Liophryne

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 : 124-126

RELATIONSHIPS WITHIN LIOPHRYNE

Liophryne similis and L. rhododactyla are an allopatric sibling pair distinguished only by different advertisement calls and by the absence of vocal slits in one. Three other species, L. rubra , L. dentata , and L. schlaginhaufeni , are morphologically distinct but more similar to one another than either is to any other species, whereas L. allisoni stands somewhat apart. The latter species is much the smallest Liophryne and has a considerably less well-defined external ear than do the other species.

The relatively large size of similis and rhododactyla is unusual within the Genyophryninae and may be considered as a derived state. The absence of teeth or toothlike structures in these species may also be a derived condition, considering that allisoni, dentata , rubra , and schlaginhaufeni all have teeth (albeit vestigial ones) or toothlike structures (see Morphology, Dentition). In karyology, however, rhododactyla has the presumably plesiomorphic chromosome number 2N = 26, whereas schlaginhaufeni is 2N = 30 (see Morphology, Karyology). Within the context of Liophryne , the small size and indistinct tympanum of allisoni may be primitive characters.

RELATIONSHIPS WITHIN OXYDACTYLA

Frogs of this genus are adapted to a cryptic existence, dwelling in such habitats as grass tussocks, saturated moss, and deep leaf litter. Morphological features that appear to relate to habits include absence or reduction of digital expansion, short hind legs, and small eyes. Considering principally these features, the five species may be arranged in an essentially linear sequence from least to most derived. O. crassa and O. coggeri are at the bottom of the scale, O. brevicrus is intermediate, with O. alpestris and O. stenodactyla occupying the most derived position.

In alpestris and stenodactyla the toetips and fingertips are rounded, showing no flattening, expansion, or terminal grooving. These species have the shortest hind legs in the genus, and stenodactyla has the smallest eyes, with those of alpestris slightly larger but matched by one other species. These two species also share the presumably derived character of a robust premaxillary bone (see Morphology, Osteology).

O. brevicrus has fingertips like those of alpestris and stenodactyla , but the toe tips, Although not expanded and lacking terminal grooves, are somewhat flattened. The legs are slightly longer and eyes slightly larger than in alpestris and stenodactyla .

Fingertips of coggeri and crassa are rounded to slightly flattened, but not clearly disclike, and may show a weak terminal groove. The toe tips of both are disclike with terminal grooves but are scarcely if at all broader than the penultimate phalanges. The legs are slightly longer than and the eye size within the range of the other species.

Whereas alpestris and stenodactyla are unquestionably each other’s closest relative, the relationship at the other end of the sequence is less certain. The features associating coggeri and crassa , while derived with respect to other genera, are plesiomorphic within Oxydactyla . The geography of the situation also raises questions. O. crassa is isolated at moderately high elevations on the southeastern tail of New Guinea, more than 600 km from the closest Oxydactyla populations in the Eastern Highlands. The intervening region has not been fully explored, but forms similar in habitat preference to crassa and other Oxydactyla have been found in the genera Aphantophryne and Austrochaperina . The possibility that including crassa within Oxydactyla renders that genus paraphyletic deserves further study if adequate material becomes available.

ZOOGEOGRAPHY

The zoogeographic relationships of the New Guinean microhylid subfamilies Genyophryninae and Asterophryinae are obscure and will remain so until a satisfying cladistic analysis of the microhylid subfamilies can be achieved. Conflicting hypotheses—perhaps better called scenarios—of Savage (1973) on the one hand and of Zweifel and Tyler (1982) and Zweifel (1985b) on the other have the Australopapuan microhylids derived from Gondwana by way of Australia or from Southeast Asia across Wallace’s Line. Either is compatible with the likely Gondwanan origin of microhylids, although the latter requires a more circuitous route by way of a drifting Indian subcontinent.

Whatever their origin, microhylids dominate the New Guinea frog fauna in number of species, constituting more than half of the total of more than 200 species. Austrochaperina has the widest distribution of the four genera treated in this monograph, with species throughout most of mainland New Guinea and on some adjacent islands as well as one species on New Britain (where only one other microhylid is known, an Oreophryne ) and a disjunct center of diversity in northern Australia. Four of the Australian species are endemic, and the fifth, A. gracilipes , inhabits seasonally dry country and may have dispersed to New Guinea when lowered sea level in the Pleistocene afforded a land connection.

Liophryne and Sphenophryne are widely distributed in New Guinea but have no known insular populations and are absent from Australia. Species of Oxydactyla are likewise restricted to New Guinea and are found in disjunct populations at high elevations.

Too little is known of the details of geographic distribution of species within New Guinea to support speculation about distribution patterns and areas of endemism. On a broader scale, however, the diversity of microhylids very likely relates to their reproductive mode that divorces them from the need to lay their eggs in water. New Guinea is an extremely mountainous island with high rainfall. Under such conditions, upland standing water habitats are not abundant, and streams tend to be torrential, but moist terrestrial and arboreal habitats are everywhere and are utilized by microhylids from sea level to the highest mountains. A parallel situation is in the Admiralty and Solomon islands, where a diversity of platymantine ranid frogs, all with direct embryonic development, dominate the faunas.