Distribution of genetic variation underlying adult migration timing in steelhead of the Columbia River basin

Fish migrations are energetically costly, especially when moving between freshwater and saltwater, but are a viable strategy for Pacific salmon and trout (Oncorhynchus spp.) due to the advantageous resources available at various life stages. Anadromous steelhead (O. mykiss) migrate vast distances and exhibit variation for adult migration phenotypes that have a genetic basis at candidate genes known as greb1L and rock1. We examined the distribution of genetic variation at 13 candidate markers spanning greb1L, intergenic, and rock1 regions versus 226 neutral markers for 113 populations (n = 9,471) of steelhead from inland and coastal lineages in the Columbia River. Patterns of population structure with neutral markers reflected genetic similarity by geographic region as demonstrated in previous studies, but candidate markers clustered populations by genetic variation associated with adult migration timing. Mature alleles for late migration had the highest frequency overall in steelhead populations throughout the Columbia River, with only 9 of 113 populations that had a higher frequency of premature alleles for early migration. While a single haplotype block was evident for the coastal lineage, we identified multiple haplotype blocks for the inland lineage. The inland lineage had one haplotype block that corresponded to candidate markers within the greb1L gene and immediately upstream in the intergenic region, and the second block only contained candidate markers from the intergenic region. Haplotype frequencies had similar patterns of geographic distribution as single markers, but there were distinct differences in frequency between the two haplotype blocks for the inland lineage. This may represent multiple recombination events that differed between lineages where phenotypic differences exist between freshwater entry versus arrival timing as indicated by Micheletti et al. (2018a). Redundancy analyses were used to model environmental effects on allelic frequencies of candidate markers, and significant variables were migration distance, temperature, isothermality, and annual precipitation. This study improves our understanding of the spatial distribution of genetic variation underlying adult migration timing in steelhead as well as associated environmental factors and has direct conservation and management implications.     

Effects of Pleistocene glaciations on population structure of North American chestnut-backed chickadees

The postglacial recolonization of northern North America was heavily influenced by the Pleistocene glaciation. In the Pacific Northwest, there are two disjunct regions of mesic temperate forest, one coastal and the other interior. The chestnut-backed chickadee is one of the species associated with this distinctive ecosystem. Using seven microsatellite markers we found evidence of population structure among nine populations of chestnut-backed chickadees. High levels of allelic variation were found in each of the populations. Northern British Columbia and central Alaska populations contained a large number of private alleles compared to other populations, including those from unglaciated regions. The disjunct population in the interior was genetically distinct from the coastal population. Genetic and historical records indicate that the interior population originated from postglacial inland dispersal. Population structuring was found within the continuous coastal population, among which the peripheral populations, specifically those on the Queen Charlotte Islands and the central Alaska mainland, were genetically distinct. The pattern of population structure among contemporary chickadee populations is consistent with a pioneer model of recolonization. The persistence of genetic structure in western North American chestnut-backed chickadees may be aided by their sedentary behaviour, linear distribution, and dependence on cedar-hemlock forests.     

Population genetic structure and ancestry of steelhead/rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) at the extreme southern edge of their range in North America

Steelhead (Oncorhynchus mykiss) populations have declined dramatically in many parts of their range in North America, most critically in Southern California, where these anadromous trout are now classified as ‘Endangered’ under the United States Endangered Species Act. The widespread introduction of hatchery rainbow trout, the domesticated freshwater resident form of the species O. mykiss, is one factor threatening the long-term persistence of native steelhead and other trout populations. To identify where native fish of coastal steelhead lineage remained, we performed a population genetic analysis of microsatellite and SNP genotypes from O. mykiss populations at the extreme southern end of their range in Southern California, USA and Baja California, Mexico. In the northern part of this region, nearly all populations appeared to be primarily descendants of native coastal steelhead. However, in the southern, more urbanized part of this region, the majority of the sampled populations were derived primarily from hatchery trout, indicating either complete replacement of native fish or a strong signal of introgression overlaying native ancestry. Nevertheless, these genetically introgressed populations represent potentially critical genetic resources for the continued persistence of viable networks of O. mykiss populations, given the limited native ancestry uncovered in this region and the importance of genetic variation in adaptation. This study elucidates the geographic distribution of native trout populations in this region, and serves as a baseline for evaluating the impacts of hatchery trout on native O. mykiss populations and the success of steelhead conservation and recovery efforts.     

