Strategies of reproduction in the zooplankton Daphnia pulex: evolutionary insight from experimental design

Abstract

The research herein concerns reproduction in the zooplankton Daphnia pulex. Chapter One introduces the discipline of sexuality research and the model organism D. pulex. The first of my two investigations focused on the possibility that the common intracellular parasite Wolbachia is responsible for reproductive life-history traits among populations of D. pulex from the Great Lakes watershed of North America (Chapter 2). No evidence of any such infection was found among populations exhibiting a variety of Wolbachia-like phenotypes. My second investigation explored the effects of crowding and maternal age upon reproduction among both facultatively parthenogenetic (occasionally sexual) and obligately parthenogenetic (strictly asexual) lines of D. pulex (Chapter 3). Crowding was found to increase resting egg production and reduce neonate offspring production among other effects. Inter-genotypic differences were often significant, as were genotypic responses to crowding. Chapter Four suggests improvements to methods of research and effluent testing using Daphnia, and proposes a large-scale life-history investigation.