Genetics and taxonomy of Chilean smooth-shelled mussels, Mytilus spp. (Bivalvia: Mytilidae)

It has been previously established that native smooth-shelled mussels in southern South America possess close evolutionary affinities with Northern-Hemisphere Mytilus edulis L. 1758 (McDonald et al. (1991) [5]). This result has since been challenged by authors claiming that Chilean mussels should be considered a local subspecies of M. galloprovincialis Lmk. 1819. Moreover, morphological, physiological, ecotoxicological and molecular genetic studies on Chilean smooth-shelled mussels still frequently refer to ‘M. chilensis’ Hupé 1854, even though the previous discovery of alien M. galloprovincialis and considerable heterogeneity in shell morphology among samples collected along the Chilean shores raise concerns that different Mytilus spp. species might have been included under ‘M. chilensis’. Here we reviewed the molecular and morphological data available on smooth-shelled mussels from Chile in an attempt to clarify both their genetic composition and their taxonomic status. Using multivariate analysis on sample × allozyme-frequency matrices, we confirmed the widespread occurrence of the Southern-Hemisphere form of M. edulis along the shores from the North Patagonia region of Chile to the southern tip of the South American continent. The populations sampled in southern central Chile showed some evidence of slight introgression from Southern-Hemisphere M. galloprovincialis. Morphological characterization of a sample from Dichato in southern central Chile was consistent with its previous genetic identification as Mediterranean M. galloprovincialis. The occurrence of Southern-Hemisphere M. galloprovincialis in Punta Arenas at the southern tip of the South American continent was also reported. Southern-Hemisphere M. edulis, including native Chilean smooth-shelled Mytilus, should be assigned subspecific rank and named M. edulis platensis d’Orbigny 1846.     

A mitochondrial phylogeography of Brachidontes variabilis (Bivalvia: Mytilidae) reveals three cryptic species

This study examined genetic variation across the range of Brachidontes variabilis to produce a molecular phylogeography. Neighbour joining (NJ), minimum evolution (ME) and maximum parsimony (MP) trees based on partial mitochondrial DNA sequences of 16S-rDNA and cytochrome oxidase (COI) genes revealed three monophyletic clades: (1) Brachidontes pharaonis s.l. from the Mediterranean Sea and the Red Sea; (2) B. variabilis from the Indian Ocean; (3) B. variabilis from the western Pacific Ocean. Although the three clades have never been differentiated by malacologists employing conventional morphological keys, they should be ascribed to the taxonomic rank of species. The nucleotide divergences between Brachidontes lineages (between 10.3% and 23.2%) were substantially higher than the divergence between congeneric Mytilus species (2.3–6.7%) and corresponded to interspecific divergences found in other bivalvia, indicating that they should be considered three different species. Analysis of the 16S-rDNA sequences revealed heteroplasmy, indicating dual uniparental inheritance (DUI) of mtDNA in the species of Brachidontes collected in the Indian Ocean, but not in the species in the Pacific nor in the species in the Red Sea and the Mediterranean Sea. When we employed the conventional estimate of the rate of mitochondrial sequence divergence (2% per million years), the divergence times for the three monophyletic lineages were 6–11 Myr for the Indian Ocean and Pacific Ocean Brachidontes sp. and 6.5–9 Myr for the Red Sea and Indian Ocean Brachidontes sp . Thus, these species diverged from one another during the Miocene (23.8–5.3 Myr). We infer that a common ancestor of the three Brachidontes species probably had an Indo-Pacific distribution and that vicariance events, linked to Pleistocene glaciations first and then to the opening of the Red Sea, produced three monophyletic lineages.     