A genetic analysis of the beluga whale Delphinapterus leucas (Cetacea: Monodontidae) from summer aggregations in the Russian Far East

The genetic structure of four summer aggregations of the Beluga Whale, Delphinapterus leucas, in Sakhalin Bay and Udskaya Bay, off the western coast of Kamchatka in the Sea of Okhotsk and in the Anadyr Estuary of the Bering Sea was analyzed through nucleotide sequencing of the mtDNA control region and detection of the allelic composition of nine microsatellite loci in nuclear DNA. It has been shown that each of the aggregations features a unique set of maternal lines, which indicates a high degree of philopatry in this species. Beluga whales of the Anadyr Estuary are genetically isolated from those of the Sea of Okhotsk. Beluga whales of the summer aggregations of Sakhalin Bay and those from Udskaya Bay share a common gene pool and belong to a single population, while the whales that summer off western Kamchatka with great consistency may be attributed to a different population. Comparison of nucleotide sequences of the mtDNA in beluga whales from various waters of the Russian Far East and North America allowed us to propose a hypothesis about how the structure of beluga whale populations formed in the North Pacific during the postglacial period.     

Differential Reproductive Success of Sympatric, Naturally Spawning Hatchery and Wild Steelhead, Oncorhynchus mykiss

Hatchery propagation of salmonids has been practiced in western North America for over a century. However, recent declines in wild salmon abundance and efforts to mitigate these declines through hatcheries have greatly increased the relative abundance of fish produced in hatcheries. The over-harvest of wild salmon by fishing mixed hatchery and wild stocks has been of concern for many years but genetic interactions between populations, such as hybridization, introgression and outbreeding depression, may also compromise the sustainability of wild populations. Our goal was to examine whether a newly established hatchery population of steelhead trout successfully reproduced in the wild and to compare their rate of reproductive success to that of sympatrically spawning native steelhead. We used eight microsatellite loci to create allele frequency profiles for baseline hatchery and wild populations and assigned the smolt (age 2) offspring of this parental generation to a population of origin. Adults originating from a generalized hatchery stock artificially selected for early return and spawning date were successful at reproducing in Forks Creek, Washington. Although hatchery females (N = 90 and 73 in the two consecutive years of the study) produced offspring that survived to emigrate as smolts, they produced only 4.4–7.0% the number produced per wild female (N = 11 and 10). This deficit in reproductive success implies that the proportion of hatchery genes in the mixed population may diminish since deliberate releases into the river have ceased. This hypothesis is being tested in a long-term study at Forks Creek.     

Discovery and characterization of single-nucleotide polymorphisms in steelhead/rainbow trout, Oncorhynchus mykiss

Single-nucleotide polymorphisms (SNPs) have several advantages over other genetic markers, including lower mutation and genotyping error rates, ease of inter-laboratory standardization, and the prospect of high-throughput, low-cost genotyping. Nevertheless, their development and use has only recently moved beyond model organisms to groups such as salmonid fishes. Oncorhynchus mykiss is a salmonid native to the North Pacific rim that has now been introduced throughout the world for fisheries and aquaculture. The anadromous form of the species is known as steelhead. Native steelhead populations on the west coast of the United States have declined and many now have protected status. The nonanadromous, or resident, form of the species is termed rainbow, redband or golden trout. Additional life history and morphological variation, and interactions between the forms, make the species challenging to study, monitor and evaluate. Here, we describe the discovery, characterization and assay development for 139 SNP loci in steelhead/rainbow trout. We used EST sequences from existing genomic databases to design primers for 480 genes. Sanger-sequencing products from these genes provided 130 KB of consensus sequence in which variation was surveyed for 22 individuals from steelhead, rainbow and redband trout groups. The resulting TaqMan assays were surveyed in five steelhead populations and three rainbow trout stocks, where they had a mean minor allele frequency of 0.15-0.26 and observed heterozygosity of 0.18-0.35. Mean F(ST) was 0.204. The development of SNPs for O. mykiss will help to provide highly informative genetic tools for individual and stock identification, pedigree reconstruction, phylogeography and ecological investigation.     

