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。     

Inference of higher-order relationships in the cycads from a large chloroplast data set

Theria includes Eutheria and its sister taxon Metatheria. Placentalia includes extant eutherians plus their most recent common ancestor. The oldest eutherian is from 125mya (million years ago). Molecular studies place this origin at about 130-185mya. Older dates cannot be refuted based on fossil evidence as earliest eutherian remains are scarce. Earliest superordinal clades (hence Placentalia) range from 64-104mya (median 84mya) based on molecules, similar to 85-90mya based on fossils. Superordinal clades Archonta, Ferungulata, Glires, and Paenungulata based on fossils are similar to molecularly based clades, except Afrotheria was not predicted by fossils. Both fossils and molecules recognize 16 of 18 extant placental orders. Fossils place the origins of orders around 65mya as do some molecular studies, but others suggest ordinal diversification as old as 100mya. Fossil evidence supports a Laurasian origin for Eutheria (and Metatheria) and Placentalia, although some molecular studies suggest a Gondwanan origin for both taxa.     

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.     

Divergence times and origin of neotropical sheath-tailed bats (tribe Diclidurini) in South America

Times of divergence and origin of sheath-tailed bats (family Emballonuridae) in the New World were approximated with a relaxed molecular clock approach using Bayesian analysis of introns from the three nuclear genetic transmission systems in mammals (autosomal, X and Y sex chromosomes). An upper constraint of 30 mya for the oldest known Neotropical emballonurid fossil and a lower constraint of 13 mya for the only pre-Pleistocene fossil of an extant genus were used as calibration points. Differentiation began in the Late Oligocene with the appearance of two subtribes as independently corroborated by each gene. Following an explosive model of evolution, the genera diversified relatively suddenly in the Early Miocene with seven of the eight genera radiating within 1.4 myr and most intrageneric speciation occurring before the Pliocene. Optimization of ancestral areas onto the phylogeny suggests that the ancestor of New World emballonurid bats has its origin in Africa and this is the third report of placental mammals colonizing South America by trans-Atlantic dispersal and subsequent speciation in allopatry.     

Dating the arthropod tree based on large-scale transcriptome data

Molecular sequences do not only allow the reconstruction of phylogenetic relationships among species, but also provide information on the approximate divergence times. Whereas the fossil record dates the origin of most multicellular animal phyla during the Cambrian explosion less than 540 million years ago(mya), molecular clock calculations usually suggest much older dates. Here we used a large multiple sequence alignment derived from Expressed Sequence Tags and genomes comprising 129genes (37,476 amino acid positions) and 117 taxa, including 101 arthropods. We obtained consistent divergence time estimates applying relaxed Bayesian clock models with different priors and multiple calibration points. While the influence of substitution rates, missing data, and model priors were negligible, the clock model had significant effect. A log-normal autocorrelated model was selected on basis of cross-validation. We calculated that arthropods emerged ~600 mya. Onychophorans (velvet worms) and euarthropods split ~590 mya, Pancrustacea and Myriochelata ~560 mya, Myriapoda and Chelicerata ~555 mya, and 'Crustacea' and Hexapoda ~510 mya. Endopterygote insects appeared ~390 mya. These dates are considerably younger than most previous molecular clock estimates and in better agreement with the fossil record. Nevertheless, a Precambrian origin of arthropods and other metazoan phyla is still supported. Our results also demonstrate the applicability of large datasets of random nuclear sequences for approximating the timing of multicellular animal evolution.     

A total-evidence phylogeny of ticks provides insights into the evolution of life cycles and biogeography.

