Boldness in extreme environments: temperament divergence in a desert-dwelling fish

Investigating how environmental factors influence within-species trait variability is critical to understanding the evolution and maintenance of individual behavioural differences (i.e. temperament or personality), and their integration into wider ecological theory. Populations of Australian desert gobies, Chlamydogobius eremius, from starkly contrasting aquatic environments in arid Australia were used to investigate how environmental differences influence temperament traits. Focusing on boldness and exploration, fish were assessed using novel environment, dispersal and novel food item assays under laboratory conditions. The results of these experiments were analysed for repeatability and for patterns of divergence within and between populations. We found consistent within-species differences in novel environment and novel food item assays, with refuge emergence and inspection latency of a novel food item both strongly repeatable behavioural axes. Although both traits can be considered measures of boldness, refuge emergence significantly diverged according to sex, while inspection latency was predicted by habitat differences. This suggests that multiple measures of boldness are diverging independently according to different ecological drivers. Specifically, we found that fish caught from environments without predators and with probable intense intraspecific competition are less active and bolder in a novel food item context. Further analysis demonstrated how extreme habitat differences are driving behavioural divergence on multiple axes, relating to boldness and dispersal behaviours. This provides valuable insights into how the environment and behaviour interact and how we define temperament traits, as well as highlighting the importance of studying temperament within a community ecology context.