Glochidia of the freshwater mussel,Anodonta anatina, affecting the anadromous European smelt (Osmerus eperlanus) from the Eider estuary, Germany

During a 2-year survey on external disease conditions of fish between January 1988 and December 1989, 0.2% of 40011 smelt, Osmerus eperlanus , from 30 stations in the German Wadden Sea and estuaries of tributary rivers, were infected with glochidia of the freshwater mussel Anodonta anatina . Seasonality was marked, with glochidia only being observed in March and April 1989, when prevalences were 37% and 15% respectively, in fish 10–20cm long at the most heavily infected site. A marked increase in prevalence in fish 15cm in length and longer, suggested that only temporarily resident spawning fish (as opposed to resident juveniles) were infected. Infection was almost exclusively restricted to the Eider estuary, where prevalence decreased with increasing salinity. It is concluded that the glochidia carried by smelt returning from their freshwater spawning sites in the Eider River to the sea would have died, thus representing a loss to the 1989 cohort of A. anatina from the Eider. The potential importance of the smelt– A. anatina relationship as indicator for the detection of (a) spawning mussel populations and of (b) possible ecological effects of climate changes is noted.     

Genetic variability among freshwater mussel Anodonta woodiana (Lea, 1834) (Bivalvia: Unionidae) populations recently introduced in Poland

The alien Chinese mussel Anodonta woodiana was first reported in Poland in the system of heated lakes near Konin in 1993. Genetic studies with use of three molecular techniques (isoenzyme electrophoresis, PCR-RFLP and sequence analysis of a COI gene fragment) were carried out on the Polish first populations of A. woodiana. The studies have revealed low genetic variation between the populations (Nei's genetic distance for 12 loci ranged 0.000 to 0.007) as well as their considerable polymorphism. Each population averaged 2.28 alleles per locus, 2.72 alleles per polymorphic locus, and 75% polymorphic loci. Restriction analysis of the COI gene fragment have not revealed variability between the analysed specimens, including males and females. Restriction enzymes, ScrFI, Csp6I, and EcoRI used in the COI gene fragment PCR-RFLP generate distinct restriction patterns, which can be molecular markers for A. woodiana. The sequence obtained for COI fragment was the same in the examined female and male specimens and represents F mitotype (DNA was isolated from somatic tissues). The divergence between A. woodiana F and M mitotypes is high (34%), however it remains within the range of the general character of the DUI (doubly uniparental inheritance) phenomenon in freshwater bivalves (Unionidae).     

Sexual,habitat‐constrained and parasite‐induced dimorphism in the shell of a freshwater mussel (Anodonta anatina,Unionidae)

Intraspecific trends in freshwater mussel (unionoid) shells that are consistently associated with differences in the mussels' sex and/or parasitic infestation can potentially be used to reconstruct sex ratios or parasitic levels of modern and ancient unionoid populations. In contrast to morphological patterns within mammal species, such dimorphic trends within unionoid species are, however, poorly understood. This study investigates, for the first time, to what extent sex, trematode infection and indirect habitat effects determine shell morphology in the freshwater mussel Anodonta anatina. Three of the five study populations displayed significant sexual shell width dimorphism. Here, shells of females were significantly wider than males, probably as a result of altered shell growth to accommodate marsupial gills. In two of these populations, female shells were additionally significantly thinner than those of males, which could be a result of resource depletion by offspring production. Two other A. anatina populations showed no significant dimorphic patterns, and our results indicate that this interpopulational difference in the degree of sexual dimorphism may reflect the overarching effect of habitat on morphology. Thus, populations in the most favourable habitats exhibit faster growth rates, attain larger maximum sizes and produce more offspring, which results in more swollen gills and consequently more inflated shells of gravid females compared to less fecund populations. None of the populations showed any evidence for sexual dimorphism in overall size, growth rate, sagittal shape and density of shells. In addition to sexual dimorphisms, infestation by bucephalid trematode parasites (Rhipidocotyle sp.) significantly altered sagittal and lateral shell shape of A. anatina in one of the populations, with infected specimens growing wider and more elongated. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Seasonal changes in the population of the mite Unionicola intermedia (Hydrachnellae,Acari) from the freshwater mussel Anodonta anatina (Unionidae)

