I have not forgotten that 2008 is Year of the Frog: if you have, or if you didn’t know this, please go back to December 2007 and read the explanatory article here. Some of you will also recall the EDGE project (EDGE = Evolutionary Distinct and Globally Endangered), and here we look at an anuran that’s one of many on the EDGE list.
Myobatrachids, or southern frogs, or Australo-Papuan frogs, include some of the most incredible and bizarre of anurans. The Turtle frog Myobatrachus gouldii looks like a toy, is apparently sometimes mistaken for a baby turtle, and is one of just a few anuran species that burrows head-first. In the (now extinct) gastric-brooding frogs Rheobatrachus, females swallowed their eggs and then turned their stomachs into a brooding chamber. The Pouched frog Assa darlingtoni of Queensland and New South Wales, first described in 1933, possesses paired hip pouches in which the males carry the metamorphosing tadpoles. A brief intro to these frogs was previously provided here.
Synapomorphies that unite these Australasian frogs have never been identified and it is has on occasion been suggested that they’re not a natural group, with some being closely allied to the sooglossids (Seychelles frogs) and others being close to the heleophrynids (ghost frogs). Frost et al. (2006) didn’t support this idea of polyphyly, but did find the Australo-Papuan frogs to group into two clades: one containing Australian swamp frogs (Limnodynastes) and relatives (which they called Limnodynastidae) and one containing the Australian froglets (Crinia), the Pouched frog, the Turtle frog, and relatives (which they called Myobatrachidae). Together, limnodynastids + myobatrachids are united as Myobatrachoidea. Their closest relatives are a number of poorly known South American taxa that I will avoid discussing for now, and all of these anurans are near the base of Hyloidea*, the neobatrachian clade that includes tree frogs, true toads and others (see adjacent cladogram: for an introduction to Hyloidea go here). The new division of Myobatrachidae sensu lato into Myobatrachidae sensu stricto and Limnodynastidae hasn’t been adopted by everyone, but does seem to be catching on.
* Though a node-based Hyloidea that includes only ‘core hyloids’ (Darst & Cannatella 2004) would exclude the myobatrachoids.
Among the limnodynastids (sometimes called Australian ground frogs) on the EDGE list is the Baw Baw frog Philoria frosti, a species restricted entirely to Victoria’s Baw Baw Plateau (a location only about 120 km east of Melbourne). Thought to number between 10,000-15,000 during the early 1980s, it was relatively common and easy to find, and Malone (1985) reported the discovery of over 4200 calling males during the first systematic survey. Things were to go horribly wrong. Soon afterwards, the species went into chronic decline and no individuals were reported between 1985 and 1988, only a few scant records were made between 1989 and 1992, and by 1996 it seemed that calling males were down to just 1-2% of the number reported a decade earlier. Some reports indicate that the species, now critically endangered, has declined to as few as 250 individuals.
It is one of six species of Philoria, all of which are sometimes called Baw Baw frogs, despite the fact that P. frosti is the only species restricted to the Baw Baw Plateau, or to Victoria: the others are from Queensland and New South Wales. Sometimes called sphagnum frogs, five of them have been named since 1940 and two (P. pughi Knowles et al., 2004 and P. richmondensis Knowles et al., 2004) were named this century. I will refer to all Philoria species as sphagnum frogs to avoid confusing the entire genus with the species P. frosti. In the montage here, from Knowles et al. (2004), the two top images show male P. kundagungun, the two middle ones show a male (left) and female (right) P. pughi, and the two bottom images show male (left) and female (right) P. richmondensis.
Sphagnum frogs are fairly robust little frogs (all less than 55 mm long) with horizontal pupils. The parotoid glands are small in some species, but very large in others: in P. frosti they are dark and extend backwards over the shoulder region (see image of P. frosti shown at very top of article). The species also differ in skin texture, with most being smooth-skinned, but P. frosti being covered with multiple tiny tubercles that give it a spiky appearance. In being ‘spiky’ and in sporting massive dark paratoid glands, P. frosti is probably the most distinctive member of the group.
