Correlation of personality with individual reproductive success in shrub-nesting birds depends on their life history style

Two questions in the research of animal personality—whether there is a correlation between a personality trait and individual reproductive success, and what is the genetic basis underlying a personality trait—remain unresolved. We addressed these two questions in three shrub-nesting birds, the Azure-winged Magpie (Cyanopica cyanus, AM), White-collared Blackbird (Turdus albocinctus, WB), and Brown-cheeked Laughingthrush (Trochalopteron henrici, BL). The personality type of an individual was first identified according to its response to a territorial intruder. Then, we compared the fleeing distance, breeding parameters, and differential expressed genes (DEGs) in the brain transcriptome between bold and shy breeders. In the three species, bold breeders exhibited more aggressiveness towards an intruder of their territory than did shy breeders. The reproductive success of bold breeders was significantly higher than that of shy breeders in AM but not in WB and BL. The three species shared one DEG, crabp1, which was up-regulated in bold relative to in shy individuals. By regulating the expression of corticotropin-releasing hormone, higher crabp1 gene expression can decrease cellular response to retinoic acid. Therefore, bold individuals are insensitive to external stresses and able to exhibit more aggressiveness to intruders than their shier counterparts. Aggressiveness is beneficial to bold individuals in AM but not in WB and BL because the former could evoke neighbors to make the same response of defending against intruders but the latter could not. Although a personality trait may have the same genetic basis across species, its correlation with reproductive success depends largely on the life history style of a species.