Assessing reproductive isolation using a contact zone between parapatric lake-stream stickleback ecotypes.

Ecological speciation occurs when populations evolve reproductive isolation as a result of divergent natural selection. This isolation can be influenced by many potential reproductive barriers, including selection against hybrids, selection against migrants and assortative mating. How and when these barriers act and interact in nature is understood for relatively few empirical systems. We used a mark-recapture experiment in a contact zone between lake and stream three-spined sticklebacks (Gasterosteus aculeatus, Linnaeus) to evaluate the occurrence of hybrids (allowing inferences about mating isolation), the interannual survival of hybrids (allowing inferences about selection against hybrids) and the shift in lake-like vs. stream-like characteristics (allowing inferences about selection against migrants). Genetic and morphological data suggest the occurrence of hybrids and no selection against hybrids in general, a result contradictory to a number of other studies of sticklebacks. However, we did find selection against more lake-like individuals, suggesting a barrier to gene flow from the lake into the stream. Combined with previous work on this system, our results suggest that multiple (most weakly and often asymmetric) barriers must be combining to yield substantial restrictions on gene flow. This work provides evidence of a reproductive barrier in lake-stream sticklebacks and highlights the value of assessing multiple reproductive barriers in natural contexts.

Evolution and origin of sympatric shallow-water morphotypes of Lake Trout, Salvelinus namaycush, in Canada's Great Bear Lake.

Range expansion in north-temperate fishes subsequent to the retreat of the Wisconsinan glaciers has resulted in the rapid colonization of previously unexploited, heterogeneous habitats and, in many situations, secondary contact among conspecific lineages that were once previously isolated. Such ecological opportunity coupled with reduced competition likely promoted morphological and genetic differentiation within and among post-glacial fish populations. Discrete morphological forms existing in sympatry, for example, have now been described in many species, yet few studies have directly assessed the association between morphological and genetic variation. Morphotypes of Lake Trout, Salvelinus namaycush, are found in several large-lake systems including Great Bear Lake (GBL), Northwest Territories, Canada, where several shallow-water forms are known. Here, we assess microsatellite and mitochondrial DNA variation among four morphotypes of Lake Trout from the five distinct arms of GBL, and also from locations outside of this system to evaluate several hypotheses concerning the evolution of morphological variation in this species. Our data indicate that morphotypes of Lake Trout from GBL are genetically differentiated from one another, yet the morphotypes are still genetically more similar to one another compared with populations from outside of this system. Furthermore, our data suggest that Lake Trout colonized GBL following dispersal from a single glacial refugium (the Mississippian) and support an intra-lake model of divergence. Overall, our study provides insights into the origins of morphological and genetic variation in post-glacial populations of fishes and provides benchmarks important for monitoring Lake Trout biodiversity in a region thought to be disproportionately susceptible to impacts from climate change.

Replicate divergence between and within sounds in a marine fish: the copper rockfish (Sebastes caurinus).

Understanding the factors that influence larval dispersal and connectivity among marine populations is critical to the conservation and sustainable management of marine resources. We assessed genetic subdivision among ten populations of copper rockfish (Sebastes caurinus) representing paired samples of outer coast and the heads of inlets in five replicate sounds on the west coast of Vancouver Island, British Columbia, using 17 microsatellite DNA loci. Overall, subdivision (F(ST)) was low (F(ST) = 0.031, P < 0.001), but consistently higher between paired coast and head of inlet sites (mean FST = 0.047, P < 0.001) compared to among the five coast sites (mean F(ST) = -0.001, P > 0.5) or among the five head of inlet sites (mean F(ST) = 0.026, P < 0.001). Heterozygosity, allelic richness and estimates of effective population size were also lower in head of inlet sites than in coast sites. Bayesian analysis identified two genetic groups across all samples, a single genetic group among only coast samples, two genetic groups among head of inlet samples and two genetic groups within each sound analysed separately. Head of inlet copper rockfish tended to be shorter with lower condition factors and grew more slowly than coast sites fish. Reduced physical connectivity and selection against immigrants in contrasting outer coast-head of inlet environments likely contribute to the evolution of population structure of copper rockfish. Based on genetic connectivity, coast sites appear to be better served by existing marine protected areas than are head of inlet sites.

