What's the secret of the mermaids purse?
It starts with an egg. But before I talk about the egg, we first need to go back to the evolutionary relationships of these skates. The ancestral relationships for (sharks, skates and rays) have been sorted out slowly since they were thrown into one big group by taxonomists nearly 250 years ago. But there hasn’t been a detailed molecular study of for a group of hard nose skates in the family Rajidae. In this study we independently evaluated relationships of the egg-laying Rajidae species based on their genetic sequences. Unlike most skate egg capsules, the capsules of the big skate (Beringraja binoculata) and the mottled skate (Beringraja pulchra) contain multiple embryos per egg capsule. The results from this study, show that these two species are closest in relatives and that they share a common ancestor, suggesting that this unusual reproductive strategy arose once during the evolutionary history of the Rajidae family. Since we had access to living egg capsules we decided to design an experiment to track survivorship of big skate egg capsules the Aquarium of the Bay in San Francisco, CA. The egg capsules contain anywhere from two to eight embryos, but the most frequent number of embryos and highest survival rates was two, so twins in these skates are the most frequent strategy may also the most fit. Click on the link below if you're interested in reading the paper.