Landscape and oceanic barriers shape dispersal and population structure in the island nematode Pristionchus pacificus

In this study evolutionary host plant patterns at ranks from order to species were analysed using spatial evolutionary and ecological vicariance analysis (SEEVA), based on a multigene phylogeny of 45 ascomycete fungal species. The objective was to understand speciation events and host associations in Ophiognomonia (Gnomoniaceae). Species of this genus are perithecial fungi that occur as endophytes, pathogens, and latent saprobes on plants in the families of Betulaceae, Fagaceae, Juglandaceae, Lauraceae, Malvaceae, Platanaceae, Rosaceae, Salicaceae, and Sapindaceae. A second objective was to determine whether speciation events are influenced by host conservatism, host specialization, or host switching at different taxonomic host ranks. Host differences between sister clades were interpreted using the divergence index (D) from the SEEVA analysis, ranging from 0 for no divergence to 1 for maximum possible divergence. Several fungal subclades showed clear patterns of host order/family conservatism (D = 1.00) for hosts in Betulaceae, Fagaceae, Juglandaceae, and Rosaceae. Clear trends of host specialization at host genus and species ranks (D = 1.00) were suggested within these host families. Independent host jumps were observed for two species at the family rank and three at the order rank. As a result of this study, host specificity and specialization is hypothesized as a mechanism that can strongly contribute to speciation patterns in fungal pathogens. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 1–16.     

Pigmy moths (Lepidoptera, Nepticulidae) from the Middle Volga Basin

Fifty-seven species of the family Nepticulidae were found in the Middle Volga Basin. The family includes four genera: Bohemannia Stainton, 1859 (1 species), Ectoedemia Busck, 1907 (15), Stigmella Schrank, 1802 (38), and Trifurcula Zeller, 1848 (3 species). The mines made by pigmy moth larvae are very specific in the study area. Larvae of the largest genus, Stigmella, make typical serpentine leaf mines. Larvae of the genera Bohemannia and Ectoedemia make blotchy mines; some larvae develop in fruits and tree bark. Most species of the genera Bohemannia, Ectoedemia, and Stigmella were recorded by their mines. At the larval stage, representatives of Trifurcula feed on stems of legumes. The pupae develop in the soil. Most species in the family Nepticulidae are leaf miners, mainly associated with Rosaceae (34.7%), Salicaceae (15.8%), Fagaceae (12.3%), and Betulaceae (12.3%). All the species investigated do not act as pests of forage plants in the area studied.     

THE EVOLUTION OF HOST-PLANT USE AND SEQUESTRATION IN THE LEAF BEETLE GENUS PHRATORA (COLEOPTERA: CHRYSOMELIDAE)

Leaf beetles in the genus Phratora differ in host plant use and in the chemical composition of their larval defensive secretion. Most species specialize on either poplars or willows (family Salicaceae), but two species feed on birch (family Betulaceae). Phratora vitellinae utilizes salicylates from the host plant to produce its larval secretion, which contains salicylaldehyde, while other Phratora species produce an autogenous secretion. To reconstruct the evolutionary history of host plant use and the larval secretion chemistry in this genus, we sequenced 1383 base pairs of the mt cytochrome oxidase I gene for six European and one North American Phratora species and three outgroup taxa. Bootstrap values of the complete nucleotide sequence were 99-100% for six of eight nodes in the maximum parsimony tree. They were 71% and 77% for the two other nodes. The maximum parsimony tree and the maximum likelihood tree based on nucleotide sequence showed the same relationships as a maximum parsimony tree based on the amino acid sequence. Beetle phylogeny overlapped broadly with host plant taxonomy and chemistry, and it revealed historical constraints influencing host plant use. However, there was one host shift from the willow family (Salicaceae) to the birch family (Betulaceae). The use of host plant phenol glycosides for the larval defensive secretion evolved along the lineage that led to P. vitellinae. Phratora vitellinae feeds on the taxonomically widest range of host plants, which are characterized by moderate to high levels of salicylates. The results support the hypothesis that the use of salicylates for the larval secretion evolved twice independently in chrysomeline leaf beetles.     