Coexistence and origin of trophic ecotypes of pygmy whitefish, Prosopium coulterii, in a south-western Alaskan lake.

Ecologically, morphologically and genetically distinct populations within single taxa often coexist in postglacial lakes and have provided important model systems with which to investigate ecological and evolutionary processes such as niche partitioning and ecological speciation. Within the Salmonidae, these species complexes have been well studied, particularly within the Coregonus clupeaformis-C. laveratus (lake and European whitefish, respectively) group, but the phenomenon has been less well documented in the other whitefish genera, Prosopium and Stenodus. Here, we examined the morphology, feeding biology and genetic structure of three putative forms of the pygmy whitefish, Prosopium coulterii (Eigenmann & Eigenmann, 1892), first reported from Chignik Lake, south-western Alaska, over 40 years ago. Field collections and morphological analyses resolved a shallow water (< 5 m depth) low gill raker count form (< 15 first arch gill rakers), a deepwater (> 30 m), low gill raker form and a deepwater, high gill raker count (> 15 gill rakers) form. The two low gill raker count forms fed almost exclusively on benthic invertebrates (mostly chironomids), while the deepwater, high gill raker count form fed almost exclusively on zooplankton; differences in diet were also reflected in differences both in δ(13) C and δ(15) N stable isotopes. All three forms were characterized by the same major mitochondrial DNA clade that has been associated with persistence in, and postglacial dispersal from, a Beringian glacial refugium. Analysis of variation at nine microsatellite DNA loci indicated low, but significant differentiation among forms, especially between the two low gill raker count forms and the high gill raker count form. The extent of differentiation along phenotypic (considerable) and genetic (subtle) axes among the Chignik Lake forms is similar to that found among distinct taxa of Prosopium found in pre-glacial Bear Lake (Utah-Idaho, USA) which is probably at least ten times older than Chignik Lake. Our analyses illustrate the potential for the postglacial differentiation in traits subject to divergent natural selection across variable environments.

Gene flow and effective population size in two life-history types of broad whitefish Coregonus nasus from the Canadian Arctic.

In this study, the magnitude and direction of gene flow and estimates of effective population sizes (N(e) ) were quantified among two life-history types (lacustrine and anadromous) of broad whitefish Coregonus nasus in the lower Mackenzie River system. The data suggest that dispersal and subsequent gene flow occurs between these groups, with the former appearing to be asymmetrical. Gene flow may potentially be directionally biased as well, a result attributed to source-sink population dynamics and the ongoing process of post-glacial colonization and contemporary range expansion. Additionally, average N(e) estimates were consistently lower for lacustrine populations of C. nasus although confidence intervals for both contemporary and historical estimates broadly overlapped. The lower average estimates of N(e) for lacustrine populations was suggested to be the result of more recent founding events following post-glacial dispersal. This study provides one of the first assessments of gene flow and N(e) in an Arctic coregonine, results that may be relevant to other freshwater and anadromous Arctic species persisting in systems near the periphery of their range.

Extent and scale of local adaptation in salmonid fishes: review and meta-analysis.

