Phrynobatrachus krefftii Boulenger, 1909

Greenwood, Laura, Loader, Simon P., Lawson, Lucinda, Greenbaum, Eli & Zimkus, Breda M., 2020, A new species of Phrynobatrachus (Amphibia: Anura: Phrynobatrachidae) from the Northern Mountains of Tanzania, Journal of Natural History 54 (1 - 4), pp. 63-85 : 70-78

Phrynobatrachus krefftii Boulenger, 1909

Lectotype (by present designation). BMNH 1947.2 .30.30 formerly 1909.10.19.14 – 15, adult male collected by Dr. Paul Krefft in Amani , East Usambara Mountains, Tanzania in 1909 February – March ( Figure 6 ).

Paralectotype. BMNH 1947.2 .30.31 formerly 1909.10.19.14 – 15, adult male collected by Dr . Paul Krefft in Amani , East Usambara Mountains, Tanzania in 1909 February – March ( Figure 7 ) .

Referred specimens. BMNH 1974.96 – 120, 1985.1011 – 1018, 1994.801 – 803, 2000.503 – 504, 2000.581 – 587, 2002.323, 2002.740 – 745, 2002.993 – 995, MCZ:Herp:A-138317-18. Please refer to Appendix 2 for further details.

Diagnosis

The species is assigned to Phrynobatrachus based on the following characteristics that can be seen on all referred specimens: lack of webbing between the fingers, presence of a mid-tarsal tubercle, an elongated inner and small round outer metatarsal tubercle, unpaired subgular vocal sacs in males, and a tympanum present. The large size of adult P. krefftii (maximum SVL of males 41 mm, of females 39 mm) distinguishes this puddle frog from most of the species of the genus, only matched or exceeded by P. ambanguluensis sp. nov., P. irangi , P. minutus , P. acutirostris , and P. sulfureogularis in East Africa. There are a number of additional morphological characteristics that are unique to this form. Apart from P. krefftii , only a few other species of Phrynobatrachus from East Africa exhibit a bright yellow throat in breeding males (including P. scheffleri , P. uzungwensis , P. dendrobates , P. sulfureogularis , P. krefftii , and P. ambanguluensis sp. nov.).

Other characteristics that can distinguish P. krefftii from the eastern species within Phrynobatrachus include: the absence of a spiny wart or tubercle on the eyelid (present in P. breviceps and P. rungwensis ); tympanum distinct and smaller than eye (not visible in P. keniensis , P. mababiensis , P. parvulus , P. rungwensis , P. scheffleri , P. stewartae , P. ukingensis , and P. uzungwensis ); throat of male being smooth and without asperities (present in P. acridoides , P. bullans , P. natalensis , P. rungwensis , P. kinangopensis ; sometimes present in P. perpalmatus , P. ukingensis , P. mababiensis , P. parvulus ); males lacking femoral glands (present in P. scheffleri , P. ukingensis , P. stewartae , P. parvulus ); finger and toe tips with swollen discs (not present in P. irangi , P. rungwensis , P. keniensis , P. auritus , P. bullans , P. perpalmatus , P. stewartae , P. parvulus ); back smooth with a limited number of tubercles (unlike P. scheffleri , P. uzungwnesis , P. rungwensis , P. natalensis , P. mababiensis , P. stewartae ); toes of male without spine-like plantar tubercles (only commonly seen in P. irangi , P. versicolor ); upper snout slightly overhanging lower jaw (whereas in P. ambanguluensis sp. nov. upper jaw is substantially extended beyond the lower jaw); tympanum cushion lighter coloured than surrounding membrane (reverse is true in P. ambanguluensis sp. nov.). Furthermore, P. krefftii differs from all congeners with published 16S rRNA sequences by an uncorrected p-distance of at least 4.75%.

