Several groups of insects have independently evolved a parasitic lifestyle. In each case, the parasitoids have lost the ability to synthesize lipids de novo. They presumably obtain enough lipids from their host, which emancipates them from the need for autonomous lipogenic ability. The mechanistic basis for the loss of lipogenesis in these insects is unknown. Recent work in our group has shown that all known genes in the lipogenesis pathway are intact and expressed in the parasitoid wasp Nasonia vitripennis. Loss of lipogenesis is thus not caused by gene loss. In this project, we will explore the possibility that loss of lipogenesis is caused by epigenetic effects.
Remarkably, lipogenic ability has re-evolved several times within the parasitoid hymenoptera. These instances offer unique opportunities for understanding the evolutionary process of loss of lipogenesis. One such case is the parasitoid wasp Leptopilina heterotoma. Populations from the Netherlands cannot synthesize lipids, whereas populations from Rennes and Lyon can. Since we know that this species can lose lipogenesis, we will attempt to induce this process through experimental evolution.
Methods and Techniques
We will collect L. heterotoma in the field in the Netherlands and France. Each of these populations will be tested for lipogenic ability using ether extraction. The genome-wide methylation patterns of four populations (two with lipogenesis and two without) will be determined using bisulfite conversion followed by next-generation sequencing.
To test if we can induce the loss of lipogenesis, we will culture L. heterotoma from two southern populations (Rennes and Lyon, France) on Sir2 mutants of Drosophila melanogaster (available from the Bloomington Stock Center), which have 20% higher levels of body fat compared to wild type larvae. Each generation, we will provide females from manipulation lines and control lines with hosts for oviposition. Subsequently, lipid content of females from both lines will be measured directly after emergence and after one week of honey feeding to assess lipogenic ability. In addition, development time, egg load, and egg size of emerging females will be measured.
This project will combine fieldwork, insect experimentation and molecular lab techniques.