Incomplete congruence between morphobiological characters and sex-specific molecular markers in pacific salmons: 2. Population and temporal variability of the phenomenon

The congruence between secondary sexual characters and molecular markers, linked to the Ychromosome was examined in Asian populations of five Pacific salmon species of the genus Oncorhynchus. Our results support the existence of discrepancy between secondary sexual characters and sex-linked molecular markers in all species examined, which suggests the existence of similar or identical mechanism responsible for this phenomenon in Pacific salmons. Clinal latitudinal directional variation of the character confirmed the possibility that this phenomenon could be adaptively important, including its importance for regulation of the population number. In addition to natural factors affecting the degree of discrepancy between morphobiological characters and molecular markers in the Pacific salmon populations, anthropogenic factors, in particular intense fishery of certain population or population group, is also important.     

Incomplete congruence between morphobiological characters and sex-specific molecular markers in Pacific salmons: II. Population and temporal variability of the phenomenon

The congruence between secondary sexual characters and molecular markers, linked to the Y chromosome was examined in Asian populations of five Pacific salmon species of the genus Oncorhynchus. Our results support the existence of discrepancy between secondary sexual characters and sex-linked molecular markers in all species examined, which suggests the existence of similar or identical mechanism responsible for this phenomenon in Pacific salmons. Clinal latitudinal directional variation of the character confirmed the possibility that this phenomenon could be adaptively important, including its importance for regulation of the population number. In addition to natural factors affecting the degree of discrepancy between morphobiological characters and molecular markers in the Pacific salmon populations, anthropogenic factors, in particular intense fishery of certain population or population group, is also important.     

<Emphasis Type="Italic">Carnobacterium maltaromaticum</Emphasis> infections in feral <Emphasis Type="Italic">Oncorhynchus</Emphasis> spp. (Family Salmonidae) in Michigan

Members of the genus Oncorhynchus were introduced from the Pacific Northwest to the Laurentian Great Lakes basin and now constitute one of its most commercially and ecologically valuable fisheries. Recently, infections by a group of Gram-positive atypical lactobacilli belonging to the genus Carnobacterium have been detected in feral and captive Oncorhynchus spp. broodstock, some of which were associated with mortalities. Out of 1564 rainbow and steelhead trout (O. mykiss), coho salmon (O. kisutch), and Chinook salmon (O. tshawytscha) that were bacteriologically examined, 57 Carnobacterium spp. isolates were recovered from the kidneys, spleen, swimbladder, and/or external ulcerations of 51 infected fish. Phenotypic and biochemical characterization, as well as partial 16S rDNA sequencing and phylogenetic analyses of 30 representative isolates identified 29 as Carnobacterium maltaromaticum and 1 as C. divergens, though some phenotypic and genotypic heterogeneity was observed. Infections with C. maltaromaticum were associated with signitures typical of pseudokidney disease, but on occasion were also observed in fish displaying the gross and histopathological changes characteristic of nephrocalcinosis. While C. maltaromaticum infections were found to be widespread in both feral and farmed spawning populations of Oncorhynchus spp. residing within the Great Lakes basin, infection prevalence varied significantly according to fish species and strain, gender, and across time, but not by sampling location according to logistic regression analysis. The findings of this study further underscore the presence of phenotypic variations among Carnobacterium maltaromaticum strains that necessitate genotypic analysis to achieve definitive identification.     

Legs of deception: disagreement between molecular markers and morphology of long‐legged flies (Diptera,Dolichopodidae)

