Litoria mira Oliver, Rittmeyer, Torkkola, Dahl, Donnellan & Richards, 2020

Oliver, Paul M., Rittmeyer, Eric N., Torkkola, Janne, Donnellan, Stephen C., Dah, Chris & Richards, Stephen J., 2021, Multiple trans-Torres Strait colonisations by tree frogs in the Litoria caerulea group, with the description of a new species from New Guinea, Australian Journal of Zoology 68, pp. 25-39 : 33-36

Litoria mira Oliver, Rittmeyer, Torkkola, Dahl, Donnellan & Richards , sp. nov.

(Chocolate tree frog)

( Figs 6 – 8 )

Litoria caerulea Tyler (1968 in part)

Litoria caerulea Dahl, Richards & Novotny (2013) Urn :lsid:zoobank.org:act: FE7D1EA3-C01E-433A-9BC7-E67FA5CFC6EF

Holotype

SAMA R71114 (field no. SJR15133), adult male, Purari River Basin (7.3518 OS, 145.1904 OE), Gulf Province, Papua New Guinea, 30 ma.s.l., collected by S. Richards and E. Nagombi on 13 February 2016.

Paratypes

All from Papua New Guinea (n = 10). SAMA R 70446 (field no. SJR 14869), subadult female; SAMA R 71655 ( SJR 15015), adult female, upper Strickland River basin (6.2763 OS, 142.1022 OE), 110 m. a.s.l., Western Province, collectedby K. Aplin and S. Richards between 4 and 10 August 2013; SAMA R 71657 R 71658, QM J97086 ( SJR 8879 – SJR 8880, 8913) adult males, Wamangu Village (3.7870 OS, 143.6520 OE), East Sepik Province, collected by C. Dahl between 26 and 30 October 2004 ; SAMA R 71117 ( SJR 15085), female, Purari River Basin (7.4910 OS, 145.2189 OE), 130 m a.s.l., Gulf Province, collectedby S. Richards and E. Nagombi 4 February 2016 ; SAMA R 71116 ( SJR 15320), female, Purari River Basin (7.7892 OS, 145.2664 OE), 5 m a.s.l., collected by S. Richards and C. Dahl 9 July 2016; SAMA R 71656 ( SJR 15336) , male, SAMA R 71115 ( SJR 15353) , male, PNGNM ( SJR 15355) , female, Purari River Basin (7.8566 OS, 145.3308 OE), 100 ma.s.l., Gulf Province, collectedby S. Richards and C. Dahl between 15 and 18 July 2016 .

Diagnosis

Litoria mira can be distinguished from all other Litoria by the unique combination of moderately large size (male SUL up to 70.8, female SUL up to 79.6 mm); vomerine teeth present; webbing on hand extending no further than base of penultimate phalanx on fourth finger; limbs without prominent white or yellow lateral folds or ornamentation; lip lacking a white stripe; limbs relatively short and robust (TL/SUL 0.41 – 0.48); parotoid gland present, but not prominent and not fused with prominent gland on top of head; head relatively narrow (HW/ HL 0.91 – 1.0), distinctly tapering from body; dorsal colouration uniformly brown, without white or yellow spots; small violet patch of skin at postero-ventral edge of eye; and ventral surfaces of limbs, torso and throat with moderate to extensive regions densely stippled with dark to medium brown.

