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

Abstract

Introgressive 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.

Divergence-with-Gene-Flow—What Humans and Other Mammals Got up to

“…0.68 km 2 ; Caughley et al 1984;Neaves et al 2010) and the production of hybrids in captivity (Kirsch and Pool 1972), there was little evidence of natural hybridization between these macropod species (Coulson and Coulson 2001). In contrast to previous analyses, Neaves et al (2010) did indeed find evidence consistent with introgressive hybridization between M. fuliginosus and M. giganteus in the area of overlap in eastern Australia. Based upon variation at both nuclear and mitochondrial loci, 7.6 % of the >200 kangaroos sampled in the sympatric region were found to be hybrids.…”

“…Based upon variation at both nuclear and mitochondrial loci, 7.6 % of the >200 kangaroos sampled in the sympatric region were found to be hybrids. As is the case with the majority of cases of introgression among both plants and animals, there was an asymmetry in the genetic exchange, in this case with 14 of the 17 hybrid individuals identified as backcrosses toward M. giganteus and the remaining three hybrids assigned to the class of backcrosses to M. fuliginosus (Neaves et al 2010). None of the hybrid genotypes were consistent with an F 1 generation; thus, these findings reflect divergence-with-gene-flow between these marsupial species.…”

“…In particular, the largest members of this assemblage, species of red and gray kangaroos, are scattered across the Australian landscape from the east to west coasts (Short et al 1983). Gray kangaroos are classified into western and eastern forms, Macropus fuliginosus and eastern M. giganteus, respectively, with a zone of sympatry between the two species located in portions of the states of Victoria, New South Wales, and Queensland (Caughley et al 1984;Neaves et al 2010). Notwithstanding such a large area of overlap (ca.…”

“…None of the hybrid genotypes were consistent with an F 1 generation; thus, these findings reflect divergence-with-gene-flow between these marsupial species. Furthermore, Neaves et al (2010) argued for the importance of genetic exchange in potentially allowing the transfer of genomic components affecting adaptive traits-such as those associated with aridity. Testing for such adaptive trait transfer has been a major emphasis in many systems and was pointed out as possibly the most important outcome of introgressive hybridization by Anderson (1949).…”

SimHyb: a simulation software for the study of the evolution of hybridizing populations. Application to Quercus ilex and Q. suber suggests hybridization could be underestimated

“…This approach was applied by Burgarella et al (2009) in sympatric Q. ilex -Q. suber populations, estimating a current introgression rate of <2%. Later on, this procedure has been applied in studies for many other species, including animals (Neaves et al 2010, Bogdanowicz et al 2012, Malde et al 2017.…”