Chromosome Evolution in Xenarthra: New Insights from an Ancient Group

Abstract

The Magnaorder Xenarthra is one of the four main supraordinal eutherian clades, together with Afrotheria, Euarchontoglires and Laurasiatheria. Xenarthra is an eminently Central and South American group of special interest in phylogenetic studies due to its possible position at the base of the eutherian tree. The use of modern cytogenetic techniques in some species of Xenarthra has provided important insights into the karyotypic evolution of mammals. Nevertheless, chromosome analyses in the group are still restricted, with only a few individuals of each species studied and karyotype descriptions mostly without banding patterns. In addition, it is likely that still unknown species exist and that the chromosome variability in the group is underestimated. We present a review of the currently available data on Xenarthra chromosomes and genomes and on the impact that their study has had in the understanding of mammalian genome evolution. It is clear that further cytogenetic analyses in Xenarthra, including banding patterns and molecular approaches, are likely to help in the identification of new species, reveal still undetected chromosome variations, provide information to support conservation strategies planning, and greatly contribute to a better understanding of mammalian genome evolution.

Cytogenetic analysis of Phyllomedusa distincta Lutz, 1950 (2n = 2x = 26), P. tetraploidea Pombal and Haddad, 1992 (2n = 4x = 52), and their natural triploid hybrids (2n = 3x = 39) (Anura, Hylidae, Phyllomedusinae)

“…Some examples have been found in insects and among ectothermic vertebrates, such as Salmonidae, Coregonidae, Catostomidae, and Thymallidae fishes, Gekkonidae reptiles, and Caudata and Anura amphibians [1,4]. In anurans, approximately 56 cases of polyploidy have been described in species, populations, and as spontaneously originated polyploid individuals [5-12]. Although the tetraploidy (4x) is relatively common, cases of octoploidy (8x) and even dodecaploidy (12x) have been well documented, such as in the Xenopus species [13,14].…”

Karyotype and Chromosome Variability in the Armadillo <b><i>Chaetophractus villosus</i></b> in Argentina

“…The superorder Xenarthra contains armadillos, anteaters, and sloths [Engelmann, 1985;Wetzel, 1985;Nowak, 1999;Delsuc et al, 2003;Gardner, 2008;Svartman, 2012]. Alongside Euarchontoglires, Laurasiatheria, and Afrothe ria, it is 1 of the 4 main supraordinal clades of Eutheria [Murphy et al, 2001].…”

“…Alongside Euarchontoglires, Laurasiatheria, and Afrothe ria, it is 1 of the 4 main supraordinal clades of Eutheria [Murphy et al, 2001]. Given its possible position at the base of the eutherian tree [McKenna, 1975;De Jong et al, 1985;Sarich, 1985;Madsen et al, 2001;Murphy et al, 2001;Delsuc et al, 2003;Svartman, 2012], it is of particular cytogenetic and phylogenetic interest. Most xenarthrans, however, have been poorly studied.…”

“…Most xenarthrans, however, have been poorly studied. Indeed, still unknown species may exist, and xenarthran chromosome variability is likely underestimated [Svartman, 2012].Armadillos (Dasypodidae) are the oldest and most diverse lineage of Xenarthra with 21 species living mostly in South America, 14 of which are found in Argentina. …”

The mylodontine ground slothGlossotherium tropicorumfrom the late Pleistocene of Ecuador and Peru

“…Today xenarthrans are represented by only 31 species distributed primarily in South and Central America (Aguiar & Fonseca ; Vizcaíno & Loughry ; Svartman ). Their fossil record demonstrates a much more varied and taxonomically abundant clade that originated in South America, and within this clade the sloths probably originated during the early Oligocene (McKenna et al .…”