Invasive and non-invasive lineages in Xenostrobus (Bivalvia: Mytilidae)

The mussel genus Xenostrobus comprises eight named extant species from the Indo-West Pacific, including Xenostrobus inconstans, Xenostrobus pulex and Xenostrobus securis from Australia, the latter two also occurring in New Zealand. Xenostrobus species are predominantly restricted to estuaries or sheltered marine habitats although X. pulex inhabits the rocky intertidal on open coasts. Xenostrobus has recently been suggested to be congeneric with the freshwater invasive species Limnoperna fortunei. Xenostrobus securis is itself invasive in the Far East and Europe. This study employed DNA sequences from cytochrome c oxidase (COI), the D1 expansion region of 28S rRNA and the internal transcribed spacers of the ribosomal cistrons to investigate species relationships and habitat transitions in Australasian Xenostrobus. It is unlikely that Xenostrobus and Limnoperna are congeneric as their COI sequences are very different. There was unexpected complexity in defining Xenostrobus species. Xenostrobus pulex from New Zealand is probably a distinct species to the Australian taxon of that name with the name X. neozelanicus available for that taxon. Xenostrobus inconstans and Australian X. pulex were not reciprocally monophyletic in COI analyses. The phylogeography of the COI haplotypes of X. securis suggests that it may be a cryptic species complex, although this possibility could not be confirmed by sequences of the other genes.     

Parasitism in species of Bathymodiolus (Bivalvia: Mytilidae) mussels from deep-sea seep and hydrothermal vents

Bivalve species, especially mussels, are biomass dominants in many deep-sea chemosynthetic ecosystems. As in shallow-water environments, parasites are likely to be important factors in the population dynamics of bivalve communities in chemosynthetic ecosystems, but there has been little study of parasitism in deep-sea seep or vent molluscs. In this study, parasite types, diversity, prevalence, infection density and non-infectious indicators of stress or disease as related to host age, reproductive condition, and endosymbiont density were assessed in mussels (Bathymodiolus heckerae) from 2 seep sites and mussels (B. puteoserpentis) from 2 vent sites. We identified 10 microbial or parasitic agents in histological sections. Parasite types included 3 viral-like gut inclusions, 2 rickettsia-like gill inclusions, a rickettsia-like mantle inclusion, a bacterial gill-rosette, a chlamydia-like gut inclusion, gill-dwelling ciliates, and an unidentified inclusion in gut tissues. Parasite species richness was greater in seep mussels than in vent mussels, with the seep mussels possessing 9 types of parasites compared to 2 in the vent mussels. One of the viral-like inclusions infecting the seep mussel B. heckerae was pathogenic, causing lysis of the digestive tubules. The prevalence and intensity of infection by this pathogen were greater in hosts with shell lengths less than 100 mm. Mussels from all 4 sites also exhibited intense infiltration of tissues and blood spaces by enlarged hemocytes. Hemocytic infiltration (hemocytosis) showed variable degrees of severity that were not associated with other host factors examined.     

A genetic determination of cryptic species (Copepoda: Calanoida) and their postglacial biogeography in North America

Allozyme electrophoresis of Hesperodiaptomus arcticus (Marsh) sensu lato at subarctic Churchill, Canada revealed significant deviations from random mating in several populations, as shown by the complete absence of certain heterozygous types. A broad geographic survey of 20 enzyme loci in 1077 individuals from 27 ponds at 11 arctic and alpine sites west of Hudson Bay demonstrated that there were three genetically distinct types. Morphological analysis of genetically classified populations uncovered consistent morphological differences that had been ignored previously. These morphological characteristics were used to reclassify preserved museum and private specimens from additional sites from the entire North American distribution of H. arcticus sensu lato. A detailed study of two of the distinct types co-occurring at Churchill showed reproduction timing and habitat differences consistent with reproductive isolation. I concluded that there are three species and each have different distributions. Most regions examined must have been repopulated by dispersal from glacial refugia after deglaciation. The nominal species is apparently restricted to western arctic localities in the vicinity of the Alaskan refugium while the other two putative taxa have dispersed widely into previously glaciated regions.     

