Neaves, L. E.Zenger, K. R.Cooper, D. W.Eldridge, M. D.B.2025-12-182025-12-180018-067XPubMed:19812615ORCID:/0000-0002-5626-1029/work/162952756https://hdl.handle.net/1885/733796557Introgressive hybridization has traditionally been regarded as rare in many vertebrate groups, including mammals. Despite a propensity to hybridize in captivity, introgression has rarely been reported between wild sympatric macropodid marsupials. Here we investigate sympatric populations of western (Macropus fuliginosus) and eastern (Macropus giganteus) grey kangaroos through 12 autosomal microsatellite loci and 626 bp of the hypervariable mitochondrial DNA (mtDNA) control region. M. fuliginosus and M. giganteus within the region of sympatry corresponded, both genetically and morphologically, to their respective species elsewhere in their distributions. Of the 223 grey kangaroos examined, 7.6% displayed evidence of introgression, although no F1 hybrids were detected. In contrast to captive studies, there was no evidence for unidirectional hybridization in sympatric grey kangaroos. However, a higher portion of M. giganteus backcrosses existed within the sample compared with M. fuliginosus. Hybridization in grey kangaroos is reflective of occasional breakdowns in species boundaries, occurring throughout the region and potentially associated with variable conditions and dramatic reductions in densities. Such rare hybridization events allow populations to incorporate novel diversity while still retaining species integrity.This work was carried out with the co-operation of N.S.W DEH under scientific license no. S11250. We have gratefully appreciated the efforts of Ern Snaith, Nicole Payne, Anne Wignall, Ian Beveridge, Taryn Ackland and Dew’s Meat for supplying tissue samples. This research was supported by Macquarie University through a Postgraduate Research Fund grant and a Research Awards in Areas and Centres of Excellence scholarship to Linda Neaves. Many thanks to Ian Beveridge, Graeme Coulson, David Briscoe and Adam Stow for discussions, and to Peter Baverstock, Steve Donnellan and Robert Wayne as well as two anonymous referees for comments on an earlier draft of the paper.11enIntrogressive hybridizationKangaroosMicrosatelliteMitochondrial DNA201010.1038/hdy.2009.13777951498215