Morphological changes in senescing adult male sockeye salmon (Oncorhynchus nerka Walbaum)

Mature male sockeye salmon ( Oncorhynchus nerka Walbaum) were measured, tagged and released into a gravel holding pond adjacent to the spawning site, then remeasured when dead for possible changes in shape or size. Body length, depth, snout length and caudal peduncle thickness decreased at the end of life, 1–2 weeks later.     

Juvenile habitat partitioning and relative productivity in allochronically isolated sockeye salmon (Oncorhynchus nerka)

Allochronic divergence, like spatial isolation, may contribute to population diversity and adaptation, however the challenges for tracking habitat utilization in shared environments are far greater. Adult Klukshu River (Yukon, Canada) sockeye salmon, Oncorhynchus nerka, return as genetically distinct "early" and "late" runs. Early and late adult spawning populations (1999 and 2000) and their subsequent fry (sampled at 7 sites in 2000 and at 8 sites in 2001 throughout Klukshu Lake and River) were genotyped at eight microsatellite loci. Bayesian assignment was used to determine the spatial distribution of early versus late fry; although intermixed, the distribution of fry significantly differed in Klukshu Lake and in the Klukshu River in 2001, based on crosstab analyses. Late-run fry predominated in Klukshu Lake at all sites, while early-run fry were most common in the north and south of Klukshu Lake and in Klukshu River. Early-run spawners had significantly higher relative productivity (early life survival) than late-run fish (2.9 times more fry produced per early-run adult in 2000, and 9.2 times more in 2001). This study demonstrates spatial habitat partitioning and differences in the contribution of allochronically isolated populations to fry abundance, and highlights annual variability that likely contributes to recruitment variation.     

Founding events influence genetic population structure of sockeye salmon (Oncorhynchus nerka) in Lake Clark, Alaska

Bottlenecks can have lasting effects on genetic population structure that obscure patterns of contemporary gene flow and drift. Sockeye salmon are vulnerable to bottleneck effects because they are a highly structured species with excellent colonizing abilities and often occupy geologically young habitats. We describe genetic divergence among and genetic variation within spawning populations of sockeye salmon throughout the Lake Clark area of Alaska. Fin tissue was collected from sockeye salmon representing 15 spawning populations of Lake Clark, Six-mile Lake, and Lake Iliamna. Allele frequencies differed significantly at 11 microsatellite loci in 96 of 105 pairwise population comparisons. Pairwise estimates of FST ranged from zero to 0.089. Six-mile Lake and Lake Clark populations have historically been grouped together for management purposes and are geographically proximate. However, Six-mile Lake populations are genetically similar to Lake Iliamna populations and are divergent from Lake Clark populations. The reduced allelic diversity and strong divergence of Lake Clark populations relative to Six-mile Lake and Lake Iliamna populations suggest a bottleneck associated with the colonization of Lake Clark by sockeye salmon. Geographic distance and spawning habitat differences apparently do not contribute to isolation and divergence among populations. However, temporal isolation based on spawning time and founder effects associated with ongoing glacial retreat and colonization of new spawning habitats contribute to the genetic population structure of Lake Clark sockeye salmon. Nonequilibrium conditions and the strong influence of genetic drift caution against using estimates of divergence to estimate gene flow among populations of Lake Clark sockeye salmon.     

Phylogeography of Asian sockeye salmon (Oncorhynchus nerka) based on analysis of mtDNA control region polymorphism

