Population-level variation in senescence suggests an important role for temperature in an endangered mollusc

Age-related declines in survival and function (senescence) were thought not to exist in wild populations as organisms, and particularly in invertebrates, do not live long enough. While, recent evidence has demonstrated that senescence is both common and measurable even in wild populations under field conditions, there are still organisms that are thought to exhibit “negligible senescence”. We explore variation in rates and patterns of senescence in the biogerontological model organism Margaritifera margaritifera across five populations, which differ in their age profile. In particular, we tested the theory of negligible senescence using time-at-death records for 1091 specimens of M. margaritifera. There is clear evidence of senescence in all populations, as indicated by an increase in mortality with age, but the nature of the relationship varies subtly between populations. We find strong evidence of a mortality plateau at later ages in some populations but this is unequivocally absent from others. We then demonstrate that the temporal scaling of the rates of senescence between five populations of M. margaritifera can be explained by the variation in the thermal environment of the population. Hence climate change may pose a threat to the demography of this long-lived, endangered species, and a greater understanding of the relationship between river temperature and population structure will be essential to secure the species against global temperature increases. Our findings demonstrate that useful insights can be drawn from a non-invasive monitoring method to derive demographic data, and we suggest a wide-scale application of this method to monitor populations across the whole latitudinal (and, hence, thermal) range of the species

The crown pearl: a draft genome assembly of the European freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758)

Since historical times, the inherent human fascination with pearls turned the freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) into a highly valuable cultural and economic resource. Although pearl harvesting in M. margaritifera is nowadays residual, other human threats have aggravated the species conservation status, especially in Europe. This mussel presents a myriad of rare biological features, e.g. high longevity coupled with low senescence and Doubly Uniparental Inheritance of mitochondrial DNA, for which the underlying molecular mechanisms are poorly known. Here, the first draft genome assembly of M. margaritifera was produced using a combination of Illumina Paired-end and Mate-pair approaches. The genome assembly was 2.4 Gb long, possessing 105,185 scaffolds and a scaffold N50 length of 288,726 bp. The ab initio gene prediction allowed the identification of 35,119 protein-coding genes. This genome represents an essential resource for studying this species' unique biological and evolutionary features and ultimately will help to develop new tools to promote its conservation.A.G.-d.-S. was funded by the Portuguese Foundation for Science and Technology (FCT) under the grants SFRH/BD/137935/2018, EF (CEECIND/00627/2017) and MLL (2020.03608.CEECIND). This research was developed under ConBiomics: the missing approach for the Conservation of freshwater Bivalves Project No. NORTE-01-0145-FEDER- 030286, co-financed by COMPETE 2020, Portugal 2020 and the European Union through the ERDF, and by FCT through national funds. Additional strategic funding was provided by FCT UIDB/04423/2020 and UIDP/04423/2020. Authors’ interaction and writing of the article was promoted and facilitated by the COST Action CA18239: CONFREMU—Conservation of freshwater mussels: a pan- European approach.info:eu-repo/semantics/publishedVersio

The role of anthropogenic habitats in freshwater mussel conservation

Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists.This publication is based upon work from COST Action CA18239, supported by COST (European Cooperation in Science and Technology). A.M.L. was financed by the Institute of Environmental Sciences Jagiellonian University (N18/DBS/000003) and K.N. by the Aragón Government. The authors acknowledge Jarosław Andrzejewski, Bartosz Czader, Anna Fica, Marcin Horbacz, Tomasz Jonderko, Steinar Kålås, Tomasz Kapela, Bjørn Mejdell Larsen, Maciej Pabijan, Katarzyna Pawlik, Ilona Popławska, Joanna Przybylska, Tomasz Przybył, Mateusz Rybak, Kjell Sandaas, Jarosław Słowikowski, Tomasz Szczasny, Michał Zawadzki and Paweł Zowada for providing detailed information on specific examples concerning freshwater mussels in anthropogenic habitats. We thank the editor and two anonymous referees for the valuable suggestions made, which increased the clarity of our manuscript.info:eu-repo/semantics/publishedVersio

