At least if you’re a spider:

Eunuchs are better fighters

Simona Kralj-Fišer, Matjaž Gregorič, Shichang Zhang, Daiqin Li, and Matjaž Kuntnera

Animal Behaviour

Volume 81, Issue 5, May 2011, Pages 933-939

doi:10.1016/j.anbehav.2011.02.010

Abstract: Genital amputation, that is, genital damage or loss, seems maladaptive because it renders the amputee functionally sterile, but is nevertheless common in sexually dimorphic spiders. In these species, male genital amputation correlates with plugging of female genitals and with sexual cannibalism. Genital amputation in male spiders may be partial or full; the latter is known as the eunuch phenomenon. We tested two adaptive hypotheses about eunuch behaviour in an orb web spider, Nephilengys malabarensis: (1) the plugging hypothesis (i.e. broken male genitals (palps) effectively plug the female genitals) and (2) the better fighter hypothesis (i.e. eunuch males are better fighters than their intact rivals). By staging mating trials, we documented genital amputation (occurrence and frequency), sexual cannibalism and genital organ reuse, morphologically examined plugs to infer their effectiveness, and conducted a series of male-male contests to determine whether eunuch males were better fighters. Copulations always resulted in amputation of the palps: 87.5% of males became eunuchs directly during copulation and plugged females, while 12.5% of males first partially damaged the palps and then severed them after copulation. Sexual cannibalism and plugging effectiveness both reached 75%. Eunuchs guarded females, were highly aggressive and active, and initiated and won contests more often, whereas intact males and half-eunuchs showed significantly lower levels of guarding behaviour, aggression and general activity. Thus, both hypotheses are supported and we conclude that the eunuch phenomenon is adaptive.

Keywords: emasculation; genital amputation; Nephilengys malabarensis; Nephilidae; orb web spider; plugging; sexual cannibalism; sexual conflict

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Don’t pick a fight with a eunuch spider. It has nothing to lose

Smithsonian Science

07 April 2011

If he’s lucky a male orb web spider of the species Nephilengys malabarensis, can count on having both his genital appendages, known as pedipalps, break off during sex. (Male spiders have two pedipalps, one located on each side of the head.) The detached appendages plug up the female spider and prevent her from mating with other males. If unlucky, he’ll also be eaten by her after copulation, which lasts about 10 seconds.

In a recent study of the mating behavior of these Asian spiders, researchers found that 87.5 percent of males had both palps amputated during copulation. “The two palps connect to the female epigynum, a sclerotized plate with double copulatory openings positioned ventrally on her abdomen,” says study co-author Matjaž Kuntner, spider expert at the Smithsonian’s National Museum of Natural History and the Slovenian Academy of Sciences and Arts.

Palps that remain intact are chewed off after sex by the males, making them voluntary eunuchs. Rendering yourself sterile may seem counterproductive to the laws of evolution, but in spiders, the researchers found, there is a distinct benefit to being a eunuch. Simply put, eunuchs are more agile, better fighters and better at defending a mate.

After copulating with a female, the castrated males remain close-by to guard her and prevent other males from approaching. In a series of staged contests between male spiders whose sexual equipment was intact and eunuchs, the eunuchs won hands down, the researchers found.

“Eunuchs guarded females, where highly aggressive and active

JesusA (imported) wrote: Fri Apr 08, 2011 1:09 pm and initiated and won contests more often,

” the scientists write in their paper in the journal Animal Behaviour. “Intact males and half-eunuchs (those with only one palp)

JesusA (imported) wrote: Fri Apr 08, 2011 1:09 pm showed significantly lower levels of guarding behavior, aggression and general activity.

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Basically, the scientists write, “a sterile male has no reproductive future and nothing to lose in a fight.” Intact males with a reproductive future are more likely to avoid fights and risk injury. “Genital amputation enhances the eunuch’s mate-guarding activity and male to male aggressiveness, which help the eunuch win contests against rivals and increase his paternal success.”

The paper “Eunuchs are Better Fighters” is co-authored by Simona Kralj-Fišer and Matjaz Gregorič, Slovenian Academy of Sciences and Arts; Shichang Zhang, National University of Singapore; Daiqin Li, Hubei University, China; and Matjaž Kuntner, National Museum of Natural History, Smithsonian and the Slovenian Academy of Sciences and Arts.

–John Barrat

http://smithsonianscience.org/2011/04/d ... g-to-lose/

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This is also true with herded animals. They protect the females and the young during most of the year. However during breeding season it is best to separate them out.

So is this a new version of ARACHNOPHOBIA?

I don't know about being a better fighter. But I did get get stuck in the middle of a fight and took a hell of a kick that would had me in the fetal position 5 years ago!