What is the extent and scale of local adaptation (LA)? How quickly does LA arise? And what is its underlying molecular basis? Our review and meta-analysis on salmonid fishes estimates the frequency of LA to be ∼55-70%, with local populations having a 1.2 times average fitness advantage relative to foreign populations or to their performance in new environments. Salmonid LA is evident at a variety of spatial scales (for example, few km to>1000 km) and can manifest itself quickly (6-30 generations). As the geographic scale between populations increases, LA is generally more frequent and stronger. Yet the extent of LA in salmonids does not appear to differ from that in other assessed taxa. Moreover, the frequency with which foreign salmonid populations outperform local populations (∼23-35%) suggests that drift, gene flow and plasticity often limit or mediate LA. The relatively few studies based on candidate gene and genomewide analyses have identified footprints of selection at both small and large geographical scales, likely reflecting the specific functional properties of loci and the associated selection regimes (for example, local niche partitioning, pathogens, parasites, photoperiodicity and seasonal timing). The molecular basis of LA in salmonids is still largely unknown, but differential expression at the same few genes is implicated in the convergent evolution of certain phenotypes. Collectively, future research will benefit from an integration of classical and molecular approaches to understand: (i) species differences and how they originate, (ii) variation in adaptation across scales, life stages, population sizes and environmental gradients, and (iii) evolutionary responses to human activities.

Pleistocene glaciations and contemporary genetic diversity in a Beringian fish, the broad whitefish, Coregonus nasus (Pallas): inferences from microsatellite DNA variation.

The contemporary distribution of genetic variation within and among high latitude populations cannot be fully understood without taking into consideration how species responded to the impacts of Pleistocene glaciations. Broad whitefish, Coregonus nasus, a species endemic to northwest North America and the Arctic coast of Russia, was undoubtedly impacted by such events because its geographic distribution suggests that it survived solely within the Beringian refuge from where it dispersed post-glacially to achieve its current range. We used microsatellite DNA to investigate the role of glaciations in promoting intraspecific genetic variation in broad whitefish (N = 14 localities, 664 fish) throughout their North American range and in one Russian sample. Broad whitefish exhibited relatively high intrapopulation variation (average of 11.7 alleles per locus, average H(E) = 0.61) and moderate levels of interpopulation divergence (overall F(ST) = 0.10). The main regions assayed in our study (Russia, Alaska, Mackenzie River and Travaillant Lake systems) were genetically differentiated from each other and there were declines in genetic diversity with distance from putative refugia. Additionally, Mackenzie River system populations showed less developed and more variable patterns of isolation-by-distance than populations occupying former Alaskan portions of Beringia. Finally, our data suggest that broad whitefish dispersed from Beringia using coastal environments and opportunistically via headwater stream connections that once existed between Yukon and Mackenzie River drainages. Our results illustrate the importance of history (e.g. glaciation) and contemporary dispersal ecology in shaping the current genetic population structure of Arctic faunas.

Risedronate dosing before breakfast compared with dosing later in the day in women with postmenopausal osteoporosis.

UNLABELLED: Two studies in postmenopausal women with osteoporosis provide information about the efficacy and safety of dosing oral risedronate 5 mg daily at a time other than before breakfast (i.e., 2 h before and 2 h after any food and drink other than plain water). A significant increase in lumbar spine BMD was observed for both treatment regimens in the two studies. However, smaller increases in lumbar spine BMD were observed with flexible dosing versus before-breakfast dosing. Geographic region, compliance, and consistency of dosing time appear to affect the amount of increase in BMD observed with flexible dosing. INTRODUCTION: Two studies in postmenopausal women with osteoporosis provide additional information about the efficacy and safety of dosing oral risedronate 5 mg daily at a time other than before breakfast (i.e., 2 h before and 2 h after any food and drink other than plain water). METHODS: One study, flexible dosing, was a 6-month North American study in 730 patients randomized to before-breakfast dosing or flexible dosing later in the day. A second study, IMPACT, was a large (N = 2382), 1-year multinational study in patients that chose their dosing regimen (before breakfast or later in the day). These studies were used to examine the bone mineral density (BMD) response with different dosing regimens. RESULTS: A significant increase in lumbar spine BMD was observed for both treatment regimens in the two studies. However, in both studies, the flexible dosing group had a smaller increase from baseline compared to the before-breakfast regimen (ratio of flexible dosing to before breakfast: flexible dosing study, 0.52; IMPACT study, 0.75). In addition, a relationship between geographic region and BMD response was observed with flexible dosing in both studies. Patients in the flexible dosing group who had greater dosing compliance (based on the number of times the bottle was opened) and consistency of dosing time (bottle opened within a 1.5-h window) had a greater increase in lumbar spine BMD. CONCLUSION: Results of these two studies demonstrate that overall flexible dosing of risedronate leads to smaller BMD gains compared to before-breakfast dosing. This result may be due to poorer adherence to the flexible dosing instructions that may be more pronounced in patients in certain geographic regions. If patients cannot abide by before-breakfast dosing and flexible dosing is an approved option, one can expect suboptimal BMD results with flexible dosing.

