The Life Cycle and Fitness of Gregarine (Apicomplexa)Parasites

Theoretical demographic models with an accompanying experimental program provide an important framework to study the life history of organisms. In this paper we seek to understand the fitness characteristics of gregarine parasites and how they are shaped by their own life cycle stages inside and outside an insect host. The population model is a continuous time dynamics for the parasite stages, and we examine stability and bifurcation of its equilibria for different production rates. Analysis leads to a key fitness parameter whose value determines the existence of a coexistent state. The model shows good cause for the establishment and long time permanence of this common parasite. The model is parameterized by extensive data gathered at Cedar Point Biological Station in western Nebraska, and numerical calculations based on those parameters illustrate the dynamics.