The evolution and suppression of male suicide under paternal genome elimination

Different genetic systems can be both the cause and the consequence of genetic conflict over the transmission of genes, obscuring their evolutionary origin. For instance, with paternal genome elimination (PGE), found in some insects and mites, both sexes develop from fertilized eggs, but in males the paternally derived chromosomes are either lost (embryonic PGE) or deactivated (germline PGE) during embryogenesis and not transmitted to the next generation. Evolution of germline PGE requires two transitions: (1) elimination of the paternal genome during spermatogenesis; (2) deactivation of the paternal genome early in development. Hypotheses for the evolution of PGE have mainly focused on the first transition. However, maternal genes seem to be responsible for the deactivation and here we investigate if maternal suppression could have evolved in response to paternally expressed male suicide genes. We show that sibling competition can cause such genes to spread quickly and that inbreeding is necessary to prevent fixation of male suicide, and subsequent population extinction. Once male-suicide has evolved, maternally expressed suppressor genes can invade in the population. Our results highlight the rich opportunity for genetic conflict in asymmetric genetic systems and the counterintuitive phenotypes that can evolve as a result.     

Genomic conflict in scale insects: the causes and consequences of bizarre genetic systems

It is now clear that mechanisms of sex determination are extraordinarily labile, with considerable variation across all taxonomic levels. This variation is often expressed through differences in the genetic system (XX‐XY, XX‐XO, haplodiploidy, and so on). Why there is so much variation in such a seemingly fundamental process has attracted much attention, with recent ideas concentrating on the possible role of genomic conflicts of interest. Here we consider the role of inter‐ and intra‐genomic conflicts in one large insect taxon: the scale insects. Scale insects exhibit a dizzying array of genetic systems, and their biology promotes conflicts of interest over transmission and sex ratio between male‐ and female‐expressed genes, parental‐ and offspring‐expressed genes (both examples of intra‐genomic conflict) and between scale insects and their endosymbionts (inter‐genomic conflict). We first review the wide range of genetic systems found in scale insects and the possible evolutionary transitions between them. We then outline the theoretical opportunities for genomic conflicts in this group and how these might influence sex determination and sex ratio. We then consider the evidence for these conflicts in the evolution of sex determination in scale insects. Importantly, the evolution of novel genetic systems in scale insects has itself helped create new conflicts of interest, for instance over sex ratio. As a result, a major obstacle to our understanding of the role of conflict in the evolution of sex‐determination and genetic systems will be the difficulty in identifying the direction of causal relationships. We conclude by outlining possible experimental and comparative approaches to test more effectively how important genomic conflicts have been.     

The evolution of haplodiploidy by male‐killing endosymbionts: importance of population structure and endosymbiont mutualisms

Haplodiploid inheritance systems, characterized by male transmission of only their maternally inherited genomic elements, have evolved more than 20 times within the animal kingdom. A number of theoretical studies have argued that infection with certain male‐killing endosymbionts can potentially lead to the evolution of haplodiploidy. By explicitly investigating the coevolutionary dynamics between host and endosymbiont, we show that the assumptions of current models cannot explain the evolution of haplodiploidy very well, as the endosymbiont will often go extinct in the long term. Here, we provide two additional mechanisms that can explain the stable evolution of haplodiploidy by male‐killing endosymbionts. First of all, a spatially structured population can facilitate the long‐term persistence of haplodiploidy, but this applies only when levels of inbreeding are very high. By contrast, endosymbionts that are mutualistic with their hosts provide a much more general and promising route to the stable evolution of haplodiploidy. This model is the first to provide a formal explanation of the supposed association between the evolution of haplodiploidy and the highly inbred lifestyles of some ancestors, while it also provides a hypothesis for the evolution of haplodiploidy in more outbred ancestors.     

