Potomida Littoralis Research Articles

The complete female mitogenome of Potomida semirugata (Lamarck, 1819)

Freshwater mussels perform important ecological functions in ecosystems, such as water filtration and energy cycling. Unlike marine bivalves, freshwater mussels have unique characteristics including internal fertilization and parental care. Some freshwater mussels are facing a high risk of extinction due to several factors such as climate change and habitat loss. Potomida semirugata (Lamarck, 1819) is one of the freshwater mussel species with a high risk of extinction and listed as Endangered in the Red List of the International Union for Conservation of Nature. Here, we present the first F-type mitogenome sequence of P. semirugata. The genome was sequenced on an Illumina high-throughput platform from a P. semirugata specimen collected from the Tersakan River (Turkey). The 16,093 bp mitochondrial genome sequence contains 13 protein-coding genes, 22 transfer RNAs, and two ribosomal RNAs. Phylogenetic analysis placed P. semirugata in the Lamprotulini clade with Potomida littoralis, as expected. Potomida semirugata is a poorly studied species and the genomic resource provided here will contribute to a better understanding of its biological characterization.

The complete mitochondrial genome of Potomida acarnanica (Kobelt, 1879)

Freshwater mussels (Bivalvia, Unionida) play essential roles in the well-functioning of ecosystems, even providing essential services to humans. However, these bivalves face numerous threats (e.g. habitat loss and fragmentation, pollution, introduction of invasive species, and climate change) which have already led to the extinction of many populations. This underscores the need to fully characterize the biology of these species, particularly those, such as Potomida acarnanica, that are still poorly studied. This study presents the first mitogenome of P. acarnanica (Kobelt, 1879), an endemic species of Greece with a distribution limited to only two river basins. The mitochondrial genome of a P. acarnanica specimen, collected at Pamisos River (Peloponnese, Greece), was sequenced by Illumina high-throughput sequencing. This mitogenome (16,101 bp) is characterized by 13 protein-coding genes, 22 transfer RNA and 2 ribosomal RNA genes. The size of this mitogenome is within the range of another Potomida mitogenome already published for the species Potomida littoralis. In the phylogenetic inference, P. acarnanica was recovered as monophyletic with P. littoralis mitogenome in the Lamprotulini tribe, as expected. This genomic resource will assist in genetically characterizing the species, potentially benefiting future evolutionary studies and conservation efforts.

Bisphenol a (BPA) aggravate the adverse effect on physiological and biochemical response in freshwater mussel potomida littoralis

ABSTRACT Bisphenol A (BPA) is a chemical compound extensively employed in plastic manufacturing, and this pollutant has been detected in diverse aquatic organisms, notably bivalves. In order to comprehend the ecological and toxicological consequences of BPA Bisphenol A in these organisms, it is essential to examine the physiological and biochemical effects and identify areas where our understanding is lacking. This knowledge is crucial for determining the environn ental threat posed by bisphenol A and assisting decision-makers in establishing the appropriate priorities. This investigation aimed to assess the impact of BPA on the biochemical and physiological parameters of the freshwater mussel Potomida littoralis. In a laboratory setting, mussels were subjected to two different levels of BPA (20 and 100 μg/L) for a duration of 21 days. Filtration rate was calculated from the clearance of neutral red, fed to mussels at different BPA concentrations. The mussel’s filtration rate capacity declined as BPA exposure intensified, potentially due to the mussel’s attempt to close its valves and minimize BPA absorption, thus preventing cellular damage. In the digestive gland tissue, key antioxidant and detoxification defenses, including catalase (CAT) activity, glutathione-S-transferase (GST) activity, and levels of H2O2 and glutathione (GSH), were activated, particularly at the 100 μg/L BPA concentration. This activation helped protect against lipid damage at higher BPA concentrations. This study underscores the significance of preventing and regulating BPA release into the environment to avert detrimental consequences for aquatic ecosystems.

Escherichia coli Phylogenetic and Antimicrobial Pattern as an Indicator of Anthropogenic Impact on Threatened Freshwater Mussels.