Conflicting hypotheses in phylogenetics and systematics, generated by different data sets (e.g. morphological versus molecular), are common in biology. The clarification of such instances may allow understanding general mechanisms involved in the speciation process in an evolutionary light. Here, we present and discuss the case of the Dolichopus plumipes species group in the long‐legged flies, Dolichopodidae. A phylogenetic survey was performed based on both morphological and molecular data. The full data set comprises 31 morphological characters and 2252 molecular characters (mitochondrial – COI: 810; 12S: 343; 16S: 514; nuclear – ITS2: 585) of 49 different species, represented by 82 specimens. The molecular phylogenetic analysis revealed a clade (composed by the species D. plumipes, Dolichopus wahlbergi, Dolichopus polleti, Dolichopus simplex, and Dolichopus nigricornis) that disagrees with the traditional morphological view based on external characters. In particular, specimens of the species D. plumipes and D. simplex were indistinguishable with the molecular markers used here. Yet, we still consider D. plumipes and D. simplex as two distinct taxa and provide explanatory hypotheses on the evolutionary background. The conspicuous male secondary sexual characters (present in plumipes but not in simplex) are key factors in sexual selection and their presumably rapid reduction in D. simplex is thought to be of main importance for the explanation of the speciation process. The plumipes–simplex case may therefore be viewed as a paradigmatic illustration showing that a better integration of the molecular and morphological approaches is needed to understand and clarify the, in some cases, complex systematics and phylogeny of organisms.     

Comparative anatomy of the dorsal hump in mature Pacific salmon

Mature male Pacific salmon (Genus Oncorhynchus ) demonstrate prominent morphological changes, such as the development of a dorsal hump. The degree of dorsal hump formation depends on the species in Pacific salmon. It is generally accepted that mature males of sockeye (O. nerka ) and pink (O. gorbuscha ) salmon develop most pronounced dorsal humps. The internal structure of the dorsal hump in pink salmon has been confirmed in detail. In this study, the dorsal hump morphologies were analyzed in four Pacific salmon species inhabiting Japan, masu (O. masou ), sockeye, chum (O. keta ), and pink salmon. The internal structure of the dorsal humps also depended on the species; sockeye and pink salmon showed conspicuous development of connective tissue and growth of bone tissues in the dorsal tissues. Masu and chum salmon exhibited less‐pronounced increases in connective tissues and bone growth. Hyaluronic acid was clearly detected in dorsal hump connective tissue by histochemistry, except for in masu salmon. The lipid content in dorsal hump connective tissue was richer in masu and chum salmon than in sockeye and pink salmon. These results revealed that the patterns of dorsal hump formation differed among species, and especially sockeye and pink salmon develop pronounced dorsal humps through both increases in the amount of connective tissue and the growth of bone tissues. In contrast, masu and chum salmon develop their dorsal humps by the growth of bone tissues, rather than the development of connective tissue.     

Sex ratio control in pink salmon (<Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis> and chum salmon (<Emphasis Type="Italic">O. keta</Emphasis>) populations: The possible causes and mechanisms of changes in the sex ratio

Long-term changes in the sex ratio have been studied in pink salmon (Oncorhynchus gorbuscha and chum salmon (O. keta) populations of Kamchatka and Sakhalin. It has been demonstrated that these changes are an adaptation to population dynamics: an increase in the population size is accompanied by a shift towards a higher proportion of males; a decrease in population size, by a shift towards a higher proportion of females. The correspondence between morphological and molecular characters in populations of the two species has been analyzed in order to determine the mechanism of sex ratio control. In some pink salmon and chum salmon populations, there is a discrepancy between sex identifications based on morphological characters and molecular markers. This discrepancy is assumed to be accounted for by sex inversion mechanisms, which may be population-or region-specific. In two cases, it has been found that the sex ratio discrepancy in populations is related to the numbers of fish in subsequent generations. These findings suggest that sex inversion may be related to population size control.     

Molecular Markers for Identification of the Hyperparasitoids Dendrocerus carpenteri and Alloxysta xanthopsis in Lysiphlebus testaceipes Parasitizing Cereal Aphids