蚧虫基因组DNA不同提取方法的比较

实验以日本龟蜡蚧CeroplastesjaponicusGreen,白蜡绵粉蚧PhenacoccusfraxinusTang ,朝鲜球蚧DidesmococcuskoreanusBorchseniush和瘤大球坚蚧EulecaniumgiganteaShinji等 4种蚧虫为材料 ,分别用十二烷基硫酸钠 (SDS)法、十六烷基三乙基溴化铵 (CTAB)法、醋酸钾 (KAc)法和氯化钠 (NaCl)法等 4种方法 ,对单只蚧虫进行基因组DNA提取 ,用 0 8%琼脂糖凝胶电泳检测所提DNA。结果表明 ,4种方法都可以提取到基因组DNA ,但是比较而言 ,CTAB法和NaCl法所提取的DNA质量明显优于SDS法和KAc法 ,并适用于PCR。因此认为 ,CTAB法和NaCl法是实验室提取单只蚧虫基因组DNA更有效而实用的方法。     

A survey of scale insects in soil samples from Europe (Hemiptera,Coccomorpha)

In the last decades, several expeditions were organized in Europe by the researchers of the Hungarian Natural History Museum to collect snails, aquatic insects and soil animals (mites, springtails, nematodes, and earthworms). In this study, scale insect (Hemiptera: Coccomorpha) specimens extracted from Hungarian Natural History Museum soil samples (2970 samples in total), all of which were collected using soil and litter sampling devices, and extracted by Berlese funnel, were examined. From these samples, 43 scale insect species (Acanthococcidae 4, Coccidae 2, Micrococcidae 1, Ortheziidae 7, Pseudococcidae 21, Putoidae 1 and Rhizoecidae 7) were found in 16 European countries. In addition, a new species belonging to the family Pseudococcidae, Brevennia larvalis Kaydan, sp. n. and a new species of Ortheziidae, Ortheziola editae Szita & Konczné Benedicty, sp. n. are described and illustrated based on the adult female stage. Revised keys to the adult females of Brevennia and Ortheziola are presented.     

蚧虫化学生态学研究进展

概述了蚧虫性信息素、植物-蚧虫-天敌三者关系中的化学联系研究进展,介绍了蚧虫化学生态学在生物防治上的应用,并探讨了蚧虫化学生态学的发展前景     

Effects of some insect growth regulators on natural enemies of scale insects (Hom.: Coccoidea)

We report and discuss effects of four insect growth regulators: buprofezin, fenoxycarb pyriproxyfen and chlorfluazuron, at concentrations recommended for agricultural use on six species of natural enemies of homopteran pests. Dipping in buprofezin had no appreciable effect on adult mortality, oviposition and development ofComperiella bifasciata (Howard), (Hymenoptera: Encyrtidae). When exposed to hosts treated with buprofezin, percentage mortality of adultEncyrtus infelix Embleton (Encyrtidae) was low; buprofezin had some detrimental effect on immature stages ofE. infelix when applied prior to parasitization, but not when introduced after parasitization. Buprofezin had a slight effect on the immature stages ofCryptochaetum iceryae Williston (Diptera: Cryptochaetidae), while fenoxycarb and pyriproxyfen had marked detrimental effects on parasitization and/or development of the parasitoid fly. None of the larvae ofRodolia cardinalis Mulsant (Coleoptera: Coccinellidae) developed into adults after application of buprofezin, fenoxycarb or pyriproxyfen. Buprofezin and chlorfluazuron completely prevented egg hatch ofChilocorus bipustulatus L. (Coleoptera: Coccinellidae). Buprofezin did not adversely affect egg hatch and larval development ofElatophilus hebraicus Pericart (Hemiptera: Anthocoridae); fenoxycarb or pyriproxyfen applied either before or after oviposition on pine needles caused total suppression of egg hatch.     