Phylogenetic characterization of three morphs of mussels (Bivalvia, Mytilidae) inhabiting isolated marine environments in Palau Islands

Marine lakes in the Palau Islands are known to harbor unique marine fauna that have remained isolated since the formation of the lakes after the Last Glacial Maximum. We analyzed mussels from marine lakes located on different islands and conducted morphological, phylogenetic and population genetic characterization to clarify their evolutionary history. The mussels were morphologically classified into three differentiated morphs: NS, ON, and MC. Their common characteristics were consistent with the Brachidontes-Hormomya complex of the Mytilidae family. Phylogenetic analysis based on the nuclear 18S ribosomal RNA gene supported the taxonomic position of the mussels among the Mytilidae. In the mitochondrial cytochrome c oxidase subunit I (COI) gene lineage, NS-and MC-morphs were highly diverged from each other; their estimated time of divergence dates back to the mid-Pleistocene. ON-morph was more closely related to MC-morph, although the shell morphologies of ON- and MC-morphs were easily distinguishable. Population genetic analysis revealed the coexistence of highly diverged haplotypes within a population of ON-morph, indicating introgression of mtDNA among the morphs. Our data suggest that morphological differentiation of marine lake mussels can occur in a relatively short period under different environmental conditions. Thus, the marine lakes provide a unique site for the study of diversification in mussels.     

Scorched mussels (Brachidontes spp., Bivalvia: Mytilidae) from the tropical and warm‐temperate southwestern Atlantic: the role of the Amazon River in their speciation

Antitropicality is a distribution pattern where closely related taxa are separated by an intertropical latitudinal gap. Two potential examples include Brachidontes darwinianus (south eastern Brazil to Uruguay), considered by some authors as a synonym of B. exustus (Gulf of Mexico and the Caribbean), and B. solisianus, distributed along the Brazilian coast with dubious records north of the intertropical zone. Using two nuclear (18S and 28S rDNA) and one mitochondrial gene (mtDNA COI), we aimed to elucidate the phylogeographic and phylogenetic relationships among the scorched mussels present in the warm‐temperate region of the southwest Atlantic. We evaluated a divergence process mediated by the tropical zone over alternative phylogeographic hypotheses. Brachidontes solisianus was closely related to B. exustus I, a species with which it exhibits an antitropical distribution. Their divergence time was approximately 2.6 Ma, consistent with the intensification of Amazon River flow. Brachidontes darwinianus, an estuarine species is shown here not to be related to this B. exustus complex. We suspect ancestral forms may have dispersed from the Caribbean to the Atlantic coast via the Trans‐Amazonian seaway (Miocene). The third species, B rodriguezii is presumed to have a long history in the region with related fossil forms going back to the Miocene. Although scorched mussels are very similar in appearance, their evolutionary histories are very different, involving major historical contingencies as the formation of the Amazon River, the Panama Isthmus, and the last marine transgression.     

Detection of invasive freshwater fish species using environmental DNA survey

Invasive species are one of the most significant problem in freshwater ecosystems. Most common non-native freshwater species in Turkish freshwater fish fauna are Prussian Carp (Carassius gibelio), North African Catfish (Clarias gariepinus), Nile Tilapia (Oreochromis niloticus) and Topmouth Gudgeon (Pseudorasbora parva).Recent studies showed that environmental DNA could be used to detect target species inhabiting the ecosystem with higher precision and less effort compared to traditional field surveys. In this study, eDNA approach was used to investigate non-native freshwater fish species from fifteen different locations of Upper Sakarya Basin. eDNA was successfully extracted from the water samples of locations where the species were visually observed. Mean amplification rate of eDNA was calculated as 77.03%.This study is the first environmental DNA study used in detection of four of the most common invasive freshwater fish species. Results clearly indicating that eDNA surveys could be used as an important molecular tool to monitor invasive fish species in freshwater ecosystems.     

