Body wiping behavior, integumentary secretions and rates of evaporative water loss (EWL) were examined in six species of Florida tree frogs (Anura: Hylidae). Additionally, morphology of the integument and dermal glands were compared among these and one other Florida tree frog (Hyla andersonii), an arid-adapted tree frog (Phyllomedusa hypochondrialis), and a highly aquatic frog (Rana utricularia). An extra-epidermal layer of lipid and mucus, presumably secreted from dermal granular glands, was detected on the skin of all Florida hylid frogs examined. Distinct body wiping behaviors were observed in the hylid frogs, but these were less complex than those described previously in phyllomedusine frogs, which occupy arid habitats, secrete lipids onto their skin, and are regarded as relatively 'waterproof'. Florida hylids occupy seasonally arid habitats and appear to have reduced rates of EWL. The suite of traits we observed in these frogs have been previously documented in a rhacophorid tree frog from seasonally arid regions of India and likely represent an evolutionary convergent response to periodic dehydration stress. The presence of lipids that are spread by simple wiping behaviors to form an extra-epidermal water barrier may represent an early stage of the more advanced adaptations described in more waterproof arboreal frogs.

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ABSTRACT.-Contamination of aquatic ecosystems with anthropogenic sources of nitrate is of increasing concern. Anurans are especially at risk for overexposure to nitrate because they occupy aquatic environments during embryonic, larval, and adult stages. Whereas there have been numerous studies examining the effect of nitrate on frog eggs and tadpoles, the effects of nitrate on adult frogs have been largely neglected. In this study, we examined whether brief exposure to environmentally relevant concentrations of aquatic nitrate influenced ovarian steroid synthesis and ovarian follicle size in adult African Clawed Frogs (Xenopus laevis). We exposed frogs for seven days to nitrate at concentrations of 24.8 or 49.5 mg/l in order to simulate a pulse of nitrate exposure. Relative to controls, nitrate-exposed frogs exhibited suppressed ex vivo synthesis of testosterone and estrogen. Follicles from nitrate-exposed frogs also exhibited an increased stage-4 diameter at both nitrate concentrations and a decreased stage-5 and -6 diameter at the highest nitrate concentration. These results indicate that anuran ovarian steroidogenesis and follicle size are modified by even a brief exposure to environmentally relevant concentrations of nitrate. Contamination ;of aquatic ecosystems by anthropogenic sources of nitrate has become an increasing global concern with respect to the health of humans and wildlife (Fried, 1991;Guillette and Edwards, 2005). Nitrate contamination of aquatic habitats occurs primarily through human activities in agricultural and urban areas, and in North American rivers, streams, and lakes, nitrate concentrations range from 1 mg/l to over 100 mg/l nitrate-as-nitrogen (Rouse et al., 1999). Within the United States, agricultural nitrogen contributions have increased 20-fold in the past 50 years, because of poorly regulated runoff of nitrogen-based fertilizers and animal wastes (Puckett, 1995;Rouse et al., 1999). Within urban areas, nitrate infiltrates aquatic ecosystems primarily through release of industrial and wastewater effluents from treatment plants, runoff of fertilizer applied to lawns and golf courses, and air pollution from the burning of fossil fuels (Rouse et al., 1999). In North America, fertilizers applied adjacent to waterways, coupled with spring rainstorms, contribute to a pulse of nitrate entering aquatic habitats that coincides with the breeding season of many amphibians (Rouse et al., 1999).Nitrate is highly soluble in water and, if ingested or absorbed transdermally, is readily transported across the epithelium of the small intestine (Ellis et al., 1998;Iizua et al., 1999). Numerous investigations of tadpoles exposed to environmentally relevant concentrations of nitrate have demonstrated altered behaviors (Hecnar, 1995;, movement patterns (Xu and Oldham, 1997), growth rates, development (Baker and Waights, 1993, 1994;Edwards et al., 2006), gonadal morphology (Orten et al., 2006), and mortality rates Smith et al., 2005Smith et al., , 2006. However, the effects of nitrate on endocrine func...

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