Analysis of the contemporary geographic distributions of mtDNA haplotypic diversity of sockeye salmon (Oncorhynchus nerka Walbaum) on the Asian part of its range and consideration of possible scenarios for microevolution of the species were performed. In total, 172 specimens of sockeye salmon from different rivers of Kamchatka, Chukotka, north coast of the Sea of Okhotsk, and from the Kuril Islands were analyzed using the entire mtDNA control region (1,010 bp) sequencing. After multiple alignments of the sequences 16 polymorphic sites were identified. Most of substitutions were detected in the first and the last thirds of the D-loop sequence, as well as one insertion was registered in the poly-T region. Two mass haplotypes (Hap_1_10T and Hap_2_13T) were revealed; they were present in most samples and differed by three substitutions and two indels. All the sequence variants were distributed among two haplogroups in compliance with the mass haplotypes. The star-shaped topology of the MST-tree points to a rapid increase in the diversity of groups, indicating a rapid expansion of the species after its number reducing in the past. The diversity of the first haplogroup was higher, but its main fraction fell on the samples from the middle reach of Kamchatka River, which seems to be a refugium during the Late Pleistocene glaciation. Presence of both haplogroups in most populations in approximately equal proportions indicates that the entire Asian part of the sockeye salmon range is a zone of secondary contact. We hypothesize that Hap_2_13T had more ancient origin and the Hap_1_10T was formed somewhat later, apparently in Asia, because almost all transitional forms between the haplogroups were found in Iturup Island populations.     

Critical swimming velocities of juvenile sockeye salmon and kokanee, the anadromous and non-anadromous forms of Oncorhynchus nerka (Walbaum)

In streams tributary to the North Pacific, anadromous sockeye salmon and non-anadromous kokanee, Oncorhynchus nerka (Walbaum), occasionally spawn sympatrically and male kokanee may act as 'sneaks’to spawn with the larger female sockeye. Despite this interbreeding, sockeye and kokanee exhibit persistent biochemical genetic differences at several enzyme loci. Genetic differences between forms may be maintained by selection against‘hybrids’due to the different life histories of sockeye and kokanee; sockeye make extensive smolt, oceanic, and spawning migrations while kokanee reside permanently in fresh water. We tested the sustained swimming abilities of juvenile sockeye, kokanee, and sockeye (female) × kokanee (male) hybrids to see if hybrids were inferior to sockeye in a trait that is probably under stronger selection in an anadromous life history. Sockeye had significantly greater mean critical swimming velocities (U_crit) than kokanee of the same size raised under identical conditions (8.3 v. 7.3 body lengths s^?1 respectively). When tested 1 month later the mean U_crit of sockeye was only marginally greater than that for sockeye × kokanee hybrids (both c. 6.6 body lengths s^?1). Sockeye swimming performance was also less variable than that of either kokanee or hybrids. Sockeye tended to have slimmer bodies and longer caudal regions than kokanee or sockeye × kokanee hybrids of the same size. Sockeye also had significantly more vertebrae than kokanee and hybrids, while hybrids had more vertebrae than kokanee. These morphological differences may have contributed to the differences in swimming performance. We concluded: (i) that juvenile sockeye and kokanee have diverged with respect to sustained swimming performance and that reduced performance by kokanee may be due to relaxed selection for sustained swimming performance associated with their non-anadromous life history, (ii) that sockeye × kokanee hybrids appear to have modestly lower swimming capabilities than pure sockeye, and (iii) if the variability in swimming performance is associated with differences in survival in nature, then such differences may promote divergence between sympatric sockeye and kokanee.     

Persistent parental effects on the survival and size, but not burst swimming performance of juvenile sockeye salmon Oncorhynchus nerka

Sockeye salmon Oncorhynchus nerka were used as a model in an artificial fertilization experiment to investigate the relationships between individual adult O. nerka and their offspring. Survival, size and burst swimming ability were assessed in fry of known parentage (adult spawners from the Weaver Creek population, British Columbia, Canada). Maternal identity significantly affected the survival rate of eggs at hatch time, though this effect did not extend to fry life stages. The results were also suggestive of a paternal effect on both egg and fry survival, though this could not be separated from the experimental block design. After 4 months of exogenous feeding, fry mass remained under significant maternal influence, though fork length did not, despite having a high correlation with mass. Burst swimming performance was highly variable among individuals, and was not significantly influenced by maternal identity or individual fry size. Collectively, the findings presented here suggest that maternal, and possibly paternal, effects can be integral components of population dynamics in the early life stages of O. nerka . A good understanding of these factors will be essential for scientists and fisheries managers in developing a more holistic view of population-level spawning success and fry survival.     