Cytogenetic characterization of the invasive mussel species Xenostrobus securis Lmk. (Bivalvia: Mytilidae)

The chromosomes of the invasive black-pigmy mussel (Xenostrobus securis (Lmk. 1819)) were analyzed by means of 4',6-diamidino-2-phenylindole (DAPI) / propidium iodide (PI) and chromomycin A3 (CMA) / DAPI fluorescence staining and fluorescent in situ hybridization using major rDNA, 5S rDNA, core histone genes, linker histone genes, and telomeric sequences as probes. The diploid chromosome number in this species is 2n = 30. The karyotype is composed of seven metacentric, one meta/submetacentric, and seven submetacentric chromosome pairs. Telomeric sequences appear at both ends of every single chromosome. Major rDNA clusters appear near the centromeres on chromosome pairs 1 and 3 and are associated with bright CMA fluorescence and dull DAPI fluorescence. This species shows five 5S rDNA clusters close to the centromeres on four chromosome pairs (2, 5, 6, and 8). Three of the four core histone gene clusters map to centromeric positions on chromosome pairs 7, 10, and 13. The fourth core histone gene cluster occupies a terminal position on chromosome pair 8, also bearing a 5S rDNA cluster. The two linker histone gene clusters are close to the centromeres on chromosome pairs 12 and 14. Therefore, the use of these probes allows the unequivocal identification of 11 of the 15 chromosome pairs that compose the karyotype of X. securis.     

Genetic covariation of the marine fungal symbiont Haloguignardia irritans (Ascomycota, Pezizomycotina) with its algal hosts Cystoseira and Halidrys (Phaeophyceae, Fucales) along the west coast of North America

The fungal endophyte Haloguignardia irritans induces gall formation on the brown algal genera Cystoseira and Halidrys occurring from Oregon to Baja California, Mexico. Here we examine genetic covariation and compare rDNA phylogenies to investigate the coevolutionary histories of H. irritans and its algal hosts. Despite recognition of H. irritans as a single morphological species, internal transcribed spacer rDNA sequences representative of its geographic range are characterized by sequence variation at the intraspecific to intrageneric levels. An assessment of parallel cladogenesis between endophyte and host phylogenies provides evidence for a combination of independent fungal divergence and host jumping, similar to that observed in terrestrial lichens. Our results suggest that reduced gene flow due to geographic isolation is a major contributing factor to more concerted covariation observed at one island site, rather than to differences among algal host species alone. Because geography and its effects on gene flow can create heterogeneous mosaics of coevolution for symbioses in terrestrial environments, our results support the notion that conservation efforts toward the maintenance of genetic diversity in marine environments should likewise consider geographic complexity and its effects on coevolving marine species.     

Isozyme variation and differentiation of morphologically cryptic species in the Brachypodium distachyon complex

Isozyme variation of nine enzymes among three morphologically cryptic species of the Brachypodium distachyon complex was studied with PAGE. Aspartate aminotransferase isozymes AAT-A and AAT-C, aryl alcohol dehydrogenase AAD-B, malate dehydrogenase MDH-A and leucine aminopeptidase LAP-A in the allotetraploid B. hybridum display fixed heterozygosities with codominant expression of homoeozymes corresponding to divergent orthozymes of diploids B. distachyon and B. stacei. The multilocus isozyme genotype inherent to most accessions of B. hybridum combines two divergent multilocus isozyme genotypes characteristic of most accessions of B. distachyon and B. stacei. The maternally inherited chloroplast-encoded RUBISCO isozymes show that B. stacei is a maternal progenitor of B. hybridum, whereas the nuclear-encoded isozymes AAD-B, AAT-A, AAT-C, LAP-A, and MDH-A confirm that B. distachyon is the paternal progenitor. These data provide a new isozyme-based support to the karyological and DNA marker data on the allotetraploid nature of B. hybridum and its origin from diploids B. distachyon and B. stacei.     

