Multi-omics for studying and understanding polar life

Polar ecosystems are experiencing amongst the most rapid rates of regional warming on Earth. Here, we discuss 'omics' approaches to investigate polar biodiversity, including the current state of the art, future perspectives and recommendations. We propose a community road map to generate and more fully exploit multi-omics data from polar organisms. These data are needed for the comprehensive evaluation of polar biodiversity and to reveal how life evolved and adapted to permanently cold environments with extreme seasonality. We argue that concerted action is required to mitigate the impact of warming on polar ecosystems via conservation efforts, to sustainably manage these unique habitats and their ecosystem services, and for the sustainable bioprospecting of novel genes and compounds for societal gain.

Contrasting continental patterns of adaptive population divergence in the holarctic ectomycorrhizal fungus Boletus edulis

In the hyperdiverse fungi, the process of speciation is virtually unknown, including for the > 20 000 species of ectomycorrhizal mutualists. To understand this process, we investigated patterns of genome-wide differentiation in the ectomycorrhizal porcini mushroom, Boletus edulis, a globally distributed species complex with broad ecological amplitude. By whole-genome sequencing 160 individuals from across the Northern Hemisphere, we genotyped 792 923 single nucleotide polymorphisms to characterize patterns of genome-wide differentiation and to identify the adaptive processes shaping global population structure. We show that B. edulis exhibits contrasting patterns of genomic divergence between continents, with multiple lineages present across North America, while a single lineage dominates Europe. These geographical lineages are inferred to have diverged 1.62-2.66 million years ago, during a period of climatic upheaval and the onset of glaciation in the Pliocene-Pleistocene boundary. High levels of genomic differentiation were observed among lineages despite evidence of substantial and ongoing introgression. Genome scans, demographic inference, and ecological niche models suggest that genomic differentiation is maintained by environmental adaptation, not physical isolation. Our study uncovers striking patterns of genome-wide differentiation on a global scale and emphasizes the importance of local adaptation and ecologically mediated divergence, rather than prezygotic barriers such as allopatry or genomic incompatibility, in fungal population differentiation.

Demographic histories and genetic diversity across pinnipeds are shaped by human exploitation, ecology and life-history

A central paradigm in conservation biology is that population bottlenecks reduce genetic diversity and population viability. In an era of biodiversity loss and climate change, understanding the determinants and consequences of bottlenecks is therefore an important challenge. However, as most studies focus on single species, the multitude of potential drivers and the consequences of bottlenecks remain elusive. Here, we combined genetic data from over 11,000 individuals of 30 pinniped species with demographic, ecological and life history data to evaluate the consequences of commercial exploitation by 18th and 19th century sealers. We show that around one third of these species exhibit strong signatures of recent population declines. Bottleneck strength is associated with breeding habitat and mating system variation, and together with global abundance explains much of the variation in genetic diversity across species. Overall, bottleneck intensity is unrelated to IUCN status, although the three most heavily bottlenecked species are endangered. Our study reveals an unforeseen interplay between human exploitation, animal biology, demographic declines and genetic diversity.

Historical hunting has caused documented declines in pinnipeds, but the extent to which hunting caused genetic bottlenecks among species was unknown. Here, the authors show evidence of severe bottlenecks in several pinniped species, particularly those that breed on land.

Evidence for frequent incest in a cooperatively breeding mammal

As breeding between relatives often results in inbreeding depression, inbreeding avoidance is widespread in the animal kingdom. However, inbreeding avoidance may entail fitness costs. For example, dispersal away from relatives may reduce survival. How these conflicting selection pressures are resolved is challenging to investigate, but theoretical models predict that inbreeding should occur frequently in some systems. Despite this, few studies have found evidence of regular incest in mammals, even in social species where relatives are spatio-temporally clustered and opportunities for inbreeding frequently arise. We used genetic parentage assignments together with relatedness data to quantify inbreeding rates in a wild population of banded mongooses, a cooperatively breeding carnivore. We show that females regularly conceive to close relatives, including fathers and brothers. We suggest that the costs of inbreeding avoidance may sometimes outweigh the benefits, even in cooperatively breeding species where strong within-group incest avoidance is considered to be the norm.

Indications for and results of surgery in ventricular septal defects

Surgical closure of VSDs is indicated mainly for those that are larger and causing either servere congestive heart failure or else pulmonary vascular disease. The latter, producing an increased pulmonary vascular resistance, is usually reversible if the VSD is closed under 2 years of age, but may become irreversible if left for longer times. Primary closure of the VSD, even in infants is in many centers done with a lower mortality than banding of the pulmonary artery and late VSD repair. Selection of patients needs great care because VSDs frequently get smaller or close spontaneously, even if initially large.

Effects outflow tract obstruction on total and regional coronary blood flow, and its influence on ventricular function

Animal experiments suggest a model of coronary blood flow in which left ventricular subendocardial muscle is perfused only in diastole, while more superficial muscle is perfused throughout the cardiac cycle. Once maximal coronary vasodilatation has occured, subendocardial flow per minute depends on the area between aortic and left ventricular diastolic pressure time heart rate [DPTI per minute]. Since left ventricular oxygen needs are related to the area under the left ventricular pressure curve in systole [SPTI], the ratio DPTI/SPTI reflects balance between myocardial oxygen supply and demand. Marked reduction in the ratio causes relative subendocardial ischemia which can be predicted from teh ratio. There is evidence that outflow tract obstructions in man also cause subendocardial ischemia by similar mechanisms, and that this ischemia occurs despite normal coronary arteries.

