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Background: The independent evolution of sympatric species pairs of threespine sticklebacks has provided a natural system to explore how divergent ecologies shape mating preferences. Research has shown that both limnetic and benthic females discriminate against heterospecific males, but not against populations of the same species from different lakes, at least when visual cues are available (Rundle et al., 2000). It is known that olfaction is used in species dis- crimination by benthic but not limnetic sticklebacks in one of the species pairs (Rafferty and Boughman, 2006), but differences across populations are unknown. Hypotheses: Females from benthic habitats make use of olfactory cues to distinguish between species but not lakes of potential mates. Limnetic females will not show preferences for males of different species or lakes when limited to only olfactory cues. Organisms: Benthic and limnetic populations of threespine stickleback (Gasterosteus aculeatus) from Paxton and Priest Lakes, British Columbia. Methods: We exposed gravid females from each population to chemical stimuli from nesting males in a Y-maze, and recorded which stimulus a female chose and how much time was taken to make a decision. Results: We did not find significant differences between female populations in the preference for conspecific over heterospecific male odours. There was also no preference for odours of males from the same or a different lake. In all populations of females, the preference for male odours of different lakes differed between the two species of male odours: benthic male odours from a different lake were selected over limnetic male odours. The amount of time taken to make a decision differed between female populations, but only when benthic females ultimately chose a limnetic male odour over a benthic one. Conclusions: The preference for conspecific over heterospecific odours, although not strong, may still contribute to reproductive isolation in sympatric sticklebacks, particularly through interactions with other senses and environmental properties.
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Conflict over fertilization underlies the transient evolution of reinforcement
When two species meet in secondary contact, the production of low fitness hybrids may be prevented by the adaptive evolution of increased prezygotic isolation, a process known as reinforcement. Theoretical challenges to the evolution of reinforcement are generally cast as a coordination problem, i.e., “how can statistical associations between traits and preferences be maintained in the face of recombination?” However, the evolution of reinforcement also poses a potential conflict between mates. For example, the opportunity costs to hybridization may differ between the sexes or species. This is particularly likely for reinforcement based on postmating prezygotic (PMPZ) incompatibilities, as the ability to fertilize both conspecific and heterospecific eggs is beneficial to male gametes, but heterospecific mating may incur a cost for female gametes. We develop a population genetic model of interspecific conflict over reinforcement inspired by “gametophytic factors”, which act as PMPZ barriers among Zea mays subspecies. We demonstrate that this conflict results in the transient evolution of reinforcement—after females adaptively evolve to reject gametes lacking a signal common in conspecific gametes, this gamete signal adaptively introgresses into the other population. Ultimately, the male gamete signal fixes in both species, and isolation returns to pre-reinforcement levels. We interpret geographic patterns of isolation among Z . mays subspecies considering these findings and suggest when and how this conflict can be resolved. Our results suggest that sexual conflict over fertilization may pose an understudied obstacle to the evolution of reinforcement.
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- Award ID(s):
- 1753632
- PAR ID:
- 10390413
- Editor(s):
- Jennions, Michael D.
- Date Published:
- Journal Name:
- PLOS Biology
- Volume:
- 20
- Issue:
- 10
- ISSN:
- 1545-7885
- Page Range / eLocation ID:
- e3001814
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1371/journal.pbio.3001814
