When partially reproductively isolated species come back into secondary contact, these taxa may diverge in mating preferences and sexual cues to avoid maladaptive hybridization, a process known as reinforcement. This ...When partially reproductively isolated species come back into secondary contact, these taxa may diverge in mating preferences and sexual cues to avoid maladaptive hybridization, a process known as reinforcement. This phenomenon often leads to reproductive character displacement （RCD） between sympatric and allopatric populations of reinforcing species that differ in their exposure to hybridization. Recent discussions have reinvigorated the idea that RCD may give rise to additional speciation between conspecific sympatric and allopatric populations, dubbing the concept ＂cascade reinforcement.＂ Despite some empirical studies supporting cascade reinforcement, we still know very little about the conditions for its evolution. In the present article, we address this question by developing an individual-based population genetic model that explicitly simulates cascade reinforcement when one of the hybridizing species is split into sympatric and allopatric populations. Our results show that when sympatric and allopatric populations reside in the same environment and only differ in their exposure to maladaptive hybridization, migration between them generally inhibits the evolution of cascade by spreading the reinforcement alleles from sympatry into allopatry and erasing RCD. Under these conditions, cascade reinforcement only evolved when migration rate between sympatric and allopatric populations was very low. This indicates that stabilizing sexual selection in allopatry is generally ineffective in preventing the spread of reinforcement alleles. Only when sympatric and allopatric populations experienced divergent ecological selection did cascade reinforcement evolve in the presence of substantial migration. These predictions clarify the conditions for cascade reinforcement and facilitate our understanding of existing cases in nature.展开更多
Anthropogenic pollutants have the potential to disrupt reproductive strategies. Little is known about how lead （Pb2＋） exposure disrupts individual-level responses in reproductive behaviors, which are important for ...Anthropogenic pollutants have the potential to disrupt reproductive strategies. Little is known about how lead （Pb2＋） exposure disrupts individual-level responses in reproductive behaviors, which are important for fitness. Drosophila melanogaster was used as a model system to deter- mine the effects of： 1） developmental lead exposure on pre-mating reproductive behaviors （i.e., mate preference）, and 2） lead exposure and mating preferences on fitness in the F0 parental generation and F1 un-exposed offspring. Wild-type strains of D. melanogaster were reared from egg stage to adulthood in control or leaded medium （250 μM PbAc） and tested for differences in： mate preference, male song performance, sex pheromone expression, fecundity, mortality, and body weight. F0 leaded females preferentially mated with leaded males （i.e., asymmetrical positive assortative mating） in 2-choice tests. This positive assortative mating was mediated by the females （and not the males） and was dependent upon context and developmental exposure to Pb. Neither the courtship song nor the sex pheromone profile expressed by control and leaded males medi- ated the positive assortative mating in leaded females. Leaded females did not incur a fitness cost in terms of reduced fecundity, increased mortality, or decreased body weight by mating with leaded males. These results suggest that sublethal exposure to lead during development can alter mate preferences in adults, but not fitness measures once lead exposure has been removed. We suggest that changes in mate preference may induce fitness costs, as well as long-term population and multi-generational implications, if pollution is persistent in the environment.展开更多
文摘When partially reproductively isolated species come back into secondary contact, these taxa may diverge in mating preferences and sexual cues to avoid maladaptive hybridization, a process known as reinforcement. This phenomenon often leads to reproductive character displacement （RCD） between sympatric and allopatric populations of reinforcing species that differ in their exposure to hybridization. Recent discussions have reinvigorated the idea that RCD may give rise to additional speciation between conspecific sympatric and allopatric populations, dubbing the concept ＂cascade reinforcement.＂ Despite some empirical studies supporting cascade reinforcement, we still know very little about the conditions for its evolution. In the present article, we address this question by developing an individual-based population genetic model that explicitly simulates cascade reinforcement when one of the hybridizing species is split into sympatric and allopatric populations. Our results show that when sympatric and allopatric populations reside in the same environment and only differ in their exposure to maladaptive hybridization, migration between them generally inhibits the evolution of cascade by spreading the reinforcement alleles from sympatry into allopatry and erasing RCD. Under these conditions, cascade reinforcement only evolved when migration rate between sympatric and allopatric populations was very low. This indicates that stabilizing sexual selection in allopatry is generally ineffective in preventing the spread of reinforcement alleles. Only when sympatric and allopatric populations experienced divergent ecological selection did cascade reinforcement evolve in the presence of substantial migration. These predictions clarify the conditions for cascade reinforcement and facilitate our understanding of existing cases in nature.
文摘Anthropogenic pollutants have the potential to disrupt reproductive strategies. Little is known about how lead （Pb2＋） exposure disrupts individual-level responses in reproductive behaviors, which are important for fitness. Drosophila melanogaster was used as a model system to deter- mine the effects of： 1） developmental lead exposure on pre-mating reproductive behaviors （i.e., mate preference）, and 2） lead exposure and mating preferences on fitness in the F0 parental generation and F1 un-exposed offspring. Wild-type strains of D. melanogaster were reared from egg stage to adulthood in control or leaded medium （250 μM PbAc） and tested for differences in： mate preference, male song performance, sex pheromone expression, fecundity, mortality, and body weight. F0 leaded females preferentially mated with leaded males （i.e., asymmetrical positive assortative mating） in 2-choice tests. This positive assortative mating was mediated by the females （and not the males） and was dependent upon context and developmental exposure to Pb. Neither the courtship song nor the sex pheromone profile expressed by control and leaded males medi- ated the positive assortative mating in leaded females. Leaded females did not incur a fitness cost in terms of reduced fecundity, increased mortality, or decreased body weight by mating with leaded males. These results suggest that sublethal exposure to lead during development can alter mate preferences in adults, but not fitness measures once lead exposure has been removed. We suggest that changes in mate preference may induce fitness costs, as well as long-term population and multi-generational implications, if pollution is persistent in the environment.
