Special Issue "Symbiosis: A Source of Evolutionary Innovation in Insects"

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A special issue of Insects (ISSN 2075-4450).

Deadline for manuscript submissions: closed (31 October 2011)

Special Issue Editor

Guest Editor
Prof. Dr. Diana Six (Website)

Department of Ecosystem and Conservation Sciences, College of Forestry&Conservation, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA
Interests: insect-microbe symbioses; mutualism; effects of climate change on symbioses/mutualism; bark beetles; ambrosia beetles; climate change roles on forest die-offs

Special Issue Information

Dear Colleagues,

This special issue will explore the importance of symbiosis as a source of evolutionary innovation in insects. Symbioses between insects and microbes are ubiquitous, and in many cases, have resulted in the development of key innovations that have greatly affected the subsequent success of each partner. The striking complementary metabolic capabilities that exist among some insect hosts and their endosymbionts exemplifies how symbiotic interactions can support reciprocal adaptation and phenotypic complexity. Symbiotic interactions can have extraordinary effects on the morphology, behavior and ecology of hosts and symbionts, alike. Symbiosis can also bring about specialization, which in turn, can lead to coevolutionary innovations that support subsequent diversification. While mutualisms are perhaps the best studied category of symbioses in the context of evolutionary innovation, other types of symbiotic interactions can also be significant sources of innovation. For example, Wolbachia, which are typically reproductive parasites, are thought to be major drivers in the evolution of eusociality, sex determination, and speciation in insects. The submission of high quality articles on symbioses involving insects and microbes that have resulted in major or interesting innovations is encouraged.

Prof. Dr. Diana L. Six
Guest Editor

Published Papers (15 papers)

