source– Male ducks respond to sexual competition by growing either an extra-long penis or a nub of flesh, a new study finds. The unusual phenomena occurred in two species studied: the lesser scaup (Aythya affinis) and the ruddy duck (Oxyura jamaicensis). It suggests that penis size — in line with many traits and behaviours meant to impress or allow impregnation of the opposite sex — involves a trade-off between the potential to reproduce and to survive.
Patricia Brennan, an evolutionary biologist at Mount Holyoke College in South Hadley, Massachusetts, compared the penises of ducks kept in male–female pairs to those housed with multiple males per female.
“If they were alone with a female, the males just grew a normal-sized penis, but if there were other males around, they had the ability to change dramatically,” Brennan says. “So evolution must be acting on the ability to be plastic — the ability to invest only in what is needed in your current circumstance.”
Because evolutionary success relies on reproduction, genitals are adapted to meet the varied circumstances that every animal faces. Some male ducks, for example, have penises in the shape of corkscrews to navigate the labyrinth-like vaginas of their female counterparts. An earlier study by Brennan found that females’ anatomy evolved to prevent access to undesirable males who force copulation. To mate successfully with their chosen partners, Brennan says, female ducks assume a posture that allows males to enter them fully and deposit sperm near eggs.
However, evolutionary changes in the size of body parts are generally thought to happen over generations, not within an individual’s lifetime. Brennan wondered whether ducks might buck this trend because some species’ penises emerge anew every breeding season and degenerate afterwards. Similarly, acorn barnacles (Semibalanus balanoides) — hermaphroditic, shelled sea creatures cemented to rocks — generate their penises only when it’s time to mate. Because they use their penises to grope for other barnacles to inseminate, the organ’s length depends on the proximity of a barnacle’s neighbours.
Brennan and her colleagues fenced off habitats so that ducks would live either in pairs or in groups with almost twice as many males as females for two breeding seasons over the course of two years. The lesser scaups grew longer penises when they were forced to compete for females than when they were coupled up. A larger reproductive organ likely improves their chances of fertilizing an egg.
But the results of the social environment on ruddy ducks were more complicated. During the first year, only the largest males in the groups grew long penises (about 18 centimetres each), whereas smaller males developed half-centimetre stubs. In the second year, smaller males grew normal-sized penises, but they lasted for just five weeks, whereas the largest males kept their penises for three months.
Clues may lie in the drama of ruddy-duck life. The birds have some of the largest penis-to-body ratios found in nature — with penises sometimes longer than their bodies. “I can’t imagine they could grow any longer,” Brennan says. The birds have also been known to fight to the death, which suggests that smaller ruddy ducks might be too stressed to develop penises normally. “Bullying may increase stress hormones, and those could counteract the effects of androgen hormones” that control penis growth, Brennan says.
This response to stress could be adaptive. The same androgen hormones that trigger penis growth every season in birds also underlie colouration. They cause the duck’s feathers to turn from dull brown to chestnut when it’s time to breed, and their bills to go from grey to bright blue. To females, the wardrobe change signals a male’s readiness. To neighbouring males, it foreshadows a fight. “I think the small ones go through it quickly so that there’s less danger of getting beaten up,” Brennan says.
The study is “really interesting”, says Charlie Cornwallis, an evolutionary biologist at Lund University in Sweden. “This suggests there is a cost to having a large penis because individuals are investing according to the competition they face from other males.” Cornwallis says that few studies have investigated the effect of environmental and social conditions on penis size, and that these evolutionary trade-offs could be more common than imagined.
(I know I posted pretty much the whole article but it was too good not to)
Oh, man. What world we live in. There’s really not a lot to add to this headline, but I’m going to fight my better instincts and do it anyway. First off, who’s idea was it to do this study in the first place? What kind of messed up penis was that duck working with that triggered someone to be like, “wow, that’s way different than what everyone else has, I should do a study to find out everything I can about two specific species of ducks’ penis sizes?” Like what the hell? I thought size didn’t matter? She told me it was fine and that I shouldn’t be embarrassed about it, but I guess not. Looks like I’ll have to start watching my back (or front, I suppose) to make sure I’m not the one who sets off the study about human penis size. That would be pretty mortifying.
I came out of this really feeling for duck men. Sounds like they live in some kind of eternal hell. They grow a new penis every year during mating season only to have it deteriorate and decay until it falls off? No thank you. I mean, sure it might be nice to play the penis lottery if you’re sick of the one you have, but talk about a terrible feeling to have. Just knowing you’ve only got a penis for one season out of the year. Not a great position to be in.
And then I’ve got to call out this article a little bit, too. They were penis-shaming everyone. The ones with penises longer than their bodies. The ones with fleshy nubs. The ones with corkscrew penises. How else are my duck friends supposed to navigate the “labyrinth-like vaginas of their female counterparts?” Everything can’t be irregular. You can’t point and laugh at everybody. Duck penises are like snowflakes- no two are the same, and that’s perfectly okay. I’d like to see the duck they based their concept of normalcy on. What kind of penis did he have that mating season? Something perfectly shaped and pliable but is also the ideal size? Cool. Not everyone can be Superman. Sorry, but I’m here to stick up for the little guys (and the irregular shaped guys). Have some empathy, here. Imagine being a duck and seeing this walk by:
What choice do you have but to grow an irregularly shaped penis? Sorry, but I refuse to throw dirt on duck males’ good name. To all the haters: lay off. It’s not the size of the boat, it’s the motion of the ocean. Sorry not everyone has a cookie-cutter penis. To all the duck males reading this: you’re not alone. You may be catching heat from all sides, including from your own potential mates, but you’ve got at least one friend out there. I’ll stand by you through your darkest days, because sometimes in times of penis-related stress, all you need is a shoulder to cry on.
Brian's Den 