Here’s an idea for the newest weight loss fad: live in a city. In her presentation at Evolution 2019, Dr. Sarah Diamond showed that the resting metabolic rate of urban acorn ants was higher than that of rural colonies. This research, conducted by Dr. Diamond and coauthors Lacy Chick and James Waters, looked at the metabolic rates of 41 acorn ant colonies collected from 5 urban and 5 rural sites near Cleveland, Ohio. The results contradicted their initial prediction based on the metabolic cold adaptation hypothesis, which states that organisms living in cold environments will have higher rates of metabolism than those in warmer locales. Because urban areas are hotter compared to the surrounding rural landscape, this hypothesis would predict slower metabolisms in urban ants. Diamond et al. also predicted that urban colonies would be less sensitive to changes in temperature. Graphically, these predictions can be represented as:
Their results so far support this second hypothesis: colonies from rural areas were 26% more sensitive to the higher temperature than their city-dwelling neighbors. Urban colonies had a higher resting metabolic rate at rearing conditions (25˚C) than rural colonies, but the difference at the higher temperature was not statistically significant.
Another important driver in the evolution of a population’s metabolic rate is pace of life. Slow-paced life histories have lower metabolic rates. Pace-of-life changes can result in rapid changes in metabolic rate in a population (see Auer et al. 2018). If the higher metabolism in urban colonies is adaptive, it may be due to the the faster-paced lives of city ants (e.g. higher rates of colony turnover and reproductive output) rather than a response to warmer temperatures. Another reason to move to the city if you want to increase your metabolism, at least if you’re an ant.
Future directions for this research include forecasting species responses to urban biomes and global climate change. Importantly, this research shows that rapid evolution to contemporary conditions is not always coincident with long term, biogeographic patterns of species’ response.
Featured image: Dr. Sarah Diamond presenting during the Evolution 2019 meeting.
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