Genetic analysis of sympatric char populations in western Alaska: Arctic char (Salvelinus alpinus) and Dolly Varden (Salvelinus malma) are not two sides of the same coin.

The North Pacific Ocean has been of great significance to understanding biogeography and speciation in temperate faunas, including for two species of char (Salmonidae: Salvelinus) whose evolutionary relationship has been controversial. We examined the morphology and genetics (microsatellite and mitochondrial DNA) of Arctic char (Salvelinus alpinus) and Dolly Varden char (Salvelinus malma) in lake systems in western Alaska, the eastern and western Arctic, and south of the Alaskan Peninsula. Morphologically, each lake system contained two forms: one (Arctic char) largely confined to lake habitats and characterized by greater numbers of pyloric caeca, gill rakers, and shallower bodies, and another (Dolly Varden) predominated in adjacent stream habitats and was characterized by fewer pyloric caeca, gill rakers, and deeper bodies. MtDNA partial (550 bp) d-loop sequences of both taxa were interspersed with each other within a single 'Bering' clade and demographic inferences suggested historical gene flow from Dolly Varden to Arctic char had occurred. By contrast, the taxa were strongly differentiated in sympatry across nine microsatellite loci in both lakes. Our data show that the two taxa are highly genetically distinct in sympatry, supporting their status as valid biological species, despite occasional hybridization. The interaction between these species highlights the importance of the North Pacific, and Beringia in particular, as an evolutionary wellspring of biodiversity.

Ecological selection against hybrids in natural populations of sympatric threespine sticklebacks.

Experimental work has provided evidence for extrinsic post-zygotic isolation, a phenomenon unique to ecological speciation. The role that ecological components to reduced hybrid fitness play in promoting speciation and maintaining species integrity in the wild, however, is not as well understood. We addressed this problem by testing for selection against naturally occurring hybrids in two sympatric species pairs of benthic and limnetic threespine sticklebacks (Gasterosteus aculeatus). If post-zygotic isolation is a significant reproductive barrier, the relative frequency of hybrids within a population should decline significantly across the life-cycle. Such a trend in a natural population would give independent support to experimental evidence for extrinsic, rather than intrinsic, post-zygotic isolation in this system. Indeed, tracing mean individual hybridity (genetic intermediateness) across three life-history stages spanning four generations revealed just such a decline. This provides compelling evidence that extrinsic selection plays an important role in maintaining species divergence and supports a role for ecological speciation in sticklebacks.

The origins of ecotypic variation of rainbow trout: a test of environmental vs. genetically based differences in morphology.

Although morphological plasticity has been observed in a variety of taxa, few experimental studies have compared the relative proportion of morphological variability that is accounted for by environmentally induced plasticity, and how much is because of genetically based differences among populations. We compared the morphology of six rainbow trout (Oncorhynchus mykiss) populations from different ecotypic categories that were raised under flowing vs. standing-water conditions. Our data indicate that both environmental conditions and ecotypic differences account for a significant proportion of variation in morphology. Among ecotype effects, however, accounted for a much larger proportion of morphological variability than environmental conditions. Rainbow trout from stream populations had deeper caudal peduncles, and longer fins than lake populations, and rainbow trout from a piscivorous population had larger mouth and head lengths than all other ecotypes. Environmentally induced differences in morphology were primarily related to differences in mouth and head lengths, as well as fin length. Relative to morphometric differences from natural rainbow trout populations, most characteristics deviated in the same direction in our experimental populations. Our data indicate that morphological differences across rainbow trout populations have a genetic basis and may represent locally adaptive characteristics and highlight the role of ecology in promoting phenotypic divergence.

