Allelic richness following population founding events--a stochastic modeling framework incorporating gene flow and genetic drift.

Gili Greenbaum,Shirli Bar-David,Alan R Templeton,Yair Zarmi,Lilach Hadany

doi:10.1371/journal.pone.0115203

Gili Greenbaum, Shirli Bar-David + Show 3 more

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https://doi.org/10.1371/journal.pone.0115203

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Abstract

Allelic richness (number of alleles) is a measure of genetic diversity indicative of a population's long-term potential for adaptability and persistence. It is used less commonly than heterozygosity as a genetic diversity measure, partially because it is more mathematically difficult to take into account the stochastic process of genetic drift for allelic richness. This paper presents a stochastic model for the allelic richness of a newly founded population experiencing genetic drift and gene flow. The model follows the dynamics of alleles lost during the founder event and simulates the effect of gene flow on maintenance and recovery of allelic richness. The probability of an allele's presence in the population was identified as the relevant statistical property for a meaningful interpretation of allelic richness. A method is discussed that combines the probability of allele presence with a population's allele frequency spectrum to provide predictions for allele recovery. The model's analysis provides insights into the dynamics of allelic richness following a founder event, taking into account gene flow and the allele frequency spectrum. Furthermore, the model indicates that the “One Migrant per Generation” rule, a commonly used conservation guideline related to heterozygosity, may be inadequate for addressing preservation of diversity at the allelic level. This highlights the importance of distinguishing between heterozygosity and allelic richness as measures of genetic diversity, since focusing merely on the preservation of heterozygosity might not be enough to adequately preserve allelic richness, which is crucial for species persistence and evolution.

Highlights

Genetic diversity is an important aspect of the dynamics of populations, as it is directly related to the evolutionary potential of the population and the deleterious effects of inbreeding [1]
It is assumed to be an ideal population at Hardy-Weinberg equilibrium, much larger than the founded population, and is assigned a static genetic description, while the founded population is dynamic in this regard
The number of migrants required for the mean allele frequency at equilibrium to recover to the same mean frequency as in the source population, Mmean, varied between 0.2 to 4.9 migrants per generation, with most scenarios requiring between 0.5–2.5 migrants, summarized in Table 1

Summary

Introduction

Genetic diversity is an important aspect of the dynamics of populations, as it is directly related to the evolutionary potential of the population and the deleterious effects of inbreeding [1]. Observed heterozygosity (HO), the frequency of heterozygous individuals in a population, or expected heterozygosity (HE), the probability that two gametes, randomly chosen from the gene pool, are of different alleles, are by far the measures most commonly used by the majority of papers that present a genetic summary of populations [4] (e.g., [5, 6]). These measures are very sensitive to the allele frequencies in the population, rather than just to the number of alleles. In practice, conclusions pertaining to these measures are often merely comparative, such as ‘‘population A has higher allelic richness than population B’’ or ‘‘the population had higher allelic richness at time T than at time S’’, and not quantitative

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