Species and sex differences in eye morphometry and visual responsivity of two crepuscular sweat bee species (Megalopta spp., Hymenoptera: Halictidae)

Beryl M. Jones, Brett M. Seymoure, Troy J. Comi, Ellis R. Loew

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Visually dependent dim-light foraging has evolved repeatedly, broadening the ecological niches of some species. Many dim-light foraging lineages evolved from diurnal ancestors, requiring immense visual sensitivity increases to compensate for light levels a billion times dimmer than daylight. Some taxa, such as bees, are anatomically constrained by apposition compound eyes, which function well in daylight but not in starlight. Even with this constraint, the bee genus Megalopta has incredibly sensitive eyes, foraging in light levels up to nine orders of magnitude dimmer than diurnal relatives. Despite many behavioural studies, variation in visual sensitivity and eye morphometry has not been investigated within and across Megalopta species. Here we quantify external eye morphology (corneal area and facet size) for sympatric species of Megalopta, M. genalis and M. amoena, which forage during twilight. We use electroretinograms to show that males, despite being smaller than females, have equivalent visual sensitivity and increased retinal responsivity. Although males have relatively larger eyes compared with females, corneal area and facet size were not correlated with retinal responsivity, suggesting that males have additional non-morphological adaptations to increase retinal responsiveness. These findings provide the foundation for future work into the neural and physiological mechanisms that interface with morphology to influence visual sensitivity, with implications for understanding niche exploitation.

Original languageEnglish
Pages (from-to)533-544
Number of pages12
JournalBiological Journal of the Linnean Society
Volume130
Issue number3
DOIs
StatePublished - Jun 26 2020

Bibliographical note

Publisher Copyright:
© 2020 The Linnean Society of London, Biological Journal of the Linnean Society.

Funding

The manuscript was significantly improved by the insightful comments of three anonymous reviewers. The authors declare no competing or financial interests. B.M.J., E.R.L. and B.M.S. designed the study. B.M.J. and B.M.S. performed experiments and wrote the manuscript. T.J.C. analysed data and helped draft the manuscript. All authors edited the manuscript and gave final approval for publication. B.M.J. was supported by an Ernst Mayr Fellowship from the Smithsonian Tropical Research Institute and the National Science Foundation Graduate Research Fellowship Program (NSF GRFP). T.J.C. acknowledges funding from the Training Program at Chemistry-Interface with Biology (T32 GM070421),the NSF GRFP, and the Springborn fellowship from the University of Illinois at Urbana-Champaign. B.M.S. was supported through the Arizona State University and Smithsonian Tropical Research Institute Partnership. Equipment for this research was funded through Sigma Xi and the Society for Integrative and Comparative Biology to B.M.S.

FundersFunder number
National Science Foundation (NSF)T32 GM070421
University of Illinois, Urbana-Champaign
Arizona State University
Smithsonian Tropical Research Institute
Sigma-Aldrich
Society for Integrative and Comparative Biology (SICB)

    Keywords

    • allometry
    • compound eye
    • electroretinograms
    • eye morphology
    • nocturnal foraging
    • visual sensitivity

    ASJC Scopus subject areas

    • Ecology, Evolution, Behavior and Systematics

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