Speciation in reverse: morphological and genetic evidence of the collapse of a three-spined stickleback (Gasterosteus aculeatus) species pair.

Historically, six small lakes in southwestern British Columbia each contained a sympatric species pair of three-spined sticklebacks (Gasterosteus aculeatus). These pairs consisted of a 'benthic' and 'limnetic' species that had arisen postglacially and, in four of the lakes, independently. Sympatric sticklebacks are considered biological species because they are morphologically, ecologically and genetically distinct and because they are strongly reproductively isolated from one another. The restricted range of the species pairs places them at risk of extinction, and one of the pairs has gone extinct after the introduction of an exotic catfish. In another lake, Enos Lake, southeastern Vancouver Island, an earlier report suggested that its species pair is at risk from elevated levels of hybridization. We conducted a detailed morphological analysis, as well as genetic analysis of variation at five microsatellite loci for samples spanning a time frame of 1977 to 2002 to test the hypothesis that the pair in Enos Lake is collapsing into a hybrid swarm. Our morphological analysis showed a clear breakdown between benthics and limnetics. Bayesian model-based clustering indicated that two morphological clusters were evident in 1977 and 1988, which were replaced by 1997 by a single highly variable cluster. The most recent 2000 and 2002 samples confirm the breakdown. Microsatellite analysis corroborated the morphological results. Bayesian analyses of population structure in a sample collected in 1994 indicated two genetically distinct populations in Enos Lake, but only a single genetic population was evident in 1997, 2000, and 2002. In addition, genetic analyses of samples collected in 1997, 2000, and 2002 showed strong signals of 'hybrids'; they were genetically intermediate to parental genotypes. Our results support the idea that the Enos Lake species pair is collapsing into a hybrid swarm. Although the precise mechanism(s) responsible for elevated hybridization in the lake is unknown, the demise of the Enos Lake species pair follows the appearance of an exotic crayfish, Pascifasticus lenisculus, in the early 1990s.

Long-chain acyl-CoA esters inhibit phosphorylation of AMP-activated protein kinase at threonine-172 by LKB1/STRAD/MO25.

Activation of the AMP-activated protein kinase (AMPK) results in acute changes in cellular metabolism and transcriptional events that make the cell more robust when encountering an energy challenge. AMPK is thought to be inhibited by glycogen, the major storage form of intracellular carbohydrate. We hypothesized that long-chain acyl-CoA esters (LCACEs) might also inhibit AMPK signaling. Cytosolic LCACEs are available for immediate transport and oxidation within the mitochondria and accordingly may be representative of the lipid energy charge of the cell. We found that LCACEs inhibited phosphorylation of AMPK by the recombinant AMPK kinase (AMPKK) LKB1/STRAD/MO25 in a concentration-dependent manner. Palmitoyl-CoA (PCoA) did not affect the activity of phosphothreonine-172 AMPK. PCoA potently inhibited AMPKK purified from liver. Conversely, PCoA stimulated the kinase activity of LKB1/STRAD/MO25 toward the peptide substrate LKB1tide. Octanoyl-CoA, palmitate, and palmitoylcarnitine did not inhibit AMPKK activity. Removal of AMP from the reaction mixture resulted in reduced AMPKK activity in the presence of PCoA. In conclusion, these results demonstrate that the AMPKK activity of LKB1/STRAD/MO25 is substrate specific and distinct from the kinase activity of LKB1/STRAD/MO25 toward the peptide substrate LKB1tide. They also demonstrate that LCACEs inhibit the AMPKK activity of LKB1/STRAD/MO25 in a specific manner with a dependence on both a long fatty chain and a CoA moiety. These results suggest that the AMPK signaling cascade may directly sense and respond to the lipid energy charge of the cell.

