Christopher M. Hofmann
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EVOLUTION OF VISUAL SIGNALS AND VISUAL SYSTEMS Overview The brilliant colors and patterns found in many animals have captivated the attention of scientists and society for centuries.  My research attempts to understand the processes responsible for generating the incredible diversity of animal colors and patterns by studying the evolution of color signals and sensory systems.  This work is interdisciplinary - combining the techniques and approaches from systematics, molecular genetics, ecology and evolution.  My post-doctoral research has focused more on the molecular genetics of vision in fish, while my thesis work focused on plumage evolution in birds.  In both groups of organisms color, and vision, have important roles in breeding behavior, adaptation to novel environments, and the formation of new species.
Vision My post-doctoral research is focused on the molecular genetics of vision.  We are using cichlid fish and damselfish as model systems for understanding how the genes that underlie visual sensitivity have evolved and are regulated.  Specifically, we are looking at opsins, a group of proteins that determine the wavelengths of light that cones respond to.  Traditionally, changes in spectral (color) sensitivity have been attributed to amino acid substitutions.  However, recent work suggests that fish have more opsin genes than they express at a given time and that turning different genes on and off may provide an extremely labile means of tuning spectral sensitivity.  In order to better understand how cone opsins have evolved and are regulated, we are attempting to identify the number and location of factors that control opsin expression.  We are also investigating how different environmental conditions may influence opsin gene expression.  Finally, we are studying how amino acid substitutions and changes in gene expression vary across different phylogenetic levels.  This project will compare opsin evolution in the relatively rapid African cichlid radiations to opsin evolution in the damselfish, a closely related, but much older group of coral reef fish.
Broader Implications This work has broad biological implications.  Vision is important in several life history tasks ranging from finding food to obtaining a mate.  Differences in visual sensitivity are thought to have played an important role in the colonization of new habitats and facilitated the process of speciation.  Furthermore, as differences in visual sensitivity develop, body coloration may also change, leading to even greater divergence between species.  Thus, vision may have had an important role in the process of speciation.  In addition, this work provides new insights into the regulation of gene expression.  Since a wide range of human diseases result from defects in gene regulation - both inherited and environmental - our work has the potential to help us better understand diseases from macular degeneration to cancer.
Color Evolution My thesis work focused on color evolution in the New World orioles – a species rich genus of birds with colors ranging from yellow to scarlet to chestnut.  We sought to investigate patterns of color change across species, taking into account their evolutionary relatedness. We found that colors can change rapidly, even among closely related species, that there is no directionality to these changes (e.g. not from yellow to red or vice versa), and the tempo of these changes is punctuated (as opposed to gradual).  Our data also suggests that many oriole colors are produced through mixtures of a class of pigments called carotenoids – and that these colors have likely evolved in a continuous pattern that is different from that of other groups of birds, including other blackbirds.  Finally, when we compared male and female coloration we found that many females were equally elaborate and indistinguishable from males.  Our findings provide strong support for dull female orioles having lost elaborate male-like coloration – a finding that is opposite that of the ‘traditional’ theory of sexual selection.
Broader implications Elucidating the patterns of evolution across species, the tempo of morphological change, and the physiological bases of these changes leads to a better understanding of the processes that generate biodiversity.  In addition to these fundamental research questions, some aspects of our work have implications for conservation.  For instance, we used our measurements of color and previously published genetic data to make a strong argument for raising the Fuertes’s oriole (Icterus spurius fuertesi) from a subspecies of Orchard oriole to full species (I. fuertesi).  Since the geographical range of the Fuertes’s oriole is very limited, this move may provide a greater impetus for evaluating the conservation status of this group of birds.