Bioacoustics of Mixophyes balbus

Description including variation. Straughan’s (1966 , 1968 ) description of variation in M. balbus included material from the southern group which we show is a new species. Here we provide detailed images of the type ( Fig. 11 ) and a revised description of variation in M. balbus that excludes material from the range of the new species. A moderate sized frog, sexually dimorphic, females larger (up to 83 mm SVL) than males (up to 71 mm SVL). Females are an average of 1.2 times the SVL of males ( Table 5 ), but they are otherwise similar in body proportions ( Table 5 ), colour in preservative and patterning. Tympanum large, conspicuous (TD/ED mean = 0.79±0.07, 0.62–0.96), oval shaped with longer axis vertical. Eyes prominent, pupil vertical, iris in life silver-blue or brown above, brown below. Head flattened, length slightly shorter than or equal to width (HL/HW mean = 0.93±0.05, 0.70–1.03); snout prominent (ED/EN mean = 1.4±0.1, 1.2–1.7), gently rounded when viewed from above and in profile; nostrils more lateral than superior; canthus rostralis well defined, slightly concave; loreal region nearly flat, inclined laterally; eye to naris distance slightly smaller than or approximately equal to internarial span (EN/IND mean = 0.88±0.1, 0.71–1.13). Vomerine teeth relatively long, oblique rows angled from anterior margin of choanae to midline between choanae. Tongue approximately rectangular, not notched posteriorly. Dorsum smooth or finely granular, belly smooth. Hind limbs long and robust (TL/SVL mean = 0.6±0.02, 0.55–0.65). Fingers moderately long, robust, unwebbed, relative length 3>2=4=1. Subarticular and palmar tubercles prominent. Finely granular brown nuptial pad on first and second finger and extends ventrally to the inner palmar tubercle in breeding males. Toes moderately webbed; on outer side of toes webbing reaches penultimate subarticular tubercle on toes 1 and 2, penultimate tubercle on toe 3, and second subarticular tubercle on toe 4. Tips of toes slightly expanded but lacking obvious discs ( Fig. 11 ). Relative lengths of toes 4>5>3>2>1. Prominent round or oval conical sub-articular tubercles present; outer metatarsal tubercle absent; inner metatarsal tubercle prominent relatively straight, with well-developed outer edge, approximately equal to length of toe 1, not sharp or keratinized, pigmentation same as plantar surface. Colour and Pattern in Life. Dorsal surfaces rich copper to tan or dark brown, sometimes with burnt orange or pink wash towards groin; a posteriorly oriented v-shaped inter-orbital bar that extends as a mid-dorsal stripe, finely edged in black and highly variable in length and shape with uneven edges terminating in mid-sacral region; remainder of dorsal surface either sparsely flecked with small black spots or a few larger blotches but not both ( Fig. 7 ). A dark triangular patch on either side of snout with apex at external nostril does not incorporate area immediately surrounding nostril. A dark lateral head-stripe extends from slightly posterior of nostril, through eye, curves over tympanum, and extends posteriorly down anterior margin of tympanum, sometimes including upper third of tympanum, terminating above axilla; width variable but in all cases posterior margin is widest. Loreal region light-brown coloured with darker patches along upper jaw (maxilla). Lateral surfaces and groin flushed with reddish tan or peach, without spots or blotches, these surfaces noticeably lighter than dorsum, with colour diffusing gradually into ventral colouration. Venter including throat and ventral surface of thighs immaculate white, cream or with light lemon-yellow wash; lower jaw edged with diffuse brown wash. In adults, iris dark brown merging into golden brown above pupil with brown to iridescent pale blue dorsal crescent. Upper third of iris in juveniles may be as above or flame orange. Upper surfaces of legs, feet, arms and hands with dark transverse cross bars, not extending on to posterior thighs; posterior surface of thighs uniform brown to burnt orange brown and slightly mottled; anterior lateral edge of shank, posterior lateral edge of arms, and plantar surface of feet and of tarsal surface dark brown; lateral palmar surfaces of outer fingers dark brown to black. Reproductive call. The male advertisement call comprises one to four short notes repeated in rapid succession. Because of the variation in the number of notes in the call we provide means and ranges for measurements of call traits for the first two notes. Mean duration for a two note call is 0.45 s (range 0.45–0.48 s). The first note is of longer duration than the second (means 0.68 and 0.41 s, ranges 0.39–0.96 s, and 0.28–0.63 s respectively), with a short inter-note interval (mean 0.36 s), and with more pulses in the first than the second note (mean 12.8, and 9.1, ranges 9–17 and 3–12 respectively). Pulse duration is much shorter (mean 0.015 s, range 0.014–0.016 s) than inter-pulse interval (0.083 s, range 0.081–0.084 s). Pulse structure varies within notes, with single pulses produced initially, followed by a series of pulses produced in couplets ( Table 2 , Fig. 9 ). The second note has more couplets than the first note ( Fig. 9 ). Pulse repetition rate in the first note is lower than the second note (16.1 pps vs 21.0 pps) ( Table 2 ). Mean inter-call interval is 4 s (range 3–8 s) and males usually produce a series of calls before a period in which all calling ceases. Calling occurs during the spring and summer seasons when climatic conditions are suitable (MM pers. obs. Details of suitable conditions not reported here). Within the calling season, calling is initiated by a male, and this stimulates calling in nearby males and a chorus of calls with a short lag time or small overlap between the call of one male and a nearby male occurs. The male encounter call which is a single note of moderate duration (mean 0.23 s, range 0.24–0.48 s) is often uttered among advertisement calls and males may produce several encounter calls in succession ( Fig. 9C ). The dominant frequency of the notes in the advertisement call differs slightly with the first note having a higher frequency than the second (817 Hz and 758 Hz, ranges 709–782, 659–961 Hz respectively). The dominant frequency of the encounter call (788 Hz, range 709 and 792Hz) is higher than the advertisement call and shows an initial narrow band frequency that expands to a broadband pattern. Advertisement and encounter calls are not frequency modulated. Representative call recordings have been deposited with the Australian Museum as multimedia record AMS R.188750.

Diagnosis. Mixophyes balbus is distinguished from M. hihihorlo by a interrupted vertebral stripe (vs. uninterrupted) and presence of dark triangular patch on upper lip in front of nostril (vs. absent); from M. iteratu s and M. carbinensis by absence of black colouration with numerous small rounded pale spots on posterior surface of thigh (vs. light brown without any pale spots); from M. coggeri by having posterior of thigh uniform (vs. with irregular pale blotches); from M. schevilli by having a discontinuous (vs. continuous) mid-dorsal stripe; from M. fleayi and M. fasciolatus by lack of prominent black spots on flanks and further from M. fasciolatus by occurrence of pigmented patches on maxilla; from M. australis sp. nov. by having five wider and more diffusely marked cross bands on thigh (vs. up to ten thin dark cross band in M. australis sp. nov. ) ; male advertisement call comprises one to four notes with mean number of pulses in first and second notes being more than in M. australis sp. nov. (mean 12.24 vs. 7.24) with more double pulses in these notes. In the field M. balbus is most likely to be confused with M. fasciolatus and M . iteratus which occur sympatrically. In addition to the features listed above, M. balbus can be distinguished from M. iteratus by the webbing on the toes reaching only to the second joint on the third toe, compared to distal joint in M. iteratus ; from M. fasciolatus by the occurrence of a metallic silver-blue crescent in the top quarter of the iris (vs. absent in M. fasciolatus ), and the absence of sharply demarcated cross bands on the limbs that form distinct triangular markings on the posterior surfaces of the arms and legs (vs. presence in M. fasciolatus ).