In shallow water, it appears that a long, spiny pelvic fin would be a disadvantage because it frequently contacts the sediment at the bottom of the pond and allows parasitic insects in the sediment to...In shallow water, it appears that a long, spiny pelvic fin would be a disadvantage because it frequently contacts the sediment at the bottom of the pond and allows parasitic insects in the sediment to invade the stickleback. Embryos from the shallow-water population expressed Pitx in the same groups of cells as the other population, with an important exception: Pitx was not expressed in the pelvic fin primordium in the shallow-water population.