Parasitoid Encapsulation as a Defense Mechanism in the Coccoidea (Homoptera) and Its Importance in Biological Control

Encapsulation is a common defense mechanism exerted by a host insect in response to invasion by a metazoan parasitoid or other foreign organisms. In the process of encapsulation, the host forms a capsule around the parasitoid egg or larva, which is usually composed of host blood cells and the pigment melanin. The capsule may kill the parasitoid and thus prevent successful parasitism. Encapsulation may adversely affect the degree of biological control effected by parasitoids as it may either prevent the establishment of exotic parasitoids in new regions or reduce parasitoid efficacy. A high incidence of encapsulation may also cause difficulties in mass rearing of parasitoids. In the Coccoidea (Homoptera), parasitoid encapsulation has so far been recorded in three families: Coccidae (soft scale insects), Diaspididae (armored scale insects), and Pseudococcidae (mealybugs). Important factors that affect the frequency of parasitoid encapsulation in the Coccoidea include: Host and parasitoid species, the host's physiological age and physiological condition, the host origin (or strain), superparasitism, the rearing and/or ambient temperature, and the host plant. The effects of these factors on the incidence of parasitoid encapsulation in the Coccidae, Diaspididae, and Pseudococcidae are described.     

The unusual reproductive system of head and body lice (Pediculus humanus)

Insect reproduction is extremely variable, but the implications of alternative genetic systems are often overlooked in studies on the evolution of insecticide resistance. Both ecotypes of Pediculus humanus (Phthiraptera: Pediculidae), the human head and body lice, are human ectoparasites, the control of which is challenged by the recent spread of resistance alleles. The present study conclusively establishes for the first time that both head and body lice reproduce through paternal genome elimination (PGE), an unusual genetic system in which males transmit only their maternally derived chromosomes. Here, we investigate inheritance patterns of parental genomes using a genotyping approach across families of both ecotypes and show that heterozygous males exclusively or preferentially pass on one allele only, whereas females transmit both in a Mendelian fashion. We do however observe occasional transmission of paternal chromosomes through males, representing the first known case of PGE in which whole‐genome meiotic drive is incomplete. Finally, we discuss the potential implications of this finding for the evolution of resistance and invite the development of new theoretical models of how this knowledge might contribute to increasing the success of pediculicide‐based management schemes.     

Predictive role of mitochondrial genome in the stress resistance of insects and nematodes

Certain insects (e.g., moths and butterflies; order Lepidoptera) and nematodes are considered as excellent experimental models to study the cellular stress signaling mechanisms since these organisms are far more stress-resistant as compared to mammalian system. Multiple factors have been implicated in this unusual response, including the oxidative stress response mechanisms. Radiation or chemical-induced mitochondrial oxidative stress occurs through damage caused to the components of electron transport chain (ETC) leading to leakage of electrons and generation of superoxide radicals. This may be countered through quick replacement of damaged mitochondrial proteins by upregulated expression. Since the ETC comprises of various proteins coded by mitochondrial DNA, variation in the composition, expressivity and regulation of mitochondrial genome could greatly influence mitochondrial role under oxidative stress conditions. Therefore, we carried out in silico analysis of mitochondrial DNA in these organisms and compared it with that of the stress-sensitive humans/mammals. Parameters such as mitochondrial genome organization, codon bias, gene expressivity and GC₃ content were studied. Gene arrangement and Shine-Dalgarno (SD) sequence patterns indicating translational regulation were distinct in insect and nematodes as compared to humans. A higher codon bias (ENC≫35) and lower GC₃ content (≫0.20) were observed in mitochondrial genes of insect and nematodes as compared to humans (ENC>42; GC3>0.20), coupled with low codon adaptation index among insects. These features indeed favour higher expressivity of mitochondrial proteins and might help maintain the mitochondrial physiology under stress conditions. Therefore, our study indicates that mitochondrial genome organization may influence stress-resistance of insects and nematodes.     

