A FIELD-BASED METHOD FOR DISTINGUISHING MELOMYS BURTONl FROM M C^7?F/A7P£5(R0DENT1A: MURIDAE) IN QUEENSLAND ANGELA FROST FROST, A. 2008 04 30: A field-based method for distinguishing Melomys burtoni from M. cervinipes (Rodenlia: Muridae) in Queensland. Memoirs of the Queensland Museum 52(2): 123-126. Brisbane. ISSN 0079-8835. Melomys burtoni and M. cen’inipes arc broadly sympatric in eastern Australia but difficult to distinguish on external criteria. Although M. cervinipes attains a larger size than M. burtoni, the two species show significant overlap in standard external measurements and reliable identification currently requires examination of a cleaned skull. The hind foot plantar pads of 20 adult individuals of each of M. burtoni and M. cervinipes were examined and found to be a consistently larger in M. cervinipes. (cid:9633) Melomys, identification, burtoni, cervinipes, foot pads. Angela Frost, School of Animal Studies, University of Queensland, Gatton, Qld, 4343 (email: angl'[email protected]): 6 September 2007. The current taxonomy of Australian Melomys investigated the utility of other aspects of hind recognises a total of four species, two of which foot morphology. (M burtoni (Ramsay) and M. cervinipes (Gould)) MATERIALS AND METHODS have extensive, overlapping geographic ranges in northeastern Australia (Watts & Aslin, 1981). As a starting point I examined all adult spirit Although M. cervinipes attains a larger size specimens of M. burtoni and M. cervinipes with than M. burtoni (Watts & Aslin, 1981) and has cleaned skulls in the collection of the Queensland a relatively shorter tail (tail length more-or-less Museum (QM). Adult status was determined on equal to the combined length of the head and reproductive criteria (teats obvious on females, body vs tail significantly longer than the head scrotal sac prominent on males). The species plus body in M burtoni (Watts & Aslin, 1981)), identity of all specimens was validated using the the two species show significant overlap in diagnostic feature of the first upper molar root standard external measurements. Pelage colour pattern, as described by Knox (1978). Additional is individually and regionally variable in both spirit specimens were then selected from the QM species (Tate, 1951) and although habitat collection to increase the sample size within the provides a useful clue to species identification documented body size range overlap between M. (Watts & Aslin, 1981), both species are known burtoni and M. cervinipes, and secondarily, to to occur outside their preferred habitats (closed ensure good coverage of the area of geographic forest for M. cervinipes, grassland for M burtoni) overlap. Skulls from these specimens were re¬ (Queensland Museum records). Thus, at present, moved and cleaned to confirm their identity. reliable morphological identification requires The final sample included 20 specimens of each vouchering and examination of a cleaned skull species (sec Table 1). (Keith, 1970; Knox, 1978). A method to identify Measurements were made of pes length the two species on external criteria would be of (from heel to base of claw on central digit), great use for field survey of small mammals in combined head plus body length (anus to tip of northeastern Australia. nose), and the length of each of the six primary plantar pads. Small accessory plantar pads are Cooper (1993; 1994) described the usefulness variably discrete or fused to the first and fourth of plantar pads on the hind foot (pes) in dis¬ interdigital pads in both Melomys species (Fig. tinguishing sympatric and morphologically I). Measurements of these pads were designed similar species of rodents in Western Australia. to avoid this secondary source of variation. A key produced more recently by Metzler & Measurements were taken with Mitutoyo electronic Clancy (1995) described the “longitudinal" pad calipers and rounded to an accuracy of 0.1mm. of the pes as curved in M. cervinipes and straight in M. burtoni. I encountered difficulties using The length of each pad