Ten to fifteen thousand years ago, all stickleback fish spent most of their lives in the ocean, venturing into fresh water only to spawn. But when the end of the last Ice Age stranded some sticklebacks in freshwater rivers and lakes, they adapted to their new environments. This has resulted in an amazing diversity of morphologies and behaviors among sticklebacks that have arisen in a very short period of time. The diverse skeletal structures, metabolisms, lifespans and complex behaviors of sticklebacks have been extensively characterized over the last century. Furthermore, large numbers of fish from the different populations and species of sticklebacks can be easily interbred in the laboratory, allowing the pinpointing of genes important for adaptive traits. These studies will be greatly accelerated by the sequencing of the stickleback genome.
The Broad Institute has sequenced a freshwater threespine stickleback from Bear Paw Lake (Gasterosteus aculeatus) to 9x coverage, and has also provided 1x Illumina coverage of sticklebacks from ten marine populations and from ten additional freshwater populations. The additional freshwater sticklebacks have been chosen from populations that have evolved similar adaptive traits to aid in the identification of the loci responsible for those traits. In addition, these sequences will contribute to our understanding of evolution itself, by helping us answer questions such as: What kinds of genes underly specific morphological differences? Does evolution use the same genes or different genes when evolving the same traits independently? And what kinds of mutations lead to new traits? For the next stage of the stickleback genome project, the Broad Institute will be performing low coverage Illumina sequencing of 150 more sticklebacks. Illumina-based RNA-seq to improve the stickleback annotation is currently underway.