Freshwater mussel conservation: A global horizon scan of emerging threats and opportunities

We identified 14 emerging and poorly understood threats and opportunities for addressing the global conservation of freshwater mussels over the next decade. A panel of 17 researchers and stakeholders from six continents submitted a total of 56 topics that were ranked and prioritized using a consensus-building Delphi technique. Our 14 priority topics fell into five broad themes (autecology, population dynamics, global stressors, global diversity, and ecosystem services) and included understanding diets throughout mussel life history; identifying the drivers of population declines; defining metrics for quantifying mussel health; assessing the role of predators, parasites, and disease; informed guidance on the risks and opportunities for captive breeding and translocations; the loss of mussel-fish co-evolutionary relationships; assessing the effects of increasing surface water changes; understanding the effects of sand and aggregate mining; understanding the effects of drug pollution and other emerging contaminants such as nanomaterials; appreciating the threats and opportunities arising from river restoration; conserving understudied hotspots by building local capacity through the principles of decolonization; identifying appropriate taxonomic units for conservation; improved quantification of the ecosystem services provided by mussels; and understanding how many mussels are enough to provide these services. Solutions for addressing the topics ranged from ecological studies to technological advances and socio-political engagement. Prioritization of our topics can help to drive a proactive approach to the conservation of this declining group which provides a multitude of important ecosystem services.This publication is based upon work from COST Action CA18239, supported by COST (European Cooperation in Science and Technology). DCA was supported by Corpus Christi College and a Dawson Fellowship at St. Catharine's College, Cambridge. MLL was supported by FCT-Fundacao para a Ciencia e a Tecnologia (2020.03608.CEECIND). ISO was supported by a Whitten Studentship. INB was supported by the Russian Science Foundation (grant no. 21-17-00126). YVB was supported by RSF project no. 21-14-00092. KD was supported by the Czech Science Foundation (19-05510 S). TZ was supported by statutory funds of IOP PAN. MK was supported by funding through the Australian National Environmental Science Program. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission

16S rRNAgene-based metagenomic analysis of the gut microbial community associated with the DUI species Unio crassus (Bivalvia: Unionidae)

What factors determine biome richness: genetic or environmental? Sex, phylogeny, and tolerance indicated by other symbionts (e.g., endosymbionts) or simply is it related to local habitat, especially if the gut biome is considered? To answer these questions, we investigated the gut microbial profile of both sexes of three Unio crassus populations, species with unique system of mitochondrial DNA inheritance called doubly uniparental inheritance (DUI), living in different ecological conditions. High-throughput sequencing of the V3-V4 hypervariable regions in the bacterial 16S rRNA gene fragment was performed, which resulted in a total of 1,051,647 reads, with 58,424 reads/65 OTUs (operational taxonomic units) per sample on average. We identified a core microbiome, with all individual mussels sharing 69 OTUs (representing 23% of the total number of OTUs). Proteobacteria was the dominant phylum in all samples, followed by Firmicutes, Actinobacteria, and Bacteroidetes. There were no significant differences in gut microbiome compositions between the two sexes of this species; however, we observed different phyla in geographically isolated populations. A non-metric multidimensional scaling plot and dendrogram showed that the bacterial profile complies with the genetic structure of populations. Although we found differences in microbiomes between populations, their genetic structure suggests that the microbiome is weakly related to habitat, and more strongly to phylogeography (on both F and M mitotypes). We found no significant differences in beta diversity between the individuals of the bacterial communities measured using the Bray-Curtis index. Finally, we also examined whether OTUs were represented by symbiotic bacteria that enable cellulose digestion and by endosymbiotic bacteria that play important functions in the biology of their hosts and also affect microevolutionary processes and population phenomena. With regard to the endosymbionts, however, there was no relation to sex of the studied individuals, which suggests that there are no straightforward relations between DUI and microbiome.Funding Agencies|Polish National Science Centre [NCN DEC-2017/01/X/NZ8/01873]; Swedish Research Councils (Vetenskapsradet) [2017-04951]</p

Playing Peekaboo with a Master Manipulator: Metagenetic Detection and Phylogenetic Analysis of Wolbachia Supergroups in Freshwater Invertebrates