Evolutionary relationships of flavobacterial and enterobacterial endosymbionts with their scale insect hosts (Hemiptera: Coccoidea)

Flavobacteria and Enterobacteriaceae have been previously reported as scale insect endosymbionts. The purpose of this work was twofold: first, to screen different scale insect families for the presence of these endosymbionts by PCR analyses and second, to elucidate the history of cophylogeny between these bacteria and the insects by analysing a portion of 16S rRNA and 18S rRNA gene sequences by two reconciliation tools, CoRe‐PA and Jane. From a survey of 27 scale insects within seven families, we identified Flavobacteria and Enterobacteriaceae as coexisting in ten species that belong to the Ortheziidae, Monophlebidae, Diaspididae and Coccidae families, and we frequently found two closely related enterobacteria harboured in the same individual. Analyses performed with CoRe‐PA and Jane suggest that Flavobacteria from the scale insects analysed have a unique origin, except for Candidatus Brownia rhizoecola (Flavobacteria of Pseudococcidae, Phenacoccinae), which seems to come from a nonscale insect. Nevertheless, cospeciation between Flavobacteria and scale insects is suggested only within the families Monophlebidae, Ortheziidae and Diaspididae, and host switches seem to have occurred from the ancestors of Monophlebidae and Ortheziidae to insects from families Coccidae, Lecanodiaspididae, Eriococcidae and Pseudococcidae. Our analyses suggest that Enterobacteriaceae underwent more evolutionary events (losses, duplications and host switches), and their phylogenies showed a lower proportion of congruent nodes between host and bacteria, indicating a more relaxed relationship with scale insects compared with Flavobacteria.     

The Clonopsis gallica puzzle: Mendelian species, polyploid parthenogens with karyotype re-diploidization and clonal androgens in Moroccan stick insects (Phasmida)

The stick insect Clonopsis gallica is a morphologically stable obligate parthenogen, ranging from North Africa to southern Europe, with a variable karyotype (54–57 chromosomes), considered diploid or triploid. Clonopsis gallica origin and relationships with Clonopsis algerica and Clonopsis maroccana remained unknown. Our Moroccan samples shared the same egg and body patterns and, in addition to C. gallica (2 n  = 54, XX), comprised the new bisexual Clonopsis sp. 1 (2 n  = 35/36, X0/XX) and the new all-female Clonopsis sp. 2 (2 n  = 72, XX), apparently forming a numerically polyploid series with re-diplodized karyotypes; C. gallica could thus be a triploid hybrid in origin. Furthermore, two strains of ameiotic males with 2 n  = 35 (X0) or 53 (X0) were found, which would maintain themselves as clonal androgens. We could conclude that in stick insects body and karyotype 'phenotypes' are considerably independent, thus preventing a sound taxonomy. Generally, the high heterozygosity of hybrids allows parthenogens to persist for long, particularly when hybrid polyploids are produced, as backcrosses of the hybrids to the parental species allow repeated incorporations of genetically diversified genomes. The distribution range of Clonopsis parthenogens appears to realize a sound instance of geographical parthenogenesis.     

The gall-inducing habit has evolved multiple times among the eriococcid scale insects (Sternorrhyncha: Coccoidea: Eriococcidae)

The habit of inducing plant galls has evolved multiple times among insects but most species diversity occurs in only a few groups, such as gall midges and gall wasps. This phylogenetic clustering may reflect adaptive radiations in insect groups in which the trait has evolved. Alternatively, multiple independent origins of galling may suggest a selective advantage to the habit. We use DNA sequence data to examine the origins of galling among the most speciose group of gall-inducing scale insects, the eriococcids. We determine that the galling habit has evolved multiple times, including four times in Australian taxa, suggesting that there has been a selective advantage to galling in Australia. Additionally, although most gall-inducing eriococcid species occur on Myrtaceae, we found that lineages feeding on Myrtaceae are no more likely to have evolved the galling habit than those feeding on other plant groups. However, most gall-inducing species-richness is clustered in only two clades ( Apiomorpha and Lachnodius  +  Opisthoscelis ), all of which occur exclusively on Eucalyptus s.s . The Eriococcidae and the large genus Eriococcus were determined to be non-monophyletic and each will require revision.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 441–452.     

