INFLUENCE OF EGG SIZE ON EMBRYOS AND LARVAE OF FUNDULUS-HETEROCLITUS (L)

Egg size for Fundulus heteroclitus (L.) populations is concordant with the distribution of the two F. heteroclitus subspecies, i.e. F. h. heteroclitus eggs are considerably larger than F. h. macrolepidotus eggs. The influence of egg size on survival of embryos during incubation and survival and growth of newly‐hatched larvae was estimated for four populations representing both subspecies along the Atlantic coast of the United States and in Delaware Bay. Survival of embryos was determined for incubation periods of 14, 21 and 28 days. Greatest differences in survival were detected following the longest incubation period where less than 50 per cent of the smaller F. h. macrolepidotus eggs survived while little or no mortality was detected among the larger F. h. heteroclitus eggs. Influence of egg size on larval survival was also greatest among those larvae hatched after 28 days where F. h. macrolepidotus larvae survived without food, for an average of 6 days, while F. h. heteroclitus larvae survived 11–12 days. F. h. heteroclitus larvae were significantly larger at hatching than F. h. macrolepidotus larvae. Larval growth rates were the same (0.4 mm day−1) in both subspecies. As a result, size differences at hatching were still maintained after 42 days of growth. The differences in egg size along with other morphological and reproductive characteristics of F. heteroclitus populations probably represent genetically based adaptations to environmental conditions, of which the length of the spawning season is one of the major components stimulating the coevolution of these traits. Copyright © 1992, Wiley Blackwell. All rights reserved