Mosaic retroposon insertion patterns in placental mammals

Area of Science:

• Evolutionary biology
• Genomics
• Mammalian evolution

Background:

• Resolving the basal origin of placental mammals has been challenging using sequence-based molecular data, leading to conflicting hypotheses.
• Retroelements, particularly retroposons, offer a neutral and homoplasy-free archive of evolutionary history through their insertion patterns.

Purpose of the Study:

• To investigate the basal origin of placental mammals using comparative retroposon insertion patterns.
• To challenge existing hypotheses by analyzing a large dataset of retroposon-containing loci.

Main Methods:

• Extraction of approximately 2 million phylogenetically informative, retroposon-containing loci from major placental mammalian lineages.
• Comparative analysis of retroposon insertion patterns to infer evolutionary relationships.

Main Results:

• Evidence was found challenging all current single hypotheses for placental mammal basal origin.
• The Exafroplacentalia, Epitheria, and Atlantogenata hypotheses received support from specific retroposon insertion counts (5, 9, and 8, respectively).
• Findings indicate a "soft" polytomy among major mammalian clades.

Conclusions:

• The mosaic retroposon insertion patterns suggest a complex evolutionary history for placental mammals.
• Ancestral hybridization events and/or incomplete lineage sorting are proposed as explanations for the observed patterns and the difficulty in establishing a clear root dichotomy.