Rapid increase in aggressive behavior precedes the decrease in brain aromatase activity during socially mediated sex change in Lythrypnus dalli

Abstract

In the bluebanded goby, Lythrypnus dalli, removal of the male from a social group results in a rapid behavioral response where one female becomes dominant and changes sex to male. In a previous study, within hours of male removal, aromatase activity in the brain (bAA) of dominant females was almost 50% lower than that of control females from a group in which the male had not been removed. For those females that displayed increased aggressive behavior after the male was removed, the larger the increase in aggressive behavior, the greater the reduction in bAA. To investigate whether decreased bAA leads to increased aggression, the present study used a more rapid time course of behavioral profiling and bAA assay, looking within minutes of male removal from the group. There were no significant differences in bAA between control females (large females from groups with the male still present), females that doubled their aggressive behavior by 10 or 20 minutes after male removal, or females that did not double their aggressive behavior within 30 minutes after male removal. Further, individual variation in bAA and aggressive behavior were not correlated in these fish. Whole brain decreases in aromatase activity thus appear to follow, rather than precede, rapid increases in aggressive behavior, which provides one potential mechanism underlying the rapid increase in androgens that follows aggressive interactions in many vertebrate species. For fish species that change sex from female to male, this increase in androgens could subsequently facilitate sex change.

Cortisol Administration Induces Sex Change from Ovary to Testis in the Protogynous Wrasse, <b><i>Halichoeres trimaculatus</i></b>

“…It is well established that sex change in many hermaphroditic fish is controlled by the social environment. Some studies have shown that changes in the social rank lead to a rapid and dramatic change of cortisol level and aggressive behavior in dominant females [Black et al, 2005[Black et al, , 2011Iwata et al, 2012]. Such alteration caused by the social situation might be closely related to the initiation of sex change.…”

Stress and serial adult metamorphosis: multiple roles for the stress axis in socially regulated sex change

“…A number of neuromodulators have been investigated as a potential biological switch important for the initiation of sex change, including neural steroid hormones (i.e., estradiol, 11-ketotestosterone, testosterone, cortisol) (Godwin, 2010; Lorenzi et al, 2012), gonadotropin-releasing hormone, arginine vasotocin (Reavis and Grober, 1999; Godwin et al, 2000; Bass and Grober, 2001), aromatase (Black et al, 2011), and serotonin (Lorenzi et al, 2009), with an increasing interest in kisspeptin (Godwin, 2010). Despite this focus, the biological link between social environment and sex change has not been resolved.…”

Peer Review #2 of "Conservation and diversity in expression of candidate genes regulating socially-induced female-male sex change in wrasses (v0.1)"

“…In bluehead wrasse, although cyp19a1b expression clearly decreased with sex change, the trend was non-significant and only noticeable from stage 2, after behavioural changes first occur at stage 1. Likewise, Black, Balthazart [81] found whole brain aromatase activity declined only after behavioural changes in female-to-male sex change of the bluebanded goby (Lythrypnus dalli). Expression of cyp19a1b in bluehead wrasse fore/midbrain closely parallels gonadal cyp19a1a mRNA levels, and may reflect peripheral changes in E2 via putative oestrogen response elements in the cyp19a1b promotor [34].…”