title: Inbreeding depression and drift load in small populations at demographic disequilibrium.
abstract: Inbreeding depression is a major driver of mating system evolution and has critical implications for population viability. Theoretical and empirical attention has been paid to predicting how inbreeding depression varies with population size. Lower inbreeding depression is predicted in small populations at equilibrium, primarily due to higher inbreeding rates facilitating purging and/or fixation of deleterious alleles (drift load), but predictions at demographic and genetic disequilibrium are less clear. In this study, we experimentally evaluate how lifetime inbreeding depression and drift load, estimated by heterosis, vary with census (Nc) and effective (estimated as genetic diversity, He) population size across six populations of the biennial Sabatia angularis as well as present novel models of inbreeding depression and heterosis under varying demographic scenarios at disequilibrium (fragmentation, bottlenecks, disturbances). Our experimental study reveals high average inbreeding depression and heterosis across populations. Across our small sample, heterosis declined with He, as predicted, whereas inbreeding depression did not vary with Heand actually decreased with Nc. Our theoretical results demonstrate that inbreeding depression and heterosis levels can vary widely across populations at disequilibrium despite similar Heand highlight that joint demographic and genetic dynamics are key to predicting patterns of genetic load in nonequilibrium systems.
authors: Department of Biology, Temple University, 1900 N. 12th Street, Philadelphia, Pennsylvania, 19122.
authors: Rachel B
authors: RB
authors: Spigler
authors: Biodiversity Conservation Laboratory, Department of Environment, University of the Aegean, University Hill, 81100, Mytilene, Greece.
authors: Konstantinos
authors: K
authors: Theodorou
authors: Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens, Georgia, 30602-7271.
authors: Shu-Mei
authors: SM
authors: Chang
mesh_terms: D040741:Genetic Load; D014644:Genetic Variation; D005828:Genetics, Population; D029965:Gentianaceae / Q000235:genetics*; D006823:Hybrid Vigor; D000071422:Inbreeding Depression; D009657:North Carolina; D011156:Population Density; D013022:South Carolina
keywords: Bottlenecks; genetic load; heterosis; mating system evolution; mutation accumulation; population size