Comparative sialomics between hard and soft ticks: implications for the evolution of blood-feeding behavior

Ticks evolved various mechanisms to modulate their host's hemostatic and immune defenses. Differences in the anti-hemostatic repertoires suggest that hard and soft ticks evolved anti-hemostatic mechanisms independently, but raise questions on the conservation of salivary gland proteins in the ancestral tick lineage. To address this issue, the sialome (salivary gland secretory proteome) from the soft tick, Argas monolakensis, was determined by proteomic analysis and cDNA library construction of salivary glands from fed and unfed adult female ticks. The sialome is composed of approximately 130 secretory proteins of which the most abundant protein folds are the lipocalin, BTSP, BPTI and metalloprotease families which also comprise the most abundant proteins found in the salivary glands. Comparative analysis indicates that the major protein families are conserved in hard and soft ticks. Phylogenetic analysis shows, however, that most gene duplications are lineage specific, indicating that the protein families analyzed possibly evolved most of their functions after divergence of the two major tick families. In conclusion, the ancestral tick may have possessed a simple (few members for each family), but diverse (many different protein families) salivary gland protein domain repertoire.     

Nuttalliella namaqua: a living fossil and closest relative to the ancestral tick lineage: implications for the evolution of blood-feeding in ticks

Ticks are monophyletic and composed of the hard (Ixodidae) and soft (Argasidae) tick families, as well as the Nuttalliellidae, a family with a single species, Nuttalliella namaqua. Significant biological differences in lifestyle strategies for hard and soft ticks suggest that various blood-feeding adaptations occurred after their divergence. The phylogenetic relationships between the tick families have not yet been resolved due to the lack of molecular data for N. namaqua. This tick possesses a pseudo-scutum and apical gnathostoma as observed for ixodids, has a leathery cuticle similar to argasids and has been considered the evolutionary missing link between the two families. Little knowledge exists with regard to its feeding biology or host preferences. Data on its biology and systematic relationship to the other tick families could therefore be crucial in understanding the evolution of blood-feeding behaviour in ticks. Live specimens were collected and blood meal analysis showed the presence of DNA for girdled lizards from the Cordylid family. Feeding of ticks on lizards showed that engorgement occurred rapidly, similar to argasids, but that blood meal concentration occurs via malpighian excretion of water. Phylogenetic analysis of the 18S nuclear and 16S mitochondrial genes indicate that N. namaqua grouped basal to the main tick families. The data supports the monophyly of all tick families and suggests the evolution of argasid-like blood-feeding behaviour in the ancestral tick lineage. Based on the data and considerations from literature we propose an origin for ticks in the Karoo basin of Gondwanaland during the late Permian. The nuttalliellid family almost became extinct during the End Permian event, leaving N. namaqua as the closest living relative to the ancestral tick lineage and the evolutionary missing link between the tick families.     

Adaptation to an extraordinary environment by evolution of phenotypic plasticity and genetic assimilation

Adaptation to a sudden extreme change in environment, beyond the usual range of background environmental fluctuations, is analysed using a quantitative genetic model of phenotypic plasticity. Generations are discrete, with time lag τ between a critical period for environmental influence on individual development and natural selection on adult phenotypes. The optimum phenotype, and genotypic norms of reaction, are linear functions of the environment. Reaction norm elevation and slope (plasticity) vary among genotypes. Initially, in the average background environment, the character is canalized with minimum genetic and phenotypic variance, and no correlation between reaction norm elevation and slope. The optimal plasticity is proportional to the predictability of environmental fluctuations over time lag τ. During the first generation in the new environment the mean fitness suddenly drops and the mean phenotype jumps towards the new optimum phenotype by plasticity. Subsequent adaptation occurs in two phases. Rapid evolution of increased plasticity allows the mean phenotype to closely approach the new optimum. The new phenotype then undergoes slow genetic assimilation, with reduction in plasticity compensated by genetic evolution of reaction norm elevation in the original environment.     

Adaptation of crops to environment

Adaptability is defined as the ability of a crop (or variety) to respond positively to changes in agricultural conditions. The trait is genetically controlled and provides an ability to exploit environmental attributes, both natural and agronomic. Values of relative adaptability can be determined by the regression of the yield of the tested crop over the average yield of compared crops from several environments. We evaluated relative adaptability of 12 staple crops in 12 European countries and compared the yield data over a 43-year period from 1961 to 2003. An additional set of average yield data was also available for the 15 European Union (EU15) member countries. A wider range of 26 crop species was investigated that allowed comparisons between Europe and the USA between 1961 and 2003. Adaptability was closely related to the annual yield increases of the crops studied (r ²=0.999 both in the EU15 and the USA). However, the adaptability of certain crops differed between the two regions. Pulse, maize, millet, wheat and sorghum showed the highest adaptability in the EU15 region, whereas strawberry, pear, tomato, walnut and maize were highest in the USA. The lowest adaptability was found for walnut, pear, apple, cauliflower and hop in the EU15 and for mustard, hop, sugar beet, millet and oat in the USA. In European countries, crops with similar biology, environment and agronomical practices (like the amount of fertilizers and pesticides applied) tended to have similar adaptability values. The data indicate that high adaptability is an important prerequisite for continued yield gains in the best environments.     

