Sydney successfully defends her Masters thesis!
Abstract: As suitable environmental conditions for species shift rapidly under anthropogenic climate change, populations that are not well adapted, or maladapted to these novel environments can face serious challenges. Evolutionary rescue of a population in decline depends on genetic variation in fitness. The adaptive potential of a population to a particular environment can be evaluated by estimating the mean and additive genetic variance in fitness itself. I used quantitative genetics coupled with ‘animal’ model MCMCglmm analysis to estimate the adaptive potential of a wild population under an expected future temperature regime. I found very low estimates of genetic variance and heritability in fitness components, however these results may correspond with the rarity of evolutionary rescue in wild populations. I did find correlations between fitness components that indicate possible selection at the germination stage of early life history stages that may be eroding genetic variance in fecundity later on.
Madeline Peters and Colin Bonner both publish in Evolution!
Abstract: Coexpression of genes in plant sporophytes and gametophytes allows correlated gametic and sporophytic selection. Theory predicts that, under outcrossing, an allele conferring greater pollen competitive ability should fix within a population unless antagonistic pleiotropy with the sporophyte stage is strong. However, under strong selfing, pollen competitiveness is immaterial as superior and inferior competitors are deposited on opposite stigmas, producing assortative competition. Because many plant species have mixed‐mating systems, selfing should be critical in the spread and maintenance of pollen‐expressed genes affecting competitiveness. We present two one‐locus, two‐allele population genetic models for the evolution of a locus controlling pleiotropic antagonism between pollen competitiveness and diploid fitness. Analytical solutions provide minimum and maximum selfing rates allowing invasion of alleles with greater diploid and haploid fitness, respectively. Further, polymorphism is only maintained when diploid selection is recessive. Fixation of the allele conferring greater pollen competitiveness may be prevented, even with weak sporophytic counterselection, with sufficiently high selfing. Finally, selfing expands and limits the range of haploid–diploid selection coefficients allowing polymorphism, depending on dominance and selfing mode. https://onlinelibrary.wiley.com/doi/abs/10.1111/evo.13597
Abstract: Urbanization is an important component of global change. Urbanization affects species interactions, but the evolutionary implications are rarely studied. We investigate the evolutionary consequences of a common pattern: the loss of high trophic‐level species in urban areas. Using a gall‐forming fly, Eurosta solidaginis, and its natural enemies that select for opposite gall sizes, we test for patterns of enemy loss, selection, and local adaptation along five urbanization gradients. Eurosta declined in urban areas, as did predation by birds, which preferentially consume gallmakers that induce large galls. These declines were linked to changes in habitat availability, namely reduced forest cover in urban areas. Conversely, a parasitoid that attacks gallmakers that induce small galls was unaffected by urbanization. Changes in patterns of attack by birds and parasitoids resulted in stronger directional selection, but loss of stabilizing selection in urban areas, a pattern which we suggest may be general. Despite divergent selective regimes, gall size did not very systematically with urbanization, suggesting but not conclusively demonstrating that environmental differences, gene flow, or drift, may have prevented the adaptive divergence of phenotypes. We argue that the evolutionary effects of urbanization will have predictable consequences for patterns of species interactions and natural selection. https://onlinelibrary.wiley.com/doi/abs/10.1111/evo.13544
Colin Bonner successfully defends his Masters!
Thesis Abstract: Adaptation to changing environmental conditions and subsequent recovery in population growth through evolutionary rescue is critical for many declining species, but it relies on populations having sufficient genetic variation. Assisted gene flow provides a solution to low genetic variance by introducing gene flow between distinct populations, allowing evolutionary rescue to proceed. Assisted gene flow, however, requires that these populations can interbreed. Many populations are divergent in reproductive phenology, reducing hybridization rates. The potential for hybridization between plant populations can be estimated from flowering schedules, but for these estimates to be useful they must be proven accurate. In a pair of two-generation experiments, I compared prospective estimates of hybridization, derived from flowering schedules, to retrospective estimates, derived from an analysis of offspring, using flowering time as a genetic marker. In both cases, hybridization was asymmetric. The prospective and retrospective strongly agreed under controlled pollination conditions, but less so under natural pollination in the field.
Bonner, C., Sokolov, N., Westover, S.E., Ho, M., and Weis, A. E. 2019. Phenological divergence impedes hybridization: experimental tests and their implications for assisted gene flow. Ecology and Evolution. PDF
Start, D., A.E. Weis and B. Gilbert. 2019. Indirect interactions shape selection in a multi-species foodweb. The American Naturalist. PDF