Microhabitat choice of tadpoles of seven anuran species

Abstract

The habitat choice of tadpoles of seven anuran species with respect to light and dark phases was studied using a choice tank with a simulated pond edge. In each trial, which lasted for 12 hrs, twenty freshly collected tadpoles (Gosner stage 32-38) of a given species were used. After introducing tadpoles into the choice tank, their number at the surface, up the water column, and on the substrate was recorded at half-hour intervals. Four trials each for day and night were conducted for each species. Tadpoles of Rana curtipes, Rana cyanophlyctis, and Rana temporalis, which possess a ventral mouth, predominantly occupied the substrate zone, whereas those of Bufo melanostictus, Polypedates maculatus, and Rana tigrina, which have an antero-ventral mouth, utilized both substrate and column zones but with a clear preference for the substrate zone. Within the substrate zone, the number of tadpoles of B. melanostictus, P. maculatus, R. temporalis, and R. tigrina was greater at night than in the daytime, whereas the opposite was true for R. curtipes. Of these five species response for day-night changes was prominent in P. maculatus. It is unclear whether variation in the number of tadpoles with respect to day and night is due to changes in the light intensity or temperature or oxygen levels. The tadpoles of R. cyanophlyctis did not show any response to day-night changes. On the other hand, the tadpoles of Microhyla ornata, which possess an antero-dorsally placed and highly simplified mouth (devoid of teeth) preferred the surface (64%) and column (28%) zones in both light and dark phases. The tadpoles of M. ornata are not easily spotted despite their surface occupancy due to their transparent appearance. The present study shows the existence of diversity in the microhabitat choice of the anuran tadpoles that correlates well with their morphological characteristics.