Social Distance and Fungal Disease in an Australian Wild Lizard Population

Abstract

Social living often confers substantial fitness benefits; however, close spatial association among individuals can also elevate opportunities for pathogen transmission, especially where the populations are dense. Despite this, the extent to which avoidance behaviours are expressed by wild reptiles facing fungal disease remains unclear. We examined Eastern Water Dragons (Intellagama lesueurii) in Roma Street Parklands, Brisbane, Australia, where a population is affected by the emerging fungal pathogen Nannizziopsis barbatae (Nb). Using a five-year dataset (2018-2023) spanning 146 individuals, we quantified social distance, as the minimum distance to the nearest neighbour, in relation to the number of diseased conspecifics that overlapped each individual seasonal core home area. Social distance was negatively associated with the number of diseased conspecifics, indicating a strong crowding effect; however, this association was weaker for diseased individuals, which were observed at larger distances than healthy individuals even when the number of diseased conspecifics was high. Together, these patterns indicate a context-dependent spacing response associated with disease status and local disease context, suggesting that infection risk constrains density-driven proximity. Our findings provide new insights into how disease pressure shapes social spacing in reptiles and contribute to a broader understanding of behavioural responses to emerging infectious fungal diseases.