Male dominance linked to size and age, but not to 'good genes' in brown trout (Salmo trutta).

BACKGROUND: Males that are successful in intra-sexual competition are often assumed to be of superior quality. In the mating system of most salmonid species, intensive dominance fights are common and the winners monopolise most mates and sire most offspring. We drew a random sample of mature male brown trout (Salmo trutta) from two wild populations and determined their dominance hierarchy or traits linked to dominance. The fish were then stripped and their sperm was used for in vitro fertilisations in two full-factorial breeding designs. We recorded embryo viability until hatching in both experiments, and juvenile survival during 20 months after release into a natural streamlet in the second experiment. Since offspring of brown trout get only genes from their fathers, we used offspring survival as a quality measure to test (i) whether males differ in their genetic quality, and if so, (ii) whether dominance or traits linked to dominance reveal 'good genes'. RESULTS: We found significant additive genetic variance on embryo survival, i.e. males differed in their genetic quality. Older, heavier and larger males were more successful in intra-sexual selection. However, neither dominance nor dominance indicators like body length, weight or age were significantly linked to genetic quality measured as embryo or juvenile survival. CONCLUSION: We found no evidence that females can improve their offspring's genetic viability by mating with large and dominant males. If there still were advantages of mating with dominant males, they may be linked to non-genetic benefits or to genetic advantages that are context dependent and therefore possibly not revealed under our experimental conditions - even if we found significant additive genetic variation for embryo viability under such conditions.

Effects of different mating scenarios on embryo viability in brown trout.

Mating with attractive or dominant males is often predicted to offer indirect genetic benefits to females, but it is still largely unclear how important such non-random mating can be with regard to embryo viability. We sampled a natural population of adult migratory brown trout (Salmo trutta), bred them in vitro in a half-sib breeding design to separate genetic from maternal environmental effects, raised 2098 embryos singly until hatching, and exposed them experimentally to different levels of pathogen stress at a late embryonic stage. We found that the embryos' tolerance to the induced pathogen stress was linked to the major histocompatibility complex (MHC) of their parents, i.e. certain MHC genotypes appeared to provide better protection against infection than others. We also found significant additive genetic variance for stress tolerance. Melanin-based dark skin patterns revealed males with 'good genes', i.e. embryos fathered by dark coloured males had a high tolerance to infection. Mating with large and dominant males would, however, not improve embryo viability when compared to random mating. We used simulations to provide estimates of how mate choice based on MHC or melanin-based skin patterns would influence embryos' tolerance to the experimentally induced pathogen stress.

Immunoelectron microscopical identification of the uncoupling protein in brown adipose tissue mitochondria.

The distribution of the uncoupling protein (UCP) in brown adipocyte mitochondria of the hibernant Muscardinus avellanarius was obtained by ultrastructural immunocytochemistry. In both cryosections and sections of Lowicryl-embedded material UCP was localized in the mitochondrial cristae of brown adipocytes, but not in liver mitochondria. It should now be possible to easily identify the morphology of cells committed to BAT differentiation in the tissue as well as in cell culture.

Genetic variants in novel pathways influence blood pressure and cardiovascular disease risk.

Blood pressure is a heritable trait influenced by several biological pathways and responsive to environmental stimuli. Over one billion people worldwide have hypertension (≥140 mm Hg systolic blood pressure or  ≥90 mm Hg diastolic blood pressure). Even small increments in blood pressure are associated with an increased risk of cardiovascular events. This genome-wide association study of systolic and diastolic blood pressure, which used a multi-stage design in 200,000 individuals of European descent, identified sixteen novel loci: six of these loci contain genes previously known or suspected to regulate blood pressure (GUCY1A3-GUCY1B3, NPR3-C5orf23, ADM, FURIN-FES, GOSR2, GNAS-EDN3); the other ten provide new clues to blood pressure physiology. A genetic risk score based on 29 genome-wide significant variants was associated with hypertension, left ventricular wall thickness, stroke and coronary artery disease, but not kidney disease or kidney function. We also observed associations with blood pressure in East Asian, South Asian and African ancestry individuals. Our findings provide new insights into the genetics and biology of blood pressure, and suggest potential novel therapeutic pathways for cardiovascular disease prevention.

Ulcerative fungal keratitis in a Brown Swiss cow.

An 11-year-old Brown Swiss cow was referred to the Farm Animal Department of the Veterinary Teaching Hospital in Zurich, Switzerland, because of lateral recumbency due to puerperal hemolytic anemia. The animal had developed enophthalmos due to dehydration at the time of presentation. Two days after hospitalization, the cow showed blepharospasm and epiphora of the right eye. Ophthalmic examination of the right eye revealed a fluorescein-positive, paraxial, superficial corneal ulcer with focal edema, and mild superficial neovascularization. White corneal stromal infiltrates were seen at the edges of the ulcer bed. After initial topical treatment with an antibiotic ointment (Neomycin 3.5 mg/g, Bacitracin 250 IU/g) three times a day, an increase in corneal infiltrates was noted on re-examination 2 days later. Several fluorescein-negative, punctate, stromal, white opacities were seen dorsal to the ulcer. Cytology demonstrated the presence of fungal hyphae. Topical treatment with 2% miconazole ointment and 0.36% K-EDTA eye drops six times daily and four times daily, respectively, from the second day and continued antibiotics three times daily resolved the clinical symptoms within 6 days. Fungal culture identified the fungal organism as Eurotium amstelodami.