Freshwater bivalves are widely used as accumulation indicators and monitoring tools for assessing contaminant effects on different levels of biological integration. This pilot study aimed to explore the phylogenetic diversity of Escherichia coli isolated from freshwater mussels (Margaritifera margaritifera and Potomida littoralis) and characterize their phenotypes and antibiotic resistance profiles. Samples were collected in the Rabaçal and Tua Rivers, in the Douro basin, Portugal-two sites representing different levels of anthropogenic contamination. Antimicrobial susceptibility testing was performed via the disk diffusion method with 21 antibiotics. Results showed that 31% of isolates were multidrug-resistant (MDR). Thus, freshwater mussels provide an effective and time-integrated approach for identifying/quantifying fecal indicators, including MDR bacteria. PCR-based assays were designed for assessing phylogenetic E. coli groups. Among the E. coli isolates, the highest prevalence (44%) was observed in group D or E, followed by group E or Clade I (25%), group A (19%), and group B1 (13%). E. coli isolated from M. margaritifera predominantly exhibited a higher prevalence of phylogroups D or E, whereas E. coli from P. littoralis showed associations with phylogroups E or clade I, B1, A, and D or E. Our results provide new insights into the phylogenetic diversity of E. coli in freshwater bivalves. Additionally, the findings highlight the possible linkage of phylogroups with the host species, the geographical location in the water stream, and human activity. Using E. coli as a bioindicator isolated from freshwater mussels helps us grasp how human activities affect the environment. This study has important implications for those interested in safeguarding water resources, especially in tackling antibiotic resistance in aquatic ecosystems.

The silent extinction of freshwater mussels in Portugal

Freshwater mussels are one of the most threatened animal groups in the world. In the European Union, threatened and protected mussel species are not adequately monitored, while species considered to be common and widespread receive even less attention. This is particularly worrying in the Mediterranean region, where species endemism is high and freshwater habitats are severely affected by water scarcity. In the absence of hard data on population trends, we report here a long-term comparison of freshwater mussel assemblages at 132 sites covering 15 different hydrological basins in Portugal. This study reveals a widespread decline of 60 % in the number of sites and 67 % in the overall abundance of freshwater mussels across Portugal over the last 20 years, indicating that all species are rapidly declining and threatened with extinction. These results show that current legislation and conservation measures are largely ineffective and highlight the importance of updating the Habitats Directive to enforce standard monitoring protocols for threatened species in the European Union and to extend monitoring to other freshwater species thought to be common and widespread. Efficient water management, restrictions on irrigation expansion in important biodiversity areas, mitigation of hydrological changes and loss of aquatic habitat connectivity caused by physical alterations are urgently needed to reverse these declining population trends. For the severely endangered species Margaritifera margaritifera, Potomida littoralis, and Unio tumidiformis, where populations are now critically low, more urgent action is needed, such as ex-situ conservation, protection of remaining populations and large-scale habitat restoration.

Biochemical and behavioral effects of zinc oxide nanorods on the freshwater mussel Potomida littoralis

ABSTRACT Our study aimed to investigate the impact of nano-zinc oxide (nZnO), a widely used pollutant in industry, pharmaceuticals, and personal care products, on the behavior and oxidative stress of freshwater mussels (Potomida littoralis) an indicator species and also a model non-target organism in ecotoxicology. To this end mussels were exposed to nZnO (50 and 100 µg/L) and Zn2+ from ZnSO4 (50 and 100 µg/L) for 7 days. ZnSO4 was used for comparison purposes and to determine if the toxicity of nZnO was due to the release of ions into the aquatic environment. We evaluated changes in oxidative stress markers, including catalase (CAT), glutathione-S-transferase (GST), acetylcholinesterase (AChE), and malondialdehyde (MDA) levels, on the mussel gills and digestive glands. Additionally, the effect of nZnO on the filtration rate of bivalves was studied. The findings showed that the mussel tissue’s different parameters were significantly affected by exposure to various concentrations of nZnO, causing changes in their behavior that led to a decrease in filtration rate. Additionally, noteworthy increments were observed in CAT activity, AChE activity, and MDA levels, whereas GST activity displayed a decreasing trend, implying that oxidative stress contributes to the toxicity of nZnO. The purpose of this review is to present a framework for comprehending the toxicological impacts of nanoparticles from an environmental standpoint. Additionally, it includes novel information about the connections between nanoparticles (NPs) and bivalve species.

