Differences in Cell Proliferation and Craniofacial Phenotype of Closely Related Species in the Pupfish Genus Cyprinodon

Understanding the genetic basis for phenotypic differences is fundamental to the study of macroevolutionary patterns of biological diversity. While technological advances in DNA sequencing have made researching genetic variation in wild taxa routine, fully understanding how these variants affect phenotype requires taking the next step to investigate how genetic changes alter cell and tissue interactions that ultimately produce phenotypes. In this article, we investigate a role for cell proliferation as a developmental source of craniofacial diversity in a radiation of 3 species of Cyprinodon from San Salvador Island, Bahamas. Patterns of cell proliferation in the heads of hatching-age fish differ among species of Cyprinodon, and correlate with differences in allometric growth rate among the jaws of 3 distinct species. Regional patterns of cell proliferation in the head are complex, resulting in an unintuitive result in which lower levels of cell proliferation in the posterior head region are associated with the development of relatively larger jaws in one species. We combine these data with previously published morphological and genomic data to show how studying the mechanisms generating phenotype at the cellular and tissue levels of biological organization can help mechanistically link genomic studies with classic morphological studies.