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Neil Losin
Department of Ecology and Evolutionary Biology
UCLA
Los Angeles CA USA

Neil Losin is a biologist, photographer, and filmmaker based in Los Angeles, CA. In his "day job," he's working on his Ph.D. in UCLA's Department of Ecology and Evolutionary Biology, studying the evolution of territorial behavior in lizards. When he's not doing science, he takes photographs of nature (especially wildlife) and documents the work of scientists who study nature.

My posts are presented as opinion and commentary and do not represent the views of LabSpaces Productions, LLC, my employer, or my educational institution.

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Recent Comments
Comment by vernon getzler in You look scrumptious tonight

Well, it’s amazing. The miracle has been done. Hat’s off. Well done, as we know that “hard work always pays off”, after a long struggle with sincere effort it’s done. ========== Read More
Apr 21, 2011, 6:34am
Comment by Marcia Neil in You look scrumptious tonight

Many species will bite each other if pushed together; among people the action can be also to shoot/stab each other with weapons/tools  --  perhaps calculated results among specific populations of. . .Read More
Apr 20, 2011, 11:05am
Comment by Neil Losin in You look scrumptious tonight

Jade: I think it's all about potential reproductive value of the females. Bigger females produce more eggs than smaller ones, so they are "better" from the male's perspective. So are virgins, becau. . .Read More
Apr 20, 2011, 12:08am
Comment by Psycasm in You look scrumptious tonight

Note: I'm not sure 'gestation' is appropriate for egg-layers... forgive my ignorance if this is the case . . .Read More
Apr 19, 2011, 12:28am
Comment by Psycasm in You look scrumptious tonight

Woah... I will never look at a redback the same way again. What a great reproductive strategy. How long is gestation in the redback? and how frequently does a female redback need to eat? Does the c. . .Read More
Apr 19, 2011, 12:26am
Monday, April 18, 2011

If you’re on a first date and it’s not going so well, what’s your exit strategy? Do you have a friend ready to call you at a predetermined time so you can give a plausible excuse? (“Heeyyy, so I’m having a really great time but my buddy Nate just called and he accidentally flushed his pants down the toilet at a gas station, so um, yeah, I gotta go help him out.”) Or do you just hit the fire alarm and run for it?

One strategy you probably haven’t considered is eating your date. For whatever reason, our society just isn’t into that. But sexual cannibalism is common in a wide variety of invertebrate species, and biologists have plenty of hypotheses to explain this odd behavior.

Closeup of a female redbacked spider (Latrodectus hasselti).

Usually, it’s females that eat males. In one remarkable spider species, the Australian redbacked spider (Latrodectus hasselti), up to 65% of males get eaten by their sexual partners. Remarkably, males even seem to offer themselves to females during mating, performing a sort of “somersault” into the female’s jaws and thereby facilitating their own demise (see a video here – the male’s “somersault” begins around 0:20). This might appears to be a poor evolutionary strategy – after all, once you’ve been eaten, your mating days are over. But biologist Maydianne Andrade has shown that this behavior actually makes sense in a macabre sort of way.

For male redbacked spiders, mating opportunities are few and far between, so when a male finds a female he needs to make the most of the opportunity. The longer a male can remain in flagrante delicto, the more offspring he will sire. Males can continue to transfer sperm even while being consumed, so by allowing themselves to get eaten while copulating, males can increase the amount of sperm transferred. Furthermore, females who eat their first mate are less likely to re-mate, further increasing the genetic contribution of the first “suicidal” male. Statistically, even if a male survives his first mating, he is very unlikely to find another female. So by investing 100% in his first and only mating by offering himself to his mate, he actually enhances the transmission of his genes to the next generation.

Much less common is reversed sexual cannibalism, in which females are consumed by males. In most cases of sexual cannibalism, females are larger than males and invest more resources in reproduction. In some species, however, the sex roles are reversed: males invest more heavily in reproduction than females, and it is conceivable that reversed sexual cannibalism could evolve in such species.

In the latest issue of the Biological Journal of the Linnaean Society, biologist Anita Aisenberg and colleagues document just such a situation: reversed sexual cannibalism in Allocosa brasiliensis, a dune-dwelling wolf spider from South America. In A. brasiliensis, males are larger than females and have been observed eating adult females in the wild. Males dig deep burrows in the dunes and line them with silk, and females require these burrows to lay their eggs. After mating, the male abandons his burrow and the female remains inside to lay and guard her eggs. Given this unusual reproductive biology, Aisenberg saw a unique opportunity to test hypotheses about sexual cannibalism in a "sex-role-reversed" species.

