LTREB: Long-term Research in Environmental Biology: Microevolution in the Fast Lane

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0211391BellLTREBIntegrating pattern and process has always been a crucial but frustrating objective forevolutionary biology. Analysis of rapid evolution in extant populations provides a unique meansto integrate evolutionary pattern and process. To that end, annual samples from the Loberg Lake,Alaska population of threespine stickleback fish, Gasterosteus aculeatus, will be used to studyrapid evolution. This population was founded by a natural invasion of anadromous (i.e., sea run)stickleback after the native stickleback population was exterminated in 1982. It has beensampled annually since 1990, and lateral plate phenotypes have been scored in all samples.Lateral plates are modified scales that form a single row of armor on each side of the body.Lateral plate morphs (i.e., complete, partial, low) and low morph-plate number are heritable,subject to strong natural selection, and exhibit extensive adaptive geographic variation in westernNorth America. This study will document maximum evolutionary rates, the trajectory of evolutionarychange, and patterns of transient polymorphism. These patterns can be integrated with knownevolutionary mechanisms. The increasing frequency of low morphs and their declining meanplate number can be explained by natural selection in many similar populations. Based on the plate phenotypes of the original Loberg Lake stickleback population before it was exterminated and comparison to other lake stickleback populations, lateral platedivergence should continue in the Loberg Lake population until the low morph is fixed and meanplate number declines to about five per side. This LTREB award will support continued annual sampling of the Loberg Lake population.This study will provide an unusually detailed account of rapid phenotypic evolution with implications for divergence during speciation and post-glacial adaptive radiation of threespine stickleback. It will complement ongoing research in paleontology, functional morphology, natural selection, genetics, phylogeogaphy, and developmental evolutionary biology of G. aculeatus. It will prolong a long series of annual samples in which rapid evolution of plates and other traits and trait correlations can be studied.