Litoria sibilus, Parkin & Rowley & Elliott-Tate & Mahony & Sumner & Melville & Donnellan, 2024

Parkin, Tom, Rowley, Jodi J. L., Elliott-Tate, Jessica, Mahony, Michael J., Sumner, Joanna, Melville, Jane & Donnellan, Stephen C., 2024, Systematic assessment of the brown tree frog (Anura: Pelodryadidae: Litoria ewingii) reveals two endemic species in South Australia, Zootaxa 5406 (1), pp. 1-36 : 28-30

Litoria sibilus sp. nov.

Suggested common name: Kangaroo Island Tree Frog

Figs 13 , 14

Holotype. SAMA R37403 (tissue voucher ABTC 33479), adult female, 1.5 km NW Rocky River, Flinders Chase National Park, Kangaroo Island, South Australia (35.94ºS, 136.73ºE), Collected by David Armstrong on 12 th November 1990.

Material examined. See Supplementary Table S1 (https://zenodo.org/record/8423599) for details of all material examined.

Holotype measurements (mm). SVL 39.4, FOL 29.7, TL 20.3, THL 20.0, HW 11.8, IOD 3.9, DFE 6.9, IND 3.2, NS 2.4, EN 3.0, ED 4.2, HDD 5.1, SL 4.9, HL 17.0, UAL 6.9, LAL 9.2, HAL 12.2, AL 20.2, FL 17.44, IMT 1.2, TMP 2.25, Fin3DW 1.69, Fin3W 1.05, Toe4DW 1.4, Toe4W 0.89.

Diagnosis. Litoria sibilus is diagnosable from all other members of the L. ewingii group by a combination of (1) adult body size 25–34 mm for males and 28–43 mm for females, (2) moderately robust build, (3) pads wider than fingers (mean Fin3W/Fin3DW = 0.6) and toes (mean Toe4W/Toe4DW = 0.7), (4) webbing on hands vestigial but relatively well-developed on the feet (extending to the 1 st subarticular tubercle on the 4 th toe [see Fig 8 , Type B]), (5) posterior edge of thigh orange-pink, usually patterned with dark spots and blotches (n= 26/27), occasionally plain (n=1/27), (6) dark spots or blotches in inguinal region usually absent (n=23/27), sometimes a single spot may be present right at the junction of the thigh and body (n=4/27), (7) genetically by apomorphic nucleotide states at 15 sites in the ND4 gene. Diagnoses of Litoria sibilus and the other species described herein are presented in Table 8 for ease of comparison.

Description of holotype. Habitus moderately slender. Head longer than wide (HW/HL = 0.7), tympanum oblong-shaped, smaller than eye (TMP/ED = 0.5), and partially obscured by a tympanic fold. Snout rounded in dorsal and lateral profiles. Fingers and toes slender, fingers unwebbed and toes with moderate webbing. Finger and toe pads wider than digits (Fin3W/Fin3DW and Toe4W/Toe4DW = 0.6). Sub-articular tubercles and metacarpal tubercles visible, inner-metatarsal tubercles prominent, oblong-shaped and approximately two-thirds the length of the fourth toe. Oviducal follicles visible from abdominal cavity indicates specimen is a gravid female.Arms and legs moderately long (TL/SVL = 0.5) and slender. Texture of dorsal surface smooth, ventral surface coarsely granular.

Colour in preservative. Dorsum uniformly silver-grey. Yellow-green grey ventral surface. A single faint dark spot present in the inguinal pocket, at the junction of the thigh and abdomen. Subtle pink posterior edge of thigh with numerous dark rounded spots. White stripe present from below eye to shoulder and above eye to upper tympanum.

Variation. Summary of variation in morphometric characters for each sex is presented in Table 6 .

Colour and pattern (in life). Variation in colour described from images taken in life ( Fig 14 ). Dorsum base light silvery grey to copper, with dark burnt brown, black-edged, longitudinally aligned, and bifurcated bands extending from between eyes to vent. Upper surface of legs coppery pink, posterior edge of thigh orange-pink usually patterned with dark spots and blotches (n= 26/27), occasionally plain (n=1/27). Dark spots or blotches in inguinal region usually absent (n=23/27), sometimes a single spot may be present right at the junction of the thigh and body (n=4/27). Silver, pink, grey to copper stripe extends from rostrum through eye to lateral zone. White stripe present from below eye to shoulder. Iris gold.

