Friday, November 07, 2008

Homosexual Beetles Increase Chances of Reproducing?

For decades, homosexual behavior observed in male flour beetles has perplexed animal behaviorists.  The beetles, 3-millimeter long Tribolium castaneum, found in temperate areas, have been the focus of several studies in an attempt to solve the mystery of their homosexual tendencies.  From an evolutionary perspective, homosexuality is counter-productive to the species’ fitness, though it has been observed in many animals, including insects, penguins and primates.  There are several theories to explain the phenomenon.  Some scientists believe the males copulate with other males as practice before attempting to mate with females.  Others suggest that the males need to get rid of old, less effective sperm before mating with females.  Other scientists have even suggested that homosexual behavior is a way of exerting social dominance over other males.  A new study threw a wrench in these hypotheses.

The study, headed by evolutionary ecologist Sara Lewis, of Tufts University, began by marking male and female flour beetles.  The team tracked their individual sexual exploits, while monitoring the paternity of any offspring born in the group.  Their results showed that homosexual encounters did not improve the male’s sexual success with females, and found no connection between homosexuality and social dominance.  What they did find came as a shock:  the sperm leaked by one male onto another during homosexual encounters could actually inseminate a female who later copulated with the second beetle.  In other words, a beetle could inseminate a female without directly breeding with her.  This proves the beetles’ homosexuality a reproductive benefit, as the males can inseminate females without spending the energy necessary for finding and mating with them.  The results were so surprising to the researchers, that the experiment was repeated several times, with the same results.  This research is a triumph for evolutionary biology, as homosexuality in animals is often written off as confusion, and is rarely explored objectively.  

Update: (11/11/2008)

Though zoologists often avoid the topic for fear of crossing into political debate, the fact is that homosexuality has been observed all across the animal kingdom, in captivity and in the wild.  It has been observed in insects, birds, sheep, fruit bats, dolphins, apes and monkeys.  At the New York Central Park Zoo, two male penguins named Ray and Silo have been displaying classic pair bonding behavior for 6 years.  This behavior includes entwining of necks, mutual preening, flipper flapping, and mating, while ignoring females.  In the wild, some male ostriches only court their own sex, and pairs of male flamingos have been known to build nests and raise foster chicks.  Homosexuality in females has been observed in Japanese macaques, though scientists are still unclear on the reason.  It is possible that these relationships have an unknown adaptive pay off, or they could just enjoy it.  In bonobo apes, a close relative of humans, 75% of all sex is non-reproductive, and almost all bonobos are bisexual.  Scientists believe that the bonobos use sex to resolve conflicts in the group.  Temporary homosexual partnering in immature dolphins is believed to be a way to form lifelong bonds.  Explaining he mystery of homosexuality in animals has only begun.  Robin Dunbar, a professor of evolutionary psychology, argues that homosexuality may be a by-product of something else and hold no evolutionary function at all. 

Homosexuality Debate

Bonobo Apes

-Jane de Verges (8)


At 2:07 PM, Blogger PWH said...

This is really interesting, I would have never guessed that one male could inseminate a female through another male! Was there any evidence that the homosexual males did father more children because they had the advantage of possibly being able to mate with females and to also have their sperm transfer from another male to a female? I think this is really amazing! Do you know if they are going to see if this works on other insects?

-Tara Quist

At 4:48 PM, Blogger PWH said...

Wow...amazing discovery. But i have two questions..why would a male allow another male (homosexual) to lower his own chances to inseminate a female with his own sperm thus decreasing his own reproductive success? Second which males do this....i'm assuming maybe older males with less energy would participate in this homosexual behavior in order to indirectly increase their own reproductive success without having to undergo copulation.

-Joanne Philippeaux

At 10:11 PM, Blogger PWH said...

Homosexual behavior in flour beetles is very interesting. However, how come they find totally different observations than other biologists? Can you explain a little bit more about this new experiment?

So Jin Lee

At 11:01 PM, Anonymous Allison Cornell said...

Whoa! I never would've thought of that as a possibility! The chances of another male's sperm inseminating the female rather than (or in addition to) that of the male who is copulating with the female seems very low. How often did it happen? The sperm of these beetles must be extremely fertile. How long can the sperm live on another male?

Allison Cornell (8)

At 5:33 PM, Anonymous Anonymous said...

This is very interesting, I've heard of certain animals "stealing" mate and such. But this is a great way of passing genes without doing all sorts of extra work.

Duy Nguyen

At 7:40 PM, Anonymous Anonymous said...

This is very different and interesting news, I would never have guessed beetles use this method to reproduce. Do any other species use this method? I wonder what the reason behind this method is, is it purely to save energy? Because they don't necessarily know if its going to work right?

-Julie Riley

At 8:26 PM, Anonymous Anonymous said...

Wow, this is really interesting. What's the viability of flour beetle sperm? I assume that outside of the reproductive tract, sperm don't live very long, which would imply that the male beetles being mounted then go and mate with a female very soon after being with the other male. I wonder if the female beetles have some sort of sense that tells them if a beetle has recently been with another male? It would seem to me that a female beetle would have a better chance of getting pregnant by a beetle that has two sets of sperm to offer, which might make mating with a male who exhibits homosexual behavior in her best interest.

-Corinne Delisle

At 8:43 PM, Blogger PWH said...

WHOA! HOW COOL! Where they able to study the genetics of the F1 generation beetles (the offspring) to see if indeed there were two fathers so to speak? How did they determine this, basically what were their methods? I can see how this behavior would seem counter-productive. As I'm understanding it, the homosexual behavior is beneficial to the species, and not the individual. How would this effect natural selection? Would it take longer to select in species that exhibit homosexual behavior and cross-fertilization? Thanks for your post!

-Amanda Sceusa

At 11:01 PM, Anonymous Anonymous said...

Interesting article. It seems like a very logical reason to why these beetles would interact in homosexual behavior. It is funny how sometimes what seems like a relatively simple explanation to an unknown behavior. I wonder if there is a trade of between the homosexual activity and actual mating with female beetles.

Alex Pavidapha

At 11:27 PM, Anonymous Anonymous said...

I never would have suspected that. How do these animals live? Do they live together mostly, or are they spread out? I wonder how good the chances are of finding a mate, and if this is a reason for their behavior. I also wonder why more species haven't evolved this way, as it seems like a good way to increase ones chances of spreading it's genes. Is the beetles sperm able to live longer while exposed to air then other animals sperm? Maybe this aided in the evolution. Neat blog.

Rachel Carboni

At 8:47 AM, Anonymous Anonymous said...

I saw on documentary TV shows that there were many species enjoying homosexuality. The programs did not really explain why such behaviors are seen. It would be interesting to see whether homosexuality increases chance of mating and reproduction in other animals too.

-Yi, Jeongsang

At 3:54 PM, Anonymous Anonymous said...

Wow, this is fascinating! I wonder if the males actually realize what they are accomplishing or if they are just mistaking males for females...nice work!

Ericka Adey

At 10:21 PM, Blogger Cecelia said...

That's really interesting, and unexpected. But does this apply to some of the other animals you mentioned?

-Cecelia Hunt


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