Phylogenetic analyses of DNA and allozyme data suggest that Gonioctena leaf beetles (Coleoptera; Chrysomelidae) experienced convergent evolution in their history of host-plant family shifts

A phylogenetic analysis of the genus Gonioctena (Coleoptera, Chrysomelidae) based on allozyme data (17 loci) and mitochondrial DNA sequence data (three gene fragments, 1,391 sites) was performed to study the evolutionary history of host-plant shifts among these leaf beetles. This chrysomelid genus is characteristically associated with a high number of different plant families. The diverse molecular data gathered in this study are to a large extent congruent, and the analyses provide a well-supported phylogenetic hypothesis to address questions about the evolution of host-plant shifts in the genus Gonioctena. The most-parsimonious reconstruction of the ancestral host-plant associations, based on the estimated phylogeny, suggests that the Fabaceae was the ancestral host-plant family of the genus. Although most of the host-plant shifts (between different host species) in Gonioctena have occurred within the same plant family or within the same plant genus, at least eight shifts have occurred between hosts belonging to distantly related and chemically dissimilar plant families. In these cases, host shifts may have been simply directed toward plant species available in the environment. Yet, given that two Gonioctena lineages have independently colonized the same three new plant families (Salicaceae, Betulaceae, Rosaceae), including four of the same new genera (Salix, Alnus, Prunus, Sorbus), some constraints are likely to have limited the different possibilities of interfamilial host-plant shifts.     

秦岭种子植物区系科的组成、特点及其地理成分研究

秦岭种子植物区系组成丰富, 共有种子植物198 科、1007 属、3446 种, 区系组成的大科及主要科共16 科, 占秦岭种子植物总数属的50.05%, 总种数的57.25%, 它们构成了秦岭植物区系组成的基本框架, 就其性质来讲, 绝大多数为温带性质。松科、壳斗科、桦木科、杨柳科、蔷薇科、杜鹃花科、禾本科、莎草科等是秦岭植被的区系组成的优势科, 从地理成分上来分析, 本区科的分布型可以划分为世界或亚世界分布科、热带分布科、温带分布科、间断分布科以及东亚和中国特有科, 其区系的起源则有明显的古老性。     

Host-associated allozyme variation in tree cambium miners,Phytobia spp. (Diptera: Agromyzidae)

The larvae of the agromyzid flies that belong to the genus Phytobia Lioy feed by mining in the differentiating xylem just below the cambium of growing forest trees. The genus, which is apparently one of the most primitive groups in the Agromyzidae, comprises over 50 currently recognized species. Most of the species are mono- or oligophagous, and the host plants belong to numerous genera in about 60 families. Thus, Phytobia is an attractive candidate for studies on the evolution of insect-plant relationships. In spite of this, the taxonomy of Phytobia is currently poorly understood, mainly because the morphological differences between species are small. We used allozyme electrophoresis to investigate whether molecular markers could be used to separate and identify species in Phytobia, and to study the patterns of host use in the group. For this, we collected Phytobia larvae from eight host tree species occurring in southern Finland. An analysis of 10 variable allozyme loci showed that there are probably five species of Phytobia that feed on the hosts included in our study: one occurs on birches (Betula pubescens Ehrh. and B. pendula Roth) and alders (Alnus incana (L.) Moench and A. glutinosa (L.) Gaertn.), one on rowan (Sorbus aucuparia L.), and three species with overlapping feeding ranges on aspen (Populus tremula L.) and two willow species (Salix phylicifolia L. and S. caprea L.). Because birches and alders belong to the plant family Betulaceae, rowan to Rosaceae, and aspen and willows to Salicaceae, the host associations of the individual fly species can be explained by the taxonomic affinities of the hosts. However, our results also show that on a larger scale the evolution of host-plant associations in Phytobia cannot be explained by strict parallel cladogenesis (cospeciation) between the flies and their hosts.     

