Burrowing behavior of the midwife toads Alytes cisternasii and Alytes obstetricans (Anura, Discoglossidae)

The European midwife toads Allies cisternasii and Alytes obstetricans are fossorial anurans that primarily use their forelimbs in burrowing. The maneuverings are quite dexterous and the forelimbs are used alternately or sometimes synchronously. The fingers (particularly III and IV) are oriented downward and scraped into the substrate. Occasionally the head is pushed into the substrate or acts in a scoop-like manner. The toads construct a system of tunnels and cavities underground. They do push-ups packing the substrate against the top of the tunnel with their head. The toads also vocalize and form aggregations (2-5 individuals) underground suggesting social interactions. The two species are quite similar in motor patterns of forward burrowing. However, A. cisternasii makes minimal use of its hind limbs (only for bracing), whereas A. obstetricans actively uses its hind limbs to kick soil posteriorly that was brought to the surface by the forelimbs. Also, A. cisternasii is a rapid, efficient forward burrower that is highly fossorial, whereas A. obstetricans is a reluctant forward burrower that lingers on the surface and prefers pre-existing holes. Differences in burrowing behavior of the two species are correlated with differences in morphology and habitats occupied. In four instances in which the burrowing of male A. obstetricans carrying eggs was studied, no differences were observed in motor patterns from other adults not carrying eggs. Kicking of the hind legs was carried out in a manner that assured the egg masses were not damaged. It is probable that the main reason forward burrowing evolved in Alytes was to assure subsurface concealment because of the involvement of the male's hind limbs in parental care.