Behavioural syndromes as a link between ecology and mate choice: a field study in a reef fish population

The link between ecology and reproductive isolation constitutes the cornerstone of the ecological hypothesis of speciation. Such a link can arise when traits under ecologically based selection are also used as cues for mating (‘magic traits’) or as a by-product of habitat choice when mating takes place within habitats. Here, we propose that behavioural syndromes may also constitute such a link. We illustrate this mechanism in the butter hamlet, Hypoplectrus unicolor, a reef fish from the wider Caribbean, with aggressive mimicry as the focal ecological trait. Aggressive mimicry is of particular interest in hamlets since it has been proposed to play a key role in the radiation of Hypoplectrus. Individuals from a natural population in Bocas del Toro, Panama, were tagged and their diurnal and spawning behaviours observed over 2 years. The results indicate that aggressive mimicry behaviour differed consistently between individuals and formed two discrete behavioural types that also differed with respect to territoriality. Differences in territoriality between the two behavioural types translated into different use of space in spawning contexts, which generated a tendency for assortative mating by behavioural type. This case study illustrates how behavioural syndromes may form a link between ecologically relevant behavioural traits and mate choice, suggesting that they might play an underappreciated role in the early stages of speciation.