Polymerase chain reaction (PCR)-based molecular markers have been developed to detect the presence of primary parasitoids in cereal aphids and used to estimate primary parasitism rates. However, the presence of secondary parasitoids (hyperparasitoids) may lead to underestimates of primary parasitism rates based on PCR markers. This is because even though they kill the primary parasitoid, it’s DNA can still be amplified, leading to an erroneous interpretation of a positive result. Another issue with secondary parasitoids is that adults are extremely difficult to identify using morphological characters. Therefore, we developed species-specific molecular markers to detect hyperparasitoids. A 16S ribosomal RNA mitochondrial gene fragment was amplified by PCR and sequenced from two secondary parasitoid species, Dendrocerus carpenteri (Curtis) (Hymenoptera: Megaspilidae) and Alloxysta xanthopsis (Ashmead) (Hymenoptera: Charipidae), four geographic isolates of the primary parasitoid, Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae), and six aphid species common to cereal crops. Species-specific PCR primers were designed for each insect on the basis of these 16S rRNA gene sequences. Amplification of template DNA, followed by agarose gel electrophoresis, successfully distinguished D. carpenteri and A. xanthopsis from all four isolates of L. testaceipes and all six cereal aphid species in this laboratory test.     

Evidence for competitive dominance of Pink salmon (<Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis>) over other Salmonids in the North Pacific Ocean

Relatively little is known about fish species interactions in offshore areas of the world’s oceans because adequate experimental controls are typically unavailable in such vast areas. However, pink salmon (Oncorhynchus gorbuscha) are numerous and have an alternating-year pattern of abundance that provides a natural experimental control to test for interspecific competition in the North Pacific Ocean and Bering Sea. Since a number of studies have recently examined pink salmon interactions with other salmon, we reviewed them in an effort to describe patterns of interaction over broad regions of the ocean. Research consistently indicated that pink salmon significantly altered prey abundance of other salmon species (e.g., zooplankton, squid), leading to altered diet, reduced total prey consumption and growth, delayed maturation, and reduced survival, depending on species and locale. Reduced survival was observed in chum salmon (O. keta) and Chinook salmon (O. tshawytscha) originating from Puget Sound and in Bristol Bay sockeye salmon (O. nerka). Growth of pink salmon was not measurably affected by other salmon species, but their growth was sometimes inversely related to their own abundance. In all marine studies, pink salmon affected other species through exploitation of prey resources rather than interference. Interspecific competition was observed in nearshore and offshore waters of the North Pacific Ocean and Bering Sea, and one study documented competition between species originating from different continents. Climate change had variable effects on competition. In the North Pacific Ocean, competition was observed before and after the ocean regime shift in 1977 that significantly altered abundances of many marine species, whereas a study in the Pacific Northwest reported a shift from predation- to competition-based mortality in response to the 1982/1983 El Nino. Key traits of pink salmon that influenced competition with other salmonids included great abundance, high consumption rates and rapid growth, degree of diet overlap or consumption of lower trophic level prey, and early migration timing into the ocean. The consistent pattern of findings from multiple regions of the ocean provides evidence that interspecific competition can significantly influence salmon population dynamics and that pink salmon may be the dominant competitor among salmon in marine waters.     

Intraspecific divergence in sperm morphology of the green sea urchin, <Emphasis Type="Italic">Strongylocentrotus droebachiensis</Emphasis>: implications for selection in broadcast spawners

Background  

Sperm morphology can be highly variable among species, but less is known about patterns of population differentiation within species. Most studies of sperm morphometric variation are done in species with internal fertilization, where sexual selection can be mediated by complex mating behavior and the environment of the female reproductive tract. Far less is known about patterns of sperm evolution in broadcast spawners, where reproductive dynamics are largely carried out at the gametic level. We investigated variation in sperm morphology of a broadcast spawner, the green sea urchin (Strongylocentrotus droebachiensis), within and among spawnings of an individual, among individuals within a population, and among populations. We also examined population-level variation between two reproductive seasons for one population. We then compared among-population quantitative genetic divergence (Q _ST) for sperm characters to divergence at neutral microsatellite markers (F _ST).     

