Suddenly and unexpectedly, I have the urge to write about frogs. Today we look briefly at the first of two behaviourally peculiar, anatomically surprising groups, both of which are endemic to sub-Saharan Africa, both of which belong to a major neobatrachian frog clade called Allodapanura, and both of which have been united in a clade vernacularly termed the ‘strange bedfellow frogs’. We’ll look more at the phylogeny and what it means later.
The short-headed or rain frogs – technically termed brevicipitines or brevicipitids – are a group of five genera of round-bodied, short-limbed African frogs, most of which are cryptic, poorly known and spend most of their time beneath the surface of the ground or submerged in leaf litter. Brevicipitids aren’t all like this though, since some species of Callulina – the so-called warty frogs or secret frogs of Tanzania and Kenya – are partially arboreal (de Sá et al. 2004, Malonza 2012), often being encountered on branches more than 1 m off the ground. Incidentally, of the nine recognised Callulina species, all but one have been named since 2004. [Adjacent photo by Patrick Kinyatta Malonza.]
By far the most familiar brevicipitids are the 16 species of Breviceps*: these were, until very recently, the only brevicipitids for which any behavioural or life history information existed [B. adspersus photo above by Ryanvanhuyssteen]. Forests, scrubland, savannah and even agricultural and suburban regions are all frequented by these frogs and they aren’t necessarily associated with places where there’s standing or running water (though they do occur near water in some places). At least some brevicipitid species are restricted to forest blocks that are being fragmented by agricultural practises and should be considered severely endangered (Malonza 2012). As suggested by one of their common names, these frogs typically emerge from the ground after rain, usually at night. When threatened, they inflate themselves with air (well, the Breviceps species certainly do this - I don't know about the others). This is why some of the animals you see in the pictures here look more rotund than others.
* I have to mention the fact that one of the most recently named species - B. bagginsi Minter, 2003 - was named after Bilbo Baggins (Minter 2003).
Breviceps frogs are very much the wrong shape to indulge in amplexus (this being the term for the ‘mating grasp’ typical of anurans), so – after emerging from the ground during the brief rainy season – males and females adhere to each other by way of a secretion produced in the male’s abdominal region. Mattison (1987, p. 82) says that “the attachment is said to be so effective that any attempt to separate the frogs would result in damage”.
A connected male-female pair then retreat to a burrow (I assume that the large female does the work and the male simply gets dragged along behind*); here, a chamber is constructed and 13 to 50 (or so) large, yolk-rich eggs are laid. The adhesive that connects male to female now dissolves, but what happens next varies between the species. In some, the male leaves and the females stays and guards the eggs. In others, the female leaves and the male stays and guards the eggs. Even more intriguing are those cases where both parents have been found in the nest chamber. Are we seeing biparental care and monogamy here, as has been reported elsewhere within Anura? (Brown et al. 2010)... or we seeing something more perfunctory? So far as I can tell, we don’t yet know.
* I assume this based on the behaviour of the other group of 'strange bedfellow frogs', the hemisotids. I’ll be discussing them later.
It seems that these attendant parents stay inside the egg chamber, right next to the eggs, but one report from 1929 described how a female B. mossambicus remained outside a sealed egg chamber (Fitzsimons & van Dam 1929). One observation refers to a female seen removing fallen soil from the top of the egg mass (Wager 1965), so it seems sensible to infer that egg-guarding Breviceps parents really do care for their eggs, presumably keeping watch for predatory invertebrates and maybe mould.
What happens next? This is another frog group that practises direct development: there is no free-swimming tadpole phase, no direct need for standing or running water during any part of the reproductive cycle, and the embryos turn into froglets thanks entirely to maternal provisioning. UPDATE: thanks to RoryD, I've been reminded of the scene in Attenborough's Life in Cold Blood which shows a mass of Breviceps tadpoles developing within a damp, foamy mass within the nest chamber. The tadpoles do, therefore, turn into froglets outside of their eggs, not within them as is the case in some other anurans that lack a free-swimming tadpole phase.
Several infertile, jelly-filled egg capsules form part of the egg mass and presumably help prevent desiccation prior to hatching. While everything that I’ve just described pertains to Breviceps, Müller et al. (2007) reported the same reproductive and developmental events in Probreviceps, a brevicipitid that might not be especially closely related to Breviceps (Müller et al. (2007) generated a phylogeny where Breviceps is the sister-taxon to a clade that contains all other brevicipitids, and Probreviceps seems to be the youngest taxon within the latter clade). Malonza (2012) also reported this Breviceps-style pattern of reproduction in Callulina. While data on the reproductive behaviour of the remaining brevicipitid taxa (Balebreviceps and Spelaeophryne) remains all but absent, it seems that direct development and clutch-guarding is present across the group and inherited from the brevicipitid common ancestor (Müller et al. 2007).
So – that’s the first group of ‘strange bedfellow frogs’ (the technical name for the clade is Xenosyneunitanura... yeah, I know). More soon.
Oh.. one more thing. Be sure to look at Dean Boshoff's (short) video of a mewing Breviceps macrops. I'd add it here but embedding videos still doesn't work.
For previous Tet Zoo articles on frogs and toads, see...
- In pursuit of Romanian frogs (part I: Bombina)
- In pursuit of Romanian frogs (part II: WESTERN PALAEARCTIC WATER FROGS!!)
- In pursuit of Romanian frogs (part III: brown frogs)
- The toads series comes to SciAm: because Africa has toads too
- 20-chromosome toads
- Glassfrogs: translucent skin, green bones, arm spines
- Everybody loves glassfrogs
- African tree toads, smalltongue toads, four-digit toads, red-backed toads: yes, a whole load of obscure African toads
- Parsley frogs: spadefoots without spades
- Megophrys: so much more than Megophrys nasuta
- North American spadefoot toads and their incredible fast-metamorphosing, polymorphic tadpoles
- Tadpole nests, past and present
- Gladiatorial glassfrogs, redux
- Frogs you may not have heard of: Brazil’s Cycloramphus ‘button frogs’
- There is so much more to flying frogs than flying frogs
Refs - -
Brown, J., Morales, V. & Summers, K. 2010. A key ecological trait drove the evolution of biparental care and monogamy in an amphibian. The American Naturalist 175 436-446.
de Sá, R. O., Loader, S P. & Channing, A. 2004. A new species of Callulina (Anura: Microhylidae) from the West Usambara Mountains, Tanzania. Copeia 2004, 219-224.
Fitzsimons, V. & van Dam, G. 1929. Some observations on the breeding habits of Breviceps. Annals of the Transvaal Museum 13, 152-153.
Mattison, C. 1987. Frogs & Toads of the World. Blandford, London.
Minter, L. R. 2003. Two new cryptic species of Breviceps (Anura: Microhylidae) from southern Africa. African Journal of Herpetology 52, 9-21.
Müller, H., Loader, S. P., Ngalason, W., Howell, K. M. & Gower, D. J. 2007. Reproduction in brevicipitid frogs (Amphibia: Anura: Brevicipitidae) – evidence from Probreviceps m. macrodactylus. Copeia 2007, 726-733.
Wager, V. A. 1965. The Frogs of South Africa. Purnell and Sons, Cape Town.