Although numbers were low in winter, males of Unionicola intermedia were found throughout the year. A mean of 2.5 (±0.26 SE) males per mussel was found with a range of 0 to 20. Females had a mean of 13.07 (±0.87 SE) per mussel and a range from 0 to 57, with the highest mean in August. The incidence of males was much lower than that of females. Nymphs and females were highly aggregated and males showed aggregation at a lower level of significance for nine months of the year. Although the primary sex ratio is unknown, the tertiary sex ratio is 86% female and on a monthly basis ranged from 68.9% to 96.7% female. It is speculated that reproduction is arrhenotokous. The sex ratio and the significant seasonal variations of the active stages may be influenced by the dispersal pattern of this species and by the biology of its host.     

Life history of the freshwater mussel Unio tumidiformis (Bivalvia: Unionidae) in a temporary Mediterranean‐type stream

Mediterranean‐type streams are characterized by great seasonal and annual variation in flow. We studied the biology of the freshwater mussel Unio tumidiformis in such a stream, the Vascão River in southern Portugal, during a period of great interannual variation in hydrology. We studied growth patterns of the mussels between 2002–2008, and the reproductive cycle between 2005–2006. Life‐history parameters were calculated and related to environmental variables and fish community patterns. Mark–recapture growth data confirmed that observed annuli were formed annually and are therefore reliable for use in growth studies of U. tumidiformis. The von Bertalanffy growth constant K and the asymptotic length L_∞ were negatively correlated. K varied between 0.20 and 0.58 and was positively correlated with factors related to eutrophication. The maximum observed age was 7 years, and the maximum observed length was 52 mm. There was no apparent sexual dimorphism, and sexual maturity was reached at the age of 2 years. Fecundity was low, between 1500–15000 glochidia per female, and positively correlated with body length. Only one annual gametogenic cycle was identified, leading to a short‐term reproductive period in spring (tachyticity). The reproductive cycle was similar in the two years sampled, between which hydrology and water quality differed greatly. The presence of glochidia was synchronized with the period when the proportion of fish hosts (genus Squalius) was higher in the fish community. Unio tumidiformis seems to be well adapted to the natural variability in flow in temporary Mediterranean‐type streams. Modifications of the natural flow regime caused by climate change or increased water exploitation may lead to rapid declines in mussel populations.     

Resolving species boundaries in the critically imperiled freshwater mussel species,Fusconaia mitchelli (Bivalvia: Unionidae)

Species are a fundamental unit of biology, and defining accurate species boundaries is integral to effective conservation and management of imperiled taxa. Freshwater mussels (Bivalvia: Unionidae) are among the most imperiled groups of organisms in North America, yet species boundaries remain uncertain for many taxa. The False Spike, Fusconaia mitchelli (Simpson in Dall, 1895), is a freshwater mussel considered to be endemic to central Texas (Brazos, Colorado, and Guadalupe drainages). Recent research revealed significant intraspecific genetic variation between geographically separated populations of F. mitchelli, which could be indicative of speciation; however, small sample sizes for several of the populations precluded formal taxonomic revision. Here, we increase taxon sampling and use multilocus DNA sequence data and traditional morphometrics to re‐evaluate species boundaries in F. mitchelli. We sequenced three loci: the protein‐coding mitochondrial DNA genes cytochrome c oxidase subunit 1 and NADH dehydrogenase 1, and the nuclear internal transcribed spacer 1. Phylogenetic analyses depicted deep genetic divergence between F. mitchelli in the Guadalupe and those in the Brazos and Colorado drainages, which was further supported by available biogeographic information. Morphometric analyses and coalescent‐based species delimitation models integrating both DNA sequence and morphological data provided strong support for the divergence observed between the two geographically isolated clades of F. mitchelli. Based on these results, we revise taxonomy accordingly by elevating the junior synonym Fusconaia iheringi (Wright, 1898) to represent the Brazos and Colorado populations and restrict the distribution of F. mitchelli to the Guadalupe River drainage. Our findings may impact pending management decisions to protect F. mitchelli under the U.S. Endangered Species Act.     

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.     

