Probing recalcitrant problems in polyclad evolution and systematics with novel mitochondrial genome resources

Area of Science:

• * Zoology
• * Molecular Evolution
• * Phylogenetics

Background:

• * Platyhelminthes (flatworms) are morphologically simple yet diverse, posing classification challenges.
• * Molecular data is crucial for understanding their evolutionary history.
• * Previous studies have undersampled mitochondrial genomes from key orders like Polycladida and Rhabdocoela.

Purpose of the Study:

• * To present nine novel mitochondrial genomes from Platyhelminthes, including the first from Rhabdocoela.
• * To reconstruct a robust molecular phylogeny for Platyhelminthes using mitochondrial genome data.
• * To clarify interrelationships within the clade and their placement within Lophotrochozoa.

Main Methods:

• * Assembly of nine novel mitochondrial genomes from short Illumina sequencing reads.
• * Comparative analysis of mitochondrial gene order and sequence data.
• * Phylogenetic reconstruction using Bayesian and Maximum Likelihood methods with nucleotide and amino acid sequences.

Main Results:

• * Novel mitochondrial genomes from Polycladida and Rhabdocoela were successfully assembled.
• * Phylogenetic analyses strongly support the monophyly of Polycladida, Acotylea, and Cotylea.
• * The study provides insights into the early emergence of Macrostomida and the placement of Platyhelminthes within Lophotrochozoa.

Conclusions:

• * The presented mitochondrial genomes significantly advance the understanding of Platyhelminthes phylogeny.
• * Molecular data confirms monophyly of key groups, aiding in resolving taxonomic disputes.
• * This research provides a foundation for future studies on flatworm classification and evolution.