''Microphallus turgidus'' is a widespread and locally common

flatworm Platyhelminthes (from the Greek language, Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a Phylum (biology), phylum of relatively simple bilaterian, Segmentation (biology), ...

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 ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

lakes and streams. Multilocus allozyme genotype data show that ''Microphallus turgidus'' is a single outbred species with high levels of

gene flow In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic variation, genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent ...

among

South Island The South Island ( , 'the waters of Pounamu, Greenstone') is the largest of the three major islands of New Zealand by surface area, the others being the smaller but more populous North Island and Stewart Island. It is bordered to the north by ...

populations. ''Microphallus turgidus'' is commonly found in the abdominal muscles of grass shrimp.

Life cycle

''Microphallus turgidus'' exclusively uses the snail '' Potamopyrgus antipodarum'' as the first

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

, a shrimp as the secondary intermediate host, and the final hosts are typically

waterfowl Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which i ...

. Embryonated ''Microphallus turgidus'' eggs are ingested from sediment and hatch in the snail's gut, penetrate the intestine, and migrate to the

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s and

digestive gland The hepatopancreas, digestive gland or midgut gland is an organ of the digestive tract of arthropods and molluscs. It provides the functions which in mammals are provided separately by the liver and pancreas, including the production of digestive ...

. Following successful establishment, the parasite then undergoes

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...

, replacing much of the host's reproductive tissue and digestive gland, which results in complete sterilization of the snail. The first visible parasite developmental stages (blastocercariae) are detectable after approximately 75 days post-exposure and

metacercariae Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two Sucker (zoology), suckers: one ventral and the other Mouth, oral. Trematodes are covered by a Tegument (helminth), tegument, that protects the o ...

are common by 90 days post-exposure at 16 °C in the lab. The life cycle continues through a secondary intermediate host, such as the glass shrimp '' Palaemonetes pugio'', and is completed when the shrimp infected by the metacercariae are consumed by waterfowl or mammals.

Host

''Microphallus turgidus'' are more common in wild animals that live in salt marshes and are considered as definite host. The first intermediate host is the hydrobiid snail, on its immature form called a cercaria, it develops into snail. The most common is the second intermediate hosts, grass shrimp, ''Palaemonetes pugio''. Metacercariae of the parasite usually encyst in grass shrimp abdominal muscle, and though adult ''P. pugio'' average only 2.9 cm in length, a shrimp can be infected with more than 100 parasites.

Symptoms / effects

Numerous reports of changes in the host behavior after the parasitic infection influenced the host-parasite survival, host predation, and parasite transmission. Parasite induced behavior changes include hyperactivity, sluggishness, fatigue, disorientation, altered habitat selection, and reduced predator avoidance. In fact, it is rare are to find a locality where the grass shrimp ''Palaemonetes pugio'' is not infected. At certain shrimp collection sites, near all specimens of ''P. pugio'' are infected, some with more than 100 parasites. The intensity of infection varies from one locality to another and may be due, at least partially, to geographic differences in salinity. Heavily infected shrimp are more likely to be eaten by a predator than uninfected shrimp, have lower swimming stamina, and spend more time swimming and less time motionless in the presence of a predator. Thus, ''M. turgidus'' may increase the predation of ''P. pugio'' in the wild.

References

{{Taxonbar, from=Q6839865 Animals described in 1958 Plagiorchiida Parasites of molluscs Parasites of birds