Environmental unpredictability and inbreeding depression select for mixed dispersal syndromes

TL;DR

This study uses mathematical and computational models to explore how environmental unpredictability and inbreeding depression influence the evolution of mixed dispersal syndromes, showing they are often the optimal strategy for population persistence.

Contribution

It demonstrates that mixed dispersal syndromes are evolutionarily favored under high environmental unpredictability and low inbreeding depression, expanding understanding of dispersal evolution.

Findings

Mixed dispersal syndromes are adaptive in unpredictable environments.

Pure dispersers or non-dispersers often lead to extinction under high costs.

Mixed strategies enable population persistence under critical conditions.

Abstract

Mixed dispersal syndromes have historically been regarded as bet-hedging mechanisms that enhance survival in unpredictable environments, ensuring that some propagules stay in the maternal environment while others can potentially colonize new sites. However, this entails paying the costs of both dispersal and non-dispersal. Propagules that disperse are likely to encounter unfavorable conditions for establishment, while non-dispersing propagules might form populations of close relatives burdened with inbreeding. Here, we investigate the conditions under which mixed dispersal syndromes emerge and are evolutionarily stable, taking into account the risks of both environmental unpredictability and inbreeding. Using mathematical and computational modeling we show that high dispersal propensity is favored whenever temporal environmental unpredictability is low and inbreeding depression high, whereas mixed dispersal syndromes are adaptive under conditions of high environmental unpredictability, but more particularly if also inbreeding depression is small. Although pure dispersers can be selected for under some circumstances, mixed dispersal provides the optimal strategy under most parameterizations of our models, indicating that this strategy is likely to be favored under a wide variety of conditions. Furthermore, populations exhibiting any single phenotype go inevitably extinct when environmental and genetic costs are high, whilst mixed strategies can maintain viable populations even under such conditions. Our models support the hypothesis that the interplay between inbreeding depression and environmental unpredictability shapes dispersal syndromes, often resulting in mixed strategies. Moreover, mixed dispersal seems to facilitate persistence whenever conditions are critical or nearly critical for survival.