Captive breeding of European freshwater mussels as aconservation tool: A review

1. Freshwater mussels are declining throughout their range. Their importantecological functions along with insufficient levels of natural recruitment haveprompted captive breeding for population augmentation and questions about the usefulness and applicability of such measures. 2. This article reviews the current state of captive breeding and rearing programmes for freshwater mussels in Europe. It considers the various species, strategies, andtechniques of propagation, as well as the different levels of effort requiredaccording to rearing method, highlighting the key factors of success. 3. Within the last 30 years, 46 breeding activities in 16 European countries have been reported, mainly of Margaritifera margaritifera and Unio crassus. Some facilities propagate species that are in a very critical situation, such as Pseudunio auricularius, Unio mancus, and Unio ravoisieri, or multiple species concurrently. Insome streams, the number of released captive-bred mussels already exceeds the size of the remaining natural population. 4. Rearing efforts range from highly intensive laboratory incubation to lowerintensity methods using in-river mussel cages or silos. Most breeding efforts are funded by national and EU LIFE(+) grants, are well documented, and consider the genetic integrity of the propagated mussels. Limited long-term funding perspectives, the availability of experienced staff, water quality, and feeding/survival during early life stages are seen as the most important challenges. 5. Successful captive breeding programmes need to be combined with restoration ofthe habitats into which the mussels are released. This work will benefit from anevidence-based approach, knowledge exchange among facilities, and an overall breeding strategy comprising multiple countries and conservation units. aquaculture, captive breeding, conservation translocation, freshwater mussel culturing, Margaritifera margaritifera, propagation, reintroduction, Unio crassusCaptive breeding of European freshwater mussels as aconservation tool: A reviewpublishedVersio

Integrative phylogenetic, phylogeographic and morphological characterisation of the Unio crassus species complex reveals cryptic diversity with important conservation implications

The global decline of freshwater mussels and their crucial ecological services highlight the need to understand their phylogeny, phylogeography and patterns of genetic diversity to guide conservation efforts. Such knowledge is urgently needed for Unio crassus, a highly imperilled species originally widespread throughout Europe and southwest Asia. Recent studies have resurrected several species from synonymy based on mitochondrial data, revealing U. crassus to be a complex of cryptic species. To address long-standing taxonomic uncertainties hindering effective conservation, we integrate morphometric, phylogenetic, and phylogeographic analyses to examine species diversity within the U. crassus complex across its entire range. Phylogenetic analyses were performed using cytochrome c oxidase subunit I (815 specimens from 182 populations) and, for selected specimens, whole mitogenome sequences and Anchored Hybrid Enrichment (AHE) data on ∼ 600 nuclear loci. Mito-nuclear discordance was detected, consistent with mitochondrial DNA gene flow between some species during the Pliocene and Pleistocene. Fossil-calibrated phylogenies based on AHE data support a Mediterranean origin for the U. crassus complex in the Early Miocene. The results of our integrative approach support 12 species in the group: the previously recognised Unio bruguierianus, Unio carneus, Unio crassus, Unio damascensis, Unio ionicus, Unio sesirmensis, and Unio tumidiformis, and the reinstatement of five nominal taxa: Unio desectus stat. rev., Unio gontierii stat. rev., Unio mardinensis stat. rev., Unio nanus stat. rev., and Unio vicarius stat. rev. Morphometric analyses of shell contours reveal important morphospace overlaps among these species, highlighting cryptic, but geographically structured, diversity. The distribution, taxonomy, phylogeography, and conservation of each species are succinctly described.We thank Ana-Maria Benedek, Monica Sîrbu and Jouni Leinikki for their assistance with the fieldwork, and to Jeroen Goud, Sankurie Pye, Fiona Ware, Emily Mitchell, and Aleksandra Skawina for their assistance with the taxonomic investigation. We would also like to thank the editor, Dr. Guillermo Ortí, and two anonymous reviewers for their time and effort in reviewing our manuscript and for their insightful comments and valuable improvements to our work. This publication is based upon work from COST Action CA18239: CONFREMU - Conservation of freshwater mussels: a pan-European approach, supported by COST (European Cooperation in Science and Technology), including STSMs, the interaction of the authors and the writing of the paper. This work was supported by the project ConBiomics: The Missing Approach for the Conservation of Freshwater Bivalves Project No. POCI-01-0145-FEDER-030286, co-financed by FEDER through POCI and by FCT - Fundaç˜ao para a Ciˆencia e a Tecnologia, through national funds. Strategic funding UIDB/04423/2020 and UIDP/04423/2020 was provided by FCT. FCT also supported DVG (2020.03848.CEECIND), EF (CEECINST/00027/ 2021/CP2789/CT0003) and MLL (2020.03608.CEECIND). INB, AVK and IVV were supported by the Russian Science Foundation under grants (19-14-00066-P), (21-17-00126) and (21-74-10130) respectively. BVB acknowledges the bioinformatics platform of UMR 8198 for the computing resources to perform time-calibrated phylogenetic analyses; this platform is in part funded by CPER research project CLIMIBIO through the French Minist`ere de l’Enseignement Sup´erieur et de la Recherche, the Agence Nationale de la Recherche, the European Fund for Regional Development (FEDER) and the region Hauts-de-France (HdF). Support to KD came from the Czech Science Foundation (19–05510S). TT and MT were supported by the National Science Fund of Bulgaria under the project ‘Conservation of freshwater mussels on the Balkan Peninsula’ (KP-06-COST-9/20.07.2022). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the United States Government.info:eu-repo/semantics/publishedVersio