Description of the lectotype

Relatively large male specimen (40 mm) with smooth skin; see Table 3 for measurements. Head shape pointed with a blunt snout. Canthus rostralis is obliquely directed and flat. Nostrils at the end of the blunt snout near the edge of the canthus rostralis positioned closer to the apex of the snout (1/3 of the total distance of the eye to the snout end) than the eye. Snout not projecting much beyond the lower jaw. Tongue present with medial conical papilla. Choanae present on anterior part of the roof of the mouth. Eyes are large, about nov. twice the size of the tympanum. Tympanum present and distinct – circular in shape. Interorbital distance is twice as large as the upper-eyelid distance. Vocal sacs are positioned as unpaired in subgular region, but not easy to decipher in the specimen. No glandular mass present under the armpits. Fingers moderately long, lacking any webbing with distal expanded toe tips – though only slightly. Nuptial pads present on the thumb. First finger shorter than second and third, with second finger longer than the third. Palm with a long, thin inner metatarsal tubercle, directed along the inner edge of the nuptial pad. An outer metatarsal tubercle is present, rounded and relatively large. Tibio-tarsal articulation reaches the snout with the knee joint adjacent to the anterior margin of the tympanum.

Legs are long with muscular thighs. Tarsal tubercle present. Toes are relatively long and thin, with extensive webbing (1e(0), 2i(1), 2e(0), 3i(0.5), 3e(0), 4i(1.5), 4e(0), 5i(0)). Tips of toes slightly swollen and expanded. Tubercle present on the inner toe, long and thin, directed along the inner edge of the first toe, a small-rounded tubercle present on the outer/mid-portion of the anterior margin of the foot. No white spines found on toes between tubercles.

The specimen is slightly faded in preservation. It has a light brown mottling dorsally, with a thin dark brown interorbital band between which is cream edged on the anterior side at the mid-line of the eyes. Snout is cream/light brown coloured. The legs are light brown with slightly darker brown banding along the legs. Ventrally, the lower jaw is edged with brown overlaying a cream colouration. The gular flap is lighter coloured with a darker cream/brown ventral region.

Variation

Phrynobatrachus krefftii shows sexual dimorphism in adult specimens; see Tables 2 and 3. Mature males with bright yellow throat with unpaired subgular vocal sac. Furthermore, nuptial pads present on thumbs in some adult males, toes with spine-like plantar tubercles, first and second toe with small spines. Females with brown and slightly light brown speckled throat lacking vocal sacs. From referred specimens, male SVL up to a maximum of 41.3 mm, female SVL up to 39.9 mm. These maximum values differ with the literature, which specifies females (41 mm maximum size) as being marginally larger than males (36 mm maximum size) ( Channing and Rödel 2019). It seems males and females reach similar maximum sizes (ca. 41 mm). Minimum SVL recorded was 14.3 mm in a juvenile (BMNH 1974.120), and the sex was indeterminate. Pattern variation between specimens of P. krefftii is largely limited, with slight differences in banding on the dorsum of the hind limbs, including bolder stripes on the forehead and more speckling on the dorsal view of the torso.

Interestingly, six specimens (BMNH 1974.96, 1974.99, 1974.101, 1985.1014, 2000.503, 2000.586) of both males and females from Amani show distinct colour differences. In these specimens, there is a distinctive light brown/orangish dorsolateral light stripe (5 mm wide) on a dark brown dorsum. They also lack strong broad infraorbital patterning as in P. krefftii – present but thinner. In all other respects, ventral colouration (throat colouration between the sexes), and diagnostic characters, these specimens are referable to P. krefftii and therefore are considered by the authors of this study as being conspecific with P. krefftii . No DNA data were available for these individuals. Further analyses might reveal additional differences to suggest them as being distinctive species. See Table 1 for a summary of all the measurements between the species and sexes.

Colouration of species in life

In life, brown above; a dark brown cross-bar between the eyes, cream-edged in front; limbs slightly lighter than torso with indistinct dark brown cross-bands; ventral parts whitishyellow; ventral surface of limbs and torso dotted with brown; a prominent brown band across the throat; another prominent brown band across the dorsal pectoral girdle; lower jaw edge defined with dark brown against a yellow throat (specific to males) (see Figure 8 ).

Colouration of species in preservative

In preservation, colouration is similar to that in life, with fading of the yellow underside to a yellow-beige (see Figures 6 and 7 ).

