Macropus, Shaw, 1790
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publication ID |
https://doi.org/10.1093/zoolinnean/zlz005 |
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persistent identifier |
https://treatment.plazi.org/id/825087EF-FFF9-200F-8F62-F7B92CCD93AD |
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treatment provided by |
Plazi |
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scientific name |
Macropus |
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Macropus View in CoL , the typically more arid-adapted, grazing red kangaroo and wallaroos of Osphranter , and the smaller, often mixed-feeding, woodland wallabies of Notamacropus ( Dawson & Flannery, 1985) . Then there is the monotypic swamp wallaby ( Wallabia bicolor ), which stands out from all other members of the Macropus complex because of its unique karyotype (2 n = 10/ 11 in females/males; Sharman et al., 1990), ecology and behaviour ( Hollis et al., 1986; Van Dyck & Strahan, 2008). Swamp wallabies occupy moderately dense forests, woodlands and swamps. Their mixed grazing–browsing ecology includes diverse plant leaves, grass and fungi ( Hollis et al., 1986; Hume, 1999; Arman & Prideaux, 2015). They exhibit a somewhat crouched gait when hopping, with their head close to the ground and tail straight, whereas other Macropus species hop more upright ( Van Dyck et al., 2008).
Before we consider the affinities of Wallabia , the phylogenetic relationships between the three subgenera included in the traditional Macropus genus concept have also been difficult to establish. The apparently rapid diversification of the group limits phylogenetic signal ( Nilsson et al., 2017), which may in turn be overshadowed by homoplasy associated with parallel evolution of larger size and grazing adaptations in different subgenera ( Meredith et al., 2009; Couzens & Prideaux, 2018). Morphology tends to group the larger, grazing Macropus and Osphranter to the exclusion of Notamacropus (e.g. Dawson & Flannery, 1985; Prideaux & Warburton, 2010; Butler et al., 2016). Molecular efforts have, until recently, been unable to resolve confidently the relationships among these clades, including studies of serology and karyotyping (Kirsch, 1977; Sharman et al., 1990) and DNA-based analyses (e.g. Kirsch et al., 1995; Meredith et al., 2008; Phillips et al., 2013). Retrotransposons ( Dodt et al., 2017) and genome-scale sequence analysis ( Nilsson et al., 2017) now reveal that the grey kangaroos ( Macropus ) fall outside of Osphranter and Notamacropus .
Ever since Desmarest (1804) described the swamp wallaby, Wallabia bicolor , its placement has complicated macropodid taxonomy. Karyotypic and serological analyses ( Sharman, 1960; Kirsch & Calaby, 1977; Kirsch, 1977) and morphological analyses (e.g. Flannery, 1989; Prideaux & Warburton, 2010) have placed Wallabia outside other members of Macropus , sometimes as their sister, sometimes deeper in Macropodinae . Further support for a taxonomic split between Wallabia and the other members of Macropus derives from molecular phylogenies based on mitochondrial DNA (mtDNA) ( Burk & Springer, 2000; Phillips et al., 2013) and supertrees and supermatrices derived from multiple data sources ( Cardillo et al., 2004; May-Collado et al., 2015). However, other molecular phylogenetic analyses based on serology, DNA hybridization and individual nuclear genes nested Wallabia in ‘ Macropus ’ ( Baverstock et al., 1989; Kirsch et al., 1995; Retief et al., 1995; Bulazel et al., 2007). The analysis by Meredith et al. (2008) of five concatenated nuclear genes weakly supported W. bicolor grouping with Notamacropus , leaving the concept of Macropus paraphyletic if Wallabia is maintained as a separate genus.
