Evolution of embryonic germ line development in insects

Abstract

During development, animals must specify and maintain the germ line, a dedicated lineage of cells uniquely capable of giving rise to the next generation of animals. Mechanisms of germ line development vary widely even within closely related animal taxa such as insects (Extavour and Akam, 2003). For instance, in insect embryos, germ cells may be specified as early as the syncytial blastoderm stage, as in the fruit fly Drosophila melanogaster (Huettner, 1923), or much later during the germ band stage, as in the cricket Gryllus bimaculatus (Ewen-Campen et al., 2013a). In this dissertation, I explore the evolution of diverse mechanisms of germ line development across insects. First, in Chapter 1, I review the literature on germ cell specification in panarthropods and discuss how the timing and mechanism of this process has shifted in evolution. Next, I take advantage of functional genetic tools in emerging model insects to study two different aspects of germ line development. In Chapter 2, I investigate the role of germ cell-less in germ line development in two hemimetabolous insects, finding that the germ line function of this gene has changed through evolution. In Chapter 3, I examine somatic gonad development in the milkweed bug Oncopeltus fasciatus and determine that its invariant gamete tube number arises from segmental specification of somatic gonad precursors. Overall, this work highlights the potential of developmental genetics in emerging model insects to address questions of insect development.