Fitness Consequences of Maternal Effects in Streblospio benedicti (Annelida: Polychaeta)

SYNOPSIS. The degree to which a female partitions resourcesbetween fecundity and per offspring investment is a centralquestion in life-history theory. Maternal effects may influencethe nature of this tradeoff through their effect on per offspringinvestment and subsequent offspring fitness. The purpose ofthis study was to determine the effect of female age and sizeon brood size (number of offspring), per offspring investment,and fitness in the polychaete Streblospio benedicti. Early stageembryos were collected from brooding females of known age andsize over a period of 100 days; these embryos were counted andanalyzed for their C and N content. Female size had a positiveeffect on brood size; larger females produced larger broods.However, brood size decreased with female age (females did notincrease in size after reaching sexual maturity). Brood sizedeclined 20–46% between 60 and 160 days of age. Duringthis same age period per offspring investment, measured in termsof C and N, increased by 25%. Offspring survivorship and sizeat two weeks post-release from the female were used as measuresof offspring fitness. Offspring survivorship increased 28% between60 and 160 days of age. Increased growth in offspring from olderfemales resulted in a 23% increase in offspring size at twoweeks. Including the maternal age effect in two population modelsfor S. benedicti increased population growth rate (). Populationgrowth was increased to a greater degree when the maternal effectwas modeled by enhancing offspring survival compared to whenfecundity was increased by the same proportional amount. Thissuggests that the maternal effect may be adaptive, particularlywhen conditions for offspring survival and growth are poor.