Sex allocation of hermaphrodites in metapopulations with frequent population extinction and recolonization

Competition among related males, male gametes, or pollen grains to fertilize a limited number of females, eggs, or ovules (local mate competition) is expected to favor female-biased progeny sex ratios in dioecious species. In hermaphrodites, local mate competition should similarly promote female-biased sex allocation, with reduced investment in sperm or pollen relative to eggs, ovules, or seeds. Because inbreeding, especially self-fertilization, tends to generate local mate competition, female-biased sex allocation should be associated with positive inbreeding, for example as measured by FIS. Although inbreeding may result from mating among relatives within local populations, it can also be generated by population turnover in metapopulations subject to frequent local extinction and recolonization. This effect of population turnover has previously been considered for species with separate sexes. Here, we use formal analysis and individual-based simulations to show that population turnover can select for strongly female-biased sex allocation in hermaphroditic metapopulations, particularly when among-deme dispersal is low. When mating within established populations is random, so that FIS is zero, female-biased sex allocation is instead associated with positive FST, a measure of inbreeding at the metapopulation level caused by population structure. Our results thus extend local mate competition theory to hermaphroditic metapopulations and identify FST as a key predictor of sex allocation when inbreeding is generated by population turnover rather than by non-random mating within demes.