Small-scale patterns in snowmelt timing affect gene flow and the distribution of genetic diversity in the alpine dwarf shrub Salix herbacea

Abstract

Current threats to biodiversity, such as climate change, are thought to alter the within-species genetic diversity among microhabitats in highly heterogeneous alpine environments. Assessing the spatial organization and dynamics of genetic diversity within species can help to predict the responses of organisms to environmental change. In this study, we evaluated whether small-scale heterogeneity in snowmelt timing restricts gene flow between microhabitats in the common long-lived dwarf shrub Salix herbacea L. We surveyed 273 genets across 12 early-and late-snowmelt sites (that is, ridges and snowbeds) in the Swiss Alps for phenological variation over 2 years and for genetic variation using seven SSR markers. Phenological differentiation triggered by differences in snowmelt timing did not correlate with genetic differentiation between microhabitats. On the contrary, extensive gene flow appeared to occur between microhabitats and slightly less extensively among adjacent mountains. However, ridges exhibited significantly lower levels of genetic diversity than snowbeds, and patterns of effective population size (N e ) and migration (N e m) between microhabitats were strongly asymmetric, with ridges acting as sources and snowbeds as sinks. As no recent genetic bottlenecks were detected in the studied sites, this asymmetry is likely to reflect current metapopulation dynamics of the species dominated by gene flow via seeds rather than ancient re-colonization after the last glacial period. Overall, our results suggest that seed dispersal prevents snowmelt-driven genetic isolation, and snowbeds act as sinks of genetic diversity. We discuss the consequences of such small-scale variation in gene flow and diversity levels for population responses to climate change.

Local Scale Genetic Diversity and its Role in Coping with Changing Climate

“…allelic richness: 8.93 ± 0.27 and 6.81 ± 0.29 for snowbeds and ridges, respectively), and gene low, measured as the number of migrants per generation, was asymmetric toward the snowbeds (Figure 3). Overall, these results are consistent with snowbeds acting as sinks of genetic diversity and seed dispersal preventing snowmelt-driven genetic isolation [22].…”

“…Lack of population structure was supported by a STRUCTURE analysis. This absence of population diferentiation, even in microhabitats with highly diferent snowmelt dates, may be mediated by high and asymmetric seed dispersal [22].…”

“…Although S. herbacea populations growing in diferent microhabitats could be diferentiated phenologically, they could not be diferentiated genetically [22] using 7 highly polymorphic molecular markers, F ST and N e m estimation and STRUCTURE analysis (see Section 4.4.1). F ST was 0.028 ± 0.003 and 0.035 ± 0.004 for within-microhabitat and between-microhabitat comparisons, P-value = 0.691.…”

“…When compared to the plot survey, the transect survey has many smaller plots with fewer total patches but covers the desired altitudinal and microhabitat variation at a beter resolution by having more total plots. This is ideal to assess ecological responses [15] or genetic isolation-by-distance and to explore trait and microhabitat-driven genomic architecture [15,22].…”

What role do plant–soil interactions play in the habitat suitability and potential range expansion of the alpine dwarf shrub Salix herbacea?

“…In a genetic study along the same transects, Cortés et al (2014) found high gene-flow in S. herbacea populations among altitudes and microhabitats. High levels of gene flow between our study populations may have counteracted local adaptation to soil microbes (Sambatti & Rice, 2006).…”