Factors influencing the genetic structure of Phacelia dubia, a species with a seed bank and large fluctuations in population size

Abstract

The potential factors that may influence the genetic structure of the gynodioecious annual Phacelia dubia were assessed using electrophoretic and ecological information at a locality in which the population size changed by about three orders of magnitude. Fluctuations in population size appeared to have little influence on the allelic composition, heterozygosity and mixed mating system of the population. Despite wide fluctuations in total population size, the estimated effective population size during (Ne =20) and after the bottleneck (N = 28) was little changed. Also, a significant spatial substructuring, evidenced by a dine in MDH and by the F-statistics, was observed before and after the bottleneck. The recovery of the population and the preservation of genetic diversity was attributable in part to the seed bank in the soil. Spatial gene flow via seeds was small compared with pollen flow and both were restricted. Nevertheless, substructuring contributes to a small portion of the total inbreeding. Also, the rate of apparent selfing of male steriles did not provide evidence of biparental inbreeding. Most of the inbreeding, however, was within subpopulations and autogamy appears to be the major contributor. It was concluded that the mating system is the leading factor determining the genetic structure and that the seed bank ensures genetic constancy in time in the face of large fluctuations in population size.

Centaurea corymbosa, a cliff-dwelling species tottering on the brink of extinction: A demographic and genetic study

“…This is consistent with other studies showing that most of the pollen is carried over very short distances by insects in animal-pollinated plants (50,(59)(60)(61)(62)(63). We would then expect to find small neighborhood areas (60,64) within which most of the pollen is dispersed.…”

Fine-scale genetic structure and clinal variation in Silene acaulis despite high gene flow

“…Recent studies report that pollen disperses over much larger distances than do seeds (e.g. del Castillo, 1994; Weiblen & Thomson, 1995). Boshier et al .…”

“…Previous studies have explored genetic structure within patches and among populations of nonclonal plant species exhibiting patchy distributions (e.g. Rasmussen & Brodsgaard, 1992; del Castillo, 1994; Tarayre et al ., 1997 ). However, only a few investigations have compared the fine‐scale genetic structure of more than one population of a patchily distributed species ( Williams, 1994; Williams & Guries, 1994; Giles et al ., 1998 ).…”

Comparison of genetic variation in populations of wild rice, Oryza rufipogon, plants and their soil seed banks

“…In addition, relatively more heterozygous genotypes occurred in seed banks (Table 1) suggests a nonrandom pattern of germination with respect to seed genotype in O. rufipogon. An increase in the apparent frequency of heterozygous genotypes in older seed populations means higher mortality rates for more homozygous seeds (e.g., Del Castillo 1994) and might reflect a selection effect for heterozygous genotypes. This process would cut down the number and type of alleles that only exist in homozygous seeds, leading to genetic differentiation.…”