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Old males rule the roost even as sex drive fades

Date:
July 19, 2010
Source:
University of Oxford
Summary:
Old roosters can still dominate the sexual pecking order even when their ability to fertilize eggs drastically declines, new research has shown.

Old roosters can still dominate the sexual pecking order even when their ability to fertilize eggs drastically declines, new research has shown.
Credit: iStockphoto/Peter Zelei

Old roosters can still dominate the sexual pecking order even when their ability to fertilise eggs drastically declines, new research has shown.

A study of feral chickens, reported recently in Current Biology, suggests an evolutionary battle between what's good for old roosters and what's good for their hens -- which would benefit from sex with younger, more potent males.

The team, led by Oxford University researchers, studied the relationship between the status of male birds, their reproductive performance, and female reproductive success, in a feral population of chickens in Sweden.

'We found that roosters decline in a number of key reproductive traits as they age -- from libido to sperm quality -- and, in groups where there's intense competition, tend to lose out to younger males,' said Dr Tommaso Pizzari of Oxford University's Department of Zoology, an author of the report. 'However, old males remain capable of dominating the pecking order: When this happens they can monopolise access to females but, because of their sexual decline, they fail to fertilise all the eggs available. This implies an evolutionary conflict between ageing roosters and fertile hens.'

The researchers used four different experiments to separate out the influence of male and female factors on reproductive success -- something that is difficult to study in wild animals. It is only recently that scientists have started to understand the significant role that age-related 'sexual decline' (reproductive senescence) plays in natural animal populations.

'In evolution there are many battlegrounds, but nothing is more important than successfully reproducing. So, for hens, being monopolised by an impotent old rooster who will cause them to lay many infertile eggs is a disaster and amounts to a declaration of war. Our study shows that this sort of sexual decline is an engine driving sexual conflict in animals,' said Dr Rebecca Dean of Oxford University's Department of Zoology, also an author of the report.


Story Source:

The above story is based on materials provided by University of Oxford. Note: Materials may be edited for content and length.


Journal Reference:

  1. Dean et al. Male Reproductive Senescence Causes Potential for Sexual Conflict over Mating. Current Biology, 2010; 20 (13): 1192 DOI: 10.1016/j.cub.2010.04.059

Cite This Page:

University of Oxford. "Old males rule the roost even as sex drive fades." ScienceDaily. ScienceDaily, 19 July 2010. <www.sciencedaily.com/releases/2010/07/100713151315.htm>.
University of Oxford. (2010, July 19). Old males rule the roost even as sex drive fades. ScienceDaily. Retrieved August 1, 2014 from www.sciencedaily.com/releases/2010/07/100713151315.htm
University of Oxford. "Old males rule the roost even as sex drive fades." ScienceDaily. www.sciencedaily.com/releases/2010/07/100713151315.htm (accessed August 1, 2014).

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