Correlation of Pairwise Genetic and Geographic Distance Measures: Inferring the Relative Influences of Gene Flow and Drift on the Distribution of Genetic Variability

Abstract

Abstract.-Attempts to relate estimates of regional F ST to gene flow and drift via Wright's (1931) equation F ST = 11(4Nm + 1) are often inappropriate because most natural sets of populations probably are not at equilibrium (McCauley 1993), as assumed by the island model upon which the equation is based, or ineffective because the influences of gene flow and drift are confounded in the product Nm. Evaluations of the association between genetic (F ST ) and geographic distances separating all pairwise populations combinations in a region allows one to test for regional equilibrium, to evaluate the relative influences of gene flow and drift on population structure both within and between regions, and to visualize the behavior of the association across all degrees of geographic separation. Tests of the model using micro satellite data from 51 populations of eastern collared lizards (Crotaphytus collaris collaris) collected from four distinct geographical regions gave results highly consistent with predicted patterns of association based on regional differences in various historical and ecological factors that affect the amount of drift and gene flow. The model provides a prerequisite for and an alternative to regional F ST analyses, which often simply assume regional equilibrium, thus potentially leading to erroneous and misleading inferences regarding regional population structure.Key words.-Correlations, Crotaphytus collaris, F-statistics, gene flow, genetic distance, Mantel's test, population structure, random genetic drift.Received March 24, 1998. Accepted June I, 1999.It is notoriously difficult to assess the individual effects of gene flow and drift on regional population structure. Traditional attempts to relate estimates of regional F ST to gene flow and drift via Wright's (1931) equation F ST = 1I(4Nm + 1) are often inappropriate because most natural sets of populations probably are not at equilibrium (McCauley 1993), as is assumed by the island model upon which the equation is based. Furthermore, the influences of gene flow and drift on regional population structure are confounded in the product Nm.In this paper we discuss a method that allows one to test for regional equilibrium before applying Wright's equation or other models that assume such a pattern. Although Nand m remain a product under this approach, it does permit evaluation of the relative historical influences of gene flow and drift on regional population structure by comparing the observed relationship between the genetic (F ST ; Reynolds et al. 1983) and geographic distances separating pairs of populations in a region (Nei 1972;Hartl and Clark 1989;Tilley et al. 1990) with those expected under a stepping-stone model of population structure (Kimura 1953;Malecot 1955;Kimura and Weiss 1964). Further refinement of the analysis is possible by taking into consideration various historical and ecological factors characteristic of a region as they pertain to the amount of drift and gene flow affecting the organisms under study. Finally, it is also p...

Improving insect pest management through population genetic data: a case study of the mosquito Ochlerotatus caspius (Pallas)

“…Moreover, the shape of the scatterplot (Fig. 1) conforms well to Hutchison & Templeton's (1999) case II, i.e. with a nonsignificant association coupled with low differentiation between populations and a low degree of scatter, in which the lack of regional equilibrium between gene flow and drift can be attributed to the prevalence of the former.…”

“…The relative importance of these forces can be evaluated by predictable and contrasted patterns of relationship between genetic and geographic distances, as well as by the degree of scatter of genetic distance over geographic distance (Hutchison & Templeton 1999). The relationship between geographic [as ln (geographic distance in km)] and genetic distances (as F ST /1-F ST ; Rousset 1997) was evaluated with a Mantel test (with 10 000 permutations), as implemented in the web version of ibd software (Jensen, Bohonak & Kelley 2005).…”

“…In order to verify the null hypothesis of the existence of equilibrium conditions between gene flow and drift at the regional scale, we used the approach proposed by Hutchison & Templeton (1999). The relative importance of these forces can be evaluated by predictable and contrasted patterns of relationship between genetic and geographic distances, as well as by the degree of scatter of genetic distance over geographic distance (Hutchison & Templeton 1999).…”

Quantifying functional connectivity: The role of breeding habitat, abundance, and landscape features on range‐wide gene flow in sage‐grouse

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“…Two conditions are necessary for a pattern of isolation by distance to occur: higher probability of short-distance than long-distance gene flow and enough time for the pattern to be established. Otherwise, a random distribution of allele frequencies will be found, with high differentiation among populations when gene flow is restricted, or with non-significant F ST values when gene flow is common (Hutchison & Templeton 1999). Given that the reinfestation of Córdoba is a relatively recent event (10-15 years), the significant pairwise F ST values would indicate that gene flow between the sampled populations is low.…”