These Mice Grow Bigger on the Rainier Sides of Mountains: It Might be a New Rule of Nature

posted by hubie on Tuesday September 06 2022, @12:21AM

from the of-mice-and-rain dept.

Arthur T Knackerbracket has processed the following story:

Scientists studying mice from the Andes Mountains in Patagonia noticed something they couldn't explain: the mice from the western side of the mountains were bigger than the ones from the east, but DNA said that they were all from the same species. The researchers examined the skulls of 450 mice from the southern tip of South America, and found that existing biological laws didn't explain the size differences. Instead, in a new paper in the Journal of Biogeography, the scientists put forth a new hypothesis: the mice on the western slopes were bigger because that side of the mountain range gets more rain, which means there's more plentiful food for the mice to eat.
[...] De la Sancha and his colleagues realized this might be related to what biologists call the "resource rule." "This rule suggests that where there are more resources, individuals from the same species tend to be larger than where there are fewer resources," says de la Sancha. "For instance, some deer mice that are found in deserts and other habitats tend to be smaller in drier portions of their habitats. Another hypothesis suggests that some animals tend to be smaller in mountains versus adjacent plains in North America. Our study found a mixed result of these rules."
The sizes of mice seemed to be following the resource rule, but the question still remained: why were there more resources on the western slopes of the southern Andes than on the eastern slopes? De la Sancha had a "Eureka!" moment while teaching a class of undergraduates at Chicago State University.
"Believe it or not, when I was teaching ecology, one of the things that I was teaching about was the rain shadow effect," says de la Sancha.

[...] In the middle of his lecture, de la Sancha realized that the rain shadow could explain why there was more food on the western side of the Andes, and thus, why the mice there were bigger. "That same day, I went home and wrote to Pablo," he remembers. "I was like, 'Dude, we need to talk about the rain shadow.'"
The rain shadow indeed neatly matched up with the rodents' sizes—the first time, to de la Sancha's knowledge, that anyone has demonstrated the effects of the rain shadow on mammal size. And while so far it's only been shown for one species of mouse, de la Sancha suspects that he and his colleagues have hit on a larger truth—perhaps even the basis for a rule of its own someday.
[...] The unclear future of these mice in the face of climate change, according to de la Sancha, is a good reason to study animals like mice that often go unnoticed. "It's important to understand how little we know about most small mammals," he says. "They can be good indicators of long-term changes in our environment. We need to study them more. Our findings also show why museum collections are so important. This study was based on museum collections from Argentina, Chile, and the US, it's an amalgamation of years and years of collecting and big data sets.
"This paper would not have been possible without museum collections and highlights the importance of museum- and collection-based research and its support worldwide," notes Teta. "This type of research helps us better understand the big-picture, universal rules of how life on Earth works."

Journal Reference:
Pablo Teta, Noé U. de la Sancha, Guillermo D'Elía, Bruce D. Patterson, Andean rain shadow effect drives phenotypic variation in a widely distributed Austral rodent, J Biogeogr, 2022. DOI: 10.1111/jbi.14468

Original Submission

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