The echinoids Pseudoboletia maculata and P. indiana have overlapping ranges on the east coast of Australia. We estimated their time since divergence using mitochondrial DNA sequences, conducted controlled crosses between the species, studied the molecular evolution of the sperm protein bindin, examined their distribution in the field, and determined their annual spawning period. We found that though the two species diverged several million years ago, they cross-fertilize easily. Easy cross-fertilization correlates with minimal divergence in the bindin gene between the species. Individuals of the two species can be found within a meter of one another in the field and their spawning periods overlap throughout the year.
