First capture success in two dimensions: The search for prey by a random walk predator in a comprehensive space of random walks

Random walk models are an important tool used for understanding how complex organisms redistribute themselves through space and time in search of targets such as food, shelter, or mates. These walks are easily studied with agent-based models, which can be used to ask which search strategy is best according to some efficiency metric. Current studies however, generally do not consider the full range of potential random walks, success metrics, and constraints on the walker, and implementation details vary widely. It is therefore difficult to compare results across studies. In this paper, we investigate predator search behaviour in a comprehensive space of key movement variables that allows the predator to select from a continuum of random walks ranging from Brownian walks (BWs) to correlated random walks (CorRWs) which include directional persistence, to composite random walks (ComRWs) which feature intensive and extensive search modes (ISMs and ESMs), and finally to more complex correlated composite random walks (CCRWs). We specifically focus on the search behaviour of a predator between the initiation of a search for a prey item and the first successful acquisition of a prey target: we call this interval the “search-to-capture” event. We measure the predator's success against three metrics of energetic cost: (1) the time elapsed, (2) the distance travelled, and (3) an equally weighted combination of time and distance. In addition, we explore the effect of three different constraints on the predator: (1) hunting success in the extensive search mode, (2) detection radius when in the extensive search mode, and (3) prey density. Our work confirms the broadly held notion that CCRW movement patterns should always outperform BWs, but find instructive cases where other walks are superior. We also show that, within the CCRW category, there is a wide range of possible walks and rank these according to measures of energetic cost. Our work also offers insights into the evolutionary pressures surrounding the “search-to-capture” event, and suggests that CCRW predators with low hunting success in one movement mode experience higher evolutionary pressures and are thus more likely to adopt a nearly optimal random walk. Our work highlights the need for comprehensive studies that examine several aspects of random walks simultaneously.     

HGT is widespread in insects and contributes to male courtship in lepidopterans

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虎杖象甲培植真菌营养特性及对菌丝附属物形成的影响

虎杖象甲培植共生真菌形成的共生体系是植菌昆虫菌业中的典型代表。共生真菌Penicillium herquei如何向虎杖象甲Euops chinensis提供营养尚未明确。本研究发现共生真菌P. herquei的菌丝表面存在大量瘤状凸起物及由凸起物衍生的附属丝等特化结构,该结构可能为虎杖象甲提供营养;对共生真菌的营养研究表明,共生真菌能高效利用山梨醇、蔗糖、海藻糖、葡萄糖等单糖或双糖,以及酪氨酸、甘氨酸、谷氨酰胺等昆虫非必须氨基酸,同时在高碳和最适碳源条件下有利于菌丝特化附属物的产生。研究结果不仅提供了植菌卷叶象甲菌业中共生真菌在营养方面的适应性进化证据,而且为进一步揭示共生真菌适应卷叶象甲的营养机制奠定了基础。     

Early vigour in wheat: Could it lead to more severe terminal drought stress under elevated atmospheric [CO2] and semi‐arid conditions?

Early vigour in wheat is a trait that has received attention for its benefits reducing evaporation from the soil surface early in the season. However, with the growth enhancement common to crops grown under elevated atmospheric CO₂ concentrations (e[CO₂]), there is a risk that too much early growth might deplete soil water and lead to more severe terminal drought stress in environments where production relies on stored soil water content. If this is the case, the incorporation of such a trait in wheat breeding programmes might have unintended negative consequences in the future, especially in dry years. We used selected data from cultivars with proven expression of high and low early vigour from the Australian Grains Free Air CO₂ Enrichment (AGFACE) facility, and complemented this analysis with simulation results from two crop growth models which differ in the modelling of leaf area development and crop water use. Grain yield responses to e[CO₂] were lower in the high early vigour group compared to the low early vigour group, and although these differences were not significant, they were corroborated by simulation model results. However, the simulated lower response with high early vigour lines was not caused by an earlier or greater depletion of soil water under e[CO₂] and the mechanisms responsible appear to be related to an earlier saturation of the radiation intercepted. Whether this is the case in the field needs to be further investigated. In addition, there was some evidence that the timing of the drought stress during crop growth influenced the effect of e[CO₂] regardless of the early vigour trait. There is a need for FACE investigations of the value of traits for drought adaptation to be conducted under more severe drought conditions and variable timing of drought stress, a risky but necessary endeavour.     

