Modifying the mosaic: How patterns in traits help animals adapt to change

Gail McCormick
June 07, 2021

UNIVERSITY PARK, Pa. — When Sean Giery started as an Eberly Postdoctoral Research Fellow at Penn State, he thought he would be asking the scientific questions he proposed in his fellowship application. Instead, thanks to a Category 5 hurricane at his research site and a global pandemic, his research projects had to adapt — not unlike the organisms he studies.

Giery has been doing research on the Abaco Islands in the Bahamas since 2009. For the last few years, he has been working in a well-established study system that includes lizards known as brown anoles. He and his colleagues have been investigating how and why some anoles have different features, why those features occur where they do, and what those differences might mean for other species around them. But then Hurricane Dorian made landfall on the islands in 2019.

“This was a really devastating disturbance, with wind gusts up to 200 miles an hour,” said Giery. “But in spite of this incredibly strong hurricane, many anoles persisted. We wanted to know if the hurricane acted as a selection event. That is, if the anoles that survived had a particular trait that may have allowed them to weather the storm, that trait would become much more common in the anole population. If that was the case, we also wanted to know if the persistence of this trait affects how the rest of the ecosystem recovers.”

brown anole on tree

Penn State biologist Sean Giery and colleagues study how and why some brown anoles have different features, why those features occur where they do, and what those differences might mean for other species around them. 

IMAGE: John Suh

To answer these questions, Giery and colleagues from Washington State University and the University of Rhode Island received a National Science Foundation RAPID grant to investigate the impacts of Hurricane Dorian. For example, recent research has suggested that anoles with larger, grippier toe pads might survive hurricanes better than anoles with smaller toe pads.

“This trait presumably evolved for everyday life, not for the sort of catastrophe that happens every hundred generations,” said Giery. “These traits are really for locomotion, which is important for things like foraging, fighting, and avoiding predators, so rapid selection on these traits may have cascading effects on other species.”

To get an updated picture of anole traits, Giery and his colleagues measured the anoles using a portable X-ray machine and plan to compare these measurements to those from prior to the hurricane. But the second part of the project, which intended to explore the impacts of selected traits on ecosystem recovery, was put on pause due to the global coronavirus pandemic.

The additional time spent in Pennsylvania has allowed Giery to invest in a separate project much closer to home, looking at the color of spotted salamander eggs. In early spring, these salamanders lay egg masses in fish-free temporary ponds across the eastern United States. Females lay masses that are either opaque white, almost like milk, or completely clear.

“The frequencies of white and clear egg masses can vary from pond to pond,” he said. “Sometimes just tens of meters apart, ponds have different frequencies. And they also vary at a regional scale—for example, Pennsylvania has one of the highest frequencies of the white morph. We would like to understand what drives this variation.”

white and clear egg masses

Penn State biologist Sean Giery is studying why some salamander egg masses are opaque white while others are completely clear. 

IMAGE: Sean Giery, Penn State

Giery surveyed hundreds of ponds across Pennsylvania this spring, observing the frequencies of white and clear egg masses as well as a number of environmental characteristics about the ponds, including temperature and nutrient concentrations in the water. Many of these ponds were also surveyed in 1990 by then Penn State graduate student Benjamin Ruth and colleagues, who were interested in similar questions.

“We have a unique opportunity to compare modern egg morph frequencies to those from 30 years ago to see if they have changed over time,” said Giery. “If the characteristics of the ponds or these frequencies have changed over time, we can infer something about the evolutionary processes that might be at work over this period. Knowing how and why traits change—or don’t—is helpful to understanding how wild populations will respond to global change.”

Giery’s research on anoles and salamanders both get at the underlying questions he has studied in a number of species throughout his career: How do traits vary across a landscape, and what causes that variation?

“I am interested in landscape-level comparison of traits, usually across isolated populations, be they literal islands like in the Bahamas or something like ponds across a region,” said Giery. “What causes the diversity across islands? What causes the diversity within an island? How does climate change and other human-induced change affect this diversity? By making observations of natural populations, we can test the ecological and evolutionary theories that explain these patterns.”

The Eberly Postdoctoral Research Fellowship, he said, has allowed him to continue to ask these kinds of questions on his own terms.

“Funding for many postdoctoral positions is tied to a specific project run by a faculty member,” he said. “By contrast, the Eberly Fellowship provides a unique opportunity to lay the foundations for my own research program, which I hope to continue at a tenure-track job in the future.”

This story first appeared in the Winter 2021 issue of the Science Journal, the Eberly College of Science magazine.

Last Updated June 07, 2021