An integrative approach to understanding the molecular mechanisms of color pattern formation and evolution in cichlid fishes.

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Coloration is an important and fascinating feature in the biology of an organism. It plays key roles in several fundamental physiological, ecological, and evolutionary processes. Moreover, these conspicuous phenotypes challenge biologists to understand the mechanistic and genetic underpinnings of color patterns and their morphogenesis as well as their ultimate causes. The color of a tissue results from the multi-layered organization of a pigment cell types with different structural and pigmentary properties. On a macroscopic scale, color patterns arise from spatial differences in pigment cell properties and arrangements to form vertical bars, horizontal stripes or other patterns. Color patterns are suggested to have adaptive significance as they are implicated in intraspecific communication, species recognition and camouflage. Understanding the underlying genetic, cellular and developmental mechanisms as well as functional relevance is crucial for gaining insights into their evolutionary diversification. Teleost fishes display an astonishing diversity of colors and color patterns. Cichlids are a particular colorful family of fishes — well captured by their German common name "Buntbarsche", or colorful perches. Coloration phenotypes play many roles in cichlid evolution, covering the entire spectrum of functions including those relevant for sexual selection (e.g. mating preferences) and adaptation (e.g. camouflage). Likewise, cichlid fishes are a famous example for repeated evolution. Their color patterns (e.g. bars and stripes) evolved several times and in parallel across the over 1200 species of East African cichlids. Still, the genetic and mechanistic basis that determines these traits and what changes cause their diversification and repeated evolution and the adaptive function of color patterns are unknown. What mechanisms control the arrangement and properties of pigment cells? How do aggregations of cells form the so diverse color patterns of cichlids? Are the underlying genetic differences shared across species with analogous patterns or are they generated by novel molecular mechanisms? Are they based on standing or novel genetic variations, regulatory or coding changes and many or few genes? And what is the adaptive function of these patterns? Cichlid fishes are well suited for addressing these fundamental topics. They provide excellent means for bridging the gap between genotypes, color pattern phenotypes and adaptive function. Thus, through an integrated approach I aim to analyze the molecular underpinnings of color patterns in cichlids. Tackling these fundamental questions will offer in-depth insights into the genomic and mechanistic substrates of color patterns and the secrets behind their astonishing evolutionary dynamics.