Etymology. The specific epithet, sibilus , is a masculine Latin 2 nd declension noun meaning whistle or hiss. It is used in apposition to the genus name.

Advertisement Call. Call description is based on the calls of six individuals. The advertisement call of Litoria sibilus has a duration of 1.48– 2.34 s (mean 1.78 s) and comprises 8–11 (mean 9) pulsed notes. Notes are typically short 0.1– 0.28 s (mean 0.17 s) with the shortest note at the beginning (83.3% of calls) and the longest note at the end (50%). Notes have limited intervals between them and are not distinctly pulsed. In 50% of calls, amplitude rose to a peak in roughly the middle of each note before descending, giving a tent-like appearance ( Fig. 7 ). Dominant frequency had a short range of 2156–2541 Hz (mean 2451 Hz).

Comparison with other species. Litoria sibilus is isolated from all other members of the L. ewingii group, separated from the closest species, L. calliscelis , across a 13 km stretch of sea known as the Backstairs Passage, which separates Kangaroo Island from the adjacent mainland. For a description of colour/pattern features potentially useful for identification where collection locality is unknown, see Litoria ewingii and L. calliscelis above.

Distribution and habitat. Endemic and widespread on Kangaroo Island (4,405 sq km), Australia’s third largest island, situated off the South Australian coast.

Habitat poorly known but has been recorded in forest, heathland and disturbed agricultural land.

Ecology and reproduction. The species is uncommonly recorded via FrogID (68 records from 10 November 2017 – 30 June 2022), but is often heard calling in disturbed areas, with 6% of FrogID records of the species documented as being in urban habitats and 74% of records in rural areas. Breeding period appears to be extended, with males recorded calling in January–November, with the majority of FrogID submissions from between March– May. Breeding habitat poorly known but appears to include static ephemeral and permanent waterbodies such as dams, ponds, swamps, inundated ditches and streamside ponds and pools. For a detailed description of tadpole development and morphology specific to this taxon, see Anstis (2017).

Conservation status. Litoria sibilus has the most restricted distribution of all species within the Litoria ewingii Group. AOO was calculated for the species at 268 km 2 and EOO 3,743 km 2. Under criterion B of the IUCN Red List guidelines, these calculations potentially qualify the taxon for Endangered listing (AOO <500 km 2; EOO <5,000km 2). However, given there is a lack of baseline information indicating severe fragmentation, decline or fluctuation in population size, we suggest a conservative listing of Data Deficient to be appropriate for this taxon until further information becomes available. Of particular concern is the potential threat posed by the devastating bushfires that occurred on Kangaroo Island in 2019–2020, which burned through 45.9% the island’s landmass ( Bonney et al. 2020). Targeted surveys of Litoria sibilus are required to establish a population baseline and assess post-fire population health and recovery.

Figures

FIGURE 7. Comparison of audio spectrograms of the advertisement calls of A) Litoria ewingii, Lake Burbary, Queenstown, Tasmania (FrogID: 166278) B) Litoria sibilus sp. nov., Pelican Lagoon, Kangaroo Island, South Australia (FrogID: 23471) and C) Litoria calliscelis, Victor Harbour, Fleurieu Peninsula, South Australia (FrogID: 242125).

FIGURE 8. Comparison of the hind feet of Litoria verreauxii and L. ewingii showing differences in toe pad size and webbing extent: Type A) Litoria verreauxii and Type B) represents Litoria ewingii, L. calliscelis and L. sibilus sp. nov. Subarticular tubercles 1 and 2 are indicated by circles.

FIGURE 13. Holotype of Litoria sibilus sp. nov., SAMA R.37403, adult female, Flinders Chase National Park, Kangaroo Island, South Australia.

FIGURE 14. Images in life of Litoria sibilus sp. nov. A–E unvouchered individuals (Mark Sanders). A) Parndana, central Kangaroo Island; B) Parndana, central Kangaroo Island, C) Vivonne Bay, southern Kangaroo Island; D) hindfoot of individual in A; E) hand of individual A; F–G unvouchered individuals, Kangaroo Island (Department of Environment and Water, South Australian Government).