Sediment particles as a cause of nacre staining in the freshwater mussel,Amblema plicata (Say) (Bivalvia: Unionidae)

Brown stains sometimes appear in the inner shell layers (nacre) of freshwater mussels. An electron microprobe was used to analyze the stained nacre of the unionid Amblema plicata (Say, 1817) from selected localities on the Mississippi River in the vicinity of LaCrosse and Prairie du Chien, Wisconsin.Several elements such as Na, Mg, Al, Si, P, S, Cl, K, and Fe are more highly concentrated in stained than in unstained nacre. Concentrations of these elements relative to Ca were found to vary significantly among the localities from which the specimens were obtained. Ratios have significantly higher variances downstream of the confluence of the Yellow and Mississippi Rivers, downstream of a barge fleeting area, near the town of Marquette, Iowa, near the site of sewage effluent for Prairie du Chien, Wisconsin and downstream of a scrap metal yard near LaCrosse, Wisconsin in contrast to control localities.Suspended silt, the result of runoff and river activity (barge traffic, dredging, pleasure boating) may be the stimulus for stain formation. Clay minerals adsorb accessory elements and in turbid water are trapped within the pallial space of A. plicata. The mussel secretes an organic-rich, periostracum-like layer over the entrapped sediment, and later reverts to prismatic and finally nacreous shell deposition. Some of the elements found in the stain could directly disturb Ca metabolism by competing with Ca for binding sites in shell aragonite.     

Historical demography of freshwater mussels (Bivalvia: Unionidae): genetic evidence for population expansion and contraction during the late Pleistocene and Holocene

Genetic variation was examined in two endangered mussel species, Epioblasma brevidens and Epioblasma capsaeformis, and in a non‐listed species, Lampsilis fasciola, in the Clinch River, Tennessee, USA, by screening mitochondrial DNA (mtDNA) sequences and nuclear DNA microsatellites. Patterns of mtDNA polymorphism exhibited different trends in long‐term population sizes for each species during the late Pleistocene and Holocene (～20 000 ya to present); namely, E. brevidens has declined over time, E. capsaeformis has remained demographically stable, and L. fasciola has expanded. However, analyses using microsatellites did not exhibit similar trends, perhaps because homoplasy had eliminated long‐term population signatures for the loci examined. For both marker types, long‐term effective population size (N_e) was low in E. brevidens, intermediate in E. capsaeformis, and high in L. fasciola. Moderately diverged mtDNA lineages, perhaps indicative of secondary contact, were observed in E. brevidens and E. capsaeformis. Perhaps the most surprising result of this study was the high level of genetic variation observed at both mtDNA and microsatellite DNA markers for L. fasciola, variation seemingly contrary to the relatively small demes that currently reside in the Clinch River. However, the data are consistent with known demographic and life‐history traits of these three mussel species and their fish hosts, namely that they each use hosts with different dispersal capabilities, ranging from low, moderate, and high, respectively. The low divergence of mtDNA sequence variation reported in this and other recent mussel studies indicates that considerable extant population genetic variation probably originated during the late Pleistocene and Holocene. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 376–397.     

An integrative approach underscores the taxonomic status of Lamellidens exolescens,a freshwater mussel from the Oriental tropics (Bivalvia: Unionidae)

