Nav: Home

Kidnapping in the Antarctic animal world?

September 10, 2018

Pteropods or sea snails, also called sea angels, produce chemical deterrents to ward off predators, and some species of amphipods take advantage of this by carrying pteropods piggyback to gain protection from their voracious predators. There is no recognisable benefit for the pteropod. On the contrary they starve: captured between the amphipod's legs they are unable to feed. Biologists working with Dr Charlotte Havermans at the Alfred Wegener Institute have investigated this phenomenon as part of a cooperation project with the University of Bremen. In an article in the journal Marine Biodiversity, they talk about kidnapping and explain the potential advantages of this association for both the host and its passenger.

Amphipods of the suborder Hyperiidea are popular prey for fish and sea birds. They play an important role in the Southern Ocean food web, which is why biologist Dr Charlotte Havermans is investigating the distribution, abundance and ecological role of various species of amphipods. To do so, she is taking samples on board the Research Vessel Polarstern from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI). She works at the University of Bremen's working group Marine Zoology. The project is funded by the DFG (German Research Foundation) in the Priority Programme on Antarctic Research.

During a Polarstern expedition that took place in the austral summer from 2016 to February 2017, she made an extraordinary discovery: "A few of the amphipods carried something unusual on their backs. On closer inspection I realised that they were carrying pteropods piggyback," reports the biologist. A literature search revealed that US researchers had already described this behaviour back in 1990 - although only for the high-Antarctic coastal waters and not for the open Southern Ocean where the ship was underway.

"We were wondering whether these tandems occur as frequently in the open ocean as in coastal waters - and whether both animals benefit from the relationship," explains Charlotte Havermans. In the coastal areas of the McMurdo Sound, most of the amphipods studied carried a pteropod rucksack. Subsequent genetic and morphological investigations provided new insights. Previously, such tandems were completely unknown for the open, ice-free waters of Southern Ocean, and now the biologists have discovered this behaviour in two species: the amphipod species Hyperiella dilatata carried a type of pteropod known as Clione limacina antarctica, while the crustacean Hyperiella antarctica was associated with the pteropod Spongiobranchaea australis. Our sample size was too small to say without doubt whether these are species-specific pairs, where only a certain amphipod carries a certain pteropod species. During the expedition along the Polar Front to the eastern Weddell Sea, the AWI biologist's team found only four such tandems.

The research team's findings regarding the benefits for the animals are very exciting. Behavioural observations of the free-living pteropods show that cod icefishes and other predators are deterred by the chemicals the gastropods produce. When amphipods take pteropods "hostage", they are not affected by their poison. Icefishes quickly learn that amphipods with rucksacks are not tasteful and so avoid those with a pteropod on their back.

Because the conditions in the open Southern Ocean are different to those in coastal ecosystems, several open questions remain: whether or not predatory squid and lanternfish, commonly found in the area, are also deterred by the chemicals has not yet been investigated. It is also still unclear to which extent the pteropod benefits from saving energy by being carried by its host. The researchers observed that the amphipod uses two pairs of legs to keep the gastropod on their back so that they are completely unable to actively hunt for suitable food where it is available. "On the basis of our current understanding, I would say that the amphipods kidnap the pteropods," sums up Charlotte Havermans with a wink.

The biggest lesson the authors draw from their discovery: "We are probably overlooking numerous such associations between species, because they are no longer visible after net sampling." Unlike shelled gastropods and crustaceans, which remain relatively intact, jellyfish and other delicate animals are crushed in the nets. "In the future we will hopefully be able to use suitable underwater technologies with high-definition cameras to investigate even the smallest life forms in their habitat. This will provide insights into the numerous exciting mysteries of interspecific interactions, which have so far remained hidden for biologists - but which undoubtedly play an important role in predator-prey relationships in the ocean."
-end-
Original publication:

Charlotte Havermans, Wilhelm Hagen, Wolfgang Zeidler, Christoph Held, Holger Auel: A survival pack for escaping predation in the open ocean: Amphipod - pteropod associations in the Southern Ocean, Marine Biodiversity 2018. DOI: 10.1007/s12526-018-0916-3, https://doi.org/10.1007/s12526-018-0916-3

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

Related Predators Articles:

Marine predators: Bigger in size with an appetite to match
The size of marine invertebrate predators has increased over the past 500 million years, while the size of their prey has not, a new study reveals.
Predators are real lowlifes
By deploying green clay caterpillar models across six continents, researchers unmasked an important global pattern.
Fish step up to lead when predators are near
Researchers from the University of Bristol have discovered that some fish within a shoal take on the responsibilities of leader when they are under threat from predators.
Restoring predators and prey together speeds recovery
Restoring predator and prey species together helps accelerate ecosystem recovery efforts compared to pursuing restoration of one species at a time, new research concludes.
Recovering predators and prey
Researchers show how simultaneously restoring predators and prey is much faster and more effective than doing so one at a time.
Reducing pressure on predators, prey simultaneously is best for species' recovery
Reducing human pressure on exploited predators and prey at the same time is the best way to help their populations recover, a new study indicates.
When it comes to predators, size matters
When it comes to predators, scientists find larger sheephead that consume bigger urchins help keep that population under control.
Birds of a feather flock together to confuse potential predators
Scientists from the universities of Bristol and Groningen, in The Netherlands, have created a computer game style experiment which sheds new light on the reasons why starlings flock in massive swirling groups over wintering grounds.
For viral predators of bacteria, sensitivity can be contagious
Scientists have shown for the first time how bacteria with resistance to a viral predator can become susceptible to it after spending time in the company of other susceptible or 'sensitive' bacteria.
How miniature predators get their favorite soil bacteria
Tiny predators in the soil can literally sniff out their prey: soil bacteria, which communicate with each other using scent.

Related Predators Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Changing The World
What does it take to change the world for the better? This hour, TED speakers explore ideas on activism—what motivates it, why it matters, and how each of us can make a difference. Guests include civil rights activist Ruby Sales, labor leader and civil rights activist Dolores Huerta, author Jeremy Heimans, "craftivist" Sarah Corbett, and designer and futurist Angela Oguntala.
Now Playing: Science for the People

#521 The Curious Life of Krill
Krill may be one of the most abundant forms of life on our planet... but it turns out we don't know that much about them. For a create that underpins a massive ocean ecosystem and lives in our oceans in massive numbers, they're surprisingly difficult to study. We sit down and shine some light on these underappreciated crustaceans with Stephen Nicol, Adjunct Professor at the University of Tasmania, Scientific Advisor to the Association of Responsible Krill Harvesting Companies, and author of the book "The Curious Life of Krill: A Conservation Story from the Bottom of the World".