Streams in the Mediterranean Region are not for mussels: Predicting extinctions and range contractions under future climate change

Climate change is becoming the leading driver of biodiversity loss. The Mediterranean region, particularly southwestern Europe, is already confronting the consequences of ongoing global warming. Unprecedented biodiversity declines have been recorded, particularly within freshwater ecosystems. Freshwater mussels contribute to essential ecosystem services but are among the most threatened faunal groups on Earth. Their poor conservation status is related to the dependence on fish hosts to complete the life cycle, which also makes them particularly vulnerable to climate change. Species Distribution Models (SDMs) are commonly used to predict species distributions, but often disregard the potential effect of biotic interactions. This study investigated the potential impact of future climate on the distribution of freshwater mussel species while considering their obligatory interaction with fish hosts. Specifically, ensemble models were used to forecast the current and future distribution of six mussel species in the Iberian Peninsula, including environmental conditions and the distribution of fish hosts as predictors. We found that climate change is expected to severely impact the future distribution of Iberian mussels. Species with narrow ranges, namely Margaritifera margaritifera and Unio tumidiformis, were predicted to have their suitable habitats nearly lost and could potentially be facing regional and global extinctions, respectively. Anodonta anatina, Potomida littoralis, and particularly Unio delphinus and Unio mancus, are expected to suffer distributional losses but may gain new suitable habitats. A shift in their distribution to new suitable areas is only possible if fish hosts are able to disperse while carrying larvae. We also found that including the distribution of fish hosts in the mussels' models avoided the underprediction of habitat loss under climate change. This study warns of the imminent loss of mussel species and populations and the urgent need of management actions to reverse current trends and mitigate irreversible damage to species and ecosystems in Mediterranean regions.

Collapse of native freshwater mussel populations: Prospects of a long-term study

Freshwater biodiversity is under threat, but long-term quantitative studies showing major demographic declines in invertebrate species are still scarce. Here we focus on a long-term study (2004 to 2019) using four native freshwater mussel species (Order Unionida) colonizing two canals of the Ebro River (Spain). Special attention was given to Pseudunio auricularius (Spengler, 1793), a critically endangered species. Generalized linear mixed models results showed significant temporal effects on mussel densities, with a continuous decline in all species present, being Anodonta anatina, Potomida littoralis and Unio mancus now considered locally extinct. Pseudunio auricularius is still present in the studied canals, but at very low densities (0.01 ind/m2). Capture-recapture data on P. auricularius show a progressive decline in its survival probability, down to 0.15 in 2020 in the Canal Imperial de Aragón, although in the Canal de Tauste it remains close to 1. Based on these results, we discuss several hypotheses that may explain this rapid collapse of unionid populations. Given the precarious conservation status of freshwater mussels in both canals, effective management measures should be urgently applied, including habitat restoration and captive breeding.

Multiresistant bacteria: Invisible enemies of freshwater mussels

Freshwater mussels are among the most endangered groups of fauna anywhere in world. The indiscriminate use of antibiotics has led to the emergence of resistant strains. These antibiotic-resistant bacteria play a key role in increasing the risk allied with the use of surface water and in spread of resistance genes. Two endangered freshwater mussel species, Margaritifera margaritifera and Potomida littoralis, were sampled at 4 sampling sites along a 50 km stretch of River Tua. Water samples were taken at same sites. Of the total of 135 isolates, 64.44% (39.26% from water and 25.19% from mussels) were coliform bacteria. Site T1, with the lowest concentration of coliform bacteria, and site T2 were the only ones where M. margaritifera was found. No E. coli isolates were found in this species and the pattern between water and mussels was similar. P. littoralis, which was present at T3/T4 sites, is the one that faces the highest concentration of bacterial toxins, which are found in treated wastewater effluents and around population centers. Sites T3/T4 have the isolates (water and mussels) with the highest resistance pattern, mainly to β-lactams. Water and P. littoralis isolates (T3/T4) showed resistance to penicillins and their combination with clavulanic acid, and to cephalosporins, precisely to a fourth generation of cephalosporin antibiotics. The analysis provides important information on the risk to water systems, as well as the need to investigate possible management measures. It is suggested that future studies on the health status of freshwater bivalves should incorporate measures to indicate bacteriological water quality.

