MALLARD PENISES BECOME LARGER THE MORE TIME THEY SPEND WITH OTHER MALLARDS
Nature has provided quite the variety of penises across different species, with many being quite strange and even shocking. But male ducks penises more than fit the bill on the strange meter. They have dis-proportionally long members that are corkscrew shaped that are the result of an evolutionary battle of the sexes. And now to make things even stranger, researchers have recognized that mallards that hang out together end of having even longer members than they would otherwise. It’s enough to give one pause.
WAR OF THE SEXES VIA EVOLUTION: MALE DUCKS ARE CORKSCREW, FEMALE DUCKS ARE THE OPPOSITE
But it’s the evolutionary battle of genitalia between the duck sexes that leaves ducks where they are today, which is quite the strange scenario. Female ducks tend to pair off with a mated partner during breeding seasons but still get harassed by mallards who never cease their advances. Scientists who make a study of duck breeding habits believe that roughly a third of all duck matings are forced, which has resulted in a twisted reproductive tract for females in response to restore their selective choice in partners. So while males penises corkscrew in the clockwise, female ducks have evolved in the reverse. So the vast majority of duck matings don’t result in fertilization.
33% OF DUCKS MATING ARE “RAPE”, LEADING FEMALE DUCKS TO PHYSICALLY MAKE SEX AS DIFFICULT AS POSSIBLE
Given the extent of this genital arms race, Patricia Brennan, an ornithologist at Mount Holyoke College, hypothesized that intense male-on-male competition may affect the development and shape of a penis over the course of a male duck’s lifetime. And so she conducted an experiment, the results of which now appear in The Auk: Ornithological Advances.
Brennan’s experiment involved two species, the very promiscuous Ruddy Duck and the pair-bonding Lesser Scaup. As would be expected, Ruddy Ducks have long members, whereas Lesser Scaups, as their name unintentionally suggests, do not. The researchers studied captive ducks of both species across two breeding seasons at the Livingston Ripley Waterfowl Conservancy in Litchfield, Connecticut, USA.
MALLARDS HANGING WITH THE GIRLS HAVE SMALLER PENISES- HEN-PECKERED?
During the mating season, male ducks were either kept together with other males (the experimental group) or with a single female (the control group, lucky them). When measuring the male penises afterwards, the researchers found that the Lesser Scaup featured longer penises on average when housed with other males. This implies that Brennan’s hypothesis of “phenotypic plasticity of penis morphology” was correct, but things were a bit more complicated for the Ruddy Duck.
SOME MALLARDS HOUSED TOGETHER MATURE MORE SLOWLY, BUT PENISES CATCH UP WHEN EXPOSED TO FEMALES, BUT ONLY BRIEFLY
For Ruddy Ducks, the act of being housed with other males caused some to experience growth and reproductive delays. Many Ruddy Ducks failed to reach sexual maturity until the second year of the experiment (most Ruddy ducks typically reach sexual maturity at two years, but fewer reached maturity at one year than normal). When they finally did, the smaller Ruddy Ducks males housed in male groups grew their penises faster than males housed with a mate—but their dicks grew out of sync with each other, staying in a reproductive condition for only short periods of time.
This “lack of sync,” both in terms of delaying sexual maturity and penis growth, may have something to do with the intense level of male-on-male competition. By offsetting their reproductive potential, the ducks were making the best of a bad situation. They weren’t all becoming sexually competitive for females at the same time, giving the smaller ducks a slight reproductive chance, rather than none at all.
“This is an excellent experimental study of penis morphology, looking at the effects of social environment on penis size in two duck species that have different mating systems,” said Bob Montgomerie of Queen’s University, an expert on reproductive strategies who was not involved in the study.
The study shows that the level of competition between males can have a pronounced effect on their genitals. But in the grand scheme of things, it’s not immediately clear if these enhanced males are any luckier when it comes to reproduction.
“The question now is whether the observed increase in penis size in Lesser Scaup under the threat of sperm competition actually gives males a competitive advantage,” said Montgomerie in a statement. “Like all good studies, this one will undoubtedly stimulate more research, as it provides both methodologies and a clear focus on interesting questions.”
In other words, the mysteries of duck penises live on.