1 Species and sex differences in eye morphology and visual sensitivity of two nocturnal 2 sweat bee species (Megalopta spp., Hymenoptera: Halictidae) 3 4 5 Running title: Megalopta eye morphology and sensitivity 6 7 Beryl M. Jones1,2‡, Brett M. Seymoure*2,3,4‡, Troy J. Comi5, Ellis R. Loew6 8 9 1. Program in Ecology, Evolution, and Conservation Biology, University of Illinois, Urbana, 10 Illinois 61801 11 2. Smithsonian Tropical Research Institute, Panama City, Panama 20521 12 3. Living Earth Collaborative, Washington University in St. Louis, St. Louis, MO, 63130 13 4. Sound and Light Ecology Team, Colorado State University, Fort Collins, CO, 80523 14 5. Department of Chemistry, University of Illinois, Urbana, IL 61801 15 6. Department of Biomedical Sciences, Cornell University, Ithaca, NY, 14853 16 17 ‡Authors contributed equally 18 * corresponding author’s information: 19 Postal Address: Brett Seymoure 20 Biology Department, Washington University in St. Louis 21 Campus Box 1137 22 One Brookings Drive 23 St. Louis, MO 63130-4899 24 phone: 269 501 8761 25 email:
[email protected] 26 27 28 29 30 31 32 1 Electronic copy available at: https://ssrn.com/abstract=3469351 33 Abstract 34 Visually dependent dim-light foraging has evolved repeatedly across taxa, broadening species 35 ecological niches. As most dim-light foraging species evolved from diurnal ancestors, visual 36 sensitivity must increase immensely to compensate for light levels a billion times dimmer than 37 daylight. Some taxa, e.g. bees, are anatomically constrained by their apposition compound 38 eyes, which function well in daylight but not starlight.