Litoria watsoni sp. nov.

Holotype. AMS R186898. An adult male collected from Parma Creek, New South Wales (- 35.02062 o S, 150.4962 o E) by Stephen Mahony on 6 September 2016.

Dimensions of holotype (mm). SVL, 50.2; HL 14.0; HW, 17.8; EN, 4.5; IN, 4.1; EYE, 5.2; TYM, 3.0; TBL, 27.1; TAL, 16.7.

Description of the holotype. The body form, colour and pattern of the holotype are illustrated with an in life image in Fig. 8D. Head longer than wide (HL/HW = 0.79); head widest at eyes; snout rounded in lateral and dorsal profiles. Nostrils prominent in dorsal profile. Single row of vomerine teeth running laterally anterior to choanae. The tympanum is circular and visible, diameter equal to eye diameter (TYM/EYE = 0.58).

Prominent terminal discs on all toes and fingers, no webbing between fingers, and toes with basal webbing. Finger length 3>4>2>1; toe length 4>5=3>2>1. Sub-articular tubercules present under fingers and toes but not prominent. Inner metatarsal tubercule present and prominent, approximately one third of the length of first toe. Nuptial pad dark brown, oval, on dorsal surface only of the proximal half of the first digit. Legs relatively long (TBL/SVL = 0.54).

Skin texture of back weakly granular, becoming more granular laterally and on the venter and thighs. Ventral surface granular. Upper surfaces of legs and arms and lower surfaces of lower legs and arms smooth.

Variation. Summary of variation in morphometric measurements for each sex is presented in Table 3 and appearance in Fig. 8. Male SVL 42–59 mm female SVL 50–64 mm; head length relative to head width variable (HL/HW range 0.66–0.97). The tympanum diameter is variable in size relative to eye length (TYM/EYE range 0.44–0.72). Legs relatively long (TBL/SVL 0.44–0.59).

Color in life. Dorsal surfaces of body and limbs light brown mottled with dark and lighter flecking of brown and yellow. The side of the face and extending back beneath the tympanum to the axil is a lighter shade of the dorsal colouring (Fig. 9). Colour on back of upper and lower leg and onto the foot, groin and posterior flanks, and on the upper axil of the forelimb is an immaculate reddish-orange wash (Fig. 9). A darker brown to black line extends from the external nostril along the canthus rostralis to the eye, continuing less intensely behind the eye over the tympanum and then onto the flank where it gradually dissipates. Ventral surface white, with the exception of the upper legs which have an orange wash. The gular region has a yellowish wash. Iris is yellowish gold.

Advertisement call. This description of the call is based on eleven individuals from four locations (Supplementary Table S1, Table 6). The call is a series of moderately strident notes sounding like “wriiik..wriiik..wriik…wriik” which increase in volume to the last note, and is placed in the “pulse repetition sound” category of Beeman (1998). The call is moderately long (mean 5.6 s), comprising (mean 6.5, range 3 to 14) repeated notes of short duration (mean 0.58 s) each separated by a shorter interval (0.40 s). The repeated notes increase in amplitude across the call, and each consists of distinct pulses (Table 6, Fig. 6). Note duration and inter-note duration also increases gradually across the call and is accompanied by a gradual increase in the number of pulses (mean 22.8, range 7 to 33) in each note. The note envelope is fully amplitude modulated with distinct short pulses separated by a duration about three times longer, with the amplitude rising to a peak followed by a rapid decay (Fig. 6). Spectrally, there is no evidence of frequency modulation in the call or in the notes. Dominant frequency of the call has a mean of 1740 Hz (range 1505 to 2018 Hz).

Etymology. Named in honour of Dr Graeme Watson, formerly of the University of Melbourne, Victoria, Australia, for his lifelong contribution to the ecology and evolutionary biology of Australian amphibians and his particular contribution to elucidating the evolutionary relationships in the L. ewingii species group.

Distribution. Found in eastern Victoria and south-eastern New South Wales, from 10 km east of Bellbird Creek and 4 km south of Brookville in eastern Victoria, along the eastern fall of the Great Dividing Range north to the Budderoo Plateau, Illawarra Region, NSW.

Altitudinally, L watsoni sp. nov. occurs from near sea level, e.g. Parma Creek (179 m asl) and Nadgee State Forest (198 m a.s.l.) to about 1,100 m a.s.l. in the upper reaches of the Mongarlowe River, near Braidwood, NSW.

