Mortality of young-of-the-year rainbow smelt (Osmerus mordax) in Lake Erie associated with the occurrence of Glugea hertwigi

An extensive mortality of young-of-the-year rainbow smelt (Osmerus mordax) occurred in Lake Erie during the fall of 1969. Dead and dying smelt were observed along the north shore from west of Long Point in the central basin to Port Maitland in the eastern basin. No other fish species was involved. Glugea hertwigi, a microsporidan parasite, was observed in 90% of the distressed smelt examined, and is believed to have been a major contributing factor to the mortality.     

Occurrence of Proteocephalus tetrastomus (Rudolphi, 1810) (Cestoda: Proteocephalidea) in larval rainbow smelt (Osmerus mordax) in North America: identification of a potential pathogen confirmed

A morphological evaluation and genetic analysis (sequencing of ITS2 region of rDNA) of proteocephalidean cestodes from rainbow smelt (Osmerus mordax) in the Saint Lawrence Estuary, Canada, has shown their conspecificity with Proteocephalus tetrastomus, a specific parasite of smelt (Osmeridae), previously known only from northern Europe, Russia, and Japan. The parasite occurs only in larval, but not adult, smelt in the Saint Lawrence Estuary. Prevalence of larval smelt infection was 42% (n = 50), mean intensity 2.1 +/- 2.4 and mean abundance 1.1 +/- 1.0.     

Characterization of a new BAC library for rainbow trout: evidence for multi-locus duplication

A 10X rainbow trout bacterial artificial chromosome (BAC) library was constructed to aid in the physical and genetic mapping efforts of the rainbow trout genome. The library was derived from the Swanson clonal line (YY male) and consists of 184,704 clones with an average insert size of 137,500 bp (PFGE) or 118,700 bp (DNA fingerprinting). The clones were gridded onto 10 large nylon membranes to produce high-density arrays for screening the library by hybridization. The library was probed with 11 cDNAs from the NCCCWA EST project chosen because of interest in their homology to known gene sequences, seven known genes, and a Y-specific sex marker. Putative positive clones identified by hybridization were re-arrayed and gridded for secondary confirmation. FPC analysis of HindIII and EcoRV DNA fingerprinting was used to estimate the level of redundancy in the library, to construct BAC contigs and to detect duplicated loci in the semi-duplicated rainbow trout genome. A good correlation (R2 = 0.7) was found between the number of hits per probe and the number of contigs that were assembled from the positive BACs. The average number of BACs per contig was 9.6, which is in good agreement with 10X genome coverage of the library. Two-thirds of the loci screened were predicted to be duplicated as the positive BACs for those genes were assembled into two or three different contigs, which suggests that most of the rainbow trout genome is duplicated.     

Temporal genetic differentiation: continuous v. discontinuous spawning runs in anadromous rainbow smelt Osmerus mordax (Mitchill)

Genetic differentiation was greater between 'early' and 'late' spawning rainbow smelt Osmerus mordax separated by a hiatus in spawning activity compared to a continuously spawning population over a similar time period. This magnitude of temporal differentiation was comparable to that seen among spatially separated populations.     

Distinguishing trophic and habitat partitioning among sympatric populations of the estuarine fish Osmerus mordax Mitchill

Sympatric populations of rainbow smelt Osmerus mordax of the St Lawrence middle estuary exhibited distinct morphologies suitable for exploiting either pelagic or benthic habitats in the absence of consistent morphological features related to specific diets. The magnitude of morphological differentiation was elevated and constant over 3 years even though statistically significant differences were observed among samples within populations. Both populations were spatially segregated in the estuary but some population mixing occurred at low densities of rainbow smelt. Diet analysis revealed that both populations opportunistically feed on large macrozooplankton. An amended version of Schoener's D was developed and used to compare the magnitude of niche overlap. It revealed that the diet of the middle estuary rainbow smelt differed according to the area where samples were collected but no differences existed between populations. The exploitation of ecologically distinct habitats appeared to be effective in maintaining morphologically distinct sympatric populations within an estuarine setting in the absence of diet differentiation.     