Population biology of a selfish sex ratio distorting element in a booklouse (Psocodea: Liposcelis)

Arthropods harbour a variety of selfish genetic elements that manipulate reproduction to be preferentially transmitted to future generations. A major ongoing question is to understand how these elements persist in nature. In this study, we examine the population dynamics of an unusual selfish sex ratio distorter in a recently discovered species of booklouse, Liposcelis sp. (Psocodea: Liposcelididae) to gain a better understanding of some of the factors that may affect the persistence of this element. Females that carry the selfish genetic element only ever produce daughters, although they are obligately sexual. These females also only transmit the maternal half of their genome. We performed a replicated population cage experiment, varying the initial frequency of females that harbour the selfish element, and following female frequencies for 20 months. The selfish genetic element persisted in all cages, often reaching very high (and thus severely female‐biased) frequencies. Surprisingly, we also found that females that carry the selfish genetic element had much lower fitness than their nondistorter counterparts, with lower lifetime fecundity, slower development and a shorter egg‐laying period. We suggest that differential fitness plays a role in the maintenance of the selfish genetic element in this species. We believe that the genetic system in this species, paternal genome elimination, which allows maternal control of offspring sex ratio, may also be important in the persistence of the selfish genetic element, highlighting the need to consider species with diverse ecologies and genetic systems when investigating the effects of sex ratio manipulators on host populations.     

The unusual cover of the armoured scale Cryptaspidiotus barbusano (Lindinger) (Hemiptera: Diaspididae: Aspidiotinae) with comments on the scale covers of other Diaspididae

Cryptaspidiotus barbusano (Lindinger 1908) is an endemic species of the Canary Islands, only known on Apollonias barbujana (Lauraceae), a plant growing in the “Laurisilva” or laurel forest, in several Macaronesian islands. Recently C. barbusano was collected on Heberdenia excelsa (Myrsinaceae), a new host plant and family, in the Jardín Botánico Canario Viera y Clavijo, Las Palmas, Gran Canaria. The recent collection of C. barbusano gives us the opportunity to redescribe its unusual adult female scale cover. The truncate cone-shaped scale cover and its peculiar reflexed exit tunnel for crawlers, with microscopic details of this rare species, are described and illustrated. The shape of the exit tunnel is discussed and the scale cover is compared with scale covers of several other diaspidid species. Finally, this study shows that C. barbusano is not a pupillarial species as formerly described.     

Preliminary study of wing interference patterns (WIPs) in some species of soft scale (Hemiptera,Sternorrhyncha, Coccoidea,Coccidae)

The fore wings of scale insect males possess reduced venation compared with other insects and the homologies of remaining veins are controversial. The hind wings are reduced to hamulohalterae. When adult males are prepared using the standard methods adopted to females and nymphs, i.e. using KOH to clear the specimens, the wings become damaged or deformed, an so these structures are not usually described or illustrated in publications. The present study used dry males belonging to seven species of the family Coccidae to check the presence of stable, structural colour patterns of the wings. The visibility of the wing interference patterns (WIP), discovered in Hymenoptera and Diptera species, is affected by the way the insects display their wings against various backgrounds with different light properties. This frequently occurring taxonomically specific pattern is caused by uneven membrane thickness and hair placement, and also is stabilized and reinforced by microstructures of the wing, such as membrane corrugations and the shape of cells. The semitransparent scale insect’s fore wings possess WIPs and they are taxonomically specific. It is very possible that WIPs will be an additional and helpful trait for the identification of species, which in case of males specimens is quite difficult, because recent coccidology is based almost entirely on the morphology of adult females.     

Links between host-plant type and site of feeding as revealed by the evolution of Palaearctic Eriococcidae (Sternorrhyncha: Coccoidea)

