Patterns of Fine-Scale Spatial Genetic Structure and Pollen Dispersal in Giant Sequoia (Sequoiadendron giganteum)

Abstract

Research Highlights: Patterns of dispersal shape the distribution and temporal development of genetic diversity both within and among populations. In an era of unprecedented environmental change, the maintenance of extant genetic diversity is crucial to population persistence. Background and Objectives: We investigate patterns of pollen dispersal and spatial genetic structure within populations of giant sequoia (Sequoiadendron giganteum). Materials and Methods: The leaf genotypes of established trees from twelve populations were used to estimate the extent of spatial genetic structure within populations, as measured by the Sp statistic. We utilized progeny arrays from five populations to estimate mating parameters, the diversity of the pollen pool, and characteristics of pollen dispersal. Results: Our research indicates that giant sequoia is predominantly outcrossing, but exhibits moderate levels of bi-parental inbreeding (0.155). The diversity of the pollen pool is low, with an average of 7.5 pollen donors per mother tree. As revealed by the Sp-statistic, we find significant genetic structure in ten of twelve populations examined, which indicates the clustering of related individuals at fine spatial scales. Estimates of pollen and gene dispersal indicate predominantly local dispersal, with the majority of pollen dispersal <253 m, and with some populations showing fat-tailed dispersal curves, suggesting potential for long-distance dispersal. Conclusions: The research presented here represent the first detailed examination of the reproductive ecology of giant sequoia, which will provide necessary background information for the conservation of genetic resources in this species. We suggest that restoration planting can mitigate potential diversity loss from many giant sequoia populations.

Genetic Diversity and Structure of Rear Edge Populations of Sorbus aucuparia (Rosaceae) in the Hyrcanian Forest

“…This is contrary to the gametophytic self-incompatibility system of woody Rosaceae [ 23 ]. Given that the size and/or density of a population can influence the outcrossing rate of self-compatible plants [ 60 ], it seems that harsh habitat conditions, small size, and low tree density, as well as a severe human intervention, has caused, contrary to expectations for the genus Sorbus [ 26 ], positive inbreeding in S. aucuparia populations in the Hyrcanian forest. Additionally, because of their often high levels of heterozygosity, outcrossing trees such as S. aucuparia can be disproportionately vulnerable to a reduction in pollen-mediated gene flow, which can mask deleterious recessive alleles that, if expressed, can lead to a reduction in population’s fitness [ 61 ].…”

Does the seed fall far from the tree? Weak fine-scale genetic structure in a continuous Scots pine population

“…In sedentary species, such as trees, spatial aggregation of related individuals often results from limited seed and/or pollen dispersal (Hardy & Vekemans 1999). In wind-pollinated species, pollen can disperse long distances, from hundreds of meters to hundreds of kilometers (e.g., Kremer et al 2012;Desilva & Dodd 2021), whereas seed dispersal has shorter average distances (Kremer et al 2012). Pollen dispersal distances in animalpollinated species are commonly shorter-from a few meters to a few kilometers (e.g., Levin & Kerster 1974;Kremer et al 2012; but see Ahmed et al 2009).…”

“…For example, in genotypephenotype association analyses, spurious associations may arise due to correlation of allele and trait frequencies in different populations, but also within a population, if the underlying genetic structure is not corrected for (Pritchard & Rosenberg 1999;Persyn et al 2018). In practical applications, where individuals are chosen from natural populations for conservation, population management or breeding programs, it is essential to know how genetic diversity and, for example, rare alleles are distributed in space to maintain high genetic diversity, avoid inbreeding and, on the other hand, unintended mixing of differentially adapted populations (Desilva & Dodd 2021;Escudero et al 2003;Smith et al 2018). When the span of spatial autocorrelation is known, sampling can be adapted to the needs of each application.…”

“…In wind-pollinated species, pollen can disperse long distances, from hundreds of meters to hundreds of kilometers (e.g., Kremer et al . 2012; Desilva & Dodd 2021), whereas seed dispersal has shorter average distances (Kremer et al . 2012).…”

“…2018). In practical applications, where individuals are chosen from natural populations for conservation, population management or breeding programs, it is essential to know how genetic diversity and, for example, rare alleles are distributed in space to maintain high genetic diversity, avoid inbreeding and, on the other hand, unintended mixing of differentially adapted populations (Desilva & Dodd 2021; Escudero et al . 2003; Smith et al .…”