We inferred the phylogeny of 33 species of ticks from the subfamilies Rhipicephalinae and Hyalomminae from analyses of nuclear and mitochondrial DNA and morphology. We used nucleotide sequences from 12S rRNA, cytochrome c oxidase I, internal transcribed spacer 2 of the nuclear rRNA, and 18S rRNA. Nucleotide sequences and morphology were analyzed separately and together in a total-evidence analysis. Analyses of the five partitions together (3303 characters) gave the best-resolved and the best-supported hypothesis so far for the phylogeny of ticks in the Rhipicephalinae and Hyalomminae, despite the fact that some partitions did not have data for some taxa. However, most of the hidden conflict (lower support in the total-evidence analyses compared to that in the individual analyses) was found in those partitions that had taxa without data. The partitions with complete taxonomic sampling had more hidden support (higher support in the total-evidence analyses compared to that in the separate-partition analyses) than hidden conflict. Mapping of geographic origins of ticks onto our phylogeny indicates an African origin for the Rhipicephalinae sensu lato (i.e., including Hyalomma spp.), the Rhipicephalus-Boophilus lineage, the Dermacentor-Anocentor lineage, and the Rhipicephalus-Booophilus-Nosomma-Hyalomma-Rhipicentor lineage. The Nosomma-Hyalomma lineage appears to have evolved in Asia. Our total-evidence phylogeny indicates that (i) the genus Rhipicephalus is paraphyletic with respect to the genus Boophilus, (ii) the genus Dermacentor is paraphyletic with respect to the genus Anocentor, and (iii) some subgenera of the genera Hyalomma and Rhipicephalus are paraphyletic with respect to other subgenera in these genera. Study of the Rhipicephalinae and Hyalomminae over the last 7 years has shown that analyses of individual datasets (e.g., one gene or morphology) seldom resolve many phylogenetic relationships, but analyses of more than one dataset can generate well-resolved phylogenies for these ticks.     

Fossil calibrations and molecular divergence time estimates in centrarchid fishes (Teleostei: Centrarchidae)

Molecular clock methods allow biologists to estimate divergence times, which in turn play an important role in comparative studies of many evolutionary processes. It is well known that molecular age estimates can be biased by heterogeneity in rates of molecular evolution, but less attention has been paid to the issue of potentially erroneous fossil calibrations. In this study we estimate the timing of diversification in Centrarchidae, an endemic major lineage of the diverse North American freshwater fish fauna, through a new approach to fossil calibration and molecular evolutionary model selection. Given a completely resolved multi-gene molecular phylogeny and a set of multiple fossil-inferred age estimates, we tested for potentially erroneous fossil calibrations using a recently developed fossil cross-validation. We also used fossil information to guide the selection of the optimal molecular evolutionary model with a new fossil jackknife method in a fossil-based model cross-validation. The centrarchid phylogeny resulted from a mixed-model Bayesian strategy that included 14 separate data partitions sampled from three mtDNA and four nuclear genes. Ten of the 31 interspecific nodes in the centrarchid phylogeny were assigned a minimal age estimate from the centrarchid fossil record. Our analyses identified four fossil dates that were inconsistent with the other fossils, and we removed them from the molecular dating analysis. Using fossil-based model cross-validation to determine the optimal smoothing value in penalized likelihood analysis, and six mutually consistent fossil calibrations, the age of the most recent common ancestor of Centrarchidae was 33.59 million years ago (mya). Penalized likelihood analyses of individual data partitions all converged on a very similar age estimate for this node, indicating that rate heterogeneity among data partitions is not confounding our analyses. These results place the origin of the centrarchid radiation at a time of major faunal turnover as the fossil record indicates that the most diverse lineages of the North American freshwater fish fauna originated at the Eocene-Oligocene boundary, approximately 34 mya. This time coincided with major global climate change from warm to cool temperatures and a signature of elevated lineage extinction and origination in the fossil record across the tree of life. Our analyses demonstrate the utility of fossil cross-validation to critically assess individual fossil calibration points, providing the ability to discriminate between consistent and inconsistent fossil age estimates that are used for calibrating molecular phylogenies.     

