Seasonal changes in coat colour and sexual size dimorphism in a subtropical ungulate

Phenotypes reflect the adaptations of organisms to their environments, with common rules defining how coloration and body size should vary based on climate and latitude. Hong Kong (HK) cattle present an opportunity to study these adaptations in one of the very few cattle populations not directly controlled by humans. These cattle are free-ranging in a subtropical climate, characterized by high humidity and temperatures during the wet season, and scarce precipitation during the dry season. We studied seasonal coat colour changes in HK feral cattle, and sexual dimorphism in body size and horn length. We provide the first evidence of seasonal changes in coat colour in cattle, with paler coats being more common in the wet season, while darker coats prevailed in the dry season. These seasonal changes were influenced by temperature, wind speed, solar radiation and body condition. We found that males were larger and had longer horns than females. Our results show a male-biased sex dimorphism in the HK feral cattle. Additionally, our findings suggest that thermoregulation costs drive coloration in these cattle. The phenotypic plasticity we demonstrate in these subtropical feral cattle improves our knowledge of the adaptations of ungulates to their habitat.