A limnetic male stickleback (top) would rather mate with a female of his own species than with the benthic female (bottom).
Courtesy of Ernie Cooper
Zoologist Jennifer Gow had a hunch. So she booted up her laptop, launched Google Earth, and zoomed in on Nelson Island, a small, largely unpopulated island along the British Columbia coastline. Gow, a postdoc at the University of British Columbia, had studied the handful of lakes where pairs of closely related fish species called threespine sticklebacks are found, and thought this region might have more. From the satellite images, one isolated, small lake on the island stood out. Little Quarry Lake sat at the right elevation above sea level. Its size, range and lack of navigable water connections matched other stickleback-containing lakes, too.
In June 2007, Gow, together with local freshwater ecologist Michael Jackson and professional guide John Dafoe, visited Nelson Island, where,...