Ant biology and behavior change for city living

"Urbanization is a growing habitat around the world, and it's becoming more important for organisms to develop ways to live when their natural settings are disturbed," says Ed Vargo. "Studies like this look at important questions regarding this change, 'Can they adapt to urban environments and how?'" (Credit: JJ Harrison/Wikimedia Commons)

A common ant species undergoes physiological and behavioral changes in unnatural settings such as development and urban sprawl, a new study shows.

“Urbanization is a growing habitat around the world, and it’s becoming more important for organisms to develop ways to live when their natural settings are disturbed,” says Ed Vargo, senior investigator and chair of the urban and structural entomology program at Texas A&M University. “Studies like this look at important questions regarding this change, ‘Can they adapt to urban environments and how?'”

The study focused on Tapinoma sessile, a relatively small ant species commonly known as the house ant or sugar ant. It is the most common house-invading ant across the US.

In its native environment, the house ant creates small, single-queen colonies typically found under leaf litter, rocks, and logs, Vargo says. But in suburban/urban settings, these house ants build ever-expanding multi-queen colonies around man-made structures such as sidewalks, plant containers, and landscape mulching.

Odorous house ants

The study provides a broad range of scientific applications related to biological and behavioral change spurred on by environmental conditions throughout the animal kingdom. It also could provide insights into how invasive species interact with environments new to them.

“The change is very similar to invasive ants once they move from their native range to an invasive range,” Vargo says. “The idea is to better understand this syndrome in an ant species that can take a small, inconspicuous colony that then becomes an economic and ecological problem when damaging colonies get larger and larger.”

For the study, published in Molecular Ecology, the researchers used a large genetic database to identify the chemical and behavioral changes that influenced the ants’ social organization, Vargo says. They explored and compared the population genetics and breeding structure within and between ants in several urban and undisturbed natural locations within their range.

Odorous house ants were observed and analyzed in natural and disturbed locations around the country including Indiana, Arkansas, Colorado, and California.

The team analyzed the ant’s chemistry, such as hydrocarbons, genetic makeups of colonies, and behaviors, such as aggression toward familial and outsider ants, and found stark differences based on the environment, Vargo says.

Ants in the city

The study found that house ants in urban and natural areas showed adaptations that resulted in genetic concentration. Vargo says house ant queens in their natural habitat typically leave the colony they were born in, fly to another suitable location, and attempt to establish a new colony. Queens in urban colonies stay in the nest and expand the colony rather than leave.

As a result, urban queens are closely related and less aggressive toward ants with genetic relation. Behavioral analyses showed ants in super-colonies are aggressive toward ants with outside genetics.

Additionally, polydomous colonies, which are ant colonies that are spatially separate but socially connected, are only present in urban habitats, Vargo says. This suggests house ants only create super-colonies in developed areas. Ants from different urban areas shared some genetic similarities, suggesting they are adapting to features that are common in the urban environment.

As a next step, the researchers plan to compare stable isotopes in the ants to look at dietary changes and how they might relate to natural vs. urban environments and possible contributing factors like temperature and the urban heat island effect.

The researchers have hypotheses but no data yet linking how and why changes occurred, Vargo says.

Alexander Blumenfeld, the study’s principal author and a former graduate research assistant in Vargo’s lab, is now a post-doctorate researcher at Yale University. He says he is interested in answering questions related to adaptive evolution in animals regardless of classification or species, and whether they are invasive or adapting to human-caused disturbances, including cities.

“The study highlights urbanization’s influence on the evolutionary course for species,” he says. “It’s important for us to answer questions related to adaptive evolution, whether it is an invasive species or a forest species adapting to city environments.”

Source: Texas A&M University