Social Environment and Sex Differentiation in the False Clown Anemonefish, Amphiprion ocellaris

Abstract

Plasticity in sex differentiation is known to be common in teleost fishes. Anemonefishes are protandrous; females are the largest and dominant members of social groups, displaying frequent aggressive behavior towards other members of groups. The second-ranked individuals become males and others remain as non-reproductive individuals. Here we examine the influence of social interaction in-group on sex differentiation in the false clown anemonefish, Amphiprion ocellaris, under laboratory conditions. Three juvenile anemonefish were kept in a tank for 180 days and their behaviors observed once a month. The social rank of individuals was distinguishable by their interactions in a group, with rank order clearly correlated with aggressive and appeasing behaviors. The dominant individuals occupied the shelter in the tank from the start to completion of the observation period. The body mass of dominant individuals increased compared to group-housed control fish, while third-ranked individuals showed growth suppression. The ratio of testicular tissue in gonads increased in dominant and second-ranked individuals but decreased in the third-ranked individuals. Differences in the plasma concentrations of estradiol, testosterone, and cortisol were not significant, but the concentration of 11-ketotestosterone was significantly higher in dominant individuals. These results suggest that, in false clown anemonefish, reproductive suppression of lower-ranked individuals becomes apparent in the first stage of group formation, and sex differentiation of upper-ranked individuals is gradually determined by long-term social interactions.

Social rank modulates brain arginine vasotocin immunoreactivity in false clown anemonefish (Amphiprion ocellaris)

“…The AVT neural phenotype occurs independently of gonadal influence (Semsar and Godwin 2003) and the A. ocellaris that we used were immature and not yet sexually differentiated. Although dominant individuals tended to have greater GSIs in the current study, our previous study demonstrated that sex differentiation was not induced within 180 days of social rank formation, during which time there were no significant differences in serum sex steroid levels or the proportion of testicular tissue in the gonads (Iwata et al 2008). Our preliminary study also revealed that there were no significant differences in the ratio of testicular or ovarian tissue, or in the development of these cells compared with GHC fish after 90 days of group formation.…”

“…AVT neurons innervate the corticotrophic cells of the pituitary in the green molly, Poecilia latipinna (Batten et al 1990), and they influence adrenocorticotropin and thus cortisol secretion in the rainbow trout, Oncorhynchus mykiss (Baker et al 1996). Plasma cortisol was not measured in the current study, and the stress level of each individual was not clear, but our previous study indicated growth and reproductive suppression in c individuals after 180 days of group housing (Iwata et al 2008). It is conceivable that AVT neurons might be involved in cortisol secretion that leads to growth or reproductive suppression in c fish.…”

“…A description of each behavior is given in Table 1. Each individual in a tank was identified by differences in the white-striped pattern on its body and classified as a (dominant), b (second-ranked), and c (subordinate) from behavioral observation on Day 0 of the experiment (Iwata et al 2008), and it was confirmed that the rank of each individual was not reversed during the whole experimental period.…”

“…Our previous study revealed that sex differentiation of false clown anemonefish Amphiprion ocellaris was not obvious until 180 days of group housing under laboratory conditions, although the group's social rank was established immediately after group formation (Iwata et al 2008). Thus, longer-term social interaction may be needed for sex differentiation in this species.…”

Immunohistochemistry of Brain Arginine Vasotocin and Isotocin in False Clown Anemonefish Amphiprion ocellaris~!2009-12-08~!2010-04-14~!2010-06-29~!

“…A PVC waterpipe joint (50 mm diameter) substituted for a host sea anem-one [6] and was placed at the center of the experimental tank as a shelter. Each individual in a tank was identified by differences in the white-striped pattern on its body and classified as (dominant) or (second-ranked) from behavioral observations on Day 0 of the experiment [6].…”