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Abstract Light intensity varies 1 million‐fold between night and day, driving the evolution of eye morphology and retinal physiology. Despite extensive research across taxa showing anatomical adaptations to light niches, surprisingly few empirical studies have quantified the relationship between such traits and the physiological sensitivity to light. In this study, we employ a comparative approach in frogs to determine the physiological sensitivity of eyes in two nocturnal (Rana pipiens,Hyla cinerea) and two diurnal species (Oophaga pumilio,Mantella viridis), examining whether differences in retinal thresholds can be explained by ocular and cellular anatomy. Scotopic electroretinogram (ERG) analysis of relative b‐wave amplitude reveals 10‐ to 100‐fold greater light sensitivity in nocturnal compared to diurnal frogs. Ocular and cellular optics (aperture, focal length, and rod outer segment dimensions) were assessed via the Land equation to quantify differences in optical sensitivity. Variance in retinal thresholds was overwhelmingly explained by Land equation solutions, which describe the optical sensitivity of single rods. Thus, at the b‐wave, stimulus‐response thresholds may be unaffected by photoreceptor convergence (which create larger, combined collecting areas). Follow‐up experiments were conducted using photopic ERGs, which reflect cone vision. Under these conditions, the relative difference in thresholds was reversed, such that diurnal species were more sensitive than nocturnal species. Thus, photopic data suggest that rod‐specific adaptations, not ocular anatomy (e.g., aperture and focal distance), drive scotopic thresholds differences. To the best of our knowledge, these data provide the first quantified relationship between optical and physiological sensitivity in vertebrates active in different light regimes.
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Thermal niche variation among individuals of the poison frog, Oophaga pumilio , in forest and converted habitats
Abstract The conversion of natural habitats to human land uses often increases local temperatures, creating novel thermal environments for species. The variable responses of ectotherms to habitat conversion, where some species decline while others persist, can partly be explained by variation among species in their thermal niches. However, few studies have examined thermal niche variation within species and across forest‐land use ecotones, information that could provide clues about the capacity of species to adapt to changing temperatures. Here, we quantify individual‐level variation in thermal traits of the tropical poison frog,Oophaga pumilio, in thermally contrasting habitats. Specifically, we examined local environmental temperatures, field body temperatures (Tb), preferred body temperatures (Tpref), critical thermal maxima (CTmax), and thermal safety margins (TSM) of individuals from warm, converted habitats and cool forests. We found that frogs from converted habitats exhibited greater meanTbandTprefthan those from forests. In contrast,CTmaxandTSMdid not differ significantly between habitats. However,CTmaxdid increase moderately with increasingTb, suggesting that changes inCTmaxmay be driven by microscale temperature exposure within habitats rather than by mean habitat conditions. AlthoughO. pumilioexhibited moderate divergence inTpref,CTmaxappears to be less labile between habitats, possibly due to the ability of frogs in converted habitats to maintain theirTbbelow air temperatures that reach or exceedCTmax. Selective pressures on thermal tolerances may increase, however, with the loss of buffering microhabitats and increased frequency of extreme temperatures expected under future habitat degradation and climate warming. Abstract in Spanish is available with online material.
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- Award ID(s):
- 1712757
- PAR ID:
- 10460590
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Biotropica
- Volume:
- 51
- Issue:
- 5
- ISSN:
- 0006-3606
- Page Range / eLocation ID:
- p. 747-756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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