Description of holotype

Adult male with the following measurements (mm): SUL 70.8; TL 29.4; HL 19.9; HW 20.7; ES 8.9; EN 6.5; IN 5.2; EYE 7.3; TYM 4.1; 3FW 3.9; 4TW 3.5. Body robust ( Fig. 6 ), head approximately as wide as long (HL/HW 0.96), narrower than body in dorsal view; snout truncate in dorsal view, rounded in lateral view; labial region very slightly flared; loreal region steeply sloping and slightly concave; canthus rostralis indistinct, weakly curved; nares rounded, much closer to tip of snout than to eyes, oriented laterally, barely visible in dorsal view. Choanae moderate sized, ovoid, separated by a distance ~1.5 times their width; vomerine teeth in rows of 5 or 6 clustered along posterior edge of bifid elevated ridge medial to choanae. Eyes rather small (EYE/SUL 0.10), moderately prominent in dorsal and lateral views, pupil horizontal. Tympanum moderately sized (TYM/SUL 0.58), annulus moderately distinct and raised, dorsal edge obscured by prominent thick downwards-curving supratympanic fold that extends from anterodorsal edge of eye to supra-axillary junction. Skin on dorsal and lateral surfaces of body, head, throat, anterior abdomen, arms and extremities of legs smooth; on posterior abdomen and upper leg coarsely rugose.

Arms robust, without skinfolds or ornamentation; fingers with relativelengths III> IV> II> I ( Fig. 7 a ); discs prominent, with circum-marginal grooves, wider than penultimate phalanx on all digits, subarticular tubercles rounded, indistinct, one on digits Iand two on II – IV, supernumerary tubercles absent, prominent palmar tubercle at base of digit I. Nuptial excrescence in single small, very indistinct, squarish pad at base of digit I ( Fig. 7 b ). All digits with prominent lateral flanges, webbing basal between Iand II, reaching first subarticular tubercles between digits II and III, and reaching second subarticular tubercles between III and IV.

Legs robust, short (TL/SUL 0.42), without skin folds or ornamentation, relative lengths of toes IV> V> III> II> I; terminal discs prominent and expanded, with circum-marginal grooves, wider than penultimate phalanges on all digits; subarticular tubercles rounded, moderately prominent, one on I – II and V, two on III – IV, prominent ovoid inner metatarsal tubercle at base of digit I. All digits webbed, webbing extends just beyond first subarticular tubercle between I – II, to base of disc on II and to first subarticular tubercle on III, to base of disc on outside of III, and to base of penultimate phalanx on both sides of IV and to base of disc on inside of V. Dermal fringes present on all digits.

Dorsal colouration in preservative dark brown over all surfaces with no obvious pattern, upper hindlimbs and digits slightly paler brown than torso. Ventral surfaces pale buff, with large area of dark brown on throat and smaller patches of lighter brown on upper torso, lower forelimbs and across hindlimbs and toes.

Variation

Mensural variation for the six males, four females and one subadult in the type series is presented in Table 2 . Females are larger than males. The smallest female (SAMA R70446, SUL 66.7 mm) does not have fully developed eggs. In colouration, all preserved specimens show the same uniformly dark-brown colouration, with tone varying slightly; larger specimens tend to be slightly paler. Venter always pale buff with brown mottling of varying extent and intensity on the throat, anterior portion of torso, fore and hindlimbs, plantar surfaces of webbing and digits.

Appearance in life

Generally similar in life as in preservative. Photographs of the holotype (SAMA R70446) show the same uniformly brown dorsal colouration in life ( Fig. 6 ) as in preservative, with the outer edge of the tympanum more sparsely pigmented, and lower lateral regions and extremities of limbs slightly more sparsely pigmented and overall lighter brown. Hidden and exposed surfaces of hindlimbs are uniform brown ( Fig. 7 c ). SAMA R71655 has a greyish dorsal ground colour in life with fine light-brown mottling and maculations. This specimen is dark brown in preservative. All specimens have a small lightviolet patch of skin at the posteroventral edge of the eye in life, which appears to be diagnostic for the species. Iris silvery grey, with dense black vermiculations and flecks.

Comparisons

Readily distinguished from all Litoria species outside the L. caerulea group by its combination of large size (adult SUL> 60 mm), limbs without prominent skinfolds or lateral ornamentation, absence of a prominent white lip stripe, nictitating membrane without flecks or reticulations, enlarged paratoid gland above tympanum obvious in life, webbing on fingers never extending beyond penultimate subarticular tubercle, snout rounded in lateral view and plain-brown dorsal colouration without any pattern.

