Life-history evolution in a Daphnia ambigua population during community assembly

Population and community dynamics influence, and are influenced by, among-individual variation in traits. However, studies examining rapid evolution during community assembly remain rare. We examined how four life-history traits in Daphnia ambigua have evolved during community assembly in a recently created lake. Microfossils, preserved in sediments, suggest that D. ambigua was one of the original zooplankton colonizers, followed by Daphnia dentifera and Daphnia pulicaria. We used water column collections and dormant eggs from sediment cores to isolate 45 isofemale lines into laboratory culture, representing four time periods of lake colonization. We measured size at birth, size and time to maturity, clutch size, and juvenile growth rate and found significant differences among time periods in two of the traits, size at maturity and first clutch size. Although isofemale lines from the founding and recent population are known to differ in their competitive ability, we found no evidence that these temporal populations differ in measured life-history traits, sensitivity to resources or population growth rate. Nevertheless, our experimental results note rapid and nondirectional evolution of two life-history traits, closely tied to fitness, during the assembly of this community.