Genetic structure and diversity of Japanese kokanee Oncorhynchus nerka stocks as revealed by microsatellite and mitochondrial DNA markers

Genetic structure and diversity of nine Japanese kokanee (landlocked) Oncorhynchus nerka stocks and anadromous O. nerka from the North Pacific and the Canadian Lake Cultus population were examined using microsatellite and mitochondrial DNA. Sequence analyses of the cytochrome b region of mtDNA for Japanese kokanee O. nerka stocks on Honshu and Hokkaido islands revealed that most Japanese stocks were monomorphic of one major haplotype, which was also dominant in the Lake Cultus population and anadromous O. nerka in the North Pacific. Assignment tests using microsatellite DNA revealed that there was no clear-cut population structure in Japanese kokanee O. nerka stocks.     

Sex differences in circulatory oxygen transport parameters of sockeye salmon (Oncorhynchus nerka) on the spawning ground

Upon reaching sexual maturity, several species of male salmonids possess a relative ventricular mass (rM_V) that may be up to 90% larger than females. This can increase maximum cardiac stroke volume and power output, which may be beneficial to increasing the oxygen transport capacity of male salmonids during the spawning period. It may be further hypothesized, therefore, that other variables within the circulatory oxygen transport cascade, such as blood oxygen-carrying capacity and heart rate, are similarly enhanced in reproductively mature male salmonids. To test this idea, the present study measured a range of circulatory oxygen transport variables in wild male and female sockeye salmon (Oncorhynchus nerka) during their spawning period, following a 150 km migration from the ocean. The rM_V of male fish was 13% greater than females. Conversely, the haemoglobin concentration ([Hb]) of female fish was 19% higher than males, indicative of a greater blood oxygen-carrying capacity (138 vs. 116 ml O₂ l⁻¹, respectively). Surgically implanted physiological data loggers revealed a similar range in heart rate for both sexes on the spawning ground (20–80 beats min⁻¹ at 10°C), with a tendency for male fish to spend a greater percentage of time (64%) than females (49%) at heart rates above 50 beats min⁻¹. Male fish on average consumed significantly more oxygen than females during a 13-h respirometry period. However, routine oxygen consumption rates ranged between 1.5 and 8.5 mg min⁻¹ kg⁻¹ for both sexes, which implies that males did not inherently possess markedly higher routine aerobic energy demands, and suggests that the higher [Hb] of female fish may compensate for the smaller rM_V. These findings reject the hypothesis that all aspects of the circulatory oxygen transport cascade are inherently superior in male sockeye salmon. Instead, it is suggested that any differences in between sexually mature male and female sockeye salmon can likely be attributed to activity levels.     

Microsatellite DNA variation in sockeye salmon Oncorhynchus nerka (Walbaum, 1792) populations of eastern Kamchatka

The allelic variations of eight microsatellite loci (Ots107, Oki1a, Oki1b, One104, One109, OtsG68, OtsG85, and Oki6) were examined in sockeye salmon Oncorhynchus nerka (Walbaum) populations of eastern Kamchatka. Samples from river basins of the Karaginskiy and Olyutorskiy districts in the northern part of the investigated region are characterized by a smaller number of allelic variants and lower heterozygosity, compared to samples from the Kamchatka River basin. A fit to the Hardy-Weinberg distribution was found at most of the loci that were studied in all samples. The average differentiation between populations (st) over the eight loci was 2.93%, which corresponds to the statistical significance level. The most highly polymorphic loci proved to be the least differentiating between the analyzed samples.     

