Data from: When does female multiple mating evolve to adjust inbreeding? Effects of inbreeding depression, direct costs, mating constraints, and polyandry as a threshold trait

Polyandry is often hypothesized to evolve to allow females to adjust the degree to which they inbreed. Multiple factors might affect such evolution, including inbreeding depression, direct costs, constraints on male availability, and the nature of polyandry as a threshold trait. Complex models are required to evaluate when evolution of polyandry to adjust inbreeding is predicted to arise. We used a genetically explicit individual-based model to track the joint evolution of inbreeding strategy and polyandry defined as a polygenic threshold trait. Evolution of polyandry to avoid inbreeding only occurred given strong inbreeding depression, low direct costs, and severe restrictions on initial versus additional male availability. Evolution of polyandry to prefer inbreeding only occurred given zero inbreeding depression and direct costs, and given similarly severe restrictions on male availability. However, due to its threshold nature, phenotypic polyandry was frequently expressed even when strongly selected against and hence maladaptive. Further, the degree to which females adjusted inbreeding through polyandry was typically very small, and often reflected constraints on male availability rather than adaptive reproductive strategy. Evolution of polyandry solely to adjust inbreeding might consequently be highly restricted in nature, and such evolution cannot necessarily be directly inferred from observed magnitudes of inbreeding adjustment.

一妻多夫制（Polyandry）通常被假说可通过演化，使雌性个体得以调整自身的近交（inbreeding）水平。诸多因素可能影响这一演化过程，包括近交衰退（inbreeding depression）、直接成本、雄性可获得性限制，以及作为阈值性状（threshold trait）的一妻多夫制本质。要预测何时会演化出用于调整近交的一妻多夫制，需借助复杂的模型开展评估。本研究采用遗传显式的基于个体的模型（individual-based model），追踪近交策略与被定义为多基因阈值性状（polygenic threshold trait）的一妻多夫制的协同演化过程。仅当存在强近交衰退、低直接成本，且初始雄性与额外雄性的可获得性均受到严格限制时，才会演化出用于规避近交的一妻多夫制。仅当不存在近交衰退与直接成本，且雄性可获得性受到同等严格的限制时，才会演化出偏好近交的一妻多夫制。然而，由于一妻多夫制的阈值特性，即便该性状受到强烈负向选择而表现为适应不良，表型层面的一妻多夫制仍常被表达出来。此外，雌性通过一妻多夫制调整近交的程度通常极低，且这种调整往往反映的是雄性可获得性的限制，而非适应性生殖策略。因此，仅为调整近交而演化出的一妻多夫制，在自然中可能受到极强的限制；且此类演化未必能直接通过观测到的近交调整程度加以推断。