Reduced fine-scale spatial genetic structure in grazed populations of Dianthus carthusianorum

Abstract

Strong spatial genetic structure in plant populations can increase homozygosity, reducing genetic diversity and adaptive potential. The strength of spatial genetic structure largely depends on rates of seed dispersal and pollen flow. Seeds without dispersal adaptations are likely to be dispersed over short distances within the vicinity of the mother plant, resulting in spatial clustering of related genotypes (fine-scale spatial genetic structure, hereafter spatial genetic structure (SGS)). However, primary seed dispersal by zoochory can promote effective dispersal, increasing the mixing of seeds and influencing SGS within plant populations. In this study, we investigated the effects of seed dispersal by rotational sheep grazing on the strength of SGS and genetic diversity using 11 nuclear microsatellites for 49 populations of the calcareous grassland forb Dianthus carthusianorum. Populations connected by rotational sheep grazing showed significantly weaker SGS and higher genetic diversity than populations in ungrazed grasslands. Independent of grazing treatment, small populations showed significantly stronger SGS and lower genetic diversity than larger populations, likely due to genetic drift. A lack of significant differences in the strength of SGS and genetic diversity between populations that were recently colonized and pre-existing populations suggested that populations colonized after the reintroduction of rotational sheep grazing were likely founded by colonists from diverse source populations. We conclude that dispersal by rotational sheep grazing has the potential to considerably reduce SGS within D. carthusianorum populations. Our study highlights the effectiveness of landscape management by rotational sheep grazing to importantly reduce genetic structure at local scales within restored plant populations.

Effects of zoochory on the spatial genetic structure of plant populations

“…First, we examined the effect of seed dispersal mode (endozoochory or synzoochory) on the presence and strength of SGS in plant species. Epizoochorously dispersed species were underrepresented; therefore, we excluded them from the analysis (Williams & Guries, ; Bonnin, Ronfort, Wozniak, & Olivieri, ; Rico & Wagner ). Second, we tested whether the presence and strength of SGS in plant species were related to the taxon of the seed dispersers (ants, bats, birds, primates, rodents).…”

Plant functional connectivity – integrating landscape structure and effective dispersal

“…Empirical genetic studies have shown that extant plant populations are functionally connected at the landscape and regional scales largely as a result of pollen flow (Dick et al . ), while seed dispersal has a larger impact at the local scale by creating fine‐scale genetic structure (Epperson ; Rico & Wagner ). Understanding the role of landscape features in determining genetic structure is essential for understanding plant functional connectivity.…”

Multiscale spatial genetic structure within and between populations of wild cherry trees in nuclear genotypes and chloroplast haplotypes

“…As mentioned previously, local density has the opposite effects on the SGS intensity, which increases due to the bias of gene dispersal toward shorter (Hardy et al, ) or decreases because the effective population density increases (Hardy & Vekemans, ). In an herb species in segregated pastures, the SGS intensity decreased as the population size in individual pastures increased (Rico & Wagner, ). In the studied cherry populations, the opposite effects may counterbalance each other, resulting in the unclear effect of local tree density on the SGS intensity.…”

“…In addition to pollen and seed dispersal systems, various factors, such as perenniality (Duminil et al, ), geographic distributional range (Duminil et al, ), colonization history (Hamrick & Trapnell, ), affect the genetic differentiation or SGS intensity. Among populations within species, habitat conditions, such as disturbance (Rico & Wagner, ) and fragmentation (Yamagishi, Tomimatsu, & Ohara, ), affect the SGS intensity in nuclear markers. Although these effects on interpopulation genetic differentiation or within‐population SGS intensity have often been evaluated using either nuclear or organelle markers, both markers have been rarely used together to evaluate those factors.…”