Third Party Mind Control

The idea of parasites manipulating their hosts for their own benefit has always been a tough one to grasp. I have even discussed previously on this blog the importance of finding the mechanism of manipulation so we do not incorrectly interpret the hosts altered behaviour as being caused by the parasite. This is very tough work and the answers unknown for many parasites although there is evidence for some genes and neurotransmitters involved. However, for one host-parasite system a new, third, party has been discovered that may be the cause of host subversion.

This story is a fascinating one because it involves parasitoid insects, which are known to be spectacular manipulators. Parasitoids lay their eggs onto or in a host which then serves as a food source and house for the developing larvae. The most well-known types of parasitoids are wasps and they often use venom or other substances to change their hosts’ behaviours in a variety of ways, including what is known as body guarding behaviour (check YouTube for some crazy videos). In this situation the host stands guard over the pupating insects after they have crawled out of its body to form cocoons. The fact that the host displays this weird behaviour once the parasitoid is no longer in physical contact suggests that some chemical or venom has been injected and continues to affect the host. New research has shed light onto this mystery manipulating substance and the result, as is often the case, is not so simple.

The parasitoid wasp, Dinocampus coccinellae, lays eggs inside of its host, Coleomegilla maculate, commonly known as the spotted lady beetle. The eggs develop inside the host, emerge and pupate next to the host. These little wasp larvae cocoons would be vulnerable to predators if it were not for the bizarre trait of the host standing guard over them. The beetle will stand motionless, save for the occasional tremor, over top of the pupating wasps, protecting them, until they have fully transformed and flown away.

Variations of this are seen in other host-parasitoid interactions but this is different for a couple of reasons. One being that after the wasps have flown away the beetle recovers regains mobility and walks off. In many other situations the bodyguard host dies soon after the adults emerge, the second being that a virus may be responsible for this bodyguard behaviour.

A recent paper from a team of researchers based in France and Canada have found a new RNA virus, Dinocampus coccinellae paralysis virus (DcPV), associated with the two players in this interaction. The virus was found in oviducts of the adult wasps, it replicates in the larvae which then transmit it to the beetle. In the beetle the virus infects nervous tissue causing neuropathy and an associated immune response. It is this action that can then cause the bodyguard behaviour which in fact is a symptom of infection: paralysis. Then after clearance of the virus normal behaviour is restored.

This research implies for the first time a third player in host manipulation rather than the parasite itself regulating the manipulation. The authours describe this phenomenon as a “biological weapon” being used by the wasp and highlight the many fascinating questions this raises. Does the virus actually gift the wasp with some fitness benefit, meaning are un-infected wasps and larvae as successful in contributing to the next generation? What is the relationship between the virus and the wasp, symbiotic? If so what is the benefit to the virus. It could be that the virus itself needs the presence of the beetle as it seemed that replication occurred in the larvae within the beetle and in the beetle itself as opposed to within the adult wasp. The nature of the timing of viral replication and clearance with the development time of the larvae suggests that this would be a symbiotic interaction that has evolved over time.

The role symbiotic or parasitic relationships play in the overall biology and ecology of organisms is an interesting one and has been shown before to have profound effects on the life histories of hosts. The bacterium Wolbachia infects many insect families and the relationship it has with its many hosts ranges from parasitic to mutualistic. This bacterium can alter the sex ratios of a population by killing males, feminizing males or inducing parthonogenic reproduction. In some cases the presence of Wolbachia is a good thing as it protects some hosts from RNA viruses, similar to DcPV. It also produces chemicals necessary for survival in other hosts.

These third party interactions illuminate the complexity of biological systems and host parasite interactions. How often does this occur in behavioural manipulation scenarios? How did they evolve and what potential fourth party may be influencing the outcome of the third party interaction? It also forces one to reconsider the concept of host manipulation, as discussed in other articles, are these truly adaptive manipulations or by products of infection; in this case not just infection with one parasite but a parasite of the parasite. The unraveling of nature’s complex interactions is never quite straightforward and this research has wonderfully added to that complexity.

