DISSERTATION RESEARCH: Determining anucleated sperm function in Lepidoptera

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The function of sperm cells is traditionally thought to be a way for males to transfer DNA to eggs and create offspring. Sperm cells that do not carry DNA cannot fertilize an egg, thus the existence of such sperm cells in butterflies and moths is puzzling. Almost all of these insects make two types of sperm: both traditional, DNA-bearing sperm, and a second type that lacks DNA. In all of these cases, males make far more of this DNA-lacking sperm than traditional sperm. The sheer abundance of this sperm type implies it plays some yet-unknown functional role in reproduction. This proposal aims to uncover the evolutionary significance of these DNA-lacking sperm cells. The research will also aid in the development of technologies that will allow scientists to maintain important genetically modified lineages in a way that is both cheaper and less vulnerable to failure than traditional rearing methods. Such protocols could even be extended to threatened species to create a gene bank. Outreach to the public will occur via summer science workshops.Production of multiple sperm types by a single male has independently arisen in many animal lineages. In all well-studied cases, evidence suggests that only one type of sperm retains its ability to fertilize eggs but the function of these non-fertilizing sperm remains unclear. Nowhere is this more apparent than in butterflies and moths; males of this order produce a secondary sperm type that lacks nuclear DNA. These anucleated cells represent a significant investment for a male, outnumbering their nucleated sperm by 20-to-1, but cannot possibly fertilize eggs to directly increase male fitness. Several hypotheses have been proposed since the discovery of anucleated sperm to explain the existence of anucleated sperm, but to-date no rigorous tests have been undertaken. This project will develop and refine artificial insemination protocols in two lepidopteran species that differ in mating strategy in order to thoroughly test the function of anucleated sperm in different selective backgrounds with a common framework.