Larval habits, host-plant associations, and speciation in nematine sawflies (Hymenoptera: Tenthredinidae)

Adaptive radiations consist of two intertwined processes, diversification of species and diversification of their ecological niches, but it is unclear whether there is a causal link between the processes. In phytophagous insects, ecological diversification mainly involves shifts in host-plant associations and in larval feeding habits (internal or external) on different plant parts, and several observations indicate that speciation is facilitated by host shifts. Data on host use in individual species suggest that internal feeders are less likely to colonize new hosts than external-feeding taxa and, consequently, increases in collective host ranges and species numbers should be slowed down in endophagous lineages. We tested these related hypotheses by using phylogenetic information to reconstruct the evolutionary history of larval resource use in the sawfly subfamily Nematinae, a group of 1000 plus species with a broad range of niches: the subfamily's combined host range includes over 20 plant families, and larvae may feed externally on leaves or needles, or internally, for example, in buds, fruits, leaves, or galls. The results show that: (1) Most internally feeding groups have evolved independently from external-feeding ancestors, but several distinct internal habits have appeared convergently multiple times; (2) Shifts among host taxa are clearly more common than changes in larval habits; (3) The majority of host switches have occurred among phylogenetically close plant groups, but many shifts are manifest among distantly related, ecologically proximate hosts; (4) Although external feeding characteristic of the common ancestor of Nematinae is associated with relatively high rates of host-shifting, internal feeders are very conservative in their host use; (5) In contrast, the effect of endophagy on speciation probabilities is more variable: net speciation rates are lowered in most internal-feeding groups, but a striking exception is found in species that induce galls on Salicaceae. The loose connection between collective host ranges and species diversity provides empirical support for theoretical models suggesting that speciation rates are a function of a complex interplay between "intrinsic" niche width and resource heterogeneity.     

Gall-induction in insects: evolutionary dead-end or speciation driver?

Background

The tree of life is significantly asymmetrical - a result of differential speciation and extinction - but general causes of such asymmetry are unclear. Differences in niche partitioning are thought to be one possible general explanation. Ecological specialization might lead to increases in diversification rate or, alternatively, specialization might limit the evolutionary potential of specialist lineages and increase their extinction risk. Here we compare the diversification rates of gall-inducing and non-galling insect lineages. Compared with other insect herbivores feeding on the same host plant, gall-inducing insects feed on plant tissue that is more nutritious and less defended, and they do so in a favorable microhabitat that may also provide some protection from natural enemies. We use sister-taxon comparisons to test whether gall-inducing lineages are more host-specific than non-galling lineages, and more or less diverse than non-gallers. We evaluate the significance of diversity bipartitions under Equal Rates Markov models, and use maximum likelihood model-fitting to test for shifts in diversification rates.

Results

We find that, although gall-inducing insect groups are more host-specific than their non-galling relatives, there is no general significant increase in diversification rate in gallers. However, gallers are found at both extremes - two gall-inducing lineages are exceptionally diverse (Euurina sawflies on Salicaceae and Apiomorpha scale insects on Eucalytpus), and one gall-inducing lineage is exceptionally species-poor (Maskellia armored scales on Eucalyptus).

Conclusions

The effect of ecological specialization on diversification rates is complex in the case of gall-inducing insects, but host range may be an important factor. When a gall-inducing lineage has a host range approximate to that of its non-galling sister, the gallers are more diverse. When the non-galler clade has a much wider host range than the galler, the non-galler is also much more diverse. There are also lineage-specific effects, with gallers on the same host group exhibiting very different diversities. No single general model explains the observed pattern.     

