NSF Award
1557678
Evolution allows organisms to adapt to their environments over many generations via genetic mutation and natural selection. In addition, some organisms can adapt to changes in their environments within just one generation without any change in their genes. Such "developmental plasticity" occurs when the environment influences how organisms develop, and allows organisms to adapt to environmental challenges more rapidly than is possible through evolutionary change. Plasticity itself has evolved through the longer process of mutation and selection, but little is known about this evolution. This project focuses on aphids, small insects that reproduce clonally and give live birth during the summer months. The summer form, however, cannot survive a cold winter. In the fall, when mother aphids sense that days are getting shorter, they chemically signal their embryonic offspring to develop into a form that can lay eggs that can survive the cold temperatures of winter and hatch in the spring. The participants in this project will investigate the molecular changes that occur in developing aphid embryos when they switch from the summer to the fall form. Participants will also investigate aphids from regions with mild winters that no longer produce the fall form and do not lay eggs, to try to understand how the response to shorter days has been lost over the course of recent evolution. The work will take place primarily at Bryn Mawr College, a women's undergraduate institution, and thus also aims to engage young women in the design and execution of hypothesis-driven experimentation and data analysis within the discipline of evolutionary developmental biology.<br/><br/>The aphid reproductive polyphenism is poised to become an important example of genetic accommodation in natural populations, one for which a good deal is known about the developmental and endocrine basis of the plasticity. Such progress, however, will require an accurate understanding of the fundamentals of the system. Although several lines of evidence suggest that juvenile hormone is involved in the photoperiod response, the precise role this hormone plays in mediating the effect is not clear. A combined approach of hormone manipulation, measurements of juvenile hormone titer, and gene expression during early specification and subsequent differentiation into the summer and fall forms will discriminate among competing hypotheses for the role that juvenile hormone plays in the process. If successful, the experiments could demonstrate an embryonic role for juvenile hormone in the specification of reproductive fate and identify other early markers of this differentiation, providing candidates and opening new doors toward understanding the switch and how it evolves to accommodate novel environments.
