The Interaction between Selection, Demography and Selfing and How It Affects Population Viability

Abstract

Population extinction due to the accumulation of deleterious mutations has only been considered to occur at small population sizes, large sexual populations being expected to efficiently purge these mutations. However, little is known about how the mutation load generated by segregating mutations affects population size and, eventually, population extinction. We propose a simple analytical model that takes into account both the demographic and genetic evolution of populations, linking population size, density dependence, the mutation load, and self-fertilisation. Analytical predictions were found to be relatively good predictors of population size and probability of population viability when verified using an explicit individual based stochastic model. We show that initially large populations do not always reach mutation-selection balance and can go extinct due to the accumulation of segregating deleterious mutations. Population survival depends not only on the relative fitness and demographic stochasticity, but also on the interaction between the two. When deleterious mutations are recessive, self-fertilisation affects viability non-monotonically and genomic cold-spots could favour the viability of outcrossing populations.

Population Genetics and the Effects of a Severe Bottleneck in an Ex Situ Population of Critically Endangered Hawaiian Tree Snails

“…Declining measures of fitness and a loss of allelic diversity in a captive population of A. lila raise concerns about the probability of extinction due to synergistic interactions between demographics and genetics [21] . Species recovery appeared possible following the severe bottleneck at the founding of the captive population, given population growth prior to 2009.…”

“…Low density and population fragmentation in the wild may have resulted in an increase in the rate of self-fertilization in A. lila , or this species may have a higher intrinsic rate of self-fertilization than close relatives. Unfortunately, populations where some self-fertilization occurs may be at an additional disadvantage, building up mildly deleterious alleles through self-fertilization, and expressing them in outcrossing individuals [21] .…”

Molecular Evolution of Freshwater Snails with Contrasting Mating Systems

“…The role of genetic factors, especially the genetic load, in population extinction has been much debated. Under hardselection, the reduction in fitness due to the accumulation of deleterious alleles can lead populations to extinction when population size decreases below a critical threshold (mutational meltdown; Lynch et al 1993;Awad et al 2014). However, under soft-selection, populations could cope with high genetic loads (e.g., Lesecque et al 2012;Charlesworth 2013, for formal analyses), and put into an ecological context, the load may have no direct consequences on population abundance or persistence (Agrawal and Whitlock 2012).…”

Structure of multilocus genetic diversity in predominantly selfing populations

“…Demographic events are also likely to affect the effective size of selfing populations where founder effects can be frequent, e.g., through the establishment of a new population by a single individual (Baker 1967). In addition, according to the "dead-end hypothesis" (Stebbins 1957), selfing populations are expected to accumulate deleterious mutations (Lynch et al 1995;Abu Awad et al 2014), and could lack the genetic diversity required to adapt to changing environmental conditions (Charlesworth and Charlesworth 1995;Lande and Porcher 2015;Abu Awad and Roze 2018). Therefore, we can expect frequent catastrophic demographic events, with strong bottlenecks or even extinctions followed by recolonization accompanied by strong founder effects (Schoen and Brown 1991).…”