Seasonal and interannual variations of sockeye salmon (Oncorhynchus nerka) microsatellite DNA in two Kamchatka lake-river systems

Seasonal and interannual variations in the sockeye salmon populations from two lake-river systems of the East and West Kamchatka were studied. Stability of allele and genotypic frequencies of six microsatellite DNA loci in the adjacent generations and spawning populations of the sockeye salmon of the Bol'shaya River was confirmed experimentally. The pairwise intersample differentiation (F(st)) of the local sockeye salmon populations from the southwestern Kamchatka coast (Ozernaya and Bol'shaya Rivers)was almost 7 times higher than the corresponding values for the spawning populations of the Bol'shaya River sockeye salmon of the adjacent years; 15 times, for the adjacent Bol'shaya River sockeye salmon generations; and four times, for the seasonal races within the Kamchatka River.     

Divergence of mitochondrial DNA in a population of sockeye salmon (Oncorhynchus nerka Walbaum) from Azabache'e lake (Kamchatka)

Variability of three PCR-amplified mtDNA regions was examined in five populations of sockeye salmon from Azabach'e Lake. Eighteen haplotypes were detected in 144 fish. Significant differences were found between seasonal races of sockeye salmon spawning in the lake. The short time of independent divergence between the seasonal races indicates that these races formed independently in each spawning region. No difference in mtDNA between lake samples of early sockeye salmon (subisolates) was revealed, which confirms the existence of gene flow between them. A high level of differences between the sockeye salmon spawning in the lake and spawning in the tributaries of the lake, the Bushuev and Lotnaya rivers, suggests that there were no migration between them during many generations and that the nature of spawning grounds (lake or river) is essential for within species differentiation in this species.     

Host-pathogen-environment interactions predict survival outcomes of adult sockeye salmon (Oncorhynchus nerka) released from fisheries

Incorporating host-pathogen(s)-environment axes into management and conservation planning is critical to preserving species in a warming climate. However, the role pathogens play in host stress resilience remains largely unexplored in wild animal populations. We experimentally characterized how independent and cumulative stressors (fisheries handling, high water temperature) and natural infections affected the health and longevity of released wild adult sockeye salmon (Oncorhynchus nerka) in British Columbia, Canada. Returning adults were collected before and after entering the Fraser River, yielding marine- and river-collected groups, respectively (N = 185). Fish were exposed to a mild (seine) or severe (gill net) fishery treatment at collection, and then held in flow-through freshwater tanks for up to four weeks at historical (14°C) or projected migration temperatures (18°C). Using weekly nonlethal gill biopsies and high-throughput qPCR, we quantified loads of up to 46 pathogens with host stress and immune gene expression. Marine-collected fish had less severe infections than river-collected fish, a short migration distance (100 km, 5–7 days) that produced profound infection differences. At 14°C, river-collected fish survived 1–2 weeks less than marine-collected fish. All fish held at 18°C died within 4 weeks unless they experienced minimal handling. Gene expression correlated with infections in river-collected fish, while marine-collected fish were more stressor-responsive. Cumulative stressors were detrimental regardless of infections or collection location, probably due to extreme physiological disturbance. Because river-derived infections correlated with single stressor responses, river entry probably decreases stressor resilience of adult salmon by altering both physiology and pathogen burdens, which redirect host responses toward disease resistance.     

Sexing birds using random amplified polymorphic DNA (RAPD) markers

We used random amplified polymorphic DNA (RAPD) markers to sex birds from small tissue (usually blood) samples. Arbitrarily chosen 10-mer PCR primers were screened with DNA from known-sex individuals for the production of a bright female-specific band. Suitable primers were found for seven bird species after screening about 30 primers (range 2–63), and no primer was found for three other species after screening about 50 primers for each species. Investigations into the reliability of RAPD markers for sexing great tits Parus major and oystercatchers Haematopus ostralegus show that: (i) when PCR reaction conditions for great tit DNA are varied, either the presence of the female-specific band correctly predicts the individual's sex or no DNA amplification occurs; (ii) the female-specific band in great tits can be sequenced, and subsequently amplified using specific PCR primers; (iii) null alleles of the female-specific fragment occur at an estimated frequency of 0% ( n = 241 females) in great tits and 0.6% ( n > 290 females) in oystercatchers; (iv) the female-specific fragment in great tits occurs in individuals from a wide geographical range encompassing two subspecies; and (v) the relative intensity of bands in great tit RAPD banding profiles is consistent across individual birds and scorers. The RAPD primers that we have identified are generally species specific, and the consequent time cost of screening for primers is the chief disadvantage of using RAPD markers to sex birds. However, with large sample sizes this disadvantage is outweighed by the relative technical simplicity and low cost of the technique.     

