The Costs of Reproduction in Brine Shrimp

Abstract

Brine shrimp were subjected to one of four reproductive regimes: complete absence of mating, mating postponed for 20 d or 40 d past sexual maturity, or continuous breeding upon sexual maturity (controls). Each of the four reproductive regimes was further subdivided into low and high feeding groups (1:10 feeding ratio). Under low food, female lifespan was negatively correlated with the length of the reproductive period. However, no such relationship was found among the four high food groups; no intrasex differences were found in survival curves or mean length of lifespan. Fertile females in the delayed reproduction groups gave birth to approximately the same total number of offspring as controls, not by lengthening lifespan but by producing larger broods, with fewer days between broods. The results indicate that although some reproductive costs are unavoidable, nutritional resources play a critical role in determining how extensively reproduction will affect lifespan.