High inbreeding, limited recombination and divergent evolutionary patterns between two sympatric morel species in China

As highly prized, popular mushrooms, morels are widely distributed in the northern hemisphere, with China as a modern centre of speciation and diversity. Overharvesting of morels has caused concern over how to effectively preserve their biological and genetic diversity. However, little is known about their population biology and life cycle. In this study, we selected two sympatric phylogenetic species, Mel-13 (124 collections from 11 geographical locations) and Morchella eohespera (156 collections from 14 geographical locations), using fragments of 4 DNA sequences, to analyse their genetic structure. Our results indicated significant differentiation among geographic locations in both species, whereas no obvious correlation between genetic and geographic distance was identified in either species. M. eohespera exhibited a predominantly clonal population structure with limited recombination detected in only 1 of the 14 geographic locations. In contrast, relatively frequent recombination was identified in 6 of the 11 geographic locations of Mel-13. Our analysis indicated that the sympatric species Mel-13 and M. eohespera might have divergent evolutionary patterns, with the former showing signatures of recent population expansion and the latter being relatively stable. Interestingly, we found no heterozygosity but strong evidence for genealogical incongruence, indicating a high level of inbreeding and hybridisation among morel species.