The evolution of host plant manipulation by insects: molecular and ecological evidence from gall-forming aphids on Pistacia

One of the most striking characteristics of gall-forming insects is the variability in gall position, morphology, and complexity. Our knowledge of the driving forces behind the evolutionary divergence of gall types is limited. Natural enemies, competition, and behavioral constraints might be involved. We present a cladogram, based on sequences of COI and COII (1952bp), of mitochondrial DNA for the evolution of 14 species of gall-forming aphids (Fordinae). These insects induce five gall types with remarkable morphological variation on Pistacia spp. hosts. The parsimony cladogram divides the Fordinae into three lineages, Fordini and Baizongiini, and a third (new) sister group including the previously Fordini member, Smynthurodes betae (West). We then use ecological data to trace and explain the evolution of gall morphology. The aphids seem to have evolved gradually towards better ability to manipulate their host plant, induce stronger sinks, and gain higher reproductive success. We suggest that the ancestral gall type was a simple, open, "pea"-sized gall located on the leaflet midvein. Some Fordini and S. betae evolved a two-gall life cycle, inducing a new gall type on the leaflet margin. The Baizongiini improved the manipulation of their host by inducing larger galls near the midvein, with stronger sinks supporting thousands of aphids. Similar gall types are induced at similar sites on different Pistacia hosts suggesting control of the aphids on gall morphology and frequent host shifts. Thus, even extreme specialization (specific gall and host) is flexible.     

Molecular characteristics of Camallanus Spp. (Spirurida: Camallanidae) in fishes from China based on its rDNA sequences

In the paper, we explored the intra- and interspecific evolutionary variation among species of Camallanus collected from different fish species in various regions of China. We determined the internal transcribed spacers of ribosomal DNA (ITS rDNA) sequences of these nematodes. The divergence (uncorrected p-distance) of ITS1, ITS2, and ITS rDNA data sets confirmed 2 valid species of Camallanus in China, i.e., C. cotti and C. hypophthalmichthys. The 2 species were distinguished not only by their different morphologies and host ranges but also by a tetranucleotide microsatellite (TTGC)n present in the ITS1 region of C. cotti. Phylogenetic analyses of the nematodes disclosed 2 main clades, corresponding to different individuals of C. cotti and C. hypophthalmichthys from different fish species in various geographical locations, although the interior nodes of each clade received poor support.     

Examination of two morphs of gall-forming Aciurina (Diptera: Tephritidae): ecological and genetic evidence for species

Aciurina bigeloviae (Cockerell) (Diptera: Tephritidae) is a gall-forming tephritid fly associated with rubber rabbitbrush, Chrysothamnus nauseosus (Pallas) Britton (Compositae), throughout the western United States. Two distinct gall morphologies were found among A. bigeloviae populations, each associated with its own morphologically distinct group of subspecies of C. nauseosus . Adults emerging from these galls can be distinguished on the basis of wing morphology and pronotal colour. Electrophoretic analysis of these two morphs suggested limited, unidirectional gene flow between them. Results of several other investigations were consistent with a restricted gene flow hypothesis. Heterotypic matings occurred in the laboratory, but at a depressed level. Host plant preferences, ovipositional success on the different host plant groups, and two life history parameters differed between the two fly types. Based on these multiple lines of evidence, we concluded that these two morphs of Aciurina represent two species: A. bigeloviae and A. trixa Curran. Reasons why these flies might be more appropriately viewed as host races are discussed as are scenarios which might account for their divergence.     

Identification of Seed Gall Nematodes of Agronomic and Regulatory Concern with PCR-RFLP of ITS1

A molecular analysis of eight described species of seed gall nematode, along with six undescribed isolates from different hosts, has revealed a strong association between nucleotide sequence polymorphism and host status. Each anguinid nematode associated with a unique host produced a unique PCR-RFLP pattern for the ITS1 region. Anguina species that had been synonymized in the past, Anguina agrostis, A. funesta, and A. wevelli (Afrina wevelli), were readily discriminated. Two undescribed species from northern New South Wales and southeastern South Australia, reported to be vectors of Rathyaibacter toxicus in the disease called ''''floodplain staggers,'''' were differentiated by a single restriction enzyme, and both could be separated easily from A. funesta, the vector of R. toxicus in annual ryegrass toxicity. Other species differentiated in this study include A. agropyronifloris, A. graminis, A. microlaenae, A. pacificae, and undescribed species from host species Dactylis glomerata, Agrostis avenacea, Polypogon monospeliensis, Stipa sp., Astrebla pectinata, and Holcus lanatus. Phylogenetic analysis of the ITS1 region suggests that considerable anguinid genetic diversification has accompanied specialization on different host species.     