It is now confirmed with retrotransposons ( Dodt et al., 2017) and genome-scale sequence analysis ( Nilsson et al., 2017) that Wallabia and Notamacropus form a wallaby clade, with the larger wallaroos and kangaroos of Osphranter and Macropus confidently placed as consecutive outgroups ( Fig. 1 View Figure 1 ). Nevertheless, the retrotransposons and genome fragments reveal substantial incomplete lineage sorting and probably introgression between Wallabia , Osphranter , Macropus , Notamacropus and an extinct ‘ Macropus ’ stem taxon. This could explain much of the previous incongruence between loci (see Phillips et al., 2013). Incidences of deep coalescence are not surprising, given that all four Macropus clades diverged in a narrow window of 1–2 Myr, during the Late Miocene or Early Pliocene ( Meredith et al., 2008; Phillips et al., 2013; Dodt et al., 2017; Nilsson et al., 2017; Couzens & Prideaux, 2018). Hereafter, ‘ Macropus ’ refers to the complex of all four clades, Macropus , Osphranter , Notamacropus and Wallabia . Unless otherwise qualified, we use Macropus for only the grey kangaroos, whereas Macropus traditionally included Macropus , Osphranter and Notamacropus .
With relationships among ‘ Macropus ’ now resolved, it is timely to address three problems: (1) the phylogeny of all extant members in the subclades; (2) the placement of the extinct Toolache wallaby ( Notamacropus greyi ); and (3) whether paraphyly of the traditional Macropus genus should be accounted for taxonomically by expanding that genus to include Wallabia or instead, by maintaining Wallabia and raising several subgenera to genera. In the present study, we build a new molecular phylogeny of macropodids based on a dataset of five nuclear and four mitochondrial genes that, for the first time, includes all living species of ‘ Macropus ’, including the extinct Toolache wallaby.
The Toolache wallaby ( N. greyi ), which became extinct in the 1930s, occurred in open grassland areas in southern Australia, often at the edge of wooded swamp habitats. It was characterized by a slender body, distinct coloration and a singular erratic gait ( Van Dyck & Strahan, 2008). Notamacropus greyi has been little studied, although it is currently included in Notamacropus close to the black-gloved (or western brush) wallaby, Notamacropus irma , possibly even as a subspecies, based on craniodental characters ( Dawson & Flannery, 1985; Jackson et al., 2015).
Taxonomic revision necessitated by paraphyly of the traditional Macropus genus concept could follow Meredith et al. (2008) and subsume Wallabia into Macropus , as its own subgenus, Macropus (Wallabia) . Jackson & Groves (2015) instead maintain Wallabia , but raise each of the three Macropus subgenera to genera. Nilsson et al. (2017) presented a third option, to raise both of the subgenera Osphranter and Macropus to genera and place Notamacropus in Wallabia . Note that as a genus, Wallabia Trouessart, 1905 has taxonomic priority over Notamacropus Dawson & Flannery, 1985 . None of these proposals has been based on strong empirical evidence incorporating multilocus (dated) DNA phylogenies and morphological characters. Meredith et al. (2008) noted the existence of Wallabia – Notamacropus hybrids. However, similar sterile/infertile hybrids also exist between Notamacropus and the far more distant Thylogale , such that consistent use of this criterion could lump almost the entire macropodine subfamily into a single genus. Jackson & Groves (2015) relied on an arbitrary 4–5 Myr cut-off for the crown age of genera, which may be overly reliant on the accuracy of molecular dates and, in many cases ( Meredith et al., 2008; Dodt et al., 2017; and herein), would variously also split wellagreed genera, such as Lagorchestes , Potorous and even Notamacropus , each into two genera. In contrast, Nilsson et al. (2017) were concerned with the limited genetic distinction of members of Notamacropus from Wallabia .
Conceptualizing and defining genera have received little attention compared with species-level taxonomy, for which the potential for combining genes in descendants of sexual species provides at least an objective ideal as a starting point.Yet, there is a common concept of an ‘adaptive zone’ (e.g. Simpson, 1944; Legendre & Vaillancourt, 1969; Lemen & Freeman, 1984; Garbino, 2015) that binds species together as genera and is perhaps traceable even to ancient folk science notions of taxonomy ( Bartlett, 1940). We take an integrated approach to ‘ Macropus ’ genus-level taxonomy, assessing monophyly and considering morphological, ecological and genetic information in comparison to well-established macropodid genera.
Alongside nuclear and mitochondrial DNA, we analyse cranial morphology to place variation among ‘ Macropus ’ in macropodid cranial morphospace more broadly. We have recently shown that landmark-based geometric morphometric quantification of macropodid cranial morphology contains substantial and significant phylogenetic signal ( Fruciano et al., 2017), and thus, it is well suited for comparison with patterns and relationships implied by molecular phylogenetics.
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