Viability and expression of sexual ornaments in the barn swallow Hirundo rustica: a meta‐analysis

Sexual selection results in the evolution of exaggerated secondary sexual characters that can entail a viability cost. However, in species where sexual ornaments honestly reflect individual quality, the viability cost of secondary sexual characters may be overwhelmed by variation in individual quality, leading to expect that individuals with the largest secondary sexual characters show higher, rather than lower viability. Here, we used meta‐analyses to test whether such expected positive relationship between sexual ornamentation and viability exists in the barn swallow Hirundo rustica, which is one of the most studied model species of sexual selection under field conditions. We found a mean positive effect size of viability in relation to the expression of secondary sexual characters of 0.181 (CI: 0.084–0.278), indicating that in this species the more ornamented individuals are more viable, and therefore of high quality. Analyses of moderator variables showed similar effects in males and females, the H. r. rustica subspecies rather than others and tail length rather than other secondary sexual characters. Future research emphasis on other subspecies than the European one and secondary sexual characters than tail length may help identify the sources of heterogeneity in effect sizes.     

Interspecific habitat associations of juvenile salmonids in Lake Ontario tributaries: implications for Atlantic salmon restoration

Diel variation in habitat use of subyearling Chinook salmon (Oncorhynchus tshawytscha), subyearling coho salmon (O. kisutch), yearling steelhead (O. mykiss), and yearling Atlantic salmon (Salmo salar) was examined during the spring in two tributaries of Lake Ontario. A total of 1318 habitat observations were made on juvenile salmonids including 367 on steelhead, 351 on Chinook salmon, 333 on Atlantic salmon, and 261 on coho salmon. Steelhead exhibited the most diel variation in habitat use and Chinook the least. Juvenile salmonids were generally associated with more cover and larger substrate during the day in both streams. Interspecific differences in habitat use in both streams occurred with Atlantic salmon (fast velocities) and coho salmon (pools) using the least similar habitat. Chinook salmon and Atlantic salmon used similar habitat in both streams. These findings should help guide future management actions specific to habitat protection and restoration of Atlantic salmon in Lake Ontario tributaries.     

Morphological and molecular analysis of <Emphasis Type="Italic">Ornithonyssus</Emphasis> spp. (Acari: Macronyssidae) from small terrestrial mammals in Brazil

Based on chaetotaxy of the dorsal shield, the taxonomic status of many species of Ornithonyssus has been considered invalid, resulting in the synonymy of all Brazilian Ornithonyssus from small terrestrial wild mammals into one of the following four species: Ornithonyssus bacoti (Hirst, 1913), Ornithonyssus matogrosso (Fonseca, 1954), Ornithonyssus pereirai (Fonseca, 1935) or Ornithonyssus wernecki (Fonseca, 1935). Despite the revision of this genus in 1980, including all known species worldwide, the knowledge of Ornithonyssus in Brazil has not progressed for more than 40 years. Considering the potential importance of these haematophagous mites in transmitting rickettsial disease agents to animals and humans, we have revised Ornithonyssus species collected from small mammals in Brazil by means of morphological and molecular studies. Types and other material deposited in the Acari Collection of the Instituto Butantan (IBSP) were examined in addition to recently collected specimens. Morphological and genetic analysis of the 16S rDNA mitochondrial gene revealed that small terrestrial mammals in Brazil are parasitized by six species of Ornithonyssus mites: Ornithonyssus brasiliensis (Fonseca, 1939), O. matogrosso, O. monteiroi (Fonseca, 1941), O. pereirai, O. vitzthumi (Fonseca, 1941), and O. wernecki. An illustrated key to females of the valid Brazilian species of Ornithonyssus is included, based on optical and scanning electron microscopy.     

Characterization of sex chromosomes in rainbow trout and coho salmon using fluorescence in situ hybridization (FISH)

With the aim of characterizing the sex chromosomes of rainbow trout (Oncorhynchus mykiss) and to identify the sex chromosomes of coho salmon (O. kisutch), we used molecular markers OmyP9, 5S rDNA, and a growth hormone gene fragment (GH2), as FISH probes. Metaphase chromosomes were obtained from lymphocyte cultures from farm specimens of rainbow trout and coho salmon. Rainbow trout sex marker OmyP9 hybridizes on the sex chromosomes of rainbow trout, while in coho salmon, fluorescent signals were localized in the medial region of the long arm of one subtelocentric chromosome pair. This hybridization pattern together with the hybridization of a GH2 intron probe on a chromosome pair having the same morphology, suggests that a subtelocentric pair could be the sex chromosomes in this species. We confirm that in rainbow trout, one of the two loci for 5S rDNA genes is on the X chromosome. In males of this species that lack a heteromorphic sex pair (XX males), the 5S rDNA probe hybridized to both subtelocentrics This finding is discussed in relation to the hypothesis of intraspecific polymorphism of sex chromosomes in rainbow trout.     

