18S rRNA variability maps reveal three highly divergent, conserved motifs within Rotifera

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Phylogenetics

Background:

• 18S ribosomal RNA (rRNA) is a crucial component of eukaryotic ribosomes and a key phylogenetic marker.
• Its conserved core structure across eukaryotes provides insights into evolutionary patterns.
• Rotifers, a diverse group of microscopic animals, are often studied using 18S rRNA due to limited alternative markers.

Purpose of the Study:

• To investigate the evolutionary patterns of 18S rRNA within the phylum Rotifera.
• To analyze sequence variability and conservation across major rotifer clades (Bdelloidea, Monogononta, Seisonacea).
• To compare evolutionary rates with other relevant taxa like Gastropoda and Acanthocephala.

Main Methods:

• Sequence alignment of 18S ribosomal DNA (rDNA) from three exemplar rotifer species.
• Fitting sequences to the eukaryotic 18S rRNA core structure to create variability maps.
• Analysis of sequence variation, conservation, and evolutionary rates across different rotifer groups.

Main Results:

• High 18S rRNA diversity was observed between the three major rotifer clades, contrasted by strong conservation within each clade.
• Approximately 60% of individual sites remained constant across all rotifers, with variable sites showing intermediate evolution rates.
• Distinct conserved motifs were identified at the primary sequence level, alongside a novel variably expressed deletion in the V3 hypervariable region of some bdelloids.

Conclusions:

• The observed patterns of 18S rRNA variation potentially explain the lack of consensus in rotifer phylogenetic relationships.
• High morphological diversity within rotifers, coupled with distinct molecular motifs, complicates phylogenetic interpretation.
• Further comparative data is needed to fully interpret the novelty and significance of these findings in rotifer evolution.