Scientists may have found a new natural rule after discovering that mice in the Andes grow larger on the wetter slopes of mountains.
Abrothrix hirta resides in Patagonia, at the southernmost tip of South America.
Researchers from Chicago’s Field Museum analyzed the skulls of 450 of these mice and discovered that, while being genetically similar, those who resided on the western side of the mountains were larger.
They hypothesize that the mice on the western slopes were larger because this side of the mountain range receives more precipitation, resulting in an abundance of food.
According to the experts, this trend could be repeated in different animals and species.
Dr. Noe de la Sancha of DePaul University in Chicago, the study’s corresponding author, noted, “There are several ecogeographic laws that scientists employ to explain recurring patterns in nature.”
“With this paper, I believe we may have discovered a new phenomenon: the rain shadow effect can trigger size and shape changes in mammals.”
As part of his doctoral thesis, one of the researchers, Pablo Teta of the Bernardino Rivadavia Natural Sciences Argentine Museum in Buenos Aires, began studying the shaggy soft-haired mice.
Dr. de la Sancha explained, “He observed that some members of the species were extremely large, while others were extremely small.”
He believed that they were of different species. However, their mitochondrial DNA revealed that they belonged to the same species, despite their vast differences.
We wanted to investigate why this is the case and determine if they were following a regulation.
There are numerous “natural laws” that explain the patterns we observe in life.
For example, Bergmann’s rule explains why identical species of animals are larger at higher latitudes.
Canadian white-tailed deer are larger and more robust than their Florida counterparts. Bergmann’s rule explains why this is the case: a thicker body in comparison to its surface area retains heat more effectively.
To uncover a trend that could explain the differences in mouse size, the researchers compared the measurements of mouse skulls in museum collections using statistical analysis.
The researchers next attempted to fit their data into several biological rules. Bergmann’s rule did not hold; there was no strong association between the size of the mouse and its latitude.
Other principles emphasize the importance of temperature or precipitation, with variable outcomes for various populations and situations.
Along with 19 other bioclimatic, temperature, and precipitation variables, latitude was ruled out as a cause of the different forms and sizes of mice. However, there appeared to be a trend about longitude, namely how far east or west they lived.
De la Sancha and his colleagues concluded that this may be related to what biologists refer to as the “resource rule.”
He stated, “This rule says that where there are more resources, individuals of the same species tend to be larger than in areas with fewer resources.”
‘For example, certain deer mice that inhabit deserts and other ecosystems tend to be smaller in the drier regions of their habitats.
‘According to a second hypothesis, certain North American species tend to be smaller in mountainous regions compared to neighboring plains. Our research revealed a mixed response to these guidelines.
While teaching a class of students at Chicago State University, he had a “eureka!” moment.
Dr. de la Sancha stated, “Believe it or not when I taught ecology, one of the topics I covered was the rain shadow effect.”
The rain shadow effect is caused by the movement of water vapor over mountain ranges. The air above the ocean absorbs water vapor, which then rises as the ocean naturally warms.
This air is pushed from the ocean to the land by prevailing winds, such as the jet stream, which blows from west to east. As the air travels through mountain ranges, it becomes colder with increasing altitude. The water vapor condenses into precipitation.
If the mountain is exceptionally tall, the air will be dry by the time it reaches the far side of the top.
Dr. de la Sancha stated, “Essentially, one side of the mountain will be humid and rainy, while the other will have chilly, dry air.”
On some mountains, the contrast is stark. One side may resemble a tropical rainforest, while the other may resemble a desert.
There is a rain shadow effect in the majority of mountains on the earth; this phenomenon is observed everywhere.
Dr. de la Sancha realized that the rain shadow could explain why there was more food and larger mice on the western side of the Andes.
Indeed, it corresponded precisely with the sizes of the rodents, marking the first time anyone has proved the impacts of the rain shadow on the size of mammals.
Dr. de la Sancha feels that he and his colleagues have uncovered a bigger truth – potentially even the foundation for a rule in the future – even though it has only been demonstrated for one mouse species.
He remarked, “It is thrilling because it has the potential to be something more universal.”
We believe it is more likely a norm than an exception. It would be beneficial to test it on numerous taxa.
According to the researchers, the discoveries may have consequences on the ability of some species to tolerate climate change.
Mice may no longer be able to thrive as they previously did if a change in weather patterns hurts the local vegetation.
Dr. de la Sancha stated, “As a result of climate change, we anticipate drastic variations in temperature and precipitation during the course of the year.”
While they may not be the most significant elements impacting the health of mice, they are crucial in determining the availability of food sources.
Dr. de la Sancha claims that animals are already climbing mountains to avoid the consequences of climate change.
He explained, “At some point, there are no more mountains.” There is no other option. We do not know what will occur, but it does not appear favorable.’
Recent research has revealed that many animals shapeshift in response to global warming. Birds are growing larger beaks, while elephants and bunnies are growing larger ears. The appendages aid in their cooling.
Dr. de la Sancha stated, “It is essential to realize how little we know about the majority of small mammals.” They can be useful markers of long-term environmental changes.
