Alvarado-Serrano, D. F. | bioRxiv Science

bioRxiv2018

Detecting spatial dynamics of range expansions with geo-referenced genome-wide SNP data and the geographic spectrum of shared alleles

Uncovering the spatial dynamics of range expansions is a major goal in studies of historical demographic inference, with applications ranging from understanding the evolutionary origins of domesticated crops, epidemiology, invasive species, and understanding specieslevel responses to climate change. Following the surge in advances that make explicit use of the spatial distribution of genetic data from georeferenced SNP variants, we present a novel summary statistic vector, the geographic spectrum of shared alleles (GSSA). Using simulations of twodimensional serial expansion, we find that the information from the GSSA, summarized with Harpendings Raggedness Index (RI), can accurately detect the spatial origins of a range expansion under serial founder models, even with sparse sampling of only ten individuals. When applying to SNP data from two species of the holarctic butterfly genus Lycaeides, the suggested origins of expansion are consistent with hindcasts obtained from ecological niche models (ENMs). These results demonstrate the GSSA to be a useful exploratory tool for generating hypotheses of range expansion with genomewide SNP data. Our simulation experiments suggest high performance even with sampling found in studies of nonmodel organisms (one sampled individual per location, no outgroup information, and only 5,000 SNP loci).

evolutionary biology↗

bioRxiv2017

Environmental Influences On The Mating System Of The Common Morning Glory

The balance between selfing and outcrossing is a life history trait of major concern with deep evolutionary consequences in mixed mating species. Yet, our current understanding of the proximate and ultimate determinants of species mating system is still unsatisfactory and largely theoretical. Indeed, evolutionary biologists are still puzzled by the often dramatic variation of mating strategies within single species. Of particular concern is the extent to which environmental conditions shape patterns of variation and covariation of mating system components within species. Here, we address this concern in the common morning glory (Ipomoea purpurea) by taking advantage of an extensive dataset of floral traits, genetic estimates of selfing and inbreeding, and relevant environmental factors compiled for 22 populations of this species distributed along a disparate set of environments along Southeast and Midwest USA. Combining a powerful array of parametric and model-free statistical approaches, we robustly identify a set of natural and anthropogenic environmental factors underlying population-level variation in selfing, inbreeding, and flower morphology. Remarkably, individual mating system components are found to be associated with different environmental factors and only loosely associated with each other, and thus potentially under multiple different selective pressures. These results not only corroborate theoretical expectations of the significant role the environment plays in the local determination of mating systems, but also provide compelling evidence of complex underlying interactions between multiple evolutionary processes.

plant biology↗