Global population structure and demographic history of the grey seal

Although the grey seal Halichoerus grypus is one of the most familiar and intensively studied of all pinniped species, its global population structure remains to be elucidated. Little is also known about how the species as a whole may have historically responded to climate-driven changes in habitat availability and anthropogenic exploitation. We therefore analysed samples from over 1500 individuals collected from 22 colonies spanning the Western and Eastern Atlantic and the Baltic Sea regions, represented by 350 bp of the mitochondrial hypervariable region and up to nine microsatellites. Strong population structure was observed at both types of marker, and highly asymmetrical patterns of gene flow were also inferred, with the Orkney Islands being identified as a source of emigrants to other areas in the Eastern Atlantic. The Baltic and Eastern Atlantic regions were estimated to have diverged a little over 10 000 years ago, consistent with the last proposed isolation of the Baltic Sea. Approximate Bayesian computation also identified genetic signals consistent with postglacial population expansion across much of the species range, suggesting that grey seals are highly responsive to changes in habitat availability.

No correlation between multi-locus heterozygosity and fitness in the common buzzard despite heterozygote advantage for plumage colour

Correlations between heterozygosity and fitness are frequently found but rarely well understood. Fitness can be affected by single loci of large effect which correlate with neutral markers via linkage disequilibrium, or as a result of variation in genome-wide heterozygosity following inbreeding. We explored these alternatives in the common buzzard, a raptor species in which three colour morphs differ in their lifetime reproductive success. Using 18 polymorphic microsatellite loci, we evaluated potential genetic differences among the morphs which may lead to subpopulation structuring and tested for correlations between three fitness-related traits and heterozygosity, both genome wide and at each locus separately. Despite their assortative mating pattern, the buzzard morphs were found to be genetically undifferentiated. Multilocus heterozygosity was only found to be correlated with a single fitness-related trait, infection with the blood parasite, Leucocytozoon buteonis, and this was via interactions with vole abundance and age. One locus also showed a significant relationship with blood parasite infection and ectoparasite infestation. The vicinity of this locus contains two genes, one of which is potentially implicated in the immune system of birds. We conclude that genome-wide heterozygosity is unlikely to be a major determinant of parasite burden and body condition in the polymorphic common buzzard.

Molecular insights into the historic demography of bowhead whales: understanding the evolutionary basis of contemporary management practices

Patterns of genetic variation observed within species reflect evolutionary histories that include signatures of past demography. Understanding the demographic component of species' history is fundamental to informed management because changes in effective population size affect response to environmental change and evolvability, the strength of genetic drift, and maintenance of genetic variability. Species experiencing anthropogenic population reductions provide valuable case studies for understanding the genetic response to demographic change because historic changes in the census size are often well documented. A classic example is the bowhead whale, Balaena mysticetus, which experienced dramatic population depletion due to commercial whaling in the late 19th and early 20th centuries. Consequently, we analyzed a large multi-marker dataset of bowhead whales using a variety of analytical methods, including extended Bayesian skyline analysis and approximate Bayesian computation, to characterize genetic signatures of both ancient and contemporary demographic histories. No genetic signature of recent population depletion was recovered through any analysis incorporating realistic mutation assumptions, probably due to the combined influences of long generation time, short bottleneck duration, and the magnitude of population depletion. In contrast, a robust signal of population expansion was detected around 70,000 years ago, followed by a population decline around 15,000 years ago. The timing of these events coincides to a historic glacial period and the onset of warming at the end of the last glacial maximum, respectively. By implication, climate driven long-term variation in Arctic Ocean productivity, rather than recent anthropogenic disturbance, appears to have been the primary driver of historic bowhead whale demography.

Rates of assay success and genotyping error when single nucleotide polymorphism genotyping in non-model organisms: a case study in the Antarctic fur seal

Although single nucleotide polymorphisms (SNPs) are increasingly being recognized as powerful molecular markers, their application to non-model organisms can bring significant challenges. Among these are imperfect conversion rates of assays designed from in silico resources and the enhanced potential for genotyping error relative to pre-validated, highly optimized human SNPs. To explore these issues, we used Illumina's GoldenGate assay to genotype 480 Antarctic fur seal (Arctocephalus gazella) individuals at 144 putative SNPs derived from a 454 transcriptome assembly. One hundred and thirty-five polymorphic SNPs (93.8%) were automatically validated by the program GenomeStudio, and the initial genotyping error rate, estimated from nine replicate samples, was 0.004 per reaction. However, an almost tenfold further reduction in the error rate was achieved by excluding 31 loci (21.5%) that exhibited unclear clustering patterns, manually editing clusters to allow rescoring of ambiguous or incorrect genotypes, and excluding 18 samples (3.8%) with unreliable genotypes. After stringent quality filtering, we also found a counter-intuitive negative relationship between in silico minor allele frequency and the conversion rate, suggesting that some of our assays may have been designed from paralogous loci. Nevertheless, we obtained over 45 000 individual SNP genotypes with a final error rate of 0.0005, indicating that the GoldenGate assay is eminently capable of generating large, high-quality data sets for non-model organisms. This has positive implications for future studies of the evolutionary, behavioural and conservation genetics of natural populations.