Endurance training increases LKB1 and MO25 protein but not AMP-activated protein kinase kinase activity in skeletal muscle.

LKB1 complexed with MO25 and STRAD has been identified as an AMP-activated protein kinase kinase (AMPKK). We measured relative LKB1 protein abundance and AMPKK activity in liver (LV), heart (HT), soleus (SO), red quadriceps (RQ), and white quadriceps (WQ) from sedentary and endurance-trained rats. We examined trained RQ for altered levels of MO25 protein and LKB1, STRAD, and MO25 mRNA. LKB1 protein levels normalized to HT (1 +/- 0.03) were LV (0.50 +/- 0.03), SO (0.28 +/- 0.02), RQ (0.32 +/- 0.01), and WQ (0.12 +/- 0.03). AMPKK activities in nanomoles per gram per minute were HT (79 +/- 6), LV (220 +/- 9), SO (22 +/- 2), RQ (29 +/- 2), and WQ (42 +/- 4). Training increased LKB1 protein in SO, RQ, and WQ (P < 0.05). LKB1 protein levels after training (%controls) were SO (158 +/- 17), RQ (316 +/- 17), WQ (191 +/- 27), HT (106 +/- 2), and LV (104 +/- 7). MO25 protein after training (%controls) was 595 +/- 71. Training did not affect AMPKK activity. MO25 but not LKB1 or STRAD mRNA increased with training (P < 0.05). Trained values (%controls) were MO25 (164 +/- 22), LKB1 (120 +/- 16), and STRAD (112 +/- 17). LKB1 protein content strongly correlated (r = 0.93) with citrate synthase activity in skeletal muscle (P < 0.05). In conclusion, endurance training markedly increased skeletal muscle LKB1 and MO25 protein without increasing AMPKK activity. LKB1 may be playing multiple roles in skeletal muscle adaptation to endurance training.

Phylogeographical lineages of Arctic grayling (Thymallus arcticus) in North America: divergence, origins and affinities with Eurasian Thymallus.

The number and location of Arctic glacial refugia utilized by taxa during the Pleistocene are continuing uncertainties in Holarctic phylogeography. Arctic grayling (Thymallus arcticus) are widely distributed in freshwaters from the eastern side of Hudson Bay (Canada) west to central Asia. We studied mitochondrial DNA (mtDNA) and microsatellite DNA variation in North American T. arcticus to test for genetic signatures of survival in, and postglacial dispersal from, multiple glacial refugia, and to assess their evolutionary affinities with Eurasian Thymallus. In samples from 32 localities, we resolved 12 mtDNA haplotypes belonging to three assemblages that differed from each other in sequence by between 0.75 and 2.13%: a 'South Beringia' lineage found from western Alaska to northern British Columbia, Canada; a 'North Beringia' lineage found on the north slope of Alaska, the lower Mackenzie River, and to eastern Saskatchewan; and a 'Nahanni' lineage confined to the Nahanni River area of the upper Mackenzie River drainage. Sequence analysis of a portion of the control region indicated monophyly of all North American T. arcticus and their probable origin from eastern Siberian T. arcticus at least 3 Mya. Arctic grayling sampled from 25 localities displayed low allelic diversity and expected heterozygosity (H(E)) across five microsatellite loci (means of 2.1 alleles and 0.27 H(E), respectively) and there were declines in these measures of genetic diversity with distance eastward from the lower Yukon River Valley. Assemblages defined by mtDNA divergences were less apparent at microsatellite loci, but again the Nahanni lineage was the most distinctive. Analysis of molecular variance indicated that between 24% (microsatellite DNA) and 81% (mtDNA) of the variance was attributable to differences among South Beringia, North Beringia and Nahanni lineages. Our data suggest that extant North American Arctic grayling are more diverse phylogeographically than previously suspected and that they consist of at least three major lineages that originated in distinct Pleistocene glacial refugia. T. arcticus probably originated and dispersed from Eurasia to North America in the late to mid-Pliocene, but our data also suggest more recent (mid-late Pleistocene) interactions between lineages across Beringia.

