Long-time Tet Zoo readers will be familiar with the long-running series on the toads of the world. It’s been running intermittently since October 2009 and is something like 50% published. Much of the text has been written but it’s the getting-hold of usable images of the relevant species that forms the main obstacle to completion. In the most recent articles in the series – they were published way back in September and November 2011 – we looked at toads that have been identified by some as belonging to an endemic African clade. Several other lineages discussed in the same part of the series aren’t necessarily part of the same clade, but do belong to the same general region of the cladogram (Van Bocxlaer et al. 2010, Pyron & Wiens 2011).

Highly simplified phylogeny for Bufonidae with some of the main evolutionary and biogeographical events marked at appropriate places. Based predominantly on Van Bocxlaer et al. (2010). Atelopus by Giovanni Alberto Chaves Portilla CC BY-SA-2.5, Rhaebo by Brian Gratwicke CC-BY-SA-2.0, Anaxyrus by LA Dawson CC BY-SA 2.5, Rhinella by Froggydarb CC BY-SA-3.0, Mertensophryne by Vladimir Dinets, used with permission, Bufo s. s. by Kruczy89 CC BY-SA 3.0, Bufotes by Richard Bartz CC BY-SA 3.0, Ansonia by Thomas Brown CC BY-SA 2.0, Duttaphrynus by L. Shyamal CC BY-SA 2.5.

Before I move on, big thanks to Spookpadda for their very lengthy message of March 2012 in which much additional information on the anatomy, phylogenetic relationships and systematic of the toad groups covered in the previous Tet Zoo toads article (these being Amietophrynus, Capensibufo, Vandijkophrynus, Mertensophryne and Poyntonophrynus) was provided. Should the article ever be republished, it will need moderate tweaking and updating.

Nectophryne, Werneria and Wolterstorffina

Nectophryne afra, photographed in Cameroon by Paul Freed. Image CC BY-NC.

The African tree toads of the genus Nectophryne (the name ‘African tree toads’ is also used for species in the genus Nectophrynoides as well) are small, poorly known rainforest toads. Hardly any information is available on them bar the fact that they lay their eggs in little shallow pools, and that the males then guard the eggs. Molecular data suggests that Nectophryne forms a clade with the smalltongue toads (Werneria) and the Wolterstorff toads (Wolterstorffina) (Frost et al. 2006, Van Bocxlaer et al. 2010, Pyron & Wiens 2011), all of which mostly occur in western Africa. If these small toads really do form a clade, they apparently represent an endemic African radiation, and the fact that they seem to have diverged ‘early on’ within Bufonidae lends additional support to the idea of a Gondwanan origin for toads as a whole.

Merten's smalltongue toad (Werneria mertensiana). Drawing by Darren Naish, based on photo by Mary E. Gartshore.

The smalltongue toads (Werneria) of Cameroon and Equatorial Guinea are small (30-40 mm SVL), nocturnal toads of fast-flowing streams. Six species are currently recognised, two of which – W. iboundji and W. submontana – were named in 2004 (Rödel et al. 2004). They are highly dependent on running water and take refuge it in when disturbed. They eat beetles and have “a dorsolateral ridge that extends from the groin to the snout” (Graybeal & Cannatella 1995, p. 122), though this is very subtle. Paratoid glands and tympani are absent and the snout protrudes relative to the position of the mouth. Smalltongue toad tadpoles are specialised stream-dwelling animals. They’re dorsoventrally compressed with a broad head, dorsally positioned eyes and nostrils and sucker-like mouth disc.

Wolterstorff toads were found by Graybeal & Cannatella (1995) to be paraphyletic with respect to a Nectophryne + Nimbaphrynoides clade, and none of the characters used to diagnose the genus appear unique. However, in at least some species the males have particularly large bony crests on their humeri, and it’s plausible that this is a synapomorphy at some level. In at least some Wolterstorff toad species, the tadpoles have a small ventral sucker.

