Panmixia and dispersal from the Mediterranean Basin to Macaronesian Islands of a macrolichen species

David Alors,Paloma Cubas,M Carmen Molina,Pradeep K Divakar,Francesco Dal Grande,Imke Schmitt,Ana Crespo

doi:10.1038/srep40879

Abstract

The Mediterranean region, comprising the Mediterranean Basin and the Macaronesian Islands, represents a center of diversification for many organisms. The genetic structure and connectivity of mainland and island microbial populations has been poorly explored, in particular in the case of symbiotic fungi. Here we investigated genetic diversity and spatial structure of the obligate outcrossing lichen-forming fungus Parmelina carporrhizans in the Mediterranean region. Using eight microsatellite and mating-type markers we showed that fungal populations are highly diverse but lack spatial structure. This is likely due to high connectivity and long distance dispersal of fungal spores. Consistent with low levels of linkage disequilibrium and lack of clonality, we detected both mating-type idiomorphs in all populations. Furthermore we showed that the Macaronesian Islands are the result of colonization from the Mediterranean Basin. The unidirectional gene flow, though, seemed not to be sufficient to counterbalance the effects of drift, resulting in comparatively allelic poor peripheral populations. Our study is the first to shed light on the high connectivity and lack of population structure in natural populations of a strictly sexual lichen fungus. Our data further support the view of the Macaronesian Islands as the end of the colonization road for this symbiotic ascomycete.

Highlights

Cryptic biodiversity is an essential component of biodiversity that will be considerably affected by global climate change in the decades[1]
We aimed at exploring the predictions of two key hypotheses: i) the sexual reproductive mode of the species leads to high intra-population genetic diversity, high mainland-island connectivity and low population structure, and ii) high frequency of sexual reproduction is reflected in a balanced representation of mating-type idiomorphs in the populations
These results are consistent with a heterothallic organization of MAT genes in P. carporrhizans

Summary

Introduction

Cryptic biodiversity is an essential component of biodiversity that will be considerably affected by global climate change in the decades[1]. The use of DNA-based molecular phylogenies for unraveling the hidden diversity in lichen-forming fungi has become increasingly common Investigations of these cryptic lineages at the population level are still far less common[10]. In the case of the exclusively sexual species Buellia frigida, a crustose lichen of continental Antarctica, an SSR-based study revealed high intra-population diversity, local population differentiation and limited dispersal, probably resulting from harsh habitat conditions and scarce spatial and temporal habitat availability[19]. In this study we analyzed intra-species genetic diversity, population structure, and mating-type distribution in natural populations of the obligate outcrossing lichen-forming fungal species Parmelina carporrhizans[24]. We aimed at exploring the predictions of two key hypotheses: i) the sexual reproductive mode of the species leads to high intra-population genetic diversity, high mainland-island connectivity and low population structure, and ii) high frequency of sexual reproduction is reflected in a balanced representation of mating-type idiomorphs in the populations

Methods

Results

Discussion

Conclusion