The European brown bear (Ursus arctos arctos) populations in the Cantabrian Mountains are currently in a phase of recovery. This is a significant turnaround considering that in the 1990s, their numbers dwindled to just over fifty individuals, despite once roaming almost the entire Iberian Peninsula.
What is the current state of their health, and what are the prospects for their continued recovery? A multidisciplinary group of Spanish scientists set out to answer these questions by analyzing bear feces and the parasites they contain to understand how well these bears are adapting to their environment.
The analyses were conducted in the parasitology laboratory of the Faculty of Veterinary Medicine at USC.
Studying wildlife can reveal strategies and realities that are far removed from human health perspectives, offering valuable insights for conservation efforts. For instance, understanding that a bear’s life goes through various phases over the year is crucial for appreciating their adaptability to their environment.
An adaptive immune system reacts based on environmental variables. There is no single response model to parasite infestation in an organism, but the immune system is always involved. When populations decline to the point of inbreeding or suffer a drastic reduction in genetic variability, this mechanism is at risk. Animals may start showing signs of maladaptation to their environment, and parasitic infections can become fatal.
In healthy populations, however, parasites coexist in a balanced way. Their presence actually promotes a response that fosters an individual’s survival. Therefore, parasitism itself does not constitute a health problem (parasitosis does).
Like any living organism, parasites seek the best way to survive and employ strategies to meet their needs through their hosts. When they reach the bear’s digestive system, certain species find an ideal environment for reproduction, which often results in the expulsion of eggs into the environment along with feces.
Once on the ground, an essential development phase occurs, leading to the infective stages. When ingested, they begin the internal cycle anew in the bear.
The data obtained from parasitic counts in brown bears over a two-year period provide interesting and useful information about the health status of this population.
Firstly, they discovered that there is seasonality related to the activity of their hosts. The time of year influences their feeding habits, and thus, parasitic frequencies vary.
In the period before entering their torpor (a light hibernation), bears undergo an intestinal cleansing process, expelling large quantities of gastrointestinal nematode eggs without it constituting a parasitic disease.
After emerging from winter, the breeding season begins, and the parasitic presence changes significantly. Helminths that were frequently detected in autumn and winter become rare and disappear from their digestive system. At the same time, the presence of trematodes, a species shared with wild and domestic ruminants, increases considerably. This is due to a primarily herbivorous diet and insectivory in the case of bears.
The seasonality of parasitic counts in feces provides valuable information about the adaptation of brown bears to their environment. It suggests that bears employ appropriate behaviors for parasite elimination and maintain an immune system capable of coexisting with pathogens without developing disease. This almost symbiotic relationship is also evidence of selective feeding adapted to specific needs according to the time of year.
With this information, we can compare our study’s conclusions with stable populations without genetic decline. It seems to confirm similar results, indicating that the Cantabrian bears are likely evolving towards the recovery of balanced populations from a health perspective.