Trophic niche overlap between native freshwater mussels (Order: Unionida) and the invasive Corbicula fluminea

Abstract Freshwater mussels (Order Unionida) are highly threatened. Interspecific competition for food sources with invasive alien species is considered to be one of the factors responsible for their decline because successful invaders are expected to have wider trophic niches and more flexible feeding strategies than their native counterparts. In this study, carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotopes were used to investigate the trophic niche overlap between the native freshwater mussel species, Anodonta anatina, Potomida littoralis, and Unio delphinus, and the invasive bivalve Corbicula fluminea living in sympatry in the Tua basin (south‐west Europe). The species presenting the widest trophic niches were C. fluminea and A. anatina, which indicate that they have broader diets than U. delphinus and P. littoralis. Nonetheless, all the species assimilated microphytobenthos, sediment organic matter, and detritus derived from vascular plants, although with interspecific variability in the assimilated proportions of each source. The trophic niche of the invasive species overlapped with the trophic niche of all the native species, with the extent varying between sites and according to the species. From the three native species analysed, Potomida littoralis may be at a higher risk for competition for food with C. fluminea in the Tua basin, if food sources become limited, because this native mussel presented the narrowest trophic niche across sites and the highest probability of overlapping with the trophic niche of C. fluminea. Given the global widespread distribution of C. fluminea, the implementation of management measures devoted to the control or even eradication of this invasive alien species should be a conservation priority given its potential for competition with highly threatened native freshwater mussels.

Multiresistant Bacteria: Invisible Enemies of Freshwater Mussels

Freshwater mussels are among the most endangered groups of fauna anywhere in world. The indiscriminate use of antibiotics has led to the emergence of resistant strains. These antibiotic-resistant bacteria play a key role in increasing the risk allied with the use of surface water and in spread of resistance genes. Two endangered freshwater mussel species, Margaritifera margaritifera and Potomida littoralis, were sampled at 4 sampling sites along a 50km stretch of River Tua. Water samples were taken at same sites. Of the total of 135 isolates, 64.44% (39.26% from water and 25.19% from mussels) were coliform bacteria. Site T1, with the lowest concentration of coliform bacteria, and site T2 were the only ones where M. margaritifera was found. No E. coli isolates were found in this species and the pattern between water and mussels was similar. P. littoralis, which was present at T3/T4 sites, is the one that faces the highest concentration of bacterial toxins, which are found in treated wastewater effluents and around population centers. Sites T3/T4 have the isolates (water and mussels) with the highest resistance pattern, mainly to β-lactams. Water and P. littoralis isolates (T3/T4) showed resistance to penicillins and their combination with clavulanic acid, and to cephalosporins, precisely to a fourth generation of cephalosporin antibiotics. We discuss the conservation status and risk to water systems and the need for research into possible management measures. It is suggested that future studies on the health status of freshwater bivalves should incorporate measures to indicate bacteriological water quality.

Decay and persistence of empty bivalve shells in a temperate riverine system

Bivalve shells can persist over a geological time, acting as important physical resources to the associated fauna. However, few studies have investigated their relevance as persistent long-term ecological attributes to the ecosystem. As such, it is relevant to investigate the shell decays in riverine systems subjected to different environmental conditions. Towards this end, shells of four bivalve species (Anodonta anatina, Corbicula fluminea, Potomida littoralis and Unio delphinus) were made available individually and in clusters of different sizes. The effects of river flow and seasonality were assessed by recording the decay rates of shells in lentic and lotic habitats throughout the year. Our results evidenced that the decays varied among species and depend on shell size, water flow and season. Thin shelled species (A. anatina and U. delphinus) showed the highest mean percentage of decay per month, 3.17% (lotic) and 2.77% (lotic), respectively, and thick shelled species (C. fluminea and P. littoralis) the lowest, 2.02% (lotic) and 1.83% (lotic), respectively. Size was a relevant variable explaining decays, with the smallest shells presenting the highest values, 1.2–2.0 times higher compared to the other size classes. Also, robustness showed to be the most relevant feature explaining the decays in thick shelled species. River flow was also a relevant descriptor of the decays, with higher decays observed in the lotic compared to the lentic habitats. Furthermore, lower decays were observed mainly during summer (lentic site), and autumn (lotic site) associated to the burial effect of leaves. In summary, shells of the native species A. anatina and U. delphinus are expected to persist and contribute less as habitat engineering species, than shells of the native P. littoralis and invasive C. fluminea species. This is especially valid to lotic habitats where the decays were up to 2.13 times higher than in lentic habitats.