Parental influences on pathogen resistance in brown trout embryos and effects of outcrossing within a river network.

Phenotypic plasticity can increase tolerance to heterogeneous environments but the elevations and slopes of reaction norms are often population specific. Disruption of locally adapted reaction norms through outcrossing can lower individual viability. Here, we sampled five genetically distinct populations of brown trout (Salmo trutta) from within a river network, crossed them in a full-factorial design, and challenged the embryos with the opportunistic pathogen Pseudomonas fluorescens. By virtue of our design, we were able to disentangle effects of genetic crossing distance from sire and dam effects on early life-history traits. While pathogen infection did not increase mortality, it was associated with delayed hatching of smaller larvae with reduced yolk sac reserves. We found no evidence of a relationship between genetic distance (W, FST) and the expression of early-life history traits. Moreover, hybrids did not differ in phenotypic means or reaction norms in comparison to offspring from within-population crosses. Heritable variation in early life-history traits was found to remain stable across the control and pathogen environments. Our findings show that outcrossing within a rather narrow geographical scale can have neutral effects on F1 hybrid viability at the embryonic stage, i.e. at a stage when environmental and genetic effects on phenotypes are usually large.

Blood pressure loci identified with a gene-centric array.

Raised blood pressure (BP) is a major risk factor for cardiovascular disease. Previous studies have identified 47 distinct genetic variants robustly associated with BP, but collectively these explain only a few percent of the heritability for BP phenotypes. To find additional BP loci, we used a bespoke gene-centric array to genotype an independent discovery sample of 25,118 individuals that combined hypertensive case-control and general population samples. We followed up four SNPs associated with BP at our p < 8.56 × 10(-7) study-specific significance threshold and six suggestively associated SNPs in a further 59,349 individuals. We identified and replicated a SNP at LSP1/TNNT3, a SNP at MTHFR-NPPB independent (r(2) = 0.33) of previous reports, and replicated SNPs at AGT and ATP2B1 reported previously. An analysis of combined discovery and follow-up data identified SNPs significantly associated with BP at p < 8.56 × 10(-7) at four further loci (NPR3, HFE, NOS3, and SOX6). The high number of discoveries made with modest genotyping effort can be attributed to using a large-scale yet targeted genotyping array and to the development of a weighting scheme that maximized power when meta-analyzing results from samples ascertained with extreme phenotypes, in combination with results from nonascertained or population samples. Chromatin immunoprecipitation and transcript expression data highlight potential gene regulatory mechanisms at the MTHFR and NOS3 loci. These results provide candidates for further study to help dissect mechanisms affecting BP and highlight the utility of studying SNPs and samples that are independent of those studied previously even when the sample size is smaller than that in previous studies.

Blood pressure loci identified with a gene-centric array.

Raised blood pressure (BP) is a major risk factor for cardiovascular disease. Previous studies have identified 47 distinct genetic variants robustly associated with BP, but collectively these explain only a few percent of the heritability for BP phenotypes. To find additional BP loci, we used a bespoke gene-centric array to genotype an independent discovery sample of 25,118 individuals that combined hypertensive case-control and general population samples. We followed up four SNPs associated with BP at our p < 8.56 × 10(-7) study-specific significance threshold and six suggestively associated SNPs in a further 59,349 individuals. We identified and replicated a SNP at LSP1/TNNT3, a SNP at MTHFR-NPPB independent (r(2) = 0.33) of previous reports, and replicated SNPs at AGT and ATP2B1 reported previously. An analysis of combined discovery and follow-up data identified SNPs significantly associated with BP at p < 8.56 × 10(-7) at four further loci (NPR3, HFE, NOS3, and SOX6). The high number of discoveries made with modest genotyping effort can be attributed to using a large-scale yet targeted genotyping array and to the development of a weighting scheme that maximized power when meta-analyzing results from samples ascertained with extreme phenotypes, in combination with results from nonascertained or population samples. Chromatin immunoprecipitation and transcript expression data highlight potential gene regulatory mechanisms at the MTHFR and NOS3 loci. These results provide candidates for further study to help dissect mechanisms affecting BP and highlight the utility of studying SNPs and samples that are independent of those studied previously even when the sample size is smaller than that in previous studies.

Cell autonomous lipin 1 function is essential for development and maintenance of white and brown adipose tissue.

