Austrochaperina

ZWEIFEL, RICHARD G., 2000, Partition Of The Australopapuan Microhylid Frog Genus Sphenophryne With Descriptions Of New Species, Bulletin of the American Museum of Natural History 2000 (253), pp. 1-130 : 123-124

RELATIONSHIPS WITHIN AUSTROCHAPERINA

The 23 species of Austrochaperina may be arranged by body size in two groups. One, composed of relatively small frogs (maximum adult size range 21–35 mm SVL), includes the New Guinean species adamantina , aquilonia , blumi, brevipes , gracilipes , kosarek, mehelyi , novaebritanniae , parkeri, polysticta , and yelaensis , as well as the four Australian endemics, two of which are the largest species in the group. The eight species of the other group are larger (38–52 mm)— archboldi, basipalmata , derongo , guttata , hooglandi, macrorhyncha, palmipes , and rivularis . I shall refer informally to the first group as the Small group, and to the others as the Large group.

Three of the five Australian members of the Small group dwell in rainforest leaf litter. The sibling species A. adelphe (Australian) and A. gracilipes (common to Australia and New Guinea) are apparent exceptions, living in seasonally dry environments and sometimes calling from sites slightly above the substratum. Only two of the New Guinean species, brevipes and novaebritanniae , are confirmed as leaf-litter inhabitants, but the morphology of the others suggests that habit.

An attempt to infer relationships within the Small group is frustrated by paucity of material—four of the New Guinean species are known from only one specimen each, another from two, and the unique specimen of another was destroyed. Second, the leaf-litter habitat preference evokes no distinctive adaptations such as the long hind legs, large eyes, and subarticular elevations of surface-active Liophryne , the enlarged finger discs of scansorial Sphenophryne , the short hind legs and pointed toe-tips of burrowing Oxydactyla , or the large digital discs and toe-webbing of riparian Austrochaperina .

The Small group is essentially what remains when the slightly better characterized Large group is removed. The Australian species (including gracilipes ) have some claim to monophyletic distinction within the Small group. They are the only Austrochaperina with unpulsed, multinote advertisement calls (Zweifel, 1985b, but the calls of many New Guinean species of both groups are yet unknown), and Mahony et al. ( 1992) cited karyological evidence for monophyly. No New Guinean endemics of the Small group have been karyotyped, while all five Australian species have the presumably primitive 2N = 26. Two of the Australian species, at maximum sizes of 33 and 35 mm SVL, are the largest species of the Small group; the largest New Guinean species attains 31 mm.

Five of the eight Large group species are riparian along small watercourses, a habitat preference unknown among other Australopapuan microhylids. A. palmipes and A. basipalmata have toe webbing (slight in the latter). These, together with A. macrorhyncha and A. rivularis , have relatively large finger and toe discs; in palmipes the finger discs may be broader than those of the toes, a condition not seen elsewhere in Austrochaperina (table 3). I consider this disc development as an adaptation to wet, slippery, rocky riparian conditions. A. derongo , with relatively small- er discs, is also riparian, but the habits of archboldi and hooglandi are unknown. The only information on A. guttata is that it calls from sheltered leaf-litter sites not closely associated with water.

The advertisement calls of four species of the Large group are prolonged bouts of short, pulsed notes: derongo , guttata, macrorhyncha , and rivularis . If, as I suspect, this is a derived call, the similarity may indicate a close relationship; calls of this sort are unknown elsewhere in Austrochaperina . I anticipate that such calls will characterize three of the other four species of the Large group as well. The fourth species, A. palmipes , may utter soft, clicking sounds (see species account). The difference in vocalization, if confirmed, may be a derived character of this species, along with lack of vocal slits, concealed tympanum, vomerine spikes, and webbed toes.

Austrochaperina palmipes is morphologically the most derived species of the Large group, but its primitive 2N = 26 karyotype contrasts with the 2N = 24 of A. derongo . A peculiar feature uniting A. rivularis and A. palmipes is a mosaic appearance to the dorsal skin; this shows well in figure 31E and F. The possession of slight toe webbing would seem to place A. basipalmata in a phylogenetic position between palmipes and the more primitive species lacking webbing. However, the unusual character of the skin suggests that palmipes and rivularis are closest relatives.

An anatomical peculiarity, presumably a derived condition, unites some species of the Large group. In these frogs the snout is rather elongate, projecting conspicuously past the lower jaw (fig. 21). Adult males tend to be more extreme in this respect, and the snout tip usually is pale, often quite white. Juveniles of both sexes generally have dark snout tips, and females only occasionally show some lightening. Parker (1940) was the first to call attention to this sexual dimorphism in A. basipalmata (as Sphenophryne macrorhyncha ). The pale condition is well developed in A. palmipes and present in A. rivularis . Adult males of three morphologically similar species— archboldi , derongo , and hooglandi —generally show this condition. In contrast to other species of the Large group, guttata and macrorhyncha have a more rounded, less projecting snout and they do not appear to develop a pale tip.

Menzies and Tyler (1977: 434) cited as one of the diagnostic characteristics of the genus Copiula , ‘‘a hypertrophied serous dermal gland whose location is distinguished externally by a translucent white, and sometimes uptilted, tip to the snout.’’ Apparently the condition in Copiula is not sexually dimorphic. The histology of the pale snout tip in Austrochaperina has not been investigat- ed, so there is no assurance that the conditions are homologous. If they are, this would suggest a possible derivation of Copiula (a leaf-litter genus with a more derived pectoral girdle) from within the clade of large Austrochaperina . A. derongo and Copiula fistulans share the derived chromosome number, 2N = 24 (Mahony et al., 1992), which may be another indication of relationship.