Invasive crayfishes as a threat to freshwater bivalves: Interspecific differences and conservation implications

Freshwater bivalves have suffered major global declines, being the introduction of invasive alien species (IAS) an important, but not well studied, mechanism of threat. This study assessed the predator-prey relationship between two non-native crayfish species (Procambarus clarkii and Pacifastacus leniusculus) and three native (Anodonta anatina, Potomida littoralis and Unio delphinus) and one non-native (Corbicula fluminea) freshwater bivalve species through experiments in laboratory and validation under natural conditions (Sabor River basin, Portugal). All native bivalve species were preyed both in laboratory and in the field; however, both crayfish species were unable to prey C. fluminea. Predation was dependent on crayfish and bivalve species but was not affected neither by crayfish nor bivalve sizes. In the laboratory, the most preyed species by both crayfishes was A. anatina. On average, this species was preyed at least 12% more than other species, when crayfishes had a choice. Similar results were found in the field. We also found signs of competition between both crayfishes, being P. clarkii more dominant and aggressive as this species, on average, manipulated the bivalves 63.6% more times and 24:33 min longer than P. leniusculus, and initiated 55.8% more agnostic bouts. Our results support the idea that P. clarkii and P. leniusculus can affect native freshwater bivalves, but clear interspecific differences were detected. Both crayfishes may have direct and indirect impacts on bivalve populations by increasing mortality or by reducing their fitness. In addition, since both crayfishes do not prey C. fluminea, they offer this IAS another advantage over native bivalves. Given the widespread distribution of both P. clarkii and P. leniusculus and the threatened status of many freshwater bivalves, the dynamics and impacts of this relationship should be taken in account in the implementation of management measures devoted to the conservation of native freshwater bivalves.

Physical legacy of freshwater bivalves: Effects of habitat complexity on the taxonomical and functional diversity of invertebrates

Bivalves may play a major role in structuring aquatic communities. This may be especially relevant in aquatic communities dominated by non-native invasive bivalves, which can contribute to the increase of habitat homogenization. In this study, we assess how habitat homogenization, through the reduction of empty bivalve shells identities, influences the macroinvertebrate assemblages. Towards this end, a manipulative experiment with the empty shells of two native (Potomida littoralis and Unio delphinus) and one non-native (Corbicula fluminea) species was performed. Seven treatments were prepared, three of them consisting of homogeneous substrates using shells of one species, and four of them consisting in heterogeneous substrates using more than one species. The associated fauna colonizing different treatments was analyzed through taxonomic and trait-based approaches. Our results showed that the substrate complexity influenced the density of macroinvertebrates, with the heterogeneous treatments significantly yielding more dense assemblages. Also, the trait patterns differed among the levels of habitat heterogeneity, influencing mainly organisms that feed on microphytes of both small and big sizes, that inhabit areas with slow to moderate water flow, and that have short and long live cycles. Further, the functional diversity was not influenced by the substrate heterogeneity. Therefore, the habitat homogenization, through the accumulation of non-native C. fluminea empty shells in the river bottom, did not affect the functional diversity of the macroinvertebrate assemblages.

