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Xenarthran phylogenetics and evolution

Reconstructing the unique evolutionary history of armadillos, anteaters, and sloths

Team members involved: Melanie Kuch, Jonathan Hughes
Project in collaboration with Frédéric Delsuc, Gillian Gibb
Funding provided by: NSERC (National Sciences and Engineering Research Council of Canada)
CNRS (Centre National de la Recherche Scientifique) and Scientific council of the Université Montpellier 2.

Xenarthran Evolution and Sequencing the Genomic Data

Armadillos, anteaters, and sloths comprise the mammalian superorder Xenarthra, representing one of the four major placental mammal groups (the others being Afrotheria, Laurasiatheria, and Euarchontoglires).  Xenarthrans evolved in South America and spread into Central and North America during the Great American Interchange. At the end of the Pleistocene, many Xenarthrans went extinct, including the emblematic giant ground sloths, glyptodonts, and pampatheres. With only 31 remaining species (many endangered), the Xenarthra represent the culmination of a deep evolutionary history that has manifested in many unique (and often peculiar) morphological adaptations. Yet despite this, relatively little is known about their genetics, especially as they relate to one another and mammals in general. How rapidly and under what circumstances did Xenarthra diverge into the three familiar forms living today? Were mysterious Xenarthrans like pampatheres and glyptodonts descendants of altogether unknown subclades within the superorder? Our research focuses on answering these questions by sequencing mitochondrial and nuclear genes from Xenarthran tissue samples, museum skins, and paleontological remains.

Until recently, Xenarthran mitochondrial genome data has been sorely lacking, with only four mitogenomes sequenced. Using high-throughput sequencing technology, we increased that number to 27, nearly completing a superorder-wide genomic survey of their phylogeny. In doing so, we discovered that commonly-assumed morphology-based species distinctions do not always correspond to mitochondrial phylogeny, with striking non-congruence among Chaetophractus armadillos especially. We are expanding this work to the remaining 4 species, and will also target nuclear genes related to the phenotypes that make Xenarthrans so unique among mammals.