Flight loss linked to faster molecular evolution in insects

The loss of flight ability has occurred thousands of times independently during insect evolution. Flight loss may be linked to higher molecular evolutionary rates because of reductions in effective population sizes (N_e) and relaxed selective constraints. Reduced dispersal ability increases population subdivision, may decrease geographical range size and increases (sub)population extinction risk, thus leading to an expected reduction in N_e. Additionally, flight loss in birds has been linked to higher molecular rates of energy-related genes, probably owing to relaxed selective constraints on energy metabolism. We tested for an association between insect flight loss and molecular rates through comparative analysis in 49 phylogenetically independent transitions spanning multiple taxa, including moths, flies, beetles, mayflies, stick insects, stoneflies, scorpionflies and caddisflies, using available nuclear and mitochondrial protein-coding DNA sequences. We estimated the rate of molecular evolution of flightless (FL) and related flight-capable lineages by ratios of non-synonymous-to-synonymous substitutions (dN/dS) and overall substitution rates (OSRs). Across multiple instances of flight loss, we show a significant pattern of higher dN/dS ratios and OSRs in FL lineages in mitochondrial but not nuclear genes. These patterns may be explained by relaxed selective constraints in FL ectotherms relating to energy metabolism, possibly in combination with reduced N_e.     

Modelling nitrate influx in young tomato (Lycopersicon esculentum Mill.) plants

The effects of light and NO3^- nutrition on ¹⁵NO3^- influx in roots were investigated in young, 19-d-old, induced tomato plants grown at a constant air and solution temperature of 20C. Nitrate influx was measured by ¹⁵N accumulation for 5 min, on plants exposed to a wide range of exogenous concentrations, from 10 x 10^-3 to 30 mol m^-3. Influx kinetics, fitted to the data following a non-linear procedure, showed multiphasic patterns. The best fits were obtained when three pure and non-additive Michaelis-Menten kinetics were applied, with phase transitions at approximately 0.8 and 4 mol m^-3. In plants grown at 3.0 mol m^-3 NO3^-, the asymptotic maximum influx rate (Imax) of each phase declined during the night until 24 h darkness. At the end of the day period, about a 2-fold enhancement of Imax was observed when plants were pretreated for 3 d with 0.2 instead of 3.0 mol m^-3 NO3^-. The influx rates measured at any given NO3^- concentration and the Imax for any phase showed a negative non-linear correlation with plant nitrate concentration. Furthermore, the results suggest the existence of a set point, approximately 66 mol m^-3 plant nitrate, for which influx is null at any given solution nitrate concentration. A model using modified Michaelis-Menten kinetics is proposed to predict the influx rate as a function of both solution and plant NO3^- concentrations.     

C-value estimates for 31 species of ladybird beetles (Coleoptera: Coccinellidae)

This study provides C-value (haploid nuclear DNA content) estimates for 31 species of ladybird beetles (representing 6 subfamilies and 8 tribes), the first such data for the family Coccinellidae. Despite their unparalleled diversity, the Coleoptera have been very poorly studied in terms of genome size variation, such that even this relatively modest sample of species makes the Coccinellidae the third best studied family of beetles, behind the Tenebrionidae and Chrysomelidae. The present study provides a comparison of patterns of genome size variation with these two relatively well-studied families. No correlation was found between genome size and body size in the ladybirds, in contrast to some other invertebrate groups but in keeping with findings for other beetle families. However, there is some indication that developmental time and/or feeding ecology is related to genome size in this group. Some phylogenetic patterns and possible associations with subgenomic features are also discussed.     

New insights into the distribution of polyploid Daphnia: the Holarctic revisited and Argentina explored

It has long been known that polyploid organisms are more prevalent in arctic than in temperate environments. Past explanations for this geographical trend have focused on the role of glacial cycles in generating polyploids and the influence of abiotic factors in favouring polyploidy in the north. In combination, these mechanisms probably suffice to explain the observed geographical cline in ploidy levels in members of the Daphnia pulex complex in the Holarctic. While only diploid members of the D. pulex complex are found in the temperate regions of North America and Europe, allozyme and DNA quantification analyses indicate that the southern Argentine pulex-complex fauna is dominated by polyploids. Indeed, the present study is the first to document the presence of polyploid members of the D. pulex complex in any temperate climate. The results of phylogeographic analyses suggest that this difference in polyploid distribution between the northern and southern hemispheres is based more on ecological and historical contingencies than direct selection for polyploidy. Specifically, competition with diploid relatives probably limits the lower latitudinal range of polyploids in the north, but appears not to have occurred in Argentina. Because of these differences, the present study provides important insights into the diverse factors that determine the distributions and evolutionary fates of polyploid organisms.     