A male Allocosa brasiliensis, photographed by Marcelo Casacuberta

If sexual cannibalism is a result of misidentification, then a female’s body size and mating history shouldn’t affect the likelihood of cannibalism. If males consume females when they are very hungry, then males in worse body condition should be more voracious cannibals. Finally, if cannibalism is an adaptation to prevent mating with undesirable females, then males should preferentially consume: 1) females in poor condition (because these females will produce few eggs), and 2) females that have already mated with another male (because the current male’s genetic contribution to the resulting clutch would not be exclusive).

Aisenberg and colleagues brought adult A. brasiliensis into the lab and allowed virgin and previously-mated females to court males with sand burrows. They observed cannibalism in more than a quarter of all courtship attempts, and the females who were attacked had, on average, a lower body weight than females who were not attacked. Males were more likely to mate with heavier females, and were more likely to mate with virgin females than previously-mated females. There was no measurable difference in the rate of cannibalism, however, based on females’ previous mating experience. (And contrary to several reports in the echo chamber of the mainstream science media, the authors did not test females of different ages, so we can’t say that male spiders “eat cougars” or any such nonsense!)

The male’s body condition did not affect his propensity to eat a courting female, so sexual cannibalism in this species probably can’t be explained simply by hunger. Instead, the evidence supports the idea that male cannibalism could be an extreme mate choice behavior: if a prospective mate isn’t up to standard, a male should just eat her and be done with it – better than wasting a perfectly good burrow!

Luckily, humans have some subtler ways of dealing with a bad date. Let’s stick with the phone call as an exit strategy.

Work cited:

Andrade, MCB. 1996. Sexual selection for male sacrifice in the Australian redback spider. Science 240:70-72.

AISENBERG, A., COSTA, F., & GONZÁLEZ, M. (2011). Male sexual cannibalism in a sand-dwelling wolf spider with sex role reversal Biological Journal of the Linnean Society DOI: 10.1111/j.1095-8312.2011.01631.x

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Blog Comments

Brian Krueger, PhD
Columbia University Medical Center
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Have you seen this video of the peacock spider yet?  If the female doesn't like his mating display, she tries to eat him!


Neil Losin
UCLA
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Yes, that video is awesome! It's about 10 times longer than it needs to be, but the behavior is so incredible I could pretty much watch it all day :)


Brian Krueger, PhD
Columbia University Medical Center
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Agreed! I don't think he needed to follow 4 different mating interactions.


Suzy
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ha ha- cougar spiders?

So they prefer to mate with heavier females and virgin females but they prefer to snack on lightweight females? Doesn't totally make sense. Maybe it has less to do with the females and more to do with the males. Did they have any data on the males who cannibilised females?

 


Psycasm
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Woah... I will never look at a redback the same way again. What a great reproductive strategy. How long is gestation in the redback? and how frequently does a female redback need to eat? Does the consumption of her lover carry her all the way through gestation?

It would seem that such a crazy behaviour would have to have major benefits to the mother and offspring, much more so than even a slight chance of re-mating...?


Psycasm
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Note: I'm not sure 'gestation' is appropriate for egg-layers... forgive my ignorance if this is the case


Neil Losin
UCLA
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Jade: I think it's all about potential reproductive value of the females. Bigger females produce more eggs than smaller ones, so they are "better" from the male's perspective. So are virgins, because 100% of a virgin female's clutch will be sired by her first mate (whereas mated females might store sperm from previous matings, and paternity would be diluted). Other than body size and mass, they don't know anything about the males used in the experiment. But they can at least say that males in good condition were no less likely to cannibalize females than males in poor condition... so "they were just hungry" is a poor explanation for the behavior.

Psycasm: Yeah, I'm not sure how long it takes for egg-laying to occur after mating. The males are pretty tiny compared to the females, so I don't think it's really the added nutrition gained by the female that makes the male's sacrifice worthwhile. Instead, it's copulation duration that seems to matter. And for whatever reason, females who eat their partners are less likely to re-mate. Pretty wild stuff :) All the "widow" spiders (genus Latrodectus) are known to be sexual cannibals (at least occasionally), but to my knowledge only the redback spider has the self-sacrificial behavior.

Marcia Neil

Guest Comment

Many species will bite each other if pushed together; among people the action can be also to shoot/stab each other with weapons/tools  --  perhaps calculated results among specific populations of the "hurt yourselves" mentality.


vernon getzler
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Well, it’s amazing. The miracle has been done. Hat’s off. Well done, as we know that “hard work always pays off”, after a long struggle with sincere effort it’s done.
==========
vernon
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