Litoria ewingii ( Duméril & Bibron, 1841 )

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 : 20-25

Litoria ewingii ( Duméril & Bibron, 1841)

Suggested common name: Brown Tree Frog

Figs 9 , 10

Hyla ewingii . Duméril, A.M.C. & Bibron, G. (1841) Erpétologie Genérale ou Histoire Naturelle Complète des Reptiles. Volume 8. Paris: Librarie Enclyclopedique de Roret

Lectotype. MNHN 4851 (designated by Guibe, 1950). Type locality: “ la terre de Van Diémen ” = Tasmania, Australia.

Synonyms.

Hyla parvidens . Holotype: ZMB 8252. Type locality: “ Australien (Port Phillip)”, Victoria, Australia. Peters, W.C.H. (1874) Über neue Amphibien ( Gymnopis, Siphonops, Polypedates, Rhacophorus , Hyla, Clyclodus, Euprepes, Clemmys ). Monatsberichte der Königlichen Preussische Akademie des Wissenschaften zu Berlin, 1874, 616–624.

Material examined. Hyla ewingii and Hyla parvidens types viewed from high-resolution images.See Supplementary Table S1 (https://zenodo.org/record/8423599) for full list of specimens used in morphometric analyses.

Revised diagnosis. Litoria ewingii is diagnosable from all other members of the ewingii group based on a combination of (1) adult body size 28–35 mm for males, 28–45 mm for females, (2) moderately robust build, (3) pads wider than fingers (mean Fin3W/Fin3 DW = 0.6) and toes (mean Toe4W/Toe4 DW = 0.7), (4) webbing vestigial on the hands but relatively well-developed on the feet (typically extending from 1 st —halfway between 1 st and 2 nd subarticular tubercle, rarely extending to the 2 nd [see Fig 8 , Type B]), (5) posterior edge of thigh orange-yellow and usually plain, unpatterned (n=27/32), but sometimes with scattered dark spots, flecks or lines (n=5/32), (6) dark spots in the inguinal region usually absent (n=29/33), although occasionally present (n=4/33), (7) genetically by apomorphic nucleotide states at 8 sites in the ND4 gene ( Table 4 ). Diagnoses of Litoria ewingii and the other species described herein are presented in Table 8 for ease of comparison.

Redescription of Holotype. We redescribe the holotype based on images of the preserved specimen after more than 180 years in preservative ( Fig. 9 ). Habitus moderately robust. Head slightly longer than wide, widest at commissure of the jaws. Tympanum smaller than eye, rounded and partially obscured by a tympanic fold. Snout rounded in dorsal and lateral profiles. Fingers unwebbed and toes with moderate webbing. Finger and toe pads wider than digits. Sub-articular tubercles visible, metacarpal tubercles prominent, inner-metatarsal tubercles somewhat prominent, oblong-shaped and approximately one-third the length of the fourth toe. Arms and legs moderately long and slender. Texture of dorsal surface finely granular, ventral surface coarsely granular, inguinal region, lower surface of tibia, upper surface of thighs and throat smooth.

Colour in preservative. Dorsum varies tonally between copper-brown—beige and cream with faded dark bifurcated markings running longitudinally from between eyes to vent. Ventral surface light coppery-yellow.

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 10 ). Dorsum base colour varies from cream, beige, grey to light copper brown, occasionally even lime green (i.e., Fig 10 /D and F), often fading in intensity posteriorly. Darker grey to copper-brown longitudinally aligned and bifurcated (occasionally completely separated) bands usually extend from between eyes to vent, although may be faded or absent in some individuals. Upper surface of legs brown, cream to grey or green with posterior edge of thigh orange-yellow and typically unpatterned (n=27/32), but sometimes with scattered dark spots, flecks or lines (n=5/32). Light cream zone usually present on posterior edge of shoulder, with grey, pink or yellow in armpit. Brown, grey or silver stripe runs from rostrum through eye and fades into the lateral zone. Cream stripe typically runs from below eye to edge of mouth, often extending to the shoulder or elbow. Iris cream to coppery.

Advertisement Call. Call description is based on the calls of 219 individuals. The advertisement call of Litoria ewingii has a duration of 1.05– 6.66 s (mean 2.42 s) and comprises 4–22 distinctly pulsed notes (mean 9) with most calls (85.4%) beginning with a long note followed by a series of shorter notes. Note duration is between 0.10– 0.48 s (mean 0.22 s). In the majority of calls (51.6%), notes rise in amplitude, appearing as a wedge shape in waveform view with a short interval between notes ( Fig. 7 ). Dominant frequency has a range of 1817–3167 Hz (mean 2485 Hz) and remains fairly stable throughout the call.

