A little hop for rabbits, a giant leap for Antarctica

Almost parallel to the arrival of borax, another alien species managed to cross the vast ice bridge connecting Antarctica to the outer world. Surprisingly, it’s not a carnivore but a herbivore, called rompo (Polarilagus briophagus). Despite its unusual appearance, its closest relatives are very familiar animals: hares and rabbits (order Lagomorpha). While marsupials were prehistorically widespread in Antarctica, this marks the first time a lagomorph has reached the continent.

However, calling this animal a hare or rabbit is a stretch. It is nearly five times the size of a hare, weighing 15–29 kg depending on sex. Its body only vaguely resembles that of a hare: short ears, a robust barrel-like torso, a relatively long tail, and more importantly a digitigrade locomotion, losing the traits that hares are known for. This posture, used both while standing and running, gives it a hopping gait that is more like a gazelle’s leap than a rabbit’s hop.

Rompos are social animals that live in small family groups of usually no more than 10 individuals and feed on almost any plant matter available, including lichens, which make up more than half of their diet in the Ponti Archipelago they recently colonized. They can digest lichens thanks to a lichenase enzyme, the same evolved by reindeers, an example of convergent evolution. However, unlike reindeer, rompos are not full ruminants. They have a two-chambered gut and large ceca that aid digestion. While not as efficient as a cow’s digestive system, it is far more advanced than their rabbit ancestors, which rely on eating their first feces to process food.
Rompos can reduce their metabolic rate by up to 40% in harsh conditions, allowing them to survive with minimal resources, a key adaptation that likely explains how they managed to cross a fragmented ice corridor spanning several hundred kilometers of barren ice. Upon reaching the Ponti Archipelago, they found a tundra ecosystem far more hospitable than the icy bridge they crossed. With no herbivores present in the region, the rompo population quickly grew with no competition. Their trampling impact on vegetation caused a shift toward a slightly more biodiverse tundra, with an increase in grasses and forbs, which improved the environment’s carrying capacity. 1,000 years after the first rompo arrived, the population of these lagomorphs exceeded 50,000 individuals in the Ponti Archipelago.

Despite their adaptations to cold, rompos had to face several predators in their new home, particularly pinpiercers, which are unique to Antarctica. They were already adapted to deal with borax, which originated from the same region, while smaller predators like ottofoxes and banchisaraptors posed a threat only to juveniles. Interestingly, rompos were crucial for the expansion of borax: although rompos could not spread to the Sanctuary Peninsula due to an even greater ice barrier, their abundance in the Ponti Archipelago provided a vital food source for borax, enabling the latter to use the region as a springboard for westward expansion. Without such abundant prey both on land and sea, borax might have stalled or even failed to reach the Sanctuary Plateau.

What lies ahead for borax and rompos on this alien continent? And what will be the fate of ottofoxes and banchisaraptors as they venture into the outer world?
The answers remain unknown...

...for now.