Moore (1958) proposed that Philoria should be split into two genera, with Kyarranus being suggested for the northern species. Kyarranus is still used by some authors for some species but, as noted by Cogger (2000), there doesn’t seem to be any good reason for this separation as the characters thought to be diagnostic for Kyarranus also occur in Philoria. A third generic name, Coplandia, was erected for the Red-and-yellow mountain frog P. kundagungun by those authors who shall remain nameless, but hasn’t been used much since. Fossils belonging to Philoria date back to the Late Oligocene or Early Miocene (Sanchiz 1998) and phylogenetic studies have found Philoria to be the sister-taxon to all other limnodynastids (Frost et al. 2006).
While also preying on arthropod larvae and other animals, sphagnum frogs may specialize on annelids. The best known peculiarity of these frogs, however, concerns their highly specialized mode of reproduction. They manufacture a transparent foam nest by beating air bubbles into the egg mass, and special flanges on the female’s digits may assist in the creation of the bubbles. This nest can be created in a variety of sites, ranging from a cavity within moist sphagnum moss to about a metre up within vegetation. The relatively immobile aquatic larvae don’t feed (and have reduced mouthparts) but retain a yolk store all the way through to metamorphosis, eventually completing development within the nest (Debavay 1993).
Why P. frosti has gone into chronic decline is of course the big question, and the real answer is that we don’t know. However, it’s hardly the only anuran where this has happened, both in Australia and worldwide, and in Australia species of both torrent frog (Taudactylus) and barred frog (Mixophyes) have been severely affected, or even made extinct. In the case of the Baw Baw Plateau, development and the forestry industry have reduced available habitat, but as a highland species it is also likely that the Baw Baw frog has been affected by environmental changes and perhaps by the spread of the Bd chytrid fungus (Pounds et al. 2006). As of 2003, the Bd chytrid known to kill frogs elsewhere had not been reported on P. frosti and there were plans to look for it on museum and living specimens.
And, for me, it’s back to the dinosaurs…
Refs – -
Cogger, H. G. 2000. Reptiles & Amphibians of Australia (Sixth Edition). New Holland Publishers, Sydney.
Darst, C. R. & Cannatella, D. C. 2004. Novel relationships among hyloid frogs inferred from 12S and 16S mitochondrial DNA sequences. Molecular Phylogenetics and Evolution 31, 462-475.
Debavay, J. M. 1993. The developmental stages of the Sphagnum frog, Kyarranus sphagnicolus Moore (Anura, Myobatrachidae). Australian Journal of Zoology 41, 151-201.
Frost, D. R., Grant, T., Faivovich, J., Bain, R. H., Haas, A., Haddad, C. F. B., De Sá, R. O., Channing, A., Wilkinson, M., Donnellan, S. C., Raxworthy, C. J., Campbell, J. A., Blotto, B. L., Moler, P., Drewes, R. C., Nussbaum, R. A., Lynch, J. D., Green, D. M. & Wheeler, W. C. 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History 297, 1-370.
Malone, B. S. 1985. Status, distribution and ecology of the Baw Baw Frog (Philoria frosti). Arthur Rylah Institute Technical Report No. 36. Arthur Rylah Institute, Department of Conservation, Victoria.
Moore, J. A. 1958. A new genus and species of leptodactylid frog from Australia. American Museum Novitates 1919, 1-7.
Pounds, J. A., Bustamante, M. R., Coloma, L. A., Consuegra, J. A., Fogden, M. P. L., Foster, P. N., La Marca, E., Masters, K. L., Merino-Viteri, A., Puschendorf, R., Ron, S. R., Sánchez-Azofeifa, G. A., Still, C. J. & Young, B. E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439, 161-167.
Sanchiz, B. 1998. Salientia. Handbuch der Paläoherpetologie, Teil 4. Verlag Dr. Friedrick Pfeil, München.