggest that the duration of acclimation alters male mating tactics. Regardless of social environment, the duration a male was conditioned influenced copulation latency. Males that were conditioned to their social environment for the duration of the experiment had differing copulation latencies between environments. Males held in isolation took longer to successfully court females, and transferred less sperm during mating then experimental males in the presence of rival males. Additionally, copulation duration correlated with the number of sperm transferred. Overall, my results suggest that the social environment and the perceived competition level affect mating strategies even without physical interactions. Since this apparatus may trick flies into believing they are a part of a social group, while controlling the male mating status, future work could examine behavioural, genetic and physiological phenotype effects of the social environment for both sexes.

Genomic consequences of mating system evolution in the Pacific coastal dune endemic, Abronia umbellata (Nyctaginaceae)

The advent of next-generation sequencing has significantly reduced the cost of obtaining large-scale genetic resources, opening the door for genomic studies of non-model but ecologically interesting species. The shift in mating system, from outcrossing to selfing, has occurred thousands of times in angiosperms and is accompanied by profound changes in the population genetics and ecology of a species. A large body of work has been devoted to understanding why the shift occurs and the impact of the shift on the genetics of the resulting selfing populations, however, the causes and consequences of the transition to selfing involve a complicated interaction of genetic and demographic factors which are difficult to untangle. Abronia umbellata is a Pacific coastal dune endemic which displays a striking shift in mating system across its geographic range, with large-flowered outcrossing populations south of San Francisco and small-flowered selfing populations to the north. Abronia umbellata is an attractive model system for the study of mating system transitions because the shift appears to be recent and therefore less obscured by post-shift processes, it has a near one-dimensional geographic range which simplifies analysis and interpretation, and demographic data has been collected for many of the populations. In this study, we generated transcriptome-level data for 12 plants including individuals from both subspecies, along with a resequencing study of 48 individuals from populations across the range. The genetic analysis revealed a recent transition to selfing involving a drastic reduction in genetic diversity in the selfing lineage, potentially indicative of a recent population bottleneck and a transition to selfing due to reproductive assurance. Interestingly, the genetic structure of the populations was not coincident with the current subspecies demarcation, and two large-flowered populations were classified with the selfing subspecies, suggesting a potential need for re-evaluation of the current subspecies classification. Our finding of low diversity in selfing populations may also have implications for the conservation value of the threatened selfing subspecies.