Late changes in spliceosomal introns define clades in vertebrate evolution

Area of Science:

• Evolutionary biology
• Genomics
• Phylogenetics

Background:

• The evolutionary history of spliceosomal introns, including their gain and loss, remains a contentious topic.
• Intron gain and loss events can serve as valuable phylogenetic markers if they are rare and unique occurrences.

Purpose of the Study:

• To investigate the phylogenetic distribution of specific spliceosomal introns in actinopterygian (ray-finned) fishes.
• To analyze intron pattern changes in the rhodopsin gene across fish evolution.
• To establish a robust intron-based cladogram for resolving complex ray-finned fish relationships.

Main Methods:

• Extensive survey of seven spliceosomal introns in Fugu genes compared to mammalian homologs.
• Investigation of intron patterns in the rhodopsin gene across various fish species.
• Construction of an intron-based cladogram to infer phylogenetic relationships.

Main Results:

• Seven spliceosomal introns were acquired by actinopterygian fishes at different evolutionary stages.
• Four introns present in the ancestral chordate rhodopsin gene were lost simultaneously in the common ancestor of ray-finned fishes.
• The intron-based cladogram resolved difficult phylogenetic relationships, positioning bichirs (Polypterus) as the sister group to all other extant ray-finned fishes.

Conclusions:

• Intron gain and loss events are significant evolutionary markers in ray-finned fishes.
• Intron patterns provide reliable data for constructing phylogenetic trees.
• This study clarifies the evolutionary position of bichirs within the ray-finned fish clade.