Litoria mira differs from L. caerulea in its smaller maximum size (maximum male SUL length 70.8 versus 77.3 mm, maximum female SUL 79.6 versus at least 99.7 mm), generally narrower head (HL/HW mean 0.97, range 0.91 – 1.0 versus mean 0.9, range 0.78 – 0.98); presence of a small violet patch of skin at posterio-ventral edge of the eye in life (versus absent), more extensive brown ventral pigmentation on throat, belly and limbs (versus scattered and generally found on throat region only); and consistently darkbrown dorsal colouration in life ( Fig. 6 , 8 a, b ) and preservative (versus typically green ( Fig. 8 c ), brownish green or sometimes brown in life, and often blue in preservative). In life, photographs of two individuals also suggest that L. mira has dark-brown hidden surfaces on the thighs ( Fig. 7 c ) (versus typically pink or yellow in L. caerulea ); however, data from more specimens are required to further test the strength of this character.

The three other species in the Litoria caerulea group do not occur in New Guinea, and all lack a pale-violet patch of skin at the posterior-ventral edge of the eye. L. mira further differs from L. cavernicola in having a plain dark-brown dorsum (versus usually olive green: Fig. 8 d ), smooth to moderately granular dorsal skin (versus strongly granular) and larger size (maximum male SUL length 70.8 versus 51.0 mm, maximum female SUL 79.6 versus 57.0 mm); from L. gilleni by its plain dark-brown dorsum (versus olive green or brown with yellow or white spots: Fig. 8 e ); and from L. splendida by its smaller maximum size (maximum male SUL length 70.8 versus 106.0 mm, maximum female SUL 79.6 versus 118.0 mm), much-less-prominent parotoid gland above eye and snout (versus always apparent in both areas on adults), and darkbrown dorsal colouration in life (versus green with scattered white or yellow flecks: Fig. 8 f ).

Distribution

The type series originates from three localities spanning provinces north and south of New Guinea’ s Central Cordillera ( Fig. 1 ). These scattered records, and low genetic divergence between samples, suggest that the species may occur more widely in the difficult-to-access lowland swamp forests across the island of New Guinea.

Tyler (1968) lists uncatalogued specimens of L. caerulea in the Australian Museum and Australian National University from near Maprik Village in northern Papua New Guinea that we have not been able to locate. These specimens are also most likely to be L. mira . We have been unable to examine one further specimen of ‘ L. caerulea ’ (RMNH 12370) from Erokwero on the Bird’ s Head Peninsula (Vogelkop) in West Papua Province listed by Tyler (1968). It requires further investigation to confirm which member of the L. caerulea group occurs in far western New Guinea.

Habitat and ecology

Collecting localities are in both disturbed and undisturbed lowland swamp forest or swampy rainforest ( Fig. 2 a, b ). The species was typically observed perched on branches within 3 m of the ground.

The advertisement call is a deep, rasping bark repeated in long series, ‘crawk, crawk, crawk ...’ ( Fig. 9 ), that is indistinguishable to the ear from that of L. caerulea . Five call series from SAMA R71658 recorded at an air temperature of 25 OC contain 33 – 48 calls (=notes) (mean = 40.4, s.d. = 6.58) produced ata rate of 2.6 – 2.8 calls s – 1 (mean = 2.66, s.d. = 0.08) lasting a total of 13 – 17.8 s (mean = 14.96, s.d. = 2.51). The first call of each series is the softest and shortest, and amplitude of calls subsequently increases during each series ( Fig. 9 a ) except for the last call, which may have a distinctly lower amplitude than the calls preceding it. Calls last 0.10 – 0.17 s, and contain 18 – 23 pulses produced at a rate of ~150 pulses s – 1.

Other Litoria collected in sympatry with L. mira at sites in southern New Guinea included the widespread lowland species L. auae , L. chloristona , L. congenita , L. infrafrenata , L. pygmaea and L. thesaurensis and in northern New Guinea included L. chrisdahli , L. infrafrenata , L. mucro , L. pygmaea and L. thesaurensis .

