Loren M. Miller

Notes: Microsatellite DNA Markers Reveal New Levels of Genetic Variation in Northern Pike

Abstract Using single-locus microsatellite markers, we have resolved higher levels of genetic variation than previously reported for northern pike Esox lucius. We isolated 14 (AC) n ·(TG) n microsatellite loci from a genomic library of northern pike. Primer pairs for the polymerase chain reaction (PCR) were developed for nine of these loci. With PCR, a DNA-amplifying technique, we were able to assess genetic variability using fish scales as our source of DNA. In four populations, we found four polymorphic loci with three or four alleles at each locus. Average heterozygosity at all loci was 0.075. Although this level of genetic variability is the highest reported for this species, it is much lower than that found for many other fish species by using microsatellite markers. Small numbers of founder fish, combined with loss of variation due to genetic drift in the small populations typical of northern pike, may explain the relatively low levels of genetic variation we found.

Spawning-Site and Natal-Site Fidelity by Northern Pike in a Large Lake: Mark–Recapture and Genetic Evidence

Abstract We supplemented physical-tagging data with genetic data to provide evidence for spawning-site and natal-site fidelity by two spawning populations of northern pike Esox lucius in Kabetogama Lake, Minnesota. A mark–recapture study supported previous reports that individual northern pike and other esocids tend to return to the spawning grounds that they used in previous years. Of 1,900 northern pike marked at two spawning sites in the first year of the study, 23% were recaptured on spawning grounds one to three times over the next 4 years. Of these recaptured fish, only 1.3% and 4.8%, respectively, of those marked at the two spawning sites were recaptured at the other site. Tag returns from anglers showed that the year-round ranges for fish from the two sites overlapped, so that lack of dispersal could not completely explain the high fidelity to spawning sites. Significant allele frequency differences at five microsatellite DNA loci between the 1983 (P = 0.03) and 1985 (P = 0.002) spawning populatio...

Lower fitness of hatchery and hybrid rainbow trout compared to naturalized populations in Lake Superior tributaries.

We have documented an early life survival advantage by naturalized populations of anadromous rainbow trout Oncorhynchus mykiss over a more recently introduced hatchery population and outbreeding depression resulting from interbreeding between the two strains. We tested the hypothesis that offspring of naturalized and hatchery trout, and reciprocal hybrid crosses, survive equally from fry to age 1+ in isolated reaches of Lake Superior tributary streams in Minnesota. Over the first summer, offspring of naturalized females had significantly greater survival than offspring of hatchery females in three of four comparisons (two streams and 2 years of stocking). Having an entire naturalized genome, not just a naturalized mother, was important for survival over the first winter. Naturalized offspring outperformed all others in survival to age 1+ and hybrids had reduced, but intermediate, survival relative to the two pure crosses. Averaging over years and streams, survival relative to naturalized offspring was 0.59 for hybrids with naturalized females, 0.37 for the reciprocal hybrids, and 0.21 for hatchery offspring. Our results indicate that naturalized rainbow trout are better adapted to the conditions of Minnesotas tributaries to Lake Superior so that they outperform the hatchery‐propagated strain in the same manner that many native populations of salmonids outperform hatchery or transplanted fish. Continued stocking of the hatchery fish may conflict with a management goal of sustaining the naturalized populations.

Microsatellite DNA Loci Reveal Genetic Structure of Yellow Perch in Lake Michigan

Abstract The genetic population structure of yellow perch Perca flavescens was assessed, with a focus on spawning groups within Lake Michigan. Six microsatellite DNA loci were evaluated, which had heterozygosities ranging from 0.21 to 0.86 in samples from seven Lake Michigan locations and six others in the north-central United States. Genetic variation within samples was somewhat higher in Lake Michigan than in surrounding inland lakes. Genetic variation was also higher in the north-central United States than in a sample from the eastern United States. Exact tests for population differentiation and the fixation index R ST indicated little differentiation among spawning groups within southern Lake Michigan or Green Bay (pairwise R ST values,−0.005 to +0.014; P > 0.05 after sequential Bonferroni correction for multiple tests). However, spawning groups in Green Bay were distinct from those in Lake Michigan, and all inland locations were distinct from one another as well as from those in Lake Michigan (P < 0....

Spatial genetic structure of northern pike (Esox lucius) in the Baltic Sea.

The genetic relationships among 337 northern pike (Esox lucius) collected from the coastal zone of the central Baltic region and the Finnish islands of Åland were analysed using five microsatellite loci. Spatial structure was delineated using both traditional F‐statistics and individually based approaches including spatial autocorrelation analysis. Our results indicate that the observed genotypic distribution is incompatible with that of a single, panmictic population. Isolation by distance appears important for shaping the genetic structure of pike in this region resulting in a largely continuous genetic change over the study area. Spatial autocorrelation analysis (Morans I) of individual pairwise genotypic data show significant positive genetic correlation among pike collected within geographical distances of less than c. 100–150 km (genetic patch size). We suggest that the genetic patch size may be used as a preliminary basis for identifying management units for pike in the Baltic Sea.

Mixed-source reintroductions lead to outbreeding depression in second-generation descendents of a native North American fish.

