Midwife Toads and Painted Frogs (Discoglossidae)

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Midwife toads and painted frogs

(Discoglossidae)

Class Amphibia

Order Anura

Family Discoglossidae

Thumbnail description
Moderate-sized, terrestrial to semiaquatic frogs with thick, disc-shaped tongues

Size
1.6–3.0 in (40–75 mm)

Number of genera, species
2 genera; 10 species

Habitat
Banks of fast-flowing streams, small ponds and swamps, and densely wooded areas

Conservation status
Extinct: 1 species; Critically Endangered: 1 species; Vulnerable: 2 species

Distribution
Northwestern Africa, central and western Europe

Evolution and systematics

The evolutionary relationships of the Discoglossidae are debatable. Many authors consider the group to include four genera: Discoglossus, Alytes, Bombina, and Barbourula. However, others suggest that Discoglossidae only includes one genus, Discoglossus, and that Alytes and Bombina should be grouped together in the Bombinatoridae without consideration of Barbourula. The most accepted hypothesis of relationships (and the one followed here) suggests that Discoglossus and Alytes are each other's closest relatives and should be grouped in the Discoglossidae, whereas Bombina and Barbourula are a separate, more distantly related group, the Bombinatoridae.

Several fossil forms have been attributed to the Discoglossidae. Of these, several forms, including Latonia (Miocene of Europe) and Eodiscoglossus (Jurassic of Spain) may be removed from the group as more information about their phylogenetic relationships becomes available. Other fossil taxa include Spondylophryne (Pleistocene of Hungary), Scotiophryne and Paradiscoglossus (Cretaceous of the United States), Prodiscoglossus (Oligocene of France), and Pelophilus (Miocene of Germany). The name Baleaphryne was given to a fossil from the Pleistocene of Spain; it was later discovered to be the same species as the living Alytes muletensis. No subfamilies are recognized.

Physical characteristics

These frogs are generally small and squat. They may have brightly colored patterns, and have distinct eyes with slitlike pupils. Several anatomical features make them distinct among frogs. These include the lack of palatine bones, eight opistocoelous, presacral vertebrae, articulation of sacrum and urostyle formed by two bony proturusions (bicondylar), a distinct sternum, and the presence of free ribs on Vertebrae II–IV. Also, the ankle bones (tibiale and fibulare, or astragalus and calcaneum) are fused only at their ends.

Distribution

These frogs occur in central and southern Europe, including the Iberian Peninsula and Italy, northwestern Africa, and Israel.

Habitat

Painted frogs occur primarily in wet or moist areas, including the edges of fast moving streams with rocky substrates. Midwife toads prefer slightly drier habitats that include wooded areas and open habitats near ponds and

streams. During the day, these frogs hide beneath cover objects such as rocks and logs.

Behavior

Frogs in this group are primarily active only at night, when they forage for insects near moist areas. During the day, they seek shelter from the sun under cover objects or in tunnels they excavate. Those that dig their own burrows do so digging head-first with their forearms through sandy soils, and they sometimes push their heads against the top of the tunnel to pack the soil tightly. The tunnel systems may be quite complex and elaborate.

Feeding ecology and diet

Larval and adult insects make up the majority of the diets of discoglossids. Stomach contents may include flies, grasshoppers, moth larvae, weevils and other beetles, ants, isopods, spiders, and snails. These frogs actively forage for prey at night.

Reproductive biology

During the breeding season, males call from in or near waters. In some species, the females also call in response to the males, but at a lower frequency. In all species, males mate with females by grabbing them around the waist (inguinal amplexus). Frogs in the genus Alytes are known for the parental care given by the males. During reproduction, males fertilize up to 100 egg strings, which they wrap around their legs. The males carry and protect these eggs until they hatch, at which time they return to the water to allow the tadpoles to swim free. In Discoglossus, females deposit up to 1,000 eggs attached to aquatic vegetation or on the bottom of the stream. Some tadpoles overwinter and metamorphose the next spring or summer. All tadpoles have keratinized mouth parts and two small fused spiracular tubes with a single anteromedial spiracle.

Conservation status

One species, Discoglossus nigriventer, is listed by the IUCN as Extinct, one (Alytes muletensis) as Critically Endangered, and two (Discoglossus montalenti and Alytes dickhilleni) as Vulnerable. Other populations seem to be robust and viable, but may eventually be affected by habitat destruction. Seven species are listed in Appendix II of the Convention on the Conservation of European Wildlife and Natural Habitats.

Significance to humans

None known.