Comparative phylogenies and host specialization in the alder ectomycorrhizal fungi Alnicola, Alpova and Lactarius (Basidiomycota) in Europe

Background  

Mycorrhizal fungi form intimate associations with their host plants that constitute their carbon resource and habitat. Alnus spp. (Betulaceae) are known to host an exceptional species-poor and specialized ectomycorrhizal (ECM) fungal community compared to other tree species, but the host-specificity pattern and its significance in terms of fungal diversification and speciation remain poorly documented. The degree of parallel speciation, host switching, and patterns of biogeography were explored in the historical associations between alders and three ECM taxa of Basidiomycetes: Alnicola (Agaricales), Alpova (Boletales), and Lactarius (Russulales). The aim was to develop an evolutionary framework on host specificity and diversification of Basidiomycetes in this highly specialized plant-fungus symbiosis.     

The genetics and ecology of sympatric speciation: A case study

Mating occurs on the larval host plant in allRhagoletis species (Diptera: Tephritidae). We show how this attribute, when coupled with certain differences in other biological traits, strongly influences the mode of speciation. In species of thesuavis species group, host shifts have never occurred during speciation, and larvae feed in the husks of any walnut species(Juglans spp.), which are highly toxic. Taxa are allopatric or parapatric and exhibit deep phylogenetic nodes suggesting relatively ancient speciation events. Traits responsible for species and mate recognition, particularly in parapatric species, are morphologically distinct and strongly sexually dimorphic. All aspects of their biology, genetics and distribution are consistent with a slow rate of allopatric speciation followed by morphological divergence in secondary contact. In contrast, speciation in thepomonella species group has always involved a shift to a new, usually unrelated, non-toxic host, and all taxa within these groups are sympatric, monophagous and morphologically indistinguishable from one another. Phylogenetic nodes are very shallow, indicating recent sympatric speciation. Sympatric divergence is promoted by genetic variation which allows a portion of the original species to shift to a new habitat or host. Evidence suggests that changes in a few key loci responsible for host selection and fitness on a new host may initiate host shifts. By exploiting different habitats, competition for resources between diverging populations is reduced or avoided. We provide evidence that in phytophagous and parasitic insects sufficient intrinsic barriers to gene flow can evolve between sister populations as they adapt to different habitats or hosts to allow each population to establish independent evolutionary lineages in sympatry.     

Austro-oriental genus Parabaliothrips Priesner (Thysanoptera: Thripidae), with a new Australian species forming male aggregations

A second Australian species of Parabaliothrips Priesner is described, P. newmani , forming male aggregations on the leaf buds of Moreton Bay fig, Ficus macrophylla (Moraceae). The genus, predominantly south-east Asian, is redefined and a key provided to the five described species. Members of this genus feed on leaves across a wide range of plant families, although each species is host specific. The host plant of the previously known Australian species, P. setifer Karny, is newly recognised as Leucopogon lanceolatus (Epacridaceae), and different south-east Asian species are associated with species of Betulaceae, Hamamelidaceae and Fagaceae.     

The significance of bottom-up effects for host plant specialization in Chrysomela leaf beetles

The leaf beetle species Chrysomela lapponica, which belongs to the so‐called C. interrupta group, forms distinct allopatric populations either on willows (Salicaceae) or birches (Betulaceae). It was recently suggested that, on several occasions, host plant shifts from Salicaceae to Betulaceae occurred independently within the C. interrupta group. Our study aims to elucidate bottom‐up effects of the host plants that might have shaped the evolution of host plant specialization in the populations of C. lapponica, and thus, to shed some light on the driving forces of host shifts within the C. interrupta group, too. We compared the oviposition behaviour and performance of two C. lapponica populations, one of which has adapted to birches and the other to willows. The studies were conducted under laboratory conditions, eliminating the impact of natural enemies. Experiments involving the transfer of individuals of the birch‐specialized population to willows and vice versa with individuals of the willow‐specialized population to birches aimed to examine the plasticity in host plant use. Females of each population almost exclusively chose their natural host plant for oviposition, when offering birch and willow in dual choice experiments. When specimens of the two C. lapponica populations were reared on their natural host plants, the birch specialists suffered higher mortality, needed a longer period of development and produced less larval defensive secretion than the willow specialists. When the birch specialists were fed with willow, these performance parameters decreased even more. Other parameters, such as body weight and fecundity, did not differ between birch and willow specialists when they were fed with their natural host plant. While individuals of the birch‐specialized population could be reared on willow, all neonate larvae from the willow‐specialized population died after being transferred to birch. The significance of these bottom‐up effects for the evolution of host plant specialization in C. lapponica is discussed.     

