Chhatre, V. E. | bioRxiv Science

bioRxiv2020

Future climate change promotes novel gene-climate associations in balsam poplar (Populus balsamifera L.), a forest tree species

A central challenge to predicting climate change effects on biodiversity is integrating information on intraspecific variation, specifically population-level local adaptation to climate. Assessing how climate change could disrupt local adaptation to climate can provide a new way of understanding population risk and vulnerability to climate change. For the wide-ranging boreal tree species, balsam poplar (Populus balsamifera L.), we used models of existing population-level genetic differentiation to estimate three key components of populations vulnerability to climate change: (1) predicted shifts in genetic composition with and without migration, (2) the potential for future novel gene-climate associations, and (3) the distance populations would need to migrate to minimize future maladaptation. When assessed across the range of balsam poplar, these three metrics suggest that vulnerability to climate change is greatest in the eastern portion of balsam poplars range, where future maladaptation peaked, migration distances to sites that minimized maladaptation were greatest, and the emergence of novel gene-climate associations were highest. Our results further suggest greater maladaptation to climate when migration distances were limited - consistent with the possibility of migration to lessen maladaptation to future climate. Our work provides a comprehensive evaluation of populations vulnerability to climate change by simultaneously assessing population maladaptation to future climate and the distances populations would need to migrate to minimize maladaptation, in a way that goes beyond species-level bioclimatic modelling. In doing so, our work helps advance towards the long-held goal of incorporating genomic information in models of species responses to climate change.

ecology↗

bioRxiv2019

Climatic niche predicts the landscape structure of locally adaptive standing genetic variation

Within a species range, intraspecific diversity in the form of adaptive standing genetic variation (SGV) may be non-randomly clustered into different geographic regions, reflecting the combined effects of historical range movements and spatially-varying natural selection. As a consequence of a patchy distribution of adaptive SGV, populations in different parts of the range are likely to vary in their capacity to respond to changing selection pressures, especially long-lived sessile organisms like forest trees. However, the spatial distribution of adaptive SGV across the landscape is rarely considered when predicting species responses to environmental change. Here, we use a landscape genomics approach to estimate the distribution of adaptive SGV along spatial gradients reflecting the expansion history and contemporary climatic niche of balsam poplar, Populus balsamifera (Salicaceae), a widely distributed forest tree with a transcontinental distribution in North America. By scanning the genome for signatures of spatially varying local adaptation, we estimated how adaptive SGV has been shaped by geographic distance from the rear range edge (expansion history) versus proximity to the current center of the climatic niche (environmental selection). We found that adaptive SGV was strongly structured by the current climatic niche, with surprisingly little importance attributable to historical effects such as migration out of southern refugia. As expected, the effect of the climatic niche on SGV was strong for genes whose expression is responsive to abiotic stress (drought), although genes upregulated under biotic (wounding) stress also contained SGV that followed climatic and latitudinal gradients. The latter result could reflect parallel selection pressures, or co-regulation of functional pathways involved in both abiotic and biotic stress responses. Our study in balsam poplar suggests that clustering of locally adaptive SGV within ranges primarily reflects spatial proximity within the contemporary climatic niche - an important consideration for the design of effective strategies for biodiversity conservation and avoidance of maladaptation under climate change.

evolutionary biology↗