Whitham, T. G. | Search bioRxiv

bioRxiv2021

A mammalian herbivore prefers locally adapted populations in a common garden: implications for climate change mitigation

O_LIClimate change is expected to alter habitat more rapidly than the pace of evolution, leading to tree populations that are maladapted to new local conditions. Assisted migration is a mitigation strategy that proposes preemptively identifying and planting genotypes that are robust to the expected climate change-induced alterations of an area. Assisted migration however, may impact the broader community, including herbivores which often coevolved with local plant genotypes and their defenses. Although this question has been examined in arthropod herbivores, few studies have assessed this question in mammalian herbivores, and fewer still have leveraged experimental design to disentangle the genetic contribution to herbivore preference. C_LIO_LIWe examined the hypothesis that North American porcupine (Erethizon dorsatum) browsing on Fremont cottonwood (Populus fremontii) is under genetic control in a common garden, which allowed us to uncouple genetic and environmental contributions to browse preference. C_LIO_LIGenerally, porcupines selected local trees and trees from climatically similar areas, where trees from local and cooler climate populations suffered over 2x more extensive herbivory than trees from warmer areas. Plant genotype was a significant factor for selection, with the most heavily browsed genotype having on average >10x more herbivory than the least heavily browsed. Because genotypes within and among populations were replicated, we calculated broad-sense heritability in which tree palatability by porcupines was H2B = 0.28 (95% CI: 0.13-0.48) among genotypes. C_LIO_LISynthesis and applications. Our results indicate a genetic component to tree defenses against porcupine herbivory that can be predicted by the climate of the source population. This result has important implications for mammalian herbivores if climate change renders local tree genotypes maladaptive to new conditions. We recommend assisted migration efforts consider this implication and plant stock from both warmer and climatically similar areas to maintain genetic diversity in a changing environment, productivity and forage for mammalian herbivores. C_LI

ecology↗

bioRxiv2021

Macrosystem community assembly patterns are predicted by foundation tree species genetic connectivity and environment across the American Southwest

Macrosystems ecology is an emerging science that aims to integrate traditionally distinct disciplines to predict how hierarchical interacting processes influence the emergence of complex patterns across local to regional and global scales. Despite increased focus on cross-scale relationships and cross-disciplinary integration, few macroecology studies incorporate genetic-based processes. Here we used a community genetics approach to investigate the pattern-process relationships underlying the emergence of macroscale biodiversity patterns. We tested the hypothesis that environmental variation, geography, and genetic connectivity in a foundation tree species differentially predict associated community assembly patterns from local to continental scales. Using genome-wide SNP data, we assessed genetic connectivity as a function of genetic similarity and structure in Fremont cottonwood (Populus fremontii) across its distribution throughout the southwestern US and Mexico. For the same trees, we measured community composition, diversity, and abundance of leaf modifying arthropods and sequenced targeted amplicons of twig fungal endophytes. Five key findings emerged. (1) We identified three primary and six secondary population genetic groups within P. fremontii, which occupy distinct climate niches. (2) Both the leaf modifying arthropod and fungal endophyte communities were significantly differentiated across host tree ecotypes, with genetic distance among sampling locations explaining 13-17% of respective macroscale community structure. (3) For arthropods, environmental distance was the strongest driver of community similarity. (4) Conversely, host genetic connectivity was the most important contributor to macroscale endophyte community structure, with no significant contribution of environmental distance. (5) Furthermore, we observed a shift in the strength of interspecific relationships, with host genetics most strongly influencing associated communities at the intermediate population scale. Our findings suggest that genetic connectivity and environmental variation play integrated roles in macroscale community assembly, and their relative importance changes with scale. Thus, conservation genetic management of the diversity harbored within foundation species is vital for sustaining associated regional biodiversity.

ecology↗