Bioacoustics of Blommersia variabilis

Etymology. The species name variabilis is an adjective referring to the remarkable variation observed in various characters of this new species, especially in the separation or connection of the lateral metatarsalia which otherwise is considered to be a very stable character within species of mantellids. Natural history. At the type locality in the vicinities of Ambodivoahangy village, B. variabilis was common outside of the forest in cultivated landscape. It was not seen or heard within primary or selectively logged forest. Calling males were observed in dense secondary vegetation on the borders of partially inundated ricefields, about 30 cm to 1 m off the ground. The male holotype was discovered while calling within a dense bush at the edge of a rice field. During the day specimens were difficult to find, hiding underneath the leaves of plants. Calling was most frequent in the evening and at night, but was also occasionally heard during the day, especially after rains. Calls were often intermingled with choruses of Aglyptodactylus sp., Guibemantis cf. kathrinae and Ptychadena mascareniensis . At Maroantsetra it is a common species living in ditches covered by dense vegetation within the town itself. Near Voloina we heard and collected the species in flooded areas in a mosaic of rice paddies, shrubs, and remains of primary rainforest. A single clutch of eggs deposited on the surface of a leaf was discovered within the village of Ambinanitelo on 1 April 2010 . Mating in this species takes place on a leaf usually overhanging lentic water and has been observed by us in Voloina. As in other Blommersia , the male and female sit vertically on a leaf, the male on top of the female with his legs extending over the female’s dorsum ( Glaw & Vences 1994 ). Vocalization. The advertisement call of B. variabilis ( Fig. 6 ) was recorded at the type locality (Ambodivoahangy) on 3 April 2010 at an estimated air temperature of 26°C. It consists of a series of short inharmonious notes, repeated at regular intervals in fast succession with a repetition rate of approximately 7.4 notes/second. Each call is composed of 3–6 notes, whereas in most cases a long call is followed by a shorter call containing fewer notes, in combination resulting in a call series with two calls. Within these call series, the interval between first and second call ranges between 500 and 720 ms. Within calls, the initial note is longer and contains more pulses than subsequent secondary notes. Numerical call parameters are as follows: call duration 344–887 ms (532 ± 219; n = 9); note duration 54–223 ms (107 ± 48; n = 23); pulses/note 3–14 (6.4 ± 3.0; n = 23); inter-note interval 21–33 ms (26.7 ± 3.2 ms; n = 19). Overall frequency is distributed in a broad band from app. 2000–6500 Hz, with a dominant frequency at around 5100 Hz. Calls were repeated at irregular intervals. Similar calls were recorded in 1991 in Maroantsetra, but due to the poor quality of the recordings we refrain from a detailed analysis. Detailed call data for various populations of B. galani , B. dejongi , and B. wittei are presented in Vences et al . (2010). In comparison, the call of B. variabilis differs from that of B. wittei by longer note duration, shorter internote intervals and a lower note repetition rate. Calls of B. galani differ from those of B. variabilis by shorter notes and much longer inter-note intervals. In calls of B. dejongi , notes are barely spaced and partly fused and separate pulses within notes are unrecognizable.

Diagnosis. Assigned to the genus Blommersia in the Mantellidae by a combination of (1) presence of intercalary elements between ultimate and penultimate phalanges of fingers and toes (verified by external examination), (2) presence of femoral glands and absence of nuptial pads in males, (3) presence of a moderately distensible, inconspicuously coloured single subgular vocal sac in males, (4) small size (adult SVL < 25 mm ), (5) semiarboreal habits and calling behaviour from vegetation above stagnant water. Among species of Blommersia , B. variabilis is distinguished from B. blommersae by vomerine teeth present (vs. absent); from B. domerguei by different colouration (absence of light brown dorsum with dark longitudinal markings) and vomerine teeth present (vs. absent); from B. grandisonae by different colouration (absence of distinct black lateral line ventrally bordered by white, vs. presence) and vomerine teeth present (vs. absent); from B. kely by larger size (male SVL 19–25 mm vs. 14–16 mm ) and vomerine teeth present (vs. absent); from B. sarotra by larger size (male SVL 19–25 mm vs. 15–17 mm ) and vomerine teeth present (vs. absent); from B. angolafa by colouration (absence of uniformly brownish dorsal colour with white dots) and vomerine teeth present (vs. absent). The new species is morphologically most similar to B. wittei from which it mainly differs by the wider distance between inner margins of femoral glands (FGD 2.8–4.5 mm vs. 1.6–2.0 in the type series of B. wittei ; see Vences et al. 2010; FGD 12–20% of SVL vs. 7–9%), connected metatarsalia in most specimens (vs. always separated by webbing), and advertisement calls consisting of a short series of 3-6 notes of a mean duration of 107 ms and a mean inter-note interval of 27 ms (vs. longer series of up to 25 notes with a mean duration of 23-46 ms and a mean interval duration of 30–72 ms). The new species forms a monophyletic group with the recently described B. dejongi and B. galani . It differs from B. galani by the presence of vomerine teeth (vs. absence) and smaller femoral glands (see Fig. 4 ; femoral gland length 3.5– 5.2 vs. 4.8–9.2 mm ). It differs from B. dejongi by a shorter distance between the inner margins of femoral glands ( Fig. 4 ; FGD 2.8–4.5 mm vs. 7.8–9.8 mm ). Furthermore, the new species differs from all nominal species of Blommersia by a substantial genetic divergence and by its advertisement call (as described below).