Wildlife Research Unit (UIRCP), Universidad de Córdoba, 14071, Córdoba, Spain.
Department of Evolutionary Ecology, Museo Nacional de Ciencias Naturales (MNCN-CSIC), 28006, Madrid, Spain.
Naturwissenschaften. 2020 Apr 24;107(3):18. doi: 10.1007/s00114-020-01674-1.
The expression of male sexual traits, which is stimulated by testosterone, entails significant costs for individuals. Consequently, natural selection is expected to favour the modulation of sexual trait development according to the balance between its costs and benefits. The proportion of rivals in a population may affect this balance by increasing or decreasing the reproductive benefits associated with the development of sex traits. Here, we explore the relationship between testosterone level and sex trait size under two populational conditions of mate competition: fenced (i.e. high male-male competition; all male age groups are present) and unfenced (i.e. low competition; most males present are juveniles). Our model species is the Iberian red deer (Cervus elaphus hispanicus), and the sex trait is the dark ventral patch that males exhibit during the rutting season. Our results showed that the positive relationship between testosterone levels and the size of the dark ventral patch depends on the environmental level of male-male competition. Only in populations where the operational sex ratio was high (i.e. high proportion of rival males), individuals with high levels of testosterone developed the sex trait. Conversely, when mate competition was low, there was no significant relationship between testosterone level and trait size. This result reinforces the idea that the effect of testosterone in promoting the development of sex traits may be mediated by the intensity of mate competition in the population, as well as the role of sexual selection in the evolution of the dark ventral patch in red deer.
雄性性特征的表达受睾酮刺激，这会给个体带来巨大代价。因此，自然选择应该有利于根据性特征发育的成本和收益之间的平衡来调节其发育。群体中竞争对手的比例可能会通过增加或减少与性特征发育相关的繁殖收益来影响这种平衡。在这里，我们探讨了在两种配偶竞争的种群条件下，睾酮水平与性特征大小之间的关系：围栏（即高雄性-雄性竞争；所有雄性年龄组都存在）和无围栏（即低竞争；大多数雄性是幼体）。我们的模式物种是伊比利亚红鹿（ Cervus elaphus hispanicus ），性特征是雄性在发情期表现出的暗腹斑。我们的研究结果表明，睾酮水平与暗腹斑大小之间的正相关关系取决于雄性间竞争的环境水平。只有在性比高（即竞争对手雄性比例高）的种群中，高水平的睾酮个体才会发育出性特征。相反，当配偶竞争较低时，睾酮水平与特征大小之间没有显著关系。这一结果进一步证实了这样一种观点，即睾酮在促进性特征发育中的作用可能受到种群中配偶竞争强度的调节，以及性选择在红鹿暗腹斑进化中的作用。
