DNA in haploid nuclei). The genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. The large genome sizes have prevented whole-genome sequencing of amphibians although a number of genomes have been published recently. The 1.7GB draft genome of Xenopus tropicalis was the first to be reported for amphibians in 2010. Compared to some salamanders this frog genome is tiny. For instance, the genome of the Mexican axolotl turned out to be 32 Gb, which is more than 10 times larger than the human genome (3GB). Feeding and diet With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. The sirens (Siren spp.) often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog (Xenohyla truncata) includes a large quantity of fruit in its diet. The Mexican burrowing toad (Rhinophrynus dorsalis) has a specially adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response. Frogs have been caught on fish hooks baited with red flannel and green frogs (Rana clamitans) have been found with stomachs full of elm seeds that they had seen floating past. Toads, salamanders and caecilians also use smell to detect prey. This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Cave-dwelling amphibians normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs (Rana spp.) lack teeth in the lower jaw, and toads (Bufo spp.) have