9 research outputs found

    Droplet digital PCR as a tool for investigating dynamics of cryptic symbionts

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    Interactions among symbiotic organisms and their hosts are major drivers of ecological and evolutionary processes. Monitoring the infection patterns among natural populations and identifying factors affecting these interactions are critical for understanding symbiont–host relationships. However, many of these interactions remain understudied since the knowledge about the symbiont species is lacking, which hinders the development of appropriate tools. In this study, we developed a digital droplet PCR (ddPCR) assay based on apicomplexan COX1 gene to detect an undescribed agamococcidian symbiont. We show that the method gives precise and reproducible results and enables detecting cryptic symbionts in low target concentration. We further exemplify the assay's use to survey seasonally sampled natural host (Pygospio elegans) populations for symbiont infection dynamics. We found that symbiont prevalence differs spatially but does not show seasonal changes. Infection load differed between populations and was low in spring and significantly increased towards fall in all populations. We also found that the symbiont prevalence is affected by host length and population density. Larger hosts were more likely to be infected, and high host densities were found to have a lower probability of infection. The observed variations could be due to characteristics of both symbiont and host biology, especially the seasonal variation in encounter rates. Our findings show that the developed ddPCR assay is a robust tool for detecting undescribed symbionts that are otherwise difficult to quantify, enabling further insight into the impact cryptic symbionts have on their hosts.peerReviewe

    Disentangling symbiont-host interactions in a group of understudied, putative parasites : the marine Apicomplexa

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    Symbiotic interactions (antagonistic, synergistic, or neutral) have been of fundamental importance in shaping evolution of their hosts as well as other symbionts infecting the same host. Understanding the diversity, drivers and outcomes of these interactions is important in resolving species capability to adapt in changing environments. Apicomplexans are known to infect a wide variety of marine invertebrates, but their diversity and how they affect their hosts’ fitness is unclear. Are they parasites or mutualists? In this thesis, I aimed to disentangle these interactions between two marine apicomplexans, Rhytidocystis sp. and Selenidium pygospionis, infecting a marine polychaete. Using molecular methods, I surveyed natural host populations for infection dynamics, coinfection dynamics and how they are affected by different host characteristic. In addition, I described apicomplexan richness in relation to their host species richness on a large spatial scale, the Baltic Sea salinity gradient. I found that infection patters vary spatially and temporally and are affected by host size, but independent of host population density and genetic diversity. The spatial differences are likely due to differences in local environmental factors affecting symbiont transmission. I also found signs of synergistic (beneficial) interactions between the two symbionts while coinfecting the same host. In addition, I found indications that the richness of host communities might inhibit infection success (dilution effect). Overall, this thesis describes the infection patterns of the understudied apicomplexans, gives an indication of factors affecting the interactions between them and their host, as well as how other factors might affect their infection success in ecologically important benthic animals. However, this thesis also emphasizes that resolving the nature of symbiotic interactions is difficult with only direct observations from nature and controlled experimental approaches are required to gain a deeper understanding of these relationships.Vuorovaikutukset symbionttisten eliöiden ja niiden isĂ€ntien vĂ€lillĂ€ (antagonistiset, synergistiset tai neutraalit) ovat olleet perustavanlaatuisessa asemassa kautta eliöiden evolutiivisen historian. NĂ€iden vuorovaikutusten moninaisuuden ja niitĂ€ yllĂ€pitĂ€vien tekijöiden tunteminen on tĂ€rkeÀÀ, jotta lajien sopeutumiskykyĂ€ muuttuviin elinolosuhteisiin voidaan ymmĂ€rtÀÀ. Apicomplexa sukuun kuuluvat eliöt ovat yleisiĂ€ merissĂ€ elĂ€vien selkĂ€rangattomien symbiontteja, mutta niiden vaikutusta isĂ€ntĂ€nsĂ€ kelpoisuuteen ei tunneta. TĂ€ssĂ€ vĂ€itöskirjassa tutkin kahden Apicomplexa -suvun symbiontin vuorovaikutusta niiden isĂ€ntĂ€nĂ€ toimivan hiekkaputkimadon kanssa, sekĂ€ symbionttien vĂ€lisiĂ€ vuorovaikutuksia eri DNA-menetelmien avulla. Tutkin symbionttien infektiotehokkuutta, sen mÀÀrÀÀ, sekĂ€ siihen vaikuttavia isĂ€ntien ominaisuuksia luonnollisissa isĂ€ntĂ€populaatioissa. LisĂ€ksi tutkin Apicomplexa -suvun symbionttien monimuotoisuutta suhteessa niiden isĂ€ntĂ€lajien monimuotoisuuteen ItĂ€meren pohjaelĂ€inyhteisöissĂ€. Tulokseni osoittivat, ettĂ€ symbionttien infektiotehokkuus vaihtelee paikallisesti ja vuodenajan mukaan. IsĂ€nnĂ€n koko vaikuttaa infektion todennĂ€köisyyteen, mutta populaatiotiheydellĂ€ tai geneettisellĂ€ monimuotisuudella ei ollut vaikutusta. NĂ€mĂ€ erot saattavat johtua paikallista ympĂ€ristötekijöistĂ€, jotka vaikuttavat symbionttien transmissioon. Korkea lajien monimuotisuus isĂ€ntĂ€populaation elinympĂ€ristössĂ€ puolestaan vaikutti alentavan symbionttien infektiotehokkuutta, mahdollisen diluutioefektin vaikutuksesta. LisĂ€ksi tulokseni viittaavat hyödylliseen vuorovaikukseen symbionttien vĂ€lillĂ€ niiden infektoidessa samaa isĂ€ntĂ€yksilöÀ (koinfektio). VĂ€itöskirjani antaa uutta tietoa tekijöistĂ€, jotka vaikuttavat nĂ€iden heikosti tunnettujen symbionttien esiintymiseen ja infektiotehokkuuteen luonnossa. Toisaalta tutkimukseni osoittavat, ettĂ€ vuorovaikutusten tutkiminen luonnossa ilman kokeellisia menetelmiĂ€ on haastavaa

