''Euhaplorchis californiensis'' is a trophically transmitted

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

(TTP) that lives in the salt-water marshes of

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...

, United States. It lives in three hosts:

shorebirds FIle:Vadare - Ystad-2021.jpg, 245px, A flock of Dunlins and Red knots Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflats in order to foraging, forage for food c ...

, horn snails, and killifish. As with many TTPs, ''E. californiensis'' modifies the behavior of the host to increase the likelihood of transmission to its next host.

Life cycle

The parasite's eggs are released in the droppings of shorebirds. Horn snails consume the droppings and become sterile. Once the parasite has lived in the snail a couple of generations, the cercariae (the disk-shaped

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e of flukes of the class

Trematoda Trematoda is a class of flatworms known as trematodes, and commonly as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is a mol ...

, which have a tail-like appendage) swim out into the marsh. The cercariae latch onto the

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

of the killifish and make their way along a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

and into the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

cavity, where, as metacercariae, they encyst in the meningeal layer on the brain surface. The

s form a “carpet-like” layer over the brain. According to Kevin D. Lafferty, infected killifish are four times more likely to “shimmy, jerk, flash, and surface” than uninfected fish. This behavior makes the infected fish 10 to 30 times more likely to be caught and consumed by a bird. Once the fish is consumed, the

lives in the bird's gut and produces eggs to be released in the stool, which is spread into the marshes and ponds. Therefore, starting the cycle again.

Effects on the ecosystem

Armand Kuris speculates that the predator in this host-parasite interaction benefits by acquiring food easily. He also claims that the susceptibility of infected killifish to be picked up by their avian predators has led to a diverse and abundant assemblage of piscivorous birds along the coasts. Lafferty did a study to observe how a population of un-parasitized snails performs in the absence of infected snails. He found that they released more eggs and became densely populated. He proposes that the snail population in the natural environment would be nearly double what it is if it weren't for the parasite ''Euhaplorchis californiensis''.

References

* * Zimmer " Parasite Rex: inside the bizarre world of nature's most bizarre creatures. Chapter: A precise Horror p. 105-111 * * * {{Taxonbar, from1=Q3387407, from2=Q18510926 Heterophyidae Mind-altering parasites Parasites of molluscs Parasites of birds Parasitic helminths of fish