Biomedical ontologies: a functional perspective

The information explosion in biology makes it difficult for researchers to stay abreast of current biomedical knowledge and to make sense of the massive amounts of online information. Ontologies--specifications of the entities, their attributes and relationships among the entities in a domain of discourse--are increasingly enabling biomedical researchers to accomplish these tasks. In fact, bio-ontologies are beginning to proliferate in step with accruing biological data. The myriad of ontologies being created enables researchers not only to solve some of the problems in handling the data explosion but also introduces new challenges. One of the key difficulties in realizing the full potential of ontologies in biomedical research is the isolation of various communities involved: some workers spend their career developing ontologies and ontology-related tools, while few researchers (biologists and physicians) know how ontologies can accelerate their research. The objective of this review is to give an overview of biomedical ontology in practical terms by providing a functional perspective--describing how bio-ontologies can and are being used. As biomedical scientists begin to recognize the many different ways ontologies enable biomedical research, they will drive the emergence of new computer applications that will help them exploit the wealth of research data now at their fingertips.     

Adaptation to a limiting environment: the phosphorus content of terrestrial cave arthropods

Stoichiometric imbalances (mismatches between elemental ratios of consumers and their food) are expected to be especially important in detritus-based systems because poor resource quality may impose severe growth constraints. Such imbalances have been highlighted in producer-based food webs and detritus-based aquatic systems, but similar investigations of detritus-based terrestrial ecosystems are absent. Cave animals are dependent on detrital subsidies from the surface and display adaptations to caves (e.g., decreased growth and metabolic rates). Here we examined how nutrient quality may constrain consumer strategies in caves. We found that the quality of cave resources was comparable to resources on the surface, but there was some evidence that cave animals may face nutritional constraints for at least a part of the year. Such constraints may be especially important for millipedes, whose C:P was particularly low (i.e., nutrient-demanding) relative to cave detritus. Based on the growth rate hypothesis, we predicted that cave-adapted species would have lower %P, lower %RNA, and a lower RNA/DNA ratio relative to surface-dwelling counterparts; however, the differences we discovered between congeneric millipedes may not necessarily be due to P scarcity. Consistent with stoichiometric theory, we found significant negative %P allometry across phylogenetic groupings of 17 cave arthropods. We did not see this allometric relationship in millipedes, perhaps because of the lowered P content of the cave-obligate species. Our results highlight the potential for stoichiometric challenges of caves to influence the adaptations of terrestrial cave animals. This novel explanation for cave adaptation may yield insights into cave biodiversity and biogeography.     

Standardized phylogenetic tree: a reference to discover functional evolution

Functional evolution is often driven by positive natural selection. Although it is thought to be rare in evolution at the molecular level, its effects may be observed as the accelerated evolutionary rates. Therefore one of the effective ways to identify functional evolution is to identify accelerated evolution. Many methods have been developed to test the statistical significance of the accelerated evolutionary rate by comparison with the appropriate reference rate. The rates of synonymous substitution are one of the most useful and popular references, especially for large-scale analyses. On the other hand, these rates are applicable only to a limited evolutionary time period because they saturate quickly--i.e., multiple substitutions happen frequently because of the lower functional constraint. The relative rate test is an alternative method. This technique has an advantage in terms of the saturation effect but is not sufficiently powerful when the evolutionary rate differs considerably among phylogenetic lineages. For the aim to provide a universal reference tree, we propose a method to construct a standardized tree which serves as the reference for accelerated evolutionary rate. The method is based upon multiple molecular phylogenies of single genes with the aim of providing higher reliability. The tree has averaged and normalized branch lengths with standard deviations for statistical neutrality limits. The standard deviation also suggests the reliability level of the branch order. The resulting tree serves as a reference tree for the reliability level of the branch order and the test of evolutionary rate acceleration even when some of the species lineages show an accelerated evolutionary rate for most of their genes due to bottlenecking and other effects.     

