Divergence in reproductive behaviors is associated with the evolutionary loss of parental care

The mechanisms underlying the divergence of reproductive strategies
between closely-related species are still poorly understood. Additionally,
it is unclear which selective factors drive the evolution of reproductive
behavioral variation and how these traits coevolve, particularly during
early divergence. To address these questions, we quantified behavioral
differences in a recently diverged pair of Nova Scotian three-spined
stickleback (Gasterosteus aculeatus) populations, which vary in parental
care, with one population displaying paternal care and the other lacking
this. We compared both populations, and a full reciprocal F1 hybrid cross,
across four major reproductive stages: territoriality, nesting, courtship,
and parenting. We identified significant divergence in a suite of
heritable behaviors. Importantly, F1 hybrids exhibited a mix of behavioral
patterns, some of which suggest sex-linkage. This system offers fresh
insights into the coevolutionary dynamics of reproductive behaviors during
early divergence and offers support for the hypothesis that coevolutionary
feedback between sexual selection and parental care can drive rapid
evolution of reproductive strategies.