Abstract
Flowers have evolved signals that exploit the sensory systems of insect visitors. In the case of visual cues, color signals are thought to have been shaped in large part by the spectral sensitivity of key pollinators, such as hymenopterans. Beetles were some of the first plant pollinators, pre-dating the angiosperm radiation but with the exception of a few well-studied species, the evolution of flower-visiting beetle visual systems is poorly understood. Thus, the ability of beetles to detect and distinguish flower color signals and perhaps their potential role in shaping flower coloration is not well understood. Traditional models of pollinator visual systems often assume a putative tri- or tetrachromatic flower-visitor, as is found in bees, flies and butterflies. Beetles are unique among modern pollinators as ancestrally they did not possess the machinery for trichromatic vision, lacking the blue-sensitive photoreceptor class. Research on the evolution of visual genes responsible for wavelength sensitivity (opsins) has revealed that beetles with putative tri- and tetrachromatic visual systems have evolved independently, along multiple lineages. We explore the evolution of beetle visual genes using newly generated and publicly available RNA-seq data from 25 species with flower associations, including previously unexplored key flower-visitor groups and 20 non-flower visiting relatives. Our findings serve as a resource to inform and guide future studies on beetle-flower interactions, where insight from both signal and receiver is needed to better understand these poorly explored systems.
Highlights
Beetles were some of the earliest pollinators and remain the primary pollinators of ancient plant group, gymnosperms (Toon et al, 2020), while functioning as common pollinators of more recent angiosperm radiations
While LW opsin duplications were not common generally, in the coleopterans sampled, they were ubiquitous among these flower-visitors
These findings suggested that there may be a selective advantage for duplications, such as an expansion of wavelength sensitivity, among species that may use floral cues
Summary
Beetles were some of the earliest pollinators and remain the primary pollinators of ancient plant group, gymnosperms (Toon et al, 2020), while functioning as common pollinators of more recent angiosperm (flowering plant) radiations. Angiosperm radiations during the Cretaceous cooccurred with accelerated diversification among the holometabolous insects that comprise the dominant insect pollinators: hymenopterans, lepidopterans, dipterans and coleopterans (Doyle, 2012; Misof et al, 2014). This co-radiation is thought to be in part due to the establishment of close associations or mutualisms between pollinator and plant, which likely contributed to the diversification of floral pollinator signals seen in modern flowers (Bronstein et al, 2006; Cardinal and Danforth, 2013). Flower associations evolved without preexisting pollination behavior (e.g., Glaphyridae) (Sabatinelli et al, 2020), as in Anthophila (bees) (Cardinal and Danforth, 2013; Peters et al, 2017)
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