Oral Presentation Australian Society for Fish Biology & Australian Freshwater Sciences Society Conference 2026

How the corals of Nyinggulu Reef shape the reproductive strategies of resident gobies (142484)

Tess L Jenkins 1 2 , Martial Depczynski 2 3 , Paige J Maroni 1 , Dianne L McLean 2 3 , Jon P Evans 1
  1. School of Biological Sciences, University of Western Australia, Crawley, WA, Australia
  2. Australian Institute of Marine Science, Perth, WA, Australia
  3. The Oceans Institute, Perth, WA, Australia

Background/Aims

Animals display a wide array of reproductive behaviours, with the Environmental Potential for Polygyny1 (EPP) and Size Advantage2,3 (SAM) models providing key frameworks for understanding their evolution. The EPP model predicts that mating systems are shaped by the spatial distribution and defensibility of resources, whereas the SAM predicts sex-change direction according to the reproductive advantage of size. Coral-dwelling fishes of the genus Gobiodon provide an ideal system to test these predictions owing to their strong dependence on individual coral colonies and diversity of mating systems and sex-allocation strategies4.

 

Methods

We surveyed social groups of the poorly studied species, Gobiodon citrinus, on the inshore reefs of Nyinggulu, Western Australia. Using photogrammetry, we quantified the surface area and structural complexity of 24 host coral colonies, alongside coral isolation, health, social group size, and gonadal development.

 

Results

In G. citrinus, coral size was a primary driver of group size, and group size was strongly associated with mating system expression. Group sizes increased significantly with coral surface area, whereas rugosity, branch packing, and coral health showed no detectable effects. Histological analyses indicated monogamous pairs in small groups and polygynous mating systems, with a single male and multiple reproductive females, in larger groups occupying larger corals, consistent with a shift from monogamy to polygyny predicted by the EPP model. Furthermore, this species appears to exhibit protogynous (female-to-male) sex-change, rather than the bidirectional sex-change reported for congeners, likely in response to its polygynous mating system as predicted by the SAM.

 

Conclusion

These findings suggest that individual coral colony size, rather than structural complexity or condition, is the principal determinant of group size in G. citrinus, ultimately shaping mating systems and sex-allocation strategies. This study provides new insights into how habitat characteristics influence reproductive strategies in small-bodied coral reef fishes. 

  1. Emlen ST, Oring LW (1977) Ecology, sexual selection, and the evolution of mating systems. Science (197) 215-223.
  2. Ghiselin MT (1969) The evolution of hermaphroditism among animals. The Quarterly Review of Biology (44) 189-208.
  3. Warner RR (1975) The adaptive significance of sequential hermaphroditism in animals. The American Naturalist (109) 61-82.
  4. Wong MY, Buston PM (2013) Social systems in habitat-specialist reef fishes: key concepts in evolutionary ecology. BioScience (63) 453-463.