Molecular genetic examination of the polymorphic Arctic charr Salvelinus alpinus of Thingvallavatn, Iceland

Thingvallavatn, Iceland contains two sympatric morphotypes (benthic and limnetic) of Arctic charr Salvelinus alpinus. Each morphotype is composed of two morphs and these differ markedly in ecology, behaviour and life history. We used molecular genetic approaches to test whether (i) genetic heterogeneity exists among morphs and (ii) if morphs arose in allopatry and came into secondary contact or arose sympatrically within the lake through genetic segregation and/or phenotypic plasticity. Direct sequencing of 275 bp of the mitochondrial DNA (mtDNA) control region, mtDNA restriction fragment length polymorphisms and single locus minisatellite analyses detected insufficient variation to test our hypotheses. Analysis of multilocus minisatellite band sharing detected no significant differences between morphs within the same morphotype. However, significant differences among morphs belonging to different morphotypes suggest some genetic heterogeneity in Thingvallavatn charr. Limnetic charr from Thingvallavatn were more similar to sympatric benthic charr than to allopatric limnetics from two other Icelandic lakes. This suggests that the Thingvallavatn morphs arose sympatrically within the lake rather than in allopatry followed by secondary contact.     

Relationships between lake ecology and morphological characters in Icelandic Arctic charr,Salvelinus alpinus

The common occurrence of parallel phenotypic patterns suggests that a strong relationship exists between ecological dynamics and micro‐evolution. Comparative studies from a large number of populations under varying sets of ecological drivers could contribute to a better understanding of this relationship. We used data on morphology of arctic charr (Salvelinus alpinus) and ecological factors from 35 Icelandic lakes to test the hypothesis that morphological patterns among monomorphic charr populations from different lakes are related to interlake variation in ecological characteristics. There is extensive phenotypic diversity among populations of Icelandic charr, and populations are easily distinguished based on overall body morphology. The results obtained in the present study showed that the morphological diversity of charr was related to large‐scale diversity in lake ecology. Variation in charr morphology was related to water origin (e.g. spring fed versus run‐off), bedrock age, and fish community structure. The present study shows how various ecological factors can shape the biological diversity that we observe. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 761–771.     

The interaction of resource use and gene flow on the phenotypic divergence of benthic and pelagic morphs of Icelandic Arctic charr (Salvelinus alpinus)

Conceptual models of adaptive divergence and ecological speciation in sympatry predict differential resource use, phenotype–environment correlations, and reduced gene flow among diverging phenotypes. While these predictions have been assessed in past studies, connections among them have rarely been assessed collectively. We examined relationships among phenotypic, ecological, and genetic variation in Arctic charr (Salvelinus alpinus) from six Icelandic localities that have undergone varying degrees of divergence into sympatric benthic and pelagic morphs. We characterized morphological variation with geometric morphometrics, tested for differential resource use between morphs using stable isotopes, and inferred the amount of gene flow from single nucleotide polymorphisms. Analysis of stable isotopic signatures indicated that sympatric morphs showed similar difference in resource use across populations, likely arising from the common utilization of niche space within each population. Carbon isotopic signature was also a significant predictor of individual variation in body shape and size, suggesting that variation in benthic and pelagic resource use is associated with phenotypic variation. The estimated percentage of hybrids between sympatric morphs varied across populations (from 0% to 15.6%) but the majority of fish had genotypes (ancestry coefficients) characteristic of pure morphs. Despite evidence of reduced gene flow between sympatric morphs, we did not detect the expected negative relationship between divergence in resource use and gene flow. Three lakes showed the expected pattern, but morphs in the fourth showed no detectable hybridization and had relatively low differences in resource use between them. This coupled with the finding that resource use and genetic differentiation had differential effects on body shape variation across populations suggests that reproductive isolation maintains phenotypic divergence between benthic and pelagic morphs when the effects of resource use are relatively low. Our ability to assess relationships between phenotype, ecology, and genetics deepens our understanding of the processes underlying adaptive divergence in sympatry.     

