Activity of Neotropical Frogs in Relation to Ambient Light

Abstract

Previous laboratory studies on phototactic behavior of five species of neotropical anurans led to predictions that they would be active in natural habitats under only a limited range of ambient illuminations relative to the range available during 24-h periods. Generally, the species were found to be active within a 2.5 log-units for the North American tailed frog Ascaphus truei (Hailman and Jaeger 1976, fig. 16), is >3 log-units for the Asian frog Kaloula pulchra (ibid. fig. 15), and is 2.8 log-units for the African striped running frog Kassina senegalensis (ibid. fig. 14). Recently, Sustare (1977) measured the adaptational shift of K. senegalensis electroretinographically, and found an adaptational range of slightly more than 2.6 log-units, which BIOTROPICA 13(1): 59-65 1981 59 This content downloaded from 207.46.13.105 on Wed, 25 May 2016 05:22:54 UTC All use subject to http://about.jstor.org/terms is in good agreement with our behavioral studies. He also determined the adaptational range to be --1.9 log-units for the wood frog Rana sylvatica and --3.7 log-units for the American bullfrog Raiza catesbeianza. With regard to daily activity rhythm, species may evolve such that the individual animals become active only during those times in which light is within the favorable range for which their eyes are constructed. Little is known about rhythmic behavior in anurans relative to illumination. However, Jaeger et al. (1976) found the neotropical dendrobatid Colostethus nubicola to have activity periods in the morning and afternoon during similar conditions of ambient illumination. Prior to the present study, no single species has been studied both in the laboratory to measure phototactic intensity preferences and in the field to measure rhythmic activity relative to ambient light. Even for the five species of this study, we know the phototactic intensity preference only under one intermediate adaptational state of the eye rather than the entire range of preferences under all states of adaptation. Consequently, predictions concerning field results are necessarily limited. We believe the following predictions to be reasonable expectations, if not real deductions, from present knowledge: (1) each species studied should have a daily rhythm such that it becomes active only during a limited range of ambient illumination relative to the full range occurring in its habitat throughout the 24-h period; (2) if the activity rhythm shows two or more peaks during the 24-h period, these peaks of activity should occur at times of similar ambient illumination; (3) specific visually cued behavioral activities, such as feeding, should also occur under a restricted range of ambient illuminations; and (4) the range of illumination predicted under (1) and (3) should not exceed 4 logunits, based on the fact that the greatest visual adaptational shift documented thus far is --3.7 log-units for the American bullfrog (Sustare 1977).