Comparison of phylogeographical structures of a lichen‐forming fungus and its green algal photobiont in western North America

Abstract

Aim Lichens comprise a symbiosis of two separate taxa that share geographical distribution but not necessarily the same evolutionary history. Comparison of phylogeographical structures of lichen symbionts provides valuable insight about the processes shaping the lichen's biogeographical pattern. In this study, we tested the extent to which the shared distribution of the widespread lichen‐forming fungus Ramalina menziesii and its photobiont Trebouxia decolorans across six major ecoregions reflect parallel genetic structure and gene flow. Location Western North America. Methods Based on DNA sequences from multiple genes, we employed distance‐based methods to assess co‐divergence of symbiosis partners. To assess historical opportunity for co‐evolution, we compare migrations among six ecoregions. Results Tests of genetic concordance between the mycobiont and the photobiont genetic variation revealed an overall significant congruent genetic structure across ecoregions. However, the photobiont and the mycobiont do not have high congruencies within ecoregions and the two taxa have different histories of migration among ecoregions. Main conclusions Congruent phylogeographical patterns in several clades between the mycobiont and the photobiont on a large spatial scale can be explained either by parallel isolation due to ecological and geographical discontinuities or by similar selective pressures on the symbionts due to common environmental conditions within each ecoregion leading to co‐divergence. At the regional spatial scale, the two taxa share some degree of evolutionary history but the weak phylogeographical congruence within ecoregions and the lack of shared migration history both indicate a flexible association between mutualists. This flexibility may facilitate the widespread geographical distribution of the lichen.

Amphitropical variation of the algal partners of Pseudephebe (Parmeliaceae, lichenized fungi)

“…This geographic structure mirrors that of the mycobiont. Congruent structure has been also detected in the epiphytic Ramalina menziesii and its photobiont Trebouxia decolorans across ecoregions in western North America (Werth and Sork 2014;Chen et al 2016), and between Lobaria pulmonaria and its green algal partner (Werth and Scheidegger 2012). Similarly, algal genetic variation in the soil-dwelling Cladonia subtenuis, Thamnolia vermicularis and the bipolar Cetraria aculeata was found to be significantly structured by geography (Yahr et al 2006;Nelsen and Gargas 2009;Fernández-Mendoza et al 2011).…”

Evolutionary lessons from California plant phylogeography

“…We discovered some similarities in their clustering with certain ecoregions, but overall the phylogenetic trees were largely incongruent among symbionts, suggesting little coevolution between fungal and algal genotypes (90). Next, we compared recent migration patterns for different types of genetic markers to see whether the symbionts were showing similar patterns of movements, which one might expect given that they coexist within the same individual and may respond to climatic fluctuations in a similar way (90). The analysis revealed that the mycobiont and photobiont of lace lichen showed a general tendency to move south, with different patterns of movement across ecoregions for each of the markers (Fig.…”

“…First, we compared the genealogical trees from a subset of samples that had mycobiont and photobiont genotypes. We discovered some similarities in their clustering with certain ecoregions, but overall the phylogenetic trees were largely incongruent among symbionts, suggesting little coevolution between fungal and algal genotypes (90). Next, we compared recent migration patterns for different types of genetic markers to see whether the symbionts were showing similar patterns of movements, which one might expect given that they coexist within the same individual and may respond to climatic fluctuations in a similar way (90).…”

“…The slightly similar clustering of haplotypes in the genealogical trees probably reflects the barriers imposed by differences across ecoregions. However, the overall lack of concordance between the phylogeographic patterns of these two symbiotic taxa might be explained better by dissimilar migration (90). In short, the differences in the dispersal abilities of the two taxa, and possibly the differences in their microhabitat preferences, illustrate that plant life history traits can disrupt cophylogeography of mutualistic cooccurring taxa.…”

A worldwide phylogeography of the whiteworm lichens Thamnolia reveals three lineages with distinct habitats and evolutionary histories

“…Lichens are formed as a symbiosis between two main partners, a mycobiont and a photobiont. Recent lichen studies strive to integrate both morphological and molecular information from the symbiotic partners (e.g., Chen, Werth, & Sork, ; Fernandez‐Mendoza et al., ; Perez‐Ortega, Ortiz‐Alvarez, Allan Green, & de Los Rios, ; Spribille et al., ; Werth & Sork, ). In this study, we focused our efforts to describe and understand the mycobiont population structure and the associated photobionts in Thamnolia .…”