Humans aren’t making it particularly easy for polar bears to survive these days. Rising global temperatures are causing the Arctic to lose significant amounts of ice, some 54,000 square kilometers (20,849 square miles), each year, which polar bears depend on to hunt, rest and breed. One particular polar bear subpopulation experienced a 40% decline in numbers between 2001 and 2010, which was blamed on sea ice changes. To make matters worse, it now turns out that certain man-made chemical pollutants could be making their penis bones more fragile, which may adversely affect reproduction.
Yes, you read correctly, polar bears have a penis bone, or baculum as it is correctly termed. Many mammals possess a baculum, including certain carnivores, rodents, bats, primates (but not humans) and insectivores. Although scientists aren’t certain of its precise function, some believe it could assist copulation by making the penis more rigid, or alternatively may serve to stimulate the female, which could facilitate sperm transport and thus increase fertilization success.
Almost ten years ago, a team of scientists demonstrated that a group of pollutants known as organohalogens seemed to be negatively affecting the reproductive organs of polar bears. Females with high levels of these chemicals had smaller ovaries, and males had smaller testes and a shorter baculum. Now, taking this one step further, the same researchers have found that one particular family of organohalogens, known as polychlorinated biphenyls (PCBs), could also be affecting polar bear bone health, as high levels of these chemicals were associated with a decrease in penile bone density.
PCBs are a group of man-made organic chemicals which were domestically manufactured from 1929 until they were banned in the U.S. in 1979 following concerns over their potential impact on human and environmental health. During that time, they were used in a wide variety of products, such as electrical equipment, inks, adhesives and paints. Although their use is now severely restricted worldwide, PCBs are unfortunately typically very stable, meaning they persist in the environment. Furthermore, they can be dispersed over long distances and therefore crop up far from where they were being used, resulting in their accumulation in regions like the Arctic.
To find out whether they could be affecting polar bear health, researchers examined 279 penis bones from polar bears born between 1990 and 2000, representing eight different subpopulations. According to New Scientist, this bone was selected because it’s the easiest to get hold of as many hunters keep them as a trophy. Using X-ray machines, the researchers looked at the mineral density of each bone and then compared this with data on environmental PCB levels.
They found that high PCB levels were associated with lower penile bone density, although this relationship was not quite statistically significant. However, they also found that PCB concentrations could be within a range that may negatively affect both reproduction and development, which is why the researchers believe the PCBs are likely affecting polar bear bone mineral density.
While a reduction in bone density is not good for overall health, a more fragile penis bone could be particularly problematic for survival of the species because fractures could reduce the chances of successful mating and fertilization. The researchers are therefore calling for further research to investigate whether these chemicals are indeed affecting reproductive health, which is important if we want to conserve the species.
[Via New Scientist and Environmental Research]