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

A study on St. Kilda, Scotland, reveals that testes size is a significant predictor of testosterone levels and reproductive behavior in male Soay sheep during the rutting season. The research found a strong positive relationship between testes size (measured before seasonal enlargement) and circulating testosterone levels, suggesting that the demand for sperm production plays a crucial role in regulating androgen levels. Unlike conventional hypotheses, body condition or competitive ability did not independently influence testosterone levels. This integration of sperm production capacity with testosterone output also affected male aggression and mate-seeking behavior, indicating a tight phenotypic link between these traits.

Preston, B. T., Stevenson, I. R., Lincoln, G. A., Monfort, S. L., Pilkington, J. G., & Wilson, K. (2011). Testes size, testosterone production and reproductive behaviour in a natural mammalian mating system. Journal of Animal Ecology, 81(1), 296–305. Portico. https://doi.org/10.1111/j.1365-2656.2011.01907.x