Bayesian inference of a historical bottleneck in a heavily exploited marine mammal

Emerging Bayesian analytical approaches offer increasingly sophisticated means of reconstructing historical population dynamics from genetic data, but have been little applied to scenarios involving demographic bottlenecks. Consequently, we analysed a large mitochondrial and microsatellite dataset from the Antarctic fur seal Arctocephalus gazella, a species subjected to one of the most extreme examples of uncontrolled exploitation in history when it was reduced to the brink of extinction by the sealing industry during the late eighteenth and nineteenth centuries. Classical bottleneck tests, which exploit the fact that rare alleles are rapidly lost during demographic reduction, yielded ambiguous results. In contrast, a strong signal of recent demographic decline was detected using both Bayesian skyline plots and Approximate Bayesian Computation, the latter also allowing derivation of posterior parameter estimates that were remarkably consistent with historical observations. This was achieved using only contemporary samples, further emphasizing the potential of Bayesian approaches to address important problems in conservation and evolutionary biology.

Geographic variation of the major histocompatibility complex in Eastern Atlantic grey seals (Halichoerus grypus)

Pathogen-driven balancing selection maintains high genetic diversity in many vertebrates, particularly in the major histocompatibility complex (MHC) immune system gene family, which is often associated with disease susceptibility. In large natural populations where subpopulations face different pathogen pressures, the MHC should show greater genetic differentiation within a species than neutral markers. We examined genetic diversity at the MHC-DQB locus and nine putatively neutral microsatellite markers in grey seals (Halichoerus grypus) from eight United Kingdom (UK) colonies, the Faeroe Islands and Sable Island, Canada. Five DQB alleles were identified in grey seals, which varied in prevalence across the grey seal range. Among the seal colonies, significant differences in DQB allele and haplotype frequencies and in average DQB heterozygosity were observed. Additionally, the DQB gene exhibited greater differentiation among colonies compared with neutral markers, yet a weaker pattern of isolation by distance (IBD). After correcting for the underlying IBD pattern, subpopulations breeding in similar habitats were more similar to one another in DQB allele frequencies than populations breeding in different habitats, but the same did not hold true for microsatellites, suggesting that habitat-specific pathogen pressure influences MHC evolution. Overall, the data are consistent with selection at MHC-DQB loci in grey seals with both varying selective pressures and geographic population structure appearing to influence the DQB genetic composition of breeding colonies.

Candidate genes versus genome-wide associations: which are better for detecting genetic susceptibility to infectious disease?

Technological developments allow increasing numbers of markers to be deployed in case-control studies searching for genetic factors that influence disease susceptibility. However, with vast numbers of markers, true 'hits' may become lost in a sea of false positives. This problem may be particularly acute for infectious diseases, where the control group may contain unexposed individuals with susceptible genotypes. To explore this effect, we used a series of stochastic simulations to model a scenario based loosely on bovine tuberculosis. We find that a candidate gene approach tends to have greater statistical power than studies that use large numbers of single nucleotide polymorphisms (SNPs) in genome-wide association tests, almost regardless of the number of SNPs deployed. Both approaches struggle to detect genetic effects when these are either weak or if an appreciable proportion of individuals are unexposed to the disease when modest sample sizes (250 each of cases and controls) are used, but these issues are largely mitigated if sample sizes can be increased to 2000 or more of each class. We conclude that the power of any genotype-phenotype association test will be improved if the sampling strategy takes account of exposure heterogeneity, though this is not necessarily easy to do.

Evidence that two main bottleneck events shaped modern human genetic diversity

There is a strong consensus that modern humans originated in Africa and moved out to colonize the world approximately 50 000 years ago. During the process of expansion, variability was lost, creating a linear gradient of decreasing diversity with increasing distance from Africa. However, the exact way in which this loss occurred remains somewhat unclear: did it involve one, a few or a continuous series of population bottlenecks? We addressed this by analysing a large published dataset of 783 microsatellite loci genotyped in 53 worldwide populations, using the program 'Bottleneck'. Immediately following a sharp population decline, rare alleles are lost faster than heterozygosity, creating a transient excess of heterozygosity relative to allele number, a feature that is used by Bottleneck to infer historical events. We find evidence of two primary events, one 'out of Africa' and one placed around the Bering Strait, where an ancient land bridge allowed passage into the Americas. These findings agree well with the regions of the world where the largest founder events might have been expected, but contrast with the apparently smooth gradient of variability that is revealed when current heterozygosity is plotted against distance from Africa.

Pinniped phylogenetic relationships inferred using AFLP markers

Amplified fragment length polymorphisms (AFLPs) are widely used for phylogenetic reconstruction in plants but their use in animal taxa has been limited, and in mammals rare. In addition, their use has been largely limited to shallow relationships amongst species or subspecies. Here, we genotype 23 pinniped species for 310 AFLP markers and find a strong phylogenetic signal, with individuals coclustering within species, and overall a good agreement between our phylogeny and those constructed using mitochondrial DNA and nuclear sequences even at nodes approximately 15 million years old. Although supporting the existing ideas about pinniped relationships, our data shed light on relationships within the hitherto relatively unresolved Phocine species group, and provide further supporting evidence for raising two subspecies of Zalophus californianus, Z. c. californianus and Z. c. wollebaeki, to species level. Plotting AFLP divergence time estimates against those based on both mtDNA and nuclear sequences we find strong linear relationships, suggesting that the different markers are evolving in a clocklike fashion. These data further emphasize the utility of AFLP markers as general tools for phylogenetic reconstruction.

