by Becky Crew
Another thing the males and females of both of these species had in common was a high level of forced copulations. This suggests that the females have been developing highly complex oviducts to prevent being successfully fertilized by forceful males’ sperm. “Female ducks cannot behaviorally avoid unwanted copulations, and often times they are subdued by multiple males who can copulate in quick succession,” says Brennan. “Females can then only use what we call copulatory or postcopulatory strategies to regain control of the reproductive decisions, in this case, which male will gain paternity of her offspring.” She adds that typically females will try to use more subtle strategies than this, such as simply ejecting sperm from unwanted males, but this technique doesn’t always work because the males can use their long penises to deposit sperm further inside the female’s oviduct than is possible to be ejected. “Since these structures only are found in female ducks in species where forced copulations occur, it is likely that they evolved in response to these unwanted copulations,” says Brennan.
According to paternity data for a number of species of duck, forced copulations can be very common—40–50 percent of all observed copulations, according to Brennan. But only 2–5 percent of a female duck’s offspring turn out to be the results of forced copulation. While a female’s mate will try to defend his paternity by mating with his female immediately after a forced copulation has taken place, it’s primarily thanks to the females’ natural chastity belt that these forced copulations are not very successful. “If the female’s own mate could defend his paternity fully, there would be no need for the females to evolve the convoluted vaginas, but the fact that they do suggests that they are primarily responsible for preventing successful fertilization of eggs by unwanted males,” says Brennan.
Not that the males are necessarily the losers of this ongoing evolutionary arms war—they have certain tricks up their sleeves, too. In late 2009, Brennan published a study in Proceedings of the National Academy of Sciences on Muscovy ducks (Cairina moschata), which are a large species native to Central and South America and Mexico. The males are around 34 inches long while the females are about 25 inches long, and they both have bare, bright red skin surrounding their eyes and beaks. Brennan wanted to study the mechanics of the Muscovy duck’s penis, so she had four 0.4-inch-diameter glass tubes created: one in a simple, straight shape; one in a counterclockwise corkscrew that matched the male’s penis spiral; one in a clockwise corkscrew that ran in the opposite direction to the male’s penis; and one with a 135-degree bend, which resembles the first dead-end kink in the female’s oviduct.
Because male ducks only have an erection directly into the female’s oviduct, as opposed to becoming erect some time before copulation, Brennan needed to very quickly intercept the male with each of the four tubes as he mounted a female to see how easily his penis could unfurl in the different shapes. She found that the male’s penis easily made it through both the straight tube and the tube that mirrored the shape of its coil, the explosive erection filling the tube in less than half a second. But the clockwise corkscrew-shaped tube and the bent tube posed a much bigger challenge. Brennan also found that when males were mating with real females, if a female was happy to mate with a male, and the copulation wasn’t forced, she would maneuver herself in a way that helped the male’s penis find its way through her twisted oviduct. This suggests that female ducks still have the upper hand in the decision of who will father their offspring, because they can control to what extent their oviducts act as a natural sperm barrier.
The Impossible Mates
GIANT PANDA
(Ailuropoda melanoleuca)
“Guys, this is so ridiculous. Haven’t any of you heard of tequila?”
IN JUST THREE MOUNTAIN ranges in central China, 1600 giant pandas are eking out an existence in the only environment in the world that can sustain their very particular lifestyle and diet. A nearby earthquake is all it would take to wipe out an enormous chunk of what habitat these pandas have left, which is exactly what happened in Sichuan in 2008. A magnitude 8.0 earthquake, which released as much energy as the detonation of 6 million tons of TNT, destroyed more than 23 percent of the wild pandas’ habitat in this province in southwest China, which researchers from the Research Center for Eco-Environmental Sciences at the Chinese Academy of Sciences in Beijing estimate to have affected 60 percent of the entire wild giant panda population.
Adding to their environmental woes are the giant pandas’ notoriously complicated reproductive needs. Female giant panda reproduction has been extensively studied, and it’s well known that they are sexually receptive at just one moment per year, between February and May. And the female panda’s estrus, which is the state of sexual excitement that comes immediately before ovulation, lasts just 24–72 hours within this three-month window. This means that the female giant panda devotes less than 1 percent of its entire life to sexual activity.
So we know how female giant pandas contribute to breeding difficulties with captive pairs, but until recently, very few studies had been carried out on the males. In April 2012, an international research team led by veterinarians Copper Aitken-Palmer of the Smithsonian Conservation Biology Institute at the American National Zoo in Washington and Rong Hou of the Chengdu Research Base of Giant Panda Breeding in Sichuan, China, published the results of a study of eight captive male pandas—the first time this many have been studied at once. Over three years, the researchers observed a range of factors in the male pandas including sperm concentration, testes size, reproductive behavior, and the levels of androgen, which are hormones that determine the development and maintenance of male features. They found that, like the females, the males exhibit seasonal waves of reproductive activity, with all of the above increasing during the October to January period, in preparation for the females’ period of reproductive activity, and well into the breeding season between February and March.
