Chromosomal Flips Propel Natural Selection

Cornell and UConn researchers find chromosomal inversions help aquatic species adapt to diverse environments

Published on Mar. 6, 2026

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New research from Cornell University and the University of Connecticut finds that chromosomal inversions - where a chunk of chromosome containing genes breaks off, flips, and reattaches - help mobile aquatic species like Atlantic silversides maintain genetic differences adapted to various regions, even when they interbreed. The inversions act as "genetic switches" that preserve beneficial gene combinations for survival in different environments, rather than having those combinations broken apart by genetic mixing.

Why it matters

This study provides insights into how certain species can adapt to a wide range of habitats and temperatures, which is increasingly important as climate change alters environments. The findings suggest that large-effect genetic changes, rather than many small mutations, may drive rapid and predictable adaptation in some species.

The details

The researchers cross-bred Atlantic silversides from Georgia and New York, raised their offspring under different temperatures, and measured key traits like growth rate and swimming performance. They found that chromosomal inversions containing genes for important adaptive traits like growth, metabolism, and vertebral number were critical for maintaining local adaptation, even when the fish interbred.

  • The study was published on March 5, 2026.

The players

Nina Overgaard Therkildsen

Associate professor of natural resources and the environment at Cornell University and co-senior author of the study.

Hannes Baumann

Associate professor at the University of Connecticut and collaborator on the study.

David Conover

Emeritus professor at the University of Oregon and collaborator on the study.

Atlantic silversides

A small fish species that lives along the Atlantic coastline of the United States and was the focus of the study.

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What they’re saying

“Each chromosomal inversion locks together a large set of genes, effectively forming a genetic switch with two states, flipped or not flipped. What's surprising here is that multiple 'switches' can combine to generate smooth, continuous variation, not just on-or-off differences.”

— Nina Overgaard Therkildsen, Associate professor of natural resources and the environment (Science)

“The work is stunning in its complexity and comprehensiveness. Silversides, like many species, have several massive inversions on multiple chromosomes. The novelty of our study is that we show that these inversions contain vital genetic information for genes that determine growth, metabolism, vertebral number and lipid content.”

— Hannes Baumann, Associate professor (Science)

What’s next

The researchers plan to further investigate how the chromosomal inversions in Atlantic silversides and other species allow them to adapt to diverse environments, which will be increasingly important as climate change alters habitats.

The takeaway

This study demonstrates how certain species can maintain genetic differences adapted to various regions through chromosomal inversions, even when they interbreed. The findings suggest that large-effect genetic changes, rather than many small mutations, may drive rapid and predictable adaptation in some species facing environmental changes.