Differential evolution of the 13 Atlantic salmon Hox clusters

Hox cluster organization represents a valuable marker to study the effects of recent genome duplication in salmonid fish (25-100 Mya). Using polymerase chain reaction amplification of cDNAs, BAC library screening, and genome walking, we reconstructed 13 Hox clusters in the Atlantic salmon containing 118 Hox genes including 8 pseudogenes. Hox paralogs resulting from the genome duplication preceding the radiation of ray-finned fish have been much better preserved in salmon than in other model teleosts. The last genome duplication in the salmon lineage has been followed by the loss of 1 of the 4 HoxA clusters. Four rounds of genome duplication after the vertebrate ancestor salmon Hox clusters display the main organizational features of vertebrate Hox clusters, with Hox genes exclusively that are densely packed in the same orientation. Recently, duplicated Hox clusters have engaged a process of divergence, with several cases of pseudogenization or asymmetrical evolution of Hox gene duplicates, and a marked erosion of identity in noncoding sequences. Strikingly, the level of divergence attained strongly depends on the Hox cluster pairs rather than on the Hox genes within each cluster. It is particularly high between both HoxBb clusters and both HoxDa clusters, whereas both HoxBa clusters remained virtually identical. Positive selection on the Hox protein-coding sequences could not be detected.     

Computational Study of Evolutionary Selection Pressure on Rainbow Trout Estrogen Receptors

Molecular dynamics simulations were used to determine the binding affinities between the hormone 17-estradiol (E2) and different estrogen receptor (ER) isoforms in the rainbow trout, Oncorhynchus mykiss. Previous phylogenetic analysis indicates that a whole genome duplication prior to the divergence of ray-finned fish led to two distinct ER isoforms, ER and ER, and the recent whole genome duplication in the ancestral salmonid created two ER isoforms, ER and ER. The objective of our computational studies is to provide insight into the underlying evolutionary pressures on these isoforms. For the ER subtype our results show that E2 binds preferentially to ER over ER. Tests of lineage specific N/S ratios indicate that the ligand binding domain of the ER gene is evolving under relaxed selection relative to all other ER genes. Comparison with the highly conserved DNA binding domain suggests that ER may be undergoing neofunctionalization possibly by binding to another ligand. By contrast, both ER and ER bind similarly to E2 and the best fitting model of selection indicates that the ligand binding domain of all ER genes are evolving under the same level of purifying selection, comparable to ER.     

Comparing climate change and species invasions as drivers of coldwater fish population extirpations

Species are influenced by multiple environmental stressors acting simultaneously. Our objective was to compare the expected effects of climate change and invasion of non-indigenous rainbow smelt (Osmerus mordax) on cisco (Coregonus artedii) population extirpations at a regional level. We assembled a database of over 13,000 lakes in Wisconsin, USA, summarising fish occurrence, lake morphology, water chemistry, and climate. We used A1, A2, and B1 scenarios from the Intergovernmental Panel on Climate Change (IPCC) of future temperature conditions for 15 general circulation models in 2046-2065 and 2081-2100 totalling 78 projections. Logistic regression indicated that cisco tended to occur in cooler, larger, and deeper lakes. Depending upon the amount of warming, 25-70% of cisco populations are predicted to be extirpated by 2100. In addition, cisco are influenced by the invasion of rainbow smelt, which prey on young cisco. Projecting current estimates of rainbow smelt spread and impact into the future will result in the extirpation of about 1% of cisco populations by 2100 in Wisconsin. Overall, the effect of climate change is expected to overshadow that of species invasion as a driver of coldwater fish population extirpations. Our results highlight the potentially dominant role of climate change as a driver of biotic change.     

Construction and preliminary characterization of a river buffalo bacterial artificial chromosome library

River buffalo genome analyses have advanced significantly in the last decade, and the genome sequence of Bubalus bubalis will be available shortly. Nonetheless, large-insert DNA library resources such as bacterial artificial chromosomes (BAC) are still required for validation and accurate assembly of the genome sequence. We constructed a river buffalo BAC library containing 52,224 clones with an average insert size of 97 kb, representing 1.7 × coverage of the genome. This genomic resource for river buffalo will facilitate further studies in this economically important species allowing for instance, whole genome physical mapping and isolation of genes and gene clusters, contributing to the elucidation of gene organization and identification of regulatory elements.     

