Intraspecific mating system evolution and its effect on complex male secondary sexual traits: Does male–male competition increase selection on size or shape?

Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread dung flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male–male competition. We predicted that populations subject to increased male–male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male‐biased SSD in both species, which was not evident in conspecific populations with female‐biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling.     

Plant respiration: Controlled by photosynthesis or biomass?

Two simplifying hypotheses have been proposed for whole‐plant respiration. One links respiration to photosynthesis; the other to biomass. Using a first‐principles carbon balance model with a prescribed live woody biomass turnover, applied at a forest research site where multidecadal measurements are available for comparison, we show that if turnover is fast the accumulation of respiring biomass is low and respiration depends primarily on photosynthesis; while if turnover is slow the accumulation of respiring biomass is high and respiration depends primarily on biomass. But the first scenario is inconsistent with evidence for substantial carry‐over of fixed carbon between years, while the second implies far too great an increase in respiration during stand development—leading to depleted carbohydrate reserves and an unrealistically high mortality risk. These two mutually incompatible hypotheses are thus both incorrect. Respiration is not linearly related either to photosynthesis or to biomass, but it is more strongly controlled by recent photosynthates (and reserve availability) than by total biomass.     

盐酸米诺环素软膏辅助龈下刮治术及根面平整术对慢性牙周炎患者龈下牙周致病菌和龈沟液炎性因子的影响

目的:探讨盐酸米诺环素软膏辅助龈下刮治术及根面平整术(FM-SRP)对慢性牙周炎(CP)患者龈下牙周致病菌和龈沟液炎性因子的影响。方法:选择2015年10月到2019年10月期间我院收治的82例CP患者,根据随机数字表法分为对照组(n=41)和观察组(n=41),对照组给予FM-SRP,观察组在对照组基础上联合盐酸米诺环素软膏辅助治疗,比较两组疗效、牙周指标、龈下牙周致病菌和龈沟液炎性因子情况,统计两组不良反应情况。结果:与对照组总有效率70.73%(29/41)相比,观察组治疗后的总有效率90.24%(37/41)更高(P<0.05)。治疗后,两组龈沟出血指数(SBI)、附着水平(AL)、菌斑指数(PLI)、牙周袋深度(PD)均下降,且观察组低于对照组(P<0.05)。治疗后,两组转化生长因子-β(TGF-β)、白介素-6(IL-6)、肿瘤坏死因子-α(TNF-α)均下降,且观察组低于对照组(P<0.05)。对比两组不良反应无差异(P>0.05)。治疗后,两组伴防线杆菌、牙龈卟啉单胞菌比例均下降,且观察组低于对照组(P<0.05)。结论:盐酸米诺环素软膏辅助FM-SRP治疗CP患者,可有效消除致病菌,缓解炎性反应,恢复牙周生态平衡,且不增加不良反应发生率,疗效确切。     

Differences between bacterial associations with two root types of Vicia faba L

Abstract

Differences between various inherent physiological characteristics of lateral roots and of taproots of faba bean plants (Vicia faba L.) have been described in the literature. The question as to whether distinct bacterial communities inhabit each of those root types calls for further investigation. This question was tackled using aeroponically grown plants, i.e., plants that were grown under conditions as homogeneous as possible. Samples of the apical 5 cm of taproots and of lateral roots were compared. Metabolic fingerprints of root bacterial communities were analyzed using the Biolog® assay. Specificity of colonization of the different root types by specific bacterial taxa was examined by the Real-Time Polymerase Chain Reaction (PCR) method. Root bacterial communities produced distinct metabolic fingerprints for each of the two root types. Herbaspirillum spp. were found to be associated with lateral roots but not with taproots both under non-saline and saline (50 mM NaCl) conditions. No significant differences were found in the abundance of bacteria with respect to either root type or salinity. It is concluded that different root types, even within single root systems, differ not only in their physiological traits but also in their bacterial associations. Such associations might have adaptive advantages.     