Werneria tadpole in lateral view. The sucker-like mouth is fringed with soft, flap-like extensions. Illustration by Darren Naish.

Four-digit toads

Didynamipus sjostedti, photographed in the wild by Václav Gvoždík. Image CC BY-SA 2.5.

Didynamipus sjostedti, sometimes called the Four-digit toad, is a small bufonid restricted to Cameroon, Equatorial Guinea and Nigeria. It also lacks a tympanum and columella (what is it with all these toads losing their ears?) and have a reduced phalangeal and digital formula (as suggested by the name, only four toes are present). Two competing phylogenetic views have been proposed for this taxon. One idea – based on an analysis of morphological characters – is that it's part of an endemic African clade that also includes Nimbaphrynoides (the Nimba toads of Liberia, Ivory Coast and Guinea), Parker’s tree toad Laurentophryne parkeri and the Nectophryne African tree toads (Graybeal & Cannatella 1995). The other idea is that, together with the Nectophrynoides tree toads, it's close to the Asian stream toads Ansonia (Pyron & Wiens 2011).

Having mentioned Parker’s tree toad: it also lacks a tympanum and columella, and in fact is like the four-digit toads in possessing only seven presacral vertebrae.

The Red-backed toad

Red-backed toad tadpole in lateral view. Illustration by Darren Naish.

Finally, for now, we look at the Red toad or Red-backed toad Schismaderma carens. This is a highly distinctive African toad, conventionally included in Bufo and regarded as representing the ‘Bufo carens group’. Its inclusion within Bufo sensu lato was also peculiar, as it lacks parotoid glands. The larvae are distinctive in possessing a U-shaped fold on the dorsal surface (Graybeal & Cannatella 1995) and adults are also easily identified thanks to their reddish backs (the underside is creamy or light grey), absence of parotoid glands, prominent lateral skin fold, and twin dark spots on the back.

Excellent illustration of Red-backed toad by Willems van der Merwe, used with permission.

The affinities of Schismaderma have been contentious. Pramuk (2006) found it to belong to a clade that also included the African 20-chromosome toads (Amietophrynus) and to be the sister-taxon to the Asian ‘Bufo melanostictus group’ (named Duttaphrynus by Frost et al. (2006)). Frost et al. (2006) also recovered Schismaderma and Duttaphrynus as close relatives, but found Bufotes (Old World green toads) and Peltophryne to form a clade with Duttaphrynus and Schismaderma too. Van Bocxlaer et al. (2009, 2010) found Schismaderma to be the sister-taxon to a Churamiti + Nectophrynoides clade while Pyron & Wiens (2011) found it to be the sister-taxon to the Old World green toads.

And with that... we’re done with another segment of the toad family tree. Well, I couldn't finish the section on the Ethiopian toads because I have yet to find any goddam pictures than I can use. On that note, more on toads at some point in the future.

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

For previous articles on hyloid anurans see...

Refs - -

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.

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.

Pramuk, J. B. 2006. Phylogeny of South American Bufo (Anura: Bufonidae) inferred from combined evidence. Zoological Journal of the Linnean Society 146, 407-452.

Pyron, R. A. & Wiens, J. J. 2011. A large-scale phylogeny of Amphibia including over 2,800 species, and a revised classification of extant frogs, salamanders, and caecilians. Molecular Phylogenetics and Evolution 61, 543-583.

Rödel, M.-O., Schmitz, A., Pauwels, O. S. G. & Böhme, W. 2004. Revision of the genus Werneria Poche, 1903, including the descriptions of two new species from Cameroon and Gabon (Amphibia: Anura: Bufonidae). Zootaxa 720, 1-28.

Van Bocxlaer, I., Loader, S. P., Roelants, K., Biju, S. D., Menegon, M. & Bossuyt, F. 2010. Gradual adaptation toward a range-expansion phenotype initiated the global radiation of toads. Science 327, 679-662.