Mantidactylus microtympanum Angel, 1935

Andreone, Franco & Nussbaum, Ronald A., 2006, A revision of Mantidactylus microtis and M. microtympanum, and a comparison with other large Madagascan stream frogs (Anura: Mantellidae: Mantellinae), Zootaxa 1105, pp. 49-68 : 57-63

Mantidactylus microtympanum Angel, 1935

( Figs. 5–11 )

Materials examined. MNHN 19735­170/171, Isaka­Ivondro, syntypes, R. Catala I.1935; MNHN 1972­601, 602, Mananjara­Bekaza, leg. Ch. P. Blanc, 10.VII.1971; MNHN 1972­ 1256 Ambana­Soavala (Chaînes Anosyennes), leg. Ch. P. Blanc, 3.XII.1971; MNHN 1972­1257/1316 Camp IV (Chaînes Anosyennes), leg. Ch. P. Blanc, XI.1971; MNHN 1972­1317/1318, Bekazaha (Chaines Anosyennes), leg. Ch. P. Blanc, XII.1971; MNHN 1994­689, eggs, Chaînes Anosyennes; MNHN 1994.690 (tadpole), Chaînes Anosyennes, MRSN A649.1–5; forest between Isaka­Ivondro and Eminiminy, leg. R. Nincheri, 25–31.VIII.1993; MRSN A724.1–2, forest between Isaka­Ivondro and Eminiminy, leg. F. Andreone, 18.IV.1994; MRSN A774, same locality and collector, 17.IV–4.V.1994; MRSN A1653.1–3, same locality and collector, 8.V.1994; MRSN A117.1–3; same locality and collector, 8.XI.1994; MRSN A753, same locality and collector, 9.V.1994 (eggs laid at the Parc Botanique et Zoologique de Tsimbazaza); MRSN A5262, Mandena, “domaine de la cascade”, Fort Dauphin, leg. F. Andreone & G. Aprea, 25.XII.1997; UMMZ 197934, Andohavola 12 km N of Tolagnaro, leg. C. J. Raxworthy, 18.IX. 1990; UMMZ 197935, Manantantely Forest, leg. R. A. Nussbaum, C. J. Raxworthy, A.P. Raselimanana & J. B. Ramanamanjato, 1.XI.1990; UMMZ 197939, same locality and collectors, 9.XI.1990; UMMZ 197943, same locality and collectors, 10.XI.1990; UMMZ 197941–197942, same locality and collectors, 11.XI.1990; UMMZ 197944, same locality and collectors, 12.XI.1990; UMMZ 197953–197954, UMMZ 214118, same locality and collectors, 30.X.1990 (skeleton) Nahampoana Forest, same collectors, 21.XI.1990; UMMZ 197955–197957, Ampamakiesiny Pass, leg. C. J. Raxworthy & A.P. Raselimanana & J. B. Ramanamanjato, 18.XII.1990; UMMZ 197958, same locality and collectors, 20.XII.1990; UMMZ 197959, same locality and collectors, 21.XII.1990; UMMZ 198933, same locality and collectors, 22.XII.1990, (tadpole and eggs); UMMZ 197966–197970, Manongotry, leg. C. J. Raxworthy & A. P. Raselimanana & J. B. Ramanamanjato, 3.I.1991; UMMZ 197971, same locality and collectors, 4.I.1991; UMMZ 213221–213223 Anosy Mountains of Andohahela, 4 Km N of Ankaramena, Antsoroko River, 50–200 m, leg. R. A. Nussbaum, 30.V.1993, UMMZ 214593, leg. A. P. Raselimanana & J. B. Ramanamanjato, 20.X.1995, Andohahela RNI 11, Parcel 1, 8 km NW of Eminiminy, 400 m; UMMZ 214594, same locality and collectors, 420 m, 22.X.1995; UMMZ 214595–214596, Andohahela RN 11, Parcel 1, NW of Eminiminy at Andranomintilina Cascade, leg. A. P. Raselimanana & J. B. Ramanamanjato, 28.X.1995; UMMZ 214597–214599, Andohahela RN 11, Parcel 1, NW of Eminiminy at Andranomintilina Cascade, leg. A. P. Raselimanana & J. B. Ramanamanjato, 28.X.1995; UMMZ 214600, Andohahela RN 11, Parcel 1, 13.5 Km NW of Eminiminy, 1120 m, leg. A.P. Raselimanana & J. B. Ramanamanjato, 13.XI.1995; UMMZ 217631, Marosohy Forest, Andranoroa Rivers waterfall, 725 m, leg. C. J. Raxworthy, 23.XI.1989; UMMZ 217632, Marosohy Forest, Andranoroa River, 290 m, leg. R A. Nussbaum, 26.XI.1989; UMMZ 217633, Marosohy Forest, Andranoroa River, 725 m, leg. R. A. Nussbaum & C. J. Raxworthy, 28.XI.1989.

Diagnosis. A large brook Mantidactylus , reaching around 100 mm SVL ( Tab. 1 and Andreone 1998). Fingers with wide sub­triangular expansions. Toes with dilatations smaller than fingers. Finger and toe expansion white. No webbing between fingers, feet completely webbed. Femoral glands absent. Sub­articular tubercles small, inner metatarsal tubercle present and longish. Outer metatarsal tubercle absent. Vomerine teeth present. Tympanum rather indistinct, about 1/4 of eye diameter. Tibiotarsal articulation of appressed hindlimb may reach as far forwards as nostrils. Skin finely granular on dorsum, smoother on belly. Nostrils nearer to tip of snout than to eye. Cloaca simple to tubular. Dorsal surface marbled grayish and brownish, with greenish shades. Ventral surface white with dark spots, spotting denser on throat. Eyes large and prominent, with golden iris, and a sub­horizontal pupilla. Upper lip and surrounding parts of eye with whitish spots. This colouration extends to lower flanks. Iris brownish­copper with fine blackish spots. The finger and toe tip expansions are whitish. Juveniles similar to adults in colouration, but more contrasted.