A comparison of variability and population structure for major histocompatibility complex and microsatellite loci in California coastal steelhead (Oncorhynchus mykiss Walbaum)

The major histocompatibility complex (MHC) contains genes integral to immune response in vertebrates. MHC genes have been shown to be under selection in a number of vertebrate taxa, making them intriguing for population genetic studies. We have conducted a survey of genetic variation in an MHC class II gene for steelhead trout from 24 sites in coastal California and compared this variation to that observed at 16 presumably neutral microsatellite loci. A high amount of allelic variation was observed at the MHC when compared to previously published studies on other Pacific salmonids. Elevated nonsynonymous substitutions, relative to synonymous substitutions, were detected at the MHC gene, indicating the signature of historical balancing selection. The MHC data were tested for correlations to and deviations from the patterns found with the microsatellite data. Estimates of allelic richness for the MHC gene and for the microsatellites were positively correlated, as were estimates of population differentiation (F(ST)). An analysis for F(ST) outliers indicates that the MHC locus has an elevated F(ST) relative to the neutral expectation, although a significant result was found for only one particular geographical subgroup. Relatively uniform allele frequency distributions were detected in four populations, although this finding may be partially due to recent population bottlenecks. These results indicate that, at the scale studied here, drift and migration play a major role in the observed geographical variability of MHC genes in steelhead, and that contemporary selection is relatively weak and difficult to detect.     

Comparative estuarine and marine migration ecology of Atlantic salmon and steelhead: blue highways and open plains

This synthesis focuses on the estuarine and ocean ecology of Atlantic salmon (Salmo salar) and steelhead (Oncorhynchus mykiss) across their southern ranges in North America. General life history and ecology share many common traits including iteroparity, duration of freshwater (0–3 years) and marine (2–5 years) rearing, ocean emigration at relatively large sizes and strong surface orientation compared to other salmonids. Despite parallels in life history and anthropogenic pressures, several differences emerged for these species. First, steelhead have greater life history diversity and a broader geographic distribution. Generally, estuary habitats serve as short-term migration corridors for both species. However, some steelhead populations used lagoon habitat in south-coast watersheds. While both species are epipelagic, Atlantic salmon exhibit more vertical migration. Atlantic salmon tend to follow migratory highways—relatively narrow bands along the coastal shelf, then crossing the Atlantic to feed inshore and in fjords of West Greenland. Conversely, steelhead exit the coastal shelf quickly, dispersing across the Pacific, and rarely use coastal environments. Despite inhabiting rivers in warm dry Mediterranean climates, the extended range and stability of southern steelhead distribution is likely buffered by cool upwelled waters of the California Current. Whereas Atlantic salmon populations are restricted by warmer Northwest Atlantic circulation patterns lacking cool upwelling with greater susceptibility to warming associated with climate change. Determining the rate of marine habitat changes in the Atlantic and Pacific Oceans is important to the conservation of these species, including subtleties of temporal and spatial habitat use, and adaptability to ocean ecosystems under climate change.     

Population Structure and the Colonization Route of One of the Oldest North American Invasive Insects: Stories from the Worn Road of the Hessian Fly,Mayetiola destructor (Say)

An integral part to understanding the biology of an invasive species is determining its origin, particularly in pest species. As one of the oldest known invasive species, the goals of this study were to evaluate the evidence of a westward expansion of Hessian fly into North America, from a potential singular introduction event, and the population genetic structure of current populations. Levels of genetic diversity and population structure in the Hessian fly were compared across North America, Europe, North Africa, Western Asia, and New Zealand. Furthermore, Old World populations were evaluated as possible sources of introduction. We tested diversity and population structure by examining 18 microsatellite loci with coverage across all four Hessian fly chromosomes. Neither genetic diversity nor population genetic structure provided evidence of a westward movement from a single introduction in North America. Introduced populations in North America did not show identity or assignment to any Old World population, likely indicating a multiple introduction scenario with subsequent gene flow between populations. Diversity and selection were assessed on a chromosomal level, with no differences in diversity or selection between chromosomes or between native and introduced populations.     

