Community ecologists are interested in the role of traits and evolutionary history in assemblages, and how these two measures are associated. Analyses are increasingly considering trait and genetic variation at multiple ecological scales, and frequently the relationship between these measures is assumed to be constant. However, micro- and macro-evolutionary processes may imply different relationships between genetic variation and trait variation at scales from the individual to species. The mechanisms promoting genetic variation and adaptation at the intraspecific level should differ from those that lead to trait evolution and adaptation over long evolutionary times. As a result it is important to explore how the relationship between trait and genetic differences may change as one scales from within-species to between species: this has relevance for questions interested in phylogenetic and functional approaches.
With a unique dataset focused on the model species Arabidopsis thaliana, we used data collected for individuals, populations, and additional European plant species to address this issue. Using a consistent set of ecologically relevant traits (e.g. SLA, seed mass, height, leaf dry matter) we calculated measures of within- and between-species trait diversity and trait differences. We also used time-calibrated estimates of evolutionary divergence to estimate within- and between-species genetic differences.
Results/Conclusions
We made comparisons between ~200 populations of A. thaliana and with ~1000 herbaceous European species. We show both qualitatively and quantitatively that the relationship between trait and genetic differences depends on the ecological scale considered. Greater trait differences—given the average time since divergence—were present in the populations of A. thaliana compared to the same values at the species level. However, most of the trait variation was associated with a single axis of phenotypic variation rather than occurring evenly across all traits. This may reflect important physiological constraints. Using simulations, we compare these results to null expectations under models of trait evolution (Brownian motion/neutral drift): our results differ from their expectation. Thus we provide one example, using a unique dataset, showing how the relationship between these two factors is dependent on context, including ecological scale and the life history characteristics of our study organism. This has relevance for phylogenetic and functional studies of diversity that occurs in population, communities, and larger regions.