The effects of androgens in a sex changing species were examined as early as 1962 in the wrasse Coris julis, but measurements of circulating levels of sex steroid hormones had to wait for the development of a technique termed ‘radioimmunoassay’ (RIA). Early studies using RIA showed that plasma levels of the primals) 17-beta estradiol (E2) were elevated in female saddleback wrasses (Thalassoma duperrey) and atically at the onset of sex change at the same time that oocytes in the gonad degenerated ( Figure 4 ). Levels of E2 remained very low across sex change and in terminal phase (TP) males. Importantly, significant increases over female 11KT levels appeared to follow rather than precede or accompany the appearance of mature spermatogenic tissues. Similar sex steroid hormone patterns are seen in the stoplight parrotfish (Sparisoma viride) and several other sex changing species that have been examined, including goby and grouper species. In an interesting twist, the anemonefish A. melanopus also shows higher plasma E2 levels in females and higher 11KT levels in males despite the direction of sex change being male-to-female and females being the larger and aggressively dominant sex ( Figure 5 ).
Profile cuatro . Relative steroid hormones profile on the plasma out-of saddleback wrasses found to own pure people and you may TP guys as well as women in the process of socially created sex change in fresh pens.
Redrawn out of Nakamura M, Kobayashi Y, Miura S, Alam MA, and you may Bhandari RK (2005) Intercourse change in coral reef fish. Fish Structure and you can Biochemistry 30: 117–122 .
Contour 5 . Cousin steroid hormone profile when you look at the plasma of one’s anemonefish Amphiprion melanopus in natural males and females so when people undergone protandrous gender transform pursuing the fresh female removals out of social communities. Cousin amounts of additional hormonal is actually illustrated up to so you’re able to level except having cortisol, where profile have been considerably large.
Redrawn out-of Godwin JR and Thomas P (1993) Intercourse changes and steroid users regarding protandrous anemonefish Amphiprion melanopus (Pomacentridae, Teleostei). Standard and you may Comparative Endocrinology 91(2): 144–157 .
The fresh new character away from steroid hormone on command over intercourse transform was supported by of numerous tests manipulating either steroid hormone physically or its synthesis. Androgen government is useful to have triggering men sex determination from inside the a good amount of fishes and that means are popular from inside the aquaculture to create smaller-growing guys. Beginning in 1955 with bluehead wrasses, androgen government was also regularly properly cause sex alter in certain intercourse modifying species. They truly are a lot of wrasses, the stoplight parrotfish S. viride, the brand new blackeye goby Coryphopterus nicholsi, and some species of groupers.
In comparison, a switch androgen inside the fishes 11-ketotestosterone (11KT), are establish during the lower levels in females and you may across intercourse changes, merely becoming increased for the TP boys
Blocking estrogen synthesis has similar effects to androgen administration in inducing female-to-male sex change. A key regulatory step in estrogen synthesis is the enzyme aromatase, a protein in the cytochrome P450 family of proteins. Fishes express two forms of this enzyme, known as gonadal and brain aromatase. Aromatase and estrogens generally appear to play key roles in sex determination in a range of species. Manipulations of estrogen signaling and aromatase activity are effective in manipulating the occurrence of sex change in several wrasse and grouper species as well as two goby species. For example, inhibiting aromatase action in the blackeye goby C. nicholsi induces sex change as effectively as 11KT implants. The bidirectionally sex changing gobies in the genus Gobiodon are especially interesting in this respect. As noted above, these gobies can change sex in either direction to form heterosexual pairs on the corals where they reside. Implants of the aromatase inhibitor fadrozole induce females to become males and males to remain male even when paired with a larger male. Conversely, E2 implants induce sex change in males paired with other males while E2-implanted females paired with other females do not change sex. Also consistent with a dominant role for estrogenic signaling in regulating sex change was a study where co-administering E2 with androgens in three-spot wrasses blocked the female-to-male sex change that would otherwise occur. Taken together, these studies suggest that estrogenic inhibition may be the critical controlling factor for gonadal sex change.
