Loving, Fighting, Peeing: The Sex Lives of Crayfish

When I'm not blogging for mental_floss, I can usually be found wearing bright orange rubber pants and gutting, cutting and selling fish at my local Whole Foods (and winning awards for it). Sometimes, my two worlds collide and I find some scientific research involving my ocean-dwelling friends that begs for a blog post. This is one of those times.

Let's pretend, all evidence to the contrary aside, that I am a beautiful woman and I want to have children, right here and right now. What do you think is the best way to go about communicating that to men? Make eyes at them from across the room? Approach and aggressively flirt?

If I were a lady crayfish (crawfish, crawdad, mudbug, whatever you prefer to call them), my plan of action would be to urinate all over the place and start throwing punches.

Female crayfish take "playing hard to get" to a whole new level. Naturally, they want the strongest, fittest mates available to produce exceptional offspring. But crayfish are in a tough spot when it comes to discerning the fitness of potential mates. Simply checking the guys out doesn't provide much info, and chemical cues aren't always reliable. So the simplest and best way for a female to find the best mate is to test males in claw-to-claw combat herself.

How does she get the ball rolling? By peeing.

In some animals, the female initiates mating with chemical stimuli, informing suitors of her receptivity to sex. In crayfish, these stimuli happen to be in the urine. Fiona Berry and Thomas Breithaupt from the University of Hull recently published the results of a study on these urine-based chemical signals. In their experiment, male and female American signal crayfish (Pacifastacus leniusculus) were introduced to each other in a tank after being blindfolded (to exclude visual disturbance from the researchers) and injected with a fluorescent dye that accumulated in the bladder (to visualize urine).

Berry and Breithaupt found that under normal conditions (well, except for the blindfolds), the females would urinate to attract the males and then respond aggressively when they approached. The females would give up the fight only if a male was able to flip her over and deposit his sperm. When females were kept from releasing urine (by the blocking of the nephropores), though, no mating behavior was observed.

Artificial introduction of female urine, via a syringe placed in the tank, re-established normal mating attempts, demonstrating that there is a sex-specific component in the females' urine that both signals aggression and elicits mating behavior (males also use urine to signal aggression when fighting other males). The mixed aggro-sexual message that the urine communicates should, the researchers say, favor strong, high-quality males.

Aside from making our own sex lives seem normal in comparison, the lessons learned from this study could aid the UK in its battle against the signal crayfish, which is an invasive species in English rivers and carries a fungus that's lethal to the country's native white clawed crayfish (Austropotamobius torrentium).

Citation: Berry, F. and Breithaupt, T. (2010). "To signal or not to signal? Chemical communication by urine-borne signals mirrors sexual conflict in crayfish." BMC Biology 8:25. DOI:10.1186/1741-7007-8-25