Cannibalism Helps Invading Invertebrates Survive Severe Conditions

Investing in the future: Researchers show how cannibalism among the invasive comb jelly enables adults to survive severe conditions at the edge of their ecological range with implications for the use and evolutionary origins of cannibalism.

Because non-native animal species drastically disrupt whole ecosystems, causing economic harm and environmental change, it is becoming increasingly important to understand they colonize new habitats. A new study, published in Communications Biology, shows that the prolific comb jelly, a marine invertebrate from North America that now frequently washes up on Baltic shores, expand their geographical range using their own young as nutrient stores through long, nutrient deprived winters. As jellies traces 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.

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Fotographischer Beweis für kannibalistisches Verhalten; Larven der Mnemiopsis leidyi („Meerwalnuss”) im Innern eines erwachsenen Tieres (neben den roten Pfeilen).

© Jamileh Javidpour

With translucent gelatinous bodies, Mnemiopsis leidyi may not look like much of a threat, but the expansion of the comb jelly 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 seem to counterproductively invest in massive ‘blooms’ of offspring unable to survive long and nutrient deprived winters. It has been assumed that the species overcame this bizarre nutritional behavior due to a lack of native predators, though evidence for this, as well as for the best management strategies for this exotic species, has remained hazy.

That was until an international team of researchers, including authors at the University of Southern Denmark and the Max Planck Institute for the Science of Human History, performed the dedicated collection of comb jellies at their northernmost range in the Baltic Sea off of northern Germany throughout the year. Lead author of the study, Jamileh Javidpour, Assistant Professor at University of Southern Denmark states “we combined a study of the population dynamics of this species with experimental feeding and geochemical tracers to show, for the first time, that adult jellies are actually consuming the blooms of their own offspring.”

This rather sinister realization behind the function of these blooms makes perfect biological sense. As a handy floating nutrient reservoir that lasts beyond the collapse of normal prey populations, the release of offspring provides adults with an additional 2-3 week window of growth, which, ecologically, can be the difference between life and death. “In some ways, the whole jelly population is acting as a single organism, with the younger groups supporting the adults through times of nutrient stress,” says Thomas Larsen, a co-author on the study at the Max Planck Institute for the Science of Human History. “Overall, it enables jellies to persist through extreme events and low food periods, colonizing further than climate systems and other conditions would usually allow,” he continues.

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Mnemiopsis ledyi is a major zooplankton predator and their impact on local fisheries can be devastating when they form great blooms.

Ecomare / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

The novel data produced by the team may allow conservationists and governments to better combat the spread of these jellies, which can disadvantage native species and bring down local fisheries. In their exotic ranges, comb jellies are particularly successful in seas impacted by rapid warming, overfishing and excessive nutrient loads. Tackling these problems could potentially reduce the food sources for these gelatinous invaders and restore the ecological balance of Eurasian seas. The study also suggests that this jelly may become a problematic species in its native ranges, with rapid bloom-and-bust cycles possible under the right conditions.

This study also speaks to wider questions of cannibalism in the animal kingdom. Cannibalism has been recorded among more than 1,500 species, including humans, chimpanzees, squirrels, fish, and dragonfly larvae. Although sometimes cannibalism occurs during periods of extreme shortage or disaster, it can also occur under regular conditions. “Because comb jellies trace their ancestry back to the beginning of most animal life as we know it during the Cambrian Period, 525 million years ago, it remains possible that it is a basic, unifying feature across the animal kingdom,” Jamileh concludes.

More research is certainly required to clarify the evolutionary origins of cannibalism among the earliest members of the animal kingdom and the and the reasons why it is particularly prominent in aquatic ecosystems. Nevertheless, these gelatinous critters have provided a calculating window into the use of this behaviour during the invasion of new habitats. While it may seem abhorrent to us, ‘investing in the future’ certainly has a very different meaning for these invertebrates.

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