Spinochordodes tellinii

Life Cycle

Adult S. tellinii live in aquatic environments- where they find a mate and reproduce. The eggs are laid in the water and hatch into microscopic pre-parasitic larvae. The pre-parasitic larva is then ingested by the orthopteran host and becomes a parasitic larva inside the host. As the parasite grows, it eventually will take up most of the host cavity. Once development is complete within the host, the nematomorph releases proteins that cause the host jump into water. The suicide of the host organism allows S. tellinii to can complete it's life cycle. Once in the water, the hairworm exits the host and immediately begins searching for a mate to reproduce (Shapiro 2012). While inside the host organism, a hairworm can grow up to 3-4 times the size of their host (Biron et al. 2005).

The two most important transitions in the life cycle of a hairworm are from aquatic larva to the terrestrial definitive host and the second being from the host to water (Biron et al. 2005). Both of these stages have a considerable amount of chance. The chances of the larva being ingested by the appropriate host are not high. In addition, causing the behavioral modification that will lead the host to water will not always work if the host is not adequately close to water to begin with.

S. tellinii are only able to alter the behavior of their host to go to the water if it is already reasonably close to a water source. As they direct the host to water, it may take several seconds to several minutes for the parasite to emerge from the grasshopper. At this stage, they are particularly vulnerable to predation. However, hairworms have an ability to emerge from the digestive tract of the predator after their host has been eaten. They have been seen to emerge, completely alive and intact, from the mouth and gills of the predator (Ponton et al. 2006).

Hairworms spend the winter in water or mud and mate in the spring. After the eggs are laid, they hatch into pre-parasitic larva around one month later. In order to continue development, a grasshopper or locust must ingest this particular larva. Approximately three months after the host is infected with the parasite, the hairworm begins altering the host’s behavior to seek out water. Adults then emerge from the host and are live in the water. Although adults have a non-functional gut and do not feed, they are able to survive for several months (Kaya 2013).

Behavioral Modification of Host

Spinochordodes tellinii influence the host to display erratic behavior rather than actively seeking out water. This erratic behavior will eventually leads the host to the water-which they enter and drown (Shapiro 2012). This behavioral modification begins with the host wandering into unusual habitats, such as out of the forest, and eventually committing suicide by entering the water source.

An experiment looking at the parasite proteomic expression before, during, and after behavioral modification found that the adult hairworm alters the normal function of a grasshopper’s central nervous system. This happens by the hairworm releasing effective molecules along with differential expression of proteins associated with neurotransmitter activity. This is most likely a case of molecular mimicry, as the proteins show similarities with other known insect proteins (Biron et al. 2005). Hairworms that have an intermediate host alter the phenotype of the host to make it inclined to higher rates of predation in order to increase the rate of transmission (Seppala et al. 2008).

Sources

Biron, D.G, et al. “Behavioural Manipulation in a Grasshopper Harbouring Hairworm: a Proteomics Approach.”Proceedings of the Royal Society B: Biological Sciences, The Royal Society, 22 Oct. 2005, www.ncbi.nlm.nih.gov/pmc/articles/PMC1559948/.

Kaya, HK. “How to Manage Pests.” UC IPM Online, Mar. 2013, ipm.ucanr.edu/PMG/PESTNOTES/pn7471.html.

Kushboo, Jain. “Phylum Nematomorpha: Characters, Classification and Affinities.” Biology Discussion, 27 May 2016, www.biologydiscussion.com/invertebrate-zoology/phylum-nematomorpha/phylum-nematomorpha-characters-classification-and-affinities/32917.

Leo, Shapiro. “Comprehensive Description of Nematomorpha.” Encyclopedia of Life, 14 Apr. 2012, eol.org/data_objects/17763486.

Ponton, F., Lebarbenchon, C., Lefe`vre, T., Biron, D. G., Duneau, D., Hughes, D. P. and Thomas, F. (2006). Parasite survives predation on its host. Nature, London 440, 756.

Schmidt-Rhaesa, Andreas, et al.“Host–Parasite Relations and Seasonal Occurrence of Paragordius Tricuspidatus and Spinochordodes Tellinii (Nematomorpha) in Southern France.” A Journal of Comparative Zoology, vol. 244, no. 1, 15 Aug. 2005, pp. 51–57., www.sciencedirect.com/science/article/pii/S0044523105000331.

Seppälä, Otto, et al. “Host Manipulation by Parasites in the World of Dead-End Predators: Adaptation to Enhance Transmission?” Proceedings of the Royal Society of London B: Biological Sciences, The Royal Society, 22 July 2008, rspb.royalsocietypublishing.org/content/275/1643/1611.