Habitat-associated intraspecific variation in behavior and stress responses in a demersal coral reef fish

Habitat heterogeneity has been linked to species diversity and abundance, but can also generate intraspecific behavioral variation that has functional consequences for how animals respond to environmental stressors. Previously, we found that bicolor damselfish Stegastes partitus inhabiting the fringing coral reefs of Curaçao exhibited intraspecific variation in agonistic behaviors in spatial patterns associated with the reef’s transition from live coral colonies to rubble. Here we demonstrate for the first time that these fish also vary in physiological stress reactivity with habitat type. Bicolor damselfish collected from live coral and rubble habitats were sampled either <2.5 min (baseline) or 20 min (stressed) after capture to assess stressor-induced responses of cortisol and mRNA abundance for stress-associated endocrine genes (corticotropin-releasing hormone [CRH], urotensin 1 [U-I], CRH-binding protein [CRH-BP], and CRH receptors 1 and 2) in the brain. Acute capture stress increased plasma levels of cortisol in male and female damselfish from both habitat types, but triggered gene transcript responses contingent on the fish’s habitat and sex. In males from both habitats, capture stress increased relative transcript abundance for CRH, U-I and CRH-BP. Females, however, exhibited stress-responsive changes in transcript abundance that were habitat-dependent, with capture stress increasing CRH, U-I and CRH-BP mRNA levels in females from live reef, but decreasing levels of these same transcripts in females from rubble. These results provide evidence that intraspecific variation in behavior in bicolor damselfish is linked to variation in physiological stress reactivity in spatial patterns reflective of the local ecological characteristics of the coral reef.