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Research

Jump to: Review

Open AccessArticle Shared Ancestry of Symbionts? Sagrinae and Donaciinae (Coleoptera, Chrysomelidae) Harbor Similar Bacteria
Insects 2012, 3(2), 473-491; doi:10.3390/insects3020473
Received: 28 March 2012 / Revised: 11 April 2012 / Accepted: 17 April 2012 / Published: 7 May 2012
Cited by 1 | PDF Full-text (367 KB) | HTML Full-text | XML Full-text
Abstract
When symbioses between insects and bacteria are discussed, the origin of a given association is regularly of interest. We examined the evolution of the symbiosis between reed beetles (Coleoptera, Chrysomelidae, Donaciinae) and intracellular symbionts belonging to the Enterobacteriaceae. We analyzed the partial [...] Read more.
When symbioses between insects and bacteria are discussed, the origin of a given association is regularly of interest. We examined the evolution of the symbiosis between reed beetles (Coleoptera, Chrysomelidae, Donaciinae) and intracellular symbionts belonging to the Enterobacteriaceae. We analyzed the partial sequence of the 16S rRNA to assess the phylogenetic relationships with bacteria we found in other beetle groups (Cerambycidae, Anobiidae, other Chrysomelidae). We discuss the ecology of each association in the context of the phylogenetic analysis. The bacteria in Sagra femorata (Chrysomelidae, Sagrinae) are very closely related to those in the Donaciinae and are located in similar mycetomes. The Sagrinae build a cocoon for pupation like the Donaciinae, in which the bacteria produce the material required for the cocoon. These aspects support the close relationship between Sagrinae and Donaciinae derived in earlier studies and make a common ancestry of the symbioses likely. Using PCR primers specific for fungi, we found Candida sp. in the mycetomes of a cerambycid beetle along with the bacteria. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessCommunication Fungiculture or Termite Husbandry? The Ruminant Hypothesis
Insects 2012, 3(1), 307-323; doi:10.3390/insects3010307
Received: 5 January 2012 / Revised: 3 March 2012 / Accepted: 7 March 2012 / Published: 16 March 2012
Cited by 8 | PDF Full-text (473 KB) | HTML Full-text | XML Full-text
Abstract
We present a new perspective for the role of Termitomyces fungi in the mutualism with fungus-growing termites. According to the predominant view, this mutualism is as an example of agriculture with termites as farmers of a domesticated fungus crop, which is used [...] Read more.
We present a new perspective for the role of Termitomyces fungi in the mutualism with fungus-growing termites. According to the predominant view, this mutualism is as an example of agriculture with termites as farmers of a domesticated fungus crop, which is used for degradation of plant-material and production of fungal biomass. However, a detailed study of the literature indicates that the termites might as well be envisioned as domesticates of the fungus. According to the “ruminant hypothesis” proposed here, termite workers, by consuming asexual fruiting bodies not only harvest asexual spores, but also lignocellulolytic enzymes, which they mix with foraged plant material and enzymes of termite and possibly bacterial origin. This mixture is the building material of the fungus garden and facilitates efficient degradation of plant material. The fungus garden thus functions as an external rumen for termites and primarily the fungi themselves benefit from their own, and gut-derived, lignocellulolytic enzymes, using the termites to efficiently mix these with their growth substrate. Only secondarily the termites benefit, when they consume the degraded, nitrogen-enriched plant-fungus mixture a second time. We propose that the details of substrate use, and the degree of complementarity and redundancy among enzymes in food processing, determine selection of horizontally transmitted fungal symbionts at the start of a colony: by testing spores on a specific, mechanically and enzymatically pre-treated growth substrate, the termite host has the opportunity to select specific fungal symbionts. Potentially, the gut-microbiota thus influence host-fungus specificity, and the selection of specific fungal strains at the start of a new colony. We argue that we need to expand the current bipartite insect-biased view of the mutualism of fungus-growing termites and include the possible role of bacteria and the benefit for the fungi to fully understand the division of labor among partners in substrate degradation. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
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Open AccessArticle Distribution of the Primary Endosymbiont (Candidatus Uzinura Diaspidicola) Within Host Insects from the Scale Insect Family Diaspididae
Insects 2012, 3(1), 262-269; doi:10.3390/insects3010262
Received: 29 December 2011 / Revised: 15 February 2012 / Accepted: 20 February 2012 / Published: 29 February 2012
Cited by 2 | PDF Full-text (129 KB) | HTML Full-text | XML Full-text
Abstract
It has long been known that armored scale insects harbor endosymbiotic bacteria inside specialized cells called bacteriocytes. Originally, these endosymbionts were thought to be fungal symbionts but they are now known to be bacterial and have been named Uzinura diaspidicola. Bacteriocyte and [...] Read more.
It has long been known that armored scale insects harbor endosymbiotic bacteria inside specialized cells called bacteriocytes. Originally, these endosymbionts were thought to be fungal symbionts but they are now known to be bacterial and have been named Uzinura diaspidicola. Bacteriocyte and endosymbiont distribution patterns within host insects were visualized using in situ hybridization via 16S rRNA specific probes. Images of scale insect embryos, eggs and adult scale insects show patterns of localized bacteriocytes in embryos and randomly distributed bacteriocytes in adults. The symbiont pocket was not found in the armored scale insect eggs that were tested. The pattern of dispersed bacteriocytes in adult scale insects suggest that Uzinura and Blattabacteria may share some homologous traits that coincide with similar life style requirements, such as dispersal in fat bodies and uric acid recycling. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessArticle Generation of Nutrients and Detoxification: Possible Roles of Yeasts in Leaf-Cutting Ant Nests
Insects 2012, 3(1), 228-245; doi:10.3390/insects3010228
Received: 14 January 2012 / Revised: 12 February 2012 / Accepted: 13 February 2012 / Published: 17 February 2012
Cited by 6 | PDF Full-text (557 KB) | HTML Full-text | XML Full-text
Abstract
The possible roles played by yeasts in attine ant nests are mostly unknown. Here we present our investigations on the plant polysaccharide degradation profile of 82 yeasts isolated from fungus gardens of Atta and Acromyrmex species to demonstrate that yeasts found in [...] Read more.
The possible roles played by yeasts in attine ant nests are mostly unknown. Here we present our investigations on the plant polysaccharide degradation profile of 82 yeasts isolated from fungus gardens of Atta and Acromyrmex species to demonstrate that yeasts found in ant nests may play the role of making nutrients readily available throughout the garden and detoxification of compounds that may be deleterious to the ants and their fungal cultivar. Among the yeasts screened, 65% exhibited cellulolytic enzymes, 44% exhibited pectinolytic activity while 27% and 17% possess enzyme systems for the degradation of protease and amylase, respectively. Galacturonic acid, which had been reported in previous work to be poorly assimilated by the ant fungus and also to have a negative effect on ants’ survival, was assimilated by 64% and 79% of yeasts isolated from nests of A. texana and Acromyrmex respectively. Our results suggest that yeasts found in ant nests may participate in generation of nutrients and removal of potentially toxic compounds, thereby contributing to the stability of the complex microbiota found in the leaf-cutting ant nests. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessArticle Phylogenetic Analysis of Fusarium solani Associated with the Asian Longhorned Beetle, Anoplophora glabripennis
