Population genetic consequences of the Allee effect and the role of offspring-number variation

TL;DR

This study uses stochastic models to explore how offspring-number variation influences genetic diversity in populations overcoming the Allee effect, revealing that higher variability can promote diversity and affect genetic drift.

Contribution

It demonstrates that offspring-number variation impacts genetic diversity in populations overcoming the Allee effect, challenging classical models that use effective population size corrections.

Findings

Higher offspring-number variability promotes genetic diversity in successful populations.

Populations with high variability escape small sizes quickly, reducing genetic drift.

Classical models may underestimate the impact of offspring variation on genetic outcomes.

Abstract

A strong demographic Allee effect in which the expected population growth rate is negative below a certain critical population size can cause high extinction probabilities in small introduced populations. However, many species are repeatedly introduced to the same location and eventually one population may overcome the Allee effect by chance. With the help of stochastic models, we investigate how much genetic diversity such successful populations harbour on average and how this depends on offspring-number variation, an important source of stochastic variability in population size. We find that with increasing variability, the Allee effect increasingly promotes genetic diversity in successful populations. Successful Allee-effect populations with highly variable population dynamics escape rapidly from the region of small population sizes and do not linger around the critical population size. Therefore, they are exposed to relatively little genetic drift. We show that here---unlike in classical population genetics models---the role of offspring-number variation cannot be accounted for by an effective-population-size correction. Thus, our results highlight the importance of detailed biological knowledge, in this case on the probability distribution of family sizes, when predicting the evolutionary potential of newly founded populations or when using genetic data to reconstruct their demographic history.