Does time since colonization influence isolation by distance? A meta-analysis

Abstract

Isolation by distance (IBD) is a phenomenon characterized by increasing genetic divergence and decreasing gene flow with increasing geographic distance. IBD is often used in conservation biology to infer the extent of gene flow among populations. An assumption inherent to this approach is equilibrium between genetic drift and gene flow, which may take thousands of years to achieve. This implies that empirical IBD studies of recently colonized areas, such as postglacial systems, should be concerned with whether or not equilibrium has been reached. Short of equilibrium, IBD should increase with the length of time since a geographical area was colonized. We test the prediction that IBD increases with increasing time since colonization through a meta-analysis based on a diverse range of empirical systems. P and r 2 values from published IBD studies were analyzed with respect to time since colonization (in generations and years), taking into account variation in sample sizes, molecular markers, divergence metrics (genetic distance, F st , Nm), and dispersal patterns (one or two dimensional). Overall, we found weak evidence for associations between time since colonization and IBD. Sample sizes, molecular markers, divergence metrics, and dispersal patterns did not appreciably influence IBD. We propose that the expected relationship between IBD and time since colonization is obscured by the influence of other factors, such as dispersal ability, geographical barriers, and proximity to glacial refugia. The possible effects of time since colonization should continue to be evaluated in empirical studies, but other potential factors should also be thoroughly explored.

Combined analysis of nuclear and mitochondrial markers provide new insight into the genetic structure of North European Picea abies

“…IBD will be at its maximum at an equilibrium between genetic drift and gene flow and will depend on the time since the populations were established and the distance from the ancestral population (Slatkin, 1993). Therefore, when the radiation time is short, only populations in close proximity to the ancestral population will show signs of IBD (Crispo and Hendry, 2005). The time to reach equilibrium between genetic drift and gene flow will also depend on the effective population size of the involved populations and the generation time of the organism (that is, longer time to equilibrium when the populations are large and when the generation time is long).…”

Isolation-by-distance in landscapes: considerations for landscape genetics

“…Ever since Wright (1943) described isolation-by-distance (IBD), patterns of spatial genetic structure have been extensively studied in population genetic simulation models (Epperson, 2003;Epperson et al, 2010) and in natural populations (Crispo and Hendry, 2005;Jenkins et al, 2010;Storfer et al, 2010). In most of these studies, migration probability is a function of geographic straight-line distance.…”

“…Most landscape genetic studies measure the level of IBD by quantifying the linear correlation between genetic (for example, F ST ) and geographic distances from all deme pairs in a data set (Crispo and Hendry, 2005;Balkenhol et al, 2009;Jenkins et al, 2010). However, to highlight dispersal barriers due to landscape elements, several authors have recently argued that landscape genetic analyses should be restricted to only those pairs of demes between which direct gene flow is possible (Angelone et al, 2011;Keller et al, 2013).…”

Population Genetic Structure of the Spotted Wolffish, Anarhichas minor, in the North Atlantic

“…IBD should reflect a balance between genetic drift and gene flow, with the former increasing and the latter decreasing genetic divergence (Hutchison E 1999) [23]. Moreover, IBD should be maximal at equilibrium between genetic drift and gene flow, which may take a considerable length of time to develop (Crispo CG 2005) [24]. Barriers to dispersal and hence gene flow are likely to disrupt IBD.…”

“…Gold MB 1999) [26]. If no such barriers appear likely, some authors conclude that populations not exhibiting IBD have been too recently colonized or have been influenced by Pleistocene glaciers (Crispo CG 2005) [24]. Other factors, such as heterogeneity of spawning habitat or gyral retention of larvae (Hansen ICES 1986) [27], may drive population differentiation at both geographically large and more localized scales.…”