Taxonomy of leafminers of the genus Phyllonorycter Hübner (Lepidoptera, Gracillariidae) associated with ulmaceous plants (Ulmaceae)

A contribution to the taxonomy of the genus Phyllonorycter Hübner (Lepidoptera, Gracillariidae) is proposed, based on the morphological study of species developing on Ulmaceae. Species trophically associated with Ulmaceae belong to two subgenera: Phyllonorycter s. str. and a new subgenus, Juxtafera Baryshnikova, subgen. n. (type species Tinea tristrigella Hw.), both representing complex taxa. Three species-groups including species feeding on Ulmaceae as well as morphologically similar species developing on Betulaceae, Fabaceae, Salicaceae, Juglandaceae, and Rosaceae are established within the nominotypical subgenus; several species are characterized by disjunct oligophagy, consuming Ulmaceae together with plants of other families. Juxtafera subgen. n., established on the basis of the development of juxta in the male genitalia, is divided into 6 species-groups whose representatives are mainly strict oligophages, being predominantly associated with plants of three unrelated families Ulmaceae, Rosaceae, and Caprifoliaceae. Based on the comparative morphology of the male genitalia, evolutionary trends in Juxtafera are hypothesized.     

Phylogenetics and evolution of host-plant use in leaf-mining sawflies (Hymenoptera: Tenthredinidae: Heterarthrinae)

The habit of mining within leaves has evolved convergently in numerous plant-feeding insect taxa. Many leaf-mining groups contain a large number of species with distinct feeding preferences, which makes them highly suitable for studies on the evolutionary history of host-plant use and on the role of niche shifts in speciation. We aimed to clarify the origin, classification, and ecological evolution of the tenthredinid sawfly subfamily Heterarthrinae, which contains c. 150 leaf-mining species that collectively feed on over 20 plant genera around the world. For this, we reconstructed the phylogeny of representative heterarthrine species and diverse outgroups from the superfamily Tenthredinoidea on the basis of DNA sequence data collected from two mitochondrial (CoI and Cytb) and two nuclear (EF-1α and NaK) genes. Thereafter, we inferred the history of niche diversification within Heterarthrinae by plotting larval host-plant associations on the trees, and by contrasting a time-calibrated leaf-miner phylogeny with the phylogeny of their host plants. The results show that: (1) heterarthrine leaf-miners constitute a monophyletic group that arose from external-feeding blennocampine lineages within the Tenthredinidae c. 110-80 million years ago; (2) heterarthrines generally radiated well after their host taxa, and extant host-plant associations therefore result from a combination of host conservatism and occasional shifts among available plant taxa; and (3) diversification in Heterarthrinae apparently occurs by multiple mechanisms, including sympatric or allopatric ecological speciation, non-ecological allopatric speciation, and possibly allochronic speciation. Overall, both present and historical host-use patterns within the Heterarthrinae exhibit striking similarities to patterns found in co-occurring herbivore taxa.     

Metabolite fingerprinting,pathway analyses,and bioactivity correlations for plant species belonging to the Cornaceae,Fabaceae, and Rosaceae families

Key message

A multi-parallel approach gauging the mass spectrometry-based metabolite fingerprinting coupled with bioactivity and pathway evaluations could serve as an efficacious tool for inferring plant taxonomic orders.