Mitochondrial DNA diversity among four sympatric morphs of Arctic charr, Salvelinus alpinus L., from Thingvallavatn, Iceland

Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were examined in progeny of four sympatric morphs of Arctic charr ( Salvelinus alpinus L.) from Thingvallavatn, Iceland. The mtDNA analysis with 46 hexanucleotide restriction enzymes indicates that the Thingvallavatn morphs are very closely related. Sequence divergence was less than 0.2% between any of the five clones detected. Although not significant, the topology of the mtDNA UPGMA dendogram was similar to that from a previous allozyme survey. Icelandic Arctic charr show greater affinity to charr from the British Isles than those from North America supporting their current taxonomic distinction.     

Polymorphic segregation in Arctic charr Salvelinus alpinus (L.) from Vatnshlidarvatn, a shallow Icelandic lake

We studied the salmonid fish Arctic charr, Salvelinus alpinus , in a small and shallow landlocked lake in NW Iceland. The lake is productive but die only fish present is Arctic charr. Despite the apparent absence of discrete benthic and limnetic habitats for fish, two forms of Arctic charr are found in the lake. They show subde differences in morphology related to swimming performance and manoeuvrability, but differences in life history such as growth, and age and size at sexual maturation are more pronounced. Both forms have benthic feeding habits with one form consuming greater number of species than the other. We suggest that the segregation of these forms is based on the evolution of a specialist from a local generalist and that this has been made possible by the absence of a common fish competitor in similar lakes, the threespined stickleback Gasterosteous aculeatus.     

Fine-scale parallel patterns in diversity of small benthic Arctic charr (Salvelinus alpinus) in relation to the ecology of lava/groundwater habitats

It is critical to study factors that are important for origin and maintenance of biological diversity. A comparative approach involving a large number of populations is particularly useful. We use this approach to study the relationship between ecological factors and phenotypic diversity in Icelandic Arctic charr (Salvelinus alpinus). Numerous populations of small benthic charr have evolved in lava springs in Iceland. These charr appear morphologically similar, but differ in important morphological features related to feeding. We found a clear relationship between diversity in morphology, diet, and ecological factors among populations. In particular, there were clear differences in morphology and diet between fish coming from habitats where the lava spring flowed on as a stream compared to habitats where the lava spring flowed into a pond. Our study shows that ecological factors are important for the origin and maintenance of biological diversity. The relationship between phenotype and ecological factors are observed on a fine scale, when comparing numerous populations that are phenotypically similar. This strongly suggests that for understanding, managing, and conserving biological diversity important ecological variables have to be taken into the account.     

Genetic analysis of four sympatric morphs of Arctic charr,Salvelinus alpinus,from Thingvallavatn,Iceland

Synopsis The degree of genetic differentiation among four morphs of Arctic charr (small benthivorous, large benthivorous, piscivorous, and planktivorous) from Thingvallavatn, Iceland, was determined electrophoretically. Five of 36 enzyme loci were found to be polymorphic (Est2, Gpi3, Ldh4, Mdh4, 5 and Pgm2). However, only Est2 and Mdh4,5 showed enough variability to permit statistical analysis of divergence among morphs. All four morphs are very closely related; the values of Nei's (D) range from 0.00004 to 0.00126. These morphs are conspecific and do not represent different evolutionary lineages. There is significant genetic differentiation between the small benthivorous charr and the other three morphs. The relative relatedness of morphs based on gene frequency data is only partially concordant with that based on morphology and ecological specialization. The biological significance of this result is unclear because of the limited number of polymorphic loci upon which the genetic analysis is based and the high degree of relatedness among morphs.     

Natural selection and the genetic differentiation of coastal and Arctic populations of the Atlantic cod in northern Norway: a test involving nucleotide sequence variation at the pantophysin (PanI) locus

To examine the role of contemporary selection in maintaining significant allele frequency differences at the pantophysin (PanI) locus among populations of the Atlantic cod, Gadus morhua, in northern Norway, we sequenced 127 PanIA alleles sampled from six coastal and two Barents Sea populations. The distributions of variable sites segregating within the PanIA allelic class were then compared among the populations. Significant differences were detected in the overall frequencies of PanIA alleles among populations within coastal and Arctic regions that was similar in magnitude to heterogeneity in the distributions of polymorphic sites segregating within the PanIA allelic class. The differentiation observed at silent sites in the PanIA allelic class contradicts the predicted effects of widescale gene flow and suggests that postsettlement selection acting on cohorts cannot be responsible for the genetic differences described between coastal and Arctic populations. Our results suggest that the marked differences observed between coastal and Arctic populations of G. morhua in northern Norway at the PanI locus reflect the action of recent diversifying selection and that populations throughout the region may be more independent than suggested by previous studies.     

