GETTING BETTER WITH AGE
Like memory, eyesight and energy levels (among many other things), an animal’s fertility declines with age. So why are the females of many species happy to choose mates that are past their best? New research on zebrafish might provide an answer.
Older male zebrafish are less virile than their more youthful competitors, producing fewer, more sluggish sperm that are less likely to fertilise an egg. But biologists have found one very good reason why females might choose to mate with them – those offspring that they do father have higher survival rates.
This suggests not only that the genetic quality of their sperm is little affected by the ageing process, but also that older males may actually pass on superior genes to their offspring. After all, animals don’t reach a ripe old age by accident – males with less genetic quality tend not to make it that far.
In species where males help raise offspring, females might be better off going for younger, fitter models, but older mates may be particularly attractive in others such as zebrafish, where males contribute nothing to reproduction other than sperm.