Arctic Lichen Frog Profile (1,566 words)
Author: Plilt
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Common Name: Arctic lichen frog
Latin Name: Fimbriatus arcticum
IUCN Status: Critically Endangered
A captive Arctic lichen frog resting on a rock, displaying her cryptic coloration.
Description: Like all lichen frogs, the Arctic lichen frog has a typical treefrog body plan, large eyed and long-legged with suckers on the toes. They're about sixteen centimeters long, though females are somewhat larger on average, and have particularly tough skin even for a lichen frog (a taxa well known for having a thick, heavily keratinized skin). Compared to other lichen frogs, their skin is relatively simple and lacks many of the frills and leafy structures that characterize related species. They have no photosynthetic capacity and are a dull gray.
Wild Arctic lichen frogs are usually malnourished. They often have a mild calcium deficiency. This deficiency is more common among male frogs than female frogs, who will eat males of their species if they grow malnourished enough.
The Qinngua Valley during summer.
Distribution: Despite their name, the Arctic lichen frog has a range that is entirely restricted to Greenland rather than being circumpolar. They inhabit the forests of the Qinngua Valley and are rare outside of it, though they are believed to have been common across much more of Greenland in the past, when more of the island was forested. It was formerly believed the species had two subspecies, a circumpolar green subspecies and a (much larger) gray subspecies from Greenland, but recent genetic work has determined that the two populations diverged half a million years ago and have very different lichen symbionts. However, as the Arctic lichen frog's holotype specimen was from Greenland, they retained the name while the circumpolar subspecies was renamed the boreal lichen frog (Fimbriatus borealis).
Evolutionary History: Fimbriatus is an old genus, stretching back at least ten million years. In comparison, the Arctic lichen frog is a young species that dates from Marine Isotope Stage 11 (often abbreviated MIS 11), an interglacial period stretching from 424,000 to 374,000 years ago. We believe that a small group of boreal lichen frogs were swept to Greenland in a storm during this period and were not present as a population earlier.
Unlike all other members of their group, the lichen symbiont of the Arctic lichen frog is non-photosynthetic. Several of the genes responsible for photosynthesis are nonfunctional or deleted in their lichen's genome. Photosynthesis would be as useful in their habitat as in the boreal forests of the rest of the Arctic, so the loss of the trait is believed to have been due to genetic drift in a small founder population. With the benefit of photosynthesis for all polar lichen frogs always rather marginal, there was no strong selective force preventing its loss.
There's evidence they were spread across much of Greenland during MIS 11. Ancient frog DNA recovered from below the ice is believed to have come from the species' ancestors, though it's not complete enough to know for sure. Regardless, if they were widespread during this period their range shrank dramatically during the next glacial period. Analysis of mitochondrial DNA shows a strongly reduced population during this time and similar population bottlenecks every time Greenland grew colder.
After the end of the Ice Age and prior to the Little Ice Age, the species ranged across most of the southwestern tip of Greenland. While forest cover was minimal, there was enough prey to support them, especially after Norse colonization of Greenland introduced house mice to the region. However, climate change eliminated most of this plant cover and the abandonment of the Norse colonies led to the regional extinction of the house mouse, and these two blows eliminated most of the species' habitat and their food sources. What remains is only a relict population.
Ethology: Male Arctic lichen frogs don't make calls, which is one reason they have not yet been discovered by mainstream science. Instead, they attract mates by releasing pheromones from modified apothecium that only appear after the lake ice melts and are quickly lost after the breeding season. Female frogs use their extraordinarily developed sense of smell to locate males from up to a kilometer away.
Being non-photosynthetic, Arctic lichen frogs don't sunbathe during the summer months like the rest of their taxa. Their lichen symbionts secrete even more antifreeze proteins than those of other lichen frogs, though, and they are particularly active in the snow layer. When hunting in winter, the frogs will burrow with only their nostrils and eyes protruding above the snow and ambush any prey that wanders past. This includes smaller frogs, though adequately fed Arctic lichen frogs aren't cannibalistic.
