Strategic Communications and Marketing News Bureau

Study: In darters, male competition drives evolution of flashy fins, bodies

CHAMPAIGN, Ill. — Scientists once thought that female mate choice alone accounted for the eye-catching color patterns seen in some male fish. But for orangethroat darters, male-to-male competition is the real force behind the flash, a new study finds.

The research, reported in the Royal Society journal Proceedings B, suggests that separate populations of orangethroat darters are evolving differing color patterns as a result of the males’ ability to distinguish their own from other species.

Darters are small, perch-like fish living in freshwater rivers and creeks in North America, said University of Illinois graduate student Rachel Moran, who led the research with animal biology professor Becky Fuller. The males are showy, with orange and blue-green stripes and patches, but the females are brown and tan.

Illinois animal biology professor Becky Fuller, left, and graduate student Rachel Moran study the factors that drive fish evolution in freshwater systems.

Illinois animal biology professor Becky Fuller, left, and graduate student Rachel Moran study the factors that drive fish evolution in freshwater systems.

“The females don’t choose their mates,” Moran said. When fertile, they simply burrow into the gravel and wait for a mate to arrive. “Males of the same species will come up and try to mate with a female and fight off other males,” she said.

Because this aggression is costly and dangerous, the males do best if they compete only with males of their own kind, Fuller said.

“To be successful, they need to distinguish between their own and other darter species,” she said.

Only orangethroats that coexist with rainbow darters have developed this ability, recent studies have found. Once they learn to avoid rainbow darters – a more distantly related species of fish – orangethroat males won’t mate or fight with even closely related orangethroat species.

In the new study, Moran raised a generation of orangethroat offspring in the lab. She obtained the parents of these lab-raised fish from different populations in the wild. The experiment revealed that the distinctive male color patterns seen in separate populations of orangethroat darters persisted from generation to generation.

“This shows that this is something that is genetically based and that those differences are not due just to the environment,” she said.

She also compared color patterns in populations of orangethroat darters that do and do not share habitat with rainbow darters.  Orangethroat populations that never encounter rainbow darters in the wild look very similar to one another, even when they live out their lives in complete isolation from each other, she noticed.

Separate populations of orangethroat darters whose territories overlap with rainbow darters look very different from one another, however. When individuals from these different populations are brought together in the lab, they ignore and avoid one another. They will neither mate with the females or fight with the other orangethroat darter males.

Moran said there is a possible explanation for why the two species have learned to avoid one another: Hybrid offspring have low survival.

 “Natural selection has favored fish that are able to distinguish between their own and the other species,” she said.

“As scientists, we often assume that female mate choice is the reason for sexual dimorphism in animal species, where females are very dull and males are flashy,” Moran said. “But here, we’re showing that male competition also plays an important role. We now know that male competition alone can drive divergence in this really flashy signal between species and also within species.”

The National Science Foundation and the U.S. Department of Agriculture supported this research.

Editor’s notes:
To reach Rachel Moran, email rmoran9@illinois.edu.
To reach Becky Fuller, email rcfuller@illinois.edu.
The paper “Agonistic character displacement of genetically based male color patterns across darters” is available online and from the U. of I. News Bureau.
DOI:

Read Next

Health and medicine Dr. Timothy Fan, left, sits in a consulting room with the pet owner. Between them stands the dog, who is looking off toward Fan.

How are veterinarians advancing cancer research in dogs, people?

CHAMPAIGN, Ill. — People are beginning to realize that dogs share a lot more with humans than just their homes and habits. Some spontaneously occurring cancers in dogs are genetically very similar to those in people and respond to treatment in similar ways. This means inventive new treatments in dogs, when effective, may also be […]

Honors From left, individuals awarded the 2025 Campus Awards for Excellence in Public Engagement are Antoinette Burton, director of the Humanities Research Institute; Ariana Mizan, undergraduate student in strategy, innovation and entrepreneurship; Lee Ragsdale, the reentry resource program director for the Education Justice Project; and Ananya Yammanuru, a graduate student in computer science. Photos provided.

Awards recognize excellence in public engagement

The 2025 Campus Awards for Excellence in Public Engagement were recently awarded to faculty, staff and community members who address critical societal issues.

Uncategorized Portrait of the researchers standing outside in front of a grove of trees.

Study links influenza A viral infection to microbiome, brain gene expression changes

CHAMPAIGN, Ill. — In a study of newborn piglets, infection with influenza A was associated with disruptions in the piglets’ nasal and gut microbiomes and with potentially detrimental changes in gene activity in the hippocampus, a brain structure that plays a central role in learning and memory. Maternal vaccination against the virus during pregnancy appeared […]

Strategic Communications and Marketing News Bureau

507 E. Green St
MC-426
Champaign, IL 61820

Email: stratcom@illinois.edu

Phone (217) 333-5010