Behold the gray mouse lemur. Among the world’s smallest primates, this teeny wide-eyed animal is – like all lemurs – endemic to the island Madagascar. A single gray mouse lemur is disarmingly adorable. Two are cuter still. Except, of course, if the second one happens to be gnawing on the disemboweled carcass of the first. Such was the gruesome scene described in a recent paper published online in the American Journal of Primatology.
As part of a pilot study conducted in Western Madagascar, the paper’s author was tracking radio-collared lemurs and discovered one of the collared female animals – which had been alive and active just an hour prior – quite dead and hanging upside down from a branch while an un-collared male enthusiastically devoured its remains. The internal organs (including the brain) were already gone by this point, but the author stood aghast watching for an additional 20 minutes as the male lemur continued, unperturbed, chewing on the spine and ribcage and whatnot before finally making his departure.
Normally, gray mouse lemurs (Microcebus murinus) get their sustenance from fruit, insects and other invertebrates, and the occasional small reptile. Does this sighting mean that the species also supplements its diet through cannibalism? Of course not. It’s just one lemur, people. Definitive conclusions can’t be drawn from this single incident any more than they can be from isolated highly publicized events of human cannibalism.* Though it certainly is a notable departure from expectations. And since mouse lemurs are shy, nocturnal things, they’re not the easiest of animals to observe in the wild. This report suggests that we may not know Microcebus murinusas as well as we thought we did.
It’s hard to say what could have led our little lemur to this act of dietary transgression. However, cannibalism is not uncommon in the animal kingdom, and while it can be a pathological response to stressful conditions (animals in captivity do some pretty messed up stuff) scientists believe that more often than not, the behavior has some adaptive value.
Cannibalism frequently goes hand in hand with infanticide, that is, larger adults killing smaller juveniles. The most obvious benefit of this is food. Particularly for animals that produce an abundance of eggs (e.g., fish) these eggs can improve individuals’ reproductive fitness either by successfully hatching into offspring or by keeping the would-be-parents from starving before their next mating opportunity. In times of food scarcity, it may make more sense to eat the kiddies than to raise them. Additionally, when facing limited resources, killing some offspring (particularly the smaller, sicklier ones) can give the remaining ones a better shot at surviving to adulthood.
Biological relatives aren’t the only ones eradicating babies. Lion prides are composed of one or two reproductive adult males who control a group of females and their young. Rival males regularly attempt coups to seize these harems. When such attacks succeed, the conquering males do away with their predecessors’ cubs. This killing not only eliminates competitors’ offspring, it also improves the new pride leaders’ chances of siring their own children. Female lions typically give birth every two years, but if their cubs are, er, removed, they’re quickly ready to mate again.† Cannibalism under these circumstances is really secondary to the killing, but after the dust settles the dead cubs may be eaten, sometimes even by their mother because, hey, it’s food.
Cannibalism of adults is less common, particularly in mammals. In primates (outside of captivity) cannibalism of adults in unheard of, with one marked exception – humans. This is what makes the grisly lemur eating episode such a find. It’s the first documented case of adult-on-adult cannibalism in non-human primates.‡
Nutritional and reproductive benefits aside, cannibalism is not without its drawbacks. In addition to the risk of being pummeled by protective lionesses (a single lioness can’t do much for her cubs, but groups sometime succeed at defending their offspring against infanticidal males), there’s also disease to worry about. Animals of the same species are vulnerable to the same pathogens, so ingesting conspecifics (member of one’s own species) can expose the cannibal to some dangerous cooties.
However, cannibalism itself isn’t the most efficient means of disease transmission. A 2007 analysis in Proceedings of the Royal Society B concluded that for cannibalism to be a significant channel for spreading disease, a single victim would have to be shared by a group. This is not the predominant form of cannibalism, which is usually more a one on one affair.§ Here again, humans deviate from animal kingdom norms. Ours is a species known to engage in group cannibalism, and this has been linked to at least one infamous ailment – Kuru, a rare but fatal prion disease that was found in Papua New Guinea populations that practiced cannibalism as part of funeral rituals (I use the past tense because this tradition ceased in the mid twentieth century.)**
As for the anomalous gray mouse lemur, it’s hard to say whether it was caught in act of actual murderous cannibalism or just opportunistically partaking of some free food. Since the female lemur had been so thoroughly eviscerated by the time it was collected and autopsied, cause of death was impossible to determine. And, given the elusive nature of the species, we’re unlikely to get any another example of this behavior anytime soon. But if nothing else, this story, coupled with the recent unearthing of a century-old study documenting the shockingly perverse (by 1915 standards, at least) sexual behavior of Adélie penguins, should give you plenty to think about if you find yourself at the cinema watching Madagascar 3. I’ll be sitting that one out. After researching this article, I’ve had my fill of animal antics.
* In case you haven’t heard, society reached a bizarre new low recently when rumors regarding a few high profile crimes resulted in the Centers for Disease Control having to issue a statement reassuring folks that a zombie apocalypse was NOT underway.
† Such self-serving massacres aren’t limited to males. In populations of giant water bugs – a species in which females compete for mates and males care for the eggs – female water bugs may destroy a male’s clutch of eggs to persuade him to accept a new mate and thus a new batch of eggs.
‡ Cannibalism is defined as eating an animal of one’s same species. So footage of chimpanzees hunting and devouring apes or monkeys of a different species, despite what Animal Planet might insinuate, does not count.
§ Fascinating tangent: in some species of lizard, partial cannibalism can have disease transmission effects similar to those of group cannibalism. Basically, a disease-carrying lizard can have its tail chewed off by a conspecific only to re-grow it and repeat the whole cootie-spreading cycle. Reptiles are amazing.
** Bovine Spongiform Encephalopathy (aka Mad Cow Disease) is another prion disease also spread by group cannibalism. Not by groups of cows attacking and eating each other, of course, but through the addition of cattle byproduct (i.e., meat and bone meal) to feed given to groups of cows.