Abstract

Thirty-four species from three plant families, namely Cornaceae (7), Fabaceae (9), and Rosaceae (18) were subjected to metabolite profiling using gas chromatography–time-of-flight-mass spectrometry (GC–TOF-MS) and ultrahigh performance liquid chromatography–linear trap quadrupole-ion trap-mass spectrometry (UHPLC–LTQ-IT-MS/MS), followed by multivariate analyses to determine the metabolites characteristic of these families. The partial least squares discriminant analysis (PLS-DA) revealed the distinct clustering pattern of metabolites for each family. The pathway analysis further highlighted the relatively higher proportions of flavonols and ellagitannins in the Cornaceae family than in the other two families. Higher levels of phenolic acids and flavan-3-ols were observed among species from the Rosaceae family, while amino acids, flavones, and isoflavones were more abundant among the Fabaceae family members. The antioxidant activities of plant extracts were measured using ABTS, DPPH, and FRAP assays, and indicated that extracts from the Rosaceae family had the highest activity, followed by those from Cornaceae and Fabaceae. The correlation map analysis positively links the proportional concentration of metabolites with their relative antioxidant activities, particularly in Cornaceae and Rosaceae. This work highlights the pre-eminence of the multi-parallel approach involving metabolite profiling and bioactivity evaluations coupled with metabolic pathways as an efficient methodology for the evaluation of plant phylogenies.

     

Molecular Phylogeny of the Small Ermine Moth Genus Yponomeuta (Lepidoptera,Yponomeutidae) in the Palaearctic

Background

The small ermine moth genus Yponomeuta (Lepidoptera, Yponomeutidae) contains 76 species that are specialist feeders on hosts from Celastraceae, Rosaceae, Salicaceae, and several other plant families. The genus is a model for studies in the evolution of phytophagous insects and their host-plant associations. Here, we reconstruct the phylogeny to provide a solid framework for these studies, and to obtain insight into the history of host-plant use and the biogeography of the genus.

Methodology/Principal Findings

DNA sequences from an internal transcribed spacer region (ITS-1) and from the 16S rDNA (16S) and cytochrome oxidase (COII) mitochondrial genes were collected from 20–23 (depending on gene) species and two outgroup taxa to reconstruct the phylogeny of the Palaearctic members of this genus. Sequences were analysed using three different phylogenetic methods (parsimony, likelihood, and Bayesian inference).

Conclusions/Significance

Roughly the same patterns are retrieved irrespective of the method used, and they are similar among the three genes. Monophyly is well supported for a clade consisting of the Japanese (but not the Dutch) population of Yponomeuta sedellus and Y. yanagawanus, a Y. kanaiellus–polystictus clade, and a Rosaceae-feeding, western Palaearctic clade (Y. cagnagellus–irrorellus clade). Within these clades, relationships are less well supported, and the patterns between the different gene trees are not so similar. The position of the remaining taxa is also variable among the gene trees and rather weakly supported. The phylogenetic information was used to elucidate patterns of biogeography and resource use. In the Palaearctic, the genus most likely originated in the Far East, feeding on Celastraceae, dispersing to the West concomitant with a shift to Rosaceae and further to Salicaceae. The association of Y. cagnagellus with Euonymus europaeus (Celastraceae), however, is a reversal. The only oligophagous species, Y. padellus, belongs to the derived western Palaearctic clade, evidence that specialisation is reversible.     

Macroevolutionary patterns in the Aphidini aphids (Hemiptera: Aphididae): diversification, host association, and biogeographic origins

Background

Due to its biogeographic origins and rapid diversification, understanding the tribe Aphidini is key to understanding aphid evolution. Major questions about aphid evolution include origins of host alternation as well as age and patterns of diversification in relation to host plants. To address these questions, we reconstructed the phylogeny of the Aphidini which contains Aphis, the most diverse genus in the family. We used a combined dataset of one nuclear and four mitochondrial DNA regions. A molecular dating approach, calibrated with fossil records, was used to estimate divergence times of these taxa.