Ultrastructure of the pituitary gland (pars distalis) in sockeye salmon (Oncorhynchus nerka) during gonad maturation

Summary The fine structure of the various hormone-producing cell types (with the exclusion of the prolactin cells) in the pituitary gland (pars distalis) of migratory sockeye salmon is described. All fish were in an advanced stage of sexual maturation. In the proximal pars distalis five cell types were distinguished: growth hormone cells, ACTH cells, gonadotrops, vesicular cells, and chromophobe cells. Gonadotrops were also found throughout the rostral pars distalis. A conspicuous feature of the gonadotrops was the presence of two kinds of secretory inclusions: small electron-dense granules (200–375 m) and large, relatively electron-translucent globules (400–2 000 m). The large vesicular cells, so called because of their conspicuous vesicular endoplasmic reticulum, were numerous and often appeared to contain some small granules. It is argued that they may represent a second type of gonadotropic cell, which, in earlier stages of gonad development, contains many granules but becomes largely degranulated near the time of reproduction when the other gonadotrops (globular gonadotrops) abound. The chromophobes, which were smaller and far less abundant than the vesicular cells, also appeared to contain small granules (120–280 m). They are probably thyrotrops.The assistance of Mr. S. Killick, of the International Pacific Salmon Fisheries Commission, who helped in the collection of salmon, is gratefully acknowledged.     

Countergradient variation and secondary sexual color: phenotypic convergence promotes genetic divergence in carotenoid use between sympatric anadromous and nonanadromous morphs of sockeye salmon (Oncorhynchus nerka)

Genetically distinct anadromous (sockeye) and nonanadromous (kokanee) morphs of the Pacific salmon, Oncorhynchus nerka, develop identical, brilliant red color at maturity during sympatric breeding in freshwater streams. The marine and lacustrine environments they occupy prior to maturity, however, appear to differ in the availability of dietary carotenoid pigments necessary to produce red coloration. We tested the hypothesis that kokanee, which occupy carotenoid-poor lakes, are more efficient at using the dietary pigments than are sockeye, which occupy the more productive North Pacific Ocean. In a 2-year controlled breeding study, flesh and skin color of mature and immature crosses fed a low-carotenoid diet were quantified with both a chromameter and by chemical extraction of carotenoid pigments. Results revealed striking countergradient variation in carotenoid use, with kokanee approximately three times more efficient at sequestering the pigments to the flesh musculature than similar age sockeye. This difference translated into virtually nonoverlapping differences between pure crosses in secondary sexual color at maturity, when the pigments are mobilized and transported to the skin. Kokanee crosses turned pinkish red over most of their body, whereas sockeye turned olive green. The olive green was similar to the breeding color of residuals in the wild, the progeny of anadromous sockeye that remain in fresh water and are believed to have given rise to kokanee on numerous independent occasions. Reciprocal hybrids were similar to each other and intermediate to the pure crosses, indicating additive genetic inheritance. Mate choice trials with sockeye males in the wild showed the ancestral morph strongly preferred red over green models. These results suggest a preference for red mates maintained in nonanadromous breeding populations drove the reevolution of the red phenotype in kokanee via more efficient use of dietary carotenoid pigments. This is a novel, yet hidden, mechanism by which sexual selection promotes the genetic differentiation of these sympatric populations.     

