Bioacoustics of Boehmantis microtympanum

Habits. This large and crepuscular­nocturnal frog usually stations upon large stones and boulders along streams, and is usually not found more than a few meters away from the water. When disturbed it jumps in the water, splashing upon the water surface until it reached other emergent objects. Smaller individuals are able to skitter more rapidly on the water surface, like M. lugubris . In no case we observed this species diving in the water, differently from M. grandidieri and M. guttulatus . Acoustic behaviour is unknown for this species. Mantidactylus microtympanum was observed preying upon Boophis luteus ( Andreone & Randriamahazo 1997 ) . In captivity at the Parc Botanique et Zoologique de Tsimbazaza (Antananarivo), some individuals were fed with live Ptychadena mascariensis and Mantidactylus alutus . This batrachophagy was confirmed by the analysis of a preserved female (MNHN 1972–1316), 86 mm long, which had in its stomach in addition to remains of a coleopteran and a freshwater crustacean a still intact (but with skin mostly digested) microhylid frog (likely a Plethodontohyla bipunctata ), 27 mm long. During a study on the population density of the species (Andreone 1998), no evident interaction or territorial behaviours were observed. The individuals seem to be mostly sedentary, using a cavity under a rock in the stream as refuge. The secondary sex­ratio did not differ significantly from the expected 1: 1 ratio. A population of 79 individuals was estimated over a surface of about 800 m ². The mean longevity was of 4.1 1.1 years in males, and 4.9 0.9 years in females, with a maximum life span of 7 years ( Guarino et al. 1998 ). Sexual dimorphism. Males are usually smaller than females. The range of SVLs in males is 40.60–64.22 mm (mean ± SD = 52.9 ± 5.6 mm ), and 61.57–96.20 mm in females (75.8 ± 10.8 mm ). These values (obtained from the measured preserved specimens) are comparable to those previously provided for live specimens by Andreone (1998) and Andreone & Guarino (1998) , although in the latter cases the sex was quite uncertain due to its determination in the field. Furthermore, the size ranges in the females in quite wide, being the smallest females about 65% of the largest one. This is due to the fact that it was not always possible to establish with certainty the status of gonadal maturation, and for this reason it is likely that some of the measured females fell within the juvenile category. In terms of other characters allowing to distinguish the sexes, it is remarkable that in this species too the cloaca is dimorphic. Differently from M. microtis (in which the males have a more derived cloaca), in M. microtympanum females have a tubular cloaca directed downwards, whereas males usually have a simple terminal cloaca with a slit. Similar species . M. microtympanum is similar to M. microtis in general morphology and frequented habitats (see above). For size and general habitat requirements it is externally similar to M. grandidieri and M. guttulatus . It differs from the latter two species in lacking femoral glands and having larger digital expansions and no marblings on the lower surface of the thighs. Juveniles are similar in colouration, general morphology, and behaviour to M. microtis and M. lugubris . While M. lugubris usually prefers vertical walls to adhere and for laying eggs, M. microtympanum rests and lays eggs on horizontal surfaces.