Seasonal freeze resistance of rainbow smelt (Osmerus mordax) is generated by differential expression of glycerol-3-phosphate dehydrogenase, phosphoenolpyruvate carboxykinase, and antifreeze protein genes

In winter, rainbow smelt (Osmerus mordax) accumulate glycerol and produce an antifreeze protein (AFP), which both contribute to freeze resistance. The role of differential gene expression in the seasonal pattern of these adaptations was investigated. First, cDNAs encoding smelt and Atlantic salmon (Salmo salar) phosphoenolpyruvate carboxykinase (PEPCK) and smelt glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were cloned so that all sequences required for expression analysis would be available. Using quantitative PCR, expression of beta actin in rainbow smelt liver was compared with that of GAPDH in order to determine its validity as a reference gene. Then, levels of glycerol-3-phosphate dehydrogenase (GPDH), PEPCK, and AFP relative to beta actin were measured in smelt liver over a fall-winter-spring interval. Levels of GPDH mRNA increased in the fall just before plasma glycerol accumulation, implying a driving role in glycerol synthesis. GPDH mRNA levels then declined during winter, well in advance of serum glycerol, suggesting the possibility of GPDH enzyme or glycerol conservation in smelt during the winter months. PEPCK mRNA levels rose in parallel with serum glycerol in the fall, consistent with an increasing requirement for amino acids as metabolic precursors, remained elevated for much of the winter, and then declined in advance of the decline in plasma glycerol. AFP mRNA was elevated at the onset of fall sampling in October and remained elevated until April, implying separate regulation from GPDH and PEPCK. Thus, winter freezing point depression in smelt appears to result from a seasonal cycle of GPDH gene expression, with an ensuing increase in the expression of PEPCK, and a similar but independent cycle of AFP gene expression.     

The effects of environmental factors on rainbow smelt Osmerus mordax embryos and larvae

Experiments were conducted to identify environmental factors that influence the survival of rainbow smelt Osmerus mordax during their early life stages. Developing rainbow smelt embryos and yolk-sac larvae were cultured under controlled conditions with different dissolved oxygen (DO; 1·09, 2·18, 4·37 and 6·55 mg l⁻¹, pH (4·0, 4·5, 5·0, 5·5, 6·0 and 7·0), nitrate ( 0·7, 3·6, 7·3, 14·6 and 29·2 mg l⁻¹), phosphate (0·04, 0·21, 0·42, 2·08 and 4·17 mg l⁻¹) and salinity (0, 5, 10, 15, 20 and 30) levels. Rainbow smelt embryos were also incubated with simulated tidal salinity fluctuations (2–28), ultraviolet radiation (irradiances of 2·8, 6·2 and 5·1 W m⁻²) and under natural conditions in two rainbow smelt spawning rivers. In the laboratory, hatch was only impaired under the lowest DO and pH conditions (0 and 13% hatch, respectively) and at highest constant salinity levels (0% hatch). Larval survival was only affected by pH levels ≤5·0. The experiment that compared hatch under natural conditions was terminated when embryos became covered with silt and fungus. These results suggest that water acidification, sediment and fungal growth may affect rainbow smelt survival during their early life stages.     

Identification and genomic structure of chemosensory proteins (CSP) and odorant binding proteins (OBP) genes expressed in foreleg tarsi of the swallowtail butterfly Papilio xuthus

Chemoreception is a key feature for selection of host plants by phytophagous insects. Female swallowtail butterflies recognize their host plants using chemosensilla present on foreleg tarsi. We constructed a cDNA library of female tarsi and a genome library of Papilio xuthus. We identified 11 chemosensory protein (CSP) genes and three odorant binding proteins (OBP) genes from the cDNA library and eight additional CSP genes from the genome library using the ESTs as probes. A sequence similarity tree of insect CSPs showed that lepidopteran CSPs constructed big branches of the order. Small numbers of CSPs have been identified from the whole genomes of several insect orders which belong to branches separated from those of Lepidoptera. The CSP gene family of Lepidoptera may have diverged in at least two steps, the first on a small scale and the second on a large scale before and after the diversification of insect orders, respectively. Seventeen of 19 CSP genes of P. xuthus clustered in a specific region of the genome, suggesting that they were diversified by gene duplication from a common ancestral gene.     

Evidence supporting the paraphyly of Hucho (Salmonidae) based on ribosomal DNA restriction maps

Relationships among the less derived genera in the subfamily Salmoninae were investigated by phylogenetic analysis of data from restriction maps of the ribosomal DNA using Osmerus mordax (rainbow smelt), Coregonus hoyi (bloater), and Thymattus arcticus (Arctic grayling) as outgroups. Analysis of the results suggests that Hucho h. taimen is more closely related to Brachymystax lenok (lenok) than to Hucho perryi (Sakhalin taimen) and that B. lenok and Hucho h. taimen (Eurasian taimen) form the most ancestral clade of the Salmoninae.