The Oriental Region harbours the second richest fauna of freshwater bivalves in the world, including many endangered endemic taxa. However, the Oriental fauna of the Unionidae have been very poorly studied using an integrative taxonomic approach, which may provide reasonable revisions of complicated (cryptic) taxa based on morphological, molecular, biogeographic and ecological evidence. Here, we present the first example of an integrative taxonomic revision concerning the status of Unio exolescens Gould (1843 Gould, A.A. (1843). Dr. Gould had examined the shells not long since announced as having been received from the Rev. Francis Mason, missionary at Tavoy, in British Burmah. Proceedings of the Boston Society of Natural History, 1, 139–141. [Google Scholar]), a nominal mussel taxon that was accepted as a valid species within the genus Trapezoideus Simpson (1900). Currently, Trapezoideus exolescens is considered the type of the genus as far as the originally designated type species, U. foliaceus Gould (1843 Gould, A.A. (1843). Dr. Gould had examined the shells not long since announced as having been received from the Rev. Francis Mason, missionary at Tavoy, in British Burmah. Proceedings of the Boston Society of Natural History, 1, 139–141. [Google Scholar]), was considered to be a synonym of T. exolescens. Using nucleotide sequences obtained from mitochondrial (COI and 16S rRNA) and nuclear (28S rDNA) genes, we found that the topotypes of Unio exolescens Gould (1843 Gould, A.A. (1843). Dr. Gould had examined the shells not long since announced as having been received from the Rev. Francis Mason, missionary at Tavoy, in British Burmah. Proceedings of the Boston Society of Natural History, 1, 139–141. [Google Scholar]) cluster together with representatives of another mussel genus, Lamellidens Simpson (1900). Based on these results and on morphological data, we transfer Unio exolescens Gould (1843 Gould, A.A. (1843). Dr. Gould had examined the shells not long since announced as having been received from the Rev. Francis Mason, missionary at Tavoy, in British Burmah. Proceedings of the Boston Society of Natural History, 1, 139–141. [Google Scholar]) from Trapezoideus to Lamellidens and propose Lamellidens exolescens (Gould, 1843 Gould, A.A. (1843). Dr. Gould had examined the shells not long since announced as having been received from the Rev. Francis Mason, missionary at Tavoy, in British Burmah. Proceedings of the Boston Society of Natural History, 1, 139–141. [Google Scholar]) comb. nov. In addition, we revisited the status of Unio foliaceus Gould (1843 Gould, A.A. (1843). Dr. Gould had examined the shells not long since announced as having been received from the Rev. Francis Mason, missionary at Tavoy, in British Burmah. Proceedings of the Boston Society of Natural History, 1, 139–141. [Google Scholar]) as a valid species and the type of the genus Trapezoideus based on the morphological study of the type specimen, although a question concerning the true position of this taxon is still open because its molecular sequences are not available. Our findings highlight that an integrative taxonomic approach is an important tool, particularly when dealing with such species-rich Unionidae fauna as those of the Oriental Realm.     

Integrative taxonomy reveals phenotypic plasticity in the freshwater mussel Contradens contradens (Bivalvia: Unionidae) in Thailand,with a description of a new species

The freshwater mussel Contradens contradens (Lea, 1838) occurs in most types of freshwater habitats throughout Thailand. The species shows extensive variation in shell morphology, which has led to the recognition of six different subspecies. In this study, the validity of these six subspecies plus one unknown species was assessed using an integrative taxonomic approach. Geometric morphometric analyses revealed significant differences in shell shapes among these six nominal morphological subspecies, although a considerable degree of overlap was detected in some groups. In contrast, the phylogenetic tree obtained from the concatenated data of mitochondrial COI and nuclear H3 gene sequences and molecular species delimitation analyses revealed only three supported clades. These clades are proposed herein as three distinct species, and strongly corresponded to the biogeographically disjunct drainage systems in Thailand. They consisted of the (i) C. contradens clade found in the Chao Phraya Basin and other rivers that drain into the Gulf of Thailand, (ii) C. crossei clade that is restricted to the Middle Mekong Basin, and (iii) a clade containing only the newly discovered species from Huai Luang River in the north-east of Thailand, which is described herein as Contradens rolfbrandti Jeratthitikul & Panha, sp. nov. Speciation among these congeners was probably caused by the restriction of gene flow due to the past geomorphology of the river systems. The intraspecific variation in the shell shape detected here does not reflect the evolution of the mussel, but rather is evidence of phenotypic plasticity.http://zoobank.org/urn:lsid:zoobank.org:pub:649B6093-E1DD-4FD8-8185-A4696C43AD36; http://zoobank.org/urn:lsid:zoobank.org:act:777DDE86-8397-4FF3-AA78-0BE0F34611F4     

Methods of DNA extraction and PCR amplification for individual freshwater mussel (Bivalvia: Unionidae) glochidia,with the first report of multiple paternity in these organisms

Freshwater mussels (Unionidae) are among North America's most imperilled organisms. Mussels produce small larvae (glochidia) that parasitize aquatic vertebrates. We modified the Epicentre QuickExtract protocol to extract DNA from a single glochidium, collected directly from the marsupium of a female mussel, to use as template in polymerase chain reactions (PCRs). Yield per glochidium in a 40 µL extraction volume provided enough DNA for ≥ 15 PCRs per individual. We were successful in using this DNA for microsatellite analysis of up to three loci per individual. Offspring from one female showed evidence for multiple paternity within her brood. Our results are the first documentation of this phenomenon in freshwater mussels.     

