Testes size, testosterone production and reproductive behaviour in a natural mammalian mating system

Authors: Preston, Brian T.¹; Stevenson, Ian R.²; Lincoln, Gerald A.³; Monfort, Steven L.⁴; Pilkington, Jill G.⁵; Wilson, Kenneth¹

Source: Journal of Animal Ecology, Volume 81, Number 1, 1 January 2012 , pp. 296-305(10)

Publisher: Wiley-Blackwell

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Abstract:

<title type="main">Summary</title>

1. Testosterone (T) is a key mediator in the expression of numerous morphological and behavioural traits in mammals, but the factors underlying individual variation in circulating T levels are poorly understood.

2. The intimate structural integration of sperm and T production within the testes, alongside the dependency of sperm production on high levels of T, suggests that T requirements for spermatogenesis could be an important driver of individual differences in T.

3. To test this hypothesis, we examine how male capacity for sperm production (as indicated by their testes size) is associated with T levels in a feral population of Soay sheep, resident on St. Kilda, Scotland, during their rutting season.

4. We found a strong positive relationship between an individual's testes size (as measured before their seasonal enlargement) and the levels of circulating T during their rut, suggesting that T requirements for spermatogenesis has a prominent influence on the production of this androgen.

5. In contrast, body condition and competitive ability did not independently predict T levels, findings that are inconsistent with conventional `condition-dependent' and `challenge' hypotheses of T production.

6. This influence of male's capacity for sperm production on T appeared to be substantial enough to be biologically relevant, as testes size also predicted male aggression and mate-seeking behaviour.

7. Our results suggest that a male's inherent capacity for sperm and T production is tightly phenotypically integrated, with potential consequences for a wide range of other T-mediated reproductive traits.

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2656.2011.01907.x

Affiliations: 1: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK 2: Sunadal Data Solutions, 18M Liberton Brae, Edinburgh EH16 6AE, UK 3: Centre for Reproductive Biology, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK 4: Smithsonian Conservation Biology Institute, 1500 Remount Road, Front Royal, VA 22630, USA 5: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK

Publication date: 2012-01-01

Testes size, testosterone production and reproductive behaviour in a natural mammalian mating system

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