South America, land of toads part II: tree toads, Truebella, Frostius... oh, and did I mention the COMMUNAL NESTS?

Lest we forget, one of my aims for 2009-2010 is TO GET THROUGH ALL THE TOADS OF THE WORLD. I don't mean every single species (because there... like, over 540 of them), but all the 'genera' at least. If you need any of the background to this grand/crazy scheme, be sure to check out the links below [image below shows Mt Kukenan in the Guyanan Highlands, and a Pebble toad Oreophrynella niger rolling downhill. Read on...].

One of the main points I've emphasised in some of the previous articles is that toads - or, crown-toads, anyway - seem to be ancestrally South American: the redbelly toads (Melanophryniscus), plump toads (Osornophryne), harlequin or stubfoot toads (Atelopus) and others all seem to be basal (cough cough, checks for presence of John Harshman...) within crown-Bufonidae, and outside the enormous clade that includes all of the more familiar, more, err, 'toady'-looking toads.

This time round, we begin with Dendrophryniscus, a clade that (currently) includes eight species of small, slender toads (body length = less than 20 mm), five of which have been named since 1994 (D. krausae was named in 2008). They're sometimes known as tree toads: the name 'tree toad' is also used for various African and Asian bufonids, none of which are close relatives of Dendrophryniscus. I'm not sure if the name is appropriate, as what little information is available on these toads indicates that they're predominantly terrestrial (all the photos I've seen show them walking around on forest floors, not climbing) [adjacent photo of D. berthalutzae © by Axel Kwet, from calphotos but also used on wikipedia].

The skin texture present in these toads is unique: they have uniformly spaced, tiny, pointed warts (Graybeal & Cannatella 1995). Some Dendrophryniscus species lay their eggs inside bromeliads while others use pools on the forest floor. The small tadpoles (which can reach 18 mm... a similar size to metamorphosed adults!) have cream-coloured bodies and transparent tail fins.

Also (probably) located in this region of the cladogram is Truebella, a clade of peculiar little toads, named in 1995 in honour of anuran expert Linda Trueb. Truebella lacks webbing between its digits (elsewhere in toads, absence of webbing is also present in the South African Cape toads (Capensibufo)), possesses a small, triangular cartilaginous projection at the tip of its snout, and has a single, small, spherical prepollical element.

Because the phylogenetic affinities of Truebella were deemed obscure when it was first named (Graybeal & Cannatella 1995), one species is named T. skoptes (skoptes means 'scoffer' or 'mocker'), and the other T. tothastes (tothastes means 'one who scorns') [in the adjacent image - from Graybeal & Cannatella (1995) - T. skoptes is shown above (SVL 27 mm) and T. tothastes is below (SVL 27.5 mm). Like most other toads from this region of the cladogram, note that these are relatively small, slender anurans with shallow, pointed snouts].

Three recently discovered toads from the western slopes of the Andes, all named since 1981, have been united in Andinophryne. They share elongate parotoid glands and extensive digital webbing, but their proposed monophyly has been questioned (Graybeal & Cannatella 1995). Again, they're gracile little toads. They possess a lateral row of enlarged tubercles. Stomach contents show that they eat ants (Hoogmoed 1989).

A small group of specialised, distinctive South American toads are unique to the sandstone mountains (or tepuis) of Venezuela and Guyana. These are the bush toads (Oreophrynella), of which nine species are currently known (seven of these have been named since 1990; O. seegobini was named in 2009) [O. weiassipuensis, named in 2005, is shown in the adjacent photo. From Señari et al. (2005)]. With the exception of O. nigra and O. quelchii, all are endemic to single mountains. Like most of the other taxa discussed here, they're small (SVLs less than 30 mm). They exhibit tuberculate dorsal skin.

Several details make these toads unusual. They have only six presacral vertebrae (eight is the typical number for toads), and of these the first two are fused (both characters are also seen in Osornophryne, the plump toads). Their fingers are toes are joined at their bases by thick, fleshy skin: rather than being webbing like that seen widely in anurans, this is continuous with the palms and soles (Señaris et al. 2005). It looks as if the digits are being 'absorbed' by the palms and soles. Their hindfeet are further unusual in that the first toe is particularly long, and is opposable to digits III-V (Graybeal & Cannatella 1995). This originally led to suggestions that these species might be arboreal, but we now know that they are rock-dwellers that are only capable of slow walking (they cannot hop or run). When threatened (big theraphosid spiders are their most likely predators), they tuck in their limbs and fold their heads down to form a ball-like shape. If this happens on a sloping surface, the toads rolls away for distances of up to 3 m. This behaviour was featured on the BBC TV series Life... a clip is here, and a still from that segment is shown at the very top (© BBC).