Species accounts

List of Species

Iberian midwife toad
Midwife toad
Painted frog
Tyrrhenian painted frog

Iberian midwife toad

Alytes cisternasii

taxonomy

Alytes cisternasii Boscá, 1879, Badamoz, Mérida, Spain. No subspecies recognized.

other common names

French: Alyte de cisternas; German: Iberische Geburtshelferkröte; Spanish: Sapo-partero ibérico; Portuguese: Sapo-parteiro ibérico, sapo partero de cisternas.

physical characteristics

The average body length ranges between 1.4 in (36 mm) for males and 1.7 in (42 mm) for females. The frogs are small and stocky, and have large eyes with a vertical pupil. Males and females also vary in several relative morphometric variables, including the diameter of external ear, the width of the head, and the length of portions of the hind limb. These frogs display several characteristics commonly found in toads, including: small parotid glands behind the ear, warty skin, and two broad bumps on each hand. Their color pattern can vary, but consists mostly of a brown background with dark spots and red warts. Rows of red warts may be present on the upper eyelids, extending down the side of the body from the ear to the hind limb.

distribution

Endemic to the Iberian Peninsula; inhabits the southwestern and central parts of this region, including southern Portugal and much of Spain.

habitat

The Iberian midwife toad is usually found in dry habitats with sandy soils. In the southern part of its distribution, it inhabits

wetter environments, particularly near small, temporary streams.

behavior

These frogs are nocturnal, spending most daylight hours hiding in burrows they dig in sandy soils.

feeding ecology and diet

Iberian midwife toads actively forage at night for small insects and crustaceans, including flies, grasshoppers, moth larvae, weevils and other beetles, and ants. To a lesser extent, they may also prey on isopods, spiders, and snails.

reproductive biology

This species is particularly known for the care that males give to their offspring. Between September and March, males call for several hours during the night. Females respond, but with a weaker call. Mating begins when the male grabs the female around the waist. After some time, the female ejects an egg mass. The male then releases his lumbar grip, takes hold of the female around the chest, and inseminates the eggs. After 10–15 minutes, the male uses his legs to wrap the egg mass around his ankles. A male can mate again, and can carry up to four egg clutches around his legs (as many as 180 eggs). Females can breed up to four times per season.

The eggs nearly double in size as they mature, likely because of water absorption. Males prevent drying of the eggs by resting in moist areas or wading in waters. When the eggs are ready to hatch, the male enters shallow water to deposit the larvae. Larvae metamorphose after 110–140 days of development; sexual maturity is not reached for at least two years.

conservation status

Not threatened. This species is fairly common throughout most of its range. However, in a few areas in Spain, populations are in decline owing to the destruction of forest habitats.

significance to humans

None known.

Midwife toad

Alytes obstetricans

taxonomy

Bufo obstetricans Laurenti, 1768, France. Three subspecies are recognized.

other common names

French: Crapaud accroucheur, alyte accoucheur; German: Geburtshelferkröte, Glockenfrosch; Spanish: Sapo partero común.

physical characteristics

Midwife toads are generally small and squat, with large heads. The average body size for both males and females is 2.17 in (55 mm). As in other midwife toads, the large eyes have a vertical, slit-shaped pupil. Small parotoid glands are present behind the eardrum. Warts are present on the skin, which may be spotted with black, brown, olive, or green. A row of large, reddish warts extends from behind the eardrum to the hind limb. The palm of the forelimb has three bumps (metacarpal tubercles). The underside is off-white, and the throat and the chest may be spotted with gray.

distribution

Alytes obstetricans occurs in eight European countries: Portugal, Spain, France, Belgium, the Netherlands, Luxembourg, Germany, and Switzerland. The distribution of the species clearly follows the habitat differences between the mountainous regions of Central Europe, where it is present, and the plains extending to the North Sea, where the species is absent. For this reason, it is absent from the coast of Belgium and most of the Netherlands.

habitat

Midwife toads prefer permanent bodies of water, such as ponds and streams, because larvae often overwinter. The type of water may vary by region, but these toads generally avoid fast-moving waters. On land, they are generally found hiding in moist, warm, sandy or loose soils with little vegetation; but they are also found under gravel, stone walls, embankments with small stones, and large stone slabs.

behavior

As with other midwife toads, their most interesting behaviors have to do with reproduction and parental care by males. These frogs are nocturnal, and spend most of the daylight hours hiding in burrows.

feeding ecology and diet

Midwife toads have a diet similar to that of other toads. They actively forage at night, mostly for insects, arthropods, isopods, and snails.

reproductive biology

As with other toads in the genus, males care for the eggs by attaching them to their legs during amplexus and carrying them until they eggs hatch. The mating season varies with climate, males carry eggs from beginning of February in some areas, but not until late March in others.

Generally, males call only at night, but may call from their hiding places during the day. Amplexus and fertilization are similar to that of other midwife toads, but males have been reported to stimulate ovulation by scratching the female with the toes of their hind limbs.