Segregation in spawning and early life history among polymorphic Arctic charr, Salvelinus alpinus, in Thingvallavatn, Iceland

The relationships among time of spawning, incubation temperature, timing of first feeding and early growth were examined in four sympatric morphs of Arctic charr in Thingvallavatn, Iceland. Large benthivorous charr spawn in July-August at sites with cold ground-water flow. Planktivorous and piscivorous charr spawn in September-November and are not confined to ground-water sites. The spawning of small benthivorous charr overlaps with that of other morphs. Progeny of large benthivorous charr start feeding 2-3 months earlier than the progeny of autumn spawners. This results in differential size distribution and growth rates of young in the spring.     

Conserving adaptive genetic diversity in dynamic landscapes

Genetic variation supplies the raw material for adaptation, evolution and survival of populations and has therefore been a key focus of conservation biology ever since its foundation (Soulé 1985). In previous decades, the neutral component of genetic diversity (generated by mutation and shaped by drift) has been the subject of intense scientific research, fuelled by the increasing availability of molecular markers. On the other hand, the adaptive component of genetic diversity, which is shaped by the action of natural selection, has long remained elusive and difficult to assess, especially at small spatial or temporal scales (Ouborg et al. 2010). Fortunately, new technological and methodological developments now make it possible to identify loci in the genome that are influenced by selection, and thus to get a more complete view of genetic diversity. One article featured in this issue of Molecular Ecology is a good example of this recent breakthrough. Richter-Boix et al. (2011) examined a network of moor frog populations breeding in contrasting habitats in order to understand how landscape features influence patterns of genetic variation. They combined information from both neutral markers and loci putatively under selection to quantify the relative roles of selection and isolation in the evolution of fine-scale local adaptations in these populations. This study nicely illustrates how data on polymorphisms of neutral and adaptive loci can now be judiciously synthesized to help identify the best strategies for preserving adaptive variation, and more generally to enlighten conservation and population-management plans.     

Ecological parasitology of polymorphic Arctic charr, Salvelinus alpinus (L.), in Thingvallavatn, Iceland

The helminth endoparasite fauna in four Arctic charr morphs, Salvelinus alpinus (L.), small benthivorous (SB), large benthivorous (LB), planktivorous (PL) and piscivorous (PI) charr, from Thingvallavatn, Iceland consisted of: Crepidostomum farionis (Trematoda: Allocreadiidae); Diplosttomum sp. (Trematoda: Diplostomatidae); Eubothrium salvelini; Diphyllobothrium dendriticum; D. ditremum (Cestoda: Pseudophyllidae); Proteocephalus longicollis (Cestoda: Proteocepha-lidae): and Philonema oncorhynchi (Nematoda: Filariidae). The morphs exhibited distinctive patterns in prevalences and parasite burdens (mean intensity and mean relative density of parasites). SB charr had high prevalence and parasite burden of the eye fluke Diplostomum sp. and none to very light infections of the other parasite species. LB charr had relatively high prevalence and parasite burden of the intestinal fluke C. farionis , whereas infections of the remaining parasite species were light to moderate. PL and PI charr had high prevalences and worm burdens of Diphyllobothrium spp. and P. longicollis . PL charr differed from PI charr in higher worm burden off P. longicollis and lighter burden of £. salvelini . Prevalences of P. oncorhynchi were high in PL and PI charr. Association of parasite intensities and age and length offish were investigated. The different infection patterns among the morphs agree well with their partitioning in food and habitat utilization, and confirm that there is a high degree of ecological segregation between the morphs. The results demonstrate the importance of ecological factors influencing transmission efficiency of parasites to the fish host.     