The case for creation of the North Pacific Ocean during the Mesozoic Era

Pangean reconstructions based on the Dymaxion Projection are discussed, and the advantages of placing cordilleran North America alongside eastern Asia are clearly seen. A detailed matching of the western North American and eastern Asian continental margins shows that the North Pacific can be closed as tightly as the Atlantic when appropriate adjustments are made to reproduce Permian geography. Closure of the North Pacific eliminates overlap of cordilleran North America with South America in the Caribbean region and permits closure of the Arctic Ocean.Geological and paleontological data are presented which permit a tentative Phanerozoic history of the North Pacific to be outlined. According to this view, cordilleran North America and the North China craton were rifted from cratonic North America at the dawn of the Phanerozoic. They drifted westward across a proto-Pacific Ocean and were temporarily sutured to the Siberian craton along the Sayanian fold belt during the world-wide Early Paleozoic orogenies. Final suture occurred along the Mongolian fold belt during the world-wide Late Paleozoic orogenies which completed the consolidation of Pangea. Separation of cordilleran North America from eastern Asia was part of the Mesozoic fragmentation of Pangea. Mesozoic sea-floor spreading carried cordilleran North America eastward and opened the present North Pacific. Cordilleran North America was sutured to cratonic North America during the world-wide Cenozoic orogenies. Suture began along the Nevadan-Sevier fold belt and was followed by under-riding along the Laramide fold belt. North America then partly over-rode the East Pacific Rise sea-floor spreading center, and dextral transform faults across the rift valley created faults and oroclines in cordilleran North America.A driving force for the disintegration of Pangea is provided by the unstable tetrahedral convection model. This model is fitted to Phanerozoic world maps for all periods beginning with the Permian to show how an opening North Pacific Ocean can be made compatible with opening of the Atlantic, Indian, and Arctic Oceans. The unstable tetrahedral convection model also provides a mechanism for opening the Cenozoic small ocean basins behind West Pacific island arcs. Such basins form above abandoned convection plumes or curtains which rise passively to the earth's surface. These plumes and curtains are abandoned when the potential energy-driving convection is locally exhausted.     

Disruption of historical patterns of isolation by distance in coastal steelhead

When natural populations exchange migrants at a rate proportional to their geographic distance, population genetics theory leads to the expectation of a pattern of isolation-by-distance (IBD), whereby geographic and genetic distance are correlated. However, the presence or absence of such patterns in modern populations may not fully reflect the historical relationships among those populations. Thus, historical samples, collected prior to modern human impacts, can often provide a critical baseline for comparison with modern populations. Steelhead, the anadromous form of rainbow trout, Oncorhynchus mykiss, are native to western North America and are endangered or threatened throughout most of California, near the southern extent of their native range. Population samples of steelhead collected in 1897 and 1909 in Central California rivers provided the opportunity to evaluate the historical genetic composition and population structure of these threatened fish. Here we show that these steelhead populations had a historically strong correlation between genetic and geographic distance that has been virtually erased in modern populations, suggesting that current relationships among modern steelhead populations are no longer reflective of natural migratory pathways. This demonstrates the critical role of migration in maintaining population relationships of threatened species and highlights the importance of natural history museums in providing historical baseline information.     

Lichenological evidence for the recognition of inland rain forests in western North America

Aim The coastal temperate rain forests of north‐western North America are internationally renowned as the archetypal expression of the temperate rain forest biome. Less well documented is the existence of somewhat similar forests 500–700 km inland on the windward slopes of the Columbia and Rocky Mountains. Here we attempt to show that these inland ‘wetbelt’ forests warrant rain forest status. Location North‐western North America. Methods We use tree‐dwelling macrolichens to assess the degree of environmental congruence between the coastal temperate rain forests and their inland counterparts. Results We report three key findings: (1) 40% of oceanic, epiphytic macrolichens found in Pacific coastal rain forests occur also in inland regions; (2) epiphytic species richness decreases with decreasing latitude, such that roughly 70% of disjunct oceanic species are restricted to regions north of 51° N; and (3) the southward decline in lichen diversity is correlated with a parallel decrease in summer precipitation, but not with mean annual precipitation. Main conclusions These observations are consistent with the recognition of an inland rain forest formation between 50 and 54° N. Inland rain forests represent a small, biologically significant ecosystem whose continued fragmentation and conversion to tree plantations warrant close scrutiny.     

Monitoring fish behaviour with a remote, combined acoustic/radio biotelemetry system

Biotelemetry is a powerful instrument for monitoring aquatic species in their natural environment. Using telemetry, animals can be monitored from a passive perspective, without the biases associated with conventional handling and sampling techniques. To monitor aquatic species in remote environments, with vast stretches of water, and in situations requiring both acoustic and radio transmissions (e.g. for diadromous fish), advances in telemetry are necessary. In this paper, a field-proven telemetry system based on a radio receiver and incorporating combined acoustic and radio smart transmitters, wireless hydrophones and two-way satellite communications is described. The system was first deployed in Bay d'Espoir, Newfoundland, Canada, in 1998. The purpose of this deployment was to determine whether aquaculture triploid steelhead trout ( Oncorhynchus mykiss Walbaum) (1.5–2.0 kg), experimentally released in the vicinity of a commercial aquaculture site, remained at the site (site fidelity) or dispersed. Two sets of fish releases, summer and winter, were performed to determine seasonal effects on the movement of aquaculture triploid steelhead trout in the wild. The results suggested strong site fidelity among steelhead trout when released during the growing season (summer). However, less fidelity was displayed for the winter released steelhead.     

