The Biological Bulletin, Vol 185, Issue 3 373-387, Copyright © 1993 by Marine Biological Laboratory

CELL BIOLOGY

Reproduction of Stylochus ellipticus (Platyhelminthes: Polycladida) in Response to Temperature, Food, and Presence or Absence of a Partner

M. M. Chintala and V. S. Kennedy
University of Maryland System, Horn Point Environmental Laboratory, P.O. Box 775, Cambridge, Maryland 21613

The common polyclad turbellarian Stylochus ellipticus is an important and abundant predator of young oysters, Crassostrea virginica, in Chesapeake Bay. Laboratory experiments revealed that higher temperature and starvation negatively affected flatworm size. Egg production, adjusted for flatworm area, was not significantly affected by flatworm size, nor by increasing number of egg batches produced. In addition, there was no significant statistical effect of higher temperature and starvation on egg production, although there were some instances of diminished egg production under these conditions. Flatworms did react to higher temperature and starvation by significantly decreasing the number of days that elapsed before egg laying began. Overall, more larvae would be produced at 21{deg}C than at 30{deg}C, by fed flatworms than starved flatworms, and by solitary flatworms than paired flatworms. When isolated animals were alternately fed and starved for five-week periods over a 20-week experimental period at 21{deg}C, 56% of individuals continued to deposit eggs, although the number of eggs laid and embryo hatching success declined with time. Stylochus ellipticus individuals can maintain a relatively high reproductive effort despite reduction in available food. Thus, this species would appear to be a "capital" breeder, relying on stored energy to produce eggs.