Pancrustacean Evolution Illuminated by Taxon-Rich Genomic-Scale Data Sets with an Expanded Remipede Sampling

Area of Science:

• * Evolutionary Biology
• * Zoology
• * Genomics

Background:

• * The evolutionary relationships within Pancrustacea (crustaceans and hexapods) remain incompletely understood, particularly concerning major groups like Branchiopoda, Copepoda, Remipedia, and Cephalocarida.
• * Previous phylogenomic studies have offered insights but left significant uncertainties regarding the sister group to hexapods and the placement of key crustacean taxa.

Purpose of the Study:

• * To resolve phylogenetic uncertainties within Pancrustacea by constructing the most comprehensive taxon-rich phylogenomic data set to date.
• * To investigate the evolutionary history and relationships of crustaceans and hexapods using diverse analytical methods.
• * To reconstruct ancestral traits of pancrustaceans, including body form and developmental patterns.

Main Methods:

• * Assembly of a large phylogenomic data set for Pancrustacea, prioritizing minimal missing data.
• * Phylogenetic analyses employing various methodological approaches to ensure robustness of recovered clades.
• * Mapping of morphological and developmental characters onto the inferred phylogeny to understand trait evolution.

Main Results:

• * Consistent recovery of clades such as Oligostraca and Altocrustacea across different analytical methods.
• * Strong support for the clade Allotriocarida, with Remipedia sister to Hexapoda (Labiocarida), and Branchiopoda sister to Labiocarida, forming Athalassocarida.
• * Identification of Cephalocarida as sister to Athalassocarida within Allotriocarida, and moderate support for Hexanauplia (Copepoda sister to Thecostraca) allied with Malacostraca.
• * Reconstruction of the ancestral pancrustacean as short-bodied, with body elongation and anamorphic development evolving later.

Conclusions:

• * The study provides a robust phylogenetic framework for Pancrustacea, resolving relationships of several previously uncertain taxa.
• * The findings support a revised understanding of crustacean and hexapod evolution, including the origin of key groups like Athalassocarida.
• * The ancestral pancrustacean body plan was likely simple and short, with complex features evolving secondarily.