Heritable variation underlies behavioural types in the mating context in male bluefin killifish.

In many species, consistent behavioural differences among individuals are linked to fitness variation. Determining the environmental and genetic factors that mould these behavioural types is crucial to understanding how behaviours might respond to selection. Male bluefin killifish, Lucania goodei, show extensive consistent behavioural variation in their levels of courtship, male-directed aggression and female-directed aggression, resulting in a range of fitness-related behavioural types coexisting within a population. To determine whether the behavioural components underlying a male's stable behavioural type in the mating context are heritable and genetically correlated, we performed paternal half-sib crosses. Using animal models, we found that all three of these mating behaviours were moderately heritable (h2 = 0.17-0.29) and courtship behaviour was also heritable as a binomial trait (court yes/no: h2 = 0.50). Including effects of dam identity/common rearing environment experienced by full sibs decreased model fit, suggesting that early social interactions might contribute to behavioural types. In addition, we found evidence consistent with the possibility that the positive phenotypic correlations among mating behaviours are underlain by positive genetic correlations. Thus, it is possible that the seemingly maladaptive aggression that males direct towards females during social interactions persist due to genetic constraints and direct selection on both male-directed aggression and courtship behaviour.