    Coinfection patterns of two marine apicomplexans are not associated with genetic diversity of their polychaete host

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    Coinfections of two or more parasites within one host are more of a rule than an exception in nature. Interactions between coinfecting parasites can greatly affect their abundance and prevalence. Characteristics of the host, such as genetic diversity, can also affect the infection dynamics of coinfecting parasites. Here, we investigate for the first time the association of coinfection patterns of two marine apicomplexans, Rhytidocystis sp. and Selenidium pygospionis, with the genetic diversity of their host, the polychaete Pygospio elegans, from natural populations. Host genetic diversity was determined with seven microsatellite loci and summarized as allelic richness, inbreeding coefficient, and individual heterozygosity. We detected nonsignificant correlations between infection loads and both individual host heterozygosity and population genetic diversity. Prevalence and infection load of Rhytidocystis sp. were higher than those of S. pygospionis, and both varied spatially. Coinfections were common, and almost all hosts infected by S. pygospionis were also infected by Rhytidocystis sp. Rhytidocystis sp. infection load was significantly higher in dual infections. Our results suggest that factors other than host genetic diversity might be more important in marine apicomplexan infection patterns and experimental approaches would be needed to further determine how interactions between the apicomplexans and their host influence infection

    Coinfection patterns of two marine apicomplexans are not associated with genetic diversity of their polychaete host

    No full text
    Coinfections of two or more parasites within one host are more of a rule than an exception in nature. Interactions between coinfecting parasites can greatly affect their abundance and prevalence. Characteristics of the host, such as genetic diversity, can also affect the infection dynamics of coinfecting parasites. Here we investigate for the first time the association of coinfection patterns of two marine apicomplexans, Rhytidocystis sp. and Selenidium pygospionis, with the genetic diversity of their host, the polychaete Pygospio elegans, from natural populations. Host genetic diversity was determined with seven microsatellite loci and summarized as allelic richness, inbreeding coefficient, and individual heterozygosity. We detected nonsignificant correlations between infection loads and both individual host heterozygosity and population genetic diversity. Prevalence and infection load of Rhytidocystis sp. were higher than that of S. pygospionis and both varied spatially. Coinfections were common and almost all hosts infected by S. pygospionis were also infected by Rhytidocystis sp.. Rhytidocystis sp. infection load was significantly higher in dual infections. Our results suggest that factors other than host genetic diversity might be more important in marine apicomplexan infection patterns and experimental approaches would be needed to further determine how interactions between the apicomplexans and their host influence infection.peerReviewe

    Selection for reproduction under short photoperiods changes diapause-associated traits and induces widespread genomic divergence

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    Abstract The incidence of reproductive diapause is a critical aspect of life history in overwintering insects from temperate regions. Much has been learned about the timing, physiology and genetics of diapause in a range of insects, but how the multiple changes involved in this and other photoperiodically regulated traits are inter-related is not well understood. We performed quasinatural selection on reproduction under short photoperiods in a northern fly species, Drosophila montana, to trace the effects of photoperiodic selection on traits regulated by the photoperiodic timer and/or by a circadian clock system. Selection changed several traits associated with reproductive diapause, including the critical day length for diapause (CDL), the frequency of diapausing females under photoperiods that deviate from daily 24 h cycles and cold tolerance, towards the phenotypes typical of lower latitudes. However, selection had no effect on the period of free-running locomotor activity rhythm regulated by the circadian clock in fly brain. At a genomic level, selection induced extensive divergence from the control line in 16 gene clusters involved in signal transduction, membrane properties, immunologlobulins and development. These changes resembled those detected between latitudinally divergent D. montana populations in the wild and involved SNP divergence associated with several genes linked with diapause induction. Overall, our study shows that photoperiodic selection for reproduction under short photoperiods affects diapause-associated traits without disrupting the central clock network generating circadian rhythms in fly locomotor activity
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