OH CAECILIAN, YOU'RE RAKIN' MY HIDE

Here's a special treat for all of you who were freaked out by my description of parental care in Dendrobates frogs. Don't thank me, thank afarensis, who alerted me to the story the day before it came out in the journal Nature.

Parental care is no rare thing in nature, nor is the nutritional provisioning of young. Most multicellular animals are supplied with yolk in early development, and certain creatures, like the Strawberry Poison Frog (Dendrobates pumilio) continue that process longer than others. Mammals, of course, secrete milk for their offspring. A strategy related to the poison frogs' is found in certain spadefoots (Scaphiopus spp.), toad-like amphibians found mostly in semi-arid lands of the western U.S. Spadefoots spend most of their lives in a state of torpor underground, but when the rains come, they emerge from their burrows to feed and breed. Since the eggs are laid in temporary pools, the young develop very quickly. Typical frog tadpoles feed on algae, but those of some spadefoots come in two forms: a regular algae-eater and a bulldog-jawed carnivorous morph. In a rainy year, large, long-lasting pools provide plenty of algae, and the herbivorous forms are more successful. In a dry year, small ephemeral pools concentrate the larvae, and the edge goes to the carnivorous ones, who eat their vegetarian siblings.

All of these forms of parental provisioning require great physical investment from the mother. An exceptional new provisioning strategy was recently discovered in the East African caecilian Boulengerula taitanus. Caecilians comprise the poorly-known amphibian order Gymnophiona, which is found throughout the tropics. Usually well under a foot in length, they resemble carnivorous earthworms, and live a similar, fossorial lifestyle, with the exception of the aquatic South American family Typhlonectidae. Most of them are unexceptional to look at, but a few are beautifully colored. A screaming canary yellow species is found on the island of Sao Thomé, in the Gulf of Guinea. Like other amphibians, caecilians develop in a variety of ways. Some give birth to live young, others lay eggs. An aquatic larval stage is present in some, other genera skip the larval stage altogether (direct development).

The African genus Boulengerula includes five egg-laying, direct-developing species. The female Boulengerula guards her eggs—no small surprise, this behavior is well documented in caecilians, but the authors of the Nature paper discovered something peculiar when they took 21 female B. taitanus into captivity along with their broods. The young caecilians were feeding on their mother's skin! During brooding, the female's epidermal cells undergo a transformation that includes a doubling in thickness and production of lipid-rich vesicles. The hatchlings have complex juvenile teeth of various shapes that are specialized for scraping and biting the skin. These are eventually replaced by simpler adult teeth. There was no sign of young B. taitanus feeding on anything but their mother. This behavior is not likely to be restricted to this species, or even to the genus Boulengerula. In the '90s the authors observed juvenile brooding, juvenile teeth and maternal skin whitening in the South American caecilian Siphonops annulatus. Although skin feeding was just discovered, the behavior has probably been occurring since the Mesozoic. Similar teeth are found in certain live-bearing caecilians, and it is thought that these young engage in prenatal feeding of the maternal oviduct lining. The authors suggest that skin feeding was a transitional behavior in the evolution of oviduct feeding. Bon appétite!

For more on B. taitanus see the post at microecos.
Special thanks to Lara Carroll.
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upper: CALL OF THE MONSOON--COUCH'S SPADEFOOT (1996) acrylic 18" x 12"
lower: Photograph of Boulengerula boulengeria by Louis Porras