Diversification of mitogenomes in three sympatric Altica flea beetles (Insecta,Chrysomelidae)

The Asian flea beetles Altica cirsicola, Altica fragariae and Altica viridicyanea are broadly sympatric and morphologically highly similar but feed on distantly related host plants. They have been suggested as a model for ecological speciation studies. However, their phylogeny and species limits remain uncertain. In this study, we added mitochondrial genomes from multiple individuals of each species to the growing database. Phylogenetic analyses based on 15 genes showed clear interspecific divergences of A. fragariae from the other species, but A. cirsicola and A. viridicyanea were not distinguishable by distance‐based or tree‐based methods of species delimitation due to non‐monophyly of mitogenomes relative to the morphologically defined entities, possibly affected by interspecific introgression. This was confirmed by wider sampling of mitochondrial COX1 (58 individuals) and the second internal transcribed spacer of nuclear ribosomal RNA cluster (ITS2; 68 individuals), which showed that ITS2, but not COX1, coincided with the morphological species limits. The full mitochondrial genomes are not able to shed further light on the species status, even with the most sensitive approach based on diagnostic characters, yet the whole mitogenome is useful to get improved estimates of intra‐ and interspecific variation, not affected by the stochastic error seen in individual genes.     

跳甲的食性及食性分化

跳甲隶属于鞘翅目叶甲科跳甲亚科,是一类具有重要经济意义的植食性昆虫。本文对跳甲食性及食性分化的研究进展进行了综述,诠释了寄主植物的概念,分析了昆虫食性专化发生的原因。跳甲亚科的寄主植物的范围虽广,但有85%的属为专食性属。一般认为,专食性的跳甲亚科和萤叶甲亚科是由食性较广的叶甲亚科进化而来的,食性分化在其中可能起了重要作用。广食性代价推动了食性分化的发生,广食性代价假说受到越来越多的实验支持。有关食性分化方向的观点倾向于寄主植物转向化学物质相似的植物,表现为寄主转移、寄主扩张和形成寄主型等;食性分化推动了同域物种形成。跳甲食性分化的研究对于丰富研究昆虫与植物相互关系的协同进化理论也有重要作用。     

From hybridization to introgression between two closely related sympatric ant species

Interspecific hybridization is becoming more frequent worldwide due to increasing global changes and translocations of organisms. For individual organisms, the most significant negative consequences are sterility or inviability of hybrid offspring. However, hybridization sometimes leads to fertile offspring, promoting introgression from one species into another. In such situations, hybridization can play a key role in evolution and speciation. Combining hypervariable DNA (microsatellites) and mitochondrial DNA markers with the use of several modeling methods allow an efficient detection of hybridization processes. The present study therefore investigates hybridization between two ant species, Tetramorium immigrans and T. caespitum, using multiple methods, and systematically comparing results with simulated data to ensure accurate identification of hybrids. Introgression was revealed both by backcross detection based on 14 nuclear microsatellite loci and by mitochondrial‐nuclear discordance based on comparison with mitochondrial DNA (cytochrome c oxidase subunit I). Results were spatially consistent, with hybrids located at latitudes where parental species are sympatric. The causes and consequences of hybridization and introgression between T. caespitum and T. immigrans remain to be further investigated, especially because T. immigrans could be an invasive species in France.     

Host specialization by reproductive interference between closely related herbivorous insects

Host specialization among closely related herbivores is common and is therefore a major theme in ecology. Despite its ecological importance, no general explanatory framework for host specialization is currently available. We introduce a new model of the evolution of host specialization in herbivorous insects. We use a two-dimensional lattice comprising 32 × 32 cells. Moreover, the model incorporates reproductive interference, defined as any negative outcomes resulting from interspecific mating, between two species of herbivores feeding on two different host plants as well as ordinary resource competition and differences in host suitability. Our simulation showed that reproductive interference, together with other factors such as host-related performance and resource competition, can actually drive the evolution of host specialization and thereby host partitioning between herbivorous insects during secondary contact. Host specialization arises particularly when levels of both reproductive interference and resource competition are intermediate. In contrast, host specialization seldom occurs if reproductive interference is absent. Thus, reproductive interference is as key to specialization as is spatial partitioning, which was not regarded as a realistic outcome when only resource competition was considered.     

Relationship between body shape and trophic niche segregation in two closely related sympatric fishes

Diet, shape and their covariation were analysed in juvenile flounder Platichthys flesus and plaice Pleuronectes platessa specimens from a tidal inshore habitat (Dublin Bay) in the Irish Sea. Stomach content analysis revealed differences in the diet, suggesting a substantial degree of resource partitioning between the species. Geometric morphometrics detected significant and discriminating differences in body shape, particularly in the head region. Most interestingly, a high degree of correlation was detected between diet and shape. The ontogenetic and ecological implications of the diet and shape covariation pattern were discussed, suggesting that morphological differences, in particular in the head region, may represent the functional platform which allows for the existence of ecologically significant differences in prey search and capture between P. platessa and P. flesus.     

