BASOLO, A.L.; University of Nebraska-Lincoln: The Effect of Predation on the Evolution of Genetically Linked Life History Traits

Adult size is often negatively correlated with the age at which an individual matures, and there are both benefits and costs associated with maturing earlier at a smaller size. Benefits to earlier maturation include a higher probability of surviving to maturation and a shorter generation time. However, if predation risk is greater for smaller individuals, delayed maturation may be favored. Few studies have examined how predation affects genetic variation in animal size, largely because the genetic basis of age and size of maturation is not well characterized for many animals. An exception is the southern platyfish, Xiphophorus maculatus, a livebearer in which allelic variation at the pituitary locus (P-locus) has a major effect on age and size at sexual maturation. In the field, a correlational study I conducted showed that adult platyfish from populations without piscivorous fish are smaller than platyfish from populations with piscivorous fish. To experimentally test the effect of predation on age and size at maturation, I have established eight populations in the laboratory with known P-allele frequencies. Four replicate populations have a predatory cichlid and four replicate populations do not. I am tracking changes in P-allele frequencies over time using genetically linked color markers. If larger size provides an advantage by lowering predation risk, the allele for later maturation is expected to increase in the predation replicates relative to the replicates without predators.