Behavioural types and life history strategies during ontogeny in the mangrove killifish, Kryptolebias marmoratus

Consistent differences in behaviour, termed behavioural types (BTs) are well documented in the animal kingdom. Relatively little is known, however, about how and why consistency is maintained within populations. In recent years, theoretical work suggests that life history trade-offs may be an important mechanism driving the maintenance of interindividual variation in BTs. We used a laboratory population of a clonal vertebrate, the mangrove killifish, as a model organism. This fish is an internally self-fertilizing simultaneous hermaphrodite that exhibits within-genotype homozygosity. We utilized 20 genotypes to examine BT plasticity (boldness and exploration), the development of behavioural correlations, and relationships between life history strategy and BTs at five age points during ontogeny. We found that BT scores increased during early ontogeny and reached an asymptote near sexual maturity. We also found considerable variation in BT developmental plasticity at the genotype level. Moreover, although genotypes exhibited high levels of plasticity in BTs, strong, significant positive correlations between exploration and boldness emerged from day 61 onwards. Furthermore, we observed no difference between genotypes in growth rate and growth was unrelated to BTs. Contrary to our predictions, we found that while genotypes differed in their age at first reproduction and reproductive output, these differences were unrelated to BT expression prior to and following sexual maturity. We discuss these results in relation to mechanisms proposed to drive interindividual variation in BTs and we highlight the potential of the mangrove killifish as a model organism for animal personality studies.