The genetics of evolutionary radiations

With the realization that much of the biological diversity on Earth has been generated by discrete evolutionary radiations, there has been a rapid increase in research into the biotic (key innovations) and abiotic (key environments) circumstances in which such radiations took place. Here we focus on the potential importance of population genetic structure and trait genetic architecture in explaining radiations. We propose a verbal model describing the stages of an evolutionary radiation: first invading a suitable adaptive zone and expanding both spatially and ecologically through this zone; secondly, diverging genetically into numerous distinct populations; and, finally, speciating. There are numerous examples of the first stage; the difficulty, however, is explaining how genetic diversification can take place from the establishment of a, presumably, genetically depauperate population in a new adaptive zone. We explore the potential roles of epigenetics and transposable elements (TEs), of neutral process such as genetic drift in combination with trait genetic architecture, of gene flow limitation through isolation by distance (IBD), isolation by ecology and isolation by colonization, the possible role of intra‐specific competition, and that of admixture and hybridization in increasing the genetic diversity of the founding populations. We show that many of the predictions of this model are corroborated. Most radiations occur in complex adaptive zones, which facilitate the establishment of many small populations exposed to genetic drift and divergent selection. We also show that many radiations (especially those resulting from long‐distance dispersal) were established by polyploid lineages, and that many radiating lineages have small genome sizes. However, there are several other predictions which are not (yet) possible to test: that epigenetics has played a role in radiations, that radiations occur more frequently in clades with small gene flow distances, or that the ancestors of radiations had large fundamental niches. At least some of these may be testable in the future as more genome and epigenome data become available. The implication of this model is that many radiations may be hard polytomies because the genetic divergence leading to speciation happens within a very short time, and that the divergence history may be further obscured by hybridization. Furthermore, it suggests that only lineages with the appropriate genetic architecture will be able to radiate, and that such a radiation will happen in a meta‐population environment. Understanding the genetic architecture of a lineage may be an essential part of accounting for why some lineages radiate, and some do not.     

Resource diversity promotes among‐individual diet variation,but not genomic diversity,in lake stickleback

Many generalist species consist of specialised individuals that use different resources. This within‐population niche variation can stabilise population and community dynamics. Consequently, ecologists wish to identify environmental settings that promote such variation. Theory predicts that environments with greater resource diversity favour ecological diversity among consumers (via disruptive selection or plasticity). Alternatively, niche variation might be a side‐effect of neutral genomic diversity in larger populations. We tested these alternatives in a metapopulation of threespine stickleback. Stickleback consume benthic and limnetic invertebrates, focusing on the former in small lakes, the latter in large lakes. Intermediate‐sized lakes support generalist stickleback populations using an even mixture of the two prey types, and exhibit greater among‐individual variation in diet and morphology. In contrast, genomic diversity increases with lake size. Thus, phenotypic diversity and neutral genetic polymorphism are decoupled: trophic diversity being greatest in intermediate‐sized lakes with high resource diversity, whereas neutral genetic diversity is greatest in the largest lakes.     

Do innate killing mechanisms activated by inflammasomes have a role in treating melanoma?

Melanoma, as for many other cancers, undergoes a selection process during progression that limits many innate and adaptive tumor control mechanisms. Immunotherapy with immune checkpoint blockade overcomes one of the escape mechanisms but if the tumor is not eliminated other escape mechanisms evolve that require new approaches for tumor control. Some of the innate mechanisms that have evolved against infections with microorganisms and viruses are proving to be active against cancer cells but require better understanding of how they are activated and what inhibitory mechanisms may need to be targeted. This is particularly so for inflammasomes which have evolved against many different organisms and which recruit a number of cytotoxic mechanisms that remain poorly understood. Equally important is understanding of where these mechanisms will fit into existing treatment strategies and whether existing strategies already involve the innate killing mechanisms.     

基于功能性状的水杉原生母树种群生境适应策略

植物的功能性状变异和表型可塑性是其应对异质生境的主要机制, 对植物的生长和分布有重要贡献。本文以湖北星斗山国家级自然保护区的水杉(Metasequoia glyptostroboides)原生母树为研究对象, 分析了母树种群功能性状对树木形态、地形因子及人为干扰的响应机制。结果表明: 水杉原生母树叶面积、叶干重和比叶面积的变异幅度大, 可塑性较强, 而枝和叶的干物质含量稳定性最高。人为干扰和4个地形因子均对每个功能性状变异方差有5%-20%的解释度, 冠幅对枝、叶干物质含量的变异方差有高达38%和76%的解释度。5个功能性状主要受海拔、坡位和人为干扰影响, 其中, 比叶面积对环境因子和干扰的响应规律不明显, 叶面积和叶干重在强烈人为干扰的环境中普遍增大, 枝和叶的干物质含量对坡向的变化最敏感。总之, 水杉原生母树种群通过功能性状变异对环境能产生一定的可塑性响应, 但人为干扰对母树生长影响较大, 建议人工辅助更新, 并适度减少农业和建筑对现存母树的影响。