Mallorcan Midwife Toad
Tagged: animal, animals, endangered animals, invertebrateAlytes muletensis
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The Mallorcan midwife toad has an unusual reproductive strategy. Confined to a restricted habitat, it is now being sustained by a captive-breeding and release program. The tiny Mallorcan midwife toad was known as a fossil long before it was discovered alive; it was found alive and named as recently as 1977. Now confined to about 10 isolated localities in the Sierra de Tramuntana, a mountainous region in western Mallorca, it once lived throughout the island. Its natural habitat is now fully protected, and a captive-breeding program is producing a steady supply of young animals that are released annually into suitable new sites. Smaller than the three species of midwife toads that live on the European mainland, the Mallorcan midwife toad became isolated about 7 million years ago, when a rise in sea level separated Mallorca from Spain. Living in streams, pools, and wells throughout the island, its survival came under threat in Roman times, when nonnative animals were introduced to the island. The viperine snake is a predator of midwife toads, while the Spanish green frog is a competitor, its tadpoles feeding on the same kind of food. Both species thrive at low altitudes, but have not been able to colonize Mallorca’s impressive mountainous regions. As a result, the Mallorcan midwife toad is confined to a few remote limestone ravines.
Call of the Wild
Following winter rains, which briefly turn their habitat into a raging torrent, Mallorcan midwife toads begin to call. The call is a soft, simple “peep” and, unusually, is produced by both sexes. It enables individuals to find each other in deep, rocky fissures. Mating, which takes place on land, is complex and protracted, and involves an elaborate series of leg movements by which a string of ten to 20 large, yolk¬filled eggs becomes tightly wrapped around the male’s hindlegs. The male then carries them around for several weeks until they are ready to hatch. The brooding period lasts for three to 10 weeks and averages four weeks; it is longer in cold weather and can be costly for males. While carrying eggs, males are not able to pursue prey actively and so tend to lose weight. In addition, the egg string sometimes becomes so tightly wrapped around a leg that its blood supply is cut off and the leg is lost. When the eggs are fully developed, the male briefly enters a pool and deposits them; soon afterward they hatch into tadpoles. Tadpole development and growth can take more than a year, and the tadpoles grow to a considerable size. Indeed, growth in the tadpole stage represents a greater proportion of total lifetime growth than in any other frog. Having passed a string of eggs to a male, the female, liberated from parental duties, develops a new batch of eggs; by the time they are mature, after about three weeks, there are males available who have gotten rid of their first batch of eggs. The breeding season lasts several months, and during it a female can lay up to three or four batches of eggs. Because females can generally produce eggs faster than males can brood them (an effect that is especially marked in cool weather), females commonly have to fight one another to mate with a willing male.
On the Brink of Extinction
When zoologists discovered the Mallorcan midwife toad alive, they realized that it was not only extremely rare, but also in danger of extinction. Its restricted habitat was a major cause for concern. It was immediately protected, and in 1985 a captive-breeding program was established involving a number of zoos and universities across Europe. The Mallorcan midwife toad thrives and breeds readily in captivity, and by 1989 large numbers of tadpoles and young adults were being shipped back to Mallorca to be released into the wild. Releases were made at localities with a suitable habitat where there were no wild toads. The species is now established at 12 new sites, in addition to the 13 natural ones. The range over which the species occurs has been doubled, and it is estimated that about 25 percent of the total population was bred in captivity. In 2004 its status was reduced from Critically Endangered to Vulnerable. The Mallorcan midwife toad illustrates the potential of captive-breeding programs in the conservation of endangered animals. It is a particularly suitable technique for amphibians because they have a high reproductive potential that is only rarely realized under natural conditions. Amphibians typically produce a large number of eggs. However, most die, either as eggs or tadpoles, through a variety of natural causes in the wild. In captivity eggs and tadpoles can be protected from such hazards so that the reproductive potential of a species can be exploited.
Mallorcan midwife toad (ferreret)
Alytes muletensis
- Family: Discoglossidae
- World population: Unknown
- Distribution: Mallorca
- Habitat: Around pools in deep ravines at high altitude
- Diet: Small invertebrates
- Breeding: Spring and summer (March-July). Male carries eggs wrapped around hindlegs for several weeks; tadpole development lasts about 1 year
- Size: Length: 1.2-1.8 in (3-4 cm)
- Form: Pale yellow or ocher with numerous dark-brown, black, or dark¬green spots
- Related endangered species: Betic midwife toad (Alytes dickhilleni)
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