Data from: An experimental test of density-dependent selection on temperament traits of activity, boldness and sociability

Temperament traits are seen in many animal species, and recent evolutionary models predict that they could be maintained by heterogeneous selection. We tested this prediction by examining density-dependent selection in juvenile common lizards Zootoca viviparascored for activity, boldness and sociability at birth and at the age of 1 year. We measured three key life-history traits (juvenile survival, body growth rate and reproduction) and quantified selection in experimental populations at five density levels ranging from low to high values. We observed consistent individual differences for all behaviours on the short term, but only for activity and one boldness measure across the first year of life. At low density, growth selection favoured more sociable lizards, whereas viability selection favoured less active individuals. A significant negative correlational selection on activity and boldness existed for body growth rate irrespective of density. Thus, behavioural traits were characterized by limited ontogenic consistency, and natural selection was heterogeneous between density treatments and fitness traits. This confirms that density-dependent selection plays an important role in the maintenance of individual differences in exploration-activity and sociability.

诸多动物物种均存在气质性状（temperament traits），近期进化模型预测，异质性选择（heterogeneous selection）可维持这类性状的存在。我们以胎生蜥蜴（Zootoca vivipara）幼体为研究对象，对该预测开展验证：分别在幼体出生时与1龄阶段，对其活动能力、大胆性与社交性进行行为评分；同时设置5个从低到高的密度梯度，构建实验种群，测定幼体存活率、体生长速率与繁殖能力三项关键生活史性状，并量化不同密度下的选择强度。研究结果显示，短期内所有行为指标均呈现稳定的个体差异，但仅活动能力与一项大胆性评分指标在幼体生命的首年中保持了跨时间一致性。在低密度种群中，生长选择偏向社交性更强的个体，而存活力选择则更青睐活动能力较弱的个体。无论种群密度如何，体生长速率均存在对活动能力与大胆性的显著负向相关选择（correlational selection）。综上，行为性状的个体发育一致性（ontogenic consistency）较为有限，自然选择在不同密度处理组与适合度性状（fitness traits）间存在异质性。本研究证实，密度依赖选择（density-dependent selection）在维持探索-活动轴与社交性的个体差异中发挥了关键作用。