Phylogenetic relationships among populations of the Nacobbus aberrans (Nematoda,Pratylenchidae) complex reveal the existence of cryptic species

The plant‐parasitic nematode Nacobbus aberrans sensu lato is an agricultural pest of quarantine importance. Due to the morphometric, physiological and genetic variability observed within the species, there is no agreement on the taxonomy of this nematode. The objective of this study was to analyse the ITS rDNA region and the D2–D3 expansion segments of 28S rDNA in 10 Argentine populations and one from Ecuador and to establish their phylogenetic relationship with other known sequences from South and North America. Phylogenetic trees of the ITS gene showed seven statistically well‐supported clades; the high and significant F_st values obtained among these groups confirmed this partitioning. The Argentine populations here considered were separated into three clades: one comprising a population from the Andean region and two grouping nematodes from lower altitudes. Three other clades were distinguished for South American populations, which included known sequences of individuals from Peru, Bolivia and north of Argentina. The other clade included sequences from Mexico, Ecuador and two Argentine populations of unknown origin. The important degree of genetic divergence observed among Andean populations suggests that the Andes may have played a crucial role in speciation of Nacobbus, which would have originated in this region. Although D2–D3 segments exhibited lower variation, they were useful for establishing phylogenetic relationships among the Argentine populations considered in this work. As there are no other GenBank sequences available for these segments, it was not possible to make comparisons with other populations from South and North America. The considerable genetic differentiation observed in ITS rDNA region among Nacobbus populations showed evidence of cryptic species within the N. aberrans s.l. complex. Integration of morphological and morphometric studies and molecular analyses considering other genes may aid in the identification of species and their phylogenetic relationships within this genus.     

Phylogenetic Relationships of Globodera millefolii,G. artemisiae,and Cactodera salina Based on ITS Region of Ribosomal DNA

Globodera millefolii and G. artemisiae are interesting because their type localities (Estonia and Russia, respectively) are geographically distant from those of the potato cyst nematodes and other Globodera species that seem to have originated in the Western world, and because the type host for each is a member of Compositae rather than Solanaceae. Sequence data for ITS1, ITS2, and 5.8S ribosomal DNA (ITS rDNA) for G. millefolii and G. artemisiae were nearly identical to sequence data for Cactodera salina from the rhizosphere of the estuary plant Salicornia bigelovii in Sonora, Mexico. The ITS rDNA sequences of these three species were all about 94% similar to those of two other Cactodera species for which ITS rDNA data were obtained. Phylogenetic analysis indicated that, based on the ITS rDNA data, G. millefolii and G. artemisiae are more closely related phylogenetically to the Cactodera species than to other nominal Globodera species. The molecular data further suggest that the genus Cactodera may comprise two or more morphologically similar but separate groups.     

Evolution of the gall wasp-host plant association

Gall wasps, or cynipids, form the second largest radiation of galling insects with more than 1300 described species. According to current views, the first cynipids were phytophagous and developed in herb stems of the Asteraceae without modifying plant growth or development. The first galls were supposedly multichambered stem swellings, and subsequent trends involved increase in gall complexity and reduction in the number of larval chambers. Gall wasps also have many of the features believed to be characteristic for phytophagous insects radiating in parallel with their host plants. We tested these hypotheses by mapping characters onto a recent estimate of higher cynipid relationships from a morphology-based analysis of exemplar taxa, controlling for phylogenetic uncertainty using bootstrapping. Characters were also mapped onto a metatree including all gall wasps, assembled from phylogenetic analyses as well as recent classifications. The results contradict many of the current hypotheses. The first cynipids with extant descendants were not Asteraceae stem feeders but induced distinct single-chambered galls in reproductive organs of herbaceous Papaveraceae, or possibly Lamiaceae. There has been a general trend toward more complex galls but the herb-stem feeders evolved from ancestors inducing distinct galls and their larval chambers are best understood as cryptic galls. Woody hosts have been colonized only three times, making the apparently irreversible transition from herbs to woody hosts one of the most conservative features of the gall wasp-host plant association. The evolution of host plant preferences is characterized by colonization of preexisting host-plant lineages rather than by parallel cladogenesis. Cynipids are mono- or oligophagous and host-plant choice is strongly phylogenetically conserved. Yet, the few major host shifts have involved remarkably distantly related plants. Many shifts have been onto plant species already exploited by other gall wasps, suggesting that interspecific parasitism among cynipids facilitates colonization of novel host plants.     