Comparative ultrastructure of the zona radiata from eggs of six species of salmonids

Summary The zona radiata from unactivated and activated eggs from chinook salmon (Oncorhynchus tshawytscha), chum salmon (O. kisutch), pink salmon (O. gorbuscha), brown trout (Salmo trutta), rainbow trout (S. gairdneri) and lake trout (Salvelinus namaycush) were examined using scanning and transmission microscopy. The zona radiata in all species examined consisted of an outer adhesive coating, a thin densely staining zona radiata externa with pore canal plugs and a thick, fibrous zona radiata interna with a fibrous network on the inner surface. There was a two layer adhesive coating over the zona radiata externa in all species except pink salmon in which only one layer was observed. There were structural differences among species in the adhesive layer, zona radiata externa and plugs in the pore-canal openings.Scientific Journal Series, Paper No. 14,627, Minnesota Agricultural Experiment StationPartially funded by Minnesota Sea Grant NA-82-AA 12-000-39, Project RF-12, Minnesota Sea Grant Contribution 168     

General patterns of sexual dimorphism in graylings (Thymallus), with a comparison to other salmonid species

Among fishes, salmonids (family Salmonidae) have attracted a great deal of research attention focused on sexual dimorphism and associated selective forces. Most of this research has been directed toward anadromous and mostly semelparous salmon and trout (Oncorhynchus, Salmo), and comparatively little is known about intersexual variability in strictly iteroparous freshwater salmonids. We examined a comprehensive data set of 28 linear morphometric characters in 11 of 15 currently recognised species of grayling (Thymallinae, Thymallus), a genus consisting of iteroparous species only, to identify general patterns of intersexual morphological variability. Overall, we found that all grayling species show common sex-specific traits particularly relating to size dimensions of the dorsal, anal, pelvic and pectoral fins. Although the magnitude of sexual dimorphism differed among species, there was no significant phylogenetic signal associated with these differences across the genus. These results are discussed in terms of the assumed selection pressures driving sexual dimorphism in graylings and are compared to existing knowledge in Salmonidae as a whole where similarities and differences with both Salmoninae and Coregoninae exist. The present study provides the first detailed genus-wide comparison of sexually dimorphic phenotypic characters in graylings, and highlights the need for more large-scale comparative studies in multiple salmonid species to better understand general macroevolutionary trends among this important group of freshwater fishes.

     

Mating system variation in Veronica (Plantaginaceae): inferences from pollen/ovule ratios and other reproductive traits

The pollen–ovule ratio (P/O) is commonly used to estimate the mode of sexual reproduction in flowering plants. In previous studies, a clear correspondence has been detected between this character and the degree of autogamy. We here investigate variation in this character and its expected correlates in the genus Veronica (Plantaginaceae). Pollen–ovule ratios of 45 species representing eleven percent of all the species in the genus were investigated and compared with results from crossing experiments from previous studies. In addition, multiple populations of 17 of the 45 studied species were sampled and a controlled‐environment experiment was conducted to evaluate the extent of intraspecific variation. Moreover, relationships between P/O and other primary and secondary reproductive characters of the Veronica flower were investigated in relation to a phylogenetic hypothesis in order to determine the phylogenetic constraints on reproductive characters. The differences in P/O among species correspond well to the diversity of mating systems in Veronica and correlate well with other floral characters such as corolla size. These characters together seem to allow a powerful and fast tool to infer mating systems. However, causes for intraspecific variation of P/O, such as different cytotypes, ecotypes or different growth conditions, need to be considered.     

