Reproduction and genetic variation in the deposit-feeding sea star Ctenodiscus crispatus

Abstract

The gonad index in the deposit-feeding asteroid Ctenodiscus crispatus (Retzius) in the Gulf of Maine (USA) is seasonally less variable than in any other sea star, ranging from 2.99 to 4.98% of dry body weight in females and from 2.28 to 3.42% in males, and varies in concert with, rather than reciprocal to, the pyloric caecum index. Biochemical composition and, hence, caloric content, of the gonads also show little seasonal change, suggesting that reproduction is aseasonal and continuous in this population. Oocyte development is asynchronous, all females having a full size range of oocytes (from less than 30 μm to greater than 400 μm diameter) throughout the year. Seasonally determined size-frequency distributions of juveniles, oocyte cytology and size-frequency distributions, responsiveness of adult females to 1-methyladenine, and oxygen uptake rates indicate that variations in reproductive intensity are superimposed on continuous reproduction, and seem related to changes in phytoplankton production rather than to temperature. The rich neutral lipid content (ca. 50% of total lipid) and large egg size (>400 μm) in the ovaries suggest that development is direct. The population is extremely variable genetically, polymorphism among 13 enzyme-coding genes being 77% and average heterozygosity being 0.174. The reproductive pattern and genetic variation in the eurybathic C. crispatus are similar to those in deep-sea echinoderms. This may be related to the constancy of the population's detrital food source, to small-scale heterogeneity of its physical environment, and to low individual vagility.