Animal behaviourists usually expect males to compete with each other for mates, with females preferring the larger, more aggressive or better-endowed winners. But this is not so for certain salmon and quail.
Some male coho salmon, known as jacks, stop growing earlier in their lives and remain smaller than their larger cousins, known as hooknoses, says behavioural ecologist Jason Watters of the University of California, Davis. When the salmon migrate from the Pacific Ocean to inland rivers to spawn, hooknoses dominate jacks and compete aggressively with each other to mate with females. But contrary to what biologists had assumed, the females prefer to mate with jacks if they get the chance. "That shakes up everybody's point of view a little," says evolutionary biologist Steve Shuster of Northern Arizona University in Flagstaff.
Watters tracked the mating experiences of 15 female coho salmon in a Californian coastal stream. The females work harder on their nests and spawn longer with jacks than with hooknoses, Watters told an Animal Behavior Society meeting in Boise, Idaho, last week. The female salmon may prefer jacks because their earlier maturation could be a sign of increased quality and success. Other males have to spend an extra year growing into hooknoses before they can mate.
The females may also prefer to avoid the physical abuse of mating with aggressive males. "Hooknoses were the only ones that chased or bit females," Watters says. "Jacks pull up beside females and wiggle. They don't touch them, they just advertise."
Female Japanese quail have similarly contrary tastes, animal behaviourist Alex Ophir of McMaster University in Ontario, Canada, told the meeting. Male Japanese quail are exceptionally aggressive towards each other, and this abuse often spills over into courtship and mating. To see how the females feel about this, Ophir let female quail watch a fight between two males, and then separated the combatants and placed them on opposite sides of a female's cage to see which one she would gravitate towards. Virgin females tended to prefer the dominant males that had won the fight, but females with a little sexual experience were more likely to choose the loser.
"People just expect the dominant guy to win," says Ophir. "But females learn through personal experience that these males can be hurtful." Shuster thinks the idea that females may not always prefer dominant males will catch on. "Conventional wisdom is that males should always try to be these macho aggressive guys," he says. "But this shows there is also a place for the nicer guys."
Author: Betsy Mason
New Scientist issue: 2 AUGUST 2003
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