Comment on Phylogenetic analyses with four new Cretaceous bristletails reveal inter-relationships of Archaeognatha and Gondwana origin of Meinertellidae

Archaeognatha (Machilida plus †Monura), with ~450 extant species worldwide, represent a key lineage for the understanding of insect evolution. In a recently published phylogenetic analysis on Archaeognatha, based on a total-evidence approach, a Machilidae key fossil (Gigamachilis triassicus) from the Middle Triassic Lagerstätte of Monte San Giorgio and a representative of †Monura (Dasyleptus triassicus) from the same fossiliferous site, were not considered. In the present study, the phylogenetic analyses performed by Zhang et al. (2018) using maximum parsimony and Bayesian inference were repeated including these two key taxa; in addition, Tricholepidion gertschi and Lepisma saccharina were included as representatives of Zygentoma. In the total-evidence Bayesian analysis, †Monura was found to be paraphyletic, whereas in the maximum parsimony analysis, performed only on morphological characters, they were monophyletic. Moreover, the attribution of G. triassicus to Machilidae is now confirmed by these analyses, indicating that members of the extant group of Machilidae were already present in the Middle Triassic, at least ~100 Myr before the previous estimate.     

Spirochete-like cells in a Dominican amber Ambylomma tick (Arachnida: Ixodidae)

Amber preserves microscopic, soft-bodies organisms and is a good medium in which to trace the evolution of pathogen–vector associations. Spirochetes-like cells (Spirochaetales: Spirochaetaceae) in the hemocoel and lumen of the alimentary tract of a larva tick (Amblyomma sp. Arachnida: Ixodidae) in Dominican amber are described in the collective fossil genus and species, Palaeoborrelia dominicanan. gen., n. sp. The size and shape of the fossil spirochetes closely resemble those of present-day Borrelia species. This discovery represents the first record of spirochete-like cells associated with fossil ticks.     

Variation in genome size of argasid and ixodid ticks

The suborder Ixodida includes many tick species of medical and veterinary importance, but little is known about the genomic characteristics of these ticks. We report the first study to determine genome size in two species of Argasidae (soft ticks) and seven species of Ixodidae (hard ticks) using flow cytometry analysis of fluorescent stained nuclei. Our results indicate a large haploid genome size (1C>1000 Mbp) for all Ixodida with a mean of 1281 Mbp (1.31+/-0.07 pg) for the Argasidae and 2671 Mbp (2.73+/-0.04 pg) for the Ixodidae. The haploid genome size of Ixodes scapularis was determined to be 2262 Mbp. We observed inter- and intra-familial variation in genome size as well as variation between strains of the same species. We explore the implications of these results for tick genome evolution and tick genomics research.     

Adaptation of ticks to a blood-feeding environment: evolution from a functional perspective

Ticks had to adapt to an existing and complex vertebrate hemostatic system from being free-living scavengers. A large array of anti-hemostatic mechanisms evolved during this process and includes blood coagulation as well as platelet aggregation inhibitors. Several questions regarding tick evolution exist. What was the nature of the ancestral tick? When did ticks evolve blood-feeding capabilities? How did these capabilities evolve? Did host specificity influence the adaptation of ticks to a blood-feeding environment? What are the implications of tick evolution for future research into tick biology and vaccine development? We investigate these questions in the light of recent research into protein superfamilies from tick saliva. Our conclusions are that the main tick families adapted independently to a blood-feeding environment. This is supported by major differences observed in all processes involved with blood-feeding for hard and soft ticks. Gene duplication events played a major role in the evolution of novel protein functions involved in tick-host interactions. This occurred during the late Cretaceous and was stimulated by the radiation of birds and placental mammals, which provided numerous new niches for ticks to adapt to a new lifestyle. Independent adaptation of the main tick families to a blood-feeding environment has several implications for future tick research in terms of tick genome projects and vaccine development.     