Life Cycle: Arctic lichen frogs congregate on the shores of Tasersuaq, a lake next to the Qinngua Valley, to breed during April. Courtship and mating happen at night to avoid predators; during the day the frogs hide past the treeline. Hatching and metamorphosis proceed quickly, within twenty days (one of the shortest maturation times of any frog), with tadpoles feeding on aquatic plants. Adults transfer the lichen symbionts to the eggs by rubbing up against egg masses. After the lichen colonizes the eggs, they secrete abundant toxins to protect against Tasersuaq's ravenous fish population.
Ecology: The frog is a ravenous predator of anything they can fit in their mouths. At sixteen centimeters, that includes rodents and newly hatched birds, and prior to the Little Ice Age both were likely their main food source. Today, however, they mostly feed on insects. During the breeding season for snow buntings they will range outside of Qinngua Valley and prey on their nests, and they will eat mice when they find them, but otherwise prey options are limited to invertebrates. This diet is broadly insufficient for the species' needs, especially their calcium and vitamin A requirements, and experiments in captivity indicate that the entire wild population is in a low-level state of malnutrition due to lack of food. This is partly due to their lichen symbionts. The strains of lichen found in Arctic lichen frog skin draw significantly more nutrients from the frog to sustain themselves. Producing the antifreeze proteins required to survive the winter is extremely energy intensive for the lichen.
In turn, Arctic lichen frogs are eaten by relatively few other species. Only the Arctic fox and raven eat them. Both avoid eating the skin and only consume the innards, which are not toxic. During the breeding season and after the tadpoles finish their final metamorphosis foxes and ravens will congregate on the shores of Tasersuaq to feast on frogs. Not only does this support the predator population, but this helps transport nutrients out of the lake and back into upland habitats. The area is somewhat more fertile than surrounding regions and modeling indicates that the presence of the frogs play a role in this.
As a consequence of their thicker skins, Arctic lichen frogs cannot easily absorb oxygen from the water. As a result, they're entirely reliant on their lungs and cannot survive underwater for as long a period as other frogs. Except during the breeding season, the adult frogs usually avoid water, though they'll immerse themselves in pools of snowmelt to rehydrate.
In-Situ Conservation Efforts: Arctic lichen frogs are rather unusual, in that while they're critically endangered they're predicted to be much less so in the future. The efforts of Greenland's government have succeeded at preserving the Qinngua Valley's forest cover and limiting pollution enough that the frogs can continue to breed. Global warming, while destructive to Greenland overall, will increase their available habitat and offer them more prey.
The main threat to the species in the wild, like all lichen frogs, is persecution. While the frogs are not anomalous, they have been concealed by the Jailors for a long time, by this point out of what we believe is inertia. The public discovery of a large frog species in a place where no frogs are supposed to exist, near populated areas well connected to global telecommunications, would invite too many questions about other cryptids. In the past the Jailors and the Bookburners have slaughtered wild populations of cryptids to keep their existence from being exposed and maintain control over so-called "normalcy," and it is not impossible that the Arctic lichen frog will suffer the same fate.
Ex-Situ Conservation Efforts: To protect against future persecution or bad luck wiping out the entire population, the Nunavut Sanctuary maintains a breeding population of the frogs. While the captive breeding program has been quite successful, the question of what to feed the frogs has been a source of controversy. Feeding them a diet of mice in addition to insects is has allowed them to breed prodigiously in captivity, and it keeps the frogs healthy as well. However, released frogs have very low survival rates for a captive breeding program even after being acclimatized to a pure arthropod diet. One of the potential reasons for this is that our breeding program has inadvertently eliminated a selective pressure ensuring that the population can survive while malnourished.
For the time being, the Nunavut Sanctuary has chosen to continue the captive breeding program as is, but also collect fertilized eggs from the wild population and freeze them using cryopreservative techniques. If the captive population proves incapable of surviving even as Greenland warms, we can use the frozen embryos to help create a more resilient captive population, modify the breeding program, and release more resilient frogs.