Data from: Variation in sexual brain size dimorphism over the breeding cycle in the three-spined stickleback

Snapshot analyses have demonstrated dramatic intraspecific variation in
the degree of brain sexual size dimorphism (SSD). Although brain SSD is
believed to be generated by the sex-specific cognitive demands of
reproduction, the relative roles of developmental and population specific
contributions to variation in brain SSD remain little studied. Using a
common garden experiment, we tested for sex-specific changes in brain
anatomy over the breeding cycle in three-spined stickleback (Gasterosteus
aculeatus) sampled from four locations in Northern Europe. We found that
the male brain increased in size (ca. 24%) significantly more than the
female brain towards breeding, and that the resulting brain SSD was
similar (ca. 20%) for all populations over the breeding cycle. Our
findings support the notion that the stickleback brain is highly plastic
and changes over the breeding cycle, especially in males, likely as an
adaptive response to the cognitive demands of reproduction (e.g. nest
construction and parental care). The results also provide evidence to
suggest that breeding-related changes in brain size may be the reason for
the widely varying estimates of brain SSD across studies of this species,
cautioning against interpreting brain size measurements from a single
time-point as fixed/static.