Piper

Under an adaptive hypothesis, the reciprocal influence between mutualistic plants and frugivores is expected to result in dispersal syndromes comprising both frugivore and plant traits that structure fruit consumption. Tests of this adaptive hypothesis, however, focus on traits of either fruits or frugivores but not both and often ignore within-species variation. To overcome these limitations, we analyze traits for the mutualistic ecological network comprising Carollia bats that feed on and disperse Piper seeds. For these analyses, we use generalized joint attribute modeling (GJAM), a Bayesian modeling approach that simultaneously accounts for multiple sources of variance across trait types. In support of the adaptive hypothesis and indicating niche partitioning among Carollia bats, we find differential consumption of a suite of Piper species influenced by bat traits such as body size; however, Piper morphological traits had no effect on bat consumption. Slow evolutionary rates, dispersal by other vertebrates, and unexamined fruit traits, such as Piper chemical bouquets, may explain the lack of association between bat Piper consumption and fruit morphological traits. We have identified a potential asymmetric influence of frugivore traits on plant-frugivore interactions, providing a template for future trait analyses of plant-animal networks.

Despite the widespread notion that animal-mediated seed dispersal led to the evolution of fruit traits that attract mutualistic frugivores, the dispersal syndrome hypothesis remains controversial, particularly for complex traits such as fruit scent. Here, we test this hypothesis in a community of mutualistic, ecologically important neotropical bats (Carollia spp.) and plants (Piper spp.) that communicate primarily via chemical signals. We found greater bat consumption is significantly associated with scent chemical diversity and presence of specific compounds, which fit multi-peak selective regime models in Piper. Through behavioural assays, we found Carollia prefer certain compounds, particularly 2-heptanol, which evolved as a unique feature of two Piper species highly consumed by these bats. Thus, we demonstrate that volatile compounds emitted by neotropical Piper fruits evolved in tandem with seed dispersal by scent-oriented Carollia bats. Specifically, fruit scent chemistry in some Piper species fits adaptive evolutionary scenarios consistent with a dispersal syndrome hypothesis. While other abiotic and biotic processes likely shaped the chemical composition of ripe fruit scent in Piper, our results provide some of the first evidence of the effect of bat frugivory on plant chemical diversity.

Mammalian olfactory receptors (ORs) are a diverse family of genes encoding proteins that directly interact with environmental chemical cues. ORs evolve via gene duplication in a birth-death fashion, neofunctionalizing and pseudogenizing over time. Olfaction is a primary sense used for food detection in plant-visiting bats, but the relationship between dietary specialization and OR repertoire diversity is unclear. Within neotropical Leaf-nosed bats (Phyllostomidae), many lineages are plant specialists, and some have a distinct OR repertoire compared to insectivorous species. Yet, whether specialization on particular plant genera is associated with the evolution of specialized OR repertoires with narrower diversity has never been tested. Using targeted sequence capture, we sequenced the OR repertoires of three sympatric species of short-tailed fruit bats (Carollia), which vary in their degree of specialization on the fruits of Piper plants. We characterized orthologous versus duplicated receptors among Carollia species, and explored the diversity and redundancy of the receptor gene repertoire. At the species level, the most dedicated Piper specialist, Carollia castanea, had lower OR diversity compared to the two generalists (C. sowelli, C. perspicillata), but we discovered a few unique sets of ORs within C. castanea with high redundancy of similar gene duplicates. These unique receptors potentially enable C. castanea to detect Piper fruit odorants better than its two congeners. Carollia perspicillata, the species with the most generalist diet, had a higher diversity of intact receptors, suggesting the ability to detect a wider range of odorant molecules. Variation among ORs may be a factor in the coexistence of these sympatric species, facilitating the exploitation of different plant resources. Our study sheds light on how gene duplication and changes in OR diversity may play a role in dietary adaptations and underlies patterns of ecological interactions between bats and plants.