Biologists are just beginning to understand the genetic basis of variable aspects of or-ganisms such as size, shape and color, to name a few. However, most traits are com-plex, their development directed by many genes whose effects are influenced by environmental conditions. These combined effects on trait variation must be mediated through the identity and behavior of cells such that, for example, some cells proliferate more to make larger cartilages, or excrete additional matrix to make stronger bones. However, little is presently known about the precise mechanisms of cellular integration, and filling this gap in knowledge is a fundamental problem in biology and is the primary focus of this project. Natural variation in threespine stickleback fish provides an excel-lent opportunity to address this question. The goal of this research is to understand how cells integrate genetic and environmental information and lead to variation in complex head and jaw traits among populations of stickleback. These structures vary tremen-dously among individuals, populations and species. Despite this diversity, all vertebrates share conserved genetic interactions for the development of head and jaw struc-tures. Thus, research on these traits is useful for understanding the situation in stickle-backs, and is also highly informative about the proper development of similar structures in other vertebrates such as humans. These conditions are the product of many genes and their interactions with the envi-ronment, and lead to variations in cellular identities or behaviors (i.e. uncontrolled cell growth in cancer). This research will provide a much better understanding of the genetic and cellular basis of complex traits, be they characters important for stickleback, or the most common types of human diseases. In addition, Alaskan stickleback populations are studied in collaboration with laboratories at the University of Alaska Anchorage, which has a large Alaska Native student population, and the unique opportunity exists to include individuals in this underrepresented group into research and educational activi-ties. Furthermore, an educational website is maintained that uses stickleback to provide educators and researchers around the world with knowledge and skills necessary to learn about and perform research with stickleback.
It is very well established that Darwinian selection overwhelmingly influences evolutionary change. The raw material for this change is genetic mutation. Yet selection acts on phenotype – the characteristics of the organism, not directly on its genotype – the set of genetic mutations within the organism that are available to produce phenotypic variation. For complex multicellular organisms the process of development is situated between genotype and eventual adult phenotype. Beginning more than twenty years ago Steven Jay Gould and others proposed that the way that the developmental process works might bias or constrain evolutionary change. Such constraint could impact, either negatively or positively, how the organism might respond evolutionarily to demands of a changing environment. For example, why have humans not evolved an extra set of appendages – wings in the style of an angel? Perhaps, as has been supposed by some authors, adding a pair of wings to the body plan is just too difficult a task for development of humans to accomplish. By this supposition, development would be negatively constraining human evolution. In this project we have examined the evolution and development of individual bones of the skulls of fishes, notably threespine stickleback and, more recently, salmonids. Stickleback provide a wonderful model for evolution, because ocean-dwelling stickleback repeatedly and independently take up residence in freshwater and evolve new morphologies in the new habitats. We reported last year in the journal Evolution that evolutionary divergence of the skull in freshwater occurs "in parallel", the nature of the change in freshwater populations is similar whether we observe populations from Alaska or Iceland (among others). Furthermore, carrying out a genetic study with Alaskan populations, we found no evidence for constraint: rather, our data suggested that Darwinian selection is the critical influence on the change in skull bone morphology. We discovered that the way a skull bone evolves a new ‘freshwater’ shape is by becoming ‘juvenilized’; i.e. a bone in the skull of an adult freshwater fish has shape characteristics of a juvenile ancestral oceanic fish. This finding presented an interesting conundrum because Gould and others have argued that juvenilization is a form of negative constraint: In Gould’s argument the freshwater descendent cannot escape from the developmental design features of the oceanic ancestor – it simply shortens the ancestral developmental process. However, as we reported in our paper in the journal Evolution and Development, the evolutionary change is not so simple. Modular design of the skull provides for some features of the evolving morphology to be juvenilized, while other features are novel. We conclude that with modularity, development does indeed influence adaptive change, but in a positive way: Modular design facilitates the organism’s ability to respond adaptively to a new environment, rather than negatively constraining useful phenotypic change. This conclusion is reinforced in our new paper now in press, in which we examine neighboring bones that function together in feeding and gill pumping In newer work we have begun to examine morphology of skull bones in salmon and trout of the Pacific Northwest. We have discovered change in the jaw structures that suggest feeding mechanics have provided a major influence on evolution within this group. Although there are a number of laboratories currently studying salmonid genomics and genetics, there is very little understanding and no quantitative studies on skeletal morphology. An important broader impact of our salmonid work is that it has the potential to inform salmonid conservation efforts as well as fish hatchery management programs. We have welcomed high school and undergraduate students into our laboratory to participate in these projects. Two of these students are co-authors of our paper now in press in The Biological Journal of the Linnean Society. Doing delicate dissections of the tiny skulls of young developing fish has appeal for many students training in biology, and the quantitative analyses of the shapes and sizes of the individual bones lets them explore multivariate analyses that are usually outside of the scope of students at their levels of training. The salmond projects, because of the local sport and commercial fishery, as well as current conservation issues reported nearly daily in the news, have particular appeal for students in our region of the country.