A hybrid zone between hydrothermal vent mussels (Bivalvia: Mytilidae) from the Mid-Atlantic Ridge

This study provides the first example of a hybrid zone between animal taxa distributed along the mid-ocean ridge system. We examined the distribution and genetic structure of deep-sea hydrothermal vent mussels (Bivalvia: Mytilidae) along a 2888-km portion of the Mid-Atlantic Ridge between 37 degrees 50' N and 14 degrees 45' N latitude. Mitochondrial DNA (mtDNA), allozymes and multivariate-morphometric evidence discriminated between individuals of a northern species, Bathymodiolus azoricus, and a southern species, B. puteoserpentis, that were separated by an intermediate ridge segment almost devoid of mussels. A small sample of mussels from Broken Spur, a vent locality along this intermediate zone, revealed a mixed population with gene frequencies and morphology that were broadly intermediate to those of the northern and southern species. Multilocus clines in mtDNA and allozyme frequencies were centred over the intermediate zone. We consider intrinsic and extrinsic processes that might limit genetic exchange across this hybrid zone.     

Allozyme analysis of cryptic species in the Asplenium niduscomplex from West Java,Indonesia

In various fern species, a large amount of rbcL sequence variation has been reported, and it is possible that these species contain several reproductively isolated cryptic species. In our previous study on Asplenium nidus L., it was suggested that the plants growing in Mt. Halimun National Park, West Java, Indonesia, consist of several cryptic species based on the results of crossing experiments among rbcL sequence types. In this study, we examined allozyme polymorphisms of five rbcL sequence types found in West Java in order to test the hypothesis that the assemblages of A. nidus delimited based on the rbcL sequences are separate Mendelian populations and gene flow is disrupted by reproductive isolation from one another. The calculated fixation indices suggested that the individuals in each rbcL type are randomly crossing at least in the investigated localities. Nevertheless, these rbcL-based assemblages were genetically differentiated in allozymes that are encoded in their nuclear genomes, and it is also suggested that gene flow is disrupted even between sympatrically distributed pairs of rbcL sequence types. Therefore, our findings support the view that the five rbcL sequence types in West Java are potential cryptic species. Electronic Publication     

Genetic diversity of Southern hemisphere blue mussels (Bivalvia: Mytilidae) and the identification of non‐indigenous taxa

The taxonomic and evolutionary affinities of Southern hemisphere smooth‐shelled blue mussels are unclear, with studies using different marker types having identified different relationships among various geographic regions. Using an existing and a new molecular assay, the present study builds on previous work to test the distribution of blue mussels native to and introduced to the Southern hemisphere. Populations of Mytilus were sampled from New Zealand, Australia, and Chile. The nuclear‐DNA marker Me 15/16 was used to identify the taxonomic status of 484 individuals. A new restriction fragment length polymorphism (RFLP) assay was used to identify the hemisphere of origin for a subset of Mytilus galloprovincialis. The Me15/16 marker identified 478 pure M. galloprovincialis from Southern hemisphere sites and six Mytilus edulis/M. galloprovincialis hybrids from the Auckland Islands (New Zealand) and Chile. A cytoplasmic RFLP identified Northern hemisphere M. galloprovincialis in almost every Southern hemisphere region. The presence of native M. galloprovincialis at high latitudes (up to 52°S) has implications for our understanding of environmentally induced selective constraints considered to determine species distributions. Widespread occurrence of invasive Northern hemisphere blue mussels in the Southern hemisphere is documented for the first time. Identification of inter‐specific hybrids (M. edulis × M. galloprovincialis) in Chile and in the Auckland Islands (subantarctic New Zealand) illustrates that environments ranging from international ports to remote protected locations are vulnerable to bioinvasion. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 898–909.     

