Contradictory Phylogenetic Signals in the Laurasiatheria Anomaly Zone

Area of Science:

• Mammalian Phylogenetics
• Molecular Evolution
• Genomics

Background:

• The evolutionary history and interordinal relationships within Laurasiatheria, a major placental mammal clade, are complex and contentious.
• Previous phylogenetic studies have yielded conflicting results, necessitating advanced genomic approaches to resolve these deep evolutionary divergences.

Purpose of the Study:

• To investigate and clarify the phylogenetic relationships among major laurasiatherian orders using two distinct genome-level analyses.
• To identify potential sources of phylogenetic conflict, such as ancestral incomplete lineage sorting, within this mammalian superorder.

Main Methods:

• Genome-level phylogenetic analysis employing two independent datasets: retrotransposon presence/absence patterns and exon sequence comparisons (nucleotide and amino acid levels).
• Comparative analysis of phylogenetic signals derived from retrotransposon insertions versus exon sequence data to identify congruence and conflict.

Main Results:

• Consistent placement of Eulipotyphla and Chiroptera as the earliest diverging lineages within Laurasiatheria across both analytical methods.
• Contradictory phylogenetic signals regarding the relationships between Perissodactyla, Cetartiodactyla, and Ferae. Retrotransposon data suggested a Cetartiodactyla-Ferae clade, while exon data supported a Cetartiodactyla-Perissodactyla clade.

Conclusions:

• The study highlights significant phylogenetic discordance within Laurasiatheria, likely attributable to high levels of ancestral incomplete lineage sorting.
• Further research involving broader taxon sampling and integrated analyses of various genomic elements (retrotransposons, exons, introns, intergenic regions) is crucial for resolving these deep mammalian evolutionary relationships.