Through analysis of mice with spatially and temporally restricted inactivation of Lpin1, we characterized its cell autonomous function in both white (WAT) and brown (BAT) adipocyte development and maintenance. We observed that the lipin 1 inactivation in adipocytes of aP2(Cre/+)/Lp(fEx2)(-)(3/fEx2)(-)(3) mice resulted in lipodystrophy and the presence of adipocytes with multilocular lipid droplets. We further showed that time-specific loss of lipin 1 in mature adipocytes in aP2(Cre-ERT2/+)/Lp(fEx2)(-)(3/fEx2)(-)(3) mice led to their replacement by newly formed Lpin1-positive adipocytes, thus establishing a role for lipin 1 in mature adipocyte maintenance. Importantly, we observed that the presence of newly formed Lpin1-positive adipocytes in aP2(Cre-ERT2/+)/Lp(fEx2)(-)(3/fEx2)(-)(3) mice protected these animals against WAT inflammation and hepatic steatosis induced by a high-fat diet. Loss of lipin 1 also affected BAT development and function, as revealed by histological changes, defects in the expression of peroxisome proliferator-activated receptor alpha (PPARα), PGC-1α, and UCP1, and functionally by altered cold sensitivity. Finally, our data indicate that phosphatidic acid, which accumulates in WAT of animals lacking lipin 1 function, specifically inhibits differentiation of preadipocytes. Together, these observations firmly demonstrate a cell autonomous role of lipin 1 in WAT and BAT biology and indicate its potential as a therapeutical target for the treatment of obesity.

Absence of the fourth cranial nerve in congenital Brown syndrome.

PURPOSE: To elucidate the aetiology of congenital Brown syndrome. METHODS: Four consecutive patients diagnosed with unilateral congenital Brown syndrome had a comprehensive standardized ocular motility examination. Any compensatory head posture was measured. Brain magnetic resonance imaging (MRI) with regard for the IV cranial nerve (CN) was performed in all patients. Orbital MRI was performed in 2/4 patients, with images acquired in eight directions of gaze and superior oblique (SO) muscle areas compared. RESULTS: CN IV could not be identified bilaterally in two patients, but was absent only on the side of the Brown syndrome in the two other patients. On the normal side, orbital MRI revealed a smaller SO muscle area in upgaze than in downgaze, demonstrating normal actions of this muscle. On the side of the Brown syndrome, the SO area remained the same in upgaze and in downgaze and approximately symmetric to the area of SO in downgaze on the normal side. CONCLUSIONS: These cases add further anatomical support to the theory of paradoxical innervation in congenital Brown syndrome. CN IV was absent in two patients on the side of the Brown syndrome, but without muscle hypoplasia. SO muscle size did not vary in up- and downgaze, which we interpreted as a sign of constant innervation through branches of CN III.

Genetic and phenotypic population divergence on a microgeographic scale in brown trout.

Salmonid populations of many rivers are rapidly declining. One possible explanation is that habitat fragmentation increases genetic drift and reduces the populations' potential to adapt to changing environmental conditions. We measured the genetic and eco-morphological diversity of brown trout (Salmo trutta) in a Swiss stream system, using multivariate statistics and Bayesian clustering. We found large genetic and phenotypic variation within only 40 km of stream length. Eighty-eight percent of all pairwise F(ST) comparisons and 50% of the population comparisons in body shape were significant. High success rates of population assignment tests confirmed the distinctiveness of populations in both genotype and phenotype. Spatial analysis revealed that divergence increased with waterway distance, the number of weirs, and stretches of poor habitat between sampling locations, but effects of isolation-by-distance and habitat fragmentation could not be fully disentangled. Stocking intensity varied between streams but did not appear to erode genetic diversity within populations. A lack of association between phenotypic and genetic divergence points to a role of local adaptation or phenotypically plastic responses to habitat heterogeneity. Indeed, body shape could be largely explained by topographic stream slope, and variation in overall phenotype matched the flow regimes of the respective habitats.

Pathogen-induced hatching and population-specific life-history response to water-borne cues in brown trout (Salmo trutta)

Hatching is an important niche shift, and embryos in a wide range of taxa can either accelerate or delay this life-history switch in order to avoid stage-specific risks. Such behavior can occur in response to stress itself and to chemical cues that allow anticipation of stress. We studied the genetic organization of this phenotypic plasticity and tested whether there are differences among populations and across environments in order to learn more about the evolutionary potential of stress-induced hatching. As a study species, we chose the brown trout (Salmo trutta; Salmonidae). Gametes were collected from five natural populations (within one river network) and used for full-factorial in vitro fertilizations. The resulting embryos were either directly infected with Pseudomonas fluorescens or were exposed to waterborne cues from P. fluorescens-infected conspecifics. We found that direct inoculation with P. fluorescens increased embryonic mortality and induced hatching in all host populations. Exposure to waterborne cues revealed population-specific responses. We found significant additive genetic variation for hatching time, and genetic variation in trait plasticity. In conclusion, hatching is induced in response to infection and can be affected by waterborne cues of infection, but populations and families differ in their reaction to the latter.