“The complexity of things-the things within things-just seems to be endless. I mean nothing is easy, nothing is simple.” -Alice Munro

By Brad van Paridon

Original Paper:

Who is the puppet master? Replication of a parasitic wasp-associated virus correlates with host behaviour manipulation.

http://www.ncbi.nlm.nih.gov/pubmed/25673681

Eaten Alive and Happy to Help

The numbers of small insects and spiders on the planet is staggering and these two groups are both immensely fascinating and terrifying all at once. They posses amazing abilities like completely transforming their bodies during metamorphosis, producing venom and silk or the evolution of the eusocial lifestyle. With all these incredible traits comes too the cold and horrifying ones that this tiny world demands as well. The swarming hive mentality of the eusocial ants that will consume and attack everything in their path, overwhelming larger insects and tearing them apart alive and taking the pieces home to feed the nest. The beauty of the spider web too gives way to a mode of feeding that is truly unimaginable in larger animals, wrapping up prey in silk, piercing it with sharp straw like appendages and slowly sucking up all the liquid insides. It is a harsh world for these tiny animals and a take no prisoners, show no sympathy way of life is required to survive here. One of the most horrifying ways of life is the parasitoid lifestyle and its adaptations that create living (for a time) nurseries for metamorphosing young.

Parasitoids are essentially parasites except that they usually only require a host for part of their life cycle and will more often than not kill and consume that host when they are done. Many species of wasps have adopted this strategy and some have evolved some impressive/heinous ways to get the job done. As fully mature adults these wasps are loners, unlike hive building eusocial wasps. They live and hunt on their own, mate and then parasitize other arthropods like cockroaches, spiders, caterpillars and all varieties of bugs. They will lay their eggs on or in these hosts which will serve as a food source for the developing young to consume alive until they are ready to become adults.

It isn’t all as easy as it sounds for these wasps though as they have to locate a host, often immobilize it long enough to plant the eggs and once present on the host the young wasps can be vulnerable to other parasitoids or predators. In order to overcome some of these difficulties some parasitoids appear to have evolved the ability to subvert the minds of their hosts for their own purposes.

A stunning example of this involves orb weaving spiders and the parasitoid wasp Hymenoepimecis argyraphaga found in Central American rain forests.The wasp will attack, paralyze the spider with venom and lay an egg on the abdomen. The spider will resume normal activity after the initial venom wears off but the wasp larva remains and feeds on the insides of its host by slowly sucking them out from its position on the abdomen.

 

Wasp larvae feeding on the spiders abdomen

Wasp larvae feeding on the spiders abdomen. From BBC Life in The Undergrowth.

As the wasp gets closer to maturity it induces the spider to forgo its normal web building process for the construction of a special cocoon web. Inside this structure the wasp molts, finishes consuming the spider, after which it spins its own pupal cocoon anchored to the specialized spider web. Here it finishes growing and emerges as an adult. By inducing the change in web building the spider creates a protective structure for the wasp to finish feeding and then to anchor its final cocoon too. Without this the young wasp would be exposed to the environment and scenarios like being washed away and killed during heavy rains.

A modified web (left) and normal web (right). Picture from: http://www.publy.ru/post/3021

A modified web (left) and normal web (right). Picture from: http://www.publy.ru/post/3021

The truly terrifying aspect of this relationship, even worse than being eaten alive, is the fact that the wasp can not just prevent a host from resisting being consumed but will actually drive the host to aid the creator of its own gruesome demise. It is believed that is done with some sort of venom because the weird spider behaviour will increase over time as the larva grows, and releases the chemical. This mechanism also seems likely as the wasp is not in direct contact with hosts brain or nervous system. The effects of altered behaviour also gradually diminish if the larval wasp is removed. All signs point to a chemical means of manipulation and this is hardly the only wasp for which mind controlling venoms have evolved. Many of the parasitoid wasps induce their hosts to protect the very things that are eating them alive. A quick YouTube search will provide ample video of these horrifying relationships many more of which will also be covered here at ZombieAnts.ca.

Original work on Hymenoepimecis argyraphaga :

Eberhard, W.G., 2000. Spider manipulation by a wasp larva. Nature 406, 255-256.

Eberhard, W.G., 2001. Under the influence: webs and building behavior of Plesiometa argyra (Araneae, Tetragnathidae) when parasitized by Hymenoepimecis argyraphaga (Hymenoptera, Ichneumonidae). Journal of Arachnology 29, 354-366.

Eberhard, W.G., 2010. Recovery of spiders from the effects of parasitic wasps: implications for fine-tuned mechanisms of manipulation. Animal behaviour 79, 375-383.