English: Head of a threespine stickleback (Gasterosteus aculeatus) stained with the fluorescent dye DASPEI to reveal clusters of sensory hair cells called neuromasts that make up the lateral line sensory system. Threespine sticklebacks from marine and freshwater habitats have evolved differences in neuromast number and patterning across the body. The genetic architecture underlying the evolution of the lateral line system in these fish was investigated with genetic linkage mapping. Image courtesy of Abigail Wark.