The infamous "master manipulators"-intracellular bacteria of the genus Wolbachia-infect a broad range of phylogenetically diverse invertebrate hosts in terrestrial ecosystems. Wolbachia has an important impact on the ecology and evolution of their host with documented effects including induced parthenogenesis, male killing, feminization, and cytoplasmic incompatibility. Nonetheless, data on Wolbachia infections in non-terrestrial invertebrates are scarce. Sampling bias and methodological limitations are some of the reasons limiting the detection of these bacteria in aquatic organisms. In this study, we present a new metagenetic method for detecting the co-occurrence of different Wolbachia strains in freshwater invertebrates host species, i.e., freshwater Arthropoda (Crustacea), Mollusca (Bivalvia), and water bears (Tardigrada) by applying NGS primers designed by us and a Python script that allows the identification of Wolbachia target sequences from the microbiome communities. We also compare the results obtained using the commonly applied NGS primers and the Sanger sequencing approach. Finally, we describe three supergroups of Wolbachia: (i) a new supergroup V identified in Crustacea and Bivalvia hosts; (ii) supergroup A identified in Crustacea, Bivalvia, and Eutardigrada hosts, and (iii) supergroup E infection in the Crustacea host microbiome community.Funding Agencies|COST Action [CA18239]; COST (European Cooperation in Science and Technology); National Science Centre, Poland [2017/01/X/NZ8/01873, 2021/43/D/NZ8/00344]; Young Scientists competition of University of Gdansk, Poland [538/L260/B149/18]; University of Gdansk, Poland [1220/146/2021]; European Molecular Biology Organization (EMBO) [7862]; Vetenskapsradets [2017-04951]; ELLIIT Call C grant; Spanish Ministry of Science and Innovation [FJC2021-046991-I]</p

Fishing for hosts: Larval spurting by the endangered thick-shelled river mussel, Unio crassus

All data and code (Brian, 2023) are available in Zenodo at https://doi.org/10.5281/zenodo.7654858.[Excerpt] Understanding the life-history characteristics of endangered species is crucial to their conservation, management, and predicting their responses to environmental change (Stark et al., 2004). Host specificity is central to the evolutionary diversification and conservation of the Unionida (Barnhart et al., 2008; Modesto et al., 2018). In the North American mussels of the Ambleminae subfamily, specificity toward a restricted host fish range that shares the same microhabitat as the mussel has resulted in remarkable morphologies and behaviors that dramatically increase the likelihood of attachment and successful transmission of larvae (glochidia). This includes modification of mantle flaps into lures and packaging of glochidia into conglutinates that resemble insect larvae upon which the host fishes preferentially feed (Barnhart et al., 2008). [...]European Cooperation in Science and Technology, Grant/Award Number: CA1823

Blood parasites shape extreme major histocompatibility complex diversity in a migratory passerine

Pathogens are one of the main forces driving the evolution and maintenance of the highly polymorphic genes of the vertebrate major histocompatibility complex (MHC). Although MHC proteins are crucial in pathogen recognition, it is still poorly understood how pathogen-mediated selection promotes and maintains MHC diversity, and especially so in host species with highly duplicated MHC genes. Sedge warblers (Acrocephalus schoenobaenus) have highly duplicated MHC genes, and using data from high-throughput MHC genotyping, we were able to investigate to what extent avian malaria parasites explain temporal MHC class I supertype fluctuations in a long-term study population. We investigated infection status and infection intensities of two different strains of Haemoproteus, that is avian malaria parasites that are known to have significant fitness consequences in sedge warblers. We found that prevalence of avian malaria in carriers of specific MHC class I supertypes was a significant predictor of their frequency changes between years. This finding suggests that avian malaria infections partly drive the temporal fluctuations of the MHC class I supertypes. Furthermore, we found that individuals with a large number of different supertypes had higher resistance to avian malaria, but there was no evidence for an optimal MHC class I diversity. Thus, the two studied malaria parasite strains appear to select for a high MHC class I supertype diversity. Such selection may explain the maintenance of the extremely high number of MHC class I gene copies in sedge warblers and possibly also in other passerines where avian malaria is a common disease

Remarkable reprodutive spurting behaviour of endangered thick shelled river mussel, Unio crassus

Freshwater mussels (Unionida) dominate the biomass and are important keystone organisms in many rivers, yet they are declining precipitously worldwide. Their dispersal is facilitated by possession of parasitic larvae (glochidia) which typically encyst and metamorphose on the gills and fins of host fishes. Long eo-evolutionary histories in some North American mussels has resulted in specificity towards single host fish species that share the same microhabitat as the mussel and has led to the development of lures and behaviours that dramatically increase the likelihood of attachment and successful transmission. Elsewhere in the world, mussels are typically more generalist in host use and thought to release glochidia freely into the water column without using specific lures and attractants. Here we show that the endangered European thick shelled river mussel, Unio crassus, displays a remarkable spurting behaviour where females migrate to river margins and project jets of water up to 1m back into the channel. Spurted material carries glochidia and attracts larval host fishes thus increasing the likelihood of successful transmission. Mature glochidia remain viable for up to 48 hours and carry long larval threads, which can wrap around fixed and floating debris thus keeping the glochidia within the water column. This unique spurting behaviour may explain the disappearance of U. crassus from regulated rivers, where margins have been lost through impoundment, or where increased sporadic discharges displace gravid females from shallow water. The reproductive behaviour of many endangered freshwater mussels is largely unknown but may be central to explaining the dramatic decline in these important ecosystem engineers.info:eu-repo/semantics/publishedVersio