Stickleback Cousins (IMAGE) University of Texas at Austin Caption Two male sticklebacks of the same age -- one from a stream (top) and one from a lake (bottom) -- are each highly adapted to their own local environment. According to Bolnick, apart from a dramatic difference in size, the fish also differ in immune traits, body shape, armor to defend against predators, and "basically anything we can think to measure." Credit Daniel Bolnick/U. of Texas at Austin Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.