Monday, April 30, 2007

Roarke's New and Hot (Week 5)

Ducks and the Coevolution of Genitalia

In class, we've discussed some interesting examples of both sexual selection and coevolution. A recent study of the genitalia of a strange species of duck provides a fascinating example of sexual coevolution.

The duck in question - the Meller's Duck from Madagascar, is certainly a rare breed. While 97% of all bird species don't even have phalluses, the Meller's Duck has incredibly long phalluses, sometimes as long as the length of its entire body.

Previous scientists assumed this long phallus evolved as a result of competition between males who wanted to get their sperm in as far as possible during forced copulation to increase their chances of producing offspring. Dr. Brennan, however, points instead to the strong correlation between long male phalluses and elaborate female genital defenses in the same species, and argues that male and female Meller's Ducks are locked in a constant sexual arms race that has resulted in the development of such unusual structures. The females have evolved elaborate oviducts with pockets and spirals to limit the success of forced copulation, and the males have in response evolved longer phalluses that allow them to force copulation despite the females' defensive measures.

Dr. Brennan's study is the clearest example of genital coevolution in vertebrates uncovered so far, though Dr. Brennan believes that more subtle examples of coevolution are likely to be discovered in other species with further research.

Read the full New York Times article here, it's quite interesting!


chickenpox said...

This reminds me of the subtle differences that I addressed in my presentation last week, whereby small changes in rhetoric can change the entire paradigm of sexual reproduction from competitive to cooperative. It's interesting to me that the article presents females and males as competing, much like two species in a parasitic relationship; why would females need to evolve "defenses" against copulation? Is it not in their best interest, as well as the male's, for the male's sperm to most efficiently reach their eggs? I would be interested to see if the researchers studying these ducks had any alternate hypotheses that accounted for this.

chickenpox said...

Forgot to sign that comment...


chickenpox said...

I agree with Becca, I don't understand why nature would try to make it harder for the organism to produce offspring. Wasn't it the point to pass down your genetic information as much as possible? We should look up the population trends for this type of duck and see if they're declining in number...

chickenpox said...

I think the point of the female's defenses is to prevent forced copulation, so that the females don't have to bear the children of males who won't be around to take care of the kids. Apparently most species of ducks are pair-bonding, so for the females, it's to their reproductive advantage to be fertilized by males who will stick around afterward and invest energy in child rearing (i.e. males who don't rape them). I think part of it is that the female's defenses prevent forced copulation but not normal copulation.