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Convergence in a mechanically complex phenotype: detecting structural adaptations for crushing in cichlid fish
C Darrin Hulsey1,2,3, Richard J Roberts2,4, Angela S P Lin2,5
1Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996.
Evolution; International Journal of Organic Evolution
|April 1, 2008
Summary
Evolutionary adaptation in cichlid fish jaws shows convergence. Mechanical stresses during mollusc crushing explain significant lower pharyngeal jaw (LPJ) variation, driving adaptive evolution.
Area of Science:
- Evolutionary biology
- Functional morphology
- Paleontology
Background:
- Morphological convergence is often cited as evidence for adaptive evolution.
- Previous studies have examined convergent morphology in two dimensions, lacking explicit functional models.
- The lower pharyngeal jaw (LPJ) in cichlid fish presents an opportunity to study adaptive evolution due to its role in processing diverse food resources.
Purpose of the Study:
- To investigate structural and mechanical similarities in the LPJ of cichlid fish that have evolved molluscivory (mollusc-crushing).
- To determine if mechanical stresses during prey processing can explain LPJ variation in mollusc-crushing cichlids.
- To explore the role of LPJ divergence in trophic differentiation and reproductive isolation.
Main Methods:
- Utilized a novel phylogeny to reconstruct the evolutionary history of molluscivory in Heroine cichlids.
- Generated three-dimensional computed tomography (CT) scans of LPJs from trophically polymorphic species and closely related pairs.
- Created finite element models to analyze stress distribution in LPJs under simulated crushing forces.
Main Results:
- Molluscivory has evolved multiple times independently within Heroine cichlids.
- Mechanical stresses during mollusc crushing explain 40% of the variation in LPJ morphology among molluscivorous species.
- LPJ structural divergence in polymorphic species may provide a basis for trophic differences in reproductively isolated cichlids.
Conclusions:
- Adaptive evolution of the LPJ in cichlids is strongly influenced by mechanical constraints and functional demands of prey processing.
- Investigating functional morphology using advanced imaging and modeling techniques provides deeper insights into evolutionary pathways.
- LPJ divergence plays a crucial role in the ecological speciation of cichlid fishes.
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