Antimicrobial and Antibiofilm Activity of Unionid Mussels from the North of Portugal

The populations of freshwater mussels belonging to the family Unionidae have been facing drastic changes in terms of diversity and numbers caused by constant aggressions on their natural habitat. Nevertheless, bivalves are capable of developing strategies of defense to overcome potential aggressors. The present work aimed to assess the potential antibacterial capacity of different species of unionid mussels from the north of Portugal. For this purpose, circulating cells (hemocytes), fluids, and mucus were obtained by nonlethal methods from the species Anodonta anatina (Linnaeus), Anodonta cygnea (Linnaeus), Potomida littoralis (Cuvier), and Unio delphinus (Spengler), and tested against bacterial reference strains and multidrug-resistant isolates. The cellular fraction of A. anatina, A. cygnea, and P. littoralis showed antibacterial activity, detected by the agar disc diffusion method, against Bacillus subtilis ATCC 6683, Pseudomonas aeruginosa ATCC 27853 and Acinetobacter baumannii ATCC 19606. Circulating cells from P. littoralis and A. anatina also inhibited Listeria monocytogenes ATCC 19111 and A. cygnea has also inhibited a multidrug-resistant isolate of Pseudomonas putida. The plasma of all mentioned freshwater mussels, used directly or diluted, showed great ability to hamper or inhibit the biofilm formation of Staphylococcus aureus ATCC 25923, P. aeruginosa ATCC 27853, and Escherichia coli ATCC 25922. Anodonta cygnea hampered the biofilm formation by Enterococcus faecalis ATCC 29212 as well. Overall, these results showed that not only cells play a relevant role in the immune system of these species but also the plasma, which likely contains antibiofilm substances. Anodonta cygnea stood out by presenting the best antibacterial inhibition potential.

Potomida littoralis(Bivalvia, Unionidae) evolutionary history: slow evolution or recent speciation?

The distribution of circum-Mediterranean fauna was dramatically affected by palaeogeographical events during the Cenozoic. The biogeographical history of freshwater mussels is related to the development of the continental watershed during the Tertiary and Pleistocene glacial cycles. Our study model is Potomida littoralis (Cuvier, 1798), a Palaearctic freshwater mussel with a patchy circum-Mediterranean distribution encompassing areas of North Africa, south-western Europe, Greece and the Levant. Our phylogenetic reconstructions, network analyses and coalescence estimations indicate that the clade Potomida has a clear geographical structure with four robust lineages from Turkey, Greece, North Africa and Iberian Peninsula plus France. This structure is only disrupted in two cases: specimens from the Ziz River (Morocco) clustered with Tunisian lineages, and samples from the north-eastern Iberian Peninsula were found to have been recently introduced from Morocco. We considered two different calibration strategies of a molecular clock to evaluate divergence times between lineages. The first, based on palaeogeographical events, resulted in substitution rates up to three times lower than the average for molluscs. When such mean values were considered for calibrating the molecular clock, the group's origin and diversification events were incongruent with the fossil record and the likelihood of gene flow between lineages. Rather than a pattern of recent speciation, our results suggest low levels of substitution and a pattern of ‘slow evolution’, probably linked to its long generation time and longevity. From a taxonomic viewpoint, the genus Potomida is currently considered monospecific. Reflecting the data presented herein, we propose the existence of an eastern species, named P. acarnanica (Kobelt, 1879) in Greece and Turkey, and another named P. littoralis (Cuvier, 1798), with a wide distribution ranging from France to Tunisia.

Phylogeny, phylogeography, and evolution in the Mediterranean region: News from a freshwater mussel (Potomida, Unionida)

The Potomida genus (Bivalvia, Unionida) has a Circum-Mediterranean distribution and like other freshwater mussel species, its populations have suffered dramatic declines. Although this genus is currently considered as monotypic, it has a long history of taxonomic revisions and presently many aspects of its systematics and evolutionary history are unclear. We sampled a total of 323 individuals from 39 different sites across the Potomida genus distribution, and sequenced two mitochondrial (16S rDNA and Cytochrome c Oxidase Subunit I) and one nuclear (28S rDNA) genes to clarify its phylogeny and phylogeographic history. Our results show that the genus includes two well-supported clades, one comprising solely the western Mediterranean species Potomida littoralis, and the other including two eastern Mediterranean species, the Greek endemic P. acarnanica and the Anatolian and Middle Eastern P. semirugata. We suggest that Potomida started radiating during the upper Miocene, and that both vicariance and dispersal events shaped the diversification and distribution of the genus along the Mediterranean region. P. littoralis is further divided in two mitochondrial lineages, one restricted to Europe and the other occurring mostly in North Africa. Moreover, some European basins present both lineages in sympatry. The conservation status of the three recognized species should be reevaluated, particularly P. acarnanica, since it is restricted to two Greek river basins presenting a high risk of extinction. Overall, our results clarify some important gaps in knowledge concerning the phylogeny, phylogeography and evolution of the Potomida genus in the Mediterranean region with important taxonomical, ecological and conservational implications.

