Schluter, P. M. | Search bioRxiv

bioRxiv2026

Fruit scent chemistry: adaptation to seed dispersal interactions

Fleshy fruits have evolved diverse traits to attract seed dispersers in response to frugivore behavior and sensory capacities. Fruit scent has been suggested to signal ripeness and nutritional quality, yet the volatile components involved and the information they convey remain poorly understood. It is unknown which information is encoded in fruit scent, whether plants actively synthesize these signals, and thus whether scent constitutes an evolved communication system shaping seed-dispersal interactions. Aliphatic esters, chemicals whose odor is often described as fruity, are abundant in some ripe fruits, especially those dispersed by animals which tend to rely on their sense of smell for fruit selection. Moreover, they have been argued to be associated with sugar content, potentially rendering them an honest signal and hence a hotspot of animal-plant chemical communication. We investigated whether aliphatic esters indicate fruit quality honestly and represent an adaptive trait shaped by disperser identity. Using 13 fig species (Ficus spp.; Moraceae) in Madagascar, we quantified seed dispersal by multiple animals using a quantitative ecological network. We then quantified chemical signals and nutritional rewards using thermal desorption gas chromatography-mass spectrometry (TD-GCMS) and high-performance liquid chromatography (HPLC), and used genome-guided transcriptome assembly to identify the candidate genes responsible for ester signaling. Our results show that (a) aliphatic esters occur more frequently in species dispersed primarily by olfactory-oriented mammals than in those dispersed by visually oriented birds; (b) ester abundance correlates positively with soluble sugar across species only in mammal-dispersed species, indicating an honest signal that is activated only when ecologically relevant; and (c) putative AAT gene revealing elevated expression associated with the increased abundance of aliphatic esters, sugars in single mammal-dispersed taxon. Together, these findings support the hypothesis that fruits have evolved to utilize the biochemical link between esters (signals) and sugars (rewards) to provide honest signals to seed dispersers.

plant biology↗

bioRxiv2025

Pollinator-relevant floral traits underlie bidirectional hybridisation in the orchid genus Gymnadenia

Reproductive isolation is mediated by ecological, phenotypic, and genetic barriers. Where such barriers are not upheld, hybridisation can occur, revealing insight about the formation of species. Here, we provide an integrative investigation of hybrid formation between the orchids Gymnadenia conopsea and G. rhellicani and potential isolating barriers in zones of overlap in the European Alps. We examine opportunities for hybridisation by quantifying hybrid frequency and pollinator assemblages of parent species. Next, we characterise floral phenotypes and genetic parentage of hybrids to examine how genetic inheritance of traits shapes ecological interactions, and thus fitness, of hybrids. We find that pollinator assemblages of parents overlap partially, consistent with observed rare hybrids (<1% of the population). Phenotypically, hybrids were intermediate across floral traits, consistent with all hybrids being identified as F1s, resulting from a primary hybridisation event between G. conopsea and G. rhellicani. No evidence of backcrossing or introgression was found, but direction of pollen transfer varied across sites. Additionally, hybrids were heterozygous for parental alleles at two loci impacting anthocyanin production, suggesting hybrids intermediate floral colour reflects inheritance of these alleles. Finally, we find little support that ploidy variation or hybrid seed infertility explains the absence of advanced generations of hybrids. Thus, we suggest that floral isolation represents an important isolating mechanism between G. conopsea and G. rhellicani in limiting the formation of uncommon, unfit hybrids and shaping species boundaries.

plant biology↗