Conclusive evidence for panmixia in the American eel

Eels are unique species in the biological world. The two North Atlantic eel species, the American eel (Anguilla rostrata) and the European eel (A. anguilla), occupy a broad range of habitats from the Caribbean to Greenland in the western Atlantic and from Morocco to Iceland in the eastern Atlantic, respectively. North Atlantic eels have a catadromous life cycle, spawning only in the Sargasso Sea and spending the majority of their lives in continental (fresh, brackish and coastal) waters. Despite such a wide distribution range, North Atlantic eels have been regarded as a textbook example of panmictic species. In contrast with the large amount of population genetic studies testing the panmixia hypothesis in the European eel, a relatively modest effort has been given to study the population structure of the American eel. In this issue of Molecular Ecology, Côté et al. ( 2013 ) present the most comprehensive American eel data set to date, which includes samples of different life stages obtained throughout all its distribution range in North America. Results show a total lack of genetic differentiation among samples and provide decisive evidence for panmixia in the American eel.     

Strong dominance of functional alleles over gene deletions in both intensely growing and deeply starved yeast cells

Previous studies with diploid yeast have shown that the deletion of one allele at a single locus typically has little impact on fitness under conditions promoting fast growth. Here, we confirm and quantify this finding. The strong dominance of functional over nonfunctional alleles is predicted by the metabolic control theory which assumes that the cell is a system of metabolic fluxes and that the total metabolic rate is equivalent to fitness. To test whether these requirements are critical, we tested dominance under conditions of long‐term starvation when metabolism is low and thus the metabolic activities of proteins are likely inadequate or imbalanced. More fundamentally, the central assumption of the model, that high metabolic rate translates into high fitness, appears implausible. Contrary to these conjectures, we found that the mean rate of survival of starving heterozygotes was affected only slightly more than was the mean rate of growth under good conditions. Under none of the two treatments the central prediction of the model, that fitness of heterozygous strains is higher for the enzymatic proteins than for nonenzymatic ones, was confirmed. Our data add to growing uncertainty whether the metabolic control theory is sufficient to explain the remarkable ubiquity of strong genetic dominance.     

TECHNICAL ADVANCES: A maximum-likelihood relatedness estimator allowing for negative relatedness values

Previously reported maximum-likelihood pairwise relatedness (r) estimator of Thompson and Milligan (M) was extended to allow for negative r estimates under the regression interpretation of r. This was achieved by establishing the equivalency of the likelihoods used in the kinship program and the likelihoods of Thompson. The new maximum-likelihood (ML) estimator was evaluated by Monte Carlo simulations. It was found that the new ML estimator became unbiased significantly faster compared to the original M estimator when the amount of genotype information was increased. The effects of allele frequency estimation errors on the new and existing relatedness estimators were also considered.     

Effects of dietary crude protein on fertility: Meta-analysis and meta-regression

Studies used to evaluate effects of dietary intervention on fertility may be subject to confounding because modification of one nutritional input requires a change in at least one other input. Meta-analytical modeling allows examination of a main intervention for a series of studies, but also an examination of a series of related effects through use of meta-regression. Effects of dietary crude protein (CP) on fertility were examined using this approach. We obtained 21 studies containing 32 comparisons that had pregnancy or conception data and met the eligibility criteria for meta-analysis of randomized controlled experiments providing information on diets used. Publications that contained data on prospective, randomized controlled experiments examining effects of dietary CP, either concentrations or degradability, or effects of a specific feed ingredient intervention on fertility were identified. Details on dietary formulation and diet intake were extracted from the publications, as were measures of urea in blood or plasma. Estimated fixed and random effects relative risks showed that risk of conception was lower in cows fed higher CP or more degradable CP diets (fixed effect (Mantel-Haenszel Relative Risk) = 0.91 (95% CI 0.84-0.98); P=0.019). This effect was homogenous (I² = 0) and not influenced by difference in blood urea N, duration of intervention, breed, parity, milk production or type of diet delivery. Significant associations among CP components of the diet and carbohydrate fractions supported the hypothesized potential for confounding, but only the amount of soluble CP eaten was a significant meta-regression covariate that reduced risk of conception. There was no evidence that the significant reduction in fiber or non-fiber carbohydrate (NFC) fractions of the diets associated with increased concentration of CP, soluble CP or rumen degradable fractions or soyabean products content of the diet influenced conception rates. Results support findings of experiments showing that increased intake of soluble CP reduced conception rates, and provides strong evidence that increased concentrations of CP or increased degradability of CP, within the ranges evaluated in the studies contributing to this meta-analysis, reduce the risk of conception in lactating dairy cattle.     

