Pomphorhynchus laevis
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| Pomphorhynchus laevis | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Acanthocephala |
| Class: | Palaeacanthocephala |
| Order: | Echinorhynchida |
| Family: | Pomphorhynchidae |
| Genus: | Pomphorhynchus |
| Species: | P. laevis |
| Binomial name | |
| Pomphorhynchus laevis Müller, 1776 | |
Pomphorhynchus laevis is an endo-parasitic acanthocephalan worm, with a complex life cycle, that can modify the behaviour of its intermediate host, the freshwater amphipod Gammarus pulex.[1] P. laevis does not contain a digestive tract and relies on the nutrients provided by its host species. In the fish host this can lead to the accumulation of lead in P. laevis by feeding on the bile of the host species.[2]
Host species
Pomphorhynchus laevis is a parasite with a complex life cycle, meaning that it needs multiple host species to complete it. The female releases eggs containing acanthor that are then ingested by an arthropod. The acanthor is then released from the egg and becomes acanthella which penetrate the host's gut wall and transforms into the infective cystacanth stage which presents as a cyst. The larval stages (cystacanths) reside in the hemocoel of the intermediate host, gammarids. From them the parasite is trophically transmitted to fish. Several fish species can serve as the definitive host, in which P. laevis infect the intestine.[3] In the fish host, bile is an important resource for the growth of P. laevis.[4]
In the wild, P. laevis is known to infect a range of fish species from several families as definitive hosts. The preferred final hosts of P. laevis are the chub and barbel when in freshwater, and the minnow when in an isolated body of water.[5] Other definitive hosts include the gudgeon, roach, vairone, nase, rudd, common dace, loach, catfish, perch, bullhead, three-spined stickleback,[6] brown trout[7] and round goby.[8]
Location of infection
Infection in the fish host is in the posterior part of the middle intestine, more specifically behind the pyloric caeca.[7] Immature P. laevis are mainly found in the proximal part of the digestive tract while mature and developing P. laevis are found near the first intestinal loop with the posterior third loop of the digestive tract being uninhabitable.[5]
Ecology
A positive association between fish biomass density and P. laevis abundance has been observed, suggesting the parasite populations increase in hosts with age, and that there is limited impact of intra-host density on parasite settlement.[6]
Environmental impacts on ecology
Pollution
In intermediate Gammarus hosts, infection leads to increased resistance against at least some insecticides. This potentially impacts the reliability of such hosts as bioindicators.[9] In a follow-up field and laboratory investigation, acanthocephalan parasites were shown to accumulate organic micropollutants at concentrations up to 35-fold higher than their Gammarus hosts. By acting as pollutant sinks and reducing the contaminant burden in infected amphipods, the parasites may further enhance host tolerance to polluted environments.[10]
In the definitive fish host, P. laevis can reduce concentrations of metals (such as arsenic, cadmium, copper, lead, and zinc) by absorption through the host's bile.[1][11] They thereby reduce heavy metal concentrations in the host bile.[4] Consequently, P. laevis is a potential indicator of pollution.[11]
Temperature
The infection success of acanthors emerging from eggs to Gammarus pulex is not affected by temperature, but developmental rate is increased at warmer temperatures (14 versus 17 °C).[12] At the same temperatures parasite infection reduces survival of these hosts, but this is not compounded by temperature.[12]