According to the study, which was published in Biology of Reproduction, the males’ testes volume and sperm concentration were at their peak from March 22 to April 15—directly coinciding with the females’ peak breeding activity. After this period, the males’ reproductive behaviors began declining from April 16 to May 31, returning to their lowest point in the year from June through September.
Despite the fact that the male pandas’ bodies spend an entire year preparing for the sliver of time that the females actually feel like having sex, captive breeders still find it extremely difficult to successfully mate a pair, with some 60 percent of male pandas in zoos or enclosed sanctuaries showing no sexual desire whatsoever. In 2002, researchers at the Wolong Nature Reserve in Sichuan tried giving their male pandas Viagra, but to no avail. In 2007, zookeepers at Thailand’s Chiang Mai Zoo tried something a little different with their giant panda pair: Chuang Chuang, a six-year-old male, and Lin Hui, a five-year-old female. First, the couple was separated in the hopes that they would begin lusting after each other, and then Chuang Chuang was put on a diet so he wouldn’t crush Lin Hui when—if—he attempted to mount her. Alone in his cage, Chuang Chuang was made to watch “panda porn,” which is video footage of other panda pairs mating, to sexually arouse him. The same technique was used in China in early 2006 to produce thirty-one cubs in a ten-month period, twenty-eight of which survived. Unfortunately for the Thai zookeepers, even after two weeks’ training, which involved making Chuang Chuang watch the porn video for fifteen minutes a day, he did not respond by being sexually aroused.
Because of their complicated reproductive needs, breeding giant pandas is becoming increasingly difficult, and the remaining population is dwindling so rapidly that a number of scientists consider it too late to save the species. In late 2011, environmental economist Dr. Murray Rudd of the University of York questioned 583 scientists via e-mail about whether we should consider setting up what’s known as a conservation triage. Where wildlife is concerned, a conservation triage means we should focus our resources on threatened species that we have a good chance of savi
ng, and give up on the more difficult or “expensive” threatened species such as pandas and tigers. Rudd reported that almost 60 percent of the scientists he polled agreed or strongly agreed that “criteria for triage decisions should be established.” It’s a sobering thought that in just a few generations’ time, there might not be any giant pandas left.
Don’t Trust Them with Your Offspring
GULF PIPEFISH
(Syngnathus scovelli)
WHEN IT COMES TO seahorses, it’s the males who bear the responsibility of pregnancy. The same goes for their relatives the pipefish, whose males are equipped with a specialized external brood pouch into which the females will deposit eggs during copulation. But a recent examination of pipefish male pregnancy and mate selection has found that this process is nothing to coo over.
Observing the reproductive behavior of twenty-two captive male gulf pipefish (Syngnathus scovelli), a small-mouthed, pencil-shaped species with a relatively poor swimming technique, biologists Kimberly Paczolt and Adam Jones from Texas A&M University discovered just how much control the males have over their prospective progeny. By pairing the males with either large or small females, the researchers found that the males wasted no time in mating with larger, more attractive females, but were significantly less eager when paired with smaller females. They also found that the eggs deposited by larger females had a much higher rate of survival to the point of birth, with the males selectively aborting those from a less attractive partner by either withholding vital nutrients, or absorbing (in other words, cannibalizing) the embryos.
By also looking at successive pregnancies in male pipefish, Jones and Paczolt were able to make sense of these rather callous tendencies. Not only do broods from smaller females have a low survival rate to begin with, but if a male first mates with an attractive female and bears a large brood, he’s unlikely to want to invest more resources into a subsequent pregnancy, particularly from a less attractive partner. Instead of nurturing these offspring, his specially evolved brood pouch allows him to retain or absorb the nutrients to ready himself for the possibility of meeting a more attractive mate.
“The bottom line seems to be, if the male likes the mum, the kids are treated better,” says Paczolt. “Why this occurs, we don’t fully understand. But our findings are quite specific about this relationship between the male pipefish and its mate. If the male prefers the female, he treats their mutual offspring better.”
That the male pipefish are actively trying to control the quality of their offspring during pregnancy is evidence of postcopulatory sexual selection, which follows the initial competition for mates by way of combat and elaborate courtship displays. But postmating sexual selection, such as things that happen within a female’s reproductive tract or the dogged competition of sperm, remains something of a mystery, just like male pregnancy. “The whole phenomenon of male pregnancy is full of conflict and far more complex than we had previously realized,” says Paczolt.
Well, gulf pipefish boys, you might think this is all pretty great, being able to pick and choose (and cannibalize) your own progeny with nary a qualm in the world. But the thing is, those ugly pipefish girls you mated with in the past—they’re not just going to disappear. The ocean might be big, but it’s not that big, and you know what they say: “Mate with one ugly pipefish that time you had nine vodkas, three gins, and no dinner, and you’ll end up with six months of whiny text messages and a lifetime of really awkward encounters whenever you try and go back to that particular bar because they have $4 spirits till 1 A.M.”