Associations between mycophagous Drosophila and their Howardula nematode parasites: a worldwide phylogenetic shuffle

Little is known about what determines patterns of host association of horizontally transmitted parasites over evolutionary timescales. We examine the evolution of associations between mushroom-feeding Drosophila flies (Diptera: Drosophilidae), particularly in the quinaria and testacea species groups, and their horizontally transmitted Howardula nematode parasites (Tylenchida: Allantonematidae). Howardula species were identified by molecular characterization of nematodes collected from wild-caught flies. In addition, DNA sequence data is used to infer the phylogenetic relationships of both host Drosophila (mtDNA: COI, II, III) and their Howardula parasites (rDNA: 18S, ITS1; mtDNA: COI). Host and parasite phylogenies are not congruent, with patterns of host association resulting from frequent and sometimes rapid host colonizations. Drosophila-parasitic Howardula are not monophyletic, and host switches have occurred between Drosophila and distantly related mycophagous sphaerocerid flies. There is evidence for some phylogenetic association between parasites and hosts, with some nematode clades associated with certain host lineages. Overall, these host associations are highly dynamic, and appear to be driven by a combination of repeated opportunities for host colonization due to shared breeding sites and large potential host ranges of the nematodes.     

Non-native plants rarely provide suitable habitat for native gall-inducing species

For insect herbivores, a critical niche requirement—possibly the critical niche requirement—is the presence of suitable host plants. Current research suggests that non-native plants are not as suitable as native plants for native herbivores, resulting in decreases in insect abundance and richness on non-native plants. Like herbivores, gall-forming insects engage in complex, species-specific interactions with host plants. Galls are plant tissue tumors (including bulbous or spindle-shaped protrusions on leaves, stems and other plant organs) that are induced by insects through physical or chemical damage (prompting plants to grow a protective tissue shell around the insect eggs and larvae). As such, we hypothesized that gall-inducing insect species richness would be higher on native than non-native plants. We also predicted higher gall-inducing insect species richness on woody than herbaceous plants. We used an extensive literature review in which we compiled gall host plant species by genus, and we assigned native or non-native (or mixed) status to each genus. We found that native plants host far more gall-inducing insect species than non-native plants; woody plants host more gall-inducing species than herbaceous plants; and native woody plants host the most gall-inducing species of all. Gall-inducing species generally are a very cryptic group, even for experts, and hence do not elicit the conservation efforts of more charismatic insects such as plant pollinators. Our results suggest that non-native plants, particularly non-native woody species, diminish suitable habitat for gall-inducing species in parallel with similar results found for other herbivores, such as Lepidopterans. Hence, the landscape-level replacement of native with non-native species, particularly woody ones, degrades taxonomically diverse gall-inducing species (and their inquilines and parasitoids), removing multiple layers of diversity from forest ecosystems.

     

Characterization and Sequence Variation in the rDNA Region of Six Nematode Species of the Genus Longidorus (Nematoda)

Total DNA was isolated from individual nematodes of the species Longidorus helveticus, L. macrosoma, L. arthensis, L. profundorum, L. elongatus, and L. raskii collected in Switzerland. The ITS region and D1-D2 expansion segments of the 26S rDNA were amplified and cloned. The sequences obtained were aligned in order to investigate sequence diversity and to infer the phylogenetic relationships among the six Longidorus species. D1-D2 sequences were more conserved than the ITS sequences that varied widely in primary structure and length, and no consensus was observed. Phylogenetic analyses using the neighbor-joining, maximum parsimony and maximum likelihood methods were performed with three different sequence data sets: ITS1-ITS2, 5.8S-D1-D2, and combining ITS1-ITS2+5.8S-D1-D2 sequences. All multiple alignments yielded similar basic trees supporting the existence of the six species established using morphological characters. These sequence data also provided evidence that the different regions of the rDNA are characterized by different evolution rates and by different factors associated with the generation of extreme size variation.     