基于系统演化视角的可持续性评价方法

可持续发展水平的衡量是可持续发展研究的重要内容,它可以为政府的可持续发展决策提供重要的科学依据。现有的可持续性评价方法可分为指标列举法、流量分析法和系统分析法。前两类方法应用广泛,但理论基础较为薄弱,在指标的选取、标准化和赋权等方面存在一定的缺陷。基于系统运行机理的系统分析法尚不多见,但能弥补前两种方法的部分不足,Ulanowicz于2009年提出的演化模型是此类方法的代表。该模型从系统演化角度出发,以网络流为研究对象,以信息论为手段,指出系统的可持续性是系统上升性(效率)和恢复力平衡的结果,并提出了可持续性评价指标R。回顾了现有研究方法的优缺点。介绍了从演化视角分析可持续性的原理和数学模型,可持续发展的阈值范围以及该方法的应用案例。总结了该方法的应用步骤及尚需解决的问题。     

Form,function and evolution of the mouthparts of blood-feeding Arthropoda

This review compares the mouthparts and their modes of operation in blood-feeding Arthropoda which have medical relevance to humans. All possess piercing blood-sucking proboscides which exhibit thin stylet-shaped structures to puncture the host's skin. The tips of the piercing structures are serrated to provide anchorage. Usually, the piercing organs are enveloped by a soft sheath-like part which is not inserted. The piercing process includes either back and forth movements of the piercing structures, or sideways cutting motions, or the apex of the proboscis bears teeth-like structures which execute drilling movements. Most piercing-proboscides have a food-canal which is separate from a salivary canal. The food-canal is functionally connected to a suction pump in the head that transports blood into the alimentary tract. The salivary canal conducts saliva to the tip of the proboscis, from where it is discharged into the host. Piercing blood-sucking proboscides evolved either from (1) generalized biting-chewing mouthparts, (2) from piercing mouthparts of predators, or plant sap or seed feeders, (3) from lapping or sponging mouthparts. Representatives of one taxon of Acari liquefy skin tissue by enzymatic action. During feeding, many blood-feeding arthropods inadvertently transmit pathogens, which mostly are transported through the discharged saliva into the host.     

Convergence to a novel environment: comparative method versus experimental evolution

Abstract Laboratory adaptation allows researchers to contrast temporal studies of experimental evolution with comparative studies. The comparative method is here taken to mean the inference of microevolutionary processes from comparisons among contemporaneous populations of diverse origins, from one or multiple species. The data contrasted here come from Drosophila subobscura populations that were introduced to the laboratory at several different times and from two different locations. Two questions were addressed. First, can we correctly infer evolutionary dynamics from comparative data collected simultaneously from disparate populations? In most cases, we could, except for the character of starvation resistance. Second, are the evolutionary dynamics inferred from the comparative approach similar to those revealed by temporal studies of experimental evolution? For fecundity characters, they were. Overall the results show that both comparative and temporal studies are useful, though the former can be uninformative for characters with complex evolutionary trajectories.     

Origin and evolution of eusociality: a perspective from studying primitively eusocial wasps

Eusocial insects are those that show overlap of generations, cooperative brood care and reproductive caste differentiation. Of these, primitively eusocial insects show no morphological differences between reproductive and worker castes and exhibit considerable flexibility in the social roles that adult females may adopt. This makes them attractive model systems for investigations concerning the origin of eusociality. The rapidly accumulating information on primitively eusocial wasps suggests that haplodiploidy is unlikely to have an important role in the origin of eusociality. General kin selection (without help from haplodiploidy) could however have been an important factor due to the many advantages of group living. Pre-imaginal caste bias leading to variations in fertility is also likely to have some role. Because workers often have some chance of becoming reproductives in future, mutualism and other individual selection models suggest themselves as important factors. A hypothesis for the route to eusociality which focuses on the factors selecting for group living at different stages in social evolution is presented. It is argued that group living originates owing to the benefit of mutualism (the ‘Gambling Stage’) but parental manipulation and subfertility soon become important (the ‘Manipulation Stage’) and finally the highly eusocial state is maintained because genetic asymmetries created by haplodiploidy are exploited by kin recognition (the ‘Recognition Stage’).     

蜱类的起源和演化

蜱类的起源和演化早期主要是通过以形态学和表型特征为依据构建的系统发生树进行推测。到20世纪90年代,通过形态学和分子生物学数据结合在一起的全证据方法进行系统发生分析,并结合生态学、比较寄生虫学、动物地理学、古生物学等方面的资料,对蜱类的起源和演化进行研究。文章综述有关蜱类起源和演化的3个代表性假说,并从蜱类起源和演化的时间、地点、原始宿主、华彩、生活史、寄生状态及蜱类区系演化等方面进行介绍。