How is adaptive potential distributed within species ranges?

Abstract

Quantitative genetic variation (QGV) represents a major component of adaptive potential and, if reduced toward range‐edge populations, could prevent a species’ expansion or adaptive response to rapid ecological change. It has been hypothesized that QGV will be lower at the range edge due to small populations—often the result of poor habitat quality—and potentially decreased gene flow. However, whether central populations are higher in QGV is unknown. We used a meta‐analytic approach to test for a general QGV‐range position relationship, including geographic and climatic distance from range centers. We identified 35 studies meeting our criteria, yielding nearly 1000 estimates of QGV (including broad‐sense heritability, narrow‐sense heritability, and evolvability) from 34 species. The relationship between QGV and distance from the geographic range or climatic niche center depended on the focal trait and how QGV was estimated. We found some evidence that QGV declines from geographic centers but that it increases toward niche edges; niche and geographic distances were uncorrelated. Nevertheless, few studies have compared QGV in both central and marginal regions or environments within the same species. We call for more research in this area and discuss potential research avenues related to adaptive potential in the context of global change.

Genetic variability and the ecology of geographic range: A test of the central‐marginal hypothesis in Australian scincid lizards

“…Only one taxon provided significant evidence against the central‐marginal hypothesis. As seen in other comparative tests of the central‐marginal hypothesis and on the underlying abundant‐centre hypothesis (Dallas et al, 2017; Lira‐Noriega & Manthey, 2014; Pennington et al, 2021; Pironon et al, 2017), we recovered support for the central‐marginal hypothesis but with numerous exceptions and significant unexplained variability.…”

“…Further, we only measured putatively neutral genetic variation, which may not correlate with genetic variation underpinning key adaptive traits (Pauls et al, 2013; Teixeira & Huber, 2021). To better explore the links between the central‐marginal hypothesis and range limits, we should ideally sample quantitative trait loci and the traits themselves (compare with Clark et al, 2021; Kennedy et al, 2020; Pennington et al, 2021; Pujol & Pannell, 2008).…”

“…Despite their intuitive appeal, both the abundant‐centre and central‐marginal hypotheses have mixed support in the literature (as reviewed in Dallas et al, 2017; Lira‐Noriega & Manthey, 2014; Pennington et al, 2021; Pironon et al, 2017). This mixed support has a few potential explanations.…”

The evolution of the additive variance of a trait under stabilizing selection after autopolyploidization

“…If the initial increase in adaptive potential can be explained theoretically, the long‐term negative effect is more surprising. It can come from other side effects associated with polyploidization, such as a shift in the mating system (Barringer, 2007; Husband et al, 2008) or a better capacity to colonize harsher environments (Rice et al, 2019), which are known to modify the evolutionary potential of populations in diploids (Clo et al, 2019; Martínez‐Padilla et al, 2017; Pennington et al, 2021). No other direct comparisons among tetraploids and diploids of the same species in controlled environments are available in the literature, but the few estimates of heritability found in natural autotetraploid populations are in the range of what is found in diploid populations (Burgess et al, 2007; Clo et al, 2019; O’Neil, 1997).…”

Linking ecological niche models and common garden experiments to predict phenotypic differentiation in stressful environments: Assessing the adaptive value of marginal populations in an alpine plant

“…One key concept, the center‐periphery hypothesis, posits that geographically disparate populations across a species’ range may have important differences, including variation in demographic, genetic, and phenotypic characteristics (Abeli et al, 2014; Gaston, 2009; Pironon et al, 2017; Sexton et al, 2009; Soule, 1973; Zakharov & Hellmann, 2008). Understanding the effects of such variation holds clear relevance under rapidly changing climate, land cover, and other environmental conditions because it may be crucial to facilitate adaptation and overcome the resulting threats (Abeli et al, 2014; Abeli & Orsenigo, 2018; Eckert et al, 2008; Gaston, 2009; Holt & Keitt, 2005; Kawecki, 2008; Pennington et al, 2021; Sexton et al, 2009; Swab et al, 2015). In this context, better predictions of future biodiversity patterns at and below the species level depend on two overlapping issues: (1) the relationship between geographic peripherality and ecological marginality, which directly influences patterns of genetic and phenotypic variation and (2) the potential adaptive value (or cost) of ecologically marginal populations under environmental change.…”