Evolutionary lessons from California plant phylogeography

Abstract

Phylogeography documents the spatial distribution of genetic lineages that result from demographic processes, such as population expansion, population contraction, and gene movement, shaped by climate fluctuations and the physical landscape. Because most phylogeographic studies have used neutral markers, the role of selection may have been undervalued. In this paper, we contend that plants provide a useful evolutionary lesson about the impact of selection on spatial patterns of neutral genetic variation, when the environment affects which individuals can colonize new sites, and on adaptive genetic variation, when environmental heterogeneity creates divergence at specific loci underlying local adaptation. Specifically, we discuss five characteristics found in plants that intensify the impact of selection: sessile growth form, high reproductive output, leptokurtic dispersal, isolation by environment, and the potential to evolve longevity. Collectively, these traits exacerbate the impact of environment on movement between populations and local selection pressures-both of which influence phylogeographic structure. We illustrate how these unique traits shape these processes with case studies of the California endemic oak, Quercus lobata, and the western North American lichen, Ramalina menziesii Obviously, the lessons we learn from plant traits are not unique to plants, but they highlight the need for future animal, plant, and microbe studies to incorporate its impact. Modern tools that generate genome-wide sequence data are now allowing us to decipher how evolutionary processes affect the spatial distribution of different kinds of genes and also to better model future spatial distribution of species in response to climate change.

Oaks: an evolutionary success story

“…High degrees of adaptive divergence for phenotypic traits have led to studies aiming to identify genomic footprints of diversifying selection based on two different approaches. In one approach, genome scans have been used to search for genome–environment associations (Rellstab et al , ; Sork et al , ,c; Martins et al , ). In the other, associations between genomic and trait variation have been explored in situations for which common‐garden results were available (Alberto et al , ).…”

Invoking adaptation to decipher the genetic legacy of past climate change

“…, Sork et al. ). For instance, Cwynar and MacDonald () documented an increasing trend of seed dispersal ability along the postglacial migration route of lodgepole pine ( Pinus contorta ) in western North America.…”

The historical context of contemporary climatic adaptation: a case study in the climatically dynamic and environmentally complex southwestern United States

“…However, such a framework is valuable when trying to understand how evolutionary processes, such as adaptation, unfold in dynamic, heterogeneous systems. For example, while the impacts of cycling glacial and interglacial periods during the Pleistocene on species' distributions across northerly latitudes are clear (Massatti and Knowles 2016, Wachter et al 2016, Knowles and Massatti 2017, Bemmels et al 2019, their effects on adaptive processes and the genetic variation available for selection to act upon has received less attention (Sork et al 2016). Considering adaptive processes is important because mismatches between species' fundamental and realized niches in glacial versus interglacial periods are expected (Jackson and Overpeck 2000), particularly in terms of the environmental space occupied (Fitzpatrick and Hargrove 2009).…”