Cannibalism helps invading invertebrates survive severe conditions

Date:May 7, 2020

Source:University of Southern Denmark

In a world where movements of non-native animal species are drastically disrupting whole ecosystems and causing economic harm and environmental change, it is becoming increasingly important to understand the features that allow them to colonize new habitats.

A new study, published in Communications Biology, shows that the prolific comb jelly, a marine invertebrate invader from North America that now frequently washes up on Baltic shores, is able to expand their geographical range thanks to the use of its own young as nutrient stores through long and nutrient deprived winters.

As jellies trace their lineage back to the beginning of all animal life, this work furthers the view of cannibalism as a pervasive trait amongst the animal kingdom.

Mysterious success

With their translucent gelatinous bodies, they may not look like much, but the expansion of the comb jelly, Mnemiopsis leidyi, from the east coasts of North and South America to Eurasian coastal waters has wreaked havoc on local environments.

Their success has remained something of a mystery especially as, instead of storing resources before wintering, they seemed to counterproductively invest in massive 'blooms' of offspring unable to survive long and nutrient deprived winters.

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Cobra cannibalism more prevalent than previously thought

Researchers in South Africa investigate cannibalism in cape cobras and others in the region

Date:  October 2, 2018

Source:  Ecological Society of America

Summary:

Researchers in South Africa's Kalahari Desert found a large male cape cobra devouring another smaller male of the same species. Surprised by the thought-to-be-rare event, they decided to investigate how common and widespread cannibalism was in cobras.

Last spring, researchers in South Africa's Kalahari Desert found a large male cape cobra devouring another smaller male of the same species. Surprised by the thought-to-be-rare event, they decided to investigate how common and widespread cannibalism was in cobras.

Apart from a few species, scientific understanding of snake diets is lacking. Snakes are elusive creatures that feed relatively infrequently, making feeding observations difficult to come by. Bryan Maritz, a researcher at the University of the Western Cape and lead author of the new study in the Ecological Society of America's journal Ecology, explains, "This work highlights a renewed effort to meaningfully quantify several aspects of snake natural history, especially in poorly studied regions such as Africa."

While cape cobras are known to eat other snake species -- up to a third of their diet -- recorded instances of cape cobras eating individuals of the same species, known as conspecifics, has been extremely rare. Scientists have treated such reported observations as aberrant behavior.

So, what caused this cape cobra to attack and eat the smaller male of its kind? How often does this happen? Do all cobras take part in cannibalism?

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Male chimpanzee seen snatching seconds-old chimp and eating it

13 October 2017

By Jessica Hamzelou

A rare sighting of a chimpanzee giving birth in the wild came to a grisly conclusion. Within seconds of the birth, the baby was snatched away and eaten by a male of the same group. The observation explains why female chimpanzees tend to go into hiding for weeks or months when they have their babies.

Little is known about how chimpanzees give birth in the wild because only five births have ever been observed, says Hitonaru Nishie of Kyoto University in Japan. Nishie and his colleagues have been studying chimpanzees in Tanzania’s Mahale mountains for the last few years.

One of the reasons so few have been witnessed is that the soon-to-be mothers often leave the group when the baby is due, and don’t return until the infant is weeks or months old. This absence has been described as a chimpanzee’s “maternity leave”.

So Nishie and his colleague Michio Nakamura were surprised when, at around 11 am one December day, a female member of the chimpanzee group they were observing began to give birth in front of the 20 other members.

As soon as the baby was out – and before the mother had even had a chance to touch it – the baby was snatched away by a male member of the group, who then disappeared into the bush. The researchers found him around 1½ hours later, sitting up a tree and eating the infant from the lower half of its body. He ate the entire body within an hour.

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Plants under attack can turn hungry caterpillars into cannibals

Date:  July 10, 2017

Source:  University of Wisconsin-Madison

Summary:  When does a (typically) vegetarian caterpillar become a cannibalistic caterpillar, even when there is still plenty of plant left to eat? When the tomato plant it's feeding on makes cannibalism the best option, report investigators.

