Offspring size and performance in variable environments: Field studies on a marine snail

This study links offspring size and energetic content to offspring performa nce (measured as growth and survivorship) in the intertidal gastropod Nucel la ostrina and examines the effect of hatching size on performance at diffe rent times of year and in contrasting environments. The relationships betwe en individual hatchling size and organic content were compared both within and among clutches of N. ostrina. Hatchling size was positively, significan tly, and predictively correlated with hatchling organic content both within and among clutches, demonstrating that hatching size could be reliably use d as an indicator of maternal investment. The slope of the relationship bet ween hatchling size and organic content varied between clutches, suggesting intrapopulation variation in embryonic growth geometry. In field outplants , hatching size always had a positive and significant effect on growth, and small hatchlings took approximately one month to reach the initial size of their larger siblings. More large hatchlings than small hatchlings were re covered in every experimental outplant. The: effect of hatching size on rec overy was not significant in short (9 d) outplants, but recovery of large h atchlings was significantly greater than recovery of small hatchlings in tw o out of three long-term (36 or 54 d) outplants. Overall recovery was lower in the summer, the long-term outplant in which size did not significantly affect recovery. In experiments testing the relationship between hatching s ize and survivorship in two environments that differed in degree of sun exp osure, size significantly and positively affected recovery in the more shad ed habitat (with higher overall recovery) but not in the sun-exposed enviro nment. Thus, larger hatching size in N. ostrina results in (1) increased ha tchling growth, (2) considerably shortened time to maturity, and (3) higher survivorship. However, the advantage of large hatching size was decreased under more severe environmental conditions, those which resulted in higher overall hatchling mortality. Contrary to predictions, poor environmental co nditions may not be more likely to select for large off spring size in inte rtidal habitats: during periods of high heat stress, mortality may be large ly random with respect to size.