Ecology of freshwater mussels in disturbed environments

The number of species extinctions is increasing at an alarming rate. Long-lived freshwater mussels of the order Unionoida, which include a parasitic stage on a host fish, are highly threatened. Habitat degradation by turbidity and sedimentation is thought to be one major reason for their decline. The objective of this thesis was to examine recruitment patterns and identify the causes of the lack of recruitment in the threatened unionoid freshwater pearl mussel (Margaritifera margaritifera). In addition, I investigated the effects of turbidity on non-endangered dreissenid mussels, where turbidity was manipulated through use of bioturbating mayflies. In a survey of 107 Swedish streams, mussel population size and trout density were both positively correlated to recruitment probability of M. margaritifera. A more in-depth study of the age-structure of nine populations revealed that four of these populations showed no signs of recruitment over the last ten years. Within-stream variation in recruitment was high as both mussels and trout had patchy distribution, and may be important for population regulation. Moreover, examination of different life stages revealed no differences in the gravid mussel stage or the stage when mussels infect salmonid fish. Instead, differences were observed for the juvenile, benthic stage, presumably related to differences in turbidity and sedimentation. High turbidity may affect filter-feeding efficiency of mussels and high sedimentation may reduce survival by clogging sediments, thereby altering, for example, oxygen and food conditions. In the study of the effects of turbidity, bioturbating mayflies increased turbidity and filter-feeding dreissenid mussels reduced turbidity. Mussel growth both decreased and increased with increasing turbidity, depending on sediment type. Turbidity and sedimentation often impact entire stream systems, and a holistic, catchment-based management strategy may be needed to reduce the effects of sedimentation on freshwater pearl mussels. The effects of restoration take a long time and must start soon if recruitment of mussels is to be re-established. Restoration may also be more urgent in some streams than in others, as the maximum age of M. margaritifera populations in my study differed by as much as 60 years. As mussel and trout densities seem to be important for recruitment success, one conservation method may be to concentrate mussels into sites where trout density is high

Biotiska och abiotiska faktorers betydelse för flodpärlmusslans fortplantning och överlevnad i Ljungans biflöden

