Cacosternum thorini, Conradie, 2014

Conradie, Werner, 2014, The King of the Dwarves: a new cryptic species of Dainty Frog (Anura: Pyxicephalidae: Cacosternum) from the eastern Great Escarpment of South Africa, Zootaxa 3785 (3), pp. 438-452 : 438-452

Cacosternum thorini sp. nov.

Hogsback Dainty Frog

( Figures 3 , 4 & 6 )

Holotype. An adult male ( PEM A10091 , Fig. 3 A&B) deposited in the Port Elizabeth Museum (PEM), South Africa. Collected 7 October 2011, by W. Conradie & C. Morrison from a small wetland below the forestry fire lookout tower, Hogsback , Eastern Cape Province, South Africa (32°34’48” S; 26°56’34” E, 3225CA , 1530 m above sea level).

Allotype. An adult female (PEM A10083 , Fig. 3 C&D), identical collecting details as Holotype .

Paratypes. 8 females ( PEM A10084 , - 10087 , - 10088 , - 10093 , - 10100 , - 10103 ; SAIAB 191643.1 ; NMB A8007 ) and 14 males ( PEM A10082 , - 10085 , - 10086 , - 10089 , - 10090 , - 10094 , - 10096 , - 10098 , - 10099 , - 10101 , - 10102 , - 10105 ; SAIAB 191643.2 ; NMB A8008 ), identical collecting details as Holotype .

Diagnosis. A species referred to the genus Cacosternum on the following characters: pupil horizontal; vomerine teeth absent; no mid-tarsal tubercle; no webbing on fingers and toes; no terminal discs on fingers and toes; tympanum hidden; smooth immaculate ventral surface with fine mottling ( Channing 2001); and molecular monophly for the 16S mitochondrial marker with other Cacosternum taxa ( Fig. 2 ).

This new species differs from other Cacosternum species with regard to the 16S fragment, by a net uncorrected p-distance value of 1.9–5.4%. The within-clade variation is zero (see Table 2 ). Although the net uncorrected pdistance between the new species and his closest relative is very low (1.9%), it is well in range with values provided by Channing et al. (2013) for other valid species. The new species forms part of the Cacosternum boettgeri complex ( Fig. 2 ).

The dorsum is smooth with no protruding skin glands or ridges, distinct from C. capense (with protruding lateral and dorsoventral skin glands), C. nanogularum and C. aggestum (hourglass pattern skin glands), and C. parvum (longitudinal dorsolateral skin ridges); no webbing between toes, distinct from C. leleupi (webbing reaches proximal subarticular tubercle of fourth toe); tympanum absent (present C. kinangopensis ); viewed from above, the nostrils are closer to the snout than in C. karooicum (nostril situated at least three nostril diameters from anterior margin of snout); supratympanic fold is indistinct, distinct from C. boettgeri , C. namaquense and C. striatum (form a thickened saddle); inner metatarsal tubercle is small, low, and equal to the width of the tip of the first toe, which distinguishes them from those where the inner metatarsal tubercle is twice the width of the tip of the first toe ( C. leleupi , C. aggestum , C. parvum and C. plimptoni ); rictal gland is smooth and uninterrupted, distinct from C. nanum and C. platys (interrupted and bumpy); no supernumerary tubercles on the palm, distinguishing it from species with 2–5 tubercles ( C. aggestum , C. boettgeri , C. capense , C. karooicum , C. leleupi , C. namaquense , C. nanogularum , C. nanum and C. platys ).

The vocal sac of breeding males is yellow-beige with a very light mottled appearance ( Fig. 3 B), which distinguishes it from species with dark throats ( C. boettgeri , C. capense , C. kinangopensis , C. leleupi , C. namaquense , C. nanogularum , C. nanum , C. parvum , and C. platys ), species where the throat is beige with bolder fine mottling ( C. aggestum , C. australis , C. karooicum ), but indistinct from species with white to yellow throats ( C. plimptoni , C. rhythmum and C. striatum ); ventrum is immaculate with lateral margins with small speckles, which distinguishes it from all other Cacosternum species except C. parvum , C. rhythmum and C. striatum .

The advertisement call consists of a string of ‘chirps’ followed by a number of longer ‘creaks’, produced with a distinctive beat. It differs from the simple series of single or multiple clicks of C. boettgeri , C. kinangopensis , C. leleupi , and C. plimptoni or the creaking calls of C. capense , C. karooicum , C. namaquense , C. nanogularum , C. parvum , and C. striatum or the brief chirps of C. nanum . It differs from those species producing a 'bouncing marble' call of pulses that speed up such as C. aggestum , C. australis and C. platys . Call structure mostly resembles that of C. rhythmum .

