Convergence in a mechanically complex phenotype: detecting structural adaptations for crushing in cichlid fish.
Morphological convergence provides strong evidence that evolution is adaptive. However, putatively convergent morphology is often examined in two dimensions with no explicit model of function. In this study, we investigated structural and mechanical similarities of the lower pharyngeal jaw (LPJ) in cichlid fish that have evolved the ability to crush hard-shelled molluscs. Using a novel phylogeny, we demonstrated molluscivory has been gained and/or been lost numerous times in Heroine cichlids. Within this comparative framework, we produced three-dimensional computed tomography (CT) scans for LPJs of both morphotypes in the trophically polymorphic Herichthys minckleyi and six evolutionarily independent pairs of closely related species. Like H. minckleyi, these species exhibit divergence between a molluscivore and a nonmolluscivore. Using the CT scans, we generated finite element models of papilliform H. minckleyi LPJs to determine where stress would concentrate in a jaw not modified to crush molluscs. Then, we examined whether stress in the papilliform LPJ predicted structural modifications in molariform H. minckleyi and other molluscivorous species. Despite potential constraints, stresses imposed during prey processing explain 40% of LPJ variation in mollusc crushing species. The structural and mechanical analyses also suggest divergence found in polymorphic species could provide the substrate for trophic differences found in reproductively isolated cichlids.
Hulsey
C Darrin
CD
Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996.|School of Biology, Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332.|E-mail: chulsey@utk.edu.
Roberts
Richard J
RJ
School of Biology, Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332.|E-mail: richard.roberts@gatech.edu.
Lin
Angela S P
ASP
School of Biology, Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332.|E-mail: angela.lin@gatech.edu.
Guldberg
Robert
R
School of Biology, Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332.|E-mail: Robert.guldberg@me.gatech.edu.
Streelman
J Todd
JT
School of Biology, Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332.|E-mail: todd.streelman@biology.gatech.edu.
D000220:Adaptation, Biological; D000818:Animals; D005075:Biological Evolution; D023681:Cichlids / Q000033:anatomy & histology / Q000235:genetics*; D019245:Compressive Strength; D004032:Diet; D020342:Finite Element Analysis; D007568:Jaw / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008974:Mollusca; D010641:Phenotype; D014057:Tomography, X-Ray Computed