Evolutionary convergence and parallelism in zebrafish pigment pattern development

University Of Washington, Seattle WA

Investigators

Abstract

Parichy ABSTRACT We know very little about the developmental genetic mechanisms underlying adult form and the differences in adult form among species. Nevertheless, identification of the genes and cell behaviors responsible for adult morphology will be essential for a fuller understanding of diversity and evolution. These studies will investigate the development and evolution of adult form using as a model pigment patterns of fishes in the genus Danio. Pigment patterns are especially interesting because of their ecological and behavioral significance, and especially tractable because many genetic and cellular mechanisms for pigment pattern formation have been identified in the zebrafish, D. rerio. Moreover, close relatives of the zebrafish exhibit a diverse array of pigment patterns that can be investigated using many of the same methods employed in studies of the zebrafish itself. Thus, analyses of pigment patterns offer the prospect of truly integrative studies spanning multiple levels of organization, from genes to cells, and from individuals to populations and species. The proposed studies will investigate an important question in evolutionary developmental biology; namely, when"and how" are genetic changes translated into morphological differences between species? First, mechanisms underlying the evolutionary loss of a striped pigment pattern will be examined in D. albolineatus. Genetic analyses identified a receptor tyrosine kinase, Fms, as a likely contributor to the difference between D. rerio (stripes) and D. albolineatus (no stripes). To test this possibility directly, interspecific differences in Fms expression and activity will be assayed and fms sequences will be examined for evidence of natural selection on this locus. This work will advance our understanding of the mechanisms underlying evolutionary changes in morphology, and will serve as a model for integrative analyses of biological variation. Second, stripe development in D. kyathit and D. shanensis will be examined to test whether the same mechanisms underlie stripe formation in these species as in D. rerio. Previous studies revealed that horizontal stripes in D. rerio depend on interactions between two classes of pigment cells. Such interactions may explain a diverse array of pigment patterns in vertebrates. This will be tested by investigating different modes of horizontal stripe development in D. kyathit and vertical stripe development in D. shanensis, using imaging, molecular marker analyses, and genetics. These studies will determine how conserved developmental mechanisms can be used to generate differences in trait expression across species, and will provide insights into pigment pattern evolution across a wide range of ectothermic vertebrates. Third, different mechanisms underlying superficially similar stripes in D. rerio and D. nigrofasciatus will be elucidated. Adult stripes in D. rerio and other species arise from stem cells at metamorphosis. Adult stripes in D. nigrofasciatus resemble those of D. rerio, yet develop largely from melanophores that differentiated at earlier stages, with little contribution from stem cells. Molecular analyses and cell transplantation experiments will elucidate how the stem cell lineage has changed in D. nigrofasciatus, and how early melanophore behaviors have been affected. These experiments will indicate the extent to which developmental mechanisms can evolve in the absence of corresponding changes in morphology, and will simultaneously address an important but understudied problem, the role of postembryonic stem cells in vertebrate development and evolution. The proposed studies will have significant broader impacts by involving undergraduates and minority students, and by providing an example of integrative research spanning molecular and organismal biology. The location of the proposed studies (University of Texas) has a high proportion of minority students, and the PI has an excellent track record of involving undergraduates in laboratory research. In addition, one of the senior personnel is female, has excellent training in organismal biology and chemistry, and already serves as an outstanding role model for female undergraduate and graduate students. Finally, the PI is a member of two departments and attracts students with interests in behavior, ecology, evolution, genetics, and developmental biology, thus providing an unusually high degree of synergism in the laboratory environment.