Seasonal changes in sea-water tolerance of Arctic charr (Salvelinus alpinus)

Summary Groups of Arctic charr,Salvelinus alpinus, which had been acclimated to water with a salinity of 7 g·l^–1 and natural temperature and photoperiod, were exposed to water with different salinities and temperatures in June, September and February. At a salinity of 15 g·l^–1, plasma osmolality, plasma Na⁺, Cl^–, Mg²⁺ concentrations and the activity of gill Na-K-ATPase were stable, irrespective of temperature and season. In June, the charr were able to regulate blood plasma ionic levels within narrow limits when exposed to a salinity of 34 g·l^–1 (sea water) and a temperature of 8°C. The hypo-osmoregulatory capacity was less, but sufficient if the temperature was only 1°C during the seawater exposure. At the start of the experiment, the gill Na-K-ATPase activity was significantly higher in June than corresponding enzyme activities in September and February. Furthermore, an increase in gill Na-K-ATPase activity during the seawater exposure (8°C) was seen in June. Irrespective of ambient temperature and salinity, no fish died during the June experiments. In September and February, exposure to sea water produced marked increases in plasma osmolality and plasma ion concentrations. There were no changes in gill Na-K-ATPase activity. Consequently, the fish became dehydrated and were moribund after a short period of seawater exposure. Highest mortality was recorded when charr were exposed to winter sea conditions (34 g·l^–1 and 1°C) in February. The results indicate that an increase in daylength induce a hypo-osmoregulatory capacity in the Arctic charr during summer. In fall and winter, however, reduced daylength are accompanied by poor hypo-osmoregulatory capacity. This leads to high mortality as a result of increased electrolyte levels and dehydration.     

Cannibalism and protective behavior of eggs in Arctic charr (Salvelinus alpinus)

From video recordings of spawning events, we quantified protective and cannibalistic behavior of Arctic charr occurring immediately after spawning. The number of fish cannibalizing on stray eggs was examined regarding (a) whether more than one male shed milt during the spawning event, that is, whether sperm competition occurred, (b) whether the sperm competition included few or many males, that is, the intensity of sperm competition, and (c) the density of fish at the spawning site. Response behavior toward egg cannibalism was also examined among females and dominant males in order to determine any parental investment toward protecting the eggs after spawning. Cannibalistic behavior was seen in almost 50% of the spawnings, and the multiple spawning events showed the highest numbers of fish cannibalizing on eggs. Both the number of males releasing milt and the number of fish approaching the spawning site were positively correlated with egg cannibalism. Sperm competition was, however, not a prerequisite for egg cannibalism. Although we also observed partial filial cannibalism, protective behavior of eggs was seen both among dominant males and females, suggesting that charr actually conduct parental care.     

Genetic differentiation among local populations and morphotypes of Arctic charr, Salvelinus alpinus

The systematica of coexisting morphotypes of Arctic charr, Salvelinus alpinus , has been a matter of dispute ever since the days of Linnaeus. Widespread allelic variation at an esterase locus has led some investigators to propose that the morphotypes reflect a complex of at least three sibling species. We tested this hypothesis by examining 42 electrophoretically detectable loci in natural and transplanted charr populations from 15 localities in S Norway. The absolute values of Nei's genetic distance between morphotypes and populations are small (typically in the order of 0.001), and morphotype changes may occur without accompanying changes in frequencies of esterase alleles. Differentiation among localities explains far more of the total gene diversity than differences between morphotypes in the four cases of naturally occurring sympatric morphotypes examined. The data are consistent with an intraspecific population structuring based on locality, and the multiple species hypothesis is rejected.     

Experimental evidence of cannibalism and prey specialization in Arctic charr,Salvelinus alpinus

Synopsis Use of a radiographic technique enabled the study of prey selection and individual specialization in Arctic charr, Salvelinus alpinus, fed with small charr and dry pellets under laboratory conditions. Both naive and experienced fish (mean weight 475 g, mean length 34.9 cm), selected the smallest individuals when offered juvenile charr (6–16 cm) as prey. The selected prey were, on average, 22% of the predator length. Cannibalism appeared to involve individual specialization, since when groups of large charr were given the opportunity to feed on juveniles one day every two weeks, the same individuals were cannibalistic throughout the sampling period of two months. When large charr were presented with alternate cycles of different food types consisting of dry pellets and fish prey, the charr exhibited a strong and consistent feeding specialization with three distinct groups being recognised: cannibals, pellet eaters and non-feeding fish.     