Stormusslorna är en av de organismgrupper i sötvatten som är allra mest hotad. En av Sveriges stormusslor är flodpärlmusslan, vilken minskar i antal inom hela sitt utbredningsområde och som sedan maj 2010 är klassad som starkt hotad i den Internationella naturvårdsunionens rödlista. Målet med föreliggande projekt var att undersöka vad som begränsar flodpärlmusslans reproduktion och överlevnad. I anslutning till undersökningarna gjordes dessutom en film som berättar om projektet. Projektet är ett samarbete mellan Karlstads universitet och Fortums nordiska miljöfond och utfördes under åren 2007 och 2008 i 26 biflöden till Ljungan i Västernorrland. Flodpärlmusslan reproducerar sig på sommaren, då musslan släpper sina glochidielarver i vattnet. Larverna måste träffa på öring eller lax, där larverna kapslas in på fiskens gälar för att sedan leva där som parasit under 10-12 månader. När de små musslorna släppt från värdfiskens gälar lever de nedgrävda i sedimentet under några år. Från 10-20 års ålder räknas musslan som vuxen och kan delta i reproduktionen. I många musselvattendrag saknas juvenila musslor. Eftersom musslan har en så komplicerad livscykel är det flera livscykelstadier som bör undersökas för att ta reda på när rekryteringen av juvenila musslor begränsas. I detta projekt undersöktes följande livscykelstadier i 26 vattendrag i Ljungans avrinningsområde: gravida musslor, glochidieinfektion på öring och juvenila musslor. För att mäta  glochidielarvernas infektion på öringen utan att avliva öringen utvecklades en ny metod att uppskatta infektionsgraden m.h.a. fotografering av larverna på öringens gälar. Dessutom undersöktes öringtätheter och förändring i musseltäthet mellan 1990-1991 och 2005-2006. Slutligen undersöktes hur abiotiska faktorer såsom turbiditet, sedimentation, sedimentvattenkemi och vattentemperaturer påverkade musslans livscykelstadier. Resultaten visade att musseltätheten ökade generellt i vattendrag med rekrytering av juvenila musslor, men minskade i vattendrag utan rekrytering från 1990-1991 till 2005-2006. En minskning i musseltäthet sker alltså idag i vattendrag utan rekrytering och har troligtvis också skett under längre tid, vilket sannolikt resulterat i den lägre musseltäthet som finns idag i vattendrag utan rekrytering i Ljungans biflöden. Därmed är situationen allvarlig, där glesare populationer kan resultera i lägre reproduktion och förändra musslornas viktiga funktioner som filtrerare och paraplyart i vattendragen. På sikt är risken stor att arten försvinner helt från dessa vattendrag om man inte finner problemen och åtgärdar dem. Gravida musslor verkar inte vara det livscykelstadium som begränsar rekryteringen, eftersom ungefär hälften av musslorna var gravida, både i vattendrag med och utan rekrytering. Däremot var musslorna gravida tidigare i vattendrag utan rekrytering än i vattendrag med rekrytering. Gravida musslor var också kortare än musslor som inte var gravida i vattendrag utan rekrytering men inte i vattendrag med rekrytering. Proportionen gravida musslor ökade också som en funktion av musseltätheten. Sammantaget visar detta att larvproduktionen kanske inte fungerar helt optimalt i vattendrag utan rekrytering. Den nya metoden att mäta larver på öringens gälar genom att fotografera gälarna som utvecklades inom projektet fungerade bra. Ett akvarieexperiment visade att tillväxt eller överlevnad hos öring inte försämrades på grund av fotometoden. Detta visar alltså på att man kan undersöka infektionen av mussellarver på öring utan att öringen tar skada. Med hjälp av fotometoden kunde infektionsstadiet av mussellarver på öring av olika ålder mätas. Infektionen av mussellarver var högre i vattendrag med rekrytering än i vattendrag utan rekrytering på årsungar och på äldre öring. För infektionen på årsungarna berodde detta främst på en högre täthet av årsungar i vattendrag med rekrytering än i vattendrag utan rekrytering. Detta tyder på att årsungarnas täthet är negativt påverkad av någon faktor, vilket i sin tur leder till färre antal larver hos årsungarna i vattendrag utan rekrytering. Skillnaden i infektionen på äldre öring var orsakad av en högre musseltäthet i vattendrag med rekrytering än i vattendrag utan rekrytering. Den minskande musseltätheten i vattendrag utan rekrytering resulterar troligtvis i sin tur i en minskad produktion av glochidielarver. Sammantaget verkar det alltså som att en lägre täthet av öringens årsungar och en låg musseltäthet bidrar till lägre antal glochidielarver i vattendrag utan rekrytering, vilket sannolikt resulterar i en lägre rekrytering av juvenila musslor. Nästa tidiga livscykelstadium, juvenila musslor, var även det påverkat av musseltäthet och årsungarnas täthet. Detta tyder på att både infektionsstadium och juvenila musslor är negativt påverkade. Tätheten av juvenila musslor var negativt relaterad till turbiditet. Hög turbiditet hänger ofta ihop med hög sedimentation, vilket kan begränsa juvenila musslors överlevnad genom låga syrehalter och höga ammoniumhalter i sedimentet. Den sämre vattenomsättningen som uppmättes i vattendrag utan rekrytering kan vara ett resultat av en hög sedimentation och därmed resultera i dåliga förhållanden i sedimenten med en låg överlevnad av juvenila musslor som följd. Dessutom kan högre vattentemperaturer, vilket uppmättes på sommaren i vattendrag utan rekrytering, försämra tillväxt och överlevnad hos juvenila musslor. Turbiditet visade sig ha högst förklaringsgrad för frånvaron av juvenila musslor, följt av vattentemperaturen, medan täthet av årsungar av öring, musseltäthet och täthet av äldre öring, i nämnd ordning, var viktiga för rekryteringen av juvenila musslor. Detta pekar på att en minskning av sedimenttillförsel till vattendragen skulle kunna vända trenden med avsaknad av musselrekrytering. Minskad sedimentation skulle också kunna förbättra öringens reproduktion och därmed även förbättra rekryteringen av musslan, om en högre sedimenttransport också påverkar öringäggens utveckling negativt. Brukande av marken bredvid vattendrag kan vara en viktig orsak till hög turbiditet och sedimentation och kan också orsaka höga vattentemperaturer på grund av ökad solinstrålning. För överlevnaden av juvenila flodpärlmusslor är det också viktigt att naturliga flödestoppar inte förhindras, utan tillåts byta ut vattnet i sedimentet. En kombination av lågt vattenflöde och avsaknad av en beväxt kantzon på sommaren kan troligtvis bidra till dåliga förhållanden i bottenvattnet och för höga vattentemperaturer, vilket kan påverka både musslor och öring negativt. För att uppnå bättre förhållanden för flodpärlmusslan bör brukandet av marken utföras så att silt och sand inte släpps ut i vattendragen. Genom att inte störa marken närmast vattendragen genom dikning och skogsavverkning kan en ökad sedimentation förhindras. Om man lämnar intakta kantzoner närmast vattendragen kan dessa även stabilisera vattendragen mot erosion. Dessutom kan ökad beskuggning av vegetationen i en intakt kantzon förhindra alltför höga vattentemperaturer sommartid. Samtidigt bör regleringen av dammar uppströms musselpopulationer vara sådan att högflödestoppar, vilka bidrar till att vatten spolas genom sedimenten, inte begränsas. Om marken bredvid bäckarna och vattenregleringen sköts på rätt sätt  kan det bidra till att rekryteringen av flodpärlmusslor återupptas. Detta bör dock ske inom en snar framtid eftersom effekter av restaurering av vattendrag ofta tar lång tid och det också tar lång tid för flodpärlmusslan att återkolonisera när tätheterna har reducerats mycket