Condition and size of the non‐native pikeperch Sander lucioperca (Linnaeus, 1758) in Portuguese river basins

We studied life‐history traits focusing on the growth and condition of the pikeperch Sander lucioperca to evaluate its phenotypic plasticity when introduced to new environments. Pikeperch is a non‐native fish introduced to Iberian freshwater fauna in 1998 that quickly spread to other river basins through human‐mediated activities, occupying now a wide variety of habitats along mainland Portugal. Condition (K and SMI), fork length at age, and length–weight relationships were studied for Portuguese populations. Pikeperch fork length for ages 1, 2, 3, and 4 was different between several populations. We applied generalized linear models (GLM) to study the influence of habitat type, latitude, altitude, time after first detection, and fish prey richness on pikeperch populations size at age 4 and condition. We observed higher condition values on populations from lower altitudes at lentic systems more recently introduced. But higher fork length at age 4 was found in populations from higher altitudes, on older populations with higher prey richness. Habitat type, time since first detection, and fish fauna composition are discussed as the main environmental factors explaining the observed phenotypic plasticity with concerns on predatory impact on native fauna.     

Ultrastructure of the spermatid of Caprimulgus europaeus Linnaeus 1758, the European nightjar (Aves; Caprimulgidae), with phylogenetic implications

The sperm of Caprimulgus europaeus is typical of other nonpasserines in many respects. Features shared with Paleognathae and Galloanserae are the conical acrosome, shorter than the nucleus; the presence of a perforatorium and endonuclear canal; the presence of a proximal as well as distal centriole; the elongate midpiece with mitochondria grouped around a central axis (here maximally six mitochondria in approximately 10 tiers); and the presence of a fibrous or amorphous sheath around the principal piece of the axoneme. A major (apomorphic) difference from paleognaths and galloanserans is the short distal centriole, the midpiece being penetrated for most of its length by the axoneme and for only a very short proximal portion by the centriole. Nonpasserines differ from paleognaths in that the latter have a transversely ribbed fibrous sheath, whereas in nonpasserines it is amorphous, as in Caprimulgus, or absent. The absence of an annulus is an apomorphic feature of Caprimulgus, apodiform, psittaciform, gruiform, and passerine sperm, homoplastic in at least some of these. In contrast to passerines, in Caprimulgus the cytoplasmic microtubules in the spermatid are restricted to a transient longitudinal manchette. The structure of the spermatid and spermatozoon is consistent with placement of the Caprimulgidae near the Psittacidae, but is less supportive of close proximity to the Apodidae, from DNA-DNA hybridization and some other analyses.     

Population genetics of the freshwater mussel, <Emphasis Type="Italic">Amblema plicata</Emphasis> (Say 1817) (Bivalvia: Unionidae): Evidence of high dispersal and post-glacial colonization

Over 70% of North American freshwater mussel species (families Unionidae and Margaritiferidae) are listed as threatened or endangered. Knowledge of the genetic structure of target species is essential for the development of effective conservation plans. Because Ambelma plicata is a common species, its population genetic structure is likely to be relatively intact, making it a logical model species for investigations of freshwater mussel population genetics. Using mtDNA and allozymes, we determined the genotypes of 170+ individuals in each of three distinct drainages: Lake Erie, Ohio River, and the Lower Mississippi River. Overall, within-population variation increased significantly from north to south, with unique haplotypes and allele frequencies in the Kiamichi River (Lower Mississippi River drainage). Genetic diversity was relatively low in the Strawberry River (Lower Mississippi River drainage), and in the Lake Erie drainage. We calculated significant among-population structure using both molecular markers (A.p. Φ_st = 0.15, θ_st = 0.12). Using a hierarchical approach, we found low genetic structure among rivers and drainages separated by large geographic distances, indicating high effective population size and/or highly vagile fish hosts for this species. Genetic structure in the Lake Erie drainage was similar to that in the Ohio River, and indicates that northern populations were founded from at least two glacial refugia following the Pleistocene. Conservation of genetic diversity in Amblema plicata and other mussel species with similar genetic structure should focus on protection of a number of individual populations, especially those in southern rivers.     

