Rigor Vitae: Life Unyielding

Tuesday, June 24, 2008

AMPHIBIAN LARVAE: SALAMNDERS vs. TOADS, part i

Here are a couple of humble portraits of the tenants in my front-yard pond: Amphibian larvae! On May 6th of this year I collected 4 Woodhouse's Toad (Bufo woodhousii) tadpoles, and on June 16th I collected 6 Barred Tiger Salamander (Ambystoma mavortium) larvae. Today I broke down and photographed them for the first time (click on the photos to see them full-size). Above is one of the salamander larvae. While the tadpoles of most anuran species are herbivorous, most salamander larvae feed on arthropods, as do those of A. mavortium. A wide range of prey is captured, but arthropods more than 25% of the larva's bodylength are rarely taken. Prey species that rest on the substrate are preferred. The salamander typically approaches potential prey nonchalantly, then quickly opens its mouth and expands its throat, pulling in a large amount of water and, more often than not, the desired item. A. mavortium is the most common amphibian of my area, and I've raised hundreds of their larvae over the years. Around here, the eggs usually hatch in early May, releasing larvae about 8mm long. They grow very quickly, metamorphosing before winter. In just over a week, these fellows have increased their length by about 30%, reaching a current total length of about 5cm. What were barely visible limb buds have become mildly respectable little legs. The lovely, feathered gills grow in inverse proportion to the amount of oxygen dissolved in the water. Tiger Salamanders growing in richly-oxygenated waters develop stumpy, sorry-looking gills. By late September, they'll be about 5 inches long and their gills will be all but gone. Their greenish color will give way to a brownish-gray with small, darker spots, and they'll haul up onto land to bury themselves and hibernate. Adult Barred Tiger Salamanders are mostly terrestrial and fossorial. They emerge at night and during rainstorms to hunt arthropod prey. Upon emerging from hibernation in the spring, the adults enter ponds or still pools in rivers to breed.

These Woodhouse's Toads are the first members of their species I've kept. According to the literature, they occur in my area, but I've never seen them this far north, only their relative, B. boreas. These individuals were taken from the Beaver Dam Wash in southwestern Utah. Like other toad tadpoles, they feed on algae, often hanging inside tangles of Spirogyra to graze. These tadpoles have grown far more slowly than the salamanders, having added only a few mm in nearly two months. Today their total length is about 4cm. About 2 weeks ago, their hind limb buds began to sprout, and they're coming along nicely, even developing some barring. I'll do my best to post new photos of both species every Tuesday.
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Both photos by CPBvK, taken on June 24, 2008

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