Demonstrating the practical impact of studies on biotic interactions and adaptation of a threatened unionoid mussel (Margaritifera margaritifera) to its host fish (Salmo trutta)

conservation evaluation, fish, invertebrates, stream1. To understand the ecological factors behind the decline of functionally important threatened species with complex life cycles, many different life-cycle stages need to be investigated. The highly threatened unionoid freshwater mussels, with their complex life cycle, including a parasitic stage on host fish, often have a large influence on biodiversity and ecosystem functioning. 2. The overall aim of the present article is to summarize and discuss the impact of two articles published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) on biotic interactions and adaptation of a threatened unionoid mussel (Margaritifera margaritifera) to its host fish (Salmo trutta). 3. The two AQC publications described research on the influence of population size and density of mussels and host fish, and host–parasite interactions between mussels and their host fish, on the recruitment of juvenile mussels. 4. The results from these publications filled gaps in knowledge and resulted in recommendations and incentives for conservation. The results and method development have been used in practical conservation work with threatened mussel species and have been implemented and cited in management handbooks. The outcome of the publications has been implemented in large conservation and restoration projects, and in several recent scientific publications. 5. Specifically, the results from one publication showed that ecological parameters such as mussel and host fish density and population size influenced recruitment of the threatened freshwater pearl mussel. The results from the second publication showed that understanding host–parasite interactions is important for comparing the suitability of host fish strains, and that host fish strains differ in their suitability for mussel infestations. In combination, the articles show that integrating ecological parameters of threatened mussels and their host fish with host– parasite interaction experiments can be an important influence on conservation recommendations, adaptive management and national management programmes for threatened species.publishedVersio