Thermoregulatory strategies in two closely related sympatric Scarabaeus species (Coleoptera: Scarabaeinae)

Abstract. The thermoregulation strategies of Scarabaeus sacer L. and Scarabaeus cicatricosus Lucas were studied in the Doñana National Park, Spain. In this area, both species coexist, showing the same habitat and food preferences. However, S. cicatricosus is active during warmer parts of the day compared to S. sacer. Both species thermoregulate their thoracic temperature but, whereas the abdomen of S. sacer is a passive thermal window, S. cicatricosus actively thermoregulates abdominal temperature by increasing heat transfer from the thorax to the abdomen at high T_a values. In the case of S. sacer, their endothermy indicates an adaptive capacity to thorax heat retention, as occurs mainly in winter‐flying insects. This mechanism, possibly related to the aerodynamic flight posture in Scarabaeinae, could be an effective barrier to retard the rate of abdominal heat loss during flight. This endothermic strategy makes flight difficult at higher temperatures, although it allows flight during cooler periods of the day. On the other hand, S. cicatricosus showed a different adaptive behaviour to S. sacer. In this case, a significant decrease in abdominal heat loss at higher ambient temperatures would indicate a decrease in heat transfer from the thorax to the abdomen, as occurs in some desert and semiarid insects. This ‘heat exchanger’ mechanism observed in S. cicatricosus could be due to the irregular posture adopted during flight, with the posterior legs clearly extended and separate from the body. This behaviour increases turbulence and convective cooling, favouring exposure of the soft abdominal tergal cuticle and, subsequently, water loss. Thus, for S. cicatricosus, the well‐adapted ‘heat exchanger’ permits flight during periods of the day when temperatures would possibly be lethal for those species with high endothermy. From an adaptive viewpoint, these mechanisms of thermoregulation may explain how both closely‐related sympatric species respond in different ways to environmental temperature, favouring their coexistence.     

Evidence for nonallopatric speciation among closely related sympatric Heliotropium species in the Atacama Desert

The genetic structure of populations of closely related, sympatric species may hold the signature of the geographical mode of the speciation process. In fully allopatric speciation, it is expected that genetic differentiation between species is homogeneously distributed across the genome. In nonallopatric speciation, the genomes may remain undifferentiated to a large extent. In this article, we analyzed the genetic structure of five sympatric species from the plant genus Heliotropium in the Atacama Desert. We used amplified fragment length polymorphisms (AFLPs) to characterize the genetic structure of these species and evaluate their genetic differentiation as well as the number of loci subject to positive selection using divergence outlier analysis (DOA). The five species form distinguishable groups in the genetic space, with zones of overlap, indicating that they are possibly not completely isolated. Among‐species differentiation accounts for 35% of the total genetic differentiation (F_ST = 0.35), and F_ST between species pairs is positively correlated with phylogenetic distance. DOA suggests that few loci are subject to positive selection, which is in line with a scenario of nonallopatric speciation. These results support the idea that sympatric species of Heliotropium sect. Cochranea are under an ongoing speciation process, characterized by a fluctuation of population ranges in response to pulses of arid and humid periods during Quaternary times.     

The genetic basis of interspecific differences in genital morphology of closely related carabid beetles

Marked diversification of genital morphology is common in internally fertilizing animals. Although sexual selection may be the primary process controlling genital evolution, factors promoting genital evolution are controversial, and the genetic background of genital morphology is poorly understood. We analyzed the genetic basis of species-specific genital morphologies in carabid beetles of the subgenus Ohomopterus (genus Carabus, Carabidae) using two parapatric species with hybrid zones. Biometric analyses on experimental F(1) and backcross populations revealed that inheritance of genital morphology is polygenic. Applying Lande's modification of the Castle-Wright estimator to population means and variances to estimate the minimum number of genes involved, we found that a relatively small number of loci is responsible for species differences in genital morphology. In addition, joint-scaling tests indicated that the additive genetic effect accounts for most interspecific differences in genital traits, but dominance and epistatic genetic effects also play roles. Overall, the genetic basis of male and female genitalia is fairly simple, enabling these traits to respond quickly to selection pressures and to diverge rapidly. Our results provide insight into the diversification of genital morphology in carabid beetles, and will hopefully stimulate further studies on the genetic basis of genitalia, such as mapping of quantitative trait loci affecting species-specific genital morphology.     

