Tadpoles with a trick: Overwintering Ecology of Tadpoles in a Himalayan Stream, Uttarakhand, India

ABSTRACT: Overwintering is a unique phenomenon of delaying metamorphosis in amphibian larvae at low-temperature conditions prevailing at high elevation and latitude. This study is the first of its kind in India to look at selected ecological aspects of overwintering tadpoles of Nanorana spp. in a Himalayan stream. I evaluated the temporal density of overwintering tadpoles in response to the temperature and disturbance gradient. Tadpole density was influenced by the time of the day, submerged leaf litter depth, canopy cover, cover item richness, and a cross over effect of water temperature and canopy cover, as inferred from Generalized Linear Mixed Effect Modelling. Mean tadpole density at night time was higher in modified pools than natural pools during winter, but there was no difference during daytime; the nocturnal pattern changed in the post-winter, where density was higher in natural pools. Tadpole activity pattern varied significantly between pool types during post-winter, where modified pool population increased daytime activity and thus the activity overlap reduced from winter (90.8%) to post-winter (64.5%). Further, I discuss the influence of temperature fluctuations on tadpole density and behavioural thermoregulation. I report the differences in relative tail length of tadpoles in modified and natural pools between seasons, where the modified pool population are larger in relative tail length compared to the natural population during post-winter. I propose two putative tadpole groups based on the morphometric measurements using PCA, and cluster analysis for further molecular identification. I present insights on the resource utilization pattern of overwintering tadpoles during winter and post-winter seasons using habitat availability and use analyses. Besides the understanding of poorly known larval ecology, the study provides some insights into the habitat simulation modelling with respect to habitat suitability criteria in the light of future altered streamflow.