Sexual dimorphism of the European Pond Turtle,Emys orbicularis (Linnaeus, 1758), in Anzali Lagoon,Iran (Reptilia: Emydidae)

The morphometric characteristics of the European Pond Turtle, Emys orbicularis, were studied at Anzali lagoon on the southern coast of the Caspian Sea. Males were on average (N=249) with 272.0?g significantly lighter than females with 447.0?g, and average carapace length was significantly smaller (123.0?mm in males, 139.0 in females). Females exceeded males also in all other studied characters (carapace width, plastron length, plastron width, and scute height). The sex ratio of male to female was 1 to 1.03, and the comparison of total tail length and cloaca-tail tip length revealed a difference between the position of the cloaca in both sexes, a character useful for sex determination in this species.     

Survival of glochidial larvae of the freshwater pearl mussel, Margaritifera laevis (Bivalvia: Unionoida), at different temperatures: a comparison between two populations with and without recruitment

The viability of free-living glochidia of the freshwater pearl mussel (Margaritifera laevis) was studied in the laboratory at water temperatures of 10 degrees C, 15 degrees C and 20 degrees C. To obtain glochidia, gravid female mussels were collected from the Chitose River, inhabited by adult and juvenile mussels, and from the Abira River, where only adult mussels were found. Daily survival rates of glochidia from each population at various water temperatures were significantly different, and survival time was longest at the lowest temperature in each population. Maintenance of some field mussel populations might become difficult at higher water temperatures due to the short survival time of glochidia and expected low density of host fish. Daily survival rates of glochidia were compared between the Abira population at 15 degrees C and the Chitose population at 20 degrees C, since these temperatures were close to the mean water temperature during the period of glochidial release in the respective rivers. Daily mean survival rates were significantly different between the Abira population at 15 degrees C and the Chitose population at 20 degrees C. Mean glochidial survival rate for the Chitose population changed from 85.3% to 66.2% from 9 to 13 h, whereas that for the Abira population dropped suddenly from 80.4% to 34.2% from 10 to 14 h after the initiation of experiment. Absence of juveniles in the Abira River might have been caused by the low glochidial viability. Survival times of free-living glochidia in Margaritiferidae tend to be shorter than in other families in Unionoida. A trade-off is suggested between high fertility and low glochidial survival rate in Margaritiferidae.     

Complete mtDNA sequence of the North American freshwater mussel,Lampsilis ornata (Unionidae): an examination of the evolution and phylogenetic utility of mitochondrial genome organization in Bivalvia (Mollusca)

Molluscs in general, and bivalves in particular, exhibit an extraordinary degree of mitochondrial gene order variation when compared with other metazoans. Two factors inhibiting our understanding the evolution of gene rearrangement in bivalves are inadequate taxonomic sampling and failure to examine gene order in a phylogenetic framework. Here, we report the first complete nucleotide sequence (16,060 bp) of the mitochondrial (mt) genome of a North American freshwater bivalve, Lampsilis ornata (Mollusca: Paleoheterodonta: Unionidae). Gene order and mt genome content is examined in a comparative phylogenetic framework for Lampsilis and five other bivalves, representing five families. Mitochondrial genome content is shown to vary by gene duplication and loss among taxa and between male and female mitotypes within a species. Although mt gene arrangement is highly variable among bivalves, when optimized on an independently derived phylogenetic hypothesis, it allows for the reconstruction of ancestral gene order states and indicates the potential phylogenetic utility of the data. However, the interpretation of reconstructed ancestral gene order states must take in to account both the accuracy of the phylogenetic estimation and the probability of character state change across the topology, such as the presence/absence of atp8 in bivalve lineages. We discuss what role, if any, doubly uniparental inheritance (DUI) and recombination between sexual mitotypes may play in influencing gene rearrangement of the mt genome in some bivalve lineages.     

The populations of the freshwater pearl mussel, <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> (Linnaeus, 1758), and the thick shelled river mussel, <Emphasis Type="Italic">Unio crassus</Emphasis> Philipsson, 1788, in Latvia

The populations of two endangered species—the freshwater pearl mussel Margaritifera margaritifera and the thick shelled river mussel Unio crassus in Latvia were studied. The specimens were counted, measured, population density and age structure were calculated. The possible host fish presence was found.