Climate-woodland effects on population genetics for two congeneric lichens with contrasting reproductive strategies

Abstract

Genetic variation is expected to be influenced by the interaction between reproductive mode and dispersal traits on the one hand and environmental and habitat setting affecting establishment success on the other. We evaluated how environmental/habitat setting affects population genetic variation (i.e. variation in genetic diversity and structure) when regulated by contrasting dispersal traits. We used fungus-specific microsatellite markers to examine genetic diversity and structure of two closely related epiphytic lichen fungi that differ in their primary reproductive mode: Nephroma laevigatum (sexually reproducing, n = 191, 10 microsatellites) and N. parile (asexually reproducing, n = 182, 12 microsatellites), along a steep climatic gradient in Scotland. Despite their reproductive differences, we found a high proportion of clones in both species and a background pattern of genetic structure related to climatic gradients. We also demonstrated that woodland connectivity, rather than geographic distance, explained genetic diversity in both species. Environmental/habitat setting, modulated by the reproductive mode of the species, affects genetic diversity and structure, but the putative dissimilarity in their reproductive mode is less important than has been previously assumed. We reinforce the importance of protecting highly connected populations, positioned along a gradient capturing the segregation of gene pool differences in response to climatic variation.

Microsatellite based genetic diversity of the widespread epiphytic lichen Usnea subfloridana (Parmeliaceae, Ascomycota) in Estonia: comparison of populations from the mainland and an island

“…The genetic diversity of L. pindarensis Räsanen was significantly influenced by altitude, revealing higher levels of genetic diversity at a high elevation in the Himalayas (Devkota et al submitted). Belinchón et al (2018) showed that Nephroma parile (Ach.) Ach.…”

Climate Change, Bioclimatic Models and the Risk to Lichen Diversity

“…It is also relevant for assessing climate change vulnerability that spatial [138][139][140] and molecular inference [141][142][143][144] point to a characteristic difference in dispersal rates between lichens reproducing sexually and generating smaller spores (frequent longer distance dispersal), and asexual reproduction with larger diaspores such as isidia or soredia (shorter distance dispersal). However, there is a degree of interspecific overlap in propagule size between spores and isidia/soredia, while the dichotomy between apparently sexual/asexual species may be less clearly apparent than is sometimes assumed [145]. Additionally, because establishment also determines the effective migration rate, species interactions could confound the outcome of dispersal; thus, there is emerging support for the 'core-fringe hypothesis' [146], in which spore-dispersed cyanolichens may require prior colonisation of habitat by asexual species, from which they sequester their photobionts [147,148].…”

“…The overlap in suitable climate space from baseline to scenarios can inform the extent to which local population adaptation is necessary to reduce vulnerability (Figure 4). Current evidence-again, principally relating to lichen epiphytes-suggests that standing genetic diversity is related to habitat quality [143,145,149,150]. This implies a reduced ability of lichen populations to adapt to future climate change in forests/woodlands that have an intensively managed and simplified habitat structure.…”

“…This implies a reduced ability of lichen populations to adapt to future climate change in forests/woodlands that have an intensively managed and simplified habitat structure. However, adaptation may also occur if standing genetic diversity is complemented through gene flow, should populations appear to be regionally adapted to contrasting climates [151] and with a climate signature to their genetic structure [145,152]. The effect of gene flow depends on an effective dispersal of conidia, documented at scales of 100-1000s m [144,153], or the spread of different genetic individuals from one population to another, which invokes limitations analogous to those for migrating propagules (see Migration, above).…”

“…The effect of gene flow depends on an effective dispersal of conidia, documented at scales of 100-1000s m [144,153], or the spread of different genetic individuals from one population to another, which invokes limitations analogous to those for migrating propagules (see Migration, above). These limitations could potentially undermine sexual reproduction among isolated small populations, restricting the recombinant evolution of genetic diversity [44,154], with population genetic diversity decreasing in landscapes with low habitat connectivity consistent with reduced gene flow [145].…”