Cardiac Mechanics Revisited

The keynote to understanding cardiac function is recognizing the underlying architecture responsible for the contractile mechanisms that produce the narrowing, shortening, lengthening, widening, and twisting disclosed by echocardiographic and magnetic resonance technology. Despite background knowledge of a spiral clockwise and counterclockwise arrangement of muscle fibers, issues about the exact architecture, interrelationships, and function of the different sets of muscle fibers remain to be resolved. This report (1) details observed patterns of cardiac dynamic directional and twisting motions via multiple imaging sources; (2) summarizes the deficiencies of correlations between ventricular function and known ventricular muscle architecture; (3) correlates known cardiac motions with the functional anatomy within the helical ventricular myocardial band; and (4) defines an innovative muscular systolic mechanism that challenges the previously described concept of “isovolumic relaxation.” This new knowledge may open new doors to treating heart failure due to diastolic dysfunction.

Female fur seals show active choice for males that are heterozygous and unrelated

Much debate surrounds the exact rules that influence mating behaviour, and in particular the selective forces that explain the evolution of female preferences. A key example is the lek paradox, in which female choice is expected rapidly to become ineffective owing to loss of additive genetic variability for the preferred traits. Here we exploit a remarkable system in which female fur seals exert choice by moving across a crowded breeding colony to visit largely static males. We show that females move further to maximize the balance between male high multilocus heterozygosity and low relatedness. Such a system shows that female choice can be important even in a strongly polygynous species, and at the same time may help to resolve the lek paradox because heterozygosity has low heritability and inbreeding avoidance means there is no single 'best' male for all females.

Genetic tagging reveals extreme site fidelity in territorial male Antarctic fur seals Arctocephalus gazella

Genetic tagging, the identification of individuals using their genotypes, provides a powerful tool for studying animals that are difficult to observe or identify using conventional techniques. However, despite being widely adopted by conservation biologists, the full potential of this approach has yet to be realized. Here we used genetic recapture data to quantify male site fidelity at a colony of Antarctic fur seals where an aerial walkway provides unprecedented access and individual positions are determined daily to 1 m accuracy. Because males are too large and aggressive to be captured and fitted with conventional tags, we remotely collected 770 tissue samples over eight consecutive seasons and used nine-locus microsatellite genotypes to reveal 306 genetic recaptures among 464 unique individuals. Within seasons, males are highly site-faithful, with any movements that occur tending to take place before the period when females come into oestrus. Of those males that return to breed over successive seasons, almost half return to within a body length of where they were before. The discovery of such extreme site faithfulness has implications for the population structure and mating system of fur seals and potentially other colonially breeding species.

Dispersal, philopatry and intergroup relatedness: fine-scale genetic structure in the white-breasted thrasher, Ramphocinclus brachyurus

Dispersal is a fundamental process influencing evolution, social behaviour, and the long-term persistence of populations. We use both observational and genetic data to investigate dispersal, kin-clustering and intergroup relatedness in the white-breasted thrasher, Ramphocinclus brachyurus, a cooperatively breeding bird that is globally endangered. Mark-resighting data suggested sex-biased dispersal, with females dispersing over greater distances while males remained philopatric. Accordingly, spatial autocorrelation analysis showed highly significant fine-scale genetic structure among males, but not among females. This fine-scale genetic structuring of the male population resulted in very high levels of relatedness between dominant males at neighbouring nests, similar to that seen within cooperative groups in many species where kin selection is cited as a cause of cooperation. By implication, between-group as well as within-group cooperation may be important, potentially creating a feedback loop in which short-distance dispersal by males leads to the formation of male kin clusters that in turn facilitate nepotistic interactions and favour further local recruitment. The strength of spatial autocorrelation, as measured by the autocorrelation coefficient, r, was approximately two to three times greater than that reported in previous studies of animals. Relatively short dispersal distances by both males and females may have a negative impact on the white-breasted thrasher's ability to colonize new areas, and may influence the long-term persistence of isolated populations. This should be taken into account when designating protected areas or selecting sites for habitat restoration.

No relationship between microsatellite variation and neonatal fitness in Antarctic fur seals, Arctocephalus gazella

Published studies of wild vertebrate populations have almost universally reported positive associations between genetic variation measured at microsatellite loci and fitness, creating the impression of ubiquity both in terms of the species and the traits involved. However, there is concern that this picture may be misleading because negative results frequently go unpublished. Here, we analyse the relationship between genotypic variation at nine highly variable microsatellite loci and neonatal fitness in 1070 Antarctic fur seal pups born at Bird Island, South Georgia. Despite our relatively large sample size, we find no significant association between three different measures of heterozygosity and two fitness traits, birth weight and survival. Furthermore, increasing genetic resolution by calculating parental relatedness also yields no association between genetic variation and fitness. Our findings are consistent with necropsy data showing that most pups die from starvation or trauma, conditions that are unlikely to be influenced strongly by genetic factors, particularly if the benefits of high heterozygosity are linked to immune-related genes.

Deep genetic subdivision within a continuously distributed and highly vagile marine mammal, the Steller's sea lion (Eumetopias jubatus)

The Steller's sea lion Eumetopias jubatus is an endangered marine mammal that has experienced dramatic population declines over much of its range during the past five decades. Studies using mitochondrial DNA (mtDNA) have shown that an apparently continuous population includes a strong division, yielding two discrete stocks, western and eastern. Based on a weaker split within the western stock, a third Asian stock has also been defined. While these findings indicate strong female philopatry, a recent study using nuclear microsatellite markers found little evidence of any genetic structure, implying extensive paternal gene flow. However, this result was at odds with mark-recapture data, and both sample sizes and genetic resolution were limited. To address these concerns, we increased analytical power by genotyping over 700 individuals from across the species' range at 13 highly polymorphic microsatellite loci. We found a clear phylogenetic break between populations of the eastern stock and those of the western and Asian stocks. However, our data provide little support for the classification of a separate Asian stock. Our findings show that mtDNA structuring is not due simply to female philopatry, but instead reflects a genuine discontinuity within the range, with implications for both the phylogeography and conservation of this important marine mammal.