This work is an assessment of the biogeographical, taxonomic, biological and phylogenetic knowledge of the poorly defined family Eriococcidae. The study of its geographical diversity shows the richness of the Palearctic fauna on which the present analysis focuses. The numerous systems dealing with the taxonomy of Eriococcidae are detailed, and the specific taxonomical status of the genus Eriococcus, which contains 155 out of the 175 known Palearctic species is reevaluated. The phylogeny of the palaearctic members of the scale insect family Eriococcidae is reconstructed, using 9 genera and 52 species. Three more scale insect species belonging to 3 families were used as outgroups. The cladistic analysis of 130 morphological characters of the adults resulted in 10 most parsimonious trees, placing Eriococcus buxi as the sister-group of all other sampled Eriococcidae. The genera Acanthococcus, Rhizococcus, Greenisca and Anophococcus appear as para- or polyphyletic, but the weakness of most of the clades does not allow to denounce strictly the monophyly of these genera. However, some clades are supported with high confidence, like (Kaweckia + Neokaweckia), (Anophococcus parvispinus(Anophococcus inermis+Greenisca placida) and (Gossyparia spuria+Acanthococcus aceris). Concerning host-plant relationships, the phylogeny supports an evolutionary scenario whereby the ancestor of the family Eriococcidae fed originally on woody plants, and more typically on leaves. The switch observed from Poaceae to other herbaceous plants is correlated to the switch from leaves as preferred site of nutrition to branches and stems. The supported scenario shows another switch, back from other herbs to Poaceae, associated to the choice of leaves as nutrition site.     

Variation in patriline reproductive success during queen production in orphaned colonies of the thelytokous ant Cataglyphis cursor

In genetically diverse insect societies (polygynous or polyandrous queens), the production of new queens can set the ground for competition among lineages. This competition can be very intense when workers can reproduce using thelytoky as worker lineages that manage to produce new queens gain a huge benefit. Selection at the individual level might then lead to the evolution of cheating genotypes, i.e. genotypes that reproduce more than their fair share. We studied the variation in reproductive success among worker patrilines in the thelytokous and highly polyandrous ant Cataglyphis cursor. Workers produce new queens by thelytoky in orphaned colonies. The reproductive success of each patriline was assessed in 13 orphaned colonies using genetic analysis of 433 workers and 326 worker-produced queens. Our results show that patrilines contributed unequally to queen production in half of the colonies, and the success of patrilines was function of their frequencies in workers. However, over all colonies, we observed a significant difference in the distribution of patrilines between workers and worker-produced queens, and this difference was significant in three of 13 colonies. In addition, six colonies contained a low percentage of foreign workers (drifters), and in one colony, they produced a disproportionably high number of queens. Hence, we found some evidence for the occurrence of rare cheating genotypes. Nevertheless, cheating appears to be less pronounced than in the Cape Honey bee, a species with a similar reproductive system. We argue that worker reproduction by parthenogenesis might not be common in natural populations of C. cursor.     

The ups and downs of genome size evolution in polyploid species of Nicotiana (Solanaceae)

BACKGROUND: In studies looking at individual polyploid species, the most common patterns of genomic change are that either genome size in the polyploid is additive (i.e. the sum of parental genome donors) or there is evidence of genome downsizing. Reports showing an increase in genome size are rare. In a large-scale analysis of 3008 species, genome downsizing was shown to be a widespread biological response to polyploidy. Polyploidy in the genus Nicotiana (Solanaceae) is common with approx. 40 % of the approx. 75 species being allotetraploid. Recent advances in understanding phylogenetic relationships of Nicotiana species and dating polyploid formation enable a temporal dimension to be added to the analysis of genome size evolution in these polyploids. METHODS: Genome sizes were measured in 18 species of Nicotiana (nine diploids and nine polyploids) ranging in age from <200,000 years to approx. 4.5 Myr old, to determine the direction and extent of genome size change following polyploidy. These data were combined with data from genomic in situ hybridization and increasing amounts of information on sequence composition in Nicotiana to provide insights into the molecular basis of genome size changes. KEY RESULTS AND CONCLUSIONS: By comparing the expected genome size of the polyploid (based on summing the genome size of species identified as either a parent or most closely related to the diploid progenitors) with the observed genome size, four polyploids showed genome downsizing and five showed increases. There was no discernable pattern in the direction of genome size change with age of polyploids, although with increasing age the amount of genome size change increased. In older polyploids (approx. 4.5 million years old) the increase in genome size was associated with loss of detectable genomic in situ hybridization signal, whereas some hybridization signal was still detected in species exhibiting genome downsizing. The possible significance of these results is discussed.