Rainy West Side of Andes Mountains Has Bigger Mice Compared to East Side, Study Says New Rule of Nature But Same DNA

According to a study, mice living in the Andes Mountains with the same DNA exhibit a new law of nature. It is discovered that those on the wet west side are larger than those on the east side.

Mice from Patagonia, South America's Andes Mountains, were studied by scientists, which revealed that the mice thriving on the western slopes were considerably larger than the mice on the eastern slopes. There is more nourishment for the mice because the western slopes receive more rain.

Mammals' size and shape can change as a result of the rain shadow effect. Noé de la Sancha is a research associate at Chicago's Field Museum.

He thinks they might have found a new way to explain animal growth and development.

de la Sancha is an assistant professor of Environmental Science and Studies at DePaul University, and also the paper's corresponding author.

Abrothrix Hirta

The shaggy soft-haired mice, Abrothrix hirta, were used in this investigation by de la Sancha and his associates. de la Sancha said that the mice live in the mountains, which makes them unique, but they're also found in lower elevations. Overall, they're not very well-studied.

To complete his Ph.D. thesis, Pablo Teta, a colleague of De la Sancha's from the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" located in Buenos Aires, Argentina, started researching the shaggy soft-haired mouse. He saw that some individuals of the species were really big, and some were small.

He thought they were different species. Despite the stark differences between them, their mitochondrial DNA indicated that they belonged to the same species.

de la Sancha recalls that they wanted to explore why that is, to see if they were following some sort of rule.

New Rules

Biologists have tried to map their findings onto other biological "rules" to see if they explain why mice are larger and white-tailed deer are bulkier at higher latitudes. They found no strong correlation between mouse size and latitude but did find a pattern with longitude. This might be related to the "resource rule," which says that where there are more resources, individuals from the same species tend to be larger.

Eureka!

The rain shadow effect results from the movement of water vapor over mountain ranges. As the air gets colder, it condenses and falls as rain. If the mountain is high, the air will run out of moisture by the time it gets to the far side of the peak.

According to de la Sancha, the mountain will essentially have a cold, dry air on one side and humid, rainy weather on the other. On some mountains, the variation is stark. There may be a tropical rainforest on one side and a nearly desert-like environment on the other. Most mountains on Earth have a rain shadow effect; this phenomenon could be seen everywhere.

There may be a tropical rainforest on one side and a nearly desert-like environment on the other. Most mountains on Earth have a rain shadow effect; this phenomenon could be seen everywhere.

According to de la Sancha, this is the first time anybody has shown how the rain shadow affects animal size. The rain shadow did, in fact, closely match the sizes of the rodents. Although it has only been demonstrated for one type of mouse so far, de la Sancha believes he and his colleagues have discovered a more general fact that might one day serve as the foundation for a new rule.

Read also: Beneath the Andes Mountains: Earth's Crust 'Dripping' Into the Planet's Interior 

The discoveries, however, might spell trouble for the shaggy soft-haired mouse and many of their animal relatives. The frightening thing, according to de la Sancha, is that we demonstrate that climatic trends, at least in part, influence the form and size of mice, either directly or indirectly through resources they can access.

de la Sancha said that as a result of climate change, the group expects large seasonal variations in precipitation and temperature. Although they might not be the factors that have the greatest impact on the mice's wellbeing, they are crucial in defining the types of food that are accessible. The mice could no longer be able to thrive as they previously did if the weather patterns change and have an impact on the plants that grow in the area.

Unclear Future

According to de la Sancha, studying typically overlooked creatures like mice is important because it will help us understand the uncertain future of the mice in the context of climate change. He asserts that it's crucial to recognize how little is known about the majority of tiny animals, Science Daily reports.

Related article: Andes Mountain Faces Low Snowfall Due to a Mega-drought Linked to Global Heating