Microsatellite genotyping errors: detection approaches, common sources and consequences for paternal exclusion

Microsatellite genotyping errors will be present in all but the smallest data sets and have the potential to undermine the conclusions of most downstream analyses. Despite this, little rigorous effort has been made to quantify the size of the problem and to identify the commonest sources of error. Here, we use a large data set comprising almost 2000 Antarctic fur seals Arctocephalus gazella genotyped at nine hypervariable microsatellite loci to explore error detection methods, common sources of error and the consequences of errors on paternal exclusion. We found good concordance among a range of contrasting approaches to error-rate estimation, our range being 0.0013 to 0.0074 per single locus PCR (polymerase chain reaction). The best approach probably involves blind repeat-genotyping, but this is also the most labour-intensive. We show that several other approaches are also effective at detecting errors, although the most convenient alternative, namely mother-offspring comparisons, yielded the lowest estimate of the error rate. In total, we found 75 errors, emphasizing their ubiquitous presence. The most common errors involved the misinterpretation of allele banding patterns (n = 60, 80%) and of these, over a third (n = 22, 36.7%) were due to confusion between homozygote and adjacent allele heterozygote genotypes. A specific test for whether a data set contains the expected number of adjacent allele heterozygotes could provide a useful tool with which workers can assess the likely size of the problem. Error rates are also positively correlated with both locus polymorphism and product size, again indicating aspects where extra effort at error reduction should be directed. Finally, we conducted simulations to explore the potential impact of genotyping errors on paternity exclusion. Error rates as low as 0.01 per allele resulted in a rate of false paternity exclusion exceeding 20%. Errors also led to reduced estimates of male reproductive skew and increases in the numbers of pups that matched more than one candidate male. Because even modest error rates can be strongly influential, we recommend that error rates should be routinely published and that researchers make an attempt to calculate how robust their analyses are to errors.

The structure and function of the helical heart and its buttress wrapping. VII. Critical importance of septum for right ventricular function

The macroscopic structure of the right ventricle includes a transverse basal loop for the free wall, and oblique septal components, originating from the descending and ascending segments of the apical loop. Data is presented that determines why right ventricular function is related principally to intraventricular septal function, and why right ventricular failure is magnified by septal stunning caused by poor myocardial protection. The background of this architectural/functional change can explain normal right ventricular function, the relationship of right ventricular performance to pulmonary vascular resistance, experimental studies that characterize right ventricular performance after architectural free wall ablation, right ventricular disconnection, right coronary occlusion, and free wall replacement. These basic science studies are related to perioperative right ventricular performance, involving methods of myocardial protection, protamine reaction, right coronary occlusion and reperfusion, right ventricular dyskinesia, chronic aortic and mitral valve replacement (MVR) replacement, congenital heart disease, right and left ventricular assist devices (LVADs), and transplantation. The predominant focus is related to the septum and how it can be evaluated perioperatively. Septal evaluation by echocardiogram should become an essential feature during intraoperative management.

Exercise-Induced Hyperemia Unmasks Regional Blood Flow Deficit in Experimental Hindlimb Ischemia

Many experimental models of hindlimb ischemia are characterized by spontaneous and rapid normalization of resting muscle blood flow (BF) rates which complicates the long-term evaluation of angiogenic therapies to reverse limb ischemia. We tested the hypothesis that peroneal nerve stimulation in an ischemic hindlimb would increase the oxygen (O(2)) demand and BF rate, thereby unmasking a severe blood flow deficit that is not apparent at rest.

METHODS

Ischemia was induced in adult rats by ligation of the left common iliac, femoral arteries, and their branches. Peroneal nerves were stimulated to allow measurement of exercise-induced regional BF rates with fluorescent microspheres. Hemodynamics were monitored. Fluorescent microspheres were injected before and after 5 min of nerve stimulation 3, 10, and 24 days postischemia. The tibialis anterior (TA) and gastrocnemius (GC) muscles and skin were harvested and weighed, and fluorescence was measured. BF rate was calculated as milliters per minute per gram of tissue and compared to normal muscle and skin of unoperated control rats. In order to determine the accuracy of BF rate measurements in ischemic muscle when <400 microspheres was delivered per specimen, 3 rats were studied by simultaneous injection of 4 x 10(5) blue and 1 x 10(5) yellow-green fluorescent microspheres. The correlation coefficient between the number of different colored microspheres delivered was measured.

