Fitness of Allozyme Variants in DROSOPHILA PSEUDOOBSCURA. I. Selection at the PGM-1 and ME-2 Loci

We have studied in Drosophila pseudoobscura the effect of allozyme variation on seven fitness components: female fecundity, egg hatchability, egg-to-adult survival under near-optimal and under competitive conditions, rate of development under near-optimal and under competitive conditions, and mating capacity of males. Three genotypes at each of two loci, Pgm-1 and Me-2, have been studied in various combinations. These two loci are highly polymorphic in natural populations of D. pseudoobscura. Statistically significant differences involving one or more genotypes exist for all components of fitness. No single genotype is best for all fitness components; rather the relative fitnesses of genotypes are reversed when different parameters are considered, or when they are studied in different environmental conditions. Also, the average egg-to-adult survival and rate of development are better when different genotypes are reared together than when they occur in pure culture. Four different modes of selection have been uncovered by our experiments. These forms of selection may account for the persistence of the two allozyme polymorphisms in nature, and for previously observed seasonal fluctuations of the allelic frequencies in natural populations.     

Feather mites (Acari: Astigmata) and body condition of their avian hosts: a large correlative study

Feather mites are arthropods that live on or in the feathers of birds, and are among the commonest avian ectosymbionts. However, the nature of the ecological interaction between feather mites and birds remains unclear, some studies reporting negative effects of feather mites on their hosts and others reporting positive or no effects. Here we use a large dataset comprising 20 189 measurements taken from 83 species of birds collected during 22 yr in 151 localities from seven countries in Europe and North Africa to explore the correlation between feather mite abundance and body condition of their hosts. We predicted that, if wing‐dwelling feather mites are parasites, a negative correlation with host body condition should be found, while a mutualistic interaction should yield positive correlation. Although negative relationships between feather mite abundance and host body condition were found in a few species of birds, the sign of the correlation was positive in most bird species (69%). The overall effect size was only slightly positive (r =0.066). The effect of feather mite abundance explained <10% of variance in body condition in most species (87%). Results suggest that feather mites are not parasites of birds, but rather that they hold a commensalistic relationship where feather mites may benefit from feeding on uropygial gland secretions of their hosts and birds do not seem to obtain a great benefit from the presence of feather mites.     

Epigenetic control of early neurodegenerative events in diabetic retinopathy by the histone deacetylase SIRT6

Diabetic retinopathy (DR ) is one of the common complications associated with diabetes mellitus and the leading cause of blindness worldwide. Recent research has demonstrated that DR is not only a microvascular disease but may be a result of neurodegenerative processes. Moreover, glucose‐induced neuron and glial cell damage may occur shortly after the onset of diabetes which makes the disease hard to diagnose at early stages. SIRT 6, a NAD ‐dependent sirtuin deacylase, modulates aging, energy metabolism, and neurodegeneration. In previous studies we showed that SIRT 6 deficiency causes major retinal transmission defects, changes in the expression of glycolytic genes, and elevated levels of apoptosis. Given the importance of glucose availability for retinal function and the critical role of SIRT 6 in modulating glycolysis, we aimed to analyze SIRT 6 participation in the molecular machinery that regulates the development of experimental DR . Using non‐obese diabetic mice, we determined by western blot that 2 weeks after the onset of the disease, high glucose concentrations induced retinal increase in a neovascularization promoting factor (vascular endothelial growth factor, VEGF ), and the loss of a neuroprotective factor (brain‐derived neurotrophic factor, BDNF) associated with reduced levels of SIRT 6 and increased acetylation levels of its substrates (H3K9 and H3K56) suggesting a deregulation of key neural factors. Noteworthy, retinas from CNS conditionally deleted SIRT 6 mice showed a resemblance to diabetic retinas exhibiting lower protein levels of BDNF factor and increased protein levels of VEGF . Moreover, cultured Müller glial cells subjected to high glucose concentrations exhibited decreased levels of SIRT 6 and increased levels of H3K56 acetylation. In addition, the increment of VEGF levels induced by high glucose was reverted by the over‐expression of SIRT 6 in this cell type. Accordingly, siRNA experiments showed that, when SIRT 6 was silenced, VEGF levels increased. Our findings suggest that epigenetically regulated neurodegenerative events may occur at an early diabetic stage prior to the characteristic proliferative and vascular changes observed at a later diabetic stage.

     

Seed lectin from pisum arvense: isolation, biochemical characterization and amino acid sequence

A glucose/mannose lectin was purified by affinity chromatography from Pisum arvense seeds (PAL) and the 50 kDa molecular mass in solution determined by size exclusion chromatography. SDS-PAGE and electrospray ionization mass spectrometry showed two distinct polypeptide chains: alpha (Mr. 5591 Da) and beta (19986 Da). The lectin was extensively characterized in terms of its biochemical and biological aspects. The amino acid sequence was established by Edman degradation of overlapping peptides. PAL in solution behaves as a dimer and has its monomeric structure formed by two distinct polypeptide chains named alpha (Mr. 5591 Da) and beta (19986 Da) by Electrospray ionization (ESI) mass spectrometry. PAL possesses identical amino acid sequences to that of pea seed lectin but undoubtedly does not exhibit sequence heterogeneity. It is discussed that P. arvense should be considered as a synonym of P. sativum. Furthermore, like pea lectin, PAL discriminates biantennary fucosylated glycan, determined by surface plasmon resonance.