July 13, 2009
New research finds attractive male chickens release fewer sperm
Attractive male chickens release fewer sperm per mating to maximise their chances of producing offspring across a range of females, according to a new paper by researchers at UCL and the University of Oxford.
The findings suggest that matings with attractive males may be less fertile than those with unattractive ones.
Previous studies have shown that in animals, males with privileged access to females produce ejaculates of lower fertilising quality than subordinate males.
In some species, females mate with many different males which increases the competition between each male's sperm, said Sam Tazzyman from the UCL.
If a male puts a lot of resources into each mating, he will get more offspring but mating, but at the expense of fewer matings. On the other hand, a male puts fewer resources into each mating will secure less paternity per mating but will be able to carry out more matings overall. Thus, there is a trade-off between the number of matings and success per mating, said Tazzyman.
Attractive males belong to the latter group, while unattractive males the former, which leads to the paradoxical prediction that matings with attractive males may be less fertile than those with unattractive males, according to Tazzyman.
Also, the sperm of dominant chickens is less motile and has lower fertilising efficiency than the sperm of subordinate chickens. Scientists can artificially change the pecking order, and when this is done, the new dominant male's sperm quickly loses motility, while that of males reduced to subordinate status increases in motility, said Tazzyman.
"Further work in this area should look at males that are similarly attractive, but have different levels of resources to allocate to sperm production, to see how this alters their sperm number and quality. The model should also be expanded to include the effects of short-term sperm depletion, which is known to affect ejaculate content when males re-mate quickly. We also would like to explore whether the lower fertility of attractive males causes females to start avoiding attractive males that mate too often, as these males reduce their fertility," Tazzyman said.
