An audacious sheep...

07oktober2009
Source: nrc.nl/wetenschap
Audacious rams can reproduce quickly, but also die young. The more patient sheep are ultimately more successful. This appeared from a study with bighorn sheep in Canada.
A wild herd of bighorn sheep (Ovis canadensis) is being studied since 1969. The reproductive success of 105 sheep was followed over the years. The researchers distinguished two kinds of rams: rams that live fast, produce offspring at a young age and die young, and the more patient kind that grow up more slowly and produce offspring at a later age. These are obviously extremes, for many rams are somewhere in between these categories. To determine how tame or audacious the rams were, two tests were performed. At the first test (audacity), the researchers had the animals walk into a trap when they were searching for salt. This is a delicacy for sheep. The more careful animals avoided the trap after they had been caught in it before, while the more audacious sheep walked into the trap several times. Tameness was determined by measuring the heart rate during routine physical examination. The more dominant animals revolted more.

When a bighorn female is in heat, all rams want to mate with her. But only the dominant males, with the largest horns, are allowed to mate, and they keep the other rams away from the ewes. The more patient rams wait until they are large, and thereby dominant, enough to be allowed to mate. The more audacious rams take a chance. They try to lure the ewes away from their protector. Sometimes they succeed in this. These rams therefore produce offspring at a relatively young age, but because they often die young due to their reckless behaviour, they do not produce very much offspring. The more patient rams, who wait for their time, ultimately produce more offspring, because dominant rams fertilize multiple females a year and often do this years in a row.

Since both strategies are successful, both personality types remain in the population. The results of this study are published in the Journal of Evolutionary Biology.