WCS Glovers Reef

Sex changes in Bluehead Wrasses

Erica Marsh and John Godwin inserting a hormone inplant

They may look a little strange, but Erica Marsh and John Godwin are doing quick precision dissection on bluhead wrasses to insert hormone implants.

Erica is a PhD student at North Carolina State University. This is the second time she is out at Glovers Reef to carry her work on the mechanisms regulating male bluehead wrasses sociosexual behaviour.

Jon Godwin, professor at the same university (http://www4.ncsu.edu/unity/users/g/godwin/www/jrgindex.html) is also of the trip this year to see if the wrasses are responding according to their hypothesis.

The research topic

Tagged blueheadwrasses which have undergone the implant operation

The bluehead wrasse, Thalassoma bifasciatum, is a protogynous or female-to-male sex changing fish that also exhibits two discrete, alternate male phenotypes. In this species, sex and role change is under social control, with females changing into males after becoming socially dominant. The bluehead wrasse is an excellent system in which to study the neuroendocrine mechanisms driving the regulation of male sociosexual behavior. The behavioral changes associated with a change in social dominance are dramatic, take place rapidly, and can be manipulated in the full complexity of the natural environment.

These experiments will generate about how social environment regulates neuroendocrine changes in the brain associated with striking changes in behavior.

(Erica Marsh and John Godwin, 2006, Research proposal submitted to WCS).

Methods

John observing the behaviour of the bluehead wrasses after the operation

The fish are caught in a net in the morning and quickly brought back to the station for operation. After giving them different hormones and in some case removing ovaries the fish recover quickly and are set free on their orginial coral bommies. Dominant males are then either relocated or not depending on the drug used.

Most of the reseracher's time in the field is spent on the surface looking at the change/lack of change of the behaviour of the fish. Does the female bluehead wrass now think she's a dominant male???

Some of the fish are sacrificed and the brain are kept for later analysis to understand the exact process and retrace the events.