So you’ll decide to risk it and go to this bar one night, all like, “Five tequila sunrises please. Oh. Hi …”
And that unattractive pipefish girl you once mated with will be like, “So how are the offspring?”
“Huh?”
“You know, the offspring. Our offspring?”
“Oh. Umm. Hmm …”
“You ate them all, didn’t you?”
“Well, technically I absorbed … Shit.”
And now you’re wearing five tequila sunrises, gulf pipefish boys. But it won’t end there, because everyone will know that you mated with her, especially her really short and ugly friends, and they’ll look at her and then at you and then back at her and figure they’ve got a shot.
So you’ll be at a completely different bar, trying to chat up some cute pipefish girl, like, “I aborted a brood hoping to meet someone so … long. How many millimeters are you, anyway? Wait right there, I’m going to buy you so many drinks.”
But you’ll only get halfway to the bar before a bunch of short and ugly ladies will crowd around you all, “Hey can I buy you a drink?”
”No.”
“You want my number? I might be only 4 inches long, but I sure know how to use each one …”
And meanwhile the cute pipefish girl will think you’re not into her, so you’ll either have to go home alone or settle for one of the short and ugly pipefish girls.
And you thought having a brood pouch would be a riot, gulf pipefish boys.
Your Mother Wants You to Eat Her
BLACK-LACE WEAVER SPIDER
(Amaurobius ferox)
LIFE AS A JUVENILE black-lace weaver spider is far from easy. As part of a group known as subsocial spiders, which describes a species that on occasion displays co-operative behavior, a black-lace spider will hatch with some 60–130 siblings and remain on a communal web with its mother. The spiderlings will live off a second batch of eggs laid by their mother, which sustains them for a week or so before they are old enough to lead the traditional solitary lifestyle of a spider.
But before the black-lace spiderlings can go out on their own, their mother will encourage them to devour her body, giving herself up as their final family meal. Research has shown that compared to spiderlings that are denied this meal, spiderlings that eat their mother are more likely to survive after they leave the nest.
This is not the only cooperative behavior displayed by young black-lace weaver spiders, which can be found in North America and Europe. In mid-2010, biologist Kil Won Kim from the University of Incheon of the Republic of Korea reported the results of the first study examining the synchronization movements in nonsocial or subsocial spiders in Insectes Sociaux. She discovered that once the spiderlings have eaten their mother and taken over her web, if they feel threatened, they will group together and contract their bodies in unison to make the web pulse. This behavior, which emerges just one day after the act of matriphagy (eating one’s mother), is typically triggered by the approach of intruding insects, mites, or worms, leading Kim to suggest that this functions as an antipredatory strategy.
An individual spiderling senses this potential threat, contracting its body, and approximately 60 percent of the other spiderlings will follow suit, contracting and relaxing their bodies to create an eerie pull-and-release effect on the web that is never performed while the mother is still alive. According to Kim, the function of this pulsing may be to fool an approaching predator into thinking that a much larger animal is nearby, convincing it to flee.
The black-lace juveniles use this technique for seven to nine days after matriphagy, by which time they appear to grow out of it, focusing their collective efforts on hunting prey up to twenty times their size instead. The spiders will continue living in a large sibling group for three to four weeks after the death of their mother and then leave the web to live alone, now old enough to fend and hunt for themselves.
Spiderling. Just … ugh. I mean, how does this work exactly? You’re all sitting around the dinner table like, “Hey Mum, look how many eggs I can fit in my mouth,” and “Do you think Justin Bieber likes spiderlings?” when suddenly she’s like, “So … who wants to start on my abdomen?”
And you’ll be all, “WTF, Mum!”
“Watch your language and eat my abdomen.”
“But Mum … Does this mean we have to pay our own school fees now?”
You’ll reluctantly slink off your chairs and edge toward h
er, telling each other that you’ll probably be grounded either way, but she’s much less likely to enforce it if you eat her. Someone will sheepishly point out that she actually tastes all right, and before you know it, you’ll be collectively digesting your mum while watching something with Selena Gomez in it.
But then what? I’m sorry to break the news, spiderlings, but huddling together on your web, contracting nervously in unison, muttering, “Oh my god, oh my god, we’re all gonna die,” isn’t going to solve your problems once the predators find out what’s really going on. You need a more sophisticated plan. And that’s where I come in. But first you’ll need:
A precocious attitude
An empty house, preferably in the initial stages of being renovated
Paint tins
Rope
Bricks
A blowtorch
Staple guns
Live electrical wires lying in a pool of—
What? Too complicated? Oh for Christ’s sake, spiderlings, haven’t you ever seen Home Alone?
Fruit Bat Fellatio
GREATER SHORT-NOSED FRUIT BAT
(Cynopterus sphinx)
“Mr. Greater Short-Nosed Fruit Bat, I’m very happy to inform you that you’re a finalist for our community achievement award. Have you got anything to add to your nomination that might give you an edge over the other finalists?”
