The Effect of Patch Size and Persistence of Host Plants on the Development of Acaricide Resistance in the Two-spotted Spider Mite Tetranychus Urticae (Acari: Tetranychidae)

Spatial and temporal characteristics of host plants can influence the population biology of the herbivores feeding on them. In this study, I examined the effect of variation in host plant characteristics on the development of acaricide resistance in the two-spotted spider mite Tetranychus urticae, a widely distributed agricultural pest. This investigation examined the geographic variation in the degree of resistance to two new types of acaricide, pyridaben and fenpyroximate. From mortality tests at field-level concentrations of the acaricides, many populations collected from fruit trees and roses had a high frequency of resistant individuals for acaricides while almost all populations collected from herbaceous crops had low frequencies of resistant individuals. These results, combined with those from a previous allozyme study, indicate that patch size and persistence of host plants regulate the population structure of the mites including gene flow between populations and, by extension, the development of acaricide resistance.     

Genetic Differentiation in Tetranychus Urticae (Acari: Tetranychidae) from greenhouses in France

The polymorphism of 4 enzymatic systems of 21 Tetranychus urticae samples collected in southern France was analyzed in order to ascertain genetic differentiation within and between greenhouses. Genetic structure was investigated in relation to mite density, geographic distribution of greenhouses and the colonized host plant. We found that mite density and distribution of infested plants influence gene flow within greenhouses. Between greenhouses isolation by distance was significant. Differentiation did not appear to be associated with the colonized plant species.     

Molecular Evidence of Reproductive Isolation in Sympatric Sibling Species of Mouse Lemurs

Recent morphological and molecular phylogenetic studies of mouse lemurs (Microcebus) living in the western and southern regions of Madagascar have shown that specific diversity had been considerably underestimated. In large part, this underestimate was due to the lack of sufficient specimens from given localities to assess properly the level of phenotypic variation within and between populations. The accurate delineation of specific boundaries has no doubt been confounded by the diminutive size, nocturnal habits, and subtle morphological variation characteristic of mouse lemurs, which can make field identification of individuals problematic. We illustrate the use of molecular phylogenetic analysis to reveal reproductive isolation in two sympatric mouse lemur species, Microcebus murinus and M. griseorufus. Their documentation in the Berenty Private Reserve in the extreme south of Madagascar verifies the historically-broad distribution of Microcebus griseorufus, a species recently resurrected from synonomy.     

Host plant associations in the spider mite Tetranychus urticae (Acari: Tetranychidae): insights from molecular phylogeography

This article integrates studies on the genetic variation of T. urticae populations and the interspecific variation of several tetranychid species. It aims at obtaining insights into the roles of the historical, geographical and ecological factors in the partitioning of variation of species. Two types of molecular markers were used to determine whether the patterns of genetic variation in mites inhabiting different host plants can shed light on the existence of host plant associations. The ribosomal sequences of the second internal transcribed spacer (ITS2), which evolves through concerted evolution, are good indicators of long-term isolation between populations and reveal exceptional homogeneity in a worldwide sampling of T. urticae. The mitochondrial cytochrome oxidase I (COI) sequences do not disclose old divergences related to host plant in this mite but rather suggest recent geographic colonization patterns of the species. Allozyme variation on a fine scale gives some evidence of host associations in the case of citrus trees. However, if any divergence of mites related to this host plant exists, it probably prevails in local populations only and it should not be old enough to be revealed by a phylogenetic analysis of mitochondrial COI sequences. The phyletic constraint in the evolution of feeding specificity in the family Tetra-nychidae is investigated based on a phylogenetic analysis of mitochondrial sequences. The results provide some support for the hypothesis that an evolutionary trend towards polyphagy has occurred in the family. Overall, it seems that the major characteristic of T. urticae is its high colonization potential. Polyphagy has enhanced its successful spread and may have led to connectivity between populations worldwide. © Rapid Science Ltd. 1998     

Sequential radiation of unrelated organisms: the gall fly Eurosta solidaginis and the tumbling flower beetle Mordellistena convicta