Molecular phylogenetics and the evolution of host plant associations in the nematode genus Fergusobia (Tylenchida: Fergusobiinae)

Fergusobia nematodes (Tylenchida: Fergusobiinae) and Fergusonina flies (Diptera: Fergusoninidae) are putative mutualists that develop together in galls formed in meristematic tissues of many species of the plant family Myrtaceae in Australasia. Fergusobia nematodes were sampled from a variety of myrtaceous hosts and gall types from Australia and one location in New Zealand between 1999 and 2006. Evolutionary relationships of these isolates were inferred from phylogenetic analyses of the DNA sequences of the nuclear ribosomal DNA near-full length small subunit (up to 1689bp for 21 isolates), partial large subunit D2/D3 domain (up to 889bp for 87 isolates), partial mitochondrial cytochrome oxidase subunit I (618 bp for 82 isolates), and combined D2/D3 and mtCOI (up to 1497bp for 66 isolates). The SSU data supported a monophyletic Fergusobia genus within a paraphyletic Howardula. A clade of Drosophila-associated Howardula, including Howardula aoronymphium, was the closest sequenced sister group. Phylogenetic analysis of sequences from D2/D3 and mtCOI, separately and combined, revealed many monophyletic clades within Fergusobia. The relationships inferred by D2/D3 and mtCOI were congruent with some exceptions. Well-supported clades were generally consistent with host plant species and gall type. However, phylogenetic analysis suggested host switching or putative hybridization events in many groups, except the lineage of shoot bud gallers on the broad-leaved Melaleuca species complex.     

Phylogenetic Relationships Among Selected Heteroderoidea Based on 18S and ITS Ribosomal DNA

In a study of relationships among selected cyst-forming and noncyst-forming species of Heteroderoidea, combined sequences comprised of DNA from part of the conserved 18S ribosomal RNA gene (rDNA) plus the complete ITS rDNA segment were more similar to analyses based on the ITS data alone than to analyses based on the 18S data alone. One of the two noncyst-forming species, Ekphymatodera thomasoni, grouped with cyst-forming species of Heteroderoidea. Bilobodera flexa, also a noncyst-forming species, was separated from all the other taxa by a long branch. Afenestrata koreana, with a weakly sclerotized cyst, grouped closely with H. bifenestra. These observations suggest that phylogenetic analyses using molecular data may aid in our understanding of the evolution of cyst formation in nematodes, including the possibility of secondary loss. The usefulness of molecular phylogenetic analyses in nematodes may depend more on the particular selection of taxa than on mere addition of data from additional genes.     

A galling aphid with extra life-cycle complexity: Population ecology and evolutionary considerations

In most gall-forming aphids, only the fundatrix is able to induce a gall on the host plant. In Smynthurodes betae Westw. (and a few other species), F₂ descendants emerge from the mother gall and induce their own, morphologically different galls. This constitutes an added complexity to the already very complex life cycle of gall-forming aphids. We investigated the ecology of S. betae on marked trees and shoots at four sites in Israel. Gall initiation, gall distribution and density, and temporal changes in clone size within the galls were investigated during two consecutive years. We discuss the possibility that the two-gall life cycle evolved from the typical one-gall system of most gall aphids, and the possible selective advantage of this added complexity in the life-history strategy of gall aphids. Although the total reproductive output of S. betae is not higher than in related species with a single gall per life cycle, there seems to be an advantage in the subdivision of each aphid clone into several galls, thus reducing the risk of the accidental extinction of the clone (genotype) by environmental factors, including parasites and predators.     

Molecular insight into systematics,host associations,life cycles and geographic distribution of the nematode family Rhabdiasidae

Rhabdiasidae Railliet, 1915 is a globally distributed group of up to 100 known species of nematodes parasitic in amphibians and reptiles. This work presents the results of a molecular phylogenetic analysis of 36 species of Rhabdiasidae from reptiles and amphibians from six continents. New DNA sequences encompassing partial 18S rDNA, ITS1, 5.8S rDNA, ITS2 and partial 28S rDNA regions of nuclear ribosomal DNA were obtained from 27 species and pre-existing sequences for nine species were incorporated. The broad taxonomic, host and geographical coverage of the specimens allowed us to address long-standing questions in rhabdiasid systematics, evolution, geographic distribution, and patterns of host association. Our analysis demonstrated that rhabdiasids parasitic in snakes are an independent genus sister to the rest of the Rhabdiasidae, a status supported by life cycle data. Based on the combined evidence of molecular phylogeny, morphology and life cycle characteristics, a new genus Serpentirhabdias gen. nov. with the type species Serpentirhabdias elaphe (Sharpilo, 1976) comb. nov. is established. The phylogeny supports the monophyly of Entomelas Travassos, 1930, Pneumonema Johnston, 1916 and the largest genus of the family, Rhabdias Stiles and Hassall, 1905. DNA sequence comparisons demonstrate the presence of more than one species in the previously monotypic Pneumonema from Australian scincid lizards. The distribution of some morphological characters in the genus Rhabdias shows little consistency within the phylogenetic tree topology, in particular the apical structures widely used in rhabdiasid systematics. Our data suggest that some of the characters, while valuable for species differentiation, are not appropriate for differentiation among higher taxa and are of limited phylogenetic utility. Rhabdias is the only genus with a cosmopolitan distribution, but some of the lineages within Rhabdias are distributed on a single continent or a group of adjacent zoogeographical regions. Serpentirhabdias, Entomelas and Pneumonema show rather strict specificity to their host groups. The evolution of the Rhabdiasidae clearly included multiple host switching events among different orders and families of amphibians as well as switching between amphibians and squamatan reptiles. Only a few smaller lineages of Rhabdias demonstrate relatively strict associations with a certain group of hosts.     