RESULTS

The ischemia caused atrophy of the TA and GC muscles. The mean muscle mass of the ischemic TA and GC as a percentage of total body weight decreased over time vs control [TA 0.13 +/- 0.05% vs 0.25 +/- 0.03%, P < 0.05; GC 0.51 +/- 0.27% vs 0.70 +/- 0.07%, P = 0.07 at 24 days (24D)]. Despite clinical evidence of severe hindlimb ischemia in experimental groups, i.e., pressure sores, muscle atrophy, and weakness, resting BF rates were not significantly different from those of control. The BF rate of the TA was of 0.11 ml/min/g after 3D of ischemia, 0.14 ml/min/g after 10D, and 0.13 ml/min/g after 24D. The mean BF rate in normal muscle of unoperated controls was 0.16 ml/min/g (P > 0.05). However, the exercise-induced hyperemia in the skeletal muscle was significantly blunted in all of the ischemic groups. The unoperated control TA had a greater than 10-fold increase in BF to 1.95 ml/min/g in response to exercise while the ischemic TA had no increase in BF at 3D, 2-fold increase at 10D, and a 5-fold increase at 24D. Parallel findings were noted in the GC muscles. There was no significant difference in the BF rate in the skin. The accuracy of this microsphere technique in measuring very low BF rates found in ischemic muscle was supported by the significant correlation coefficient (r = 0.99) comparing two quantities of microspheres injected simultaneously.

CONCLUSION

Despite clinical signs of severe hindlimb ischemia, resting BF rates in the ischemic groups were not significantly decreased. Peroneal nerve stimulation resulted in up to 10-fold increase in BF rate and unmasked a severe deficit in vascular reserve in the ischemic groups. Resting BF rate is not always an accurate reflection of the flow deficit in models of critical limb ischemia, and this model of exercise-induced hindlimb hyperemia may allow better long-term evaluation of angiogenic therapies designed to reverse critical limb ischemia.

Population genetics of the schistosome intermediate host Biomphalaria pfeifferi in the Zimbabwean highveld: implications for co-evolutionary theory

Co-evolutionary theory proposes that polymorphisms in co-evolved traits may be maintained through differential selection in spatially heterogeneous environments. Spatial heterogeneity of the schistosome intermediate host, Biomphalaria pfeifferi, was investigated here, using RAPD markers. Overall, 256 individuals, collected at 32 sites on 13 rivers in the Chiweshe region of Zimbabwe, were analysed. Significant genetic differentiation was demonstrated, both between populations from the different rivers and between populations collected at different sites on each of several of the rivers investigated. However, the presence of spatial differentiation between populations from individual rivers varied with river type. It was not apparent in permanent, deep, fast-flowing rivers, where high levels of migration, through passive dispersal along the rivers, are likely. The snails collected from shallow, semi-permanent rivers not only showed relatively high levels of population subdivision but also high levels of within-site genetic diversity, consistent with the existence of 'co-evolutionary hot-spots' where schistosome infection may be prevalent. These results are discussed with reference to the population biology of B. pfeifferi and to host-parasite co-evolution.

Evaluation of fetal heart dimensions from 12 weeks to term

To evaluate whether fetal cardiac measurements can be made in the second trimester, we examined a cohort of normal pregnancies between 12 and 18 weeks' gestation using state-of-the-art ultrasound equipment. We examined this population longitudinally at intervals of 2 weeks, as well as at 32 weeks' gestation. From the 4-chamber view we measured the ventricular and atrial cavity dimensions, the thickness of the ventricular walls and septum at end-diastole, and the annulus dimensions of the mitral and tricuspid valves. Using a variety of views we also measured the long and cross-sectional diameters of the atria, the aorta, the pulmonary artery and its main left and right branches, the ductus arteriosus, and the superior and inferior vena cavae. To test the frequency with which measurements could be made, we divided them into measurements that were clear and easy to define (statistically good), to those that were unclear (statistically bad), or those that were not measured at all (none). Data were then analyzed by regression analysis, analysis of variance, and covariance. The frequency of reliable measurements varied inversely with gestational age. The inflection point for measurements was approximately at 16 weeks. Data from this longitudinal study were evaluated against those obtained from our previous study. Because no statistical differences were found in measurements between these studies where they overlapped, the data were pooled into 1 large group and the mean and SEEs calculated for all variables. Our study demonstrates that with current transabdominal imaging, fetal cardiac measurements can be made reliably in normal fetuses from 16 weeks' gestation onward. The frequency of obtaining data in younger normal fetuses suggests it is unlikely that reliable observations can be made routinely in abnormal fetuses < 16 weeks old, although this might be possible in individual fetuses.

Effects of increased pressure inside or outside ventricles on total and regional myocardial blood flow

Increasing pressures to 30 mmHg in right (RV) and left (LV) ventricles and surrounding heart (SH) in isolated, arrested, maximally vasodilated, blood-perfused dog hearts shifted pressure-flow (PF) curves rightward and increased zero flow pressure (P(zf)) by an amount equal to the RV applied pressure, SH applied pressure, or two-thirds of the LV applied pressure. There were comparable increases in coronary venous pressures. Increasing LV or SH pressures decreased coronary blood flows, especially in the subendocardium. Decreases in driving pressure decreased flows in all layers, but even with driving pressure of 5 mmHg, a few subepicardial pieces had flow. We conclude with the following: 1) raising pressures inside or outside the heart shifts PF curves and raises P(zf) by increasing coronary venous pressure; 2) the effects are most prominent in the subendocardial muscle layer; and 3) as driving pressures are decreased, there is a range of P(zf) in the heart with the final P(zf) recorded due to the last little piece of muscle to be perfused.

Problems of coronary flow reserve

Coronary flow reserve is used to aid understanding why myocardial oxygen consumption may fail to meet demand. Its general aspects are well known, but the problems of using it are not. This manuscript describes three important factors that need to be considered when assessing coronary flow reserve. (1) Maximal flow is usually achieved by giving either increasing doses or else what is thought to be a maximal dose of a vasodilator, or by examining peak reactive hyperemia. Evidence that both these approaches are flawed is provided. (2) Existing methods in humans allow only total reserve to be determined, but this might be inadequate because changes in total reserve might not reflect changes in subendocardial flow reserve. (3) Because there is marked heterogeneity of flow reserve in the left ventricle, measuring total flow reserve does not indicate when small regions are becoming ischemic. More basic research is needed to overcome these difficulties.