Principal Findings

Most generic divergences in Aphidini occurred in the Middle Tertiary, and species-level divergences occurred between the Middle and Late Tertiary. The ancestral state of host use for Aphidini was equivocal with respect to three states: monoecy on trees, heteroecy, and monoecy on grasses. The ancestral state of Rhopalosiphina likely included both heteroecy and monoecy, whereas that of Aphidina was most likely monoecy. The divergence times of aphid lineages at the generic or subgeneric levels are close to those of their primary hosts. The species-level divergences in aphids are consistent with the diversification of the secondary hosts, as a few examples suggest. The biogeographic origin of Aphidini as a whole was equivocal, but the major lineages within Aphidina likely separated into Nearctic, Western Palearctic, and Eastern Palearctic regions.

Conclusions

Most generic divergences in Aphidini occurred in the Middle Tertiary when primary hosts, mainly in the Rosaceae, were diverging, whereas species-level divergences were contemporaneous with diversification of the secondary hosts such as Poaceae in the Middle to Late Tertiary. Our results suggest that evolution of host alternation within Aphidini may have occurred during the Middle Tertiary (Oligocene) when the secondary hosts emerged.     

不同寄主植物叶片上蚜虫的形态适应

昆虫对寄主植物之间的形态适应性是两者相互关系的重要组成部分, 本文以植食性蚜虫为研究对象, 研究其对不同种类寄主植物叶片的形态适应。选取寄生于禾本科、 杨柳科、 壳斗科和松科4科7属植物叶片上的26种蚜虫, 基于有翅孤雌蚜和无翅孤雌蚜, 在光学显微镜下观察、 测量并统计比较了37个形态特征及其种内变异。以克隆平均值为基础数据,选取与蚜虫取食和附着于植物表面相关的形态特征（喙末端、跗节Ⅰ、Ⅱ和爪）为变量,分别得出无翅、 有翅孤雌蚜和所有蚜型3个聚类分支图,并将各种蚜虫的寄主植物科、 属分别对应到分支图上。结果表明：体型、腹管和触角的形态在不同蚜虫的科间有一定差别, 喙末端、 跗节Ⅰ、跗节Ⅱ及爪的形态则在不同的寄主植物间存在差异; 在蚜虫种内各形态特征存在一定变异, 变异系数的范围为1.89%~26.08%。3个聚类分析的结果显示,不同种类蚜虫形成的分支基本对应不同科、属的寄主植物;而杨一条角蚜Doraphis populi、三堡瘿绵蚜Epipemphigus imaicus和杨柄叶瘿绵蚜Pemphigus matsumurai则处在较为特殊的分支位置, 那是因为前者为次生寄主型, 后两者均能产生虫瘿。研究结果表明寄生于不同植物相同部位上的蚜虫存在形态特征的明显分异, 对应不同的寄主植物, 蚜虫与寄主植物之间存在着形态适应关系。     

Adaptation to different host plant ages facilitates insect divergence without a host shift

Host shifts and subsequent adaption to novel host plants are important drivers of speciation among phytophagous insects. However, there is considerably less evidence for host plant-mediated speciation in the absence of a host shift. Here, we investigated divergence of two sympatric sister elm leaf beetles, Pyrrhalta maculicollis and P. aenescens, which feed on different age classes of the elm Ulmus pumila L. (seedling versus adult trees). Using a field survey coupled with preference and performance trials, we show that these beetle species are highly divergent in both feeding and oviposition preference and specialize on either seedling or adult stages of their host plant. An experiment using artificial leaf discs painted with leaf surface wax extracts showed that host plant chemistry is a critical element that shapes preference. Specialization appears to be driven by adaptive divergence as there was also evidence of divergent selection; beetles had significantly higher survival and fecundity when reared on their natal host plant age class. Together, the results identify the first probable example of divergence induced by host plant age, thus extending how phytophagous insects might diversify in the absence of host shifts.