Polar bear penis bone may be weakened by pollution

Earth 26 January 2015
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PCBs are one thing you don’t want to take to spice up your sex life

(Image: Paul Nicklen/NGS)

First climate change, now penile fracture – polar bears have got it pretty rough. Chemical pollutants may be reducing the density of the bears’ penis bones, putting them at risk of breaking this most intimate part of their anatomy.

Various mammals, though not humans, have a penis bone, also known as penile bone or baculum. Its exact function is unclear: it could be just a by-product of evolution, or it may help support the penis or stimulate the female during mating.

Christian Sonne at Aarhus University, Denmark, and colleagues had previously shown that polar bears with high levels of pollutants called organohalogens in their bodies had both smaller testes and a smaller penis bone.


Sonne and his team have now shown that a particular class of organohalogens, the polychlorinated biphenyls (PCBs), is associated with a less dense baculum. This could prevent successful mating, the team suggest.

PCBs were used industrially for several decades from the late 1920s onwards. They had hundreds of applications, including in production of paints and rubber products. Then evidence emerged that they can harm health and cause cancer, and were banned by a UN treaty signed in 2001. But they are slow to break down, so can accumulate in the environment.

Polar deposits

The Arctic has particularly high concentrations of pollutants like PCBs, says Margaret James at the University of Florida in Gainesville. “These chemicals enter the atmosphere at lower latitudes where they were used, and are then deposited down from the cold polar air, so Arctic animals are more highly exposed than animals in more temperate or equatorial regions.”

To see what effect high concentrations of PCBs might be having on the bears’ mating, Sonne’s team collaborated with researchers in Canada to examine baculum specimens from 279 polar bears from north-east Greenland and Canada, all born between 1990 and 2000.

They studied this bone because it’s easy to come by. “It’s the kind of bone that’s taken by local trophy hunters and subsistence hunters. It’s an actual sign that you have hunted and shot a bear,” says Sonne.

They used a hospital X-ray technique to calculate the density of calcium in each bone. Comparing their figures against data on locally recorded levels of a range of harmful pollutants, they found a link between high PCB levels and low baculum density, although James notes that the analysis was not strong enough statistically to prove that PCBs are the cause of lower bone densities.

Even though the function of the polar bear’s penile bone is unknown, Sonne believes that a weaker baculum is likely to be problematic during mating. “If it breaks, you probably won’t have a bear which can copulate.”

Twin stresses

Sonne believes that, especially considering the stresses on polar bears from climate change, chemical pollutants are likely to be having an effect on populations too – but it’s difficult to say how much of one. “We don’t know because it’s so hard and expensive to go and do satellite tracking and repeated measures of the same bears,” says Sonne.

Andrew Derocher at the University of Alberta in Edmonton, Canada, agrees that the interaction between climate change and pollution is a concern. Climate change increases break-up of ice and so reduces the bear’s ability to forage. “Skinny bears have higher levels of circulating pollutants, so the concern is that a bear that is nutritionally stressed may become more vulnerable to the effects of pollution at the same time,” says Derocher.

Sonne and his team now want to investigate whether food stress and pollutants have been driving evolutionary change in the bears. He believes that the chemicals are likely to have killed many bears over recent decades, so may have shaped changes in the species’ genetic make-up.

Journal reference: Environmental Research, DOI: 10.1016/j.envres.2014.12.026

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