Comparisons with similar species. Litoria ewingii may occur in sympatry with L. verreauxii and L. paraewingi where identification can be challenging, particularly for hybrid individuals. It shares a broad zone of overlap with Litoria verreauxii in eastern Victoria and southern NSW where occasional hybridisation occurs due to mis-mating ( Smith et al. 2012). In addition, Litoria ewingii shares a narrow hybrid “tension” zone with L. paraewingi in central Victoria ( Watson et al. 1971, Smith et al. 2013). Non-hybrid Litoria ewingii can be readily distinguished from L. verreauxii using the following characters: finger and toe pads distinctly wider than digits ( L. ewingii mean Fin3W/ Fin3DW 0.6; Toe4W/Toe4DW 0.7 versus L. verreauxii mean Fin3W/Fin3DW 0.9; Toe4W/Toe4DW 1.0, n = 47), extensive webbing on the toes ( L. ewingii webbing usually extends to the 1 st or halfway between the 1 st and 2 nd subarticular tubercle on the 4 th toe versus extending to the 2 nd subarticular tubercle on the 4 th toe for L. verreauxii [see Fig 8 for comparison]), and by an absence of patterning in the inguinal region (versus present in L. verreauxii ). Distinguishing Litoria ewingii from L. paraewingi may be especially problematic where their distributions overlap, and mating-calls are unavailable. Watson et al. (1971) note in the original description of Litoria paraewingi that the species is morphologically indistinguishable from northern L. ewingii , however, L. paraewingi can be distinguished from southern populations of L. ewingii by smaller adult body size, relatively longer head and a straight versus rounded canthus rostralis.

Litoria ewingii is allopatric with L. sibilus and L. calliscelis , separated from the latter by a gap of approximately 80 km across the Coorong region and adjacent northern Naracoorte Coastal Plain. Dispersal across this landscape is likely hindered due to a lack of suitable breeding habitat—the Coorong is characterised by an expanse of saline coastal flats and the predominantly dry, mallee-dominated northern Naracoorte Coastal Plain is lacking in sufficient surface waters for breeding. Despite significant overlap in morphological characters between Litoria ewingii , L. calliscelis and L. sibilus , some aspects of colour/pattern may be useful for identification. Litoria ewingii usually have a plain, unpatterned posterior edge of the thigh (n=27/32), compared to thigh patterning comprising dark spots and blotches for L. calliscelis (n=10/11) and L. sibilus (n=26/27). L. ewingii can be further distinguished from L. calliscelis by a typical absence of inguinal patterning (n=29/33) versus inguinal pattern usually comprising a single dark spot at the junction of the thigh and abdomen (n=7/11).

Distribution and habitat. Widespread throughout south-eastern Australia including Tasmania and the south-eastern mainland coast, ranging from southern New South Wales, across Victoria, as far west as Deepwater in South Australia.An introduced population exists in New Zealand, believed to be introduced from Tasmania in 1875 ( Bazin et al. 2007, Rexer-Huber et al. 2015). Occurs from near sea level to an elevation of at least 1200 m ( Watson et al. 1985). Possesses a remarkable tolerance to sub-zero temperatures ( Bazin et al. 2007, Rexer-Huber et al. 2015).

Considered a habitat generalist, Litoria ewingii occurs in a variety of habitats including wet and dry sclerophyll forests, heathland and highly disturbed agricultural and urban areas.

Ecology. The species is recorded commonly via FrogID (>18,000 records from 10 November 2017 – 30 June 2022), and is relatively commonly heard calling in disturbed areas, with 24% of FrogID records from urban habitats and 47% of records from rural areas. Litoria ewingii have been recorded calling year-round in association with rainfall, with a distinct peak July–November based on FrogID submissions. Breeding occurs in static ephemeral or permanent waterbodies, including dams, ponds, swamps, inundated ditches and streamside ponds and pools ( Anstis 2017, Parkin pers. obs). For a detailed description of tadpole development and morphology, see Anstis (2017). Tadpoles are highly sensitive to increases in salinity (Chinanthamby et al. 2006).

Conservation status. Based on its widespread distribution (> 200,000 km 2), relative abundance in FrogID submissions, and the lack of evidence for a population decline, Litoria ewingii likely qualifies for the listing of Least Concern under the IUCN Red List criteria ( IUCN 2022).

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 9. Images of the holotype of Hyla ewingii, MNHN 4851 in A) dorsal; B) ventral and C) lateral profile. Images obtained from the Muséum National d’Histoire Naturelle online portal (Frédéric Braux 2012).

FIGURE 10. Images in life of Litoria ewingii. A) NMV D 76462 (JJLR5913), adult female, Halls Gap, Grampians, Victoria; B) NMV D 76454 (JJLR6056), Lyonville, Victoria. C) NMV D 76455 (JJLR5894), adult male, Colquhoun/Boyanga Gidi SF, south-eastern Victoria; D) NMV D 76461 (JJLR5910), adult male, Mount Clay State Forest, south-western Victoria; E–G unvouchered individuals photographed by Stephen Mahony; E) Naringal, Victoria; F) Mornington Peninsula, Victoria. G) Toongabbie, Victoria; H) TMAG C1531 (JJLR5389), adult male, Temma, Tasmania; I) TMAG C1533 (JJLR5394), adult female, Zeehan, Tasmania.