Nepenthes is a genus of carnivorous pitcher plants with high intra-and interspecific morphological diversity. Many species produce dimorphic pitchers, and the relative production rate of the two morphs varies interspecifically. Despite their likely ecological importance to the plants, little is known about the selective context under which various pitcher traits have evolved. This is especially true of color-related traits, which have not been examined in a phylogenetic context. Using field observations of one polymorphic species (N. gracilis) and phylogenetic comparative analysis of 85 species across the genus, we investigate correlations between color polymorphism and ecological factors including altitude, light environment, and herbivory. In N.gracilis, color does not correlate to amount of prey-capture, but red pitchers experience less herbivory. Throughout the genus, color polymorphism with redder lower pitchers appears to be evolutionarily favored. We found a lack of phylogenetic signal for most traits, either suggesting that most traits are labile or reflecting the uncertainty regarding the underlying tree topology.This work highlights ecological correlates of the vast phenotypic diversity of this group of tropical plants. We point to a need for future work examining herbivores of Nepenthes and experimental investigations on color polymorphism.
Characteristics of host species can alter how other, interacting species assemble into communities by acting as ecological filters. Pitchers of tropical pitcher plants (Nepenthes) host diverse communities of aquatic arthropods and microbes in nature. This plant genus exhibits considerable interspecific diversity in morphology and physiology; for example, different species can actively control the pH of their pitcher fluids and some species produce viscoelastic fluids. Our study investigated the extent to which Nepenthes species differentially regulate pitcher fluid traits under common garden conditions, and the effects that these trait differences had on their associated communities. Sixteen species of Nepenthes were reared together in the controlled environment of a glasshouse using commonly-sourced pH 6.5 water. We analyzed their bacterial and eukaryotic communities using metabarcoding techniques, and found that different plant species differentially altered fluid pH, viscosity, and color, and these had strong effects on the community structure of their microbiota. Nepenthes species can therefore act as ecological filters, cultivating distinctive microbial communities despite similar external conditions, and blurring the conceptual line between biotic and abiotic filters.
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