Genetic variation and structure of house sparrow populations: is there an island effect?

Abstract

Population genetic structure and intra-population levels of genetic variation have important implications for population dynamics and evolutionary processes. Habitat fragmentation is one of the major threats to biodiversity. It leads to smaller population sizes and reduced gene flow between populations and will thus also affect genetic structure. We use a natural system of island and mainland populations of house sparrows along the coast of Norway to characterize the different population genetic properties of fragmented populations. We genotyped 636 individuals distributed across 14 populations at 15 microsatellite loci. The level of genetic differentiation was estimated using F-statistics and specially designed Mantel tests were conducted to study the influence of population type (i.e. mainland or island) and geographic distance on the genetic population structure. Furthermore, the effects of population type, population size and latitude to the level of genetic variation within populations were examined. Our results suggest that genetic processes on islands and mainland differed in two important ways. Firstly, the intra-population level of genetic variation tended to be lower and the occurrence of population bottlenecks more frequent on islands than the mainland. Secondly, although the general level of genetic differentiation was was low to moderate it was higher between island populations than between mainland populations. However, differentiation increased in mainland populations somewhat faster with geographical distance. These results suggest that population bottleneck events and genetic drift have been more important in shaping the genetic composition of island populations compared to populations on the mainland. Such knowledge is relevant for a better understanding of evolutionary processes and conservation of threatened populations.2

Genetic diversity and colony structure of Tapinoma melanocephalum on the islands and mainland of South China

“…Geographic characteristics can affect dispersal range and gene flow of invasive species and further influence genetic diversity of introduced populations (Barrett & Husband, 1990; Moody & Mack, 1988). For islands, a natural barrier has the potential to influence species diversity or population size (Jensen et al., 2013). In our study, the genetic diversity of the mainland populations of T. melanocephalum was slightly higher than that of the island populations, but there were no significant differences.…”

Avian β-defensin variation in bottlenecked populations: the Seychelles warbler and other congeners

“…Drift is the predominant evolutionary force shaping genetic variation in small populations Miller and Lambert 2004;Jensen et al 2013), and its effects on genetic variation often outweigh the influence of selection (Miller and Lambert 2004;Alcaide 2010;Grueber et al 2013). Nevertheless, various studies have shown that within small natural populations, variation at specific key loci can be elevated above that of the genome-wide average, and be maintained across bottleneck events as a result of balancing selection (Aguilar et al 2004;Tompkins 2007;van Oosterhout et al 2006).…”

A longitudinal genetic survey identifies temporal shifts in the population structure of Dutch house sparrows

“…Indeed, analyses based on this assumption earlier proved to perform well under weak levels of population differentiation (Guillot, 2008;Safner et al, 2011), in particular for detecting recent barriers to gene flow (Coulon et al, 2006;Safner et al, 2011;Blair et al, 2012). In our study, post-decline population clusters most likely resulted from a progressive connectivity loss at the landscape level, rather than from a distinct geographical barrier to dispersal (Jensen et al, 2013). At a smaller spatial scale, Vangestel et al (2011) earlier revealed higher average levels of genetic relatedness among house sparrows from more urbanized areas in Flanders, most likely reflecting reduced dispersal in more built-up habitats.…”

“…Such philopatric behavior may result in local extinctions not being compensated by recolonization, and hence may transform contiguous populations into patchy ones-a pattern currently observed in highly built-up areas (Shaw et al, 2008;Vangestel et al, 2011). Despite this highly sedentary behavior of house sparrows, several studies failed to detect large-scale genetic differentiation in the absence of geographical barriers (Fleischer, 1983;Parkin and Cole, 1984;Kekkonen et al, 2011b; but see Jensen et al, 2013 for the island effect), even after a severe population decline (Kekkonen et al, 2011a;Schrey et al, 2011). This lack of differentiation may be explained by the fact that even few individuals dispersing in a stepping-stone pattern already suffice to maintain genetic homogeneity across large geographic distances (Allendorf, 1983).…”