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

Abstract

The process of adaptation can be highly dependent upon historical and contemporary factors, especially in environmentally and topographically complex regions affected by Pleistocene glaciations. Here, we investigate Hilaria jamesii (Poaceae), a dryland C 4 graminoid, to test how patterns of adaptive genetic variation are linked to its glacial and post-glacial history. We show that the species persisted in a single, southern refugium during the last glacial period and subsequently migrated throughout its current distribution concurrent with post-glacial warming. The species' putative adaptive genetic variation correlates with climatic gradients (e.g. monsoon precipitation and mean diurnal temperature range) that covary with the species' probable route of demographic expansion. The short timescale and multiple climatic dimensions of adaptation imply that natural selection acted primarily upon standing genetic variation. These findings suggest that restoration and conservation practices should prioritize the maintenance of standing genetic variation to ensure that species have the capacity to respond to future environmental changes.

Assessment of population genetics and climatic variability can refine climate‐informed seed transfer guidelines

“…For example, Massatti et al () estimated migration rates between adjacent population pairs of bluebunch wheatgrass ( Pseudoroegneria spicata ) and resolved (relatively) high per generation migration rates between one pair of adjacent populations and rates close to zero between all other comparisons. Parallel results were reported for James' galleta grass ( Hilaria jamesii ) across the Colorado Plateau (Massatti & Knowles ). In such circumstances, it may be determined that exchanging plant materials between the two populations with higher migration rates poses fewer risks, which would reduce the total number of comparisons.…”

“…If significant environmental heterogeneity exists within the population boundaries of a restoration species, practitioners would still best be served by developing multiple NPMs to maximize local adaptation—development may be directed by using population‐constrained CSTZs, focal point seed zones, or molecular data (e.g. Massatti & Knowles ), but ideally should be based on field‐based trials such as reciprocal transplants or common gardens (e.g. Kilkenny ).…”

“…approximately 500 generations sensu Frankham et al , see also McKay et al ). This amount of separation (or significantly more) is common in topographically heterogeneous landscapes affected by Pleistocene glaciations (Massatti et al ; Massatti & Knowles ). Our use of the term “population” throughout the text refers to units within a species composed of all individuals across geographic space (which can cover small or large areas) that have a common history and shared recent gene flow.…”

“…Genetic patterns among species are often unique due to processes ranging from chance to species‐specific interactions with their environments based on life history characteristics (Papadopoulou & Knowles ), and they do not necessarily coincide with CSTZs (e.g. Listl et al , ; Massatti et al ; Massatti & Knowles ).…”

Unexpected hybridization reveals the utility of genetics in native plant restoration

“…Raw data were generated by sequencing a RADseq library on an Illumina HiSeq4000, which produced 100 base pair, single‐end reads. SNPs were identified utilizing stacks v2.2 (Catchen et al ; see Massatti & Knowles for processing details). The evolutionary history among the three species was inferred using SVDQuartets (Chifman & Kubatko , ) as implemented in PAUP* v4.0a166 (Swofford ).…”