DNA barcoding of coastal ichthyofauna from Bahia,northeastern Brazil,South Atlantic: High efficiency for systematics and identification of cryptic diversity

In spite of the utility of DNA barcoding in discriminating marine fish species, few studies using this technique are available along the Brazilian coast, which encompasses nearly 9000 km, distinct biogeographic regions and endemism rates. Therefore, in the present work, we provided the first DNA barcode library based on sequencing of the mitochondrial gene cytochrome c oxidase subunit I (COI) for Actinopterygii fish from northeastern coast of Brazil. The database included 459 specimens from 54 genera, 31 families and 13 orders, with mean interspecific genetic distance of and mean intraspecific distance of 0.15%. As a result, the neighbor-joining (NJ) tree resulted in the molecular identification of 78 taxa. Cryptic species were indicated in Eucinostomus (mojarras) since the 82 specimens morphologically identified as Eucinostomus melanopterus or Eucinostomus sp. formed five clusters with intraspecific genetic distances up to 0.31% and lowest interspecific distance of 11.14%. Eucinostomus jonesii and Eucinostomus harengulus were identified for the first time in ichthyofauna inventories from northeastern Brazil. The present work has also added new records to the Barcode of Life Data System (BOLD), thereby favoring the identification of other specimens at different life stages or in forensic studies. The present dataset reinforces the reliability of DNA barcoding to estimate the overlooked richness of marine fish in Brazilian coast with application in conservation, ecology, systematics and fisheries.     

Genetic and morphometric characterization of mussels (Bivalvia: Mytilidae) from mid-atlantic hydrothermal vents.

Mussels were collected from deep-sea hydrothermal vents along the Mid-Atlantic Ridge. Specimens from the Snake Pit site were previously identified genetically and anatomically as Bathymodiolus puteoserpentis, but the relationships of mussels from other sites (Logatchev and Lucky Strike) were unclear. Molecular genetic and morphological techniques were used to assess differences among these mussel populations. The results indicate that the range for B. puteoserpentis extends from Snake Pit to Logatchev, and that an unnamed second species, B. n. sp., occurs at Lucky Strike. Analysis of mitochondrial NADH dehydrogenase subunit 4 (ND4) revealed 13% sequence divergence between the two species. Nei's genetic distance (D) based on 14 allozyme loci was 0.112. A multivariate morphometric analysis yielded a canonical discriminant function that correctly identified individuals from these sites to species 95% of the time.     

Larval development of the invasive charru mussel,Mytella strigata (Bivalvia: Mytilidae)

ABSTRACT

The South American charru mussel, Mytella strigata, was recently recorded in Singapore waters, possibly introduced into Southeast Asia through shipping. The mussels have rapidly spread across estuarine coastal mudflats. Adult mussels were collected, spawned in aquaria and larvae were successfully cultured to the juvenile stage in the laboratory. The larval morphology and development of M. strigata is described in this paper. D-shaped veligers were produced within 20 h of fertilization and were approximately 75 µm in shell length. These larvae were capable of settlement two weeks post fertilization. Given an adequate amount of food, they were able to grow up to 1 mm in shell length within 30 days. The larval shell of M. strigata possesses anterodorsal G2 hinge teeth as distinct wavy ledges, with a pitted resilial ridge clearly evident in the juvenile shell.     

Reach- and catchment-scale determinants of the distribution of freshwater mussels (Bivalvia: Unionidae) in south-eastern Michigan, U.S.A.

1. We investigated the diversity and distribution of freshwater mussels at 40 sites in an agricultural catchment, the River Raisin in south‐eastern Michigan, to relate mussel assemblages and individual taxa to reach and catchment‐scale variables. Unionids were surveyed by timed searches in 100‐m reaches, and in‐stream and riparian habitat were quantified as well as flow, water chemistry and channel morphology. Land use/cover and surficial geology were determined for site subcatchments and riparian buffers. 2. Some 21 mussel species were found overall; richness ranged from 0 to 12 living species per site. From the upper to middle to lower catchment, the number of individuals, number of species, Shannon–Weaver diversity and relative abundance of intolerant unionids all declined significantly. 3. Four groupings based on overall mussel diversity and abundance were significantly related to reach‐scale habitat variables. The richest mussel assemblages were associated with sites with higher overall habitat quality, greater flow stability, less fine substratum, and lower specific conductance. 4. Stepwise multiple regressions revealed that the distribution and abundance of the total mussel assemblage, as well as the most common species, could be predicted from a combination of reach‐ and catchment‐scale variables (R² = 0.63 for total mussels, R² = 0.51–0.86 for individual species). 5. Flow stability, substratum composition and overall reach habitat quality were the most commonly identified reach‐scale variables, and measures of surficial geology were the most effective catchment‐scale variables. The spatial pattern of geology is likely to be responsible for the diversity gradient from the upper to the lower catchment. 6. Prior studies, attempting to explain mussel distributions from local habitat features alone, have found relatively weak relationships. By employing a combination of reach‐ and catchment‐scale habitat variables, this study was able to account for a substantial amount of the spatial variability in mussel distributions.     

