Strabomantidae

Family Strabomantidae

Rudolf von May, University of California, Berkeley
February 2013

General Introduction
Characteristics
Distribution
Ecology
References

Pristimantis bacchus
Photo by Esteban Alzate
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1. General Introduction

The family Strabomantidae was proposed by S. B. Hedges, W. E. Duellman, and M. P. Heinike in 2008, in a study on phylogenetics and systematics of ground-breeding frogs (Hedges et al. 2008). The type genus for the family, Strabomantis, was proposed by W. C. H. Peters in 1863.

As of February 7st, 2013, the family Strabomantidae contained 600 species belonging to 19 genera, making it one of the most speciose families of amphibians. Species in the family Strabomantidae are commonly referred to as terrestrial-breeding frogs, as, presumably, all species have direct development (i.e., there are no free-living tadpoles). This specialized reproductive mode allows them to exploit a variety of habitats, as long as they contain sufficient moisture.

A recent study (Pyron & Wiens 2011) determined that Strabomantidae is nonmonophyletic and considered the group to be a subfamily (Strabomantinae ) within the Craugastoridae (which was also proposed by Hedges et al. 2008). However, Blackburn and Wake (2011) reviewed the taxonomy of these groups and retained the original delimitation proposed by Hedges et al. (2008). Thus, Strabomantidae and Craugastoridae are considered separate families.

2. Characteristics

a. External Morphology and general body shape.
The following morphological characteristics are present in most strabomantid species: a fully developed and free first toe (toe I); a single, a subgular vocal sac, visible in males of most species; vocal slits present in males' vocal sac. In most species, there is a skin pad on the underside of fingertips and toetips; this pad is typically defined by a circumferential groove, and is prominent in many arboreal taxa. In some terrestrial taxa, the pad and groove are absent.

b. Ecomorphotype.
This family exhibits ecomorphological forms that are primarily terrestrial and small-bodied. Some genera (e.g. Pristimantis, Strabomantis) include many arboreal species. Typically, these arboreal species have expanded disks on the outer fingers and toes.

c. Size.
Frogs in this family are small to medium-sized, with snout-to-vent lengths typically smaller than 80 mm (Duellman & Lehr 2009). The family contains the smallest frog in the Andes (Noblella pygmaea), which also ranks amongst the smallest frogs known to date.

d. Growth and development.

e. Osteology
Strabomantids have at least 40 osteological characteristics that have been used to define the family (Hedges et al. 2008). Among others, these include a cartilaginous sternum, eight presacral vertebrae, and vomers of variable size. Additionally, the toes bear terminal phalanges that are knobbed or T-shaped, or bear hook-like lateral processes.

f. Behavior.
Little is known of the behavioral ecology for most species in this family. The advertisement call of relatively few strabomantid species has been described, even though recent publications have highlighted their utility in systematic studies of the group (Padial & De la Riva 2009).

g. Larvae.
As far as it is known, strabomantids have no free-living larvae (i.e., tadpole), and instead, are direct developers.

h. Genomics.
As of February 7th, 2013, there were 2,229 individual nucleotide sequences from Strabomantidae available in GenBank (National Center for Biotechnology Information), representing several dozens of mitochondrial and nuclear loci. Additionally, a recent treatise on the chromosomes of terraranan frogs has characterized the structure and number of chromosomes of many strabomantids (Schmid et al. 2010).

To explore available genetic data for Strabomantidae in GenBank, click here.

3. Distribution

a. Geographical distribution.
The family is primarily distributed in South America. These species are concentrated in the Andes, reaching the highest diversity on the eastern versant, with additional species in the Amazon Basin, the Orinoco Basin, the Guyana Shield, the Chocó region, and the Atlantic Forest. Some strabomantid species are present in Central America and the Lesser Antilles (Hedges et al. 2008). Lowland species typically have wide geographic distributions compared to species found in montane areas. Many montane or high-elevation species are known from a single locality.

b. Elevational range.
Strabomantids are distributed from sea level to over 4,000 m. There are considerable differences in the elevational range of species. On the eastern side of the Andes, for example, the known elevational distribution of most species is in the order of several hundred meters to over 1,000 m. Only a few species have elevational ranges extending over 2,500 m. In contrast, many high-elevation strabomantids are known from a single locality and their currently known ranges cover less than 100 m; additional surveys are required to determine the elevational distributions in these species.

4. Ecology

a. Trophic biology.
In general, strabomantids are assumed to consume a range of leaf litter arthropods.

b. Type of microhabitat(s).
Species in all genera can be found within or on the leaf litter of the forest floor. Additionally, many species in some genera (e.g. Pristimantis, Oreobates, Strabomantis) are arboreal, occupying different forest strata, from the understory to the canopy.

c. Life history. All species of of this family are believed to have direct development. Little is known for many of these species and more work needs to be done.

5. References

Note: Rather than focus on supplying references to all literature (or even all literature including species descriptions), the below list aims to capture diverse aspects of the biology of taxa in this family. In some cases, this includes significant taxonomic works, especially revisionary studies.

Blackburn DC, Wake DB. 2011 Class Amphibia Gray, 1825. In: Zhang Z.-Q (ed.) Animal biodiversity: an outline of higher-level classification and survey of taxonomic richness. Zootaxa 3148: 38-54.

Duellman, W.E., and E. Lehr. 2009. Terrestrial-breeding Frogs (Strabomantidae) in Peru. Natur und Tier Verlag, Münster, Germany.

Hedges, S.B., Duellman, W.E., and M.P Heinicke. 2008. New World direct-developing frogs (Anura: Terrarana): molecular phylogeny, classification, biogeography, and conservation. Zootaxa 1737: 1-182.

Heinicke, M.P., Duellman, W.E., and S.B. Hedges. 2007. Major Caribbean and Central American frog faunas originated by ancient oceanic dispersal. Proceedings of the National Academy of Sciences of the United States of America 104: 10092-10097.

Lehr, E., and A. Catenazzi. 2009. A new species of Noblella (Anura: Strabomantidae) from southern Peru: the smallest frog of the Andes. Copeia 2009:148-156.

Padial J. M. & I. De la Riva. 2009. Integrative taxonomy reveals cryptic Amazonian species of Pristimantis (Anura: Strabomantidae). Zoological Journal of the Linnean Society 155: 97-122.

Pyron A, Wiens JJ. 2011 A large-scale phylogeny of Amphibia with over 2,800 species, and a revised classification of extant frogs, salamanders, and caecilians. Mol Phy Evol 61: 543-583.

Schmid M, Steinlein C, Bogart JP, Feichtinger W, Leon P, La Marca E, Diaz LM, Sanz A, Chen S-H, Hedges SB. 2010. The chromosomes of terraranan frogs: insights into vertebrate cytogenetics. Cytogenetics and Genome Research 130-131: 1-568.