Populations are often challenged to live in novel or rapidly changing environments. This is probably most clear in cities where new habitat is being created causing native species to encounter novel habitat features. But because of this, cities set the stage to help researchers understand the plastic and evolutionary shifts that occur in wild organisms.
Dr. Ryan Martin, from Case Western University, along with Dr. Lacy Chick, Aaron Yilmaz, and Dr. Sarah Diamond are investigating these changes in acorn ants. Specifically, they are interested in how populations of acorn ants respond to urban heat islands?
Acorn ants are a ground-nesting species that live in free form cavities. Each colony consists of about 50-200 workers and one queen with offspring that have low dispersal. These ants are found in forest patches in urban and natural environments, meaning that their local environment is similar. However, cities are often a few degrees warmer than the surrounding environment meaning that the ambient temperature experienced by ants living in urban and rural colonies is different.
Previous common garden work suggested that ants had both plastic and evolutionary responses to urban heat islands. However, this work could not distinguish between evolution and transgenerational plasticity. Transgenerational plasticity may be important when parents can anticipate the environment their offspring will live in. To overcome this, Martin et al. conducted multigeneration common garden experiments, therefore eliminating single-generation environmental effects. After collecting acorn ants from urban and rural environments they bred them in the lab. Martin et al. crossed the offspring of urban and rural ants that had been lab-reared. They found no evidence that transgenerational plasticity explains the urban-rural evolutionary divergence in thermal tolerance. Interestingly hybrids resembled the urban-urban crosses for maximum temperature but resembled rural-rural hybrids for minimum temperature. This points to separate mechanisms that underlie maximum temperature and minimum temperature, and that hybrids potentially realize greater thermal tolerance breadth than either parental populations.
To learn more about this research check out the full paper here:
Martin, R.A., L. Chick, A. Yilmaz, S.E. Diamond. 2019. Evolution, not transgenerational plasticity, explains the adaptive divergence of acorn ant thermal tolerance across an urban-rural temperature cline. Evolutionary Applications. https://onlinelibrary.wiley.com/doi/10.1111/eva.12826
Featured image © Tom Murray. Sourced from BugGuide and PBase under a CC-BY-ND-NC
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