Tag Archives: CTmin

Evolution 2016: It’s Getting Cold in Here!

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Tamara Fetters with her poster at Evolution 2016

Tamara Fetters, from the McGlothlin lab at Virginia Tech, reported on her ongoing work on thermal physiology in Anolis sagrei during the first poster session here at Evolution 2016 in Austin, Texas. Tamara looked at thermal tolerance and sprinting abilities at different temperatures and how that related to the latitude of the population. Specifically, she asked if lower temperatures regularly experienced by the Northern populations influence cold tolerance and performance at those temperatures. She expected that Anolis sagrei, native to Cuba and the Bahamas and introduced into the Southern U.S., would show signs of adaptation to its new, colder home in the more Northern mainland populations compared to the native range island populations in the South.

Tamara’s poster focused on two main experiments. In the first she calculated thermal tolerance to cold temperatures using a classic critical thermal minimum (CTmin) setup: with an ice bath she slowly lowered the body temperature of each animal until it was unable to right itself. This method approximates the minimum temperatures that the animals can handle in the wild. She found a clear trend showing a decrease in the minimum temperature tolerated as latitude increased. In short, Northern populations could handle the cold and Southern populations could not.

In the second experiment, Tamara acclimated the lizards to 6 temperatures ranging from 12-41 °C before running them up a track to calculate sprint speed. Tamara used an impressive 25-50 animals from each of 5 populations! She calculated sprint speed from the high-speed video she took using the program Kinovea. Tamara found that across all temperatures the most Southern population ran the slowest while the most Northern population ran the fastest, with the differences remaining fairly constant.

So what’s next for Tamara? She is planning on rearing animals in a common garden setup with some animals in hot temperatures with low variability between day and night (mimicking the native range, Southern habitats) and some animals in cool temperatures with high variability between day and night (as is experienced in the Northern habitats). She hopes that these studies will help her understand the genetic basis of this thermal tolerance and the extent of plasticity in thermal adaptation.

One last note – Tamara wanted to thank Anole Annals for helping her determine her study locations. She was able to determine which areas were likely to have Anolis sagrei and how far North they have spread because of Anole Annals posts (like this one) and comments.

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Click to view a bigger version of Tamara’s poster