Unexpected heterozygosity in an island mouflon population founded by a single pair of individuals

Abstract

In population and conservation genetics, there is an overwhelming body of evidence that genetic diversity is lost over time in small populations. This idea has been supported by comparative studies showing that small populations have lower diversity than large populations. However, longitudinal studies reporting a decline in genetic diversity throughout the whole history of a given wild population are much less common. Here, we analysed changes in heterozygosity over time in an insular mouflon (Ovis aries) population founded by two individuals in 1957 and located on one of the most isolated locations in the world: the Kerguelen Sub-Antarctic archipelago. Heterozygosity measured using 25 microsatellite markers has actually increased over 46 years since the introduction, and exceeds the range predicted by neutral genetic models and stochastic simulations. Given the complete isolation of the population and the short period of time since the introduction, changes in genetic variation cannot be attributed to mutation or migration. Several lines of evidence suggest that the increase in heterozygosity with time may be attributable to selection. This study shows the importance of longitudinal genetic surveys for understanding the mechanisms that regulate genetic diversity in wild populations.

Individual genetic diversity correlates with the size and spatial isolation of natal colonies in a bird metapopulation

“…Given that random terms were not significant in the multivariate mixed model (table 3), we used sample size to give observations of different weights in a weighted least-squares analysis (e.g. Kaeuffer et al 2007;Ortego et al 2007c). As above, average colony heterozygosity was negatively associated with squared distance to the nearest colony of the lesser kestrels (H O : tZK3.521, pZ0.001; HL: tZ3.190, pZ0.002) and positively associated with colony size (H O : tZ3.521, pZ0.001; HL: tZK2.753, pZ0.008).…”

Introduction history overrides social factors in explaining genetic structure of females in Mediterranean mouflon

“…Similarly, Kaeuffer et al. (2007) revealed a higher than expected heterozygosity in another introduced mouflon population. Contrary to heterozygosity, allelic richness values in the study population were closer to those observed in the Cyprus population (see Supplementary Material F, Tables S5 and S6).…”

“…In closed populations, N a can only be restored by mutations; heterozygosity is thus expected to be restored faster and to be easier to save than N a when conditions are favorable. In our population, founders from three different origins (Table 1) were released on four occasions, and growth rate after introduction is thought to have been as high as in other introduced mouflon populations (e.g., Kaeuffer et al., 2007) and most herbivore populations (Forsyth & Caley, 2006). These conditions could thus have favored heterozygosity maintenance at a relatively high level, comparable to unbottlenecked populations, while allelic richness still bears the scars of the founder events.…”

Selection and the rate of loss of genetic variation: Natural selection and genetic diversity

“…The latter occurs because individuals within the population vary in their inbreeding levels. Kaeuffer et al (2006) suggest that their results are more likely to be due to local than general effects, but admit that there is no concrete way to test this. The inability to discriminate between these two hypotheses is not, in my opinion, of great concern as ultimately all genome-wide effects must have a local cause.…”

“…This is of particular concern with regard to the conservation of endangered species of plants and animals, as the loss of genetic diversity through random genetic drift can compromise the future ability of populations to evolve in the face of changing environmental conditions. Thus, a recent paper published in the Proceedings of the Royal Society B (Kaeuffer et al, 2006) demonstrating that an isolated population of mouflon (Ovis aries) introduced to a remote island as a single founding male-female pair, has apparently increased in heterozygosity (a measure of genetic variation) over the course of approximately 23 generations is of great interest. Kaeuffer et al (2006) suggest that this increase in heterozygosity is due to natural selection acting against inbred individuals.…”