Males carry up to 150 eggs (from three different females) until they hatch, about three to six weeks after breeding. Larvae overwinter and metamorphose the following year.

conservation status

Although not threatened according to the IUCN, this species is in decline in several areas, including the northernmost portions of its distribution, where several populations have disappeared entirely. The primary cause of population declines seems to be habitat destruction and alteration.

significance to humans

None known.

Painted frog

Discoglossus pictus

taxonomy

Discoglossus pictus Otth, 1837, Sicily. Three subspecies are recognized.

other common names

French: Discoglosse peint; German: Gemalter Scheibenzüatngler; Spanish: Sapillo pintojo.

physical characteristics

Painted frogs have stout bodies with flat, wide heads, and their pupils are shaped like upside-down teardrops. Average body size is 2.76–3.15 in (70–80 mm). They are quite colorful (as the common name implies), and vary from having large dark spots with bright edges, two dark brown bands, or a band along the back and two along the sides. They may also have longitudinal glands on the back.

distribution

Mediterranean Africa in Tunisia, northern Algeria, and Morocco; Sicily (Italy), Malta, and Gozo (Ghawdax); one subspecies introduced to France and Spain.

habitat

Painted frogs seem to prefer human-made habitats, including orchards and vineyards, stone-sided cisterns, irrigation pipes and canals in cultivated areas, campsites, and cattle tracks filled with water. They can also be found near small brooks, as well as in holes they dig under stones. One subspecies lives and breeds in brackish water.

behavior

Most of the knowledge of this species has been acquired from studies of the introduced populations and regards their reproductive behavior. They are primarily nocturnal, and excavate small, flat burrows under stones to use as refugia.

feeding ecology and diet

Painted frogs actively forage at night for insects and other invertebrates.

reproductive biology

Mating season occurs from January to early November. Males clasp females in the lumbar region, and after 35 seconds to two hours, depending on the subspecies, females will lay up to 50 eggs. Females mate with several males consecutively, laying up to 1,000 eggs in one night. The eggs have no common jelly coating, and form a loose mass on the water surface, or sink to the bottom. Eggs usually hatch within six days of mating, and in one to three months, tadpoles metamorphose. Adulthood is reached after one year.

conservation status

Not threatened. However, in Europe, populations that live in or near agricultural habitats appear to be in decline because of the loss of farmlands. Those living near rivers and seasonal ponds seem to be less threatened. Populations in France are protected, and several in northern Africa are endangered.

significance to humans

None known.

Tyrrhenian painted frog

Discoglossus sardus

taxonomy

Discoglossus sardus Tschudi, 1837, Sardinia. No subspecies recognized.

other common names

English: Sardinia painted frog; French: Discoglosse sarde; German: Sardischer Scheibenzüatngler.

physical characteristics

This is a small, squat frog that can be dark brown, dark gray, reddish, or red-brown, with or without dark brown spots. Average body size is 2.76–3.15 in (70–80 mm).

distribution

These frogs are restricted to Sardinia, Corsica, and several small islands of the Tyrrhenian Sea. They are also found on the Italian mainland on the small peninsula Monte Argentario (Tuscany).

habitat

These frogs occur in a variety of habitats, including open, windy, desolate coastlines and coniferous forest streams. They prefer stagnant water or slow-running brooks, but have also been found in slightly brackish waters.

behavior

What is known seems to be similar to that of other frogs in the genus.

feeding ecology and diet

Insects and other invertebrates make up most of the diet of these frogs.

reproductive biology

Reproduction seems to be similar to that of other frogs in the genus. Females lay eggs in small clumps or singularly on the bottom of a stream or on or near aquatic vegetation.

conservation status

Not threatened. However, because populations are so small, the species may be at greater risk of decline owing to habitat destruction and fragmentation.

significance to humans

None known.

Resources

Books

Crespo, E. G. Contribuição para o conhecimento da Biologia dos Alytes ibéricos, Alytes obstetricans Boscai Latase, 1879 e Alytes cisternasii Boscá, 1879 (Amphibia-Salientia):—A Problemática da Especiação de Alytes cisternasii. Ph.D. Dissertation, Universidade de Lisboa, 1979.

Duellman, William. E., and Trueb, Linda. Biology of Amphibians. Baltimore: Johns Hopkins University Press, 1994.

Garcia Paris, Mario. Los Anfibios de España. Madrid: Ministerio de Agricultura, Pesca y Alimentacion, 1985.

Gasc, Jean-Pierre, et al., eds. Atlas of Amphibians and Reptiles in Europe. Paris: Societas Europea Herpetologica and Muséum National d'Histoire, 1997.

Herrmann, Hans-Joachim. Terrarien Atlas Band 1. Melle, Germany: Mergus Verlag GmbH, 2001.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology. 2nd edition. San Diego: Academic Press, 2001.