Antipredator pheromones in amphibians: a review

Specific chemosignals (pheromones) have an important role in the antipredator behaviour in amphibians and other vertebrates. However, relatively little is known about the occurrence of chemical alarm cues just in amphibians. The site of chemosignals perception is vomeronasal system. The presence of the vomeronasal system in aquatic amphibians indicates that it did not arise as an adaptation to terrestrial life. Predators may inhibit mate search of some species, and male newts probably take greater risks during the breeding season. Field tests demonstrated different responses to male newt extract – probably trade-off that incorporates risk and resource sensitivity. Response to chemical alarm signals has been documented for tadpoles of frog and for several species of salamander. The response of tadpoles to predator includes morphological modifications and influence of coloration, growth and development retardation. Tadpoles of Rana aurora release a chemical that provides conspecifics with an early warning of predator presence. Bufo boreas tadpoles living in the presence of conspecific alarm cues and chemosignals of specific predators reduce the time of metamorphosis in order to reduce the time in the presence of its predators. Presence of conspecific alarm substances in water and predators’ waste products have an important role in the chemical detection of predators by tadpoles of Rana temporaria and Bufo bufo. Tadpoles of Rana utricularia significantly decreased the growth and increased the mortality of Hyla cinerea tadpoles on the basis of behavioral and chemical interference. Rana utricularia tadpoles apparently use both chemical interference and aggressive behavior in securing a competitive advantage over H. cinerea tadpoles. The response of tadpoles of Rana aurora to tadpoles of Taricha granulosa appear be similar to their response to tadpole extract in eliciting alarm, while insect-fed newts would have less of an effect since predators consuming other species may be less of a threat. In some cases (e.g. in Bufo bufo and B. calamita) chemosignals released in response to threat by predators (direct attack or detection of the predator scents) exert their effects across species.

Structural analysis of a new series of oligosaccharide-alditols released by reductive β-elimination from oviducal mucins of Rana utricularia

Egg jelly coats from Rana utricularia are formed by components secreted along the oviduct. These secretion products overlay the oocytes as they pass along the different oviducal portions. In this study, carbohydrate chains of the jelly coat surrounding the eggs of R. utricularia were released by alkali/borohydride treatment. Fractionation of O-linked oligosaccharide-alditols was achieved by a combination of chromatographic techniques comprising anion-exchange chromatography, gel-permeation chromatography and HPLC on a silica column bonded with aminopropyl groups. Structural characterization was performed by one- and two-dimensional 1H-NMR spectroscopy in combination with matrix-assisted laser-desorption ionization-time of flight MS and methylation analysis. Ten oligosaccharide structures possessing a core consisting of Galβ(1 → 3)GalNAc-ol with or without branching through a GlcNAc residue linked β(1 → 6) to the GalNAc residue (core type 2 or core type 1 respectively) are described. The most representative carbohydrate sequences are: GlcNAc(β1-3)[Fuc(α1-4)]GlcNAc, GalNAc(α1-3)[Fuc(α1-2)]Gal(β1-4)GlcNAc(β1-3)GlcNAc and Gal(β1-3)GlcNAc(α1-3)[Fuc(α1-2)]Gal(β1-4)GlcNAc. The carbohydrate chains isolated from R. utricularia are quite different from those found in other amphibian species, in which the presence of species-specific material has been characterized. Since the jellies surrounding amphibian eggs are involved in egg-sperm interactions, these structural investigations can provide biochemical support for investigation of the fertilization process.

Tadpole bullies: examining mechanisms of competition in a community of larval anurans

We examined interference competition during interspecific interactions of larval anurans to determine its importance. We conducted laboratory experiments to examine behavioral and chemical interference competition between tadpoles of the southern leopard frog (Rana utricularia) and those of the green treefrog (Hyla cinerea). Water preconditioned byR. utricularia tadpoles significantly decreased the growth and increased the mortality of H. cinerea tadpoles compared with control treatments. In addition, R. utricularia tadpoles inhibited the feeding rate ofH. cinerea tadpolesby harassing them, and these interactions significantly decreased the growth and increased the mortality of theH. cinerea tadpoles. Rana utricularia tadpoles apparently use both chemical interference and aggressive behavior in securing a competitive advantage over H. cinerea tadpoles, and the H. cinerea tadpoles suffer from these interactions. Intraspecific chemical and behavioral interference competition also significantly decreased the growth of larval H. cinerea. In natural ponds, R. utricularia tadpoles that inhibit the growth and increase the mortality of H. cinerea tadpoles may increase their own chances of survival and metamorphosis, while H. cinerea tadpoles that avoid interactions with conspecifics and with R. utricularia tadpoles may increase their own chances of survival and metamorphosis.

Structural analysis of the oligosaccharide-alditols released by reductive β-elimination from the jelly coat of Rana utricularia eggs

The O-linked oligosaccharides of the jelly coat surrounding the eggs of Rana utricularia were analysed by 1H-NMR spectroscopy. Comparison of their structures with those characterized from seven other amphibians confirms that the carbohydrate chains of the jelly coat mucins are markers of the species. The new sequence GlcNAc(β1-3)GlcNAc(β1-6)[Gal(β1-3)]GalNAc-ol is characteristic of Rana utricularia. The presence of blood group A determinants constitutes the main feature of this mucin.