Immigration and the ephemerality of a natural population bottleneck: evidence from molecular markers

Abstract

Population bottlenecks are often invoked to explain low levels of genetic variation in natural populations, yet few studies have documented the direct genetic consequences of known bottlenecks in the wild. Empirical studies of natural population bottlenecks are therefore needed, because key assumptions of theoretical and laboratory studies of bottlenecks may not hold in the wild. Here we present microsatellite data from a severe bottleneck (95% mortality) in an insular population of song sparrows (Melospiza melodia). The major ¢ndings of our study are as follows: (i) The bottleneck reduced heterozygosity and allelic diversity nearly to neutral expectations, despite non-random survival of birds with respect to inbreeding and wing length. (ii) All measures of genetic diversity regained pre-bottleneck levels within two to three years of the crash. This rapid recovery was due to low levels of immigration. (iii) The rapid recovery occurred despite a coincident, strong increase in average inbreeding. These results show that immigration at levels that are hard to measure in most ¢eld studies can lead to qualitatively very di¡erent genetic outcomes from those expected from mutations only. We suggest that future theoretical and empirical work on bottlenecks and metapopulations should address the impact of immigration.

Low Genetic Variation in the Heath Hen Prior to Extinction and Implications for the Conservation of Prairie-Chicken Populations

“…Our study indicates that within as little as 4 years some current populations of prairie-chickens may reach the low levels of genetic variation found in Heath Hens. Genetic variation and fitness can be restored with translocation of individuals from other populations (Westemeier et al 1998;Madsen et al 1999;Keller et al 2001;Vila´et al 2003); however, adequate knowledge of phylogeography and demography (population bottlenecks) from historic data sets may be important for choosing an appropriate source population for translocation. As we have shown with historic data from Greater Prairie-chickens in Wisconsin, analyses based solely on contemporary populations may be severely affected by genetic drift and give misleading evolutionary relationships.…”

Genomic signatures of population bottleneck and recovery in Northwest Atlantic pinnipeds

“…On the other side of this demographic trajectory, evolutionary biologists have theorized that growing populations should experience a rise in genetic diversity over time, at a base level of the rate of mutation in closed populations (Nei et al., 1975) and at a higher rate with contributions from migrants in an open population or metapopulation system (Hansson et al., 2000; Keller et al., 2001). Furthermore, geographically expanding populations are predicted to vary spatially, with lower overall genetic diversity at the edge of their expansion wave and differences in the frequency of specific genetic variants as a result of sampling bias or selection for certain traits in successful migrants (reviewed in Excoffier, Foll, & Petit, 2009).…”

Bottlenecks and rescue effects in a fluctuating population of golden-mantled ground squirrels (Spermophilus lateralis)

“…All of these conditions are expected to increase a population's risk of extinction (Frankel and Soulé 1981;Saccheri et al 1998), although questions over the relative importance of genetic diversity to extinction risk in natural populations remain (Lande 1993;Keller et al 2001;Reed and Frankham 2003;Spielman et al 2004).…”