Host plant related properties of the antennal olfactory system in the oak flea weevil, Rhynchaenus quercus. Electroantennogram study

Electroantennogram (EAG) recordings from the antennae of a highly specialized phytophagous species — the oak flea weevil, Rhynchaenus quercus L. — revealed two general properties of its antennal olfactory system: (1) a high and to some extent selective sensitivity to chemotaxonomically nonspecific compounds, namely the so-called general green leaf volatiles as well as to geraniol and linalool, (2) a lack of marked differences in the general excitation level caused by stimulation with vapours from leaves of both host plants and non-host plants. It was also observed, that the shapes of EAG's evoked by vapours from cut leaves and general green leaf volatiles differed from those elicited by corresponding concentrations of geraniol and linalool, where recovery was distinctly slower.The results of EAG tests suggest that the general green leaf volatile complex is important in host-odour perception by the oak flea weevil. A possible function of these compounds in host-plant odour discrimination is discussed.

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Zusammenfassung Elektroantennographische Aufzeichnungen an Fühlern einer hochspezialisierten phytophagen Art, des Eichenblattflohs Rhynchaenus quercus L. zeigten zwei allgemeine Eigenschaften des Geruchsystems der Antennen:Erstens ist eine hohe und teilweise selektive Empfindlichkeit auf chemotaxonomisch nicht spezifische Verbindungen, besonders auf die allgemeinen Blattgründämpfe wie auch auf Geraniol und Linalool vorhanden.Zweitens fehlen ausgeprägte Unterschiede im allgemeinen Erregungsniveau hervorgerufen durch flüchtige Stoffe von Wirtspflanzen einerseits und Nichtwirtspflanzen andererseits. Es wurde auch beobachtet, dass die Form der EAGs hervorgerufen durch zerschnittene Blätter oder allgemeine Blattgründämpfe verschieden war von denjenigen verursacht durch Geraniol und Linalool, wo die Erholung eindeutig langsamer war.Die Resultate der EAG deuten darauf hin, dass der Komplex der allgemeinen Blattgründämpfe wichtig ist bei der Wahrnehmung der Wirtspflanzengerüche durch Rhynchaenus quercus. Eine mögliche Funktion dieser Verbindungen bei der Erkennung der Wirtspflanzen wird diskutiert.

     

Anti-predator defence drives parallel morphological evolution in flea beetles

Complex morphological or functional traits are frequently considered evolutionarily unique and hence useful for taxonomic classification. Flea beetles (Alticinae) are characterized by an extraordinary jumping apparatus in the usually greatly expanded femur of their hind legs that separates them from the related Galerucinae. Here, we examine the evolution of this trait using phylogenetic analysis and a time-calibrated tree from mitochondrial (rrnL and cox1) and nuclear (small subunits and large subunits) genes, as well as morphometrics of femora using elliptic Fourier analysis. The phylogeny strongly supports multiple independent origins of the metafemoral spring and therefore rejects the monophyly of Alticinae, as defined by this trait. Geometric outline analysis of femora shows the great plasticity of this structure and its correlation with the type and diversity of the metafemoral springs. The recognition of convergence in jumping apparatus now resolves the long-standing difficulties of Galerucinae-Alticinae classification, and cautions against the value of trait complexity as a measure of taxonomic significance. The lineage also shows accelerated species diversification rates relative to other leaf beetles, which may be promoted by the same ecological factors that also favour the repeated evolution of jumping as an anti-predation mechanism.     

Patterns in the autotomized adults of two sympatric,closely related grasshopper species in their natural habitat

Insects have various defense responses to natural enemies, including autotomy. Detailed knowledge of autotomy patterns and frequencies in the wild is required to make reliable inferences concerning the fitness benefits and costs of the consequences of autotomy. However, few quantitative surveys have been conducted on the frequency of autotomized insects in the wild. Here, I examined data on autotomy in adult Parapodisma tanbaensis and Parapodisma subastris grasshoppers, which are sympatric, closely related species, collected over two consecutive years at three field sites in Kyoto, Japan. To investigate what traits were related to the frequency of autotomized adults, I recorded the species, sex, body size, and hind leg status after sampling adults because, according to previous research, these four parameters can be used to make predictions about the frequency of autotomized adults in the wild. There was a significant interaction effect between grasshopper sex and the sampling season on the frequency of autotomized adults and a non-linear increase in the frequency of autotomized adults as the season advanced. However, there were no significant effects caused by species or body size. Thus, a sexual difference existed in the occurrence and disappearance of autotomized adults in the wild as the season advanced. The ecological and evolutionary factors and mechanisms causing this pattern are discussed.     

