Behaviour 2019
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Do social structures of coral-dwelling gobies change along a spatial gradient?
Catheline/YM Froehlich1, Siobhan/J Heatwole1, O Selma Klanten2, Martin/L Hing1, Marian/YL Wong1. 1University of Wollongong, Wollongong, NSW, Australia; 2University of Technology Sydney, Sydney, NSW, Australia

Many animals live in social groups throughout their geographic range and group members are organised into a dominance hierarchy. In fishes, hierarchies are based on the size of individuals to promote cooperation, because getting too large may lead to eviction from higher ranks. However, social structures like group composition and the structure of dominance hierarchies are assumed to remain similar among environments and within a genus. To examine whether social structures are plastic spatially and within a genus, we observed 7 coral-dwelling goby species (genus Gobiodon) from three geographical areas: Papua New Guinea (PNG = most northern site), Lizard island (LI; upper Great Barrier Reef, GBR), and One Tree Island (OTI; lower GBR). Surprisingly, we found a social gradient from north to south: most often we observed group living within a single species in PNG, pair living within a single species at LI, and mixed species groups at OTI. When groups were encountered though, size hierarchies were often maintained among species. The study underscores the effect that environmental factors have on sociality and highlights the need for quantifying sociality on a broader spatial scale.