Population genetic diversity and fitness in multiple environments

Abstract

BackgroundWhen a large number of alleles are lost from a population, increases in individual homozygosity may reduce individual fitness through inbreeding depression. Modest losses of allelic diversity may also negatively impact long-term population viability by reducing the capacity of populations to adapt to altered environments. However, it is not clear how much genetic diversity within populations may be lost before populations are put at significant risk. Development of tools to evaluate this relationship would be a valuable contribution to conservation biology. To address these issues, we have created an experimental system that uses laboratory populations of an estuarine crustacean, Americamysis bahia with experimentally manipulated levels of genetic diversity. We created replicate cultures with five distinct levels of genetic diversity and monitored them for 16 weeks in both permissive (ambient seawater) and stressful conditions (diluted seawater). The relationship between molecular genetic diversity at presumptive neutral loci and population vulnerability was assessed by AFLP analysis.ResultsPopulations with very low genetic diversity demonstrated reduced fitness relative to high diversity populations even under permissive conditions. Population performance decreased in the stressful environment for all levels of genetic diversity relative to performance in the permissive environment. Twenty percent of the lowest diversity populations went extinct before the end of the study in permissive conditions, whereas 73% of the low diversity lines went extinct in the stressful environment. All high genetic diversity populations persisted for the duration of the study, although population sizes and reproduction were reduced under stressful environmental conditions. Levels of fitness varied more among replicate low diversity populations than among replicate populations with high genetic diversity. There was a significant correlation between AFLP diversity and population fitness overall; however, AFLP markers performed poorly at detecting modest but consequential losses of genetic diversity. High diversity lines in the stressful environment showed some evidence of relative improvement as the experiment progressed while the low diversity lines did not.ConclusionsThe combined effects of reduced average fitness and increased variability contributed to increased extinction rates for very low diversity populations. More modest losses of genetic diversity resulted in measurable decreases in population fitness; AFLP markers did not always detect these losses. However when AFLP markers indicated lost genetic diversity, these losses were associated with reduced population fitness.

How closely does genetic diversity in finite populations conform to predictions of neutral theory? Large deficits in regions of low recombination

“…This prediction has been supported in meta-analyses of data from animal and plant species (r¼0.45 (Reed and Frankham, 2003); rB0.3 (Leimu et al, 2006); r¼0.40, 0.49 (Markert et al, 2010)). By contrast, little relationship is expected between individual multilocus genetic diversity for near-neutral loci and reproductive fitness within populations, unless there is heterozygote advantage, inbreeding or population structure.…”

Genetic erosion in the snailLittoraria subvittata(Reid, 1986) due to mangrove deforestation

“…In general, we found that salt-pond populations had a reduced effective population size as compared with natural populations. Lower genetic diversity has been observed as a factor compromising reproductive fitness in affected populations, increasing the risk of local extinction (Markert et al, 2010). More migrants were observed from salt ponds towards natural mangroves than vice versa.…”

Evolutionary rescue in vertebrates: evidence, applications and uncertainty

“…For instance, the animal model [80] is now commonly used in the wild to estimate additive genetic variation, a critical component of the evolutionary potential of a trait. To our knowledge, no examples of the application of the animal model to ER yet exist; however, several authors have highlighted its potential [81][82][83]. High throughput genomic techniques with large sets of microsatellites loci and/or high-density SNP data provide helpful tools to achieve this objective [80].…”