On the correlation between heterozygosity and fitness in natural populations

Three primary hypotheses currently prevail for correlations between heterozygosity at a set of molecular markers and fitness in natural populations. First, multilocus heterozygosity-fitness correlations might result from selection acting directly on the scored loci, such as at particular allozyme loci. Second, significant levels of linkage disequilibrium, as in recently bottlenecked-and-expanded populations, might cause associations between the markers and fitness loci in the local chromosomal vicinity. Third, in partially inbred populations, heterozygosity at the markers might reflect variation in the inbreeding coefficient and might associate with fitness as a result of effects of homozygosity at genome-wide distributed loci. Despite years of research, the relative importance of these hypotheses remains unclear. The screening of heterozygosity at polymorphic DNA markers offers an opportunity to resolve this issue, and relevant empirical studies have now emerged. We provide an account of the recent progress on the subject, and give suggestions on how to distinguish between the three hypotheses in future studies.     

Contrasting results from GWAS and QTL mapping on wing length in great reed warblers

A major goal in evolutionary biology is to understand the genetic basis of adaptive traits. In migratory birds, wing morphology is such a trait. Our previous work on the great reed warbler (Acrocephalus arundinaceus) shows that wing length is highly heritable and under sexually antagonistic selection. Moreover, a quantitative trait locus (QTL) mapping analysis detected a pronounced QTL for wing length on chromosome 2, suggesting that wing morphology is partly controlled by genes with large effects. Here, we re‐evaluate the genetic basis of wing length in great reed warblers using a genomewide association study (GWAS) approach based on restriction site‐associated DNA sequencing (RADseq) data. We use GWAS models that account for relatedness between individuals and include covariates (sex, age and tarsus length). The resulting association landscape was flat with no peaks on chromosome 2 or elsewhere, which is in line with expectations for polygenic traits. Analysis of the distribution of p‐values did not reveal biases, and the inflation factor was low. Effect sizes were however not uniformly distributed on some chromosomes, and the Z chromosome had weaker associations than autosomes. The level of linkage disequilibrium (LD) in the population decayed to background levels within c. 1 kbp. There could be several reasons to why our QTL study and GWAS gave contrasting results including differences in how associations are modelled (cosegregation in pedigree vs. LD associations), how covariates are accounted for in the models, type of marker used (multi‐ vs. biallelic), difference in power or a combination of these. Our study highlights that the genetic architecture even of highly heritable traits is difficult to characterize in wild populations.     

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.     

Composition and chromosomal localization of cetacean highly repetitive DNA with special reference to the blue whale,Balaenoptera musculus

Three highly repetitive DNA components — the common cetacean component, the heavy (GC-rich) satellite and the light (AT-rich) satellite — were studied in the blue whale. Consensus sequences of the common component and the heavy satellite were determined on the basis of three repeats of the common component and eight repeats of the heavy satellite. The tandemly organized common cetacean component, which comprises a large portion of all cetacean — both odontocete (toothed whale) and mysticete (whalebone whale) — genomes has a repeat length of 1,760 bp and the three clones analysed showed a high degree of conformity. The repeat contains a 72 bp sequence with dyad symmetry and striking intrastrand complementarity. The rest of the repeat comprises a unique sequence. The repeat unit of the heavy satellite of the blue whale is 422 bp. Also this component is tandemly organized. About half the length of the repeat constitutes a unique sequence and the other half is made up of subrepeats with TTAGGG as a frequent motif. The light satellite has not been sequenced and its basic repeat unit has not yet been identified. The chromosomal localization of the three components was determined by in situ hybridization using ³H-labelled cloned fragments as probes. The common cetacean component was located in most interstitial and terminal C-bands. The heavy satellite occurred primarily in terminal C-bands. When the two components hybridized to the same terminal C-bands, the localization of the heavy satellite was distal to that of the common cetacean component. Neither component shared localization with the light satellite which is located in centromeric C-bands in just a few chromosome pairs.     

Primary structure of the hemoglobin alpha-chain of rose-ringed parakeet (Psittacula krameri)

The structure of the hernoglobin -chain of Rose-ringed Parakeet was determined by sequence degradations of the intact subunit, the CNBr fragments, and peptides obtained by digestion with staphylococcal Glu-specific protease and trypsin. Using this analysis, the complete -chain structure of 21 avian species is known, permitting comparisons of the protein structure and of avian relationships. The structure exhibits differences from previously established avian -chains at a total of 61 positions, five of which have residues unique to those of the parakeet (Ser-12, Gly-65, Ser-67, Ala-121, and Leu-134). The analysis defines hemoglobin variation within an additional avian order (Psittaciformes), demonstrates distant patterns for evaluation of relationships within other avian orders, and lends support to taxonomic conclusions from molecular data.     

