Scientists Baffled By Mysterious Reduction Of Mice Sizes

One of the most common mammals in the U.S., the North American deer mouse, has been observed to be getting smaller in size over the last 70 years. Florida Museum of Natural History researchers studied seven decades worth of information on the rats and discovered their body mass had been slowly decreasing without any clear indication as to the cause.

A Mystery

In a press release, Dr. Robert Guralnick, Associate Curator at the Florida Museum of Natural History and the co-lead author of the study, said the most exciting part of their research is the size of the deer mice getting smaller as time passes by, with the real cause continuing to elude scientists. He added, however, that the reduction in their body mass does not appear to be directly related to urbanization or climatic drivers.

The study, which was published Monday in the journal Scientific Reports, seeks to test Bergmann’s rule, a belief claiming that species in colder environments tend to be larger while species in warmer climates are smaller. This principle proposes that having more bulk than the heat-releasing body surface makes it easier for bigger-bodied species to retain heat. On the other hand, having more body surface than bulk helps smaller species to quickly dissipate heat and keep themselves cool.

A Look At Global Warming

The researchers had wanted to find out whether global warming plays a role in the mysterious shrinking of the deer mice’s bodies. Scientists collated thousands of past and current mouse body measurements to see whether deer mice are indeed becoming smaller. Researchers were surprised to discover that they are.

Dr. Guralnick said that their discovery is very intriguing, particularly since they are clueless as to what drives this decline in mass. While they hypothesize that it may be an evolutionary response to the changes happening around them, as well as allow them to better hide from human beings and respond to effects of urban heat on food resources, Guralnick and his team admit more research is needed.

A Confusing Twist

In an apparent confusing twist, scientists also discovered that only the smaller-bodied deer mice experience a reduction in body mass. Larger-bodied deer mice, on the other hand, were found to have been getting even bigger. Researchers theorized that this may be likely caused by “an increasingly fragmented landscape.” Scientists explained that even in small mammals like the deer mice, the slightest change in body mass could play an important role in optimizing energy.