Patterns of vegetative growth and gene flow in Rhizopogon vinicolor and R. vesiculosus (Boletales, Basidiomycota)

Abstract

We have collected sporocarps and tuberculate ectomycorrhizae of both Rhizopogon vinicolor and Rhizopogon vesiculosus from three 50 x 100 m plots located at Mary's Peak in the Oregon Coast Range (USA); linear map distances between plots ranged from c. 1 km to c. 5.5 km. Six and seven previously developed microsatellite markers were used to map the approximate size and distribution of R. vinicolor and R. vesiculosus genets, respectively. Genetic structure within plots was analysed using spatial autocorrelation analyses. No significant clustering of similar genotypes was detected in either species when redundant samples from the same genets were culled from the data sets. In contrast, strong clustering was detected in R. vesiculosus when all samples were analysed, but not in R. vinicolor. These results demonstrate that isolation by distance does not occur in either species at the intraplot sampling scale and that clonal propagation (vegetative growth) is significantly more prevalent in R. vesiculosus than in R. vinicolor. Significant genetic differentiation was detected between some of the plots and appeared greater in the more clonal species R. vesiculosus with Phi(ST) values ranging from 0.010 to 0.078*** than in R. vinicolor with Phi(ST) values ranging from -0.002 to 0.022** (*P < 0.05, **P < 0.01, ***P < 0.001). When tested against the null hypothesis of no relationship between individuals, parentage analysis detected seven likely parent/offspring pairs in R. vinicolor and four in R. vesiculosus (alpha = 0.001). Of these 11 possible parent/offspring pairs, only two R. vinicolor pairs were still supported as parent/offspring when tested against the alternative hypothesis of being full siblings (alpha = 0.05). In the latter two cases, parent and offspring were located at approximately 45 m and 28 m from each other. Challenges to parentage analysis in ectomycorrhizal fungi are discussed.

Dominance of a Rhizopogon sister species corresponds to forest age structure

“…Previous studies in a DF forest, comprised of 40-to 80-year-old trees, reported higher frequencies of R. vesiculosus tubercules per unit area compared with R. vinicolor and a greater number of R. vinicolor genotypes per unit area compared with R. vesiculosus (Kretzer et al 2005;Dunham et al 2013). In our study, the number of R. vesiculosus tubercules varied among plots, and R. vinicolor accounted for the majority of tubercules encountered in five out of 12 plots.…”

“…We predicted that a change in the number or relative abundance of R. vesiculosus and R. vinicolor tubercules and genotypes would not be related to a change in the percent of DF seedlings, saplings and/or trees <50 years old. We based this prediction on previous studies showing that R. vesiculosus consistently had more tubercules than R. vinicolor, R. vinicolor consistently had more genotypes than R. vesiculosus, and both species associated with roots from DF of all ages (Kretzer et al 2005;Beiler et al 2010;Dunham et al 2013). …”

“…However, recent studies, focusing on the spatial patterns of individual R. vesiculosus and R. vinicolor genotypes, have uncovered differences in the autecological traits of these species. For example, R. vesiculosus genotypes have been found to span greater distances than those of R. vinicolor in both coastal and interior Douglas-fir forests (Kretzer et al 2005;Dunham et al 2013;Beiler et al 2015). Population genetic analysis of an Oregon population revealed that R. vesiculosus genotypes are closely related to their neighbors, whereas R. vinicolor appears to disperse away from related individuals (Dunham et al 2013).…”

“…The coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) forest at Mary's Peak, Oregon, experiences a relatively high annual precipitation, has a dense tree and shrub understory, and consists primarily of 40-to 80-year-old trees, which established following a stand-replacing disturbance (Kretzer et al 2005). In contrast, the interior Douglas-fir (var.…”

Investigating the Allelic Evolution of an Imperfect Microsatellite Locus in the Hawaiian Mushroom Rhodocollybia laulaha

“…A search for variable microsatellite loci in the mushroom Laccaria laccata isolated only 5 loci, 2 of which were imperfect and each displaying only 3-6 alleles (Wadud et al 2006). Nevertheless, several investigations have used fungal microsatellite loci to differentiate fungal genets and discern some population level patterns (Kretzer et al 2003(Kretzer et al , 2005, and there are those who argue that the potential to develop informative microsatellite loci across the fungi is promising (Lim et al 2004).…”