Urban fish grow into different shapes than their rural relatives

April 27 (UPI) — City fish evolve different body shapes than their rural peers, new research out of North Carolina State University shows.

Dozens of surveys have focused on urban-rural differences in animal health and behavior or water quality, but the latest study looked at the ways stream structure and water flow impact the fish shape of fish living in the city and the country.

Because urbanization encourages greater stream flow variability and faster currents when storm runoff floods local waterways, scientists hypothesized that fish living in and around urban development would need to adapt their body shape to thrive.

To test their hypothesis, scientists surveyed body shape patterns among fish populations in western and central North Carolina. Researchers also studied museum specimens of relevant species to estimate body shape changes over time.

Field surveys indicated minnow species, the western blacknose dace, Rhinichthys obtusus, became sleeker — as predicted — in order to adapt to urban stream conditions. However, the dace’s close relative, the creek chub, Semotilus atromaculatus, developed a deeper, less-sleek body.

“One species showed morphological changes that nicely matched evolutionary predictions of increased streamlining to better handle the altered condiions, but the other species showed a change that did not match our simple prediction, highlighting how different species can solve similar problems in different manners,” Brian Langerhans, associate professor of biology at NC State, said in a news release.

Museum specimens showed a similar urban-rural divide in creek chub body shape dating back several decades. In the lab, scientists found individuals from rural and urban areas developed similar body shapes when they were raised in the same environs and exposed to the same water flows, suggesting the body shape differences are inspired by nature, not nurture.

“Human activities are having real-time evolutionary impacts on the organisms capable of living in our human-dominated environments; some of these changes may be predictable and some may be difficult to predict,” Langerhans said.

Researchers published their findings Friday in the journal Global Change Biology.