I know that most fish develop their sex after they’ve been born, spending a small time of their lives as sexually indifferent. I also know that some types of fish are hermaphrodites during their entire livelihood in the sense that are able to mate with either males or females… but polar bears?
The first incident of female hermaphrodite-like bears was during a survey that took place in Alberta, Canada, in 1984-1986. It was found that four female black bears and a female brown bear had abnormal sexual differentiation, meaning that each bear was a female with some degree of male genital development. The most extreme case was a 7-years-old female black bear that had a 120mm penis-like structure, with urethra, at the vaginal opening. The penis of an average male black bear is 165-180 mm.
Later in 1996, during a scientific study in the Arctic island Svalbard, two baby polar bears were captured, together with their 11-years-old mother. After a close examination it was found that the two babies had a normal vaginal opening together with a 20 mm penis, located where it would be located in males. The baby polar bears had both male and female sex organs, which made it difficult to identify their sex by the classical look-underneath-examination. By doing genetic studies scientists found that the twin polar bears where females as they couldn’t detect the Y chromosome, present only in males (females are XX and males are XY). They were classified as pseudo-hermaphrodites (“pseudo” means false; if it was a real hermaphrodite it would have both male and female genes, whereas here only female genes were detected). In two separate occasions (1990 and 1997) two more female adult polar bears were found in Svalbard, this time with an enlarged clitoris and they were also classified as pseudo-hermaphrodites.
Later, in 1999, more incidents of pseudo-hermaphrodite female polar bears with an enlarged clitoris were detected, eleven in Nunavat, Canada and one in Greenland. All of the above show that this phenomenon, the pseudo-hermaphroditism of female bears, is not limited to one country but it is spread out in various countries within and around the arctic region.
The cause behind the pseudo-hermaphrodite female bears has not been found. To say the obvious, it is difficult to carry on non-destructive long-term studies on polar bears. It has been suggested that it may be caused by external factors, such as their exposure to pollutants. We know that contaminants such as heavy metals (e.g. mercury), persistent organic compounds (e.g. PCBs, DDTs, dioxins, petrol by-products) and radioactivity from human activities are transported to the Arctic by winds, ocean currents and rivers. It has been seen that persistent organic pollutants specifically (known as POPs), travel together with the atmosphere from the southern countries from where they are produced and when they reach the colder climates they condense and fall into the sea contaminating the marine ecosystems. Thus, these contaminants enter into the plankton, which is eaten by the fish and they slowly travel up the marine food web. Marine predators, which eat bigger fish and mammals, contain the highest amounts of pollutants. The nature of some POPs, such as the organochlorine compounds (OCs), is such that they accumulate in the fat of the exposed organism, including human, and are not easily metabolised. Seals that store a lot of fat are one of the most contaminated animals and predators, such as polar bears that feed on seals, are greatly exposed to these contaminants.
In a study carried out in Svalbard island, blood samples taken from polar bears in 1967 and then in 1993-1994, were analysed for contaminants and then compared. The scientists analysed the samples for OCs that their production and use is now banned, at least in the developed world. These pollutants were: PCBs (synthetic compounds used as coolants and insulators in industry), DDT and metabolites (pesticide), toxaphene (insecticide), hexachlorobenzene (fungicide), lindane (pesticide) and chlordane (insecticide). All the chemicals were detected in the blood of polar bears and only two of these pollutants (one PCB and a DDT metabolite) showed to have decreased between 1967 and 1994. The amounts of the rest of the studied contaminants either remained unchanged or showed an increase.
In a different study, this time on Greenland polar bears, it was selected to examine the adipose tissue (body fat) for OCs. In the samples they took during 1999-2001 they found significant amounts of DDT (and its metabolite DDE), PCBs, hexachlorobenzene, chlordane and lindane. Fortunately, the concentration of most of these chemicals in the adipose tissue was lower than the one observed in another study in Greenland during 1990. It is believed that the level of OCs increased from 1960 to the late 1980s followed by a likely decrease from 1990 to 2007, which is confirms the decrease seen here.
OCs such as PCBs and DDTs are known to be endocrine disrupting chemicals (EDCs; see my previous article “Leave my hormones alone”) which interfere with the hormones in the body and may produce cancer, birth defects, diminished intelligence, immune and reproductive system abnormalities, such as the development of male sexual characteristics in females that we have seen here. Even though it is difficult to prove whether exposure to EDCs is the cause for the pseudo-hermaphrodite female polar bears of the Arctic region, the facts are very much in favour of it. First of all scientific data show that polar bears have more EDCs in their body than other animals. This means that the babies of the female polar bears are exposed to such chemicals during their embryo stage and lactation. Exposure to EDCs during early development may result to permanent abnormal sexual differentiation as it has been seen with other animals. Therefore it is very possible, even though not scientifically proven, that hermaphroditism in polar bears is due to exposure to these EDCs that reach the arctic region.
The production of many of the OCs mentioned above is banned but obviously the banning process was not accomplished in one day. With the developed world on the lead, countries started banning the use of POPs in the 70s and finally, in 2004, the Stockholm Convention on Persistent Organic Pollutants entered into force, where all its parties are required to eliminate or reduce the release of POPs into the environment. To date 170 parties/countries have signed the Convention. Although the use of some POPs is prohibited or restricted, most of them are still present in the environment and will take several years to clean them up. Even if their production is restricted, some of these chemicals exist within materials that are still used and thus, landfill and incineration sites are a continuous source of contamination. In addition, in many cases these chemicals were banned after they had been produced, leaving huge stocks of them stored in warehouses with no further directions of what to do with them. Sadly, it has been found that many of these chemicals are either sent to the third world or are mixed with other chemicals and are released in the market illegally.
With new chemicals entering the Arctic there is great uncertainty on what impact they will have upon the arctic ecosystem. Already, in human populations, Canadian Inuit mothers that feed on fish and seal blubber, have more POPs in their milk than mothers from other parts of the world, which is totally unfair as they have never produced or used these chemicals. Having these chemicals in their breast milk, their new-born babies feed on contaminated milk during their early development. I guess in few years, when the babies grow old, we will see what effects these chemicals had upon them… The irony is that chemical pollutants that are no longer produced or used in many parts of the world are contaminating the Arctic and its inhabitants, which was once the cleanest ecosystem on earth.