Short Communication: Analysis of effective light in different photobioreactors: its influence on growth,photosynthetic activity and glycerol production by the freshwater green alga Chlamydomonas reinhardtii

The unicellular green alga Chlamydomonas reinhardtii synthesizes glycerol as an osmoregulatory metabolite when exposed to high saline concentrations (200 mM NaCl). Response to osmotic stress can be used for biotechnological production of this compound. When synthesis of a substance is linked to photosynthetic capacity and consequently to effective light, the production on a large scale makes an efficient utilization of light necessary. In the present work a model for evaluation of effective light has been tested.     

Genetic relationships among Chinese pigs and other pig populations from Hunan Province, China

In this study, protein-level polymorphisms of transferrin, pre-albumin, hemopexin, ceruloplasmin and amylase were investigated in Hunan native pigs and Large Yorkshire pigs collected from Hunan (a province of China), allowing calculations of allele frequencies, average heterozygosities, inbreeding coefficients and genetic distances. The genetic relationship between Southeast Asian native pigs and American pigs was more distant than those among Southeast Asian native pig breeds. The genetic relationship between Southeast Asian native pig breeds and Hampshire pigs was the most distant.     

Spatial genetic patterns generated by two admixing genetic lineages: a simulation study

Two formerly geographically separated lineages of the zebra mussel Dreissena polymorpha had been given the opportunity to mix extensively across the newly built German Main–Danube canal. We had monitored this admixture of mussel lineages and had described spatial patterns in different genetic measures [Müller et al. 2001 (Heredity, 86: 103); 2002 (Proc. R. Soc. Lond., 269: 1139)]. Here, we present an individual-based model to assess the potential of spatial genetic patterns of detecting and quantifying admixture of mussel lineages. Genetic measures studied are (1) allele frequencies, (2) deviations from Hardy–Weinberg expectations of loci (deficit of heterozygotes, HWD) and (3) linkage disequilibria between unlinked loci (LD). For allele frequencies, we observed a cline over the zone of admixture in all simulations of mixing mussel lineages suggesting that these are appropriate for verification of their mixture. The point of the first contact between lineages was always detectable from their intermediate allele frequencies. LD and HWD were only spatially informative for diagnostic loci or loci with very strong differences in allele frequencies of lineages. For such loci, the probability of disequilibria was highest where lineages had met and decreased towards both sources of lineages Main and Danube. The overall probability of detecting any disequilibrium was higher for LD than for HWD and increased with an increasing rate of genetic interchange. Our simulation results are corroborated by our zebra mussel data and studies from literature. They are applicable to any case of two known linearly mixing genetic lineages.     

Population structure and impact of supportive breeding inferred from mitochondrial and microsatellite DNA analyses in land-locked Atlantic salmon Salmo salar L.

Four tributaries of Lake St-Jean (Québec, Canada) are used for spawning and juvenile habitat by land-locked Atlantic salmon. Spawning runs have drastically declined since the mid-1980s, and consequently, a supportive-breeding programme was undertaken in 1990. In this study, we analysed seven microsatellite loci and mtDNA, and empirically estimated effective population sizes to test the hypotheses that (i) fish spawning in different tributaries form genetically distinct populations and (ii) the supportive breeding programme causes genetic perturbations on wild populations. Allele frequency distribution, molecular variance and genetic distance estimates all supported the hypothesis of genetic differentiation among salmon from different tributaries. Gene flow among some populations was much more restricted than previously reported for anadromous populations despite the small geographical scale (40 km) involved. Both mtDNA and microsatellites revealed a more pronounced differentiation between populations from two tributaries of a single river compared with their differentiation with a population from a neighbouring river. The comparison of wild and F₁-hatchery fish (produced from breeders originating from the same river) indicated significant changes in allele frequencies and losses of low-frequency alleles but no reduction in heterozygosity. Estimates of variance and inbreeding population size indicated that susceptibility to genetic drift and inbreeding in one population increased by twofold after only one generation of supplementation.