Description of the holotype (all measures in mm). Small adult male, SUL 14.0. Body slender, widest at midbelly, with a narrow head (HW/SUL 0.3). The head is acutely rounded from above and in profile. Head length measured from the angle of the jaw is moderate (HL/SUL 0.4). Canthus rostralis rounded, straight from eye to nostril, loreal region convex; nostrils small, rounded, directed laterally. The nostrils are placed closer to the snout than to the eye (EN/SL 0.5). Internostril distance is less than distance between eye and nostril (NN/EN 1.2). Eyes directed anterolaterally, the eyes protrude, and barely visible from below, relatively small (ED/HW 0.4; ED/SUL 0.1), nearly equal to snout (ED/SL 0.8). Distance between anterior corners of eyes nearly double the internostril distance (NN/EE 0.5). The angle of the jaw is posterior to a line drawn vertically from the back of the eye. Tympanum not visible. Jaws without dentition; choanae small, round, located at anterior margins of roof of mouth; vomer processes and teeth absent; tongue long (2.9), narrow proximally, broad distally (maximum 2.0), slightly bifurcated distally, proximal third attached to lower jaw. No median lingual papilla present.

The dorsal surfaces of the head, trunk and limbs are smooth, with no glands and skin folds present; the rictal gland is smooth, continuing posteriorly unbroken to just before arm insertion. Supratympanic fold inconspicuous to absent. Ventrally smooth, with very light mottled appearance, vocal sac yellow-beige with a slight mottled appearance ( Fig. 3 B).

The forelimb is slender, hand small (HAN/SUL 0.3), finger tips bluntly rounded without discs. Relative finger lengths I<II<IV<III; subarticular tubercles distinct, rounded, with one on fingers I and II, two on finger IV and three on finger III, with the proximal subarticular tubercle on finger III small but distinct. No webbing between fingers. Thenar tubercle small, rounded, partially obscured by nuptial pad that reaches the distal phalanx of the first finger; palmar tubercles and inner metacarpal tubercle small, rounded; outer metacarpal tubercle minute. No supernumerary tubercles are present on the palm.

Hind limbs moderately long (TIB/SUL 0.4; FOT/SUL 0.5), foot longer than tibia (TIB/FOT 0.8); thighs are moderately developed, with rough glands on the inner posterior faces; relative toe lengths are I<II<V<III<IV. The toe tips are not expanded; subarticular tubercles: one on toes I and II, two on toes III and V, and three on toe IV. Only a trace of webbing between toes V and IV and toes IV and III, reaching the proximal subarticular tubercule. Inner metatarsal tubercle conical and prominent, outer metatarsal tubercle present as a small pale raised spot.

Colour in life ( Fig 3 A–D). The dorsum is brown with small black speckles and white blotches. Ventrum is yellow with slight black mottling and white blotches. Nuptial pads prominent dark brown to black. Colour in preservative. Dorsally uniform dark brown to grey. Ventrally immaculate white with fine black pigmentation. The undersides of the hands and feet are pigmented, thighs and arms are slightly pigmented.

Paratype variation. The paratypes are similar in body proportions to the holotype (see Table 3 ). The males range in SUL from 11.0–14.0, with the females from 12.5–15.6. The rictal gland is identical in all the paratypes, while the subarticular tubercles of the hand vary slightly, from round to a sharper cone-shape. Dorsal colouration in life varies from uniform grey to uniform brown, and with only three showing green dorsal colouration ( Fig. 4 ). The belly is immaculate in all the paratypes, with none showing prominent black spots. Eggs are visible through the belly skin of one female. Females lack nuptial pads.

Advertisement call. Air temperature at time of recording around 12 °C. Males were calling both diurnally and nocturnally. Typical calls recorded at the type locality (n=4) consist of two different call types, e.g. a shorter single or double ‘chirp’ followed by a longer ‘creak’ ( Fig. 5 ). The ‘chirp’ call comprises a series of evenly spaced pulse notes (up to 10), each comprising 5–7 pulses, emitted at a rate of 170 (range 136–208) pulses per second; call duration of 35 (range 24–51) milliseconds; dominant frequency range between 4.0–4.6 kHz. This is followed by a longer ‘creak’ call which comprises of a series of pulse notes (up to 13), each comprising 12–29 (mean 21) pulses, emitted at a rate of 69 (55–88); call duration of 303 (213–410) milliseconds; and dominant frequency range between 4.4–4.6 kHz.