Diurnal nitrate uptake in young tomato (Lycopersicon esculentum Mill.) plants: test of a feedback-based model

A simple model is proposed to describe diurnal net nitrate uptake rate patterns observed experimentally on young plants grown under constant non-limiting nutrition. It rests on two hypotheses: net uptake rate is under negative feedback control by internal plant nitrate content, and nitrogen metabolism occurs only during the light period. The model parameters were determined from the results of three independent experiments performed under non-disturbing conditions in a growth room at constant air and solution temperatures. Net hourly nitrate uptake rate was measured through a diurnal cycle and after an extended 28 h period of darkness. It increased continuously during the light period and decreased during the dark period. Under prolonged darkness, net uptake declined to an asymptotic positive uptake rate of about 10^-5 mol h^-1 g^-1 total plant dry weight. The measured hourly nitrate uptake rate values were consistent with independent determinations of long-term nitrate and total N accumulations in the plant. Realistic simulations of experimental data are achieved with the proposed model. Furthermore, the maintenance of a positive net uptake rate, measured in non-growing plants subjected to prolonged darkness, is explained in the model by the continuous increase of plant water content. The importance of the diurnal variations of plant water content for nitrate uptake rate is emphasized and gives consistency to the homeostasis hypothesis of the model. The diurnal changes in nitrate uptake predicted by the model are strongly dependent on the assumption made for diurnal changes in nitrate assimilation. While the purely photosynthetic assumption is convenient, a more realistic metabolism sub-model is needed.     

Immunohistochemical localization of phosphodiesterase 10A in multiple mammalian species.

A monoclonal antibody directed against the amino terminal of rat phosphodiesterase 10A (PDE10A) was used to localize PDE10A in multiple central nervous system (CNS) and peripheral tissues from mouse, rat, dog, cynomolgus macaque, and human. PDE10A immunoreactivity is strongly expressed in the CNS of these species with limited expression in peripheral tissues. Within the brain, strong immunoreactivity is present in both neuronal cell bodies and neuropil of the striatum, in striatonigral and striatopallidal white matter tracks, and in the substantia nigra and globus pallidus. Outside the brain, PDE10A immunoreactivity is less intense, and distribution is limited to few tissues such as the testis, epididymal sperm, and enteric ganglia. These data demonstrate that PDE10A is an evolutionarily conserved phosphodiesterase highly expressed in the brain but with restricted distribution in the periphery in multiple mammalian species.     

Patients with unsolved congenital disorders of glycosylation type II can be subdivided in six distinct biochemical groups

Defects in the biosynthesis of N- and core 1 O-glycans may be found by isoelectric focusing (IEF) of plasma transferrin and apolipoprotein C-III (apoC-III). We hypothesized that IEF of transferrin and apoC-III in combination with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of apoC-III may provide a classification for congenital disorders of glycosylation (CDG) patients. We analyzed plasma from 22 patients with eight different and well-characterized CDG subtypes and 19 cases with unsolved CDG. Transferrin IEF (TIEF) has been used to distinguish between N-glycan assembly (type 1 profile) and processing (type 2 profile) defects. We differentiated two different CDG type 2 TIEF profiles: The "asialo profile" characterized by elevated levels of asialo- and monosialotransferrin and the "disialo profile" characterized by increased levels of disialo- and trisialotransferrin. ApoC-III IEF gave two abnormal profiles ("apoC-III(0)" and "apoC-III(1)" profiles). The results for the eight established CDG forms exactly matched the theoretical expectations, providing a validation for the study approach. The combination of the three electrophoretic techniques was not additionally informative for the CDG-Ix patients as they had normal apoC-III IEF patterns. However, the CDG-IIx patients could be further subdivided into six biochemical subgroups. The robustness of the methodology was supported by the fact that three patients with similar clinical features ended in the same subgroup and that another patient, classified in the "CDG-IIe subgroup," turned out to have a similar defect. Dividing the CDG-IIx patients in six subgroups narrows down drastically the options of the primary defect in each of the subgroups and will be helpful to define new CDG type II defects.     

Mutation in the Sp1 motif of the bovine leptin gene affects its expression

Leptin is expressed mainly by adipocytes and plays a crucial role in the regulation of energy expenditure, food intake, and adiposity. Using PCR-heteroduplex analysis and sequencing, we investigated a C/G substitution in the promoter region of the bovine leptin gene. Application of the electrophoretic mobility shift assay showed that the C→G transversion decreased the leptin gene promoter binding capacity for nuclear proteins. With real-time PCR and Western blotting, we showed that the leptin expression level was higher in cattle with the CC than with the GG genotype.