Characteristic features of ecology of the Pacific saury Cololabis saira (Scomberesocidae, Beloniformes) in open waters and in the northeast Pacific ocean

The results of long-term studies of the spatial distribution, size composition, and spawning intensity of the Pacific saury Cololabis saira in open waters of the North Pacific Ocean and the northeastern part of the Pacific Ocean off the west coast of North America are presented. In the open waters of the Pacific Ocean, saury forms aggregations early in summer; intraseasonal changes in their distribution pattern have been identified. Migrations of Pacific saury stocks in the northeastern part of the Pacific Ocean were considered, and assumptions about their causes were made. The differences in the size composition of Pacific saury in different parts of the range are associated with the peculiarities of occurrence of favorable conditions for the formation of aggregations. Intensive spawning of Pacific saury in the northeastern part of the Pacific Ocean is observed in winter and spring, and that in open waters is observed in summer. The distribution of the early progeny of Pacific saury is associated with the systems of currents; its findings in the extreme northern regions in the 1980s are explained.     

The survival and growth of Gammarus tigrinus Sexton (Crustacea: Amphipoda) in relation to salinity and temperature

Field collections from an inland saline lake indicated that a rapid increase in numbers of a population of Gammarus tigrinus was positively correlated with high summer temperatures and salinities. The laboratory experiments on growth are an attempt to determine whether high summer temperatures or optimum salinity were primarily responsible for the rapid increase in numbers. Furthermore, G. tigrinus was not found in either of two adjacent lakes; one non-saline, the other at a higher salinity. The laboratory experiments on survival are an attempt to determine whether the restricted distribution of G. tigrinus was related to salinity. The implications of the field and laboratory studies are discussed and compared with other data from Europe and North America.     

不同倍性虹鳟幼鱼对急性温度胁迫的抗氧化响应

虹鳟属于冷水性鱼类,其生存的最适温度为12~18 ℃,温度胁迫是虹鳟在夏秋季养殖过程中经常遇到的问题.枫叶鲑和硬头鳟均为品质优良的虹鳟选育种.为探讨急性温度胁迫对两种倍性虹鳟抗氧化响应的影响,本研究选取二倍体枫叶鲑和三倍体硬头鳟幼鱼,分别在13、17、21和25 ℃下进行热应激试验.在达到目标温度后的0、1、6和12 h取样,之后将受试鱼恢复至13 ℃的适宜温度下培养,并在恢复培养的1、12、24和48 h后取样,测定受试鱼肝脏中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、谷胱甘肽过氧化物酶(GPx)的活性,以及脂质过氧化物(LPO)、丙二醛(MDA)和热激蛋白70(HSP70)含量.结果表明: 枫叶鲑和硬头鳟的3种抗氧化酶活性在17 ℃组没有出现显著升高;21 ℃组枫叶鲑和硬头鳟的SOD活性在热应激期间出现显著升高,但枫叶鲑的SOD活性在恢复过程中恢复到正常水平;25 ℃组枫叶鲑和硬头鳟的SOD、CAT和GPx的活性均显著提高;但在恢复试验进行24 h后,CAT和GPx的活性恢复到正常水平.枫叶鲑在17、21和25 ℃组HSP70的产生量显著高于13 ℃组,而硬头鳟仅在21和25 ℃组HSP70的产生量显著高于13 ℃组.通过整合生物标志物响应指标值对多种抗氧化参数进行分析,发现枫叶鲑在17和21 ℃组急性温度胁迫下的抗氧化响应显著高于硬头鳟,但在25 ℃组硬头鳟的抗氧化响应高于枫叶鲑.这表明不同倍性虹鳟幼鱼在不同温度急性胁迫下的抗氧化响应有所差异.     

Survival and behavior of juvenile steelhead trout (Oncorhynchus mykiss) in two estuaries in Oregon, USA