Eggs and tadpoles. Single dissected female paratype (PEM A10100) contained 42 eggs with an average diameter of 1.0 mm. Eggs (n=52) laid overnight on 7 October 2011 by two pairs in amplexus were raised to metamorphosis. Eggs were deposited individually batched together in clumps of up to 5–10 attached to floating vegetation in a tupperware container (dimensions 30 x 30 cm). Eggs hatched after 2–4 days. Free swimming stage was reached after five days and was fed daily with either fish flakes or boiled lettuce leaves. Water was changed daily with dechlorinated water. Tadpoles reached metamorphosing stages on day 42. Development took 49 days. Maximum size 20.4 mm TL and 7.9 mm BL, Gosner stage 42.

The following description is based on a single tadpole from PEM T642 series at Gosner stage 35. All measurements in mm. Lateral view ( Fig. 6 A): Body round to ovoid; body little wider than high (BH/BW 0.9); snout oblique; mouth directed near ventral; nasals rounded, very small, positioned dorsally, situated midway between snout and eyes (SND/NOD 1.1); eyes moderately sized (ED 17% of BL), round in shape, positioned and directed laterally; spiracular tube sinistral, tubular, small, joined to body wall, positioned laterally and situated closer to vent than snout (SS 62% of BL), spiracle opening oval directed slightly upwards, at the height of the middle of the lower part of the caudal muscle; tail just over one and a half of body length (TAL/BL 1.6) and two thirds of total length (TAL/TTL 0.6), tail musculature narrow (TMH 41% of BH and 62% of MTH), tapering gradually to a slightly pointed tail tip; tail fins of moderate size, deepest midway down tail; upper fin extending onto body, slightly convex to the end of the tail; lower fin slightly convex to the end of tail. Dorsal view ( Fig. 6 B): Body oval, little wider than high (BW/ BH 1.1), widest just in front of the spiracle opening; snout rounded; nasals moderately spaced; interorbital distance nearly equal to internarial distance (IOD/ IND 1.1); tail muscle width 33% of body width (TMW/BW 0.3). Ventral view ( Fig. 6 C): Eyes bulging and not visible in ventral view; vent tube supramarginal, dextral and short with an oval vent opening. Oral disc ( Fig. 6 D): Positioned and directed near ventral, moderately large (ODW 46% of BW); LTRF: 3(2-3)/3(1), third posterior row nearly equal in length of the first and second row; jaw sheaths moderately pigmented, capsulated and rounded; lateral process moderately short; single row of posterior marginal papillae, a single row of anterior marginal papillae only in corners, anterior gap free of papillae (up to 80% free); posterior corners with no submarginal papillae; lateral margins of oral disc slightly indented. Colouration: Body moderately pigmented, brown with randomly scattered golden spots, eyes dark, iris with golden lining, dorsum dark, ventrum paler with scattered darker pigmentation, internal collided intestine barely discernable through skin, obscured by a silvery lining with golden reflection; tail musculature slightly more pigmented than fins; fins finely mottled and translucent. Measurements: TTL 16.5; BL 6.6; TAL 9.9; BH 3.1; BW 3.4; TMW 1.1; MTH 2.2; TMH 1.4; IOD 1.3; IND 1.2; NOD 1.0; SND 1.0; SOD 2.0; SS 3.8; ED 1.0; ODW 1.6.

Natural history. Specimens were collected diurnally by dip netting small montane wetland pools, with abundant vegetation, where calls were heard from. Pools varied in size, but never bigger than 50 cm and deeper than 50 cm. The species is highly territorial as each pool contained only a single calling male. Cacosternum nanum was found sympatrically, but preferred the bigger pools with more surface water and less vegetation. The only other frog species found in the same habitat was Strongylopus grayii .

Distribution. Currently the new species is only known from the montane grassland surrounding Hogsback, but is expected to be more widely distributed in the Amatola Mountain range and surrounding mountain ranges ( Fig. 1 ). It is geographically well separated from C. leleupi , C. plimptoni and C. kinangopensis (more than 2500 km); from Western Cape and Northern Cape endemics ( C. aggestum , C. australis , C. capense , C. karooicum , C. namaquense , and C. platys ); and from KwaZulu-Natal endemics ( C. nanogularum , C. rhythmum , and C. striatum ); but overlaps with C. boettgeri , C. nanum and potentially C. parvum .

