Microsatellite analysis of spatial structure among seedlings in populations of Pinus strobus (pinaceae)

Abstract

In a detailed analysis of how limited seed dispersal can create spatial structuring of genetic variation, several nuclear microsatellites were assayed in seedlings from two forests of Pinus strobus, one old growth (OG) and the other (second site, SS) logged in ca. 1900. By using loci with a large number of alleles and new statistical methods on averaged spatial correlation coefficients, unusually precise estimates of spatial genetic structure were obtained, even though the structure was expected to be very weak. This high precision allowed the spatial patterns to be contrasted across loci and populations. At the OG site, the average spatial correlation coefficient for short distances (<15 m) exceeded its random expected value by 0.035, providing an indirect estimate of ca. 230 for Wright's neighborhood size. The value is similar to that estimated in a previous study of adult trees at OG and probably represents the natural level of spatial structure. A very similar value, 0.030, was obtained for seedlings at SS, despite the fact that unlike OG, genotypes of adults are randomly distributed, a likely result of logging. The results show that a single cycle of limited seed dispersal recreated the natural level of spatial structuring. In addition, one microsatellite, Rps50, had far greater amounts of allele variation, likely implicating it as having a higher mutation rate. The spatial structure of Rps50 also was significantly reduced, in a way that could be consistent with theoretical effects of high mutation rates (up to μ = 10(-2)). The choice of markers may influence estimates of spatial genetic structure. For example, if Rps50 is omitted the values are nearly doubled to 0.058 and 0.051 for SS and OG, respectively, both indicating a much smaller neighborhood size of ca. 100.

Estimating dispersal from short distance spatial autocorrelation

“…By this method, it was estimated that Rps50 has a mutation rate that is approximately six-or seven-fold greater than the average for other loci. The same differences in spatial structure and estimated relative mutation rates between Rps50 and other loci was also observed in the white pine seedlings found in the same forest (Walter and Epperson, 2004). This is an important lesson, particularly because the general and otherwise supported tendency is to choose microsatellites (or other markers) that have the highest numbers of alleles.…”

Low genetic diversity and significant population structuring in the relict Amentotaxus argotaenia complex (Taxaceae) based on ISSR fingerprinting

“…Unexpect- edly, in this study, most of the genetic variation was partitioned among populations in each species of the A. argotaenia complex. Significant population structuring and extremely small Nm values, 0.094 for A. argotaenia and 0.085 for A. yunnanensis, suggest that the range of windmediated pollen flow may not be as far as generally expected, as recently illustrated in pines (Dyer and Sork 2001;Walter and Epperson 2004). In addition, gravity-and small animal-disseminated seeds of A. argotaenia complex may promote mating between individuals in close proximity within populations.…”

Spatial genetic structure of two sympatric neotropical palms with contrasting life histories

“…These differences may have resulted in differential densities, and hence weaker spatial genetic structure in the site of the common, wind-pollinated and understory species. For long-lived species, especially polycarpic plants, overlapping generations and seed shadows may greatly mask the genetic relatedness among individuals of the same age (Chung et al, 2003a;Walter and Epperson, 2004). The lower spatial genetic structure of C. tepejilote could thus be the result of a more diverse mixture of family patches, each containing a larger number of individuals, longer generations and higher genetic variation within populations, as compared to C. elatior.…”