Anadromous salmonids are viewed as a prized commodity and cultural symbol throughout the Pacific coast of North America. Unfortunately, several native salmonid populations are threatened or at risk of extinction. Despite this, little is known about the behavior and survival of these fish as the juveniles transition from freshwater to the ocean. Our primary objectives were to estimate survival of juvenile steelhead migrating between trapping sites and the ocean and evaluate whether survival in the estuary varies temporally (within a year) or spatially (within and between estuaries) within the same distinct population segment. We also evaluated whether flow or fork length were correlated with survival and collected information on variables that have been demonstrated to affect smolt survival in other studies to lend insight regarding differences in survival estimates between basins. We compared run timing, migration rate, survival, condition factor, age composition and time of residence in the estuary for steelhead outmigrants from each basin and measured parasite loads in outmigrating steelhead to evaluate potential differences in parasite density and parasite community between basins. In 2009, we implanted acoustic transmitters in 139 wild steelhead smolts in two small rivers on the Oregon Coast. In general, only 40–50 % of the wild steelhead smolts tagged at upstream smolt traps were detected entering the ocean. The majority of mortality occurred in the lower estuary near the ocean. Wild steelhead smolts typically spent less than 1 day in the estuary in both basins. Using similar data from previous studies in the Nehalem and Alsea basins, we showed that survival appears to be negatively correlated with flow in most releases, and in 2009 fork length was not correlated with survival. Our observations provide baseline information on factors that could influence smolt survival through the estuary as well as smolt to adult survival in these basins, and emphasize the importance of monitoring smolt survival in the estuary.     

Climate change and the origin of migratory pathways in the Swainson's thrush, Catharus ustulatus

Aim  To provide a spatially explicit model of how geographic distributions at the last glacial maximum (LGM) and post-glacial colonization routes shaped current migratory pathways in the Swainson's thrush, Catharus ustulatus , a long-distance migratory bird.
Location  The Swainson's thrush breeds in boreal forest regions of the United States and Canada as well as in riparian woodlands along the Pacific coast of North America.
Methods  Palaeodistribution modelling is combined with mtDNA phylogeography to predict the breeding range of the Swainson's thrush at the LGM. Quantitative environmental analysis and bioclimatic modelling are used to reconstruct the most likely post-glacial colonization pathways. A maximum likelihood method for estimating growth rates is used to approximate the relative change in population size since the LGM.
Main conclusions  The palaeodistribution models are concordant with the Swainson's thrush mtDNA phylogeography, suggesting that the inland and coastal groups were geographically isolated in eastern (inland) and western (coastal) regions at the LGM. Estimates of change in population size based on genetic data are remarkably consistent with estimates of change in range size, suggesting that the coastal group has undergone a 2- to 3-fold demographic and range expansion, while the inland group has undergone a 6- to 12-fold demographic and range expansion since the LGM. Bioclimatic analyses strongly support the hypothesis that populations expanding out of the east into previously glaciated areas in the west were undergoing a natural extension of their range by tracking the changes in climatic conditions. The combination of bioclimatic and molecular analyses is consistent with the idea that coastal and inland groups expanded from separate eastern and western regions after the LGM and that the current migratory pathway of the inland group retraces its post-glacial colonization route.     

Sequence signatures from DNA amplification fingerprints reveal fine population structure of the dogwood pathogen Discula destructiva

Abstract Isolates of Discula destructiva Redlin and an undescribed species of Discula , the filamentous fungi that cause anthracnose of flowering ( Cornus florida L.) and Pacific ( Cornus nuttalli Aud.) dogwoods, were analyzed for genetic variation by nucleic acid scanning with arbitrary mini-hairpin oligonucleotide primers. While the fungal population was highly homogeneous throughout the disease range in eastern and western North America, the generation of arbitrary signatures from amplification profiles (ASAP) distinguished isolates from the northeast, middle and southern Appalachian mountain range, and western United States and Canada. ASAP involves a dual-step arbitrary primer-based amplification procedure that generates a large number of informative allelic characters by amplification of monomorphic DNA fingerprints. ASAP analyses showed a fine fungal population structure consistent with the recent and separate introduction of the pathogen on the west and east coasts of North America.     

Daily temperature experience and selection by adfluvial bull trout (<Emphasis Type="Italic">Salvelinus confluentus</Emphasis>)

Bull trout (Salvelinus confluentus) are a thermally sensitive cold-water species with a threatened conservation status across much of North America. To improve our understanding of bull trout thermal ecology, we tagged more than 150 adults with temperature-sensing acoustic biotelemetry transmitters and monitored the animals in a British Columbia reservoir for two years. Thermal resource selection was estimated in open water from the summer to autumn as the system transitioned to isothermal conditions. On average, bull trout thermal history tracked seasonal changes and remained close to the optimum temperatures for growth and metabolism. As summer progressed, bull trout increasingly selected temperatures of 11–15 °C as they became less available within the water column. Selection indicated the movement to shallower waters where 11–15 °C temperatures existed. The results show that bull trout mainly occupy a narrow range of temperatures which suggests the importance of cold-water refuge for the species.