Trait differentiation and adaptation of plants along elevation gradients

Abstract

Studies of genetic adaptation in plant populations along elevation gradients in mountains have a long history, but there has until now been neither a synthesis of how frequently plant populations exhibit adaptation to elevation nor an evaluation of how consistent underlying trait differences across species are. We reviewed studies of adaptation along elevation gradients (i) from a meta-analysis of phenotypic differentiation of three traits (height, biomass and phenology) from plants growing in 70 common garden experiments; (ii) by testing elevation adaptation using three fitness proxies (survival, reproductive output and biomass) from 14 reciprocal transplant experiments; (iii) by qualitatively assessing information at the molecular level, from 10 genomewide surveys and candidate gene approaches. We found that plants originating from high elevations were generally shorter and produced less biomass, but phenology did not vary consistently. We found significant evidence for elevation adaptation in terms of survival and biomass, but not for reproductive output. Variation in phenotypic and fitness responses to elevation across species was not related to life history traits or to environmental conditions. Molecular studies, which have focussed mainly on loci related to plant physiology and phenology, also provide evidence for adaptation along elevation gradients. Together, these studies indicate that genetically based trait differentiation and adaptation to elevation are widespread in plants. We conclude that a better understanding of the mechanisms underlying adaptation, not only to elevation but also to environmental change, will require more studies combining the ecological and molecular approaches.

Plant performance and survival across transplant experiments depend upon temperature and precipitation change along elevation

“…We acknowledge that these metrics vary largely depending on the individuals, species and study under consideration; however, these metrics were all measured as indicators of plant reproductive output along elevations (see e.g. Halbritter et al, 2018). We only included leaf size values when it was reported as the area of the leaf (m 2 ), excluding leaf diameter, length or width.…”

“…Despite recent syntheses involving transplant and common‐garden experiments to elucidate patterns of plant performance and adaptation change along environmental gradients (Halbritter et al, 2018; Leimu & Fischer, 2008; Pulido et al, 2019), little efforts have been payed to summarize recent literature on the intraspecific responses along elevation across multiple reciprocal transplant experiments. Only Halbritter et al (2018) to our knowledge, reported a systematic review including transplant experiments across elevations showing significant evidence of higher biomass and survival in local individuals compared with foreign ones. However, their analysis on reciprocal transplants did not disentangle climatic variation (in temperature and precipitation) along elevation across transplant sites and focused on 22 species and 14 reciprocal transplant experiment studies available up to 2015.…”

Parallel alpine differentiation inArabidopsis arenosa

“…Alternatively, drift, divergent selection to locally-specific conditions and/or limited variation in the source populations would lead to regionally specific patterns of foothill-alpine differentiation (3). Independently of the region of origin, alpine A. arenosa populations exhibited consistently shorter stems and larger flowers demonstrating parallelism in typical traits associated with 'alpine syndrome' that are considered adaptive in alpine environments (25,50). Elevation gradients belong to the most frequently studied environmental gradients in plant evolutionary ecology since the rise of this field (51,52), however, cases of phenotypic parallelism demonstrated by a combination of genetic and experimental data are still very rare in plant literature (53).…”

Pre-adaptation to climate change through topography-driven evolution of traits and their plasticity

“…Fine-scale environmental variation has frequently been associated with high levels of adaptive phenotypic variation. In particular, the highly heterogeneous landscapes from mountain ranges provide ample opportunity for adaptive radiation at fine spatial scales (Halbritter et al 2018; Waterhouse et al 2018). Moreover, high-altitudinal secondary valleys and cold air sinks typical of topographically complex landscapes designate topographical factors other than altitude as contributing determinants of temperature and soil moisture levels (Körner 2007; Günther et al 2016; O’Brien et al 2017; Pfennigwerth et al 2017).…”