Environmental complexity during early life shapes average behavior in adulthood

Personality has been identified in a range of animal taxa during the last
few decades, with important ecological and evolutionary implications.
Investigating the effects of environmental factors during early life can
provide important insights into the ontogeny of animal personality. We
reared newborn mosquitofish, Gambusia affinis, in tanks of different
structural complexities, and measured their behavioral traits (i.e.,
shyness, exploration, and sociability) when they reached sexual maturity.
Univariate linear mixed-effects models were fitted to test the effects of
environmental complexity and sex on population-average behavior, whereas
multivariate models were fitted to quantify behavioral repeatability (i.e.
personality) and among-individual correlations (i.e., behavioral
syndromes). On average, females were shyer and more social than males, and
the fish reared in complex environments were shyer, less explorative, and
more social than those reared in open environments. Among-individual
differences were consistently large across trials for all behaviors,
indicating that personality variation was present in mosquitofish of both
sexes reared in different environments. Repeatability did not differ among
behaviors, and there were no differences in repeatability in any behavior
between sexes or among environments. A negative correlation between
shyness and exploration was found in mosquitofish from all treatments at
both phenotypic and among-individual levels, with the latter indicating a
strong shyness-exploration behavioral syndrome. Our study provides robust
evidence that average levels of personality might vary when mosquitofish
are raised in different levels of structural complexity during early life.