Evolutionary constraints on disparity of ericaceous pollen grains

Abstract

Background and Aims Flowering plants show a high diversity of pollen morphology, assumed to reflect not only variations in the underlying design, but also stress imposed by ecological conditions related to pollen survival and germination. Both components are expected to constrain the accumulation of pollen disparity. However, this assumption has rarely been tested using empirical data. • Methods This study is designed to test this hypothesis by inferring the accumulation of pollen disparity in Ericaceae, a large eudicot family with recent, ongoing radiations, with focus on three functionally significant pollen characters using a dated phylogeny. • Key Results Multiple lines of evidence supported the hypothesis that pollen disparity in Ericaceae did not evolve steadily but rather pulsed over time, clearly decoupling from the relative constant rate pattern of species diversification inferred. In a 3-D pollen morphospace, most major clades appear to occupy distinct neighbouring regions, whereas the subfamily Epacridoideae overlaps extensively with other subfamilies. No evidence for correlations was found between dimension of pollen disparity and species diversity at either the subfamily or generic level. Furthermore, the distribution of species in present pollen morphospace showed a strong central tendency, with the core compartment containing a large number of species from species-rich genera. • Conclusions The recovered evidence fits well with the expectations of limitations on available pollen morphological disparity, and suggests that innovation of pollen germination traits may have little effect on species diversification.

Evolution of phenotypic disparity in the plant kingdom

“…However, these observations have been based largely on studies of animal clades and it is unclear whether they are more generally applicable. Analyses of plant phenotypic disparity have focused on single groups of characters such as branching architecture 3 , 4 , reproductive organs 5 – 9 , leaf architecture or shape 10 , 11 and vasculature 12 , and have been restricted to subclades or individual lineages 13 – 15 . Here we attempt an integrated characterization of the evolution of phenotypic disparity in the plant kingdom with the aim of testing the generality of macroevolutionary patterns observed in the animal kingdom.…”