Cacosternum karooicum Boycott, de Villiers & Scott, 2002
Diagnosis: This species can be diagnosed as a member of the genus Cacosternum by the following characteristics: clavicle absent, omosternum severely reduced, small size, irregularly spotted abdomen, tympanum not visible, no toe webbing, no midtarsal tubercle, no medial lingual process. It can be distinguished from the similar species C. namaquense by a lack of longitudinal dorsal glands in C. karooicum (vs. paired, rust-colored glands in C. namaquense), having a thick musculus cutaneous pectoris (vs. absent in C. namaquense), medioventral ends of coracoids only occasionally faintly nicked (vs. pronounced bifurcation in C. namaquense), wider frontoparietal bones compared to C. namaquense, adpressed Toe V reaching to or beyond second subarticular tubercle of Toe IV (vs. Toe V falling short in C. namaquense), fringing on digits absent or rudimentary (vs. well-developed in C. namaquense, except for the population from far northern Namibia), presence of small outer metatarsal tubercle (vs. usually absent in C. namaquense, dorsum covered with small, round, evenly spaced warts (vs. smooth dorsum, rarely having warts, in C. namaquense), dorsal coloration uniform olive-brown to khaki-brown, sometimes with orange or red tint (vs. dark blotches or rosettes on a mottled lighter background in C. namaquense), no interorbital bar (vs. pale triangular patch with the base making an interorbital bar in C. namaquense), no inverted V-shaped patch on mid-dorsum (vs. inverted V-shaped patch present in C. namaquense) (Boycott et al. 2002).
Description: Cacosternum karooicum measures from 23.3 to 30.8 mm SVL. The body shape is flattened and thin in appearance. The snout is rounded. The tympanum is not visible. The supratympanic fold is present but not well-developed, with the back portion becoming part of a glandular fold of excess skin. A poorly defined glandular ridge is in line with the edge of the upper jaw and stretches almost to the base of the forelimb. The skin is evenly covered with small round glandular warts. Limbs are moderate in length. Finger tips are slightly rounded with the third finger longest in length, followed by the fourth, second, and first. Supernumerary tubercles of hands were well-defined while the palmar tubercle was divided, with both sections equivalent in size. Toes possess slight lateral fringes, along with a trace of webbing along the base of the toes between the second and third, third and fourth, and fourth and fifth toes. The fourth toe is the longest, followed by the third, fifth, second, and first. The outer metatarsal tubercle is present. The inner metatarsal tubercle is medium-sized, conical, and outward-projecting. Subdigital tubercles of the feet are conical, small, and prominent; in comparison, subdigital tubercles of the hands are larger and more rounded. Males have nuptial pads on the upper surfaces of the first and second finger, and a vocal sac (Boycott et al. 2002).
This species is olive-brown dorsally, sometimes with a shade of reddish-brown or bronze. The venter is white with large, irregularly shaped yellow-brown patches. Ventral surfaces of the limbs are dirty mustard yellow-brown ventrally, with the yellow bordered by gray and white markings (Boycott et al. 2002).
Tadpoles measure 41 mm at Gosner stage 34. The tails are long. Nostrils are oval and rimmed. The spiracle is sinistral and situated along the body. The vent is basicaudal and dextral. The large mouth is ventral, and not visible dorsally. A marginal row of oral papillae with a wide rostral gap is present. Intramarginal papillae can be found at the posterior of the mouth and laterally to labial tooth rows only; there are estimated to be about 5 per row. There are only 2 single papillae anteriorly per side (Boycott et al. 2002).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: South Africa
Cacosternum karooicum is known from several localities in the Western Cape Province, South Africa (Boycott et al. 2002) as well as in the North Cape Province (Scott and Minter 2004). The distribution appears to be somewhat disjunct but it may occur in suitable habitat in the intervening areas (Scott and Minter 2004).
This species is found in Little Succulent Karoo and Lowland Succulent Karoo at elevations below 600 m and where there are less than 300 mm of precipitation yearly (Boycott et al. 2002). In the Succulent Karoo biome, low cyclonic winter rainfall and arid summers are prevalent (Boycott et al. 2002). Temperatures in excess of 40 degrees Celsius occur in the summer and hot "Berg" winds as a result of adiabatic heating are common (Boycott et al. 2002). C. karooicum can be found in areas with temporary streams (Boycott et al. 2002). Habitat includes dry shrubland, semi-desert areas, and rocky localities (Scott and Minter 2004).
Life History, Abundance, Activity, and Special Behaviors
The flattened appearance of these frogs hints that that they are lithophilic, hiding in rock cracks and crevices during extended periods of dryness (Boycott et al. 2002).
Breeding begins in January and February with heavy rains and flooding. These frogs have a preference for temporary stream beds. Watercourses only flow for short periods after rainfalls; thus, tadpoles are forced into the longer lasting pools along these watercourses (Boycott et al. 2002). This species is an opportunistic breeder, and will breed whenever rainfall is sufficiently high. It makes use both of naturally occurring stream pools as well as man-made water sources (Scott and Minter 2004).
The species produces two types of calls: advertisement and territorial. The advertisement call is described as a lengthy coarse rattle. It lasts 1320-1488 ms, however calls of 700 ms were also recorded, with the interval between these calls lasting from 1130-1350 ms. The territorial calls in contrast are much shorter with a duration of 568-762 ms (Boycott et al. 2002).
During the day, males were heard calling beneath overhanging rocks in the shallows at the water's edge, or from hidden spots beneath rocks and vegetation along the stream's course near and away from the water's edge. At night, some males called from exposed positions among rocks in the streams. Amplexus takes place mainly in deeper water located at covered spots on the downstream side of rocks or overhanging vegetation. The frogs are submerged throughout oviposition and eggs are laid in submerged vegetation. In order to complete this process successfully, a female must grasp the oviposition site with the forelimbs, and press her hindquarters against the oviposition site in short intervals while depositing the eggs directly onto the site (Boycott et al. 2002).
The species tend to engage in defensive responses similar to death shamming when captured: the back becomes hunched and the upper eyelids are flattened, and the limbs become rigid and are pulled close to the body for several minutes (Boycott et al. 2002).
Trends and Threats
The species epithet karooicum refers to the type locality, a semidesert region in South Africa. "Karoo" is derived from the Khoi-Khoi word "Karo", meaning thirsty (Boycott et al. 2002).
Boycott, R., Villiers, A., and Scott, E. (2002). ''A new species of Cacosternum Boulenger, 1887 (Anura: Ranidae) from the Karoo region of South Africa.'' Journal of Herpetology, 36(3), 333-341.
Scott, E., and Minter, L. (2004). Cacosternum karooicum. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.1. www.iucnredlist.org. Downloaded on 20 April 2010.
Originally submitted by: Keith Lui (first posted 2009-01-26)
Edited by: Kellie Whittaker (2010-04-19)
Species Account Citation: AmphibiaWeb 2010 Cacosternum karooicum: Karoo Caco <https://amphibiaweb.org/species/6028> University of California, Berkeley, CA, USA. Accessed Sep 29, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 29 Sep 2023.
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