Sex Change you say???

 

So what should you know about the bluehead wrasse (Thalassoma bifasciatum)? Well, there are two major divisions in the reef social heirarchy of this species: 1) initial phase (IP) and 2) terminal phase (TP) individuals. IP fish can be either male or female and have a characteristic yellow body with some black markings. TP fish are always male and exhibit a green body, blue head (hence the common name of this species), and a distinctive black-white-black collar. In addition to these morphological differences, IP and TP males also display dissimilar behavior....but first off, let me paint a small portrait of life on the reef.

Life on the reef starts out early in the morning (much earlier than I roll out of bed to face my biochemistry class)...and basically the wrasse move from the grass beds where they spent the night back onto the reef (prime feeding and displaying area!!!). Initially all the fish spend their time concentrating on feeding....that is until it is time to spawn!!! Yes, that's right...females spawn every day (pretty much like clockwork)...so the afternoon spawning period is when we see some real behavior.

Females will visit certain sites on the reef to release their eggs because they have good currents to carry their eggs off the reef where they will develop...and it would be a shame to spawn at the top of the reef -up current- because then all sorts of animals would have a chance to snack on potential offspring). Okay, so now that we know where the females go...we have a good idea where the males will be- patrolling the area around these prime spawning sites! Well, this is what TP males do- however, this is biology, so nothing is completely straight forward...while most TP males aggressively defend spawning sites and court females, other TP males just hang around and keep on eating (we will call these T-TP males and NT-TP males respectively, to indicate their territorial or non-territorial practices).

What about those IP males then? Good question...individually they can't compete with the bigger and aggressive T-TP males for spawning sites....so they tend to sneak into a male-female pair....release sperm....and hightail it out of there (kind of a kamikazee act of love???). Of course, IP males can get close to these spawning pairs because they tend to resemble females (pretty sneaky trick...hence they're often called sneaker males- LOTS of fish do this!).

IP males also engage in large group spawns in which there can be over FIFTY males per female...imagine that sperm competition!!!! (any wonder IP males have a much higher GSI-gonadosomatic index- than TP males).

So we have females spawning daily like clockwork and two types of males (with subtypes of behavior in each- sneaking...snacking...pair spawning...group spawning....etc)...now to the really wild side of bluehead sexual strategies (yes, there is more!!!)

If TP males are removed from the social group (either by predators, fish store owners, scientists, or what have you...) then the most dominant IP fish (usually correlates well with size) assumes the TP role.

BUT WAIT....I thought you said IP fish could be male OR female? That's right folks....the header at the top of this page ("Sex Change You Say?") wasn't just a tease!!! IP males can role change and become TP males OR IP females can sex change and become TP males!!!

PHEW!!! So what are some of the necessary changes for an IP female to complete this trick? Well, scientists have found that many neuroendocrine changes are critical for sex change. These sex-changing females show immediate changes in behavior (i.e. they become aggressive and start courting females- How typically male!). Therefore, we have looked for changes in the brain and found increasing levels of the neurohormone arginine vasotocin (AVT)- this hormone (along with its mammalian homologue arginine vasopressin) have been implicated in modulating social and sexual behavior in numerous species. Of course, most of us realize that boys and girls are different (aside from our brains)..so yes, sex-changing fish must convert their ovaries into functioning testes (sperm and all). This of course goes along with the whole production of 11-ketotestosterone (the primary androgen in the bluehead wrasse).

Well, how's that for a basic introduction to sex change in the bluehead wrasse- very sexy and very interesting!!! WHO KNEW FISH COULD BE SOOO COOL?!?!?! I know one guy- check out his website at: http://www.gsu.edu/~biomgx/