#141: Trolls - a species profile.

This piece has also been published over on the new science communication site, Scientific Kitty. 

Troll Hunter is the documentary that exposes the existence of trolls in the Norwegian mountains. I cast a biologist's eye over these elusive giants. (May contain spoilers)

With their 1000-year lifespan, rock eating tendencies, and slight aversion to light, Øvredal’s trolls are the most unlikely of creatures. But it turns out that they do exist, and have just been hiding in the mountains of Norway. So let’s suspend our disbelief and take at look at the biology of these beasts.

Fundamentally, there are two types of troll, which constitute at least two unique species – the mountain and forest dwellers. Where the troll species line is drawn, however, is unclear, with a variety of sub-types of troll within each general group. Trolls are fiercely territorial mammals, living either as lone individuals or in close social groups. They “eat, shit, mate with and devour everything around them.” Mostly rocks.

Evolution
A major question that arises as we consider the trolls’ existence is their evolution. With an incredibly slow lifecycle and very low reproductive output (lifespan: 1000-1200 years, average offspring produced: 1), adaptation will have been an incredibly slow process. Their life history falls at the extreme “k-selected” end of the spectrum, and their adaptation to environmental and situational changes will have been very slow.  Furthermore, small population sizes (and associated low genetic diversity) caused by very large territories, and a constant vulnerability to basic elements (light), mean that their evolution is almost miraculous. It is likely that they expanded into their current lifestyle and size around the early Cenozoic period, following the demise of the dinosaurs.

The trolls’ greatest asset, that has undoubtedly been a primary reason for their survival despite the evolutionary constraints of their slow life cycles, is their nutritional versatility. That is, “when you eat rocks, it isn’t hard to survive”. Of course above all, the major barrier this fascinating species has had to overcome is their susceptibility to explosion when exposed to light. They therefore have an obligate nocturnal behavioural pattern, and this may in fact have allowed them to exploit night-time resources and avoid conflict with other megafauna during their early evolution.

Being confined to darkness has lead to a strong reliance on a powerful sense of smell, as can be seen by their capacity for sniffing out the scent of people of certain beliefs (although it is as yet unclear whether this penchant for religious folk extends beyond just Christianity – further research is needed). Trolls are not, however, totally blind, and the extra heads grown by certain troll variants reveal the importance of visual communication in social situations. These “protrusions” (for they are not fully functioning heads) primarily play a role in mating rituals and intra-specific conflict, and are likely to have evolved along a similar evolutionary pathway as that of the peacock train and battle cries of red deer stags.

Living underground and deep inside mountains means that trolls are likely to share certain characteristics with burrow dwelling rodents. Living in enclosed environments brings problems of temperature control and oxygen access, and as such they will have specialised respiratory physiology.

One defining feature of the troll life history is likely to be a huge amount of parental investment, both before and after birth. With a gestation period of 10-15 years, the parental investment is huge, and given that most trolls reproduce only once in their lifetime, the expenditure afforded on offspring is large. Parents will defend their offspring with violent determinism, and likely prioritise the life of their child above their own, with young trolls likely only becoming fully self sufficient after a few hundred years. The role that social interactions in communal dens may play in parental care is unclear, although given the species characteristics, cohabiting groups are likely to have a high degree of relatedness and hence altruistic care of offspring is not unlikely.

These trolls present a truly unique case of evolution, and require a great deal of study to see how they managed to overcome the problems of their lifestyle. It is unclear where their closest extant relations are, and whether they are more closely related to the bears or primates, or a monophyletic taxa unto themselves. The benefits of being huge and able to eat almost anything seem to have outweighed the issues they face. It is hard to see how their fragile lifestyle ruled by an inability to deal with vitamin D has allowed them to flourish, but seemingly it has.

On a worrisome note, however, I fear that the trolls face a troubled future. As mentioned above, they will adapt very slowly to large changes in the environment, and as global warming rapidly alters their habitat, it is hard to know if they will be able to amend their behaviour to fit with the new landscape. They’re unlikely to take up sunbathing and bask in the joy of a warmer world. If ever there was a good reason to curb emissions and think about the planet, this is it. Save the trolls, before it’s too late. 

Troll hunter is in cinemas now, and provides a witty, original and entertaining break from the norm. Go check it out.