The functions of ghrelin, a novel weight-regulatory peptide, have not been intensively investigated in amphibians. The aim of this experiment was to study the effects of exogenous, mammalian ghrelin on the carbohydrate and lipid metabolism of two Palearctic Anurans: the common toad (Bufo bufo) and the common frog (Rana temporaria). Twenty-eight common toads and 20 common frogs were injected daily with purified human Ser3-acylated ghrelin at 10 μg kg–1d–1 or with 0.9 % saline into the dorsal lymph sac for four days. Exogenous ghrelin decreased the plasma total cholesterol (Chol) and LDL-Chol concentrations and increased the HDL-LDL ratios of the common frogs. The liver lipase activities decreased but the fat body lipase activities increased due to the ghrelin treatment. Ghrelin did not influence the measured variables in the common toad. In addition to stimulating growth hormone and prolactin secretion in amphibians, ghrelin also influences their lipid metabolism.
Research in freshwater ecology has traditionally focused on water courses or large still waters. However, ponds support proportionately high levels of biodiversity relative to other inland waters in Europe, and foraging by Eurasian otter Lutra lutra (L., 1758) could have considerable impacts on species composition in these small water bodies. The aim of the present study was to analyse otter spraints around ponds during two contrasting seasons (winter and spring) in north Norfolk (eastern England), where both otter and ponds are of particular conservation concern. Spraint density, prey diversity and the consumption of river-associated species were higher in spring than winter. In both seasons, birds were the most important prey category as ingested biomass. European eel Anguilla anguilla (L., 1758) and amphibians, specifically common frog Rana temporaria L., 1758 and common toad Bufo bufo (L., 1758), were more consumed in spring, whereas northern pike Esox lucius L., 1758 and tench Tinca tinca (L., 1758) were taken in winter. Non-native common carp Cyprinus carpio L., 1758 was important in both seasons, whereas threatened native crucian carp Carassius carassius (L., 1758) was a minor prey item. Massive kills of common toad, which involved a new handling technique for predation on this species, were observed mainly in spring. The study demonstrated otters to display great plasticity in foraging behaviour and contributes to the
understanding of otter predatory pressure on pond biodiversity, with implications for landscape management.