14 DAY TRIAL // To assess genetic quality, animal females have no other option than to rely on external cues.
For a long time it was thought that female animals looked for outward cues, called sexual ornaments, like a peacock's vibrant feathers, to see genetic quality. But how can the correlation between male genetic quality and ornament quality be maintained?
Ornament giving mating advantages will lead to a rapid evolution where all males - regardless of genetic quality - carry high-quality ornaments. "Female mate choice is likely a very important evolutionary force that does much more than select for ornaments in a few species," said John Byers of the University of Idaho. "It may be universally important in maintaining population genetic quality."
Male pronghorns, an antelope-like hoofed mammal that evolved in North America (the fastest mammal in North America)(photo), lack any ornament, so females rely on assessing males' behavior instead, to find the best mate.
Byers investigated the genetics of a pronghorn population in the National Bison Range, a 30-square-mile National Wildlife Refuge in northwestern Montana. During the mating time, females visit the harems of potential mates to observe how well a particular partner defends his harem, in order to judge his quality. "Rogue males will try to infiltrate the harem" and the male has to "just run back and forth, hour after hour" to defend the females,Byers said, otherwise the entire harem will leave."
"The females' mate sampling creates a small group of males that each year sire more than one-half of all young," said Byers. "These are the males that, under the stringent female sampling process, have shown they are the most vigorous. [?] It's the vigorous guys that get all the matings."
Byers made a genetic profile for all pronghorns in the population and assigned paternity to the offspring. He found the offspring of the vigorous males are more likely to survive to weaning. "This advantage is due to faster growth rates," he said.
These fawns suckle less from their mothers than do the offspring resulted from less-attractive males. The fast growing fawns are less likely to be eaten by a coyote. Monitoring the population for several years, Byers discovered that the offspring of the high quality males had a survival advantage for as long as five years.