The Mitral Regurgitation Index: an echocardiographic guide to severity

OBJECTIVES

The purpose of this study was to develop a semiquantitative index of mitral regurgitation severity suitable for use in daily clinical practice and research.

BACKGROUND

There is no simple method for quantification of mitral regurgitation (MR). The MR Index is a semiquantitative guide to MR severity. The MR Index is a composite of six echocardiographic variables: color Doppler regurgitant jet penetration and proximal isovelocity surface area, continuous wave Doppler characteristics of the regurgitant jet and tricuspid regurgitant jet-derived pulmonary artery pressure, pulse wave Doppler pulmonary venous flow pattern and two-dimensional echocardiographic estimation of left atrial size.

METHODS

Consecutive patients (n = 103) with varying grades of MR, seen in the Adult Echocardiography Laboratory at UCSF, were analyzed retrospectively. All patients were evaluated for the six variables, each variable being scored on a four point scale from 0 to 3. The reference standards for MR were qualitative echocardiographic evaluation by an expert and quantitation of regurgitant fraction using two-dimensional and Doppler echocardiography. A subgroup of patients with low ejection fraction (EF < 50%) were also analyzed.

RESULTS

The MR Index increased in proportion to MR severity with a significant difference among the three grades in both normal and low EF groups (F = 130 and F = 42, respectively, p < 0.0001). The MR Index correlated with regurgitant fraction (r = 0.76, p < 0.0001). An MR Index > or =2.2 identified 26/29 patients with severe MR (sensitivity = 90%, specificity = 88%, PPV = 79%). No patient with severe MR had an MR Index <1.8 and no patient with mild MR had an MR Index >1.7.

CONCLUSIONS

The MR Index is a simple semiquantitative estimate of MR severity, which seems to be useful in evaluating MR in patients with a low EF.

Extensive genetic variation revealed in adjacent populations of the schistosome intermediate host Biomphalaria pfeifferi from a single river system

Random amplified polymorphic DNA (RAPD) analysis was used to study genetic variation among schistosome hosts of the species Biomphalaria pfeifferi. The analysed snails came from 15 sites along a 6-km stretch of a Zimbabwean river, providing data on genetic-geographical relationships over, probably, the smallest scale yet studied for any snail intermediate host species. Only 6% of the DNA fragments were common to all snails, and snail populations as geographically close as 100 m were genetically distinct. The most genetically polymorphic snail populations were those collected within and downstream from human water-contact sites.

Echocardiographic hemodynamic and morphometric predictors of survival after two-ventricle repair in infants with critical aortic stenosis

OBJECTIVES

The purpose of this study was to identify echocardiographic hemodynamic and morphometric factors that would predict which infants with critical aortic stenosis could undergo relief of left ventricular outflow obstruction as opposed to the Norwood procedure.

BACKGROUND

Echocardiographic predictors of survival in infants with critical aortic stenosis after two-ventricle repair have been mainly limited to morphometric factors, which have limitations. Echocardiographic hemodynamic predictors of survival in these patients have not previously been studied.

METHODS

Doppler color flow mapping and pulsed Doppler techniques were used to obtain hemodynamic measurements of flow in the ascending, transverse and descending aorta, the ductus arteriosus, and across the aortic and mitral valves in infants with critical aortic stenosis. Morphometric measurements of the left heart structures were obtained, and comparisons were made between survivors and nonsurvivors for the hemodynamic and morphometric factors.

RESULTS

Twenty-eight infants (mean age 1 +/- .6 days, mean weight 3.6 +/- .6 kg) with critical aortic stenosis were evaluated. Nineteen had a two-ventricle repair initially attempted, and nine had a Norwood operation. Among the patients with a two-ventricle repair, the hemodynamic factors associated with survival after two-ventricle repair included predominant or total antegrade flow in the ascending (p < 0.01) and transverse aorta (p < 0.05). Aortic valve gradient, mitral valve inflow and direction of flow in the ductus arteriosus and descending aorta were unrelated to outcome. The morphometric factors associated with survival after two-ventricle repair included the indexed aortic annulus (p < 0.0002), aortic root (p < 0.003), ascending aorta (p < 0.008) and left ventricular long-axis length (p < 0.01). Left ventricular volume, mass, ejection fraction and mitral valve area were not related to outcome after two-ventricle repair.

CONCLUSIONS

In infants with critical aortic stenosis, predominant or total antegrade flow in the ascending and transverse aorta was associated with survival after two-ventricle repair. Determination of a one- versus two-ventricle repair remains a complex issue in infants with critical aortic stenosis. In addition to established morphometric predictors, hemodynamic information on the direction of flow in the aorta may help to define candidates for the Norwood operation.

Fetal diaphragmatic hernia: echocardiography and clinical outcome

It is difficult to predict survival of fetuses diagnosed prenatally with congenital diaphragmatic hernia. Some studies suggest that left heart underdevelopment is associated with poor outcome, but fetal echocardiographic variables have not been conclusively proven to be good predictors of postnatal survival. The authors reviewed detailed fetal echocardiographic studies in twelve fetuses with congenital diaphragmatic hernia. Ten echocardiographic variables, including left and right ventricular width, left ventricular volume, and left ventricular mass, were examined from a four-chamber view, corrected for gestational age, and compared with normal data. The results of this study showed no significant differences between survivors and nonsurvivors in the ten variables analyzed. Although left heart dimensions and left ventricular volume in fetuses with congenital diaphragmatic hernia were below the expected normal range, these results did not predict postnatal outcome.