Evidence for bimodal hybrid zones between two species of char (Pisces: Salvelinus) in northwestern North America.

Dolly Varden (Salvelinus malma, Pisces: Salmonidae) and bull trout (Salvelinus confluentus) have widely overlapping, but largely parapatric ranges in watersheds in northwestern North America from Washington State to northern British Columbia. Genetic analysis of natural populations using diagnostic molecular markers revealed widespread local sympatry and hybridization with hybrids comprising 0-25% of the local samples. In a detailed analysis of hybridization using four nuclear DNA markers and mitochondrial DNA within the Thutade Lake watershed, northcentral British Columbia, hybrid genotypes constituted up to 9% of the population of juvenile char. There were significant deviations from Hardy-Weinberg, gametic, and cytonuclear equilibria, and local samples showed bimodal frequency distributions of genotypes. Pure parental and inferred backcross genotypes were most common, and F1 and F(n) hybrids were comparatively rare. Interspecific hybridization was asymmetrical, with most F1 hybrids (five of six) bearing S. confluentus mtDNA. The introgression of nuclear and mitochondrial alleles was asymmetrical, with S. confluentus mtDNA and Growth Hormone 2 introgressing into S. malma significantly more than either introgression of the three other nuclear loci, or introgression of S. malma alleles into S. confluentus. Substantial prezygotic isolation between the species likely depends on the large body size difference between them in sympatry: S. malma have small bodies and a stream resident life history (12-21 cm adult fork length at maturity), while S. confluentus are larger and adfluvial, i.e., they migrate to Thutade Lake where they grow to maturity before returning to tributary streams to spawn (40-90 cm at maturity). These traits may limit interspecific pairings because of size assortative pairing and size-dependent reproductive habitat use.

Population subdivision in westslope cutthroat trout (Oncorhynchus clarki lewisi) at the northern periphery of its range: evolutionary inferences and conservation implications.

Westslope cutthroat trout (Oncorhynchus clarki lewisi, Salmonidae) are native to the upper Columbia, Missouri, and South Saskatchewan river drainages of western North America and are at the northern periphery of their range in southeastern British Columbia, Canada. We examined geographical variation in allele frequencies at eight microsatellite loci in 36 samples of westslope cutthroat trout from British Columbia to assess levels of population subdivision and to test the hypothesis that different habitat types (principally mainstem vs. above migration barrier habitats) would influence levels of genetic diversity, genetic divergence among populations, and attainment of equilibrium between gene flow and genetic drift. Across all samples, the mean number of alleles per locus was 3.9 and mean expected heterozygosity was 0.56. Population subdivision was extensive with an overall Fst (theta) of 0.32. Populations sampled above migration barriers had significantly fewer alleles, lower expected heterozygosity, but greater average pairwise Fst than populations sampled from mainstem localities. We found evidence for isolation-by-distance from a significant correlation between genetic distance and geographical distance (r = 0.31), but the pattern was much stronger (r = 0.51) when above barrier populations and a population that may have been involved in headwater exchanges were removed. By contrast, isolation-by-distance was not observed when only above barrier populations were tested among themselves. Our data support the maintenance of separate demographic management strategies for westslope cutthroat trout inhabiting different river systems and illustrate how differing habitat structure (e.g. presence of migration barriers) may influence patterns of biodiversity and gene flow-drift equilibrium.

The influence of history and contemporary stream hydrology on the evolution of genetic diversity within species: an examination of microsatellite DNA variation in bull trout, Salvelinus confluentus (Pisces: Salmonidae).