Reintroductions are commonly employed to preserve intraspecific biodiversity in fragmented landscapes. However, reintroduced populations are frequently smaller and more geographically isolated than native populations. Mixing genetically, divergent sources are often proposed to attenuate potentially low genetic diversity in reintroduced populations that may result from small effective population sizes. However, a possible negative tradeoff for mixing sources is outbreeding depression in hybrid offspring. We examined the consequences of mixed‐source reintroductions on several fitness surrogates at nine slimy sculpin (Cottus cognatus) reintroduction sites in south‐east Minnesota. We inferred the relative fitness of each crosstype in the reintroduced populations by comparing their growth rate, length, weight, body condition and persistence in reintroduced populations. Pure strain descendents from a single source population persisted in a greater proportion than expected in the reintroduced populations, whereas all other crosstypes occurred in a lesser proportion. Length, weight and growth rate were lower for second‐generation intra‐population hybrid descendents than for pure strain and first‐generation hybrids. In the predominant pure strain, young‐of the‐year size was significantly greater than any other crosstype. Our results suggested that differences in fitness surrogates among crosstypes were consistent with disrupted co‐adapted gene complexes associated with beneficial adaptations in these reintroduced populations. Future reintroductions may be improved by evaluating the potential for local adaptation in source populations or by avoiding the use of mixed sources by default when information on local adaptations or other genetic characteristics is lacking.

Optimizing techniques to capture and extract environmental DNA for detection and quantification of fish

Few studies have examined capture and extraction methods for environmental DNA (eDNA) to identify techniques optimal for detection and quantification. In this study, precipitation, centrifugation and filtration eDNA capture methods and six commercially available DNA extraction kits were evaluated for their ability to detect and quantify common carp (Cyprinus carpio) mitochondrial DNA using quantitative PCR in a series of laboratory experiments. Filtration methods yielded the most carp eDNA, and a glass fibre (GF) filter performed better than a similar pore size polycarbonate (PC) filter. Smaller pore sized filters had higher regression slopes of biomass to eDNA, indicating that they were potentially more sensitive to changes in biomass. Comparison of DNA extraction kits showed that the MP Biomedicals FastDNA SPIN Kit yielded the most carp eDNA and was the most sensitive for detection purposes, despite minor inhibition. The MoBio PowerSoil DNA Isolation Kit had the lowest coefficient of variation in extraction efficiency between lake and well water and had no detectable inhibition, making it most suitable for comparisons across aquatic environments. Of the methods tested, we recommend using a 1.5 μm GF filter, followed by extraction with the MP Biomedicals FastDNA SPIN Kit for detection. For quantification of eDNA, filtration through a 0.2–0.6 μm pore size PC filter, followed by extraction with MoBio PowerSoil DNA Isolation Kit was optimal. These results are broadly applicable for laboratory studies on carps and potentially other cyprinids. The recommendations can also be used to inform choice of methodology for field studies.

Effects of maternally transferred organochlorine contaminants on early life survival in a freshwater fish

Laboratory research has shown that female fish can pass toxic organochlorines (OCs) from their bodies to their eggs, killing their offspring if sufficient quantities are transferred. We conducted a controlled incubation study using gametes from a wild, OC-contaminated walleye (Sander vitreus) population (Bay of Quinte, Lake Ontario, Canada) in order to assess among-female variation in offspring early life survival in relation to ova concentrations of planar OCs (polychlorinated dibenzo-p-dioxins and furans and planar polychlorinated biphenyls) and a suite of other maternal and ova characteristics. Equal volumes of ova from each female were fertilized, pooled, and incubated together as an experimental cohort. Relative survival of each females offspring was estimated as the proportion of surviving larvae (at approximately 5 d posthatch) that she contributed to the cohort as determined by microsatellite DNA parentage assignment. Total planar OC concentration (expressed as toxic equivalency of 2,3,7,8-tetrachlorodibenzo-p-dioxin) of ova was positively related to maternal age and size and to ova lipid content. However, early life survival did not decline with increasing ova planar OC concentrations. Similarly, we observed no significant relationships between early life survival and ova thiamine content, ova fatty acid composition, or maternal age or size. Early life survival was more strongly correlated with date of spawn collection, thyroid hormone status of the ova, and ovum size. Maternally transferred planar OCs do not appear to negatively influence female reproductive success in this walleye population.

A Review of Northern Pike Population Genetics Research andIts Implications for Management

Abstract Conserving genetic diversity within and among populations of northern pike Esox lucius is important for maintaining their short-term fitness and long-term evolutionary potential. Northern pike have consistently shown low within-population variation, as detected by allozymes, mitochondrial DNA, and randomly amplified polymorphic DNA. Microsatellite DNA loci reveal considerably greater variation in northern pike, yet microsatellite variation tends to be less than that in other fish species. Low genetic variation within populations may result from compounding factors of low effective population size and bottlenecks. Allozyme, randomly amplified polymorphic DNA, and microsatellite markers have revealed significant differentiation of populations located in different continents and major drainages, but only microsatellites have differentiated populations on finer geographic scales. Within the north-central United States, analyses with microsatellites have detected genetic differences among most populat...

Conservation Genetics of Lake Superior Brook Trout: Issues, Questions, and Directions

Abstract Parallel efforts by several genetic research groups have tackled common themes relating to management concerns about and recent rehabilitation opportunities for coaster brook trout Salvelinus fontinalis in Lake Superior. The questions that have been addressed include the evolutionary and genetic status of coaster brook trout, the degree of relatedness among coaster populations and their relationship to riverine tributary brook trout populations, and the role and effectiveness of stocking in maintaining and restoring coasters to Lake Superior. Congruent genetic results indicate that coasters are an ecotype (life history variant) rather than an evolutionarily significant unit or genetically distinct strain. Regional structure exists among brook trout stocks, coasters being produced from local populations. Introgression of hatchery genes into wild populations appears to vary regionally and may relate to local population size, habitat integrity, and anthropogenic pressures. Tracking the genetic diver...