Getting stuck in a tight corner with a bully is never pleasant, but when fish are trapped in close proximity to an aggressive individual, they really suffer. Which is why Assaf Barki and Ilan Karplus are keen to understand what drives aggression in cultivated fish and crustaceans. So when crayfish were introduced to the Israeli aquaculture industry, Barki turned his attention to the tasty little crustaceans. Barki's colleague, Amir Sagi already knew that the male's androgenic gland, is responsible for controlling the development of a few physical male-characteristics. Could the gland affect male behaviour too? Scientists at the Sagi laboratory transplanted the male's gland into juvenile females and patiently watched the youngster's physical development. Over a year the implanted females developed external male features, but the gland did not transform the females into fully functional males. However, when Barki turned his attention to their behaviour, he was astonished by the gland's effects. The implanted females' behaviour was so convincing that they completely fooled the normal females into believing that they were sexually mature males, to the extent that they even began mating()!
But before Barki and his colleagues could begin looking for the gland's effects on crayfish behaviour, they had to be certain that the transplanted tissue was functioning. Barki explains that after surgery, the team waited a whole year, to be sure that the gland was producing enough male sex hormones to alter the female's physical appearance. Sure enough, within twelve months,the implanted females had developed the male's red claw, and their ovaries remained inactive. But the crayfish were still essentially female, they never developed testes.
However Barki explains that he was `most curious to see what would happen when an unaltered and an implanted female came face to face'. Under normal circumstances when crayfish of the same gender come across each other, they begin battling until the vanquished animal backs off. He was delighted when some females just wandered around each other and didn't enter into combat;which is just how natural males and females respond when attracted to each other. But he was really astonished when several pairs of female crayfish began attempting to copulate!
Barki explains that it's hard enough to get normal crayfish couples to mate in experimental situations, so this wasn't a subtle behavioural alteration;this was a completely unprecedented role reversal! The altered female behaved just like bona fide male, rolling its tail under its body ready for the real female to roll it onto its back for intercourse. But this also requires a high degree of cooperation from the female, adds Barki. She must pick up all the right signals before she is convinced that the creature crouching before her is a male. Somehow, the altered females were sending out the right messages, as if they were fully `male' crayfish.
Barki admits that this is a `black box study'. He knows what was inserted into the females, and the effect that it had on the crayfish's physiology and behaviour, but he doesn't have a clue what hormones the androgenic gland produces, or what the mechanism is behind the behavioural change; `in humans we know more about androgens, their nature and modes of action' he adds. Having found that the androgenic gland has the power to divert the crustaceans war-like behaviour to more sexy ends, Barki and his colleagues are keen to identify the hormones and neuroendocrine mechanisms behind this powerful effect.