Host shifts and the formation of insect-host races are likely common processes in the speciation of herbivorous insects. The interactions of goldenrods Solidago (Compositae), the gall fly Eurosta solidaginis (Diptera: Tephritidae) and the beetle Mordellistena convicta (Coleoptera: Mordellidae) provide behavioural, ecological and genetic evidence of host races that may represent incipient species forming via sympatric speciation. We summarize evidence for Eurosta host races and show that M. convicta has radiated from goldenrod stems to Eurosta galls to form host-part races and, having exploited the galler's host shift, has begun to differentiate into host races within galls. Thus, host-race formation has occurred in two interacting, but unrelated organisms representing two trophic levels, resulting in 'sequential radiation' (escalation of biodiversity up the trophic system). Distributions of host races and their behavioural isolating mechanisms suggest sympatric differentiation. Such differentiation suggests host-race formation and subsequent speciation may be an important source of biodiversity.     

Feeding History Affects the Response of the Predatory Mite Typhlodromus Kerkirae (Acari: Phytoseiidae) to Volatiles of Plants Infested with Spider Mites

The response of adult females of the predatory mite Typhlodromus kerkirae (Acari: Phytoseiidae) to volatiles emitted from bean leaves infested with Tetranychus urticae (Acari: Tetranychidae) or from leaves of Oxalis corniculata infested with Petrobia harti (Acari: Tetranychidae) was studied in the laboratory using a Y-tube olfactometer. Typhlodromus kerkirae females reared from larvae through to adults on T. urticae and pollen of Vicia faba responded to volatiles of bean leaves infested with T. urticae, either when they had a choice between infested and non-infested bean leaves or between bean leaves infested with T. urticae and O. corniculata leaves infested with P. harti. However, they did not respond when they had been reared only on the carotenoid-deficient pollen of V. faba. Female T. kerkirae that had been reared from larva to the tenth day of adult life on T. urticae and subsequently fed for 1 week on V. faba pollen did not respond to volatiles of bean leaves infested with T. urticae. In contrast, those that had been reared on V. faba pollen to the tenth day of adult life and subsequently fed for 1 week on T. urticae responded to volatiles of infested bean leaves.     

The song of the old mother: Reproductive senescence in female drosophila

Among animals with multiple reproductive episodes, changes in adult condition over time can have profound effects on lifetime reproductive fitness and offspring performance. The changes in condition associated with senescence can be particularly acute for females who support reproductive processes from oogenesis through fertilization. The pomace fly Drosophila melanogaster is a well-established model system for exploring the physiology of reproduction and senescence. In this review, we describe how increasing maternal age in Drosophila affects reproductive fitness and offspring performance as well as the genetic foundation of these effects. Describing the processes underlying female reproductive senescence helps us understand diverse phenomena including population demographics, condition-dependent selection, sexual conflict, and transgenerational effects of maternal condition on offspring fitness. Understanding the genetic basis of reproductive senescence clarifies the nature of life-history trade-offs as well as potential ways to augment and/or limit female fertility in a variety of organisms.     

葡萄幼苗在温度胁迫交叉适应过程中对水杨酸的应答

在温度锻炼诱导葡萄幼苗对交叉温度逆境的适应过程中叶片内源SA变化的结果表明,0℃低温胁迫期间,葡萄幼苗叶片细胞膜系统受到严重伤害,丙二醛(MDA)含量明显升高;此时自由态SA含量呈波动性变化,并随着胁迫进程的延长,内源SA含量明显低于正常叶片水平。而经过高温锻炼的幼苗,在低温胁迫初期自由态SA含量迅速达到一个高峰,之后回落并保持在正常叶片的SA水平,MDA含量也相应降低且相对稳定。结合态SA的变化相对较平稳,并且总SA含量变化趋势与自由态SA含量的变化趋势相吻合。在45℃高温胁迫期间,经过低温锻炼的幼苗的上述各项指标的变化规律与经过高温锻炼的幼苗在低温胁迫期间的变化趋势相似。     

New species and new record of Tetranychus Dufour from Australia, with a key to the major groups in this genus based on females (Acari: Prostigmata: Tetranychidae)

A new species of spider mite, Tetranychus bunda sp. n., is described and illustrated from Australia. It was found damaging the foliage of Desmodium tortuosum (Sw.) DC. (Fabaceae) in Darwin, Northern Territory. In addition, the geographical range of Tetranychus fijiensis Hirst is extended to include Australia. This species was found in the Northern Territory feeding on frangipani ( Plumeria sp., Apocynaceae), betel palm ( Areca catechu L., Arecaceae) and Macarthur feather palm ( Ptychosperma macarthurii [H. Wendl. ex Veitch] (H. Wendl. ex Hook. f., Arecaceae)). Details of the biology of T. bunda sp. n. and T. fijiensis are given. A key to the major groups of Tetranychus Dufour of the world, based on females, is presented and species known to occur in Australia are outlined.     

