Laterality is Universal Among Fishes but Increasingly Cryptic Among Derived Groups

Area of Science:

• Evolutionary Biology
• Comparative Anatomy
• Zoology

Background:

• Laterality in vertebrates is primarily studied in brain and behavior, with less focus on morphological asymmetry.
• Fish asymmetry was first noted in cichlids, showing a genetic basis linked to feeding behaviors.
• This trait has since been observed across diverse fish taxa, necessitating a broader investigation.

Purpose of the Study:

• To investigate the prevalence of morphological laterality across a wide range of fish species.
• To determine the evolutionary origins and patterns of morphological asymmetry in fishes.
• To explore potential ecological drivers and the inheritance of laterality in vertebrates.

Main Methods:

• Examined morphological laterality using indicators of lateral differences in mandibles and head inclination.
• Surveyed representative species from all 60 extant gnathostome fish orders (bony and cartilaginous).
• Included agnathans (hagfish and lamprey) to assess early evolutionary appearance.

Main Results:

• Morphological laterality was found in all surveyed gnathostome fish orders and in agnathans.
• The trait appears to have originated early in fish evolution and persisted across lineages.
• A decrease in asymmetry was unexpectedly observed in phylogenetically recent bony fish groups.

Conclusions:

• The universality of laterality in fishes suggests a monophyletic origin, potentially present in vertebrate ancestors.
• Ecological factors, especially predator-prey dynamics, likely influence the evolution and maintenance of laterality.
• Laterality is likely inherited by tetrapods, offering insights into vertebrate behavioral and sensory lateralization.