By the way, the behaviour isn't without risk. Bush toads are poor swimmers and one individual seen to roll into a deep pool then drowned.

Bush toad reproductive behaviour is also really interesting. At least some species of these little toads come together to form special communal nesting areas, nestled within the dense patches of ground-hugging vegetation that are so characteristic of tepuis. Networks of tunnels run through the nesting areas and connect the numerous entrances. In a communal nest reported by McDiarmid & Gorzula (1989) from the summit of Kukenan-tepui (or Mount Kukenan) in Guyana, 102 toads and 321 eggs were discovered. The eggs were in clumps of 8-35 and each clump was attended by several adults: because 70 of the toads present at the site were males, McDiarmid & Gorzula (1989) suggested that males may remain at the nest site (as egg guards?) for a prolonged period. As expected in toads that lay their eggs in clumps of vegetation on the tops of mountains, there's no tadpole phase: the embryos grow directly into metamorphosed juveniles while within the egg.

Communal nesting in toads. Another reminder that neat social behaviour is far from restricted to those silly endotherms.

Some South American toads originally included in Atelopus (the harlequin toad genus looked at in part I) have turned out to be worthy of recognition as distinct 'genera'. This isn't surprising given that Atelopus - currently with 86 species - is well on its way to becoming one of those super-huge genera that actually encompasses quite a lot of morphological disparity.

One species originally included in Atelopus, A. pernambucensis Bokermann, 1962 was argued by Cannatella (1986) to be quite distinct: unlike the others, it does not lack a tympanum, nor does it have the fused first and second vertebrae or V-shaped pelvis of the Atelopus species [the vertebral and pelvic skeletons of Atelopus and Frostius are compared in the adjacent figure, from Cannatella (1986)]. Accordingly, he coined the new genus Frostius for this species (named in honour of Darrel Frost). While the tadpoles of Atelopus live in streams and have suckers on their bellies, Frostius tadpoles live inside bromeliads and lack a belly sucker (Cannatella 1986). A second species of Frostius, F. erythrophthalmus, was named in 2007.

Next: Blomberg's toad and its omosternum-bearing buddies. The entire toads series is pretty much written, I just keep getting distracted.

For previous articles in the Tet Zoo toads series see...

• Toadtastic - the invasion begins!
• Bidder's organ and the holy quest for synapomorphies
• Our sex lives in words and pictures (or, On the reproductive biology of the Bufonidae)
• Skulls, crests, snouts and giant poison glands: the heads of toads
• Toads of the world: first, (some) toads of the north
• The Natterjack, its life and times
• The resurrection of Anaxyrus
• South America, land of toads, part I: harlequins, redbellies and plump toads

For previous articles on hyloid anurans see...

• Britain's lost tree frogs: sigh, not another 'neglected native'
• Ghost frogs, hyloids, arcifery.. what more could you want?
• Green-boned glass frogs, monkey frogs, toothless toads
• It's the Helmeted water toad!
• Horn-headed biting frogs and pouches and false teeth
• More wide-mouthed South American horned frogs
• We need MORE FROGS

Refs - -

Cannatella, D. C. 1986. A new genus of bufonid (Anura) from South America, and phylogenetic relationships of the Neotropical genera. Herpetologica 42, 197-205.

Graybeal, A. & Cannatella, D. C. 1995. A new taxon of Bufonidae from Peru, with descriptions of two new species and a review of the phylogenetic status of supraspecific bufonid taxa. Herpetologica 51, 105-131.

Hoogmoed, M. S. 1989. On the identity of some toads of the genus Bufo from Ecuador, with additional remarks on Andinophryne colomai Hoogmoed, 1985 (Amphibia: Aanura: Bufonidae). Zool. Verh. Leiden 250, 1-32.

McDiarmid, R. W., & Gorzula, S (1989). Aspects of the reproductive ecology and behavior of the Tepui toads, genus Oreophrynella (Anura, Bufonidae Copeia, 1989, 445-451

Señaris, J. C., DoNascimiento, C. & Villarreal, O. 2005. A new species of the genus Oreophrynella (Anura; Bufonidae) from the Guiana Highlands. Papéis Avulsos de Zoologica, Museu de Zoologia da Universidade de São Paulo 45, 61-67.