Comparative development and evolution of two lateral line phenotypes in lake Malawi cichlids

Area of Science:

• Developmental biology
• Evolutionary biology
• Ichthyology

Background:

• The lateral line system in fishes detects water movement.
• Cranial lateral line canals exhibit diverse morphologies, including narrow and widened forms.
• Heterochrony, a change in developmental timing, is a proposed mechanism for evolutionary morphological change.

Purpose of the Study:

• To test the hypothesis that widened lateral line canals evolved from narrow canals via heterochrony.
• To provide a detailed, quantitative description of widened lateral line canal development in teleosts.
• To investigate the developmental basis of morphological variation in the lateral line system of Lake Malawi cichlids.

Main Methods:

• Histological analysis of cranial development in three cichlid species.
• Scanning electron microscopy to examine canal and neuromast morphology.
• Comparative analysis of canal and neuromast development patterns.

Main Results:

• Canal neuromast number and canal morphogenesis patterns are conserved across species with different adult canal phenotypes.
• Heterochrony, specifically dissociated heterochrony, explains the evolution of widened canals and intra-specific variation in canal diameter and neuromast size.
• Lateral line canals and associated dermal bones can evolve independently, challenging traditional views of skull modularity.

Conclusions:

• Developmental timing (heterochrony) is a key driver in the evolution of diverse lateral line canal morphologies in cichlids.
• The development of the lateral line system shows a combination of conserved and independently evolving components.
• Skull modularity in teleosts is more complex than previously understood, with independent evolution of skeletal elements and associated sensory systems.