Absence of Mate Choice and Postcopulatory Benefits in a Species with Extreme Sexual Size Dimorphism

Most hypotheses related to the evolution of female‐biased extreme sexual size dimorphism (SSD) attribute the differences in the size of each sex to selection for reproduction, either through selection for increased female fecundity or selection for male increased mobility and faster development. Very few studies, however, have tested for direct fitness benefits associated with the latter – small male size. Mecaphesa celer is a crab spider with extreme SSD, whose males are less than half the size of females and often weigh 10 times less. Here, we test the hypotheses that larger size in females and smaller size in males are sexually selected through differential pre‐ and postcopulatory reproductive benefits. To do so, we tested the following predictions: matings between small males and large females are more likely to occur due to mate choice; females mated to small males are less likely to accept second copulation attempts; and matings between small males and large females will result in larger clutches of longer‐lived offspring. Following staged mating trials in the laboratory, we found no support for any of our predictions, suggesting that SSD in M. celer may not be driven by pre‐ or post‐reproductive fitness benefits to small males.     

Kinetic Characterization of 100 Glycoside Hydrolase Mutants Enables the Discovery of Structural Features Correlated with Kinetic Constants

The use of computational modeling algorithms to guide the design of novel enzyme catalysts is a rapidly growing field. Force-field based methods have now been used to engineer both enzyme specificity and activity. However, the proportion of designed mutants with the intended function is often less than ten percent. One potential reason for this is that current force-field based approaches are trained on indirect measures of function rather than direct correlation to experimentally-determined functional effects of mutations. We hypothesize that this is partially due to the lack of data sets for which a large panel of enzyme variants has been produced, purified, and kinetically characterized. Here we report the k_cat and K_M values of 100 purified mutants of a glycoside hydrolase enzyme. We demonstrate the utility of this data set by using machine learning to train a new algorithm that enables prediction of each kinetic parameter based on readily-modeled structural features. The generated dataset and analyses carried out in this study not only provide insight into how this enzyme functions, they also provide a clear path forward for the improvement of computational enzyme redesign algorithms.     

Diminished proliferation of human immunodeficiency virus-specific CD4+ T cells is associated with diminished interleukin-2 (IL-2) production and is recovered by exogenous IL-2

Virus-specific CD4(+) T-cell function is thought to play a central role in induction and maintenance of effective CD8(+) T-cell responses in experimental animals or humans. However, the reasons that diminished proliferation of human immunodeficiency virus (HIV)-specific CD4(+) T cells is observed in the majority of infected patients and the role of these diminished responses in the loss of control of replication during the chronic phase of HIV infection remain incompletely understood. In a cohort of 15 patients that were selected for particularly strong HIV-specific CD4(+) T-cell responses, the effects of viremia on these responses were explored. Restriction of HIV replication was not observed during one to eight interruptions of antiretroviral therapy in the majority of patients (12 of 15). In each case, proliferative responses to HIV antigens were rapidly inhibited during viremia. The frequencies of cells that produce IFN-gamma in response to Gag, Pol, and Nef peptide pools were maintained during an interruption of therapy. In a subset of patients with elevated frequencies of interleukin-2 (IL-2)-producing cells, IL-2 production in response to HIV antigens was diminished during viremia. Addition of exogenous IL-2 was sufficient to rescue in vitro proliferation of DR0101 class II Gag or Pol tetramer(+) or total-Gag-specific CD4(+) T cells. These observations suggest that, during viremia, diminished in vitro proliferation of HIV-specific CD4(+) T cells is likely related to diminished IL-2 production. These results also suggest that relatively high frequencies of HIV-specific CD4(+) T cells persist in the peripheral blood during viremia, are not replicatively senescent, and proliferate when IL-2 is provided exogenously.     

Study of possible interactions of tubulin, microtubular network, and STOP protein with mitochondria in muscle cells

We studied possible connections of tubulin, microtubular system, and microtubular network stabilizing STOP protein with mitochondria in rat and mouse cardiac and skeletal muscles by confocal microscopy and oxygraphy. Intracellular localization and content of tubulin was found to be muscle type-specific, with high amounts in oxidative muscles, and much lower in glycolytic skeletal muscle. STOP protein localization and content in muscle cells was also muscle type-specific. In isolated heart mitochondria, addition of 1 μM tubulin heterodimer increased apparent K _m for ADP significantly. Dissociation of microtubular system into free tubulin by colchicine treatment only slightly decreased initially high apparent K _m for ADP in permeabilized cells, and diffusely distributed free tubulin stayed inside the cells, obviously connected to the intracellular structures. To identify the genes that are specific for oxidative muscle, we developed and applied a method of kindred DNA. The results of sequencing and bioinformatic analysis of isolated cDNA pool common for heart and m. soleus showed that in adult mice the β-tubulin gene is expressed predominantly in oxidative muscle cells. It is concluded that whereas dimeric tubulin may play a significant role in regulation of mitochondrial outer membrane permeability in the cells in vivo, its organization into microtubular network has a minor significance on that process.     