An understanding of the relative roles of historical and contemporary factors in structuring genetic variation is a fundamental, but understudied aspect of geographic variation. We examined geographic variation in microsatellite DNA allele frequencies in bull trout (Salvelinus confluentus, Salmonidae) to test hypotheses concerning the relative roles of postglacial dispersal (historical) and current landscape features (contemporary) in structuring genetic variability and population differentiation. Bull trout exhibit relatively low intrapopulation microsatellite variation (average of 1.9 alleles per locus, average He = 0.24), but high levels of interpopulation divergence (F(ST) = 0.39). We found evidence of historical influences on microsatellite variation in the form of a decrease in the number of alleles and heterozygosities in populations on the periphery of the range relative to populations closer to putative glacial refugia. In addition, one region of British Columbia that was colonized later during deglaciation and by more indirect watershed connections showed less developed and more variable patterns of isolation by distance than a similar region colonized earlier and more directly from refugia. Current spatial and drainage interconnectedness among sites and the presence of migration barriers (falls and cascades) within individual streams were found to be important contemporary factors influencing historical patterns of genetic variability and interpopulation divergence. Our work illustrates the limited utility of equilibrium models to delineate population structure and patterns of genetic diversity in recently founded populations or those inhabiting highly heterogeneous environments, and it highlights the need for approaches incorporating a landscape context for population divergence. Substantial microsatellite DNA divergence among bull trout populations may also signal divergence in traits important to population persistence in specific environments.

Long-term regulation of AMP-activated protein kinase and acetyl-CoA carboxylase in skeletal muscle.

Evidence is accumulating for roles of AMP-activated protein kinase (AMPK) in controlling glucose uptake, fatty acid oxidation and gene expression in skeletal muscle. Relatively little is known, however, about the control of expression of the AMPK subunit isoforms. Marked differences are noted in subunit expression as a function of muscle fibre type. Expression of the gamma3 subunit isoform increases in fast-twitch red fibres of the rat in response to training. All subunit isoforms are expressed to a lesser extent in rats treated with propylthiouracil (PTU; an inhibitor of thyroid hormone synthesis) for 3 weeks compared with rats given excess thyroid hormones for 3 weeks. An approx. 2-fold increase in acetyl-CoA carboxylase was observed in gastrocnemius of hyperthyroid rats compared with experimentally hypothyroid rats. Thyroid state therefore appears to be one important factor controlling expression of these proteins in skeletal muscle.

Population mixing and the adaptive divergence of quantitative traits in discrete populations: a theoretical framework for empirical tests.

Empirical tests for the importance of population mixing in constraining adaptive divergence have not been well grounded in theory for quantitative traits in spatially discrete populations. We develop quantitative-genetic models to examine the equilibrium difference between two populations that are experiencing different selective regimes and exchanging individuals. These models demonstrate that adaptive divergence is negatively correlated with the rate of population mixing (m, most strongly so when m is low), positively correlated with the difference in phenotypic optima between populations, and positively correlated with the amount of additive genetic variance (G, most strongly so when G is low). The approach to equilibrium is quite rapid (fewer than 50 generations for two populations to evolve 90% of the distance to equilibrium) when either heritability or mixing are not too low (h2 > 0.2 or m > 0.05). The theory can be used to aid empirical tests that: (1) compare observed divergence to that predicted using estimates of population mixing, additive genetic variance/covariance, and selection; (2) test for a negative correlation between population mixing and adaptive divergence across multiple independent population pairs; and (3) experimentally manipulate the rate of mixing. Application of the first two of these approaches to data from two well-studied natural systems suggests that population mixing has constrained adaptive divergence for color patterns in Lake Erie water snakes (Nerodia sipedon), but not for trophic traits in sympatric pairs of benthic and limnetic stickleback (Gasterosteus aculeatus). The theoretical framework we outline should provide an improved basis for future empirical tests of the role of population mixing in adaptive divergence.