Natural endocrine profiles of the group-living skunk anemonefish Amphiprion akallopisos in relation to their size-based dominance hierarchy
Résumé
Group-living animals commonly display differences in behaviour, physiology and endocrine profiles
between conspecifics within the group, which are tightly linked to reproduction. Teleosts exhibit a
variety of social systems, where social status, as well as sex, has been linked to different androgen
and oestrogen profiles. Levels of gonadal androgen and oestrogen were investigated as a function of
sex and position in a social hierarchy in free-living individuals of the skunk anemonefish Amphiprion
akallopisos, 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 as
conversion ratios from T, were measured by ELISA from 111 individuals along a linear hierarchy
from 38 social groups in the wild. Blood plasma levels of 11-KT and E 2 showed sex differences, being
higher in males and females respectively as expected based on their role as the major androgen and
oestrogen in fish reproduction. However, no sex differences were found for T, which may represent
its role in territorial defence or simply as a precursor for the synthesis of 11-KT and E 2 . In terms of
the hierarchical social system within males, 11-KT levels decline as the hierarchy is descended, which
may represent their decreasing reproductive opportunity, as well as the decreasing levels of aggression
towards males lower in the hierarchy. In summary, the size-based dominance hierarchy is associated
with distinct steroid levels of 11-KT and E 2 between individual free-living A. akallopisos that closely
resemble those of species in which breeding individuals suppress reproduction of conspecifics lower
in the hierarchy.