The effectiveness of flower strips and hedgerows on pest control,pollination services and crop yield: a quantitative synthesis

Floral plantings are promoted to foster ecological intensification of agriculture through provisioning of ecosystem services. However, a comprehensive assessment of the effectiveness of different floral plantings, their characteristics and consequences for crop yield is lacking. Here we quantified the impacts of flower strips and hedgerows on pest control (18 studies) and pollination services (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips, but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However, effects on crop pollination and yield were more variable. Our synthesis identifies several important drivers of variability in effectiveness of plantings: pollination services declined exponentially with distance from plantings, and perennial and older flower strips with higher flowering plant diversity enhanced pollination more effectively. These findings provide promising pathways to optimise floral plantings to more effectively contribute to ecosystem service delivery and ecological intensification of agriculture in the future.     

High temperatures limit plant growth but hasten flowering in root chicory (Cichorium intybus) independently of vernalisation

An increase in mean and extreme summer temperatures is expected as a consequence of climate changes and this might have an impact on plant development in numerous species. Root chicory (Cichorium intybus L.) is a major crop in northern Europe, and it is cultivated as a source of inulin. This polysaccharide is stored in the tap root during the first growing season when the plant grows as a leafy rosette, whereas bolting and flowering occur in the second year after winter vernalisation. The impact of heat stress on plant phenology, water status, photosynthesis-related parameters, and inulin content was studied in the field and under controlled phytotron conditions. In the field, plants of the Crescendo cultivar were cultivated under a closed plastic-panelled greenhouse to investigate heat-stress conditions, while the control plants were shielded with a similar, but open, structure. In the phytotrons, the Crescendo and Fredonia cultivars were exposed to high temperatures (35 °C day/28 °C night) and compared to control conditions (17 °C) over 10 weeks. In the field, heat reduced the root weight, the inulin content of the root and its degree of polymerisation in non-bolting plants. Flowering was observed in 12% of the heat stressed plants during the first growing season in the field. In the phytotron, the heat stress increased the total number of leaves per plant, but reduced the mean leaf area. Photosynthesis efficiency was increased in these plants, whereas osmotic potential was decreased. High temperature was also found to induced flowering of up to 50% of these plants, especially for the Fredonia cultivar. In conclusion, high temperatures induced a reduction in the growth of root chicory, although photosynthesis is not affected. Flowering was also induced, which indicates that high temperatures can partly substitute for the vernalisation requirement for the flowering of root chicory.     

Manipulation of flavour and aroma compound sequestration and release using a glycosyltransferase with specificity for terpene alcohols

Glycosides are an important potential source of aroma and flavour compounds for release as volatiles in flowers and fruit. The production of glycosides is catalysed by UDP‐glycosyltransferases (UGTs) that mediate the transfer of an activated nucleotide sugar to acceptor aglycones. A screen of UGTs expressed in kiwifruit (Actinidia deliciosa) identified the gene AdGT4 which was highly expressed in floral tissues and whose expression increased during fruit ripening. Recombinant AdGT4 enzyme glycosylated a range of terpenes and primary alcohols found as glycosides in ripe kiwifruit. Two of the enzyme's preferred alcohol aglycones, hexanol and (Z)‐hex‐3‐enol, contribute strongly to the ‘grassy‐green’ aroma notes of ripe kiwifruit and other fruit including tomato and olive. Transient over‐expression of AdGT4 in tobacco leaves showed that enzyme was able to glycosylate geraniol and octan‐3‐ol in planta whilst transient expression of an RNAi construct in Actinidia eriantha fruit reduced accumulation of a range of terpene glycosides. Stable over‐expression of AdGT4 in transgenic petunia resulted in increased sequestration of hexanol and other alcohols in the flowers. Transgenic tomato fruit stably over‐expressing AdGT4 showed changes in both the sequestration and release of a range of alcohols including 3‐methylbutanol, hexanol and geraniol. Sequestration occurred at all stages of fruit ripening. Ripe fruit sequestering high levels of glycosides were identified as having a less intense, earthier aroma in a sensory trial. These results demonstrate the importance of UGTs in sequestering key volatile compounds in planta and suggest a future approach to enhancing aromas and flavours in flowers and during fruit ripening.     

Removing Phosphorus from Ecosystems Through Nitrogen Fertilization and Cutting with Removal of Biomass

High amounts of phosphorus (P) are in soil of former farmland due to previous fertilizer additions. Draining these residues would provide conditions for grassland plant species diversity restoration amongst other ecosystem benefits. Nitrogen (N) fertilization followed by cutting with subsequent removal of biomass has been suggested as a P residue removal method. We present a general model of N and P ecosystem cycling with nutrients coupled in plant biomass. We incorporate major P pools and biological and physico-chemical fluxes around the system together with transfers into and out of the system given several decades of management. We investigate conditions where N addition and cutting accelerate fertilizer P draining. Cutting does not generally accelerate soil P depletion under short-term management because the benefits of biomass removal through decreased P mineralization occur on too long a timescale compared to cutting’s impact on the ability of plants to deplete nutrients. Short-term N fertilization lowers soil fertilizer P residues, provided plant growth remains N limited. In such situations, N fertilization without biomass removal increases soil organic P. Some scenarios show significant reductions in available P following N addition, but many situations record only marginal decreases in problematic soil P pools compared to the unfertilized state. We provide explicit conditions open to experimental testing. Cutting might have minimal adverse impacts, but will take time to be successful. N fertilization either alone or in combination with cutting is more likely to bring about desired reductions in P availability thus allowing grassland restoration, but might have undesired ecosystem consequences.