集中供热分户计量:公鸭囧科学：阴茎多长？别人做主！

苏珊·米利厄斯

2010年8月2日，英国《连线》科学版讯

 WILLIAMSBURG, Virginia — New measurements find that the maximum length of a duck’s penis depends on the company he keeps. And in this case, it’s his fellow males who make the difference.

　　美国弗吉尼亚州威廉斯堡：最新研究显示，公鸭阴茎的最大长度取决于牠的同侪——具体一点也就是说，公鸭自己的阴茎能长多长，是由牠的公鸭伙伴们所决定的。

A drake’s penis substantially wastes away at the end of one breeding season and then regrows as the next season begins. Among lesser scaup and ruddy ducks, the regrowth varies in length or timing depending on whether males have to compete with a bunch of other guys, said Patricia Brennan of Yale University.

　　通常，随着繁殖期渐入尾声，公鸭的阴茎会大大萎缩，直到下一次繁殖期来临时，才会重新长回原先的长度。据耶鲁大学研究者派翠西亚·布瑞南（Patricia Brennan）介绍，小潜鸭及棕硬尾鸭阴茎重新发育的程度与时间，受其是否须与其他雄性竞争影响。

Her new measurements offer the first evidence in vertebrates that social circumstances influence penis growth, she reported July 29 at the annual meeting of the Animal Behavior Society.

　　今年7月29日，布瑞南在动物行为学会（Animal Behavior Society）年会上公布了此项研究的数据。她的这项新研究结果，首度为研究脊椎动物阴茎长度的社会环境影响提供了证据。

In many bird species, males don’t grow specialized organs to deliver sperm. Ducks typically do, their penises sometimes reaching considerable lengths (9.8 inches for a ruddy duck, more than half its body length). That extra length may give a male a competitive advantage in delivering sperm when females have multiple mates. Brennan’s past research has documented strong sexual conflict in ducks, with males forcing copulation and females employing strategies such as corkscrew-shaped vaginas, developed over the course of duck evolution, that apparently thwart male control of reproduction.

　　有很多种鸟类，其雄性并不会发育出专门用于传播精子的器官；但亦有一些鸟类具备此类器官，其中鸭子就相当典型，且其阴茎颇长。例如棕硬尾鸭的阴茎可长达9.8英寸（约25厘米），超过其身长的一半。这可能是因为：当母鸭有一个以上配偶时，雄鸭的阴茎越长，其传播精子的竞争力或许就更高。布瑞南在之前的研究中，曾记录到鸭子间强烈的两性冲突：公鸭常会强迫母鸭交配，母鸭因此演化出一些应对策略，譬如长出螺旋状的阴道——这样显然可以抵制繁殖期雄性的专横控制。

To see whether competition among males influences penis growth, Brennan housed some of her drakes in groups of seven to eight males with just five or six females. Other males lived with just one female.

　　为了了解雄性彼此间的竞争是否会影响其阴茎长度，布瑞南隔离了部分公鸭分组饲养，有的每组七到八只，配以五到六只母鸭；其他的则仅配以一只母鸭。

Among the scaup, males competing in groups grew penises 15 percent longer, and sometimes up to 25 percent longer, than drakes with no mating rivals, Brennan reported.

　　结果发现，有同性竞争压力的雄性小潜鸭，与没有竞争对手的对照组相比，其阴茎长度高出15%，最长者甚至高出25%。

The corkscrew-shaped penis of a ruddy duck, with a 2-centimeter (0.8-inch) bar for scale.

棕硬尾鸭的螺旋状阴茎。图中短横线为2厘米（0.8英寸）参照比例尺。

The scaup species doesn’t show many signs of conflict between males and females, though, she said. Scaup drakes, for example, rarely force themselves on a resistant female. In contrast, ruddy duck relations seem rife with conflict, with males often forcing themselves on females in chaotic mating scenes.

