The Variety of Amphibian Reproduction
Of all the vertebrates the amphibians have the widest range of reproduction methods, with differences even within the same order. Fertilization of the salamander makes for a good example, where it is internal for most salamanders, but external for the giant and Asiatics. There are even some mole salamanders where the sperm initiates development, but doesn’t contribute genetically! The typical salamander fertilization has the sperm transferred in spermatophores, which the female picks up with her cloacal lips either to use or store in her spermatheca glands for later use.
One feature of amphibians reproduction is that almost all frogs fertilize externally, but the sperm is deposited on the egg as it is laid, with the male frog holding onto the female with his front legs in a sex-like manner. There are some variations on this – frogs without front legs have to add the sperm after the egg is laid, and the narrow-mouthed frogs become glued together during fertilization. With the North American Tailed frog, it is the frogs tail itself which is inserted into female cloaca.
Most amphibians lay their eggs (oviparous) rather than store them in their body (viviparous). Frogs lay between one and 25,000 eggs at a time, depending on the species, with salamanders up to a few dozen. The method of laying eggs varies from clusters, to strands, but common to all is the slimy coating that protects them. Of the amphibians that give birth to fully-formed young most are viviparous.
The eggs of amphibians reproduction are laid in all sorts of places, with each species selecting a preferred site from a range including: still water, running water, under rocks, under leaves, in the stem of plants, and mud homes build by the male.
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