Etymology. The species name is derived from Thorin II Oakenshield, a fictional character in the J.R.R. Tolkien novel ‘The Hobbit’. Thorin is the Prince of the Dwarves and eventually becomes the King Under the Mountain; he is also greatly admired for being a singer of note. Thorin also means ‘dwarf’ in Old Norse. It is widely known and accepted that Hogsback was the inspiration behind J.R.R. Tolkien’s novels the ‘The Hobbit’ and the ‘Lord of the Rings’ series. The name references its small size, its complicated call and the fact that it is found at the base of a large mountain in Hogsback.

Figures

FIGURE 1. Map showing the type locality of C. thorini sp. nov. (red circle), dotted line represents the Great Winterberg – Amatola Mountain range (and potential distribution of the new species), blue lines represent major rivers, colour represents altitudinal gradient. Insert: photo of type locality.

FIGURE 2. Bayesian consensus phylogram for populations of Cacosternum examined in this study. Node support with posterior probabilities> 0.95 and maximum likelihood bootstrap> 70 % are indicated with a black circle. Nodes supported only by posterior probabilities are indicated with a white circle.

FIGURE 3. Cacosternum thorini sp. nov. from Hogsback, South Africa (A—lateral view of male holotype, B—ventral view of male holotype, C—lateral view of female allotype and D—ventral view of female allotype).

FIGURE 4. Paratype colour variation of Cacosternum thorini sp. nov. from Hogsback, South Africa.

FIGURE 5. The advertisement call of Cacosternum thorini sp. nov. from Hogsback, South Africa (A—initial single or double ‘ chirp’ and B—longer ‘ creak’).

FIGURE 6. The tadpole of Cacosternum thorini sp. nov. (PEM T 517) from Hogsback, South Africa (A—lateral view, Bdorsal view, C—ventral view and D—line drawing of LTRF).

Tables

TABLE 2. Average uncorrected p-distance between Cacosternum species based on 16 S sequences.

		1	2	3	4	5	6	7	8
1	M. capensis	-
2	C. aggestum	0.085
3	C. australis	0.085	0.041
4	C. boettgeri	0.094	0.048	0.031
5	C. capense	0.087	0.048	0.039	0.045
6	C. karooicum	0.091	0.054	0.045	0.048	0.043
7	C. kinangopensis	0.095	0.052	0.038	0.036	0.056	0.056
8	C. leleupi	0.102	0.048	0.054	0.045	0.045	0.056	0.067
9	C. namaquense	0.091	0.043	0.028	0.036	0.024	0.043	0.048	0.045
10	C. nanogularum	0.105	0.061	0.057	0.057	0.054	0.045	0.059	0.052
11	C. nanum	0.085	0.050	0.053	0.039	0.046	0.042	0.048	0.050
12	C. parvum	0.100	0.052	0.054	0.045	0.054	0.050	0.058	0.050
13	C. platys	0.102	0.054	0.028	0.033	0.048	0.050	0.037	0.056
14	C. plimptoni	0.094	0.044	0.022	0.026	0.048	0.044	0.044	0.046
15	C. rhythmum	0.091	0.050	0.030	0.012	0.048	0.041	0.030	0.043
16	C. striatum	0.093	0.048	0.030	0.025	0.050	0.050	0.030	0.054
17	C. thorini sp.nov.	0.100	0.052	0.030	0.021	0.048	0.048	0.041	0.050

TABLE 3. Morphological features (mm) of Cacosternum thorini sp. nov. See Material and Methods for explanation of abbreviations.

	Males (n = 15)		Females (n = 9)
	Mean	Standard Deviation	Mean	Standard Deviation
SUL	12.9	0.8	14.3	1.1
TIB	5.3	0.3	5.7	0.3
FOT	7.3	0.3	7.5	0.5
EN	1.0	0.1	1.0	0.1
SL	1.8	0.2	2.0	0.2
EE	2.1	0.1	2.1	0.2
ED	1.5	0.1	1.6	0.2
NN	1.2	0.1	1.3	0.1
HW	4.2	0.3	4.4	0.3
RAD	2.6	0.2	2.8	0.1
HAN	3.3	0.3	3.6	0.1