The Northern Treeshrew, a small, bushy-tailed mammal native to South and Southeast Asia, defies two of the most widely tested ecological “rules” of body size variation within species, according to a new study coauthored by Yale anthropologist and Director of the Yale Institute for Biospheric Studies (YIBS), Eric J. Sargis.

The unexpected finding, researchers say, may be attributable to climate change — the body size rules reversed in Northern Treeshrews as average temperatures climbed — and likely exists in other species.

The first-of-its-kind study, published Nov. 29 in the journal Scientific Reports, found that the Northern Treeshrew (Tupaia belangeri) breaks both Bergmann’s rule and the island rule. The former describes a common pattern wherein individuals of a warm-blooded species inhabiting colder climates — generally located at higher latitudes — have larger average body sizes than those in warmer climates, which are usually at lower latitudes. The latter predicts that small mammal species evolve larger body sizes on islands than their mainland counterparts, whereas island-bound large mammals evolve smaller body sizes. For more information, click here for an article published by Yale News.