Genetic differentiation in Eurasian populations of the postfire ascomyceteDaldinia loculata

The genetic population structure of the postfire ascomycete Daldinia locula ta was studied to test for differentiation on a continental scale. Ninety-s ix samples of spore families, each comprising mycelia from six to 10 spores originating from single perithecia, were sampled from one Russian and six Fennoscandian forest sites. Allelic distribution was assayed for six nuclea r gene loci by restriction enzyme analyses of polymerase chain reaction (PC R)amplified gene fragments. In addition, the full sequence of the gene frag ment was analysed for a subset of haploid single-ascospore isolates in a mu ltiallelic approach. A third data set was generated by using arbitrary-prim ed PCR with the core sequence of the phage M13 as primer. Although there wa s a reduction in heterozygosity in the total population from what would hav e been expected at random mating, the levels of genetic differentiation amo ng the Eurasian subpopulations of D. loculata were low. All subpopulations were found to be in Hardy-Weinberg equilibrium and gametic equilibrium was observed between all investigated nuclear gene loci. The results obtained b y the different markers were consistent; we confirmed low levels of genetic differentiation among the Eurasian subpopulations of D. loculata. The diff erentiation did not increase with distance; the Russian subpopulation, samp led more than 7000 km from the Fennoscandian subpopulations, was only moder ately differentiated from the others (F-ST = 0.00-0.14). In contrast, one o f the Swedish populations was the most highly differentiated from the other s, with F-ST and G(ST) values of 0.10-0.16. The results suggest that D, loc ulata consists of a long-lived backround Eurasian population of latent myce lia in nonburned forests, established by sexual ascospores dispersed from s cattered burned forest sites. Local differentiation is probably due to foun der effects of populations in areas with low fire frequency. A tentative li fe cycle of D. loculata is presented.