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Cannibal 'T. Rex' Ants Seen Live for 1st Time Ever (and They're Shy)

By Stephanie Pappas, Live Science Contributor | May 16, 2017 02:14pm ET 

An ant named after the fierce, carnivorous dinosaur Tyrannosaurus rex has been observed alive for the first time — and it failed to live up to the dinosaur's reputation.

Tyrannomyrmex rex is a timid, finicky eater, new research finds. The ants can, however, turn to cannibalism in times of need.

Until now, these Asian ants were a complete mystery to science, despite being discovered more than 20 years ago. No one had ever collected more than a single specimen, and no one had ever observed a T. rex ant alive for an extended period of time. So when biologist Mark Wong stumbled across a colony of T. rex ants while conducting an ant diversity survey in Singapore, he knew he had something important.

He and his colleague Gordon Yong from the National University of Singapore carefully collected the colony, which consisted of 13 workers, as well as eggs, larvae and pupae (the liminal stage between larva and adulthood). They then observed the ants in an attempt to figure out what makes them tick. Because the study is the first of its kind, everything the researchers discovered is new, Wong told Live Science.

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Male poison frogs become cannibals after taking over territories - via Herp Digest

Science Daily, 2/28/17, University of Veterinary Medicine -- Vienna

In general, male poison frogs of the species Allobates femoralis are observed as very caring and attentive fathers. Eva Ringler and her team were able to show that territorial males care for all clutches inside their territory, even if they had not fertilised a single clutch in the previous weeks.

The current study showed, however, that they quickly stop their child-friendly behaviour when they succeed in taking over a new territory. In this case, the dedicated fathers became cannibals. They ate all the clutches in the new territory.

Cannibalism and infanticide are not uncommon in the animal kingdom. Among others, feline predators, primates, insects, fish and birds show these kind of behaviours. Eating unrelated offspring is often sexually motivated. In species with female parental care, mothers usually become ready to mate more quickly without offspring. Thereby, the perpetrators actually "kill two birds with one stone": on one hand, they reduce the reproductive success of other rivals -- on the other hand, they increase their chances of future mating success.

In poison frogs, we find a completely different situation. Here, males are the ones responsible for parental care. Thus, infanticide by males does certainly not serve to manipulate females, but rather to reduce the risk of costly parental care towards unrelated offspring. Thereby, it seems that males' parental and cannibalistic behaviours are mediated by a single simple trigger.

In both cases -- care and cannibalism -- the territory, in particular the territorial behaviour, of male frogs, is the crucial factor. Inside their own territory which is prominently and vigorously defended, it doesn't cross the male frogs' minds that one of the clutches might not be their own. That is why they will transport all tadpoles that are located inside their territory to suitable water bodies, as soon as they are ready-to-go.

However, if they take over the territory of rival, male poison frogs become cannibals and take advantage in several respects. First, they completely clear the territory from their rivals that do not only lose their territories but also their offspring. Eating up all clutches of their precursor also means that the male frogs can be sure that all future clutches contain exclusively their own offspring. Furthermore, clutches are very nutritious and probably constitute a valuable source of energy.

Simple behavioural rule instead of complex decision-making procedure

Ringler and her team -- starting from a field observation in the species' natural habitat -- were able to experimentally test this behaviour in the lab, where they let a group of male Allobates femoralis effectively take over new territory by transferring them into a novel terrarium. A second group stayed in their original terrarium. In both cases, the researchers put unrelated clutches into their terrariums. The males in the "takeover" group became cannibals and preyed on the unrelated clutches, whereas the males in the 'resident' group spared the unrelated eggs and even transported them to the available water sites in most of the cases.

According to Ringler, the behaviour in the wild is likely very effective. "In the species' natural habitat, there are regular fights for territories and also territory takeovers. We expect that cannibalism commonly occurs in such situations," explained Ringler. Furthermore, cannibalism deprives the rivals of a motive to retake this specific territory because their former offspring are lost.

