City living is changing rodent skulls in Chicago
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Tiny rodents living in a major American city are unique examples of evolution playing out in real time.
Like geologic time itself, the process of evolution itself is generally a very slow process with teeny tiny changes passed down over several generations. All of these small changes eventually result in new adaptations and potentially new species over thousands or millions of years. However, in the face of dramatic shifts in the world around them from climate change to human encroachment, species sometimes must rapidly adapt or die.
They found small–but significant–changes in the rodents’ (chipmunks and voles) skulls over the past 100 years. For the chipmunks, their skulls became larger over time, while the row of teeth along the sides of the mouths shrank. The bony bumps in the voles’ skulls that hold the inner ear became smaller over time. However, why the skulls were changing was not immediately clear.
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“Over the last century, chipmunks in Chicago have been getting bigger, but their teeth are getting smaller,” said Feijó. “We believe this is probably associated with the kind of food they’re eating. They’re probably eating more human-related food, which makes them bigger, but not necessarily healthier.
Meanwhile, their teeth are smaller—we think it’s because they’re eating less hard food, like the nuts and seeds they would normally eat.”
By contrast, the voles had smaller auditory bullae–bone structures associated with hearing.
“We think this may relate to the city being loud—having these bones be smaller might help dampen excess environmental noise,” said Smith.
