Genetic diversity in introduced populations with Allee effect

TL;DR

This study uses stochastic modeling to explore how the Allee effect influences genetic diversity in small introduced populations, revealing that it can either increase or decrease diversity depending on initial conditions and introduction history.

Contribution

It provides a novel analysis of the impact of the Allee effect on genetic diversity, including how multiple introductions and critical population size can be inferred from genetic data.

Findings

Allee-effect populations derive from larger founders and have higher initial genetic variation.

They spend fewer generations at small sizes but more time near the critical size, affecting genetic drift.

Multiple introductions increase genetic diversity in Allee-effect populations.

Abstract

A phenomenon that strongly influences the demography of small introduced populations and thereby potentially their genetic diversity is the Allee effect, a reduction in population growth rates at small population sizes. We take a stochastic modeling approach to investigate levels of genetic diversity in populations that successfully overcame a strong demographic Allee effect, a scenario in which populations smaller than a certain critical size are expected to decline. Our results indicate that compared to successful populations without Allee effect, successful Allee-effect populations tend to 1) derive from larger founder population sizes and thus have a higher initial amount of genetic variation, 2) spend fewer generations at small population sizes where genetic drift is particularly strong, and 3) spend more time around the critical population size and thus experience more drift there. Altogether, the Allee effect can either increase or decrease genetic diversity, depending on the average founder population size. In the case of multiple introduction events, there is an additional increase in diversity because Allee-effect populations tend to derive from a larger number of introduction events than other populations. Finally, we show that given genetic data from sufficiently many populations, we can statistically infer the critical population size.