May 2016 Features

The Evolution of Plasticity

Aphids

Everyone knows about natural selection and the long arc of evolutionary time. Less well known is the fact that many organisms can adapt to changes in their environments within one or two generations—without any genetic change.

Called “plasticity,” this phenomenon occurs when the environment influences how individual organisms develop, with the result that adults are better suited to their environments.

“Although developmental plasticity, when it occurs, is not itself an example of evolution, the ability to respond adaptively to the environment has evolved through the longer process of mutation and selection,” says Bryn Mawr Associate Professor of Biology Greg Davis. “While a fair amount is known about the mechanisms of developmental plasticity, we don’t yet know a lot about how it evolves.”

Davis and his collaborators, Bryn Mawr Assistant Professor of Biology Josh Shapiro and Florida International University Professor of Biology Fernando Noriega, have received a $311,000 grant from the National Science Foundation to fund research aimed at gaining a better understanding of that evolution.

Based on preliminary data collected by Emily Spica ’15, Gemma Johnson ’16, and Maho Okumura ’16, the research will look at the molecular changes that occur in developing aphid embryos.

These small insects reproduce asexually and give birth during the summer months. But this asexual form cannot survive a cold winter. Thus, in the fall, when asexual mothers sense that days are getting shorter, they send a presumably hormonal signal to their embryonic offspring to develop into a sexual form that can lay eggs that are able to survive the cold temperatures of winter and hatch in the spring.

The researchers will investigate the molecular changes that occur in developing aphid embryos when they switch their development from the asexual to the sexual form. Participants will also investigate aphids from regions with mild winters, which are reported to no longer produce the sexual form nor lay eggs, to try to understand how the response to shorter days has been lost over the course of recent evolution.

“Emily Spica produced the first data in our group demonstrating that reproductive fate could be altered by manipulating insect hormones. Gemma Johnson worked with Professor Shapiro to try to find differences in gene expression between embryos destined to become asexual and sexual. And Maho Okumura explored differences in the sexual response between our New York strain and a strain of aphids from Tucson, Arizona,” explains Davis. “It’s been nice to see the work of different students converge and point the way forward.”

In addition to following up on these results, Davis and his students plan to work closely with Professor Noriega’s Florida lab to assay levels of hormones thought to be involved in the switch.

Davis also plans to use the research to expand beyond the lab. In past years, his students have brought active investigations to groups not typically targets of science outreach efforts. These included projects with students at a special-needs school in Malvern, middle-schoolers in a college-bound program in Norristown, and women incarcerated at the Riverside Correctional Facility in Philadelphia.

“I find that these sorts of outreach efforts put students in the position of having to think hard about how to make accessible the scientific knowledge that they’ve recently gained, which is an increasingly important part of what it means to be a scientist,” says Davis.

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