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Conservation ecology of the thick-shelled river mussel Unio crassus : The importance of parasite-host interactions
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences. (Naturresurs rinnande vatten)ORCID iD: 0000-0003-3524-0883
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Unionoid mussels are globally threatened and their conservation requires species-specific knowledge on their ecology and parasite-host interaction. Unio crassus is one of Europe’s most threatened unionoid species and has a temporary obligate parasitic life stage (glochidia) on fish. A lack of suitable hosts is probably a major limitation for mussel recruitment, but host species composition, suitability and availability in time and space have yet to be fully explored. This thesis examines different aspects of the host fish species, including their composition, suitability and ecological importance, in relation to U. crassus, using both field and laboratory studies. The effects of mussel and host density on mussel reproductive potential were considered, as were aspects of evolutionary adaptations between mussels and fish and how climate change may affect their interaction.

The results show that U. crassus is a host generalist, parasitizing a variety of fish species. Host suitability and density, which varied among fish species and rivers, affected the level of glochidia encapsulation, hence mussel reproductive potential, more so than the density of mussels taking part in reproduction. Ecologically important hosts included both highly suitable primary hosts, and less suitable hosts that were highly abundant. Whether or not U. crassus has specific adaptations to its hosts to enhance juvenile transformation remains unclear. No distinct pattern of local adaptation was found, nor was there an effect of host fish presence on the timing of glochidia release by adult mussels. Instead, temperature played a major role, with results suggesting that changes in spring water temperature regimes can cause temporal and spatial mismatches in the mussel-host interaction. This thesis indicates that investigations of local mussel-host interactions help in identifying mechanisms important for unionoid conservation management and prioritization.

Abstract [sv]

Många sötvattenmusslor har en komplex livscykel där larverna (glochidier) under sin utveckling till frilevande musslor parasiterar på gälarna hos lämpliga värdfiskar. Flera av våra musslor, såsom den tjockskaliga målarmusslan (Unio crassus), är globalt hotade och för att kunna bevara och förvalta dessa arter på bästa sätt behöver vi lära oss mer om deras ekologi och samspelet mellan musslan och dess värdfiskar. Avsaknaden av värdfiskar innebär förmodligen en stor begränsning för rekryteringen av juvenila musslor, men det finns trots detta en begränsad kunskap om hur artsammansättningen i fisksamhället och dess tillgänglighet påverkar musselpopulationer. 

Min avhandling undersöker olika aspekter av interaktioner mellan U. crassus och dess värdfiskar, som hur värdfisksamhällen och fiskarters värdlämplighet påverkar musslans reproduktionspotential. Jag har även studerat hur tätheter av olika fiskarter och vuxna musslor påverkar rekryteringen, eventuella evolutionära anpassningar samt om en förhöjd temperatur skulle kunna påverka interaktionen mellan U. crassus och dess värdfiskar.

Resultaten visar att U. crassus är en generalist som parasiterar på en mängd olika fiskarter. Jag fann dock en stor variation i dominerande fiskarter och lämpliga värdar mellan olika åar, vilket påverkade reproduktionspotentialen hos musslorna mer än vad tätheten vuxna musslor som deltog i reproduktionen gjorde. Som ekologiskt viktiga värdar fanns således både särskilt lämpliga, primära värdarter, men också mindre lämpliga arter som förekom i höga tätheter. Ingen tydlig lokal anpassning kunde observeras, och fiskens närvaro påverkade inte tidpunkten för när de vuxna musslorna släppte sina glochidielarver. Däremot fann jag att temperaturen spelade en viktig roll för musslans reproduktion, där ökad temperatur föreslås ha negativa effekter på interaktionen mellan musslan och dess värdfiskar.

Avhandlingen visar på vikten av att studera interaktioner mellan den tjockskaliga målarmusslan och dess värdar på lokal skala för att bättre kunna identifiera och prioritera viktiga naturvårdsåtgärder.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2017. , 157 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2017:7
Keyword [en]
Endangered species; freshwater mussels; host fish species; parasite-host; river; stream; Unio crassus; Unionoida
National Category
Ecology
Research subject
Biology
Identifiers
URN: urn:nbn:se:kau:diva-47636ISBN: 978-91-7063-749-0 (print)ISBN: 978-91-7063-750-6 (electronic)OAI: oai:DiVA.org:kau-47636DiVA: diva2:1067005
Public defence
2017-02-24, Sjöströmsalen 1B309, Universitetsgatan 2, 651 88 Karlstad, 10:15 (English)
Opponent
Supervisors
Projects
UnioCrassusforLIFE (European LIFE+ project: LIFE10 NAT/SE/000046)
Funder
EU, European Research Council, LIFE10 NAT/SE/000046
Available from: 2017-02-03 Created: 2017-01-14 Last updated: 2017-02-03Bibliographically approved
List of papers
1. Manuscript: Effects of mussel and host fish density on reproduction potential of a threatened unionoid mussel: prioritization of conservation locations in management trade-offs
Open this publication in new window or tab >>Manuscript: Effects of mussel and host fish density on reproduction potential of a threatened unionoid mussel: prioritization of conservation locations in management trade-offs
(English)Manuscript (preprint) (Other academic)
Keyword
Host fish availability, host-parasite system, Unio crassus, Unionoida, reproduction period
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-47686 (URN)
Projects
UnioCrassusforLIFE (LIFE10 NAT/SE/000046)
Funder
EU, European Research Council, LIFE10 NAT/SE/000046
Available from: 2017-01-19 Created: 2017-01-19 Last updated: 2017-01-19
2. Host-Fish Composition And Glochidia Encapsulation For The Endangered Thick-Shelled River Mussel Unio Crassus
Open this publication in new window or tab >>Host-Fish Composition And Glochidia Encapsulation For The Endangered Thick-Shelled River Mussel Unio Crassus
Show others...
(English)Manuscript (preprint) (Other academic)
Keyword
Endangered species, glochidia density, host fish density, rivers, survey studies, Unio crassus, Unionoida
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-47687 (URN)
Projects
UCforLIFE (LIFE10 NAT/SE/000046)
Funder
EU, European Research Council, LIFE10 NAT/SE/000046
Available from: 2017-01-19 Created: 2017-01-19 Last updated: 2017-04-20
3. Manuscript: Local adaptation studies and conservation: parasite-host interactions between freshwater mussels and fish
Open this publication in new window or tab >>Manuscript: Local adaptation studies and conservation: parasite-host interactions between freshwater mussels and fish
(English)Manuscript (preprint) (Other academic)
Keyword
Benthos, endangered species, invertebrates, river, stream, Unio crassus
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-47688 (URN)
Projects
UCforLIFE (LIFE10 NAT/SE/000046)
Funder
EU, European Research Council, LIFE10 NAT/SE/000046
Available from: 2017-01-19 Created: 2017-01-19 Last updated: 2017-01-19
4. Manuscript: Spring temperature-dependent reproduction in the parasitic freshwater mussel Unio crassus
Open this publication in new window or tab >>Manuscript: Spring temperature-dependent reproduction in the parasitic freshwater mussel Unio crassus
(English)Manuscript (preprint) (Other academic)
Keyword
Freshwater mussel conservation, glochidia release, glochidia survival, temperature fluctuations
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-47689 (URN)
Projects
UCforLIFE (LIFE10 NAT/SE/000046)
Funder
EU, European Research Council, LIFE10 NAT/SE/000046)
Available from: 2017-01-19 Created: 2017-01-19 Last updated: 2017-01-19

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