By studying an evolutionarily recent transition from egg-laying to live-bearing in a marine snail, collaborative research by three global institutions has shed new light on the genetic changes that allow organisms to make the switch. The egg did come first. Egg-laying arose deep in evolutionary time, long before animals even made their way onto land. The seaside marine snail Littorina saxatilis is the most misidentified creature in the world. Although live-bearing is the only trait that distinguishes L. saxatilis from its egg-laying relatives, L. saxatilis did not seem to form a single evolutionary group. “We were able to identify 50 genomic regions that together seem to determine whether individuals lay eggs or give birth to live young,” says Sean Stankowski from the Institute of Science and Technology Austria (ISTA). “We don’t know exactly what each region does, but we were able to link many of them to reproductive differences by comparing patterns of gene expression in egg-laying and live-bearing snails.” Overall, the results suggest that live-bearing evolved gradually through the accumulation of many mutations that arose over the last 100,000 years.
