Genetic combinations of symbionts in a vegetatively reproducing lichen,Parmotrema tinctorum, based on ITS rDNA sequences

Abstract

The genetic combinations between mycobionts and photobionts in Parmotrema tinctorum collected from ca. 60 km2 of the Shimizu district, of Shizuoka City in Japan was investigated based on ITS rDNA sequences. This lichen produces apothecia quite rarely, and in principle propagates vegetatively by isidia. The genetic diversity of the mycobiont comprised four types, while that of the photobiont comprised 21 types. There were 28 different combinations between mycobiont and photobiont. All the photobionts were identified as Trebouxia corticola (s. lat.), based on both molecular phylogenetic results and morphological observation of culture strains obtained in this study. Therefore, P. tinctorum is considered to be highly selective toward the photobiont. The 28 combinations from the small area represent an unexpectedly high diversity, because P. tinctorum is thought to propagate vegetatively. Four possible mechanisms to account the high genetic combinations are suggested: i.e., photobiont exchange, fusion of thalli, and long-distance dispersal of isidia or ascospores. The genetic diversity of photobionts was poor in the urban area, but rich in suburbs and mountainsides. This might be caused by a bottleneck or founder effect in the population recovering from former damage by heavy air pollution, or variable selectivity of P. tinctorum depending on the environments.