The male and female complete mitochondrial genome sequences of the Endangered freshwater mussel Potomida littoralis (Cuvier, 1798) (Bivalvia: Unionidae)

Freshwater mussels of the family Unionidae exhibit a particular form of mitochondria inheritance called double uniparental inheritance (DUI), in which the mitochondria are inherited by both male and female parents. The (M)ale and (F)emale mitogenomes are highly divergent within species. In the present study, we determine and describe the complete M and F mitogenomes of the Endangered freshwater mussel Potomida littoralis (Cuvier, 1798). The complete M and F mitogenomes sequences are 16 451 bp and 15 787 bp in length, respectively. Both F and M have the same gene content: 13 protein-coding genes (PCGs), 22 transfer RNA (trn) and 2 ribosomal RNA (rrn) genes. Bayesian analyses based on the concatenated nucleotide sequences of 12 PCGs and 2 rrn genes of both genomes, including mitogenome sequences available from related species, were performed. Male and Female lineages are monophyletic within the family, but reveal distinct phylogenetic relationships.

Differences in the macrozoobenthic fauna colonising empty bivalve shells before and after invasion by Corbicula fluminea

Bivalve shells can potentially alter the structure of aquatic benthic communities. However, little is known about the effect that different shell morphologies have on their associated fauna. This study aimed to understand how empty shells, from four different freshwater bivalve species, affect macrozoobenthic communities, using the River Minho (Iberian Peninsula) as a study area. Three native (Anodonta anatina, Potomida littoralis, Unio delphinus) and one non-indigenous (Corbicula fluminea) species were used for this research. Comparisons among species and between scenarios (i.e. before and after invasion by C. fluminea) were performed. Our results suggest that macrozoobenthic community structure did not vary among treatments, with the exception of species richness, which was higher on shells of native species. Furthermore, little difference was detected when comparing scenarios with and without C. fluminea shells, despite dissimilarities in size and morphology between species. The empty shells of C. fluminea partially (in terms of density and biomass, but not in species richness) replaced the role of empty shells of native species as a physical substratum for the associated macrozoobenthic community.

Contrasting decay rates of freshwater bivalves’ shells: Aquatic versus terrestrial habitats

Freshwater flow regimes are particularly vulnerable to global climate change with changes to the volume and regime of water contributing to global declines in freshwater biodiversity. Droughts or floods can cause massive mortalities of freshwater bivalves, facilitating the accumulation of shells in the aquatic but also in adjacent terrestrial habitats. In order to fully understand the long term impact of these massive mortality events, it is important to assess how bivalve shells persist in the environment. Given that, the present study aimed at studying the shell decays of four different bivalve species ( Anodonta anatina , Corbicula fluminea , Potomida littoralis and Unio delphinus ) in aquatic (i.e. river) versus terrestrial (i.e. sand soil) habitats. Shell decay rates were significantly different among species and habitats. In the aquatic habitat the shell decay rates varied among species, with the native species A . anatina , which have the largest and thinnest shell, showing the highest decay rate. Alternatively, in the terrestrial habitat the shell decay rates were more even among species and not related to a particular shell feature or morphology, with the native U . delphinus showing the fastest decay. The shell decay rates were 6 to 12 times higher in aquatic than in the terrestrial habitat. These results suggest that bivalve shells can persist for long periods of time on both habitats (but mainly in terrestrial), which may perhaps trigger significant changes on the ecosystem structure and functioning.