Divergent trait and environment relationships among parallel radiations inPelargonium(Geraniaceae): a role for evolutionary legacy?

Abstract

Functional traits in closely related lineages are expected to vary similarly along common environmental gradients as a result of shared evolutionary and biogeographic history, or legacy effects, and as a result of biophysical tradeoffs in construction. We test these predictions in Pelargonium, a relatively recent evolutionary radiation. Bayesian phylogenetic mixed effects models assessed, at the subclade level, associations between plant height, leaf area, leaf nitrogen content and leaf mass per area (LMA), and five environmental variables capturing temperature and rainfall gradients across the Greater Cape Floristic Region of South Africa. Trait-trait integration was assessed via pairwise correlations within subclades. Of 20 trait-environment associations, 17 differed among subclades. Signs of regression coefficients diverged for height, leaf area and leaf nitrogen content, but not for LMA. Subclades also differed in trait-trait relationships and these differences were modulated by rainfall seasonality. Leave-one-out cross-validation revealed that whether trait variation was better predicted by environmental predictors or trait-trait integration depended on the clade and trait in question. Legacy signals in trait-environment and trait-trait relationships were apparently lost during the earliest diversification of Pelargonium, but then retained during subsequent subclade evolution. Overall, we demonstrate that global-scale patterns are poor predictors of patterns of trait variation at finer geographic and taxonomic scales.

Leaf margins in a deciduous lineage from the Greater Cape Floristic Region track climate in unexpected directions

“…Our results suggest that the negative pattern between MAT and tooth density is largely based on seasonality (whether it be driven by temperature as in the northern hemisphere or by precipitation in our study). The significance of rainfall regime across multiple Pelargonium species has been demonstrated for several leaf traits (Moore et al., ) and for leaf lobing within a single species, P. scabrum (Moore et al., ). Using a global data set, Peppe et al.…”

“…With respect to climate variables, we chose to focus on mean annual temperature (MAT) given its strong legacy as an explanatory variable in the paleoclimate literature, mean annual precipitation (MAP), and winter precipitation seasonality given its recognition as an important climatic driver in the GCFR (Bradshaw and Cowling, ). These climate features have been associated with other leaf traits in Pelargonium (Moore et al., ). Climate data were extracted from Schulze () based on our georeferenced collection sites.…”

“…Second, Moore et al. () found strong effects of subclade on trait and environment relationships for a different set of traits, but no substantial effect of within‐subclade phylogenetic structure. Species not included by van de Kerke et al.…”

Impact of rainfall seasonality on intraspecific trait variation in a shrub from a Mediterranean climate

“…Contrasting climate gradients between Mediterranean and non-Mediterranean climates have important implications for how plants thermoregulate and manage water status: plants in winter rainfall regions must survive the hottest times of the year without water, while summer/all-year rainfall-growing plants have access to water when evaporative demand is high. These distinct patterns in rainfall seasonality should result in divergent patterns of relationships between traits and climate, or even trait-trait relationships (Moore, Schlichting, Aiello-Lammens, Mocko, & Jones, 2018), but how a single species might respond along such gradients has never been explicitly examined. Given that climate change is likely to alter rainfall seasonality and amount (Ashfaq et al, 2016;Bal, Pathak, Mishra, & Sahany, 2019), understanding intraspecific variation in trait-climate relationships across contrasting patterns in seasonal rainfall should enhance predictions of plant responses to future climate change.…”

“…In contrast, rainfall and temperature are relatively decoupled across summer rainfall regions. These contrasting relationships among climatic variables appear to impose divergent selection pressures on winter and summer populations, in turn leading to weakened or even inverted patterns of integration of the plant traits themselves, producing distinctive changes in plant functional architecture(Moore et al, 2018;Schlichting, 1989;Figure 3). The results we present are striking because they suggest that the responses of P. scabrum functional traits to climate are related not just to MAT, MAP and PET individually, but to how these variables interact with rainfall seasonality.…”