was plotted against this feature to identify Queensland Melomys and pes length to identify the measurement giving 124 MEMOIRS OF THE QUEENSLAND MUSEUM TABLE 1. Location of specimen, sex, hind foot length, first interdigital pad length and head-body length of Melomys cervinipes and M. burtoni used in this study. Measurements in mm. Species QM rcgistralion Sex Location Pes length First interdigilal pad Head body number length length Melomys cervinipes JM9323 M Ayr. Banratta Ck, 3km upstream of Bruce 25.0 2.4 91 Hwy JMII570 Cowley Bch Training area, 1.75km NNE 25.2 2.4 101 Main Camp SEW1444 25.5 2.8 96 JM224 F Innisfail Common 25.4 2.7 96 JMI383 F Cape Hillsborough 27.3 2.7 115 JM1099I F Mt Inkerman 26.2 2.6 110 JMIISI F Credilon 24.8 2.7 93 JMI4423 Ba>'view Heights, Meringa 26.0 2.7 109 JM1329 M Caloundra 27.4 2.8 113 JM6724 Nitch^ Bridge. 3.5km W 25.3 2.9 108 Koombooloomba JM10593 F Hinchinbrook Is 25.5 3.4 no JM1147 F Crcditon 25.2 2.7 97 JM5274 F Shipion's Flat 26.7 3.0 Ill JM8337 Kirrama Ra SF 26.1 2.7 lOI JM14436 M Noosa Heads NP (western side) 27.5 3.1 126 JMni74 M Nam hour Bypass 26.5 2.8 122 JM5337 F Hinchinbrook Is.Gayundah Ck 28.3 2.7 98 JM534I F Hinchinbrook Is. Scraggy Pt 27.4 2.8 105 JMU43 F Credilon 26.7 2.9 114 Awoonga Dam. from Boyne Valley to JMI4361 Miriam Vale 25.3 3.3 97 M. burtoni J20I73 M Mackay 25.4 1.9 112 JM 13957 M Buihcn Buthen, Nesbit Rd, Mcllwraiih Ra 23.6 1.8 105 JMI3559 Yabulu 24.0 1.8 111 JMI0500 Rutland Plains Hold, 1 l.5km NW Rankin’s 25.9 1.2 no Well J2018I Mackay 23.9 2.0 114 J17785 M Ml Molloy, 3km N 24.1 1.9 94 JM3823 F Eurimbulah NP 25.4 1.8 97 J20I10 Mackay 24.4 1.7 100 JM 11390 M Jenners Rd. nr Sarina 25.3 1.6 110 JM2615 M Kauri Ck. inlet 25.3 1.7 100 JM382I F Eurimbulah NP 25.2 1.8 99 JM12570 M Saunders Bch, nr Townsville (Nth) 24.9 1.9 107 J20179 M Mackay 26.0 2.0 112 JM1382 M Cape Hillsborough 24.8 1.5 104 J2I856 F Nth Stradbroke Is 25.8 2.2 97 JM3820 M Eurimbulah NP 27.9 1.9 123 JMI4560 Princess Hills House Dam 26.5 i: 104 JM 14563 Princess Hill House Dam 27.4 1.9 110 JM4267 Pine R Bay. 23km WNW Weipa, Rocky Pt 24.9 2.3 112 J20101 F Mackay 23.8 1.9 97 DISTINGUISHING MELOMYSBURTONIYROU M. CERVINIPES 125 FIG. 1. Pes of A, Melomys burtoni and B, M cei’vinpipes showing the relatively larger size of all plantar pads in M. cervinipes (plantar pads outlined in both). C, Outline of pes of M. cennnipes showing method of measuring total pcs length (a) and the length of the first interdigilal pad (b). Measurements of the first interdigital pad should be taken on the inner side of the pad to avoid the variation in the small accessory plantar pads which may be either discrete or fused. Specimens figured are from the CSIRO ANWC wildlife collection: A, M. burtoni adult male (CM 16369) from Shoalwater Bay; B. M cervinipes adult female (CM 16349) from Shoalwater Bay, Species identifications based on upper molar root number, after Knox (1978). the best discrimination. This proved to be the of the plantar pads of M cervinipes are relatively length of the first interdigilal pad (terminology larger than those of M. burtoni. Measurements follows Brown & Yalden, 1973). The method of confirmed this visual impression, and further measurement for pes length and first interdigital pad length is indicated in Fig. I. RESULTS The pes of M. cervinipes averages slightly longer than that in M burtoni (mean ± s.d.: 26.17 dr 1.02 vs 25.22 ± 1.16; raw data in Table 1) and it also appears slightly broader for its length (Fig. 1). However, the two species show almost complete overlap in measurement ranges for pes length (24.8-28.3 vs 23.6-27.9) and any difference in width would be very difllcult to quantify. pes length (mm) In contrast, foot pad size provides a reliable FIG. 2. Hind foot length versus first interdigital pad means of distinguishing the two species. As is length in adult M burtoni (solid squares) and M obvious in side-by-side comparison (Fig. 1), all cervinipes (open diamonds). 