Evolution of hematophagy in ticks: common origins for blood coagulation and platelet aggregation inhibitors from soft ticks of the genus Ornithodoros

Identification and characterization of antihemostatic components from hematophagous organisms are useful for the elucidation of the evolutionary mechanisms involved in adaptation to a highly complex host hemostatic system. Although many bioactive components involved in the regulation of the host's hemostatic system have been described, the evolutionary mechanisms of how arthropods adapted to a blood-feeding environment have not been elucidated. This study describes common origins of both blood coagulation inhibitors and platelet aggregation inhibitors (PAIs) from soft ticks of the genus Ornithodoros. Neighbor-joining analysis indicates that fXa, thrombin, and PAIs share a common ancestor. Maximum parsimony analysis and a phylogeny based on root mean square deviation values of alpha-carbon backbone structures suggest a novel evolutionary pathway by which different antihemostatic functions have evolved through a series of paralogous gene duplication events. In this scenario, the thrombin inhibitors preceded the fXa and PAIs. This evolutionary model explains why the tick serine protease inhibitors have inhibition mechanisms that differ from that of the canonical bovine pancreatic trypsin inhibitor (BPTI)-like inhibitors. Higher nonsynonymous-to-synonymous substitution rates indicate positive Darwinian selection for the fXa and PAIs. Comparison with hemostatic inhibitors of hard ticks suggests that the two main tick families have independently evolved novel antihemostatic mechanisms. Independent evolution of these mechanisms in ticks points to a rapid divergence between tick families that could be dated between 120 and 92 MYA. This coincides with current molecular phylogeny views on the early divergence of modern birds and placental mammals in the Late Cretaceous, which suggests that this event might have been a driving force in the evolution of hematophagy in ticks.     

蜱类系统学研究进展

本文介绍了近年来蜱的编目和分类及系统发育和演化等方面的研究进展。对软蜱科(Argasidae)说明了属的变动;硬蜱科(Ixodidae)介绍了璃眼蜱亚科(Hyalomminae)和凹沟蜱亚科(Bothriocrotoninae)以及相应变动的属(新建的凹沟蜱属Bothriocroton和须角蜱属Cornupalpatum,合并的牛蜱属Boophilus、暗眼蜱属Anocentor和盲花蜱属Aponomma)。根据新的分类变更对已知种类进行了分析。至2006年,世界已知蜱类有3科18属897种,中国有2科10属119种。阐明了有关蜱类系统发育研究的主要观点,并讨论了其不足和有待深入研究的问题。目前,把形态学和分子生物学数据结合在一起的全证据方法,并结合蜱类和不同宿主之间的关系、动物地理学、古生物学以及比较寄生虫学的资料,成为解决蜱类系统发育问题的有效途径。     

A biogeographical analysis of Muhlenbergia (Poaceae: Chloridoideae: Cynodonteae: Muhlenbergiinae)

A phylogeny based on the analysis of six DNA sequence markers (ITS, ndhA intron, rpl32-trnL, rps3, rps16 intron, and rps16-trnK) is used to infer ancestral areas and divergence times, and reconstruct the biogeographical history and evolution of 150 of the 183 (82%) species of Muhlenbergia. Our results suggest that the genus originated 9.3 mya in the Sierra Madre (Occidental and Oriental) in Mexico, splitting into six lineages: M. ramulosa diverging 8.2 mya, M. subg. Muhlenbergia at 5.9 mya, M. subg. Pseudosporobolus at 5.9 mya, M. subg. Clomena at 5.4 mya, M. subg. Bealia at 4.3 mya, and M. subg. Trichochloa at 1 mya, each of these with a high probability of Sierra Madrean origin. Our results further suggest that founder-event speciation from Sierra Madre to South America occurred independently multiple times in all five subgenera during the Pleistocene and late Pliocene. One long-distance dispersal event most likely originating from Central or Eastern North America to East and Central Asia occurred 1.6–1 mya in M. subg. Muhlenbergia. In our cladogram, members of M. subg. Trichochloa show little genetic resolution, suggesting very low levels of divergence among the species, and this may be a consequence of rapid radiation.     