Body masses,functional responses and predator–prey stability

The stability of ecological communities depends strongly on quantitative characteristics of population interactions (type‐II vs. type‐III functional responses) and the distribution of body masses across species. Until now, these two aspects have almost exclusively been treated separately leaving a substantial gap in our general understanding of food webs. We analysed a large data set of arthropod feeding rates and found that all functional‐response parameters depend on the body masses of predator and prey. Thus, we propose generalised functional responses which predict gradual shifts from type‐II predation of small predators on equally sized prey to type‐III functional‐responses of large predators on small prey. Models including these generalised functional responses predict population dynamics and persistence only depending on predator and prey body masses, and we show that these predictions are strongly supported by empirical data on forest soil food webs. These results help unravelling systematic relationships between quantitative population interactions and large‐scale community patterns.     

Unimodal size scaling of phytoplankton growth and the size dependence of nutrient uptake and use

Phytoplankton size structure is key for the ecology and biogeochemistry of pelagic ecosystems, but the relationship between cell size and maximum growth rate (μ_max) is not yet well understood. We used cultures of 22 species of marine phytoplankton from five phyla, ranging from 0.1 to 10⁶ μm³ in cell volume (V_cell), to determine experimentally the size dependence of growth, metabolic rate, elemental stoichiometry and nutrient uptake. We show that both μ_max and carbon‐specific photosynthesis peak at intermediate cell sizes. Maximum nitrogen uptake rate (V_maxN) scales isometrically with V_cell, whereas nitrogen minimum quota scales as V_cell^0.84. Large cells thus possess high ability to take up nitrogen, relative to their requirements, and large storage capacity, but their growth is limited by the conversion of nutrients into biomass. Small species show similar volume‐specific V_maxN compared to their larger counterparts, but have higher nitrogen requirements. We suggest that the unimodal size scaling of phytoplankton growth arises from taxon‐independent, size‐related constraints in nutrient uptake, requirement and assimilation.     

Mitotic chromosome size scaling in Xenopus

As rapid divisions without growth generate progressively smaller cells within an embryo, mitotic chromosomes must also decrease in size to permit their proper segregation, but this scaling phenomenon is poorly understood. We demonstrated previously that nuclear and spindle size scale between egg extracts of the related frog species Xenopus tropicalis and Xenopus laevis, but show here that dimensions of isolated mitotic sperm chromosomes do not differ. This is consistent with the hypothesis that chromosome scaling does not occur in early embryonic development when cell and spindles sizes are large and anaphase B segregates chromosomes long distances. To recapitulate chromosome scaling during development, we combined nuclei isolated from different stage Xenopus laevis embryos with metaphase-arrested egg extracts. Mitotic chromosomes derived from nuclei of cleaving embryos through the blastula stage were similar in size to replicated sperm chromosomes, but decreased in area approximately 50% by the neurula stage, reproducing the trend in size changes observed in fixed embryos. Allowing G2 nuclei to swell in interphase prior to mitotic condensation did not increase mitotic chromosome size, but progression through a full cell cycle in egg extract did, suggesting that epigenetic mechanisms determining chromosome size can be altered during DNA replication. Comparison of different sized mitotic chromosomes assembled in vitro provides a tractable system to elucidate underlying molecular mechanisms.     

Texture perception through direct and indirect touch: An analysis of perceptual space for tactile textures in two modes of exploration

Considerable information about the texture of objects can be perceived remotely through a probe. It is not clear, however, how texture perception with a probe compares with texture perception with the bare finger. Here we investigate the perception of a variety of textured surfaces encountered daily (e.g., corduroy, paper, and rubber) using the two scanning modes—direct touch through the finger and indirect touch through a probe held in the hand—in two tasks. In the first task, subjects rated the overall pair-wise dissimilarity of the textures. In the second task, subjects rated each texture along three continua, namely, perceived roughness, hardness, and stickiness of the surfaces, shown previously as the primary dimensions of texture perception in direct touch. From the dissimilarity judgment experiment, we found that the texture percept is similar though not identical in the two scanning modes. From the adjective rating experiments, we found that while roughness ratings are similar, hardness and stickiness ratings tend to differ between scanning conditions. These differences between the two modes of scanning are apparent in perceptual space for tactile textures based on multidimensional scaling (MDS) analysis. Finally, we demonstrate that three physical quantities, vibratory power, compliance, and friction carry roughness, hardness, and stickiness information, predicting perceived dissimilarity of texture pairs with indirect touch. Given that different types of texture information are processed by separate groups of neurons across direct and indirect touch, we propose that the neural mechanisms underlying texture perception differ between scanning modes.