Molecular phylogeny,diagnostics, and diversity of plant‐parasitic nematodes of the genus Hemicycliophora (Nematoda: Hemicycliophoridae)

The genus Hemicycliophora (Nematoda: Hemicycliophoridae) contains 132 valid species of plant‐parasitic nematodes, collectively known as ‘sheath nematodes’. Hemicycliophora spp. are characterized morphologically by a long stylet with rounded basal knobs and a cuticular sheath, present in juvenile and adult stages. Populations of 20 valid and 14 putative species of Hemicycliophora and Loofia from several countries were characterized morphologically using light (LM) and scanning electron microscopy (SEM) and molecularly using the D2‐D3 segments of 28S rRNA and internal transcribed spacer (ITS) rRNA gene sequences. LM and SEM observations provided new details on the morphology of these species. PCR‐restriction fragment length polymorphisms (PCR‐RFLPs) of the D2‐D3 of 28S rDNA were proposed for identification of the species. Phylogenetic relationships within populations of 36 species of the genus Hemicycliophora using 102 D2‐D3 of 28S rDNA and 97 ITS rRNA gene sequences as inferred from Bayesian analysis are reconstructed and discussed. Ancestral state reconstructions of diagnostic characters (body and stylet length, number of body annuli, shape of vulval lip and tail), using maximum parsimony and Bayesian inference, revealed that none of the traits are individually reliable characters for classifying the studied sheath nematode. The Shimodaira–Hasegawa test rejected the validity of the genus Loofia. This is the most complete phylogenetic analysis of Hemicycliophora species conducted so far. © 2014 The Linnean Society of London     

The effect of the taxon and geographic range size of host eucalypt species on the species richness of gall-forming insects

Abstract This field study was designed to test whether the taxonomic group and geographic range size of a host plant species, usually found to influence insect species richness in other parts of the world, affected the number of gall species on Australian eucalypts. We assessed the local and regional species richness of gall-forming insects on five pairs of closely related eucalypt species. One pair belonged to the subgenus Corymbia, one to Monocalyptus, and three to different sections of Symphyomyrtus. Each eucalypt pair comprised a large and a small geographic range species. Species pairs were from coastal or inland regions of eastern Australia. The total number of gall species on eucalypt species with large geographic ranges was greater than on eucalypt species with small ranges, but only after the strong effect of eucalypt taxonomic grouping was taken into account. There was no relationship between the geographic range size of eucalypt species and the size of local assemblages of gall species, but the variation in insect species composition between local sites was higher on eucalypt species with large ranges than on those with small ranges. Thus the effect of host plant range size on insect species richness was due to greater differentiation between more widespread locations, rather than to greater local species richness. This study confirms the role of the geographic range size of a host plant in the determination of insect species richness and provides evidence for the importance of the taxon of a host plant.     