Generic scan using AFLP markers as a means to assess the role of directional selection in the divergence of sympatric whitefish ecotypes

Under the ecological theory of adaptive radiation, adaptation and reproductive isolation are thought to evolve as a result of divergent natural selection. Accordingly, elucidating the genetic basis of these processes is essential toward understanding the role of selection in shaping biological diversity. In this respect, the number of genes that evolved by selection remains contentious. To address this issue, the pattern of genetic differentiation obtained using 440 AFLP loci was compared with that expected under neutrality in four sympatric pairs of lake whitefish ecotypes that evolved adaptive phenotypic differences associated with the exploitation of distinct ecological niches. On average, 14 loci showed restricted gene flow relative to neutral expectation, suggesting a role of directional selection on their divergence. Among all loci that are most likely under directional selection, six exhibited parallel patterns of divergence, which provided further support for the role of selection in driving their divergence. Overall, these results indicate that only a small proportion of scored AFLP loci (between 1.4% and 3.2%) might be linked to genes implicated in the adaptive radiation of lake whitefish.     

Herbivorous insects: model systems for the comparative study of speciation ecology

Does ecological divergence drive species-level evolutionary diversification? How so and to what degree? These questions were central to the thinking of the evolutionary synthesis. Only recently, however, has the ecology of speciation become an important focus of empirical study. Here, we argue that ecologically specialized, phylogenetically diverse, and experimentally tractable herbivorous insect taxa offer great opportunities to study the myriad mechanisms by which ecology may cause reproductive isolation and promote speciation. We call for the development and integrated experimental study of a taxonomic diversity of herbivore model systems and discuss the availability and recent evaluation of suitable taxa. Most importantly, we describe a general comparative framework that can be used to rigorously test a variety of hypotheses about the relative contributions and the macroevolutionary generality of particular mechanisms. Finally, we illustrate important issues for the experimental analysis of speciation ecology by demonstrating the consequences of specialized host associations for ecological divergence and premating isolation in Neochlamisus bebbianae leaf beetles.     

Molecular evidence of host-associated genetic divergence in the holly leafminer Phytomyza glabricola (Diptera: Agromyzidae): apparent discordance among marker systems

Host races play a central part in understanding the role of host plant mediated divergence and speciation of phytophagous insects. Of greatest interest are host-associated populations that have recently diverged; however, finding genetic evidence for very recent divergences is difficult because initially only a few loci are expected to evolve diagnostic differences. The holly leafminer Phytomyza glabricola feeds on two hollies, Ilex glabra and I. coriacea, that are broadly sympatric throughout most of their ranges. The leafminer is often present on both host plants and exhibits a dramatic life history difference on the two hosts, suggesting that host races may be present. We collected 1393 bp of mitochondrial cytochrome oxidase I (COI) sequence and amplified fragment length polymorphism (AFLP) data (45 polymorphic bands) from sympatric populations of flies reared from the two hosts. Phylogenetic and frequency analysis of mitochondrial COI sequence data uncovered considerable variation but no structuring by the host plant, and only limited differentiation among geographical locations. In contrast, analysis of AFLP frequency data found a significant effect with host plant, and a much smaller effect with geographical location. Likewise, neighbour-joining analysis of AFLP data resulted in clustering by host plant. The AFLP data indicate that P. glabricola is most likely comprised of two host races. Because there were no fixed differences in mitochondrial or AFLP data, this host-associated divergence is likely to have occurred very recently. P. glabricola therefore provides a new sympatric system for exploring the role of geography and ecological specialization in the speciation of phytophagous insects.     

