Environment‐dependent inbreeding depression: its ecological and evolutionary significance

Summary Inbreeding depression is a major evolutionary and ecological force that influences population dynamics and the evolution of inbreeding‐avoidance traits such as mating systems and dispersal. There is now compelling evidence that inbreeding depression is environment‐dependent. Here, we discuss ecological and evolutionary consequences of environment‐dependent inbreeding depression. The environmental dependence of inbreeding depression may be caused by environment‐dependent phenotypic expression, environment‐dependent dominance, and environment‐dependent natural selection. The existence of environment‐dependent inbreeding depression challenges classical models of inbreeding as caused by unconditionally deleterious alleles, and suggests that balancing selection may shape inbreeding depression in natural populations; loci associated with inbreeding depression in some environments may even contribute to adaptation to others. Environment‐dependent inbreeding depression also has important, often neglected, ecological and evolutionary consequences: it can influence the demography of marginal or colonizing populations and alter adaptive optima of mating systems, dispersal, and their associated traits. Incorporating the environmental dependence of inbreeding depression into theoretical models and empirical studies is necessary for understanding the genetic and ecological basis of inbreeding depression and its consequences in natural populations. Contents Summary 395 I. Introduction 396 II. What is inbreeding depression? 396 III. Causes of environment‐dependent inbreeding depression 397 IV. Ecological and evolutionary consequences of environment‐dependent inbreeding depression 401 V. Feedbacks when inbreeding depression influences the environment 404 VI. Conclusions and future directions 405 Acknowledgements 406 References 406