The ranges of Litoria watsoni sp. nov. and L. littlejohni appear to abut at the southern boundary of the Sydney Basin Bioregion. The southern end of the Sydney Basin Bioregion is characterised by ranges of sedimentary sandstones and silts that are deeply dissected by rivers forming steep escarpments and v-shaped valleys, and has been recognised as a biogeographic barrier for several taxa (Bryant & Krosch 2016). However it does not appear to be associated with a distinct drier and warmer landscape change as is the case for other biogeographical barriers in north-eastern Australia such as the St Lawrence and Burdekin gaps. Additional research is required at the southern border of the Sydney Basin Bioregion and the northern border of the South East Corner Bioregion to better understand the distribution of L. littlejohni and L. watsoni sp. nov. to determine whether they are sympatric in the zone where these two bioregions meet.

Habitat. Litoria watsoni sp. nov. occurs in several different vegetation communities including numerous sites of post-forest harvest regrowth (Daly & Craven 2007, Lemckert 2010, Gillespie et al. 2016). At the northern extent of its distribution in the Shoalhaven River catchment (Parma Creek Nature Reserve and Barren Grounds Nature Reserve on the Budderoo Plateau), where it appears to be most abundant, it is generally associated with upland heath and dry sclerophyll forest communities. In southern NSW and eastern Victoria records are generally in wet forests (Gillespie et al. 2016), although there are two historic records in heath in Nadgee Nature Reserve in south-eastern NSW (ALA accessed June 2020). Where L. watsoni sp. nov. is associated with heathland, the soils are sandy, and the parent geology is sandstone. In these locations the breeding sites are in streams that flow slowly across a mostly horizontal bedding plane on a plateau or steppe, and are not found in the v-shaped valleys or coastal valleys that form once the streams descend from the plateau (Fig. 10). Dense heath vegetation, comprising various species of Banksia and Grevillia, border and overhang the streams, and males typically call from branches up to a 1.5 m above the stream or from deep within large clumps of ferns. Preferred streams are shallow, characterized by rocky or sandy bases, potholed and with lateral rocks bars creating pools that are either completely isolated from surrounding water bodies, or larger connected pools (Fig. 10). Where associated with wet forests communities the field records cite roadside ditches and puddles in south-eastern NSW and eastern Victoria (Littlejohn & Watson 1966). Whether L. watsoni sp. nov. prefers these landscape features, or is apparently absent from larger more permanent water bodies and streams due to field survey design, is difficult to determine from available data. We know of no records in heavily modified landscapes such as farmlands or urban areas, and there is some debate about whether the species is affected by forestry practices (Lemckert 2004, 2010; Gillespie et al. 2016).

Breeding Biology. Little is known about the larval ecology of L. watsoni sp. nov. and studies are a matter of priority given its threatened conservation status (see below).

Males call along permanent streams in all seasons of the year particularly following rainfall (Gillespie et al. 2016). Males have been observed calling at a small forest pond at Nadgee and Yadboro State Forest in far southeastern NSW after summer rain (Bilney pers. obs.). Calling behaviour by L. littlejohni in relation to season and permanent streams and ephemeral habitats is very similar to that of L. watsoni sp. nov. (Lemckert & Mahony 2008, Lemckert 2010, Mahony 1993, White et al. 1994).

In a composite description based on samples from the Cann River, Victoria, the Mongarlowe River, NSW and Budderoo Plateau, NSW (referable to L. watsoni sp. nov.) and from the Watagan Mountains, NSW (referable to L. littlejohni), Anstis (2017) described oviposition sites, egg mass structure, and embryo morphology, without noting any differences in these attributes among the sampled locations. Martin & Littlejohn (1966) described the larvae of L. watsoni sp. nov. from Cann River, Victoria (as L. jervisiensis).

Diagnosis. Litoria watsoni sp. nov. can be distinguished from all other members of the L. ewingii species group except L. littlejohni by the occurrence of immaculate orange markings on the anterior and posterior surfaces of the femur and tibia, in the groin and posterior flanks, and by its larger size (see Anstis [2017] for comparative measurements). The call can be distinguished from that of L. littlejohni by the lower number of pulses in each note (mean 22.8 compared to 27.8) (Table 4). From a genetic perspective, apomorphic nucleotide states at 21 sites in the mitochondrial ND4 gene reliably diagnose L. watsoni sp. nov. from L. littlejohni (Table 3).