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Gilbert SF. Developmental Biology. 6th edition. Sunderland (MA): Sinauer Associates; 2000.

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Developmental Biology. 6th edition.

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Raising Tadpoles

Most temperate zone frogs do not invest time or energy in providing for their tadpoles. However, among tropical frogs, there are numerous species in which adult frogs take painstaking care of their tadpoles. The poison arrow frog, Dendrobates, for example, is found in the rain forests of Central America. Most of the time, these highly toxic frogs live in the leaf litter of the forest floor. After laying eggs in a damp leaf, a parent (sometimes male, sometimes female) stands guard over the eggs. If the ground gets too dry, the frog will urinate on the eggs to keep them moist. When the eggs mature into tadpoles, the guarding frog allows them to wriggle onto its back (see Figure 18.6A). The frog then climbs into the canopy until it finds a bromeliad with a small pool of water in its leaf base. Here it deposits one of its tadpoles, then goes back for another, and so on, until the brood has been placed in numerous small pools. Then each day the female returns to these pools and deposits a small number of unfertilized eggs into them, replenishing the dwindling food supply for the tadpoles until they finish metamorphosis (Mitchell 1988; van Wijngaarden and Bolanos 1992; Brust 1993). It is not known how the female frog remembers—or is informed about—where the tadpoles have been deposited.

Marsupial frogs carry their developing eggs in depressions in their skin, and they will often brood their tadpoles in their mouths. When the tadpoles undergo metamorphosis, the frogs spit out their progeny. Even more impressive, the gastric-brooding frogs of Australia, Rheobatrachus silus and Rheobatrachus vitellinus eat their eggs. The eggs develop into larvae, and the larvae undergo metamorphosis in the mother's stomach. About 8 weeks after being swallowed alive, about two dozen small frogs emerge from the female's mouth (Figure 18.6B; Corbenet al. 1974; Tyler 1983). What stops the eggs from being digested or excreted? It appears that the eggs secrete prostaglandin hormones that stop acid secretion and prevent peristaltic contractions in the stomach (Tyler et al. 1983). During this time, the stomach is fundamentally a uterus, and the frog does not eat. After the oral birth, the parent's stomach morphology and function return to normal. Unfortunately, both of these remarkable frog species are now feared extinct. No member of either species has been seen since the mid-1980s.▪

Figure 18.6. Parental care of tadpoles.

Figure 18.6

Parental care of tadpoles. (A) Tadpoles of the reticulate poison dart frog Dendrobates are carried on their parent's back to small pools of water in the Peruvian rain forest canopy. (B) The female Rheobatrachus of Australia brooded over a dozen tadpoles (more...)

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