Covariation and repeatability of aggressive and risk-taking behaviours in a terrestrial salamander (Plethodon cinereus)

Behavioural syndromes receive attention from many disciplines for their potential evolutionary significance. Personality traits and behavioural syndromes often vary among species and even within species (i.e. between sexes and populations). Whether correlations among behaviours emerge as an adaptive response or a developmental constraint, however, is still debated. As a foundation for future studies to test the adaptive versus constraint hypotheses, we investigated repeatability and covariation of aggression and boldness between two genetically distinct populations of eastern red-backed salamanders, Plethodon cinereus, and between sexes in those populations. We predicted that individuals would show consistency in behavioural traits across trials (i.e. their behaviour would be repeatable) and that aggressive behaviour would be positively correlated with boldness. We also predicted that behavioural syndromes would vary between genetic groups and sexes. Salamanders were exposed to standard resident/intruder territorial trials to assess their aggressive behaviour. We then conducted a refuge-emergence assay to determine boldness, which involved calculating a boldness index from latency to emerge and time spent back inside refuge after initial emergence. We found that our boldness index and two aggressive displays (all-trunk-raised and look towards) were repeatable. Further analysis indicated a positive correlation between boldness and aggressiveness, suggesting the presence of a behavioural syndrome in our sample. However, we did not find strong evidence for geographical or sex differences. Our results warrant future research to determine whether a shared behavioural syndrome in our sample has resulted from adaptive or constraining mechanisms in these populations.