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Natural endocrine profiles of the group-living skunk anemonefish Amphiprion akallopisos in relation to their size-based dominance hierarchy
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International audience. Group-living animals commonly display differences in behaviour, physiology and endocrine profilesbetween conspecifics within the group, which are tightly linked to reproduction. Teleosts exhibit avariety of social systems, where social status, as well as sex, has been linked to different androgenand oestrogen profiles. Levels of gonadal androgen and oestrogen were investigated as a function ofsex and position in a social hierarchy in free-living individuals of the skunk anemonefish Amphiprionakallopisos, a protandrous pomacentrid fish with a size-based dominance hierarchical social system.Plasma levels of 11-ketotestosterone (11-KT), testosterone (T) and 17훽-oestradiol (E 2 ), as well asconversion ratios from T, were measured by ELISA from 111 individuals along a linear hierarchyfrom 38 social groups in the wild. Blood plasma levels of 11-KT and E 2 showed sex differences, beinghigher in males and females respectively as expected based on their role as the major androgen andoestrogen in fish reproduction. However, no sex differences were found for T, which may representits role in territorial defence or simply as a precursor for the synthesis of 11-KT and E 2 . In terms ofthe hierarchical social system within males, 11-KT levels decline as the hierarchy is descended, whichmay represent their decreasing reproductive opportunity, as well as the decreasing levels of aggressiontowards males lower in the hierarchy. In summary, the size-based dominance hierarchy is associatedwith distinct steroid levels of 11-KT and E 2 between individual free-living A. akallopisos that closelyresemble those of species in which breeding individuals suppress reproduction of conspecifics lowerin the hierarchy.
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