Habitat and natural history

The species is diurnal and found in submontane forest and streams in the East Usambara Mountains (600 – 1250 m) and Magrotto Mountains. Phyrnobatrachus krefftii has not been observed in deforested habitats, but it has been found in modified stream habitats inside forests. Breeding takes place in damp and moist areas alongside streams, and egg masses (15 – 30 eggs darkly pigmented) are attached to rocks or vegetation above the water. Adults have been observed in close proximity to egg masses, which might suggest some type of guarding from predation or regulation of the egg mass environment ( Channing and Rödel 2019). Males are believed to be territorial, they approach one another with inflated brightly coloured yellow vocal sacs, which don't emit any sound. This unique signalling behaviour was observed in Phrynobatrachus kreffti in Amani, East Usambara Mountains ( Hirschmann and Hödl 2006). It was observed that 77% of inflations of vocal sacs were purely visual, and only 23% were bimodal, and accompanied by sound production (see below for details on vocalisations).

Vocalisations

Phrynobatrachus kreffti has two call types, with one most frequent. Hirschmann and Hödl (2006) thoroughly documented the variation from Amani, the type locality, and they are directly quoted from their paper in full for completeness:

‘Call-type 1 (1127 out of 1909 calls) was most frequently recorded. It consists of a single note, with a duration of 177–374 ms (x ± SD = 268.0 ± 66.3 ms; n = 9). The dominant frequency is 1.97– 2.60 kHz (x ± SD = 2.20 ± 0.20 kHz; n = 9). When other individuals were absent or at least not visible to us, 52% of the acoustic signals given consisted of call-type 1. The mean SPL of call-type 1, recorded at 0.75 m distance of vocalising individuals, measured 61.5 dB (SD = 3.3 dB; n = 9) and thus exceeded the ambient SPL by 10 dB. Call-type 2 ( Figure 4 ) consisted of 4 to 6 notes. The mean duration of call-type 2 was 950 ms (SD = 100.6 ms; range 842.2–1180.4 ms; n = 7). The first note of call-type 2 lasted from 243 to 335 ms (x± SD = 278.7 +/- 31.8 ms; n = 7) and possessed a dominant frequency at 2.075–2.52 kHz (x± SD +/- 0.14 kHz; n = 7) and thus resembles call-type 1. The duration of the following notes is much shorter: 34–47 ms (x ± SD = 39.3 ± 4.4 ms; n = 28), with a dominant-frequency range between 1.92 and 2.575 kHz (x ± SD = 2.20 +/- 0.24 kHz; n = 28). Each note was separated by an interval of 108.7–146 ms (x ± SD = 123.8 ± 9.6; n = 27). The SPL of call-type 2 (x ± SD = 62.9 ± 1.8 dB; n = 7) exceeded the ambient SPL by 11.4 dB.’

Figures

Figure 4. Morphological variation between males of P. krefftii and P. ambanguluensis. Direct comparisons of characters (abbreviations shown for traits described in the methods section) in P. krefftii (orange) and P. ambanguluensis (blue). For each trait, boxplots show the median, interquartile ranges and overall ranges of measurements, with outliers indicated by circles. Significantly different traits between P. krefftii and P. ambanguluensis after correcting for multiple tests are indicated with an asterisk. PCA analyses of the three species (P. krefftii, P. ambanguluensis, and the single North Pare male (purple)) showing PC1 and PC2 are shown in the bottom right corner. No differences were observed.

Figure 6. Dorsal, ventral, lateral and close-up views of the male lectotype (BMNH 1947.2.30.30) of Phrynobatrachus krefftii. Left: ventral view of left foot (top); ventral view of left hand (bottom). Right: dorsal view of body (top); ventral view of body (middle); lateral view of body (bottom). Scale bar is 1 mm.

Figure 7. Dorsal, ventral, lateral and close-up views of the male paralectotype (BMNH 1947.2.30.31) of Phrynobatrachus krefftii. Left: ventral view of left hand (top); ventral view of left foot (bottom). Right: dorsal view of body (top); ventral view of body (middle); lateral view of body (bottom). Scale bar is 1 mm.

Figure 8. Phrynobatrachus krefftii in life from the type locality (Amani Nature Reserve), a) male and female in amplexus, b) male, c) close-up of Phrynobatrachus krefftii eggs, and, d) male, showing bright yellow gular patch. Photos provided by James Vonesh. Non-vouchered specimens.