Make Nice or Else
If they were human, adult male crayfish efforts to establish dominance and hierarchy in congested colonies would be nothing short of horrendous.
But in the animal world where day-to-day survival is rife with brutality and free of human morality, a ritualized form of sexual behavior among males may help establish social hierarchy, order and even harmony among crayfish populations, suggests research published recently by professor Donald Edwards.
In the Nov. 7 issue of Current Biology, Edwards and doctoral student Fadi Issa present evidence showing survival among competing dominant male crayfish is virtually guaranteed when warring males pretend to mate with each other in what's known as pseudocopulation.
The lesser of two competing males assumes what is normally the female's position as a way of signaling his submission to the other. The ritual, which appears to be mutual, nearly ensures an immediate end to aggression between the males, as well as the survival of the lesser male, Edwards has found.
"The animal world isn't pretty, is it?" Edwards said. "But I think what we're seeing here indicates the importance to reduce aggression in a social hierarchy."
This behavior by male crayfish has been observed in the wild, but until Edwards' research, no theory had been stated to explain the ritual. Among vertebrates, the practice is fairly well known – even among humans.
Edwards noted how the ritual could draw comparisons to assaults in confined prison populations, but there is no psychological cruelty with the crayfish. "This appears to be an efficient way of ending aggression that’s costly to both competing males," he said.
Scientists have previously known that crayfish establish social hierarchies where the biggest and strongest earn top rank in a colony. In typical circumstances, lesser males assume lower ranks, avoiding contact with their superiors. By avoiding a fight, both males increase their odds at passing on their genes to a new generation of crayfish, Edwards said.
However, fights break out that often threaten the survival of both competing males when they cannot avoid each other. In the study, male crayfish were paired and then observed. After 24 hours, the dominant male killed his lesser about half the time in cases where the ritual did not occur. In cases where the ritual did occur, there were no deaths.
"That's the real zinger. The aggression was all over in the first day with those males who did pseudocopulate. Order was established."