White Ibis (Eudocimus albus)
White Ibis (Eudocimus albus)

Back in October 2008 I wrote about the phenomenon of same-sex marriage between female Laysan Albatrosses at the Hawaiian island of Oahu. There I noted a report in the August 2008 edition of the Royal Society’s Biology Letters entitled Successful same-sex pairing in Laysan Albatrosses by Linda C. Young, Brenda J. Zaun and Eric A. VanderWerf:

Thirty-one percent of Laysan Albatross pairs on Oahu were female-female, and the overall sex ration was 59% females as a result of female-biased immigration. Female-female pairs fledged fewer offspring that male-female pairs, but this was a better alternative than not breeding. In most female-female pairs that raised a chick in more than one year, at least one offspring was genetically related to each female, indicating that both females had opportunities to produce.”

That report was followed up earlier this year with reports from New Zealand that a pair of female Royal Albatross had successfully raised a chick. In an article in The Times of London titled Lesbian albatrosses become proud parents Sophie Tedmanson reported that:

It began with a love triangle between two female royal albatrosses and a wannabe male suitor. But girl power prevailed and the ladies dumped their man and set up a same-sex family together at the world’s only mainland albatross breeding colony in New Zealand. Last week the female seabirds successfully incubated a chick in their all-girl household in the Royal Albatross Colony on South Island, which was hailed by Prince Charles when he visited in 2005 for its successful breeding programme for the rare and endangered birds.

Same-sex pairing is not unusual among the seabirds – the New Zealand breeding colony has had three female pairings over the past 70 years, and at a colony in Hawaii almost a third of chick-raising pairs of Laysan albatrosses have been found to be all-female. But what is unusual about this pair is that they have successfully incubated a chick which is also one of 17 to hatch from 17 eggs at the colony, the first time in 16 years the colony has had a 100 per cent success rate of fertile eggs produced in one season. The previous female pair at the colony lasted for 20 years, but 90 per cent of their eggs were infertile.

Now in a paper – again presented by the Royal Society – in The Proceedings of the Royal Society B (Biological Sciences) entitled “Altered pairing behaviour and reproductive success in white ibises exposed to environmentally relevant concentrations of methylmercuryPeter Frederick of the University of Gainesville, Florida and Nilmini Jayasena of the University of Peradeniya, Sri Lanka have released their findings from research into the effects of exposure to mercury pollution of a population of American White Ibises (Eudocimus albus) from south Florida that consumed methylmercury (MeHg), the most easily absorbed and very toxic form of environmentally available mercury.

Their results indicate that the breeding success and viability of wild White Ibises could be negatively affected by exposure to mercury, causing males to pair with other males. Birds that absorbed the mercury were more likely to enter into same-sex pairings than birds that were not exposed – a previously unknown phenomenon in wild populations of this species.

The Abstract for of the paper says that:

Methylmercury (MeHg) is the most biologically available and toxic form of mercury, and can act as a powerful teratogen, neurotoxin and endocrine disruptor in vertebrates. However, mechanisms of endocrine impairment and net effects on demography of biota are poorly understood. Here, we report that experimental exposure of an aquatic bird over 3 years to environmentally relevant dietary MeHg concentrations (0.05–0.3 ppm wet weight) resulted in dose-related increases in male–male pairing behaviour (to 55% of males), and decreases in egg productivity (to 30%). Dosed males showed decreased rates of key courtship behaviours, and were approached less by courting females in comparison to control males. Within dosed groups, homosexual males showed a similar reduction when compared with dosed heterosexual males. We found an average 35 per cent decrease in fledgling production in high-dose birds over the study duration. These results are of interest because (i) MeHg exposure is experimentally tied to demographically important reproductive deficits, (ii) these effects were found at low, chronic exposure levels commonly experienced by wildlife, and (iii) effects on reproductive behaviour and sexual preference mediated by endocrine disruption represent a novel and probably under-reported mechanism by which contaminants may influence wild populations of birds.

Over at NatureNews, Joseph Milton notes the following from his examination of the paper (which I’ve not been able to access a complete copy of):

Birds exposed to any mercury displayed courtship behaviour less often than controls and were also less likely to be approached by females when they did. As the level of mercury exposure increased, so did the degree and persistence of homosexual pairing. Males that engaged in homosexual parings were also less likely to switch partners from year to year, which Frederick says ibises tend to do if they have been unsuccessful in mating during their first breeding season. Because the levels of methylmercury used in the experiment were typical of those found in the birds’ natural wetland habitats, “the implication is that this is probably happening in wild bird populations”, says Frederick.

Milton notes that Peter Frederick cautions against leaping to conclusions that mercury consumption may cause gayness:

Frederick and Köhler both caution that the findings cannot simply be extrapolated to other species, even of birds. “Their behaviour may be less fragile and more robust to methylmercury,” says Köhler. Frederick is concerned that “people will read this and immediately jump to the conclusion that humans eating mercury are going to be gay. I want to be very explicit that this study has nothing to say about that,” he says.

I note that homosexual behaviour in animals is relatively commonplace and has been the subject of controversy – as much for the fact that it happens as for the cultural implications of transferring the emotional and political baggage that accompanies much of the discussion of homosexuality in human society. As this Wiki article notes, use of the term ‘homosexuality‘:

…has been controversial for two main reasons: animal sexuality and motivating factors have been and remain poorly understood, and the term has strong cultural implications in western society that are irrelevant for species other than humans. Thus homosexual behavior has been given a number of terms over the years. When describing animals, the term “homosexual” is preferred over “gay”, “lesbian” and other terms currently in use, as these are seen as even more bound to the human condition.

And homosexual behaviour in animals may be more widespread and occur for different reasons than in humans than previously believed. In this article from LiveScience, Clara Moskowitz notes that:

According to University of Oslo zoologist Petter Böckman, about 1,500 animal species are known to practice same-sex coupling, including bears, gorillas, flamingos, owls, salmon and many others. If homosexuality is natural in the animal kingdom, then there is the question of why evolution hasn’t eliminated this trait from the gene pool, since it doesn’t lead to reproduction.

It may simply be for pleasure. “Not every sexual act has a reproductive function,” said Janet Mann, a biologist at Georgetown University who studies dolphins (homosexual behavior is very common in these marine mammals). “That’s true of humans and non-humans.”

Some scientists have proposed that being gay may serve its own evolutionary purpose. “It could be a way that you strengthen bonds — that’s one hypothesis,” Mann told LiveScience. “Another is that it could be practice for heterosexual sex. Bottlenose dolphin calves mount each other a lot. That might benefit them later on.” Marlene Zuk, a biologist at the University of California, Riverside, suggested that gay individuals contribute to the gene pool of their community by nurturing their relatives’ young without diverting resources by having their own offspring.

One thing that does seem to be exclusive to humans is homophobia.

posted: 16 May 2008

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