　　布瑞南指出，潜鸭属鸭类的两性关系看起来颇为和睦，例如一旦雌性表现出抵制态度，则雄性几乎不会强迫与其交配。但棕硬尾鸭则并非如此，其两性、同性冲突似乎更为普遍；棕硬尾鸭群一到交配季节就战得昏天黑地，雄鸭常趁乱“霸王硬上弓”。

Among ruddies, penis length did not differ overall between males in competitive crowds and those in lucky privacy. What did differ was timing.

　　就雄性棕硬尾鸭而言，不管交配期有没有竞争对手，其阴茎长度总体来说并无差异；但其阴茎生长、萎缩的时间则有区别。

In the competitive groups, a few big males grew prodigious organs as if dominating the group. Other males grew more moderate penises, which started wasting away weeks earlier than those of dominant males or males with no competition.

　　在有竞争对手的观察组中，少数几只体型较大的雄鸭发育出了惊人的巨大性器官，似在群体中占据支配地位；同组中其他雄鸭的阴茎大小则相当一般，且与占支配地位的雄性、或无竞争对手的对照组雄鸭相比，其阴茎也会较早开始萎缩，时间点相差达数周。

Thus, Brennan said, male ducks are “prudent.” In a crowd, a ho-hum male apparently doesn’t bother sustaining a big investment in tissue that’s not going to pay off.

　　因此，布瑞南总结说，雄性棕硬尾鸭很懂得“谨慎投资”：在群体中没有竞争力的雄性，既已清楚无望交配，也就懒得浪费大量精力去维持没搞头的性器官了。

The results shed light on how ducks became so well-endowed compared with other birds, Brennan said. “It’s really likely that having a longer penis evolved in male-male competition.” Guy-versus-guy battles then could have started playing a role in battles between the sexes.

　　布瑞南的研究为我们提供了一些线索，或可解释为何在众多鸟类中，唯独鸭类演化出了如此显著的性器官。她说：“雄性间的竞争极有可能导致演化出较长的阴茎。”因此，在两性战争中，男男之间的竞争或许也起到了一定的影响作用。

“Elegant,” says evolutionary ecologist Maydianne Andrade of the University of Toronto Scarborough, who has studied sexually cannibalistic spiders. The experiment shows that ducks “are essentially engineering their own phallus in response to social challenges.” Now she’d like to know more about just how this duck physiology works and whether any other species respond to sexual competition the same way.

　　多伦多大学士嘉堡校区（University of Toronto Scarborough）演化生态学者梅蒂安娜·昂德耶（Maydianne Andrade）评价此项研究“简明扼要”。她认为这项研究说明鸭子“通过从本质上改造雄性生殖器的手段，应对社会挑战。”昂德耶本人曾就蜘蛛因性别因素影响而食用同类的现象做过研究。她表示，接下来，她希望了解鸭子的这种生理机能具体如何运作，以及是否还有其他物种也以同样的方式应对性别竞争。

See Also:

Female Ducks’ Twisty Tracts Defend Against Screwy Males 
Duck Genitalia Tells an Evolutionary Tale 
Penis Jousting and 7 Other Great Animal Mating Rituals 
Frogs Leap Farther When Competing at County Fair 
Pigeon Flocks Let the Best Bird Lead 
Feathered Dinosaurs Molted Like Birds 

相关文章：

·为防雄鸭硬上弓，雌鸭性器螺旋绷（Female Ducks’ Twisty Tracts Defend Against Screwy Males）

·鸭子性器官娓娓道出进化史传说（Duck Genitalia Tells an Evolutionary Tale）

·赛“枪”大会，及另外七种神奇的动物交配仪式（Penis Jousting and 7 Other Great Animal Mating Rituals）

·乡村人蛙友谊赛，青蛙跳得比人远（Frogs Leap Farther When Competing at County Fair）

·鸽群总以佼佼者领队飞行（Pigeon Flocks Let the Best Bird Lead）

·恐龙长羽毛，像鸟一样换毛（Feathered Dinosaurs Molted Like Birds）

Image: 1) Flickr/milesizz. 2) Patricia Brennan.

（图片来源：1、Flickr/milesizz；2、Patricia Brennan）