For Ringler, these results open up a novel perspective on cannibalism in the animal kingdom. "We have seen in poison frogs that a simple trigger is sufficient to switch from very destructive actions to parental care." In other animal species, individuals become cannibals out of sexual motivation or hunger, whereas territorial status seems to be the trigger in male poison frogs.

The behaviour of male poison frogs somehow reminds, among others, of conflicts in the Middle Ages, where during conquests not only the ruler was brought down and killed but also his offspring. This was to prevent them from claiming the throne. "But there was no cannibalism," concluded Ringler.

Creepy Cannibals: Squid Have No Qualms About Eating Their Own Kind

By Laura Geggel, Senior Writer | September 22, 2016 11:12am ET

The deep-sea diving Gonatus squid has a hearty appetite, even when it comes to eating its own kind, a new study finds.

The cannibalism finding came about during a 20-year study (1995–2015) in which marine researchers used a remotely operated vehicle (ROV) to study and video-record the eating habits of more than 100 different squid of the Gonatus genus in Monterey Submarine Canyon, off the California coast.

In particular, two species of Gonatus squid — Gonatus onyx and Gonatus berryi — showed a voracious appetite for munching on their own species, the researchers said. In fact, after looking at video they took of 109 squid eating meals, researchers found 42 percent of the prey G. onyx ate were other G. onyx squid. 

 
In addition, the researchers — Henk-Jan Hoving, an evolutionary ecologist of Marine Fishes at the Helmholtz Centre for Ocean Research Kiel in Germany, and Bruce Robison, a senior scientist and midwater ecologist at the Monterey Bay Aquarium Research Institute (MBARI) in California — never observed G. onyx feeding on G. berryi, but G. berryi routinely fed on G. onyx. 

 
Why cannibalism?
Cannibalism isn't uncommon in the deep sea, but this is the first time that scientists have proof that Gonatus squid engage in cannibalistic behavior, the researchers said.

They stressed the importance of having live-video evidence (in addition to stomach contents) of the cannibalism, since looking only at stomach contents of squid caught in trawling nets can be misleading. That's because squid and other marine creatures in trawling and jigging environments often become stressed and engage in unnatural behaviors, including cannibalism.

Though ROV lights and noises may also disturb marine creatures, in this study the researchers found that most of the prey capture happened before ROV the arrived, the researchers said.

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Studying poop shows ancient shark ate its own young

by Chuck Bednar

An ancient group of sharks living approximately 300 million years ago were cannibalistic and would even devour their own young, according to fossil evidence collected as part of research detailed in Thursday’s edition of Palaeontology.

Lead author Aodhán Ó Gogáin, a Ph. D. student in the Trinity College Dublin School of Natural Sciences, and his colleagues studied coprolites (or fossilized feces) of adult Orthacanthus sharks and found that they contained tiny teeth belonging to young members of their own species.

Orthacanthus sharks, the study authors explained, lived in coastal swamps along the equator and used protected lagoons to raise their offspring – but when food started to become scarce, they did not hesitate to cannibalize their own young in order to obtain much-needed sustenance.

“Orthacanthus was a three-metre-long xenacanth shark with a dorsal spine, an eel-like body, and tricusped teeth,” Ó Gogáin explained in a statement. “There is already evidence from fossilized stomach contents that ancient sharks like Orthacanthus preyed on amphibians and other fish, but this is the first evidence that these sharks also ate the young of their own species.”

Why bother eating your own young?

Ó Gogáin’s team found evidence of shark cannibalism in unusual spiral-shaped coprolites found in the Minto Coalfield of New Brunswick. Because of the shape of the fossilized dung, they were able to link it to Orthacanthus, as the shark possessed a unique corkscrew-shaped rectum.

In-depth analysis of the coprolites found they contained many fossilized teeth belonging to juvenile Orthacanthus, confirming that the creatures engaged in fillial cannibalism (which is just a fancy way of saying they would eat their own young). This discovery is not unprecedented, since as BBC News noted, modern-day bull sharks are also know to consume their own offspring.

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