Efficacy of an infectious hematopoietic necrosis (IHN) virus DNA vaccine in Chinook Oncorhynchus tshawytscha and sockeye O. nerka salmon

The level of protective immunity was determined for Chinook Oncorhynchus tshawytscha and sockeye/kokanee salmon (anadromous and landlocked) O. nerka following intramuscular vaccination with a DNA vaccine against the aquatic rhabdovirus, infectious hematopoietic necrosis virus (IHNV). A DNA vaccine containing the glycoprotein gene of IHNV protected Chinook and sockeye/kokanee salmon against waterborne or injection challenge with IHNV, and relative percent survival (RPS) values of 23 to 86% were obtained under a variety of lethal challenge conditions. Although this is significant protection, it is less than RPS values obtained in previous studies with rainbow trout (O. mykiss). In addition to the variability in the severity of the challenge and inherent host susceptibility differences, it appears that use of a cross-genogroup challenge virus strain may lead to reduced efficacy of the DNA vaccine. Neutralizing antibody titers were detected in both Chinook and sockeye that had been vaccinated with 1.0 and 0.1 pg doses of the DNA vaccine, and vaccinated fish responded to viral challenges with higher antibody titers than mock-vaccinated control fish.     

基于RAPD的群体标记法分析苜蓿种质遗传多样性

苜蓿种质资源的分子遗传多样性分析对于种质资源保存和育种利用具有重要指导意义。本研究选用群体标记法对来自甘肃省的16个苜蓿品种的DNA进行RAPD扩增,旨在研究其遗传多样性,并在此基础上筛选品种特异性引物用于进一步的品种鉴定。依据16个苜蓿品种间的Roger’s遗传距离进行UPGMA聚类分析结果显示,品种间亲缘关系与其选育背景紧密相关,供试的16个品种被划为4个类群,其中,匍匐型品种Jindera与其他直立型品种差异显著,自成1个类群,引进品种和甘肃省内具有国外种质来源的育成品种被划为同1类群,而甘肃地方品种聚为2个类群。10个RAPD引物中有4个引物OPE4、OPE5、OPE6和OPE7分别检测到5个品种甘农3号、甘杂27、Jindera、陇东和Algonuin的特异性条带,可进一步用于开发设计特异性引物进行品种鉴定工作。以上结果进一步证实,利用RAPD标记研究苜蓿系谱发育关系和选择杂交亲本应采用群体标记法。     

Effects of river temperature and climate warming on stock‐specific survival of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka)

Mean summer water temperatures in the Fraser River (British Columbia, Canada) have increased by ～1.5 °C since the 1950s. In recent years, record high river temperatures during spawning migrations of Fraser River sockeye salmon (Oncorhynchus nerka) have been associated with high mortality events, raising concerns about long‐term viability of the numerous natal stocks faced with climate warming. In this study, the effect of freshwater thermal experience on spawning migration survival was estimated by fitting capture–recapture models to telemetry data collected for 1474 adults (captured in either the ocean or river between 2002 and 2007) from four Fraser River sockeye salmon stock‐aggregates (Chilko, Quesnel, Stellako‐Late Stuart and Adams). Survival of Adams sockeye salmon was the most impacted by warm temperatures encountered in the lower river, followed by that of Stellako‐Late Stuart and Quesnel. In contrast, survival of Chilko fish was insensitive to the encountered river temperature. In all stocks, in‐river survival of ocean‐captured sockeye salmon was higher than that of river‐captured fish and, generally, the difference was more pronounced under warm temperatures. The survival–temperature relationships for ocean‐captured fish were used to predict historic (1961–1990) and future (2010–2099) survival under simulated lower river thermal experiences for the Quesnel, Stellako‐Late Stuart and Adams stocks. A decrease of 9–16% in survival of all these stocks was predicted by the end of the century if the Fraser River continues to warm as expected. However, the decrease in future survival of Adams sockeye salmon would occur only if fish continue to enter the river abnormally early, towards warmer periods of the summer, as they have done since 1995. The survival estimates and predictions presented here are likely optimistic and emphasize the need to consider stock‐specific responses to temperature and climate warming into fisheries management and conservation strategies.