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Free keywords:
ecological speciation; gamete precedence; Gasterosteus aculeatus; fertilization success; ecotype
Abstract:
Ecology can play a major role in species diversification. As individuals are
adapting to contrasting habitats, reproductive barriers may evolve at multiple
levels. While pre-mating barriers have been extensively studied, the evolution
of post-mating reproductive isolation during early stages of ecological
speciation remains poorly understood. In diverging three-spined stickleback
ecotypes from two lakes and two rivers, we observed differences in sperm
traits between lake and river males. Interestingly, these differences did not
translate into ecotype-specific gamete precedence for sympatric males in competitive
in vitro fertilization experiments, potentially owing to antagonistic
compensatory effects. However, we observed indirect evidence for impeded
development of inter-ecotype zygotes, possibly suggesting an early stage of
genetic incompatibility between ecotypes. Our results show that pre-zygotic
post-copulatory mechanisms play a minor role during this first stage of ecotype
divergence, but suggest that genetic incompatibilities may arise at early
stages of ecological speciation.
