Replicated radiations in the South American marsh pitcher plants (Heliamphora) lead to convergent carnivorous trap morphologies.

PREMISE: The evolution of carnivorous pitcher traps across multiple angiosperm lineages represents a classic example of morphological convergence. Nevertheless, no comparative study to-date has examined pitcher evolution from a quantitative morphometric perspective. METHODS: In the present study, we used comparative morphometric approaches to quantify the shape space occupied by Heliamphora pitchers and to trace evolutionary trajectories through this space to examine patterns of divergence and convergence within the genus. We also investigated pitcher development, and, how the packing of pitchers is affected by crowding, a common condition in their natural environments. RESULTS: Our results showed that Heliamphora pitchers have diverged along three main axes in morphospace: (1) pitcher curvature; (2) nectar spoon elaboration; and (3) pitcher stoutness. Both curvature and stoutness are correlated with pitcher size, suggesting structural constraints in pitcher morphological evolution. Among the four traits (curvature, spoon elaboration, stoutness, and size), all but curvature lacked phylogenetic signal and showed marked convergence across the phylogeny. We also observed tighter packing of pitchers in crowded conditions, and this effect was most pronounced in curved, slender pitchers. CONCLUSIONS: Overall, our study demonstrates that diversification and convergent evolution of carnivory-related traits extends to finer evolutionary timescales, reinforcing the notion that ecological specialization may not necessarily be an evolutionary dead end.

Phylogeny and biogeography of South American marsh pitcher plant genus Heliamphora (Sarraceniaceae) endemic to the Guiana Highlands.

Heliamphora is a genus of carnivorous pitcher plants endemic to the Guiana Highlands with fragmented distributions. We present a well resolved, time-calibrated, and comprehensive Heliamphora phylogeny estimated using Bayesian inference and maximum likelihood based on nuclear genes (26S, ITS, and PHYC) and secondary calibration. We used stochastic mapping to infer ancestral states of morphological characters and ecological traits. Our ancestral state estimations revealed that the pitcher drainage structures characteristic of the genus transformed from a hole to a slit in single clade, while other features (scape pubescence and hammock-like growth) have been gained and lost multiple times. Habitat was similarly labile in Heliamphora, with multiple transitions from the ancestral highland habitats into the lowlands. Using a Mantel test, we found closely related species tend to be geographically closely distributed. Placing our phylogeny in a historical context, major clades likely emerged through both vicariance and dispersal during the Miocene with more recent diversification driven by vertical displacement during the Pleistocene glacial-interglacial thermal oscillations. Despite the dynamic climatic history experienced by Heliamphora, the temperature changes brought by global warming pose a significant threat, particularly for those species at the highest elevations.

How to approach the study of syndromes in macroevolution and ecology.

Syndromes, wherein multiple traits evolve convergently in response to a shared selective driver, form a central concept in ecology and evolution. Recent work has questioned the existence of some classic syndromes, such as pollination and seed dispersal syndromes. Here, we discuss some of the major issues that have afflicted research into syndromes in macroevolution and ecology. First, correlated evolution of traits and hypothesized selective drivers is often relied on as the only evidence for adaptation of those traits to those hypothesized drivers, without supporting evidence. Second, the selective driver is often inferred from a combination of traits without explicit testing. Third, researchers often measure traits that are easy for humans to observe rather than measuring traits that are suited to testing the hypothesis of adaptation. Finally, species are often chosen for study because of their striking phenotypes, which leads to the illusion of syndromes and divergence. We argue that these issues can be avoided by combining studies of trait variation across entire clades or communities with explicit tests of adaptive hypotheses and that taking this approach will lead to a better understanding of syndrome-like evolution and its drivers.