940.
Common midwife toad
(Alytes obstetricans)
LC
Overview
The common midwife toad is in fact a warty frog, and spends most of its time on land.  Its warts produce a potent poison to protect itself from would-be predators, and it is nocturnal and lives in burrows to avoid drying out.  It is named after its unusual breeding behaviour, in which the males carry strings of eggs wrapped around their hind legs for several weeks, keeping them moist until ready to hatch.  Midwife toads began to evolve independently of all other modern day species about five million years before birds appear in the fossil record.  The common midwife toad has a wide range in Europe but, like so many other amphibian species, has suffered population extinctions at the hands of the devastating chytrid fungus.
Urgent Conservation Actions
Distribution
Europe.
Evolutionary Distinctiveness
Order: Anura
Family: Alytidae
The Alytidae are an ancient family found in Europe, the Middle East and northwestern Africa, and comprise the midwife toads (Alytes) and painted frogs (Discoglossus).  Overall, this family is now named after the midwife toads.  The family name was formerly Discoglossidae or ‘disc-tongued frogs’ because, unlike the slender tongues of many amphibians, midwife toads and painted frogs possess a round and flattened tongue.  They diverged from all other amphibians about 210 millions years ago at the end of the Triassic period, around the same time that the first primitive mammals started to appear.  The midwife toad family therefore evolved at the feet of some of the earliest dinosaurs, and survived the dinosaur’s demise nearly 150 million years later.

Within the family Alytidae, the midwife toads diverged from their closest relatives, the painted frogs, about 155 million years ago, about 5 million years before the first birds started to appear in the fossil record.  Midwife toads are therefore more different from their closest relatives than kangaroos are to elephants, as they started to evolve independently about 10 million years before the common ancestor of these two mammal groups.

There are just five species of midwife toad surviving today.  The common midwife toad has considerable morphological and genetic diversity.  This complicates attempts to specify how long ago it diverged from its closest relatives, but it is thought to have diverged from all other living species between 5 and 10 million years ago.  The sub species Alytes obstetricans almogavarii was isolated for many millions of years forming its own lineage, but later hybridised with A. obstetricans and the lines merged.  This may explain the high level of genetic diversity and ability to withstand a range of environments seen in the modern species.
Description
Midwife toads are in fact frogs with stout bodies and toad-like warty skin.  They have short, unwebbed fingers and long toes which are webbed at the base.  Their eyes are large, with vertical slit-shaped pupils.

The common midwife toad has large warts on the underarms, ankles and in a row from the tympanum (ear drum) to the groin area, often reddish in colour.  Body colouration varies from pale to brownish with small black dots, brown dots, olive or green spots, with spots of grey on the throat and chest.

Males grow up to 42mm in total length, whilst females are larger and can reach 50mm.  The size difference between males and females of this species is not larger than that seen in other species of anurans (frogs and toads) which do not display male parental care, discrediting the theory that their smaller size is a result of a reduction in sexual selection amongst males, as the maximum number of mates for any one male is limited due to this behavioural trait.
Ecology
Midwife toads are nocturnal and highly terrestrial, living in water only as tadpoles.  To prevent themselves from drying out, common midwife toads dig into the soil and bury themselves, or hide in crevices or under logs.  This species prefers to use pre-existing holes, but can use its forelimbs to scrape away the sandy soil and its head to scoop it out of the way.  Once underground, they do push-ups to pack the soil above them into the roof of the tunnel. 

Males call out to nearby females for several hours every night during breeding season.  Females call back in response (unusual amongst the frogs and toads), and seek out the male of their choice.  Competition between males is strictly non-aggressive and occurs only during the vocalisation stage; females prefer the males whose calls are most frequent.

A female will then present herself to a male by positioning herself in front of him, at which point the male will mount the female and clasp her around the waist.  The male then uses a series of rocking body movements to prepare the female for ovulation, and then squeezes her sides causing her to release her eggs all at once.  The female bends her hind limbs and presses her heels together and against her body to form a cup-shaped receptacle, into which a string of eggs is ejected.  The male then fertilises the eggs.  This method of sudden egg release and fertilisation is another adaptation to terrestrial life and conservation of water.

