The evolution of male-biased dispersal under the joint selective forces of inbreeding load, and demographic and environmental stochasticity

Sex-biased natal dispersal is widespread, and its significance remains a central question in evolutionary biology. However, theory so far fails to predict some of the most common patterns found in nature. To address this, we present novel results from an individual-based model investigating the joint roles of inbreeding load, demographic stochasticity, environmental stochasticity, and dispersal costs for the evolution of sex-biased dispersal. Most strikingly, we found that male-biased natal dispersal evolved in polygynous systems as a result of the interplay between inbreeding avoidance and stochasticity, whereas previous theory, in contrast to empirical observations, predicted male philopatry and female-biased natal dispersal under inbreeding load alone. Furthermore, the direction of the bias varied according to the nature of stochasticity. Our results therefore provide a unification of previous theory, yielding a much better qualitative match with empirical observations of male-biased dispersal in mate defense mating systems.

性别偏向性出生扩散（sex-biased natal dispersal）广泛存在，其演化意义始终是进化生物学领域的核心研究议题。然而，现有理论迄今仍无法准确预测自然界中观测到的部分最常见扩散模式。为解决这一问题，我们基于个体模型（individual-based model）展开研究，揭示了近交负荷（inbreeding load）、种群统计随机性（demographic stochasticity）、环境随机性（environmental stochasticity）以及扩散成本对性别偏向性扩散演化的共同调控作用，并呈现了全新的研究结果。最引人注目的是，我们发现在一夫多妻制系统（polygynous systems）中，由于近交回避与随机性的协同互作，演化出了雄性偏向的出生扩散模式；而此前仅考虑近交负荷的理论预测结果为雄性留居（male philopatry）、雌性偏向的出生扩散，这与实际实证观测结果相悖。此外，扩散偏向的方向会随随机性的本质特征发生变化。综上，我们的研究统一了此前的理论框架，使其与配偶防御型交配系统（mate defense mating systems）中雄性偏向扩散的实证观测结果在定性层面实现了更高程度的匹配。