Gonadal differentiation and hormonal sex reversal in Arctic charr (Salvelinus alpinus)

The purpose of this study was to develop a practical protocol for the production of female populations of Arctic charr (Salvelinus alpinus). Achieving this required knowledge of the timing of gonadal differentiation. Undifferentiated gonads were observed microscopically to be present by 194 degrees C-days post-hatch and definitive germ cells by 346 degrees C-days post-hatch, where " degrees C-days" denote acquired thermal units calculated as the product of temperature and days. Some of the gonads had developed a lumen by 510 degrees C-days post-hatch, and by 681 degrees C-days post-hatch anatomical divergence into two types of gonads was clear. Two protocols (immersion and feeding) were tested for hormonal sex reversal of genotypic females using the synthetic androgen 17alpha-methyldihydrotestosterone (MDHT). Six-hour MDHT immersions (0.5, 1, 3, 5 and 10 mg/L) were carried out weekly from hatch to first feeding (140 degrees C-days post-hatch), whereas daily feeding treatments (0.5 mg/kg) went from 140 to 600 degrees C-days post-hatch. The sex ratios of all immersion experimental groups were significantly different from the control, with the proportion of presumptive males increasing as MDHT concentration increased. The highest immersion treatment, 10 mg/L, yielded a population of 90% presumptive males and 10% with atypical gonads. However, the most effective treatment, yielding a population of 90% presumptive males and no fish with atypical gonads, was the feeding treatment. Given that female salmonid fishes are homogametic, sex-reversed (masculinized) genotypic females produced in this way can serve as broodstock for the creation of all-female charr populations for aquaculture.     

Quantitative protein requirements of Arctic charr, Salvelinus alpinus (L)

Arctic charr, Salvelinus alpinus , require diets with protein energy (PE): total energy (TE) ratios of at least 0.35 in order to maintain good rates of growth. The protein requirement is, therefore, similar to that of rainbow trout, Salmo gairdneri . Protein retention efficiency (PPV) declined as the protein content of the diet was increased, the relationship being described by the equation: It is suggested that charr will maintain good rates of growth if fed on diets used for commercial culture of rainbow trout and special formulations for charr should not be necessary.     

Seasonal and ontogenetic shifts in the diet of Arctic charr Salvelinus alpinus in a subarctic lake

Seasonal and ontogenetic shifts in the diet of Arctic charr Salvelinus alpinus were studied in a deep, ultra‐oligotrophic lake in subarctic Finland from both stomach contents and the stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope compositions of muscle and liver tissues. Both diet and isotope results indicated that the S. alpinus population relied mainly on littoral benthic energy sources. The strong littoral reliance appeared largely independent of season or fish size, although the data lacked small (total length, L_T, <130 mm) and young (<3 years) S. alpinus. Liver isotope values of intermediate‐sized S. alpinus (200–350 mm), however, suggested exploitation of the increase in the abundance of pelagic zooplankton in the late open‐water season. The results suggest that, in general, a strong littoral reliance of fishes can be a feature in subarctic lakes throughout the year. Due to its faster isotopic turnover rate and thus higher resolution for temporal diet changes, liver could be more commonly used in stable‐isotope studies of fish trophic niche shifts instead of using only the less responsive muscle tissue.     

湖北海棠的等位酶变异和遗传多样性研究

采用超薄平板微型聚丙烯酰胺等电聚焦电泳方法对湖北海棠（Malus hupehensis)的9个野生居群和2个人工栽培居群的等位酶变异和遗传多样性进行了初步研究。通过对12个酶系统29个酶位点的检测,结果表明湖北海棠有25个酶位点的等位基因频率分布差异,,有10个居群发现稀有等位基因,并有11个（37．9％）重复位点;湖北海棠的遗传多样性水平很高,等位基因平均数A＝2．127,多态位点百分率P＝74．927,平均预期杂合度He=0.376;居群间的基因分化系数GST＝0．224。与其他苹果属植物相比,湖北海棠具有中等丰富的遗传变异水平。居群间的基因流仅为Nm=0.866,表明遗传漂变是影响居群遗传变异和遗传结构的一个重要因素。