Evolution of gall morphology and host-plant relationships in willow-feeding sawflies (Hymenoptera: Tenthredinidae)

Abstract.— There are over 200 species of nematine sawflies that induce galls on willows (Salix spp.). Most of the species are monoor oligophagous, and they can be separated into seven or eight different groups based on the type of gall that they induce. We studied the evolution of different gall types and host plant associations by reconstructing the phylogeny of five outgroup and 31 ingroup species using DNA sequence data from the mitochondrial cytochrome b gene. Maximum-parsimony and maximum-likelihood analyses resulted in essentially the same phylogeny with high support for important branches. The results show that: (1) the galling species probably form a monophyletic group; (2) true closed galls evolved only once, via leaf folders; (3) with the possible exception of leaf rollers, all gall type groups are mono- or paraphyletic; (4) similar gall types are closer on the phylogeny than would be expected by a random process; (5) there is an apparent evolutionary trend in galling site from the leaf edge towards the more central parts of the host plant; and (6) many willow species have been colonized several times, which excludes the possiblity of parallel cladogenesis between willows and the gallers; however, there are signs of restrictions in the evolution of host use. Many of the patterns in the evolutionary history of nematine gallers have also been observed in earlier studies on other insect gallers, indicating convergent evolution between the independent radiations.     

Molecular phylogeny of Fordini (Hemiptera: Aphididae: Pemphiginae) inferred from nuclear gene EF-1 alpha and mitochondrial gene COI

The tribe Fordini is a fascinating group because of its complicated life history, primary host specificity and gall-forming characteristic. Different species produce galls with different morphology on different parts of the host plants. The EF-1alpha-based, COI-based and combined sequences-based phylogenetic trees with three algorithms MP, ML and Bayes all strongly suggest that Fordini is a monophyletic group with two clades corresponding to two subtribes, Fordina and Melaphidina, each also monophyletic. Some important morphological characters and primary host plants of aphids were mapped onto the phylogenetic tree to analyse the division of subtribes and to uncover at which level the aphids correspond to their primary hosts, Pistacia and Rhus. Results suggest that the division of subtribes in Fordini is closely related to host selection of aphids. The evolution of gall morphology and the probable driving force behind it in this tribe were also discussed. The Fordini aphids seem to have evolved towards a better ability to manipulate their host plant, induce strong sinks and gain high reproductive success. Galls in this tribe evolved mainly along two directions to attain this goal: (i) by enlarging the gall from small bag to spherical, even big cauliflower-like, and changing the galls' location or forming two galls in their life cycle (Fordina); (ii) by moving the gall position from midrib, petiole of the leaflet, and eventually to the common petiole of the compound leaf (Melaphidina).     

Reticulate evolution and the origins of ribosomal internal transcribed spacer diversity in apomictic Meloidogyne

Among root knot nematodes of the genus Meloidogyne, the polyploid obligate mitotic parthenogens M. arenaria, M. javanica, and M. incognita are widespread and common agricultural pests. Although these named forms are distinguishable by closely related mitochondrial DNA (mtDNA) haplotypes, detailed sequence analyses of internal transcribed spacers (ITSs) of nuclear ribosomal genes reveal extremely high diversity, even within individual nematodes. This ITS diversity is broadly structured into two very different groups that are 12%-18% divergent: one with low diversity (< 1.0%) and one with high diversity (6%-7%). In both of these groups, identical sequences can be found within individual nematodes of different mtDNA haplotypes (i.e., among species). Analysis of genetic variance indicates that more than 90% of ITS diversity can be found within an individual nematode, with small but statistically significant (5%-10%; P < 0.05) variance distributed among mtDNA lineages. The evolutionarily distinct parthenogen M. hapla shows a similar pattern of ITS diversity, with two divergent groups of ITSs within each individual. In contrast, two diploid amphimictic species have only one lineage of ITSs with low diversity (< 0.2%). The presence of divergent lineages of rDNA in the apomictic taxa is unlikely to be due to differences among pseudogenes. Instead, we suggest that the diversity of ITSs in M. arenaria, M. javanica, and M. incognita is due to hybrid origins from closely related females (as inferred from mtDNA) and combinations of more diverse paternal lineages.     

中国9种嗜子宫线虫系统发育的初步研究

为了探讨鱼类寄生嗜子宫线虫的系统发育关系,测定了8种嗜子宫线虫的ITS rDNA(核糖体转录内间隔区核 糖核酸)序列和9种嗜子宫线虫的18S rDNA(小亚基核糖体核糖核酸)部分序列,并构建了18S rDNA序列的系统发 育树。在比较和分析ITS rDNA和18S rDNA两种分子标记对嗜子宫科线虫系统发育适用性的基础上,分析了嗜子 宫线虫的系统发育关系。结果表明:中国嗜子宫线虫是单系起源;黄颡鱼似嗜子宫线虫、赣州似嗜子宫线虫和棍头 嗜子宫线虫亲缘关系非常接近,可能是较晚形成的种;似嗜子宫线虫属可能应该被细分为更多的属。