Once fertilised, the male moves his hind limbs through the sting of eggs, tangling it around his ankles.  He carries the eggs for three to six weeks, keeping them moist by visiting pools of water, and discards them into a water body as the larvae hatch into tadpoles.  Males can breed with more than one female per season, carrying up to three clutches of eggs around their legs, collecting a total of 150 eggs or more.  The emergent tadpoles grow from 15mm up to 80mm in length, before metamorphosing into toadlets the next year.

Aside from their highly unusual breeding behaviour, midwife toads are also known for having a powerful defence mechanism against potential predators.  The warts on their back produce a strong-smelling toxin when the toad is threatened, with enough potency to kill an adder (a venomous snake) in a matter of hours.
Habitat
This species of midwife toad can tolerate a range of environments, making it much more adaptable than other species.  It is known to inhabit temperate forests, semi-arid areas, walls, embankments, slopes with small stones and sparse vegetation, modified habitat such as traditional agricultural land and even urban areas, and has been found at elevations up to 2,000 metres above sea level.  Aquatic environments are required for breeding only, but again these can range from slow moving rivers, ponds and pools to gravel and clay pits.
Distribution
The common midwife toad is native to Belgium, France, Germany, Luxembourg, The Netherlands, Portugal, Spain and Switzerland.  Its range extends from the northern half of Portugal and Spain, through France, to southern Belgium, southeastern Netherlands, Luxembourg, western and north-central Germany, and western and northern Switzerland.  There is thought to be at least one established population in the UK, where it is an introduced species.
Population Estimate
The IUCN Red List of Threatened Species reports that the common midwife toad population is in decline and has become extinct in some localities, but that it is still common in many areas.  Populations in Portugal and Spain are said to be very fragmented, and coastal populations west of Lisbon are now extinct.
Population Trend
Decreasing.
Status
This species has been listed under the Least Concern category in the 2006 IUCN Red List of Threatened Species.  It has a wide distribution and can tolerate a range of habitats, unlike other species of midwife toad.
Threats
As with so many amphibian species, several local declines of A. obstetricans have been documented and attributed to disease.  Chytridiomycosis is caused by a fungal parasite and has had devastating effects on amphibian species across several continents, causing sudden, mass mortalities in populations naïve to the fungus.  There is much debate about the origin of the chytrid fungus (Batrachochytrium dendrobatidis), one theory hypothesising that it could have always been globally present but that recent environmental change has caused it to have more catastrophic effects on amphibian species, and another proposing that the fungus originated in Africa and has been spread across the globe by man.  Populations of A. obstetricans in protected areas of central Spain have been affected by the fungus, some having disappeared completely.

Mortalities resulting from ‘red-lung disease’ and iridovirus have also been reported, the latter having been transferred to Carris Lake in Peneda-Gerês National Park, Portugal via the introduction of a non-native fish species, the pumpkinseed.  This species also predates on the common midwife toad, as do other introduced predatory fish, causing further decline.

Loss of habitat is also affecting A. obstetricans, especially in areas of agricultural development.  The fragmentation of populations in Spain and Portugal is a further threat to the species.
Conservation Underway
A. obstetricans is listed as ‘strictly protected’ in EU legislation (under Appendix II of the Bern Convention and Annex IV of the Natural Habitats Directive), and is also protected by national legislation in many of the countries constituting its native range.  It is thought to occur in a number of protected areas.
Conservation Proposed
The IUCN Red List of Threatened Species calls for further research into the current decline, particularly into the impacts of disease.
Links
AmphibiaWeb           http://amphibiaweb.org/

Global Amphibian Assessment       http://www.iucnredlist.org/amphibians

Midwife Toad             http://en.wikipedia.org/wiki/Midwife_toad

Tree of Life Web Project      http://tolweb.org/tree/
References
Amphibiaweb: Information on amphibian biology and conservation [web application]. 2008. Berkeley, California: AmphibiaWeb. Available: http://amphibiaweb.org/. Accessed: 22 December 2008.

