When one eye is better than two

摘要

Evolution has generated a bewildering variety of life forms on this planet. Curiously, it has also occasionally produced animals from entirely different families that seem to have converged on a similar design plan — apparently as a result of similar lifestyles and environmental pressures. One instance of this, reported by Pettigrew et al. and Fritsches and Marshall in Current Biology, is vision in the chameleon and in the sandlance Limnychthyes fasciatus, a small teleost fish. The chameleon catches insects with a quick flick of its long tongue. The sandlance lies concealed in underwater sand beds with only its eyes protruding above the surface, then lunges at tiny, unsuspecting copepods (aquatic crustaceans) that stray too near. Pettigrew et al. and Fritsches and Marshall now show that there are extraordinary parallels between these two behaviours, and between the visual systems that mediate them.