Genetic relationships between brooding and brooded Actinia tenebrosa

Abstract

SEA anemones of the genus Actinia seem to be dioecious and reproduce sexually, yet males, females, and individuals without gonads brood juveniles for much of the year^1–3. How this occurs is still not understood and knowledge on the subject is scant. Gillespie⁴ considered that eggs develop to ciliated blastulae and then directly into “a cylindrical form … which develops tentacular buds”. Chia and Rostron³ found no pre-planula larval stages in the coelen-terons of hundreds of specimens they examined and postulated that most embryos must leave the mother as morulae or blastulae and later resettle in the coelenteric cavities of other adult A. equina where they metamorphose to post-Edwardsia juveniles. According to this hypothesis, juveniles contained in an adult should be derived from a number of different parents and would be expected to show a range of phenotypes characteristic of the population rather than the brooding adult. Cain⁵ however found that in phenotypically varied populations of A. equina young anemones invariably had the same colour as the adult from which they were released. He considered it likely that A. equina is a protandric hermaphrodite which mainly self-fertilises and retains larvae within the parent, even though Carlgren² thought this “hardly probable”.