Evolutionary history is generally studied by comparing species that shared a common ancestor thousands to millions of generations ago, but evolutionary processes are studied over relatively few generations. Hence, conclusions from studies on processes must be extrapolated through time and among species to interpret history. This project makes use of a unique study system involving the stickleback fish, in order to directly integrate evolutionary history and process. A sea-run stickleback population colonized an Alaskan lake in the 1980's and subsequently underwent rapid evolution. When first sampled in 1990, it closely resembled sea-run sticklebacks in body shape and size, the shape of the gill cover, armor plates, feeding structures, and the genes that control armor and regulate the salt concentration in body fluids. Annual sampling revealed progressive evolutionary change of every trait towards those of older lake populations, from which it is now almost indistinguishable. This project will continue the long term study of this lake population, and expand the work to study the evolution of fish immunity to disease agents that are prevalent in freshwater lakes. This project also initiates new research on additional sea-run stickleback populations that are at the earliest stages of colonization of freshwater lakes. Evolution of these sea-run populations simulates the history by which countless freshwater populations have evolved since the last ice age.
This study has broader relevance to predicting the adaptability of fish species in the face of global climate change and intensive fishing pressure on commercial species. It will also provide valuable information on the evolution of immune response to emerging infectious disease. The project gives undergraduate students hands-on research experience. Data from this project will be posted annually on a publically accessible website, and the time series of fish collections documenting rapid evolution will be deposited in the Yale Peabody Museum for further study.
Evolution has traditionally been viewed as a slow process that takes millennia, if not millions of years, and cannot be studied by direct observation in the present. In recent years, however, it has become evident that "contemporary evolution" can produce dramatic, heritable changes within a few generations in response to environmental change. Contemporary evolution can provide novel insights into evolutionary mechanisms and compelling validation of the reality of evolution for students and the public at large. Moreover, it has practical implications for public health, pest control, management of exploited wild populations (e.g., commercial fisheries), and adaptability of wild populations to global climate change. This NSF Long Term Research in Environmental Biology (LTREB) grant supported collection between 2009 and 2013 of annual samples from a population of Threespine Stickleback fish (Gasterosteus aculeatus) that had colonized Loberg Lake, Alaska between 1983 and 1988 from the ocean. The marine and freshwater environments of Threespine Stickleback differ sharply for water chemistry, predation regime, prey availability, and other properties, and marine and resident freshwater Threespine Stickleback populations differ conspicuously for many heritable anatomical, physiological, and behavioral traits. Thus, the new Loberg Lake population might be expected to experience contemporary evolution. Anatomical samples from the Loberg Lake Threespine Stickleback population in the 1990’s using samples made mostly with personal funds plus a small LTREB grant showed that many traits evolved from their typical condition in marine stickleback toward those of freshwater ones. The present small LTREB grant provided partial support to sample the population from 2009 to 2013, revealing continuation of earlier trends. The most conspicuous trend was for the number of lateral armor plates, which averaged about 33 per side in the earliest sample (identical to marine stickleback) but only about seven (like many freshwater stickleback) in recent years. Body size and shape, the shape of the gill cover (operculum), and number of gill rakers (bones that strain food particles in the throat) all have evolved toward their typical conditions in freshwater stickleback. In addition, the relative abundance of the freshwater version (allele) of a gene for salt transport increased from low to intermediate values, and freshwater alleles for the gene that most strongly influences the number of lateral armor plates increased in parallel with the relative abundance of variants with reduced plate number. Within 24 years (about 12 generations), the Loberg Lake Threespine Stickleback population has evolved from being indistinguishable from the marine form to resembling other lake populations for many conspicuous traits. Indeed, the earliest and latest samples from the Loberg Lake Threespine Stickleback are as different from each other as are other pairs of populations that are considered to be separate species. During the period of this LTREB grant, nearly 20 technical publications were produced, providing insights into evolutionary mechanisms and also attracting the interest of molecular geneticists, genomicists, and parasitologists. The Loberg Lake evolutionary time series was discussed in Zimmer and Emilen’s textbook, Evolution: Making Sense of Life, and this coverage will be expanded in the second edition. It has also been discussed in several popular magazine articles in the US, France, and Denmark. It is a prime example in the "Learn.Genetics" website, which is hosted by the Genetic Science Learning Center, University of Utah and designed for high school students. Thus, this example of contemporary evolution is well on its way to becoming one of the classic cases of contemporary evolution in response to environmental change. Regrettably, finding it embarrassing, creationist websites have distorted and misinterpreted this compelling example of dramatic evolution. Despite the proven theoretical and educational value of this long-term study and the public interest it has attracted, the National Science Foundation has declined to support its continuation.