Effects of flea beetles on the yield of radish

The yield of dry matter of radish attacked by adult flea beetles in the field was negatively and linearly related to the number of feeding lesions/unit area of leaf, when both sets of values were transformed logarithmically. The nature of the relationship is discussed.

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Zusammenfassung Die Beziehungen zwischen der Anzahl erwachsener Erdflöhe, Verletzungen der Rettichblätter und dem Ertrag an Wurzeln und Blättern wurde untersucht. Da die Käfer sehr lebhaft sind und es daher im Freiland schwierig ist, ihre jeweilige Anzahl zu erfassen, wurde der Befall durch Auszählen der Löcher geschätzt, die ihr Fraß an den Blättern erzeugt. Die Anzahl der Löcher pro Pflanze stand weder zur Blattfläche noch zum Trockengewicht der Pflanzen in Beziehung, aber die Anzahl Löcher pro cm² Blattfläche bei der Ernte war mit dem Ertrag an Trockensubstanz negativ linear korreliert, wenn beide Wertreihen logarithmisch transformiert wurden. Der Einfluß der Löcher auf den Ertrag war dichteabhängig, d.h. die einzelnen Löcher hatten einen relativ größeren Effekt auf den Ertrag, je geringer ihre Anzahl pro cm² Blattfläche war. Diese Beziehung wurde mit früher veröffentlichten Ergebnissen der Verfasser über die Fraßwirkung der Larven von Phaedon cochleariae und Plutella maculipennis auf Retticherträge verglichen, wobei sich eine negative lineare Beziehung zwischen Anzahl der Insekten und Ertrag ergeben hatte. Es wird daraus geschlossen, daß die Unterschiede in der Beziehung zwischen den quantitativen Ausmaßen des Befalls und dem Ertrag bei diesen beiden Schädlingen und den Erdflöhen lediglich die verschiedenen Methoden der Erfassung des Befalls widerspiegeln, nicht aber auf unterschiedlichen Reaktionen der Wirtspflanzen gegenüber der Beschädigung durch verschiedene Insekten beruhen.

     

Ecological differentiation and reproductive isolation of two closely related sympatric species of Oenanthe (Apiaceae)

Oenanthe conioides is a lower Elbe endemic plant species growing in the freshwater tidal zone around Hamburg (Germany). Its closest relative Oenanthe aquatica is widely distributed in Eurasia and grows in calm and shallow freshwater. The two species differ in habitat requirements but are otherwise sympatrically distributed, suggesting that ecological divergence has to be maintained in the face of gene flow. In the present study, we investigated ecological differentiation and reproductive isolation in these two species. An amplified fragment length polymorphism analysis found clear genetic differentiation between the two species implying reproductive isolation. A reciprocal transplantation experiment including artificial F₁ hybrids showed strong selection against immigrants. In the two parental habitats, the non‐native species are less fit than the native species. Hybrids are less fit in the habitat of Oe. aquatica but perform as well as the native species in the habitat of Oe. conioides. We hypothesize that selection against immigrants is the most important component of reproductive isolation between the two species, and that selection against immigrants is the result of exposure to cold and wind in the tidal habitat of Oe. conioides and to herbivory in the habitat of Oe. aquatica. These results are congruent with a role for differential ecological selection in the formation and maintenance of these two species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 526–535.     

Host plant scents attract rolled-leaf beetles to Neotropical gingers in a Central American tropical rain forest

Leaf volatile chemicals are known to reduce herbivory rates by repelling or intoxicating insect herbivores and by attracting the predators and parasitoids of herbivores. However, leaf volatiles may also be used by insect herbivores as cues to locate their host plants. Leaf volatiles are suggested to be important host search cues for herbivores in structurally complex and diverse habitats, such as tropical rain forests. A group of insect herbivores, the rolled-leaf beetles (Coleoptera: Chrysomelidae: Hispinae), have maintained a highly specialized interaction with Neotropical gingers (Zingiberales) for ca. 60 million years. In this study, we explored chemical attraction to host plants under controlled laboratory conditions, using four sympatric rolled-leaf beetle species, Cephaloleia dorsalis Baly, Cephaloleia erichsonii Baly, Cephaloleia fenestrata Weise, and Cephaloleia placida Baly. For each beetle species, we investigated (i) whether it was repelled or attracted by leaf scents produced by four host and four non-host plant species, including Neotropical gingers in the families Marantaceae, Costaceae, and Zingiberaceae; and (ii) its ability to use scents to detect its host plant. We found that rolled-leaf beetles can detect and are attracted by leaf volatiles from both host and non-host gingers. Additionally, when beetles were simultaneously exposed to leaf volatiles from host and non-host plants, three rolled-leaf beetle species were significantly more attracted by volatiles from their host plants than from non-hosts. Only one of the beetle species was not able to discriminate between host and non-host scents.