Determination of ventricular volumes in human fetal hearts by two-dimensional echocardiography

In conclusion, ventricular volume calculation from 2DE is feasible in the human fetus and improves the ability to calculate fetal ventricular size and ejection fraction. The right ventricle is clearly dominant at midgestation, but approaches left ventricular size at term. Calculation of the ventricular output from 2DE volume measurements is an accurate alternative to Doppler measurements.

Changes in contractility and afterload have only slight effects on subendocardial systolic flow impediment

To test the hypothesis that contractility did not greatly influence systolic impediment to subendocardial flow we perfused the coronary artery at 70 mmHg and altered aortic pressure in 7 dogs and contractility in another 7. We measured myocardial systolic flow impediment (SFI) by comparing regional flows while beating and during asystole. Cardiac contraction impeded 29% of subendocardial asystolic flow, which was not affected by either intervention. In subepicardium, contraction increased flow by 25%, but dobutamine impeded systolic flow. Subepicardial SFI was only 16% of subendocardial SFI. Dobutamine slightly decreased estimated percent systolic myocardial blood flow (%SMBF) in subendocardium (+/- 12%) but decreased subepicardial %SMBF (45.5 to 17.4%). Phasic coronary flow pulsatility increased more with dobutamine than increased afterload, and pulsatility and SFI correlated only in subepicardium. Systolic-to-total coronary flow ratio and %SMBF did not correlate closely in subendocardium. SFI was most prominent in the subendocardium, whereas subepicardial SFI mainly determined epicardial coronary flow pulsatility. We conclude that the effects of contractility changes differ when evaluating regional SFI vs. phasic flow pulsatility.

Effects of inhibiting neutral endopeptidase and kininase II on coronary and systemic hemodynamics in rats

To determine whether neutral endopeptidase (NEP) and kininase II (angiotensin-converting enzyme, ACE) influence coronary hemodynamics, we compared the effects of inhibiting NEP, ACE, or both before and after isoproterenol (50 mg/kg ip). We measured flow and resistance using radioactive microspheres in 90 anesthetized rats which received the NEP inhibitor phosphoramidon (2.5 mg/kg), the ACE inhibitor captopril (2.5 mg/kg), both combined, or vehicle alone. Before isoproterenol, inhibiting NEP, ACE, or both increased left ventricular blood flow by 48 +/- 10 (SE), 33 +/- 9, and 10 +/- 6%, respectively, and decreased left ventricular vascular resistance by 26 +/- 6, 31 +/- 10, and 10 +/- 6%, respectively. After isoproterenol, NEP inhibition augmented the decrease in left ventricular vascular resistance (25 +/- 6% decrease within 90 s of isoproterenol vs. 8 +/- 5% in controls). ACE inhibition did not augment the decrease in resistance but inhibiting both enzymes did so to a lesser extent than inhibiting NEP. These effects cannot be explained by vascular responses secondary to changes of myocardial oxygen consumption. We conclude that NEP and ACE are regulators of myocardial blood flow.

Incidence of congenital heart disease: II. Prenatal incidence

The incidence of congenital heart disease appears to be about 1 per 100 liveborn infants. In infants who die before term, however, there is a much higher incidence of congenital heart disease, with a tendency for an excess of complex lesions. Some but not all of these lesions are associated with gross chromosomal abnormalities, which occur frequently in first-trimester abortions. Most of these chromosomal abnormalities are associated with such maldevelopment of many organ systems that fetal death occurs in utero. Monosomy X (45, XO), has a high association with congenital heart disease. Most fetuses with this abnormality die in utero, but because the abnormality is not inevitably lethal a small increase in survival of these fetuses would cause a large increase in the total incidence of congenital heart disease.

Incidence of congenital heart disease: I. Postnatal incidence

The incidence of congenital heart disease (CHD) in the Western industrialized world has varied from a low value of about 3 to 5 per 1000 live births to about 12 per 1000 live births. Most of the lower incidence figures were obtained before there were sufficiently well trained pediatric cardiologists and before the success of cardiac surgery put a premium on early and correct diagnosis of CHD. The advent of echocardiography with Doppler color flow measurements has made it possible to diagnose lesions that are asymptomatic, minor, and even without murmurs. Given these differences, there does not appear to have been a significant increase in the incidence of CHD over the last 20-30 years. The incidence of CHD in underdeveloped countries is not known, but the distribution of different lesions is fairly similar to those in developed countries except perhaps for fewer with aortic stenosis and coarctation of the aorta.

Heterogeneity of myocardial blood flow

Myocardial blood flow is heterogeneous, whether considered by chamber, by layers of the ventricular walls, or by microregions within layers. There is also variability of myocardial flow reserve, particularly in layers and microregions, even when the heart is arrested. The variability of flow during arrest may be associated with the resistance pathways to each region, but the variability of flows in the beating heart with vascular tone is probably due to regional differences in work and thus oxygen demand. Heterogeneity by layer may be responsible for the subendocardial ischemia that is common to many forms of heart disease. Microheterogeneity may account for the patchy necrosis that occurs with chronic ischemia.