ABSTRACT
Studies on genetic relationships of sea urchins in the genus Echinometra from the Indo-Pacific support the idea that four morphological types of E. mathaei are reproductively isolated from each other, and are separate species. These are the most closely related echinoid species for which genetic relationships have been measured. In at least one pair of these closely related urchins, strong reproductive isolation has evolved by reciprocal gamete incompatibility. Observations of gamete interactions suggest that the sea urchin sperm protein bindin is involved in this incompatibility. The evolution of gamete surface recognition proteins like bindin is likely to be important in maintaining reproductive isolation between populations of high-dispersal marine organisms.
