City and Country Fish Evolve Differently

Urban creek chub like the one pictured above have deeper bodies and are less streamlined than rural counterparts. (Image: courtesy of Elizabeth Kern)
Urban creek chub like the one pictured above have deeper bodies and are less streamlined than rural counterparts. (Image: courtesy of Elizabeth Kern)

A North Carolina State University study examining the effects of urbanization on the evolution of fish body shape produced both expected and surprising results: One fish species became more sleek in response to urbanization, while another species became deeper bodied in urban areas.

Generally, urbanization produces conditions that make water in streams flow more variably and more quickly during rain storms. So NC State biologists hypothesized that fish would quickly evolve a body shape that improves swimming efficiency in response to changes in stream water velocity caused by urbanization.

Brian Langerhans, associate professor of biology at NC State and senior author of a paper describing the research, said:

The study combined fieldwork in streams to document contemporary patterns across different fish species and regions in North Carolina, examination of museum specimens to track changes in fish body shape over time, and lab experiments to understand whether nature or nurture affect fish body shape changes.

In the field, one species of fish, a type of minnow called the western blacknose dace (Rhinichthys obtusus), reflected predicted changes: its body shape became more streamlined in urbanized areas. Langerhans said the body shape changes likely help make it better able to handle changing water conditions.

Meanwhile, its body shape in more rural areas, regions largely devoid of urban influence, remained less sleek. Yet the study also showed that a minnow cousin, the creek chub (Semotilus atromaculatus), actually became less sleek in more urbanized areas.

Creek chubs in rural areas remained at the baseline shape, while those living in streams surrounded by large amounts of impervious surfaces like roads and sidewalks developed deeper bodies, Langerhans explained:

Museum specimens of rural and urban creek chub dating back half a century showed historical urban creek chub body shapes similar to those in modern urban areas: more boxy and less streamlined.

Historically rural areas, meanwhile, had more sleek creek chub, similar to those observed in these streams today. However, in streams urbanized around 30 years ago, creek chub bodies changed over time from a sleek shape characteristic of rural streams toward deeper bodies characteristic of modern urban creek chub.

Lab-raised creek chub showed nature had a bigger influence than nurture, as creek chub individuals from rural and urban areas raised in a common environment showed the same differences as modern-day field samples, with urban creek chub less streamlined than rural.

The paper appears in the journal Global Change Biology. NC State Ph.D. alumna Elizabeth Kern, who now works at Ewha Women’s University in South Korea, is the paper’s lead author.

Provided by: North Carolina State University [Note: Materials may be edited for content and length.]

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