Dispersal and mating system, defined as suites of physiological, morphological and behavioural traits involved in individual movements leading to spatial gene flow (dispersal), and in obtaining and choosing mates (mating system), are fundamental in determining species’ ecology and evolution. As main drivers of gene flow in space and time, they determine a species’ evolutionary potential by influencing maintenance of genetic variation and individuals’ fitness variation. Dispersal and mating system are tightly interconnected, influencing each other’s evolution, such that a variety of dispersal-mating system syndromes is observed (e.g. correlations between sex-biased dispersal and mating system, or between seed dispersal and self-fertilization). However, the study of dispersal and mating system has largely proceeded separately, leaving a critical knowledge gap regarding how dispersal and mating system jointly evolve and the consequences this might have for how populations, species and communities can respond to environmental change. While several hypotheses exist, especially for plants, we lack theory explaining the variation of dispersal-mating system syndromes existing in nature.
Inbreeding (mating with self or relatives) is central in linking dispersal and mating system. Both strategies determine the opportunity for inbreeding by shaping populations’ relatedness structures. Conversely, the balance between inbreeding depression and inclusive fitness benefits determines evolution of inbreeding strategies (avoidance, tolerance or preference) such as self-fertilization, mate choice, female multiple mating and sex-biased dispersal, and influence evolution of sociality. Especially for species’ with biparental reproduction, inbreeding has been mostly studied separately for mating system and dispersal, leaving unaddressed fundamental questions about its role in dispersal and mating system evolution. Additionally, we do not know what spatial patterns of dispersal-mating system co-variation are to be expected; how environmental changes impact on their joint evolution; and what this means for populations’ viabilities and responses to changes. We lack theory on how inbreeding risk and depression vary in space and are affected by spatial processes such as habitat loss/fragmentation or range expansion/shifting, and therefore affect patterns of dispersal-mating system co-variation. For example, increased selection for inbreeding avoidance (through dispersal and/or mating system) might be expected at range margins, as inbreeding risk increases in small populations. However, mate scarcity might increase selection for inbreeding tolerance, contrary to the current paradigm associating dispersal with inbreeding avoidance, with consequent purging/fixation of deleterious mutations, and consequences for species’ ability to range expand/shift.
Answering these questions is critical for predicting species’ potentials to respond to environmental changes, as feed-backs between inbreeding, inbreeding depression and inbreeding strategies will affect maintenance and distribution of genetic variation. However, we lack theory that can predict geographical patterns of dispersal-mating system syndromes, both in static and changing environments. Addressing these questions will be the core of my recently funded (1st October 2017 start) Royal Society University Research fellowship.