Strong spatial genetic structure in peripheral but not core populations of Sitka spruce [Picea sitchensis (Bong.) Carr.]

Abstract

We examined spatial genetic structure within eight populations of Sitka spruce classified as core or peripheral based on ecological niche, and continuous or disjunct based on species distribution. In each population, 200 trees were spatially mapped and genotyped for eight cDNA-based sequence tagged site (STS) codominant markers. Spatial autocorrelation was assessed by estimating p(ij), the average co-ancestry coefficient, between individuals within distance intervals. The distribution of alleles and genotypes within core populations was almost random, with nonsignificant co-ancestry values among trees as close as 50 m in core populations. In contrast, the distribution of alleles and genotypes within peripheral populations revealed an aggregation of similar multilocus genotypes, with co-ancestry values greater than 0.20 among trees up to 50 m apart and significant, positive values between trees up to 500 m. The relatively high density of reproductive adults in core populations may lead to highly overlapping seed shadows that limit development of spatial genetic structure. However, in peripheral populations with a lower density of adults, the distribution of alleles and genotypes was highly structured, likely due to offspring establishment near maternal trees and subsequent biparental inbreeding, as well as more recent population establishment at the leading edge of post-Pleistocene range expansion. Conserving genetic diversity in peripheral populations may require larger reserves for in situ conservation than required in core populations. These data on spatial genetic structure can be used to provide guidance for sampling strategies for both ex situ conservation and research collections.

Population size, center–periphery, and seed dispersers’ effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon

“…It is often assumed that peripheral populations are small, isolated, and occur in ecologically marginal habitats where selection pressures are likely to be more intense (Brown, Stevens, & Kaufman, 1996; Eckert et al., 2008; Lawton, 1993; Lesica & Allendorf, 1995; Pulliam, 2000). Such populations can have low genetic diversity as a consequence of high inbreeding, genetic drift, and directional selection and may also show strong genetic structure due to reduced gene flow (Arnaud‐Haond et al., 2006; Durka, 1999; Gapare & Aitken, 2005; Lammi et al., 1999; Schaal & Leverich, 1996). However, it is not known to what extent the effects of periphery are confounded by those of population size.…”

Wide variation in spatial genetic structure between natural populations of the European beech (Fagus sylvatica) and its implications for SGS comparability

“…Furthermore, such fine-scale characterization of the genetic structure of populations can inform appropriate strategies for stand management and conservation, including in-situ and ex-situ conservation of genetic resources and collection strategies for genetic resource harvesting (Gapare and Aitken, 2005). Conversely, overlooking such structure in reserve design or resource collection might lead to over-representing some genotypes whilst under-representing population genetic diversity in collected material (Gapare and Aitken, 2005).…”

Spatial Genetic Structure within Populations of Sorbus torminalis (L.) Crantz: Comparative Analysis of the Self-incompatibility Locus and Nuclear Microsatellites

“…Spatial genetic structure (SGS) is defined as the nonrandom spatial distribution of genotypes and alleles within populations, meaning that genetic similarity is higher among neighbors than among more distant individuals (Gapare and Aitken, 2005). SGS has been described in various plant groups, usually in the form of within population fine-scale aggregation (Vekemans and Hardy, 2004).…”