Phylogenetic and systematic study of Korean <Emphasis Type="Italic">Orius</Emphasis> species (Heteroptera: Anthocoridae) on the basis of molecular and morphological data

A phylogenetic and systematic study of Orius species (Heteroptera: Anthocoridae) from Korea has been conducted using both morphological and molecular characters. Thirty morphological character states were coded for 10 strains of 9 species. Five molecular markers, partial cytochrome c oxidase I (COI), cytochrome b (CytB), 16S rRNA (16S), 18S rRNA (18S), and 28S rRNA (28S), from mitochondrial and nuclear genes, were tested. Phylogenetic analyses based on molecular data were conducted by minimum evolution, maximum parsimony, maximum likelihood, and Bayesian phylogenetic (BP) analyses. Analysis of morphological data was performed using the parsimony programs NONA, and the combined dataset of morphological and molecular data was analyzed using BP analyses. The results of this study indicate that use of COI and CytB enabled relatively effective identification of species, whereas the sequences of 16S, 18S and 28S did not enable identification of closely related species such as Orius minutus and O. strigicollis. We discuss the usefulness of the five molecular markers for determining phylogenetic relationships and identifying the species.     

Morphological assessment of the Octopus vulgaris species complex evaluated in light of molecular‐based phylogenetic inferences

Cryptic species are common in the ocean, particularly among marine invertebrates such as octopuses. Delineating cryptic species is particularly problematic in octopus taxonomy where the plasticity recorded among taxonomic characters often results in low resolution at the species level. This study investigated the morphological relationships among seven phylogenetic clades (identified using cytochrome c oxidase subunit I) of the broadly distributed Octopus vulgaris species complex and close relatives. Morphological analyses in this study were successful in delimiting O. sinensis, Brazilian O. vulgaris and O. vulgaris sensu stricto, which was congruent with the molecular findings of this study. Analyses based on male morphology were successful in distinguishing 14 of 15 total pairwise comparisons and proved to be a more reliable indicator of species‐level relationships in comparison with female morphology. The majority of characters with the greatest discriminatory power were male sexual traits. Significant morphological differences were also recorded among sampling localities of conspecifics, with phenotype showing correlation with local environmental data. The findings of this study support the hypothesis that multiple O. vulgaris‐like species are currently being incorrectly treated under a single species name, O. vulgaris. Octopuses being exported globally under the name O. vulgaris are of extremely high fisheries market value and profile. Our findings have potentially significant implications for the naming and conservation of commercially harvested members of this species complex throughout their ranges.     

Annual changes in the population size of the salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) on high-seas Pacific Salmon (Oncorhynchus spp.), and relationship to host abundance

The population size of the salmon louse, Lepeophtheirus salmonis, was monitored annually in the summers of 1991–1997 by examining six species of Pacific salmon (Oncorhynchus spp.) caught by surface long-lines in oceanic offshore waters of the North Pacific Ocean and Bering Sea. The annual copepod population size on all salmonids caught was estimated by combining the calculated number of copepods carrying on each salmonid species. The copepod population fluctuated markedly from year to year, which resulted largely from marked annual changes in abundance of pink salmon (O. gorbuscha). Since pink salmon were most frequently and heavily infected and since their abundance changed every year, the copepod population was high in the years when this salmonid species was abundant, but low when it was rare. On the contrary, chum salmon (O. keta) did not show high prevalence and intensity of infection, but the annual abundance of this host species was consistently high, i.e. chum salmon carried many copepods every year. Copepods on other salmonid species (sockeye salmon O. nerka, coho salmon O. kisutch, chinook salmon O. tshawytscha, and steelhead trout O. mykiss) constantly formed a small percentage of the total copepod population. Both chum and pink salmon are the most important hosts in terms of their substantial contribution to support the copepod population, but the importance as hosts of each species is definitely different between the species. Chum salmon is a stable important host supporting the copepod population at a relatively high level every year, while the number of copepods on pink salmon annually exhibits marked fluctuations, and this salmonid species is regarded as an unstable important host.