Molecular data from 27 proteins do not support a Precambrian origin of land plants

Heckman et al. (Science 293: 1129-1133) used sequences obtained from GenBank to infer divergence times in fungi and green plants. They estimated that the crown group of land plants originated in the Precambrian, at 703 ± 45 mya, a date much older than dates implied by the fossils, which are no older than about 450 mya. This paper presents an analysis of an entirely different set of sequence data from 27 plastid protein-coding genes in 10 land plants and a green algal outgroup. It uses a calibration point closer to the origin of land plants and inference methods that do not assume a molecular clock. This leads to estimates ranging from 425 to 490 mya, which brackets the age suggested by the fossil record. Possible explanations for the differing conclusions in the two studies include differences in calibration points and use of single-copy plastid genes rather than nuclear gene families.     

Factors affecting the virulence of entomopathogenic nematodes to engorged female Boophilus annulatus ticks

The laboratory trials rank the virulence of entomopathogenic nematode strains (3 heterorhabditids and 6 steinernematids) to engorged female Boophilus annulatus ticks according to 3 parameters of the infection process: the effect of exposure time on tick mortality, the quantity of nematodes that penetrate ticks, and the rate of tick mortality after the injection of 1, 2, or 3 nematodes. Exposure of the ticks to heterorhabditid strains for 6 hr resulted in >80% mortality, but only 20 or 65% mortality after exposure to most steinernematids. The quantity of nematodes recovered per tick exposed to nematodes for 6 days averaged from 16 to 141. For steinernematids, a negative correlation was obtained between tick mortality and the average quantity of nematodes recovered. Injecting 1 infective juvenile from 1 of 2 heterorhabditid strains into each tick resulted in close to 100% mortality. Increasing the quantity of nematodes injected into each tick had little or no additive effect on tick mortality.     

Dispersal and distribution of the tick Ixodes uriae within and among seabird host populations: the need for a population genetic approach

The aim of this study was to characterize the spatial distribution of the tick Ixodes uriae within and among populations of its seabird hosts and to consider the potential insight that could be gained by a population genetic approach to the issue of dispersal of this tick. Analyses of data collected around the Avalon Peninsula, Newfoundland, indicated that both the prevalence and mean abundance of ticks varied significantly among sample locations. Whereas ticks were found on all 4 host species examined (Rissa tridactyla, Uria aalge, Alca torda, Fratercula arctica), infestation prevalence and mean abundance differed among the species. On R. tridactyla, ticks were significantly aggregated at the among-nest scale and nestling infestation was spatially autocorrelated. Conversely, ticks were not aggregated among chicks within nests. These results enabled us to make a priori predictions regarding tick dispersal and host specificity and suggest there may be spatial structure of Ixodes uriae populations at both macro- and microgeographic scales. Investigating the population genetic structure of ticks within and among populations of hosts with different breeding biologies should provide direct insight into the metapopulation dynamics of such a spatially structured system.     

Hyalomma ticks on northward migrating birds in southern Spain: Implications for the risk of entry of Crimean‐Congo haemorrhagic fever virus to Great Britain

Crimean‐Congo haemorrhagic fever virus (CCHFV) is a zoonotic virus transmitted by Hyalomma ticks, the immature stages of which may be carried by migratory birds. In this study, a total of 12 Hyalomma ticks were recovered from five of 228 migratory birds trapped in Spring, 2012 in southern Spain along the East Atlantic flyway. All collected ticks tested negative for CCHFV. While most birds had zero Hyalomma ticks, two individuals had four and five ticks each and the statistical distribution of Hyalomma tick counts per bird is over‐dispersed compared to the Poisson distribution, demonstrating the need for intensive sampling studies to avoid underestimating the total number of ticks. Rates of tick exchange on migratory birds during their northwards migration will affect the probability that a Hyalomma tick entering Great Britain is positive for CCHFV. Drawing on published data, evidence is presented that the latitude of a European country affects the probability of entry of Hyalomma ticks on wild birds. Further data on Hyalomma infestation rates and tick exchange rates are required along the East Atlantic flyway to further our understanding of the origin of Hyalomma ticks (i.e., Africa or southern Europe) and hence the probability of entry of CCHFV into GB.