Taxonomy and distribution of the grey kangaroos, Macropus giganteus Shaw and Macropus Fuliginosus (Desmarest), and their subspecies (Marsupialia : Macropodidae)

Abstract

Of all the Macropodidae, grey kangaroos cover the widest range in Australia. There is considerable geographical variation in morphology and opinions have differed as to the taxonomic status of the various kinds. This investigation supports a primary division of grey kangaroos into two species-eastern and western on the basis of serological, reproductive, and morphological distinctions. The eastern species, M. giganteus, is found in all eastern states, Queensland, New South Wales, Victoria, and Tasmania, plus south-east South Australia, while the western species, M. fuliginosus, occurs in south-western Western Australia and southern South Australia including Kangaroo I., extending into western Victoria and south-western New South Wales, where the ranges of the two species overlap. Transferrin polymorphism was detected by starch-gel electrophoresis, revealing three phenotypes, A, AB, and B. Western populations possess all three phenotypes, but eastern populations have type A only. Western and eastern grey kangaroos also have characteristic antigens. Eastern animals when immunized with sera from western kangaroos produced antibodies which during double-diffusion analysis reacted with sera from western individuals. Likewise the reverse immunization acted as expected. Thus the origin of individuals, from western or eastern populations, could be determined. Hybrids were not found in the field, but matings between captive western males and eastern females the reverse mating never occurred produced hybrids whose antigens were characteristic of both parental types. In eastern grey kangaroos the mean length of oestrous'cycle, 45.6 days, and gestation period, 36.4 days, is longer than in western kangaroos, with mean lengths 34.9 and 30.6 days. Oestrous cycles of hybrid females and gestation periods of all hybrids are of intermediate length, 37.6 and 34.1 days respectively. The colour of eastern grey kangaroos ranges from light to dark grey while western kangaroos are brown. The history of the previously described taxa and the effect of the current findings on the nomenclature relating to grey kangaroos are discussed.

Molecular detection of hybridization between sympatric kangaroo species in south-eastern Australia

“…Captive-based studies indicate that with no chromosomal differences (Hayman and Martin, 1969;Hayman, 1990), successful hybridization between grey kangaroos may occur despite differences in several reproductive traits such as gestation length and the timing and length of the oestrus cycle (Kirsch and Poole, 1972;Poole and Catling, 1974). However, hybridization appears unidirectional, with the only F1s produced resulting from matings between M. giganteus females and M. fuliginosus males, the reciprocal never occurred (Poole and Catling, 1974).…”

“…Female F1 hybrids successfully bred with males of both species, but it was not until the third-generation backcross that spermatogenesis and sperm were present in male offspring (Kirsch and Poole, 1972;Poole and Catling, 1974). F1 hybrids show reproductive and morphological traits intermediate to the parental species, whereas backcrosses were more difficult to distinguish, typically appearing similar to the species to which the hybrid is backcrossed (Kirsch and Poole, 1972;Poole and Catling, 1974).…”

“…When the number of simulated hybrids was reduced (that is, rare hybridization; see Supplementary Material), the proportion of correct assignments in optimized NEWHYBRIDS remained higher relative to STRUCTURE and default NEW-HYBRIDS (see Supplementary Material). Therefore, as hybridization in our study system was potentially low (Kirsch and Poole, 1972), this method was chosen to examine the empirical microsatellite data set. However, as 5.2% of the simulated first-generation backcrosses were incorrectly assigned to the F1 category using this method, the empirical data set was also examined using both the default NEWHYBRIDS and STRUCTURE to determine the presence or absence of F1 hybrids within the wild sample.…”

“…Previous molecular studies of sympatric grey kangaroo populations detected no evidence of hybridization (Kirsch and Poole, 1972). However, the separation of the species, based on the presence of an unshared polymorphism and no fixed differences at a single locus (transferrin), limited even the number of captive bred backcrosses that could be detected (6/14; Kirsch and Poole, 1972).…”

“…However, the separation of the species, based on the presence of an unshared polymorphism and no fixed differences at a single locus (transferrin), limited even the number of captive bred backcrosses that could be detected (6/14; Kirsch and Poole, 1972). Since then, the sensitivity of molecular genetic and statistical techniques available for investigating introgression have substantially improved (Pritchard et al, 2000;Anderson and Thompson, 2002;Manel et al, 2005 and references therein); although the accuracy of these techniques differs (Randi and Lucchini, 2002) and an increased likelihood of detecting hybrids potentially generates false positives.…”