Effect of Age on Human Brain Serotonin (S-1) Binding Sites

The effect of age on the binding of [3H]5-hydroxytryptamine [( 3H]5-HT, serotonin) to postmortem human frontal cortex, hippocampus, and putamen from individuals between the ages of 19 and 100 years was studied. One high-affinity binding site was observed in adult brains, with a mean KD of 3.7 nM and 3.2 nM for frontal cortex and hippocampus, respectively, and 9.2 nM for putamen. Decreased binding capacities (Bmax) with age were detected in frontal cortex and hippocampus. In putamen a decrease in affinity was noted. Postmortem storage did not significantly contribute to the age-related changes. No significant sex differences were detected. [3H]5-HT binding was also studied in brains from human neonates. The specific binding was 1.5-3 times lower than in adult frontal cortex and putamen, and Scatchard analysis suggested more than one binding site. In infant hippocampus a single binding site was observed and except for a premature individual, the binding capacity approximated adult values.     

Chlorophyll synthetase activity is relocated from transforming prolamellar bodies to developing thylakoids during irradiation of dark-grown wheat

Analyses of the esterification of newly formed chlorophyllide in irradiated dark-grown leaves of wheat ( Triticum aestivum L. cv. Kosack) suggest a translocation of chlorophyll synthetase activity from transforming prolamellar bodies to developing thylakoids. We have fractionated plastid inner membranes from dark-grown leaves and from leaves irradiated for 5, 10, or 20 min and compared the in vitro esterification of chlorophyllide in two fractions, corresponding (in density) to the prolamellar body and the prothylakoid fraction of dark-grown leaves. The relative amounts of chlorophyllide, and total protein, as well as the specific esterification activity, increased with irradiation time in the prothylakoid fraction. The esterification of chlorophyllide seems to depend on a transformation of the prolamellar body structure. The results are discussed also in relation to other events initiated by irradiation, such as the Shibata-shift and the altered distribution of NADPH-protochlorophyllide oxidoreductase (EC 1.3.1.33).     

Impact of climate change factors on the clonal sedge Carex bigelown: implications for population growth and vegetative spread

Hypothesized life-cycle responses to climate change for the arctic, clonal perennial Carex bigelown are constructed using a range of earlier observations and experiments together with new information from monitoring and an environmental perturbation study These data suggest, that under current climate change scenarios, increases in CO₂, temperature and nutrient availability would promote growth in a qualitatively similar way The evidence suggests that both tiller size and daughter tiller production will increase, and be shifted towards production of phalanx tillers which have a greater propensity for flowering Furthermore, age at tillering as well as tiller life span may decrease, whereas survival of younger age classes might be higher Mathematical models using experimental data incorporating these hypotheses were used to a) integrate the various responses and to calculate the order of magnitude of changes in population growth rate (γ). and b) to explore the implications of responses in individual demographic parameters for population growth rate The models suggest that population growth rate following climate change might increase significantly, but not un-realistically so. with the younger, larger, guerilla ullers being the most important tiller categones in contributing to X The rate of vegetative spread is calculated to more than double, while cyclical trends in flowering and populauon growth are predicted to decrease substantially     

Nitric oxide synthase-containing, peptide-containing, and acetylcholinesterase-positive nerves in the cat lower oesophagus

Summary The innervation of the cat lower oesophagus, including the lower oesophageal sphincter, was studied by enzyme histochemistry, immunohistochemistry, and confocal microscopy. In the lower oesophageal sphincter, and at a level 2 cm above it, no apparent differences were seen in the nerve distribution pattern. Among the nerve populations studied, acetylcholinesterase (AChE)-positive nerves were the most abundant in both these regions. The density of AChE-positive nerves was particularly marked in the circular muscle layer. A rich supply of nitric oxide synthase (NOS)-containing nerves was identified by using an antiserum against neuronal NOS, or by enzyme histochemical staining for NADPH diaphorase activity. Vasoactive intestinal peptide (VIP)-immunoreactive nerves had a similar distribution pattern as NOS-immunoreactive nerves, and nerves displaying immunoreactivity for NOS and VIP often showed profiles coinciding with AChE-positive nerves. As judged by confocal microscopy, immunoreactivities for helospectin, pituitary adenylate cyclase-activating peptide (PACAP) and VIP, to a large extent were found in the same nerves. At a level 7 cm above the lower oesophageal sphincter, the total nerve supply was less than in the sphincter itself and 2 cm above it. Immunoreactivity towards VIP, PACAP and helospectin was also found to co-exist with NOS and neuropeptide Y within the same nerve structures. It is concluded that there is an intricate innervation pattern in the feline lower oesophagus reflecting the complexity in the regulation of its motility.