''Euhaplorchis californiensis'' is a trophically transmitted

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...

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

Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...

. It lives in three hosts:

shorebirds 245px, A flock of Dunlins and Red knots">Red_knot.html" ;"title="Dunlins and Red knot">Dunlins and Red knots Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflat ...

, horn snails, and

killifish A killifish is any of various oviparous (egg-laying) cyprinodontiform fish (including families Aplocheilidae, Cyprinodontidae, Fundulidae, Profundulidae and Valenciidae). All together, there are 1,270 species of killifish, the biggest family ...

. 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 (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e of flukes of the class

Trematoda Trematoda is a class of flatworms known 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 usually a snail. The definitive h ...

, 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

and make their way along a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...

and into the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

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

are four times more likely to “shimmy, jerk, flash, and surface” than uninfected fish. This behavior makes the infected fish 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.

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, from=Q3387407 Heterophyidae Mind-altering parasites Parasites of molluscs Parasites of birds Parasitic helminths of fish