Penis Problems for Polar Bears

The polar bear, Ursus maritimus, is often publicised for its ever growing struggle to survive in a changing landscape. With sea ice loss due to climate change the amount of prey, such as ringed seals, available to polar bears has been restricted causing drastic population declines. It is predicted we will see a further 30% decline in population numbers over the next 35-50 years.

 

However loss of habitat is not the only problem polar bears are facing. A recent study carried out by Christian Sonne and his team at Aarhus University in Denmark has gained further insight into the effects chemical pollutants have had on polar bears in particular the baculum bone more commonly known as the penis bone.

 

Sea-Otter-Baculum

The baculum can be found in many mammals species even those as closely related to us as the chimpanzee. Although its function is not fully understood it is thought to aid mating success by maintaining stiffness during penetration. Size and density of the bone are important factors in relation to mating success.

 

Chemical pollutants known as endocrine disrupting chemicals (EDCs) are a huge environmental stressor in the Arctic. PCBs are a common type of EDC, they were first used in the 1920s in a wide range of products such as coolants and plasticisers and were only banned in 2001. They were released across the world mostly in industrialised areas and were then atmospherically transported to the Arctic where they are now present in high concentrations with contamination highest in the West. They break down very slowly and build up in the food chain to very high concentrations in apex predators such as polar bears through a process known as biomagnification.

 

Sonne’s study looked at 8 subpopulations of polar bears born between 1990 and 2000 in Greenland and Canada, in total 279 polar bears were included. The density and size of the baculum were measured and compared with EDC concentrations in published literature. It was found the density and size of the baculum were reduced as well as the size of the testes in contaminated areas, with a negative correlation between density and EDC concentration.

 

EDC concentration was lowest in Canada and Canadian bears were found to be in the best general health and had the largest and most dense baculum. The northeastern Greenland subpopulation was at the highest risk of negative health effect and had the least dense baculum. There was also a relationship between likelihood of fracture of the baculum and the density, less dense baculum can easily fracture making copulation impossible.

 

If the polar bears have high fetal and neonatal exposure to EDCs this disrupts normal bone development and may even induce osteoporosis. This research has given new insight into polar bear breeding and the long term effects of chemical pollution. This information could be used to better understand the reproductive health of polar bears in relation to their geographic location and therefore EDC exposure.

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Madeleine Berry

Wildlife enthusiast and recent Biology graduate of Queen Mary, University of London.

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