Suggested IUCN red list status

Litoria mira is known from widely separated sites in difficultto-access and relatively undisturbed areas of lowland New Guinea. There are large areas of suitable lowland habitat in the intervening areas, and human population density in most of this region remains low. We suggest that the species be listed as Least Concern.

Etymology

The name mira is the feminine form of the Latin adjective mirum, for surprised or strange, stemming from our surprise in discovering an undescribed member of the predominately Australian L. caerulea group occurring widely across lowland swampy rainforest in New Guinea.

Figures

Fig. 6. Litoria mira holotype (SAMA R70446) from the Purari River Basin in life. Photograph: S. Richards.

Fig. 7. Litoria mira holotype (SAMA R70446) in life: (a) details of webbing and tubercles on hand, (b) weakly pigmented nuptial pads, and (c) dark purplish brown colouration on hidden surfaces of thighs. All photographs S. Richards.

Fig. 8. Species in the Litoria caerulea group in life: (a) L. mira paratype SAMA R70446 from upper Fly River Region, Papua New Guinea, (b) L. mira paratype SAMA R71656 from Purari River Basin, Papua New Guinea, (c) L. caerulea from near Kuranda, Australia, (d) L. cavernicola from Theda Station, Australia, (e) L. gilleni from Simpson’s Gap, Australia, and (f) L. splendida from the King Leopold Ranges, Australia. Photographs: (a–c) S. Richards, (d) B. Schrembri, (e) C. Jolly and (f) P. Horner.

Fig. 1. Distribution of nominal species in the Litoria caerulea group across Australia and New Guinea. Samples previously identified as L. caerulea from non-savannah habitats across New Guinea are indicated by orange triangles and an asterisk above the species name. In New Guinea, the largest areas of savannah are found in the Trans-Fly region and Central Province. Distributional data are largely from the Atlas of Living Australia.

Fig. 2. Images of habitat for species in the Litoria caerulea group: (a) temporary pool in disturbed lowland swamp rainforest in the Purari River Region, New Guinea, collecting locality for non-savanna L. caerulea; (b) temporary pool in lowland rainforest in the Upper Fly River Region, New Guinea, collecting locality for non-savanna L. caerulea; (c) flooded open sclerophyll savannah in the Trans-Fly region of southern Papua New Guinea, habitat of L. caerulea; and (d) limestone ranges in semiarid savannah in the southern Kimberley region, Australia, habitat for L. caerulea and L. splendida. Photographs: (a–c) S. Richards and (d) P. Oliver.

Fig. 9. Waveform (a) and spectrogram (b) of an advertisement call series produced by Litoria mira (SAMA R71658) at an air temperature of 25OC near Wamangu Village, Papua New Guinea.

Tables

Table 2. Summary of raw morphological data for adult Litoria mira Values shown are means and ranges

	Males (n = 9)	Females (n = 3)
SUL	65.4 (59.5 – 70.8)	72.2 (66.7 – 79.6)
TL	28.9 (27.8 – 29.8)	30.8 (29.1 – 33.3)
HL	20.4 (18.0 – 22.0)	21.7 (20.9 – 23.3)
HW	20.9 (18.2 – 22.5)	22.8 (21.9 – 24.4)
ES	8.8 (7.5 – 9.2)	10.0 (9.6 – 10.3)
EN	6.1 (5.1 – 7.2)	6.8 (6.2 – 7.4)
IN	5.5 (4.3 – 6.1)	6.3 (5.6 – 7.0)
TYM	4.5 (3.6 – 5.2)	4.7 (4.3 – 5.0)
EYE	7.3 (6.1 – 7.8)	7.9 (7.4 – 8.6)
3FW	4.0 (3.1 – 4.8)	3.9 (3.5 – 4.4)
4TW	3.6 (2.7 – 4.2)	3.6 (3.4 – 3.7)