Ecological Divergence a Factor in Reproductive Isolation, Genetic Diversity

FAYETTEVILLE, Ark. — Although Darwin’s theory of natural selection has been around for more than 100 years, little proof existed to show that adaptation to environmental changes can drive the development of news species — until now.

William Etges, professor of biological sciences at the University of Arkansas, and biologists Daniel J. Funk of Vanderbilt University and Patrick Nosil of Simon Fraser University examined the genetic diversity and ecology of hundreds of species of birds, butterflies, fish, frogs and fruit flies, and they found that ecological divergence is positively associated with species formation across all species and habitats.

They report their findings in the Feb. 28 issue of the Proceedings of the National Academy of Sciences.

“This research goes back to the question of what is driving biodiversity,” Etges said. “Our research is suggestive of a general pattern that no one has documented in a rigorous fashion before.”

Etges, a professor in the J. William Fulbright College of Arts and Sciences, specializes in the study of the ecology and genetic history of Drosophila, sometimes known as fruit flies. He focuses on species that populate cacti in North and South America. Because fruit flies have diversified into thousands of species, reproduce quickly and create many generations in a short time, scientists use them to study evolution, population genetics and diversification.

In many cases, genetic information on fruit flies is obtained from laboratories, a setting that bears little resemblance to the insect’s typical surroundings. But Etges has spent a lot of time studying cactophilic Drosophila in their natural habitat — different types of cactus plants.

“We’ve got a host of ecological information on these desert flies,” Etges said. The ecological, behavioral and genetic information combine to create a more thorough portrait of the history of species formation.

Species formation is considered to be a matter of reproductive isolation over time — in other words, two organisms become so different that they cannot mate to produce viable offspring. Etges and his colleagues wanted to see how ecological changes — using a different type of food, for instance, or moving from a wet to a dry climate — might affect reproductive isolation over time. However, finding ecological data across species proved challenging.

Drosophila proved to be a particular challenge even though some species have become the “lab rats” of the insect world.

“When you look across 100 different Drosophila species in nature, there’s a humongous amount of fieldwork involved,” Etges said.

“People trap them instead of going out into nature and finding out what they do in the wild,” Etges said.

Still, he and his colleagues were able to find 500 species from eight groups of animals to work with — including the fruit flies Etges studies. They performed statistical analyses that included ecological divergence, reproductive isolation and genetic distance over time to reach their conclusions.

“In almost every case, the ecological component was associated with reproductive isolation,” Etges said “This is important for those of us interested in the generation of biodiversity.

“This contributes to the literature on how new species form,” Etges said. With more ecological studies, it may be possible for researchers to discover more about how such ecological changes contribute to species formation.