RESUMEN
It is generally considered that sexual organisms show faster evolutionary adaptation than asexual organisms because sexuals can accumulate adaptive mutations through recombination. Yet, empirical evidence often shows that the geographic range size of sexual species is narrower than that of closely related asexual species, which may seem as if asexuals can adapt to more varied environments. Two potential explanations for this apparent contradiction considered by the existing theory are reproduction assurance and migration load. Here, we consider both reproductive assurance and migration load within a single model to comparatively examine their effects on range expansions of sexuals and asexuals across an environmental gradient. The model shows that higher dispersal propensity decreases sexuals' disadvantage in reproductive assurance while increasing their disadvantage in migration load. Moreover, lower mutation rate constrains adaptation more strongly in asexuals than in sexuals. Thus, high dispersal propensity and high mutation rates promote that asexuals have wider range sizes than sexuals. Intriguingly, our model reveals that sexuals can have wider geographic range sizes than asexuals under low dispersal propensity and low mutation rates, a pattern consistent with a few exceptional empirical cases. Combining reproductive assurance and migration load provides a useful perspective to better understand the relationships between species' mating systems and their geographic ranges.
Asunto(s)
Evolución Biológica , Reproducción , Reproducción/genética , Adaptación Fisiológica , Mutación , Tasa de Mutación , Reproducción Asexuada/genéticaRESUMEN
AbstractIn animal-pollinated plants, the growth environment and pollination environment are two important agents of natural selection. However, their simultaneous effects on plant speciation remain underexplored. Here, we report a theoretical finding that if plants' local adaptation to the growth environment increases their floral rewards for pollinators, it can strongly facilitate ecological speciation in plants. We consider two evolving plant traits, vegetative and floral signal traits, in a population genetic model for two plant populations under divergent selection from different growth environments. The vegetative trait determines plants' local adaptation. Locally adapted plants reward pollinators better than maladapted plants. By associative learning, pollinators acquire learned preferences for floral signal traits expressed by better-rewarding plants. If pollinators' learned preferences become divergent between populations, floral signal divergence occurs and plants develop genetic associations between vegetative and floral signal traits, leading to ecological speciation via a two-allele mechanism. Interestingly, speciation is contingent on whether novel floral signal variants arise before or after plant populations become locally adapted to the growth environment. Our results suggest that simultaneous selection from growth and pollination environments might be important for the ecological speciation of animal-pollinated plants.