Reproductive maturation in the large pine weevil Hylobius abietis: the relative importance of larval and adult diet

1 Larval and adult Hylobius abietis (L.) can feed and, in the case of the adults, cause commercially significant damage to many species of conifer. The present study aimed to evaluate the impact of larval and adult feeding on different host plants on subsequent reproductive fitness. 2 Hylobius abietis larvae were reared on logs of four host species known to vary in suitability for development; Pinus nigra ssp. laricio, Picea sitchensis, Larix kaempferi and Pseudotsuga menziesii. Adult females were collected on emergence and allocated to complete maturation feeding on one of four seedling conifer species, P. nigra spp. laricio, P. sitchensis, P. menziesii and Larix ×marschlinsii. It was assumed that variation in both larval and adult host plant quality had the potential to influence subsequent reproductive behaviour. 3 The time taken for females to attain reproductive maturity was assessed, and reproductive output was measured over an average period of 17 days. 4 The best predictor of the time to attain reproductive maturity was found to be the initial adult body weight. This was strongly related to the larval host species, with the largest adults emerging from P. nigra ssp. laricio. The time taken to begin oviposition was in the range 10–49 days (mean 23 days). The subsequent mean rate of oviposition for individual females was in the range 0.1–3.7 eggs per day. Egg volumes varied between and within individual females, in the range 0.241–1.079 mm³. 5 The species of seedling provided for maturation feeding had no significant impact on reproductive behaviour over the course of the experiment. It is possible, however, that the quality of the adult diet might exert a greater influence on behaviour over a longer period because H. abietis is a relatively long‐lived species.     

Ancient lakes revisited: from the ecology to the genetics of speciation

Explosive speciation in ancient lakes has fascinated biologists for centuries and has inspired classical work on the tempo and modes of speciation. Considerable attention has been directed towards the extrinsic forces of speciation—the geological, geographical and ecological peculiarities of ancient lakes. Recently, there has been a resurgence of interest in the intrinsic nature of these radiations, the biological characteristics conducive to speciation. While new species are thought to arise mainly by the gradual enhancement of reproductive isolation among geographically isolated populations, ancient lakes provide little evidence for a predominant role of geography in speciation. Recent phylogenetic work provides strong evidence that multiple colonization waves were followed by parallel intralacustrine radiations that proceeded at relatively rapid rates despite long‐term gene flow through hybridization and introgression. Several studies suggest that hybridization itself might act as a key evolutionary mechanism by triggering major genomic reorganization/revolution and enabling the colonization of new ecological niches in ancient lakes. These studies propose that hybridization is not only of little impediment to diversification but could act as an important force in facilitating habitat transitions, promoting postcolonization adaptations and accelerating diversification. Emerging ecological genomic approaches are beginning to shed light on the long‐standing evolutionary dilemma of speciation in the face of gene flow. We propose an integrative programme for future studies on speciation in ancient lakes.     

The contribution of the y chromosome to hybrid male sterility in house mice

Hybrid sterility in the heterogametic sex is a common feature of speciation in animals. In house mice, the contribution of the Mus musculus musculus X chromosome to hybrid male sterility is large. It is not known, however, whether F(1) male sterility is caused by X-Y or X-autosome incompatibilities or a combination of both. We investigated the contribution of the M. musculus domesticus Y chromosome to hybrid male sterility in a cross between wild-derived strains in which males with a M. m. musculus X chromosome and M. m. domesticus Y chromosome are partially sterile, while males from the reciprocal cross are reproductively normal. We used eight X introgression lines to combine different X chromosome genotypes with different Y chromosomes on an F(1) autosomal background, and we measured a suite of male reproductive traits. Reproductive deficits were observed in most F(1) males, regardless of Y chromosome genotype. Nonetheless, we found evidence for a negative interaction between the M. m. domesticus Y and an interval on the M. m. musculus X that resulted in abnormal sperm morphology. Therefore, although F(1) male sterility appears to be caused mainly by X-autosome incompatibilities, X-Y incompatibilities contribute to some aspects of sterility.     

