Cold life of the subtropical highlands

The Antarctic Peninsula (once forming the Weddell and Ellsworth islands) is divided by a large mountain range called Peninsular Alps, home to relictual patches of alpine tundra that have a less marked seasonality due to their mid-latitude position. The botanical biodiversity of this alpine habitat is extremely high: with more than 250 plant species per square km, this ecoregion cannot be compared to any other antarctic mountain tundra, which rarely exceeds 100 species per square km.

Peninsular Alps are inhabited by otterwatchers (Pseudomarmota grahamii), probably the first-ever cold-adapted rodent of Antarctica. Anatomically similar to a prairie dog with a very long tail, the otterwatcher feed mostly on soft vegetation, sometimes integrating its diet with invertebrates. They live in familiar groups composed of 4-15 individuals that feed together near their den, while one of the members stays alert to spot potential threats.
Otterwatchers' cubs can sometimes fall prey to lipidragons, a very successful group of large viviparous lizards that are capable of easily accumulating fat due to a mutation of the phosphatidic acid phosphatase enzyme, which helps to survive winter hibernation.
Some species are lizard-like while others are more serpentine, like the snow lipidragon (Pinguilacerta polaris), which has evolved short limbs to creep inside otterwatchers' dens. During summer, these reptiles are capable of self-regulate their body temperature to speed up their gestation. This adaptation is very efficient at high altitudes because of the short warm periods (less than 3 months): at these conditions, the faster you can raise your young, the lower their mortality.
It's known that all these such bizarre characteristics for a reptile were indirectly selected for farming purposes by Aves ex Machina: fatter livestock that can reproduce faster is more caloric and productive from the point of view of a farmer. What Aves ex Machina didn't know is that this livestock, once escaped, would take advantage of this adaptation and become feral species.
However, as with all artificial breeds, seemingly helpful traits can bring also issues: fat accumulation is not well regulated by lipidragons metabolism, which can sometimes overly accumulate when food is overabundant: it's not surprising, then, that lipidragons suffer more frequently to cardiovascular problems and other obesity-induced diseases.