126 MEMOIRS OF THE QUEENSLAND MUSEUM demonstrated that length of the first interdigital growth and that younger animals will show a pad gave the most complete separation between less clear distinction. the two species when plotted against pes length For these reasons, I recommend that length (Fig. 2). Importantly, length of this pad is not of the first interdigital pad be added to the list significantly correlated with pes length in either of features currently used to identify eastern species, hence the single measurement appears to have diagnostic value across the full range of Australian Melomys (i.e. overall body size, adult body size of both species. The cut off point relative tail length) and that particular care be appears to lie at 2.3mm—in all specimens of taken to assess the individual age of a captured M. hurtoni the first interdigital pad was shorter specimen. than 2.3mm, whilst in M cennnipes this pad ACKNOWLEDGEMENTS was consistently longer than 2.3mm. Thanks to both Dr Steve van Dyck from the DISCUSSION Queensland Museum and to Dr Ken Aplin This study has demonstrated a consistent diff¬ from the CSIRO Australian National Wildlife erence in foot pad morphology between adults Collection for advice and assistance with species of M cervinipes and M burtoni across their identification and preparation of this manuscript. area of geographic overlap, with M cet-vinipes having measurably larger plantar pads than M. LITERATURE CITED burtoni. Large plantar pads in murine rodents BROWN, J.C. & YALDEN, D.W. 1973. The are commonly associated with scansorial or description of mammals - 2: Limbs and arboreal habits and the difference in pad size is locomotion of terrestrial mammals. Mammal consistent with the known ecological contrast Review 3: 107-134 between the more arboreal M cervinipes and COOPER, N.K. 1993. Identification of Pseudomys the more terrestrial M burtoni (Watts & Aslin, chapmani, P. hermambergemis. P delicatulus 1981). Further studies could now extend this work and Mus musculus using footpad patterns. to other species pairs within Melomys, such as M Western Australian Naturalist 19: 69-73 capensis and M burtoni that co-occur regionally COOPER, N.K. 1994. Identification of Pseudomys on Cape York Peninsula albocinereus, P occidentalLs, P shortridgei, Rattus Although the present method appears to re¬ rattus and R. fuscipes using footpad patterns. present an advance over previous criteria for Western Australian Naturalist 19: 279-283 field identification of Australian Melomys, for KEITH, K. 1970. The occurrence of a second species several reasons I urge caution in its application. of naked-tail rat, genus Melomys, in New South First, the reference series are relatively small Wales. CSIRO Wildlife Research 15:19-26 (20 specimens per species) and did not sample the KNOX, E. 1978. A note on the identification of Melomys entire region of geographic overlap, e.g. sympatric species (Rodentia: Muridae) in Australia. Journal populations in northern NSW were not included. of Zoology, London 185: 276-277 Accordingly, it is likely that with more exhaustive METZLER, K. & CLANCY G.P. 1995. A key to the sampling of rriuseum specimens, some overlap rodents of far north-eastern New South Wales, in: in first interdigital pad length will be detected. NSW NPWS: Vertebrate Fauna of Upper North Second, the utility of the measurement has not East New South Wales, a report for the Natural been tested for sub-adull and juvenile animals. Resources Audit Council, NSW National Parks Murid rodents as a group undergo significant & Wildlife Service, Sydney. changes in body proportions during growth from TATE, G.H.H. 1951. Results of the Archbold juveniles to adults, and caution must always be Expeditions. The rodents of Australia and New exercised in applying any diagnostic criterion Guinea. Bulletin of the American Museum of beyond the limits of the original dataset. In the Natural History 97: 183-430 present case, it is likely that the inter-specific WATTS, C.H.S. & ASLIN, H.J. 1981. The Rodents difference in plantar pad size develops during of Australia. (Angus and Robertson, Sydney).