Distribution. (1) Isaka­Ivondro (TT); (2) Ambana­Soavala; Ampamakiesiny Pass; (3) Andohahela RN 11, Parcel 1, 13.5 Km NW of Eminiminy; (4) Andohahela RN 11, Parcel 1, NW of Eminiminy at Andranomintilina Cascade; (5) Andohahela RNI 11, Parcel 1, 8 km NW of Eminiminy; (6) Andohahela, RN 11, Parcel 1, between Isaka­Ivondro and Eminiminy; (7) Anosy Mountains of Andohahela, 4 Km N of Ankaramena; Antsoroko River; (8) Bekazaha; (9) Mandena, “domaine de la cascade”, next to Fort Dauphin; (10) Chaînes Anosyennes; (11) Manantantely; (12) Manongotry; (13) Marosohy; (14) Nahampoana. Altitude range: 50–1120 m a.s.l.

Eggs and tadpoles. Eggs collected at Isaka­Ivondro within a small pool in a depression on a stone (MRSN A752 and A757) are attributed to M. microtympanum based on close similarity in morphology, colouration, and size to those laid in captivity (MRSN A753), and others taken in nature currently held at Paris (MNHN 1994­689/690). They are small (mean diameter of about 2 mm, with the jelly capsule about 6.5 mm), and whitish ( Andreone & Randriamahazo 1997). The dissection of one female (MNHN 1972­1316) revealed 373 eggs, and another female (UMMZ 197941) 320 eggs: a subsample of them (n = 47) yielded a mean diameter of 2.1 ± 0.3 mm. Tadpoles tentatively attributed to M. microtympanum are housed in Paris (MNHN 1994­689/690) and Ann Arbor (UMMZ 128933). We also found much similar tadpoles at Andohahela (MRSN A 752), in the same small depression full of water where we collected eggs (MRSN A757). We are confident that the tadpoles belong to M. microtympanum , since no other Mantidactylus was seen to live within the stream (excepting M. lugubris , that has a very specialised tadpole: see Glaw & Vences 1994). The putative tadpoles attributed to M. microtympanum are of the benthic type ( McDiarmid & Altig 1999), and have a typical ranoid form. The body is elliptical in lateral and ovoid in dorsal view. The snout is dorsally rounded, while in lateral view it slopes gently to the oral region and then turns strongly. The external nares are located dorsolaterally, almost half way from eyes to snout tip. The eyes are small and directed dorsally. The tail fins are low and of about equal height; while the dorsal fin are lower than the ventral at the plane of the vent tube. The origin of dorsal fin is a little before the tailbody junction and origin of ventral fin at the posterior ventral terminus of the body. The maximum tail height is reached at the middle of the tail. The tail tip is slightly pointed with the tail muscle almost reaching the tip of the fins. The spiracle is sinistral, with a midlateral opening directed posteriorly. The vent tube is parallel to the ventral margin of the fin, tubular in shape, and displaced dextrally with a medial aperture. The oral disc is anteroventral, sub­elliptical, with a uniserial row of marginal papillae in the lower labium and on the lateral side of the upper labium. The labial tooth row formula is 4(2–4)/3. Basing upon the sample MRSN A761, represented by 12 tadpoles at Gosners (1960) stage 25, the overall measuration are as follows: total length 23.9 ± 2.8 mm (range 20.0– 28.3 mm), body length 9.8 ± 1.3 mm (range 7.5–11.9 mm), tail height 4.4 ± 0.6 mm (range 3.4–5.2). In life, the tadpoles are uniformly brownish and speckled with some sparse melanophores, more dense in the dorsal and lateral posterior part of the body. The tail fins are transparent, scattered with dark spots, especially on the dorsal fin. After about ten years of preservative the tadpoles are brownish on the body, while the muscular part of the tail is whitish.

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.

Figures

FIGURE 5. Mantidactylus microtympanum. Live individual from Parc National d’Andohahela, between Isaka­Ivondro and Eminiminy (photo by F. Andreone).

FIGURE 6. Mantidactylus microtympanum: Live juvenile from Parc National d’Andohahela, between Isaka­Ivondro and Eminiminy (TL = 50 mm) (photo by F. Andreone).

FIGURE 7. Mantidactylus microtympanum. Preserved specimens from Parc National d’Andohahela, between Isaka­Ivondro and Eminiminy, 400 m. (MRSN A 649): (A) dorsal side, (B) ventral side.

FIGURE 8. Details of the cloaca in a Mantidactylus microtympanum: A, male (MNHN 1972 ­ 1312); B, female (MNHN 1972 ­ 1274). The arrow indicates the tubular cloaca visible in most adult females.

FIGURE 9. Eggs of Mantidactylus microtympanum photographed in the field between Isaka­ Ivondro and Eminiminy, Andohahela (MRSN A 752).

FIGURE 10. Eggs of Mantidactylus microtympanum laid in captivity by individuals collected between Isaka­Ivondro and Eminiminy, Andohahela (MRSN A 753).

FIGURE 11. Putative tadpole of Mantidactylus microtympanum. (MRSN A 761), collected between Isaka­Ivondro and Eminiminy, Andohahela: A, lateral side; B, dorsal side (TL = 28 mm).