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JYX - Studies of the life history of a parasite : a basis for effective population management
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Jyväskylä studies in biological and environmental science
Kalatäit ovat pintaloisia, jotka imevät kaloista verta. Ne liikkuvat kalan pinnalla ja vaurioittavat ihon pintaa. Ihovauriot ja niistä johtuvat bakteeri- ja sienitaudit heikentävät kalojen arvoa ja voivat johtaa kasvun hidastumiseen ja kalan kuolemaan. Kalatäiden torjunta kalanviljelylaitoksissa on ollut vaikeaa ja tehotonta, koska niiden ekologiaa ja elinvaiheita ei ole tunnettu, kertoo Teija Hakalahti. Hakalahti tutki Argulus coregoni -kalatäin ekologiaa ja käyttäytymistä loisen elinkierron eri vaiheissa, joita ovat munat, munista kuoriutuvat vapaana elävät nuoruusvaiheet ja kalassa aikuistuvat loiset.
In this thesis, the life history traits of the ectoparasite Argulus coregoni were examined during its life cycle. Water temperature was a key determinant of temporal patterns of A. coregoni population abundance and dynamics; neither parasites attached to the host nor egg-hatching were recorded at temperatures below ~10ºC. Parasite transmission to their hosts was characterized by peak recruitment in spring followed by extended, but slower recruitment. Egg-hatching was triggered by cooling treatments, the magnitude of which was dependent on the period of cooling. Each female parasite, however, produced eggs that hatched over many hatching opportunities. This delayed emergence pattern can be seen as an adaptation to unpredictable, risky environments, where such bet-hedging may allow some infection to occur even after periodic absences of hosts. Female A. coregoni preferred to lay their eggs on dark substrates in the deepest water in a 2 m-deep canal, with the egg population showing an aggregated distribution pattern. Non-random distribution of eggs coupled with variable hatching may result in differences in host exposure to parasites, which was shown to be a dominant causative factor behind the observed aggregated distribution of A. coregoni on their rainbow trout (Oncorhynchus mykiss) hosts. Rainbow trout did not seem to develop any resistance mechanisms to prevent parasite settlement after first encounters with A. coregoni nor any general trend in repeated susceptibility of fish to parasite attachment observed. Both these findings suggest that the fish were of equal genetic susceptibility. Nevertheless, the attachment of parasite infective stages, that carried a finite energy resource for host seeking, seemed to be opportunistic and non-selective. Although the infectivity of A. coregoni remained high up to death, delayed starts with respect to host searching time were reflected on growth in the altered growth rate of settled parasites. Over time, parasites that had spent more time searching for a host reached the length of parasites that attached to a host faster. A. coregoni thus appeared to compensate for delayed growth resulting from an extended period off-host by accelerated growth, although, this was shown to incur a cost through decreased life-expectancy. This study has shown that individual parasites are more flexible in their life history strategies than has hitherto been understood. The results from this thesis provide parameter estimations for a detailed host-macroparasite model that will capture both host and parasite population dynamics, and can be used for planning cost-effective management against ectoparasite infestations at fish farms ...
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kalat loiset kalatäit lisääntyminen populaatiot torjunta elinkierto
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Larval life history, transmission strategies, and the evolution of intermediate host exploitation by complex life-cycle parasites
Benesh, Daniel (University of Jyväskylä, 2007)
Complex life-cycle parasites use their intermediate hosts both as an energy source and as a vessel for transmission to the next host in the life cycle. Parasites that grow rapidly to a large size may have high fitness (e.g. ...
Effect of parasite load on developmental mode polymorphism in Pygospio elegans : a preliminary test
In parasite-host interactions, hosts can respond to parasites by alteration of life history traits. Intraspecific larval developmental polymorphism in some polychaetes, termed poecilogony, might be a plastic response to ...
Increasing temperatures accentuate negative fitness consequences of a marine parasite
Godwin, Sean C.; Fast, Mark D.; Kuparinen, Anna; Medcalf, Kate E.; Hutchings, Jeffrey A. (Nature Publishing Group, 2020)
Infectious diseases are key drivers of wildlife populations and agriculture production, but whether and how climate change will influence disease impacts remains controversial. One of the critical knowledge gaps that ...
Host manipulation by parasites : adaptation to enhance transmission?
Seppälä, Otto (University of Jyväskylä, 2005)
Otto Seppälä tutki väitöskirjassaan loisten kykyä manipuloida isäntiään mahdollisena strategiana tehostaa loisten siirtymistä uusiin isäntäyksilöihin. Monien loisten on havaittu vaikuttavan mm. isäntiensä käyttäytymiseen ...
Evolutionary ecology of complex life cycle parasites : from genotypes to species assemblages
Louhi, Katja-Riikka (University of Jyväskylä, 2012)
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