The evolution of gall parasitism accompanied by a host shift in the gall aphid, Eriosoma yangi (Homoptera: Aphidoidea)

Eriosoma aphids form leaf-roll galls on various elm species. Eriosoma yangi occurring on the Japanese elm is an obligatory cuckoo parasite, invading and usurping galls of other Eriosoma species. But another host race of E. yangi induces its own galls on the Chinese elm. Multivariate morphometries show that the two host races differ significantly in quantitative characters. Overwintering eggs of the parasitic form were experimentally transferred to the Chinese elm. The resultant larvae still exhibited a parasitic habit and developed into adults, which multivariate morphometries classified as the parasitic form. This form is considered different enough from the gall maker to be given a species rank. Eriosoma aphids facultatively invade other Eriosoma galls, where they sometimes deposit offspring. It is hypothesized that the parasitic form on the Japanese elm originated from a founder population which had migrated from the Chinese elm. On this new host, only those fundatrices that invade other species' galls will be able to leave offspring, because aphid fundatrices cannot gall plants other than their primary hosts. It is assumed that the parasitic form was established under intense selective pressure following a population bottleneck. This hypothesis was corroborated by field investigations at sites where the two forms occur sympatrically.     

Adaptive divergence and the evolution of reproductive isolation in the wild: an empirical demonstration using introduced sockeye salmon

Populations exposed to different ecological environments should diverge for phenotypic traits that influence survival and reproduction. This adaptive divergence should reduce gene flow between populations because immigrants become less fit than residents and because hybrids perform poorly in either environment (i.e., ecologically-dependent reproductive isolation). Here I demonstrate adaptive divergence and the evolution of reproductive isolation in populations of sockeye salmon (Oncorhynchus nerka) introduced from a common ancestral source into a new lake system (Lake Washington, Washington). The introduced fish founded several new populations, two of which experience very different environments during breeding and early development (Cedar River v.s. Pleasure Point beach). Over 13 generations, the two populations diverged for adult traits (female body size, male body depth; measured in the wild) and embryo traits (survival to hatching, development rate, size at emergence; measured in a common environment). The rates of divergence for these characters were similar to those observed in other examples of rapid evolution, and can best be attributed to natural selection. Partial reproductive isolation has evolved in concert with adaptive divergence: the rate of exchange of adults between the populations (determined using natural tags) is higher than the rate of gene flow (determined using DNA microsatellites). The demonstration that adaptive divergence can initiate reproductive isolation in less than 13 generations suggests that the first signs of ecological speciation may appear soon after new environments are first colonized.     

Temperature Effects on the Temporal Properties of Calling Songs in the Crickets <Emphasis Type="Italic">Gryllus fultoni</Emphasis> and <Emphasis Type="Italic">G. vernalis</Emphasis>: Implications for Reproductive Isolation in Sympatric Populations

Two closely related wood-cricket species, Gryllus fultoni (Orthoptera: Gryllidae) and G. vernalis, produce similar calling songs, consisting of 3-pulse chirps. Analysis of field and laboratory recordings of calling songs showed that, after correction to a common temperature, there was a divergence in chirp and pulse rates between far allopatric populations of G. fultoni and populations sympatric with G. vernalis. To determine whether the divergence in calling songs potentially provides reproductive isolation between G. fultoni and G. vernalis throughout the temperature range over which these insects sing, we recorded calling songs of lab-reared G. fultoni and G. vernalis populations between 18 and 28°C. Mean chirp rate significantly differed between sympatric and far allopatric G. fultoni populations as well as between sympatric G. fultoni and G. vernalis populations. Although there was a significant difference in mean pulse rate between sympatric G. fultoni and G. vernalis populations, pulse rate did not differ between sympatric and far allopatric G. fultoni populations in the laboratory study. Considering the magnitudes of differences in calling song characters discriminated by females of G. fultoni and the mean differences and the variability in calling song characters between the two species, the joint difference in chirp and pulse rates may be adequate for species discrimination over most of the range at which these crickets breed.     

A New Approach to the Isolation of Genomic DNA from Yeast and Fungi: Preparation of DNA-containing Cell Envelopes and Their Use in PCR

A simple and rapid procedure for the preparation of yeast and fungal DNA samples useful in PCR amplification was developed. The DNA was purified from proteins, lipids, polysaccharides, and other impurities by high-temperature extraction (in a boiling water bath) with buffer solutions containing chaotropic salts. Under these conditions, yeast and fungal cell envelopes remain unbroken and retain the original DNA and RNA that could be used for direct PCR amplification. We called the proposed PCR technique as the PCR using DNA-containing cell envelopes.