Thermal sensitivity of metabolic enzymes in subarctic and temperate freshwater mussels (Bivalvia: Unionoida)

Temperature has a major impact on the physiological processes of freshwater invertebrates. Despite the endangered status of many freshwater mussel species and the potential effect of global warming on North America’s northern aquatic habitats, thermal sensitivity of the metabolic apparatus of freshwater bivalves has received little attention. By examining the thermal sensitivity of 10 key metabolic enzymes and in situ growth rates of latitudinally separated populations (temperate and subarctic) of two closely-related Pyganodon species from northeastern North America, we provide the first insights into thermal sensitivity of key enzymes of energy and reactive oxygen species metabolism in relation to habitat localization and growth performance. The subarctic population of Pyganodon grandis displayed higher in situ growth rates than the temperate population of Pyganodon fragilis. The subarctic population of P. grandis had a lower mitochondrial capacity as expressed by citrate synthase and cytochrome c oxidase but displayed similar electron transport system (ETS) and higher isocitrate dehydrogenase capacities. Our results suggest that higher growth performance of the subarctic population of P. grandis is not associated with higher aerobic capacity. The high thermal sensitivity of mitochondrial enzymes in subarctic population of P. grandis might rather reflect enhanced stenothermy. The higher electron transport system/cytochrome c oxidase ratio for the subarctic P. grandis species than P. fragilis might affect mitochondrial regulation or reactive oxygen species production. Antioxidant enzymes displayed lower Q₁₀s suggesting thermal independence of antioxidant capacity.     

Influence of salinity on the physiological conditions in mussels, Perna perna and Perna viridis (Bivalvia: Mytilidae)

Perna genus was introduced to Venezuela, but nowadays, Perna perna and Perna viridis coexist and are commercially exploited from their natural beds. The aim of this work was to determine the effect of salinity on the physiological conditions of these species by studying RNA/DNA and Protein/DNA ratios. The organisms were collected from natural beds at La Esmeralda, Sucre State, Venezuela, and acclimatized for 15 days under laboratory conditions at 25 degrees C, 36 per thousand salinity, pH between 7 and 8 and more than 90% of oxygen saturation. Later, they were divided in two groups: for one group, the salinity concentration was increased (36 to 45 per thousand), and for the other, the salinity was decreased (36 to 15 per thousand). The rate of change was 1 per thousand every day. Ten organisms per group of both species were taken at each of 15, 20, 25, 30, 36, 40 y 45 per thousand salinity concentrations. Protein (colorimetric method) and nucleic acids (RNA and DNA by fluorometric method) concentrations were measured in the digestive gland, gills and adductor muscle tissues. Results indicate that P. perna can physiologically compensate the increase in salinity, but not when the salinity decreased, when proteins are the most needed macromolecules. The Protein/DNA index is directly related to salinity changes in both cases. P. viridis shows physiological compensation to salinity increases and decreases. The RNA/DNA index value in both cases supports this. Digestive gland and muscle tissues are the regulating tissues in both species. These results show that P. viridis has a higher degree of adaptability to salinity changes and, therefore, a greater potential for aquaculture than P. perna.