Behler, J. L. and Behler, D. A. 2005. Frogs: A Chorus of Colours. Sterling Publishing, USA.

Bosch, J., Beebee, T., Schmidt, B., Tejedo, M., Martínez-Solano, I., Salvador, A., García-París, M., Gil, E. R., Arntzen, J. W., Paniagua, C. D. and Marquez, R. 2006. Alytes obstetricans. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 22 December 2008.

Brown, L. E., Crespo, E. G. 2000. Burrowing behaviour of the midwife toads Alytes cisternasii and Alytes obstetricans (Anura, Discoglossidae). Alytes 17(3-4): 101-113.

Fromhage, L., Vences, M. and Veith, M. 2004. Testing alternative vicariance scenarios in Western Mediterranean discoglossid frogs. Molecular Phylogenetics and Evolution 31: 308-322.

Frost, D. 2008. Amphibian Species of the World: an Online Reference. Version 5.2 (22 December 2008). Electronic Database accessible at: http://research.amnh.org/herpetology/amphibia/index.php. American Museum of Natural History, New York, USA.

Halliday, T. and Adler, K. 2002. The New Encylopedia of Reptiles and Amphibians. Oxford University Press , UK.

Johnson, M. L. and Speare, R. 2005. Possible modes of dissemination of the amphibian chytrid Batrachochytrium dendrobatidis in the environment. Diseases of Aquatic Organisms 65: 181-186.

Martinez-Solano, I., Goncalves, H. A., Arntzen, J. W. and Garcia-Paris, M. 2004. Phylogenetic relationships and biogeography of midwife toads (Discoglossidae: Alytes).  Journal of Biogeography 31(4): 603-618.

Marquez, R., Bosch, J. and Xavier, E. 2008. Intensity of female preference quantified through playback setpoints: call frequency versus call rate in midwife toads. Animal Behaviour 75(1): 159-166.

Marquez, R., Esteban, M. and Castanet, J. 1997. Sexual size dimorphism and age in the midwife toads Alytes obstetricans and A. cisternassi. Journal of Herpetology 31(1): 52-59.

Marquez, R. and Verrell, P. 1991. The courtship and mating of the Iberian midwife toad Alytes cisternasii (Amphibia: Anura: Discoglossidae). Journal of Zoology 225: 125-139.

Roelants, K., Gower, D. J., Wilkinson, M., Loader, S. P., Biju, S. D., Guillaume, K., Moriau, L. and Bossuyt, F. 2007. Global patterns of diversification in the history of modern amphibians. PNAS 104(3): 887-892.

Stuart, S. N., Hoffmann, M., Chanson, J. S., Cox, N. A., Berridge, R. J., Ramani, P. and Young, B. E. (eds.) 2008. Threatened Amphibians of the World. Lynx Edicions, Barcelona, Spain; IUCN, Gland, Switzerland; and the Conservation International, Arlington, Virginia, USA.

Tree of Life Web Project. 2008. Alytes. Version 25 November 2008 (temporary). http://tolweb.org/Alytes/17056/2008.11.25 in The Tree of Life Web Project, http://tolweb.org/

Weldon, C., du Preez, L. H., Hyatt, A. D., Muller, R. and Speare, R. 2004. Origin of the Amphibian Chytrid Fungus. Emerging Infectious Diseases 10(12): 2100-2105.

Distribution dataset:  IUCN 2008. 2008 IUCN Red List of Threatened Species. http://www.iucnredlist.org

if you can provide new information to update this species account or to correct any errors, please email us at info@edgeofexistence.org


Forum comments

There are as yet no comments for this species.

Add a comment

You must log in to post. If you don't have a login, it's easy to register.