Insects 2012, 3(1), 141-160; doi:10.3390/insects3010141
Received: 21 December 2011 / Revised: 1 February 2012 / Accepted: 8 February 2012 / Published: 10 February 2012
Cited by 5 | PDF Full-text (423 KB) | HTML Full-text | XML Full-text
Abstract
Culture-independent analysis of the gut of a wood-boring insect, Anoplophora glabripennis (Coleoptera: Cerambycidae), revealed a consistent association between members of the fungal Fusarium solani species complex and the larval stage of both colony-derived and wild A. glabripennis populations. Using the translation elongation [...] Read more.
Culture-independent analysis of the gut of a wood-boring insect, Anoplophora glabripennis (Coleoptera: Cerambycidae), revealed a consistent association between members of the fungal Fusarium solani species complex and the larval stage of both colony-derived and wild A. glabripennis populations. Using the translation elongation factor 1-alpha region for culture-independent phylogenetic and operational taxonomic unit (OTU)-based analyses, only two OTUs were detected, suggesting that genetic variance at this locus was low among A. glabripennis-associated isolates. To better survey the genetic variation of F. solani associated with A. glabripennis, and establish its phylogenetic relationship with other members of the F. solani species complex, single spore isolates were created from different populations and multi-locus phylogenetic analysis was performed using a combination of the translation elongation factor alpha-1, internal transcribed spacer, and large subunit rDNA regions. These analyses revealed that colony-derived larvae reared in three different tree species or on artificial diet, as well as larvae from wild populations collected from three additional tree species in New York City and from a single tree species in Worcester, MA, consistently harbored F. solani within their guts. While there is some genetic variation in the F. solani carried between populations, within-population variation is low. We speculate that F. solani is able to fill a broad niche in the A. glabripennis gut, providing it with fungal lignocellulases to allow the larvae to grow and develop on woody tissue. However, it is likely that many F. solani genotypes could potentially fill this niche, so the relationship may not be limited to a single member of the F. solani species complex. While little is known about the role of filamentous fungi and their symbiotic associations with insects, this report suggests that larval A. glabripennis has developed an intimate relationship with F. solani that is not limited by geographic location or host tree. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessArticle Ant Larval Demand Reduces Aphid Colony Growth Rates in an Ant-Aphid Interaction
Insects 2012, 3(1), 120-130; doi:10.3390/insects3010120
Received: 13 December 2011 / Revised: 6 January 2012 / Accepted: 11 January 2012 / Published: 2 February 2012
Cited by 1 | PDF Full-text (119 KB) | HTML Full-text | XML Full-text
Abstract
Ants often form mutualistic interactions with aphids, soliciting honeydew in return for protective services. Under certain circumstances, however, ants will prey upon aphids. In addition, in the presence of ants aphids may increase the quantity or quality of honeydew produced, which is [...] Read more.
Ants often form mutualistic interactions with aphids, soliciting honeydew in return for protective services. Under certain circumstances, however, ants will prey upon aphids. In addition, in the presence of ants aphids may increase the quantity or quality of honeydew produced, which is costly. Through these mechanisms, ant attendance can reduce aphid colony growth rates. However, it is unknown whether demand from within the ant colony can affect the ant-aphid interaction. In a factorial experiment, we tested whether the presence of larvae in Lasius niger ant colonies affected the growth rate of Aphis fabae colonies. Other explanatory variables tested were the origin of ant colonies (two separate colonies were used) and previous diet (sugar only or sugar and protein). We found that the presence of larvae in the ant colony significantly reduced the growth rate of aphid colonies. Previous diet and colony origin did not affect aphid colony growth rates. Our results suggest that ant colonies balance the flow of two separate resources from aphid colonies- renewable sugars or a protein-rich meal, depending on demand from ant larvae within the nest. Aphid payoffs from the ant-aphid interaction may change on a seasonal basis, as the demand from larvae within the ant colony waxes and wanes. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessArticle Adopting Bacteria in Order to Adapt to Water—How Reed Beetles Colonized the Wetlands (Coleoptera, Chrysomelidae, Donaciinae)
Insects 2011, 2(4), 540-554; doi:10.3390/insects2040540
Received: 28 October 2011 / Revised: 16 November 2011 / Accepted: 25 November 2011 / Published: 9 December 2011
Cited by 5 | PDF Full-text (511 KB) | HTML Full-text | XML Full-text
Abstract
The present paper reviews the biology of reed beetles (Donaciinae), presents experimental data on the role of specific symbiotic bacteria, and describes a molecular method for the detection of those bacteria. Reed beetles are herbivores living on wetland plants, each species being [...] Read more.
The present paper reviews the biology of reed beetles (Donaciinae), presents experimental data on the role of specific symbiotic bacteria, and describes a molecular method for the detection of those bacteria. Reed beetles are herbivores living on wetland plants, each species being mono- or oligo-phagous. They lay their eggs on the host plant and the larvae live underwater in the sediment attached to its roots. The larvae pupate there in a water-tight cocoon, which they build using a secretion that is produced by symbiotic bacteria. The bacteria are located in four blind sacs at the foregut of the larvae; in (female) adults they colonize two out of the six Malpighian tubules. Tetracycline treatment of larvae reduced their pupation rate, although the bacteria could not be fully eliminated. When the small amount of bacterial mass attached to eggs was experimentally removed before hatching, symbiont free larvae resulted, showing the external transmission of the bacteria to the offspring. Specific primers were designed to detect the bacteria, and to confirm their absence in manipulated larvae. The pupation underwater enabled the reed beetles to permanently colonize the wetlands and to diversify in this habitat underexploited by herbivorous insects (adaptive radiation). Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessArticle Use of the Internal Transcribed Spacer (ITS) Regions to Examine Symbiont Divergence and as a Diagnostic Tool for Sodalis-Related Bacteria
Insects 2011, 2(4), 515-531; doi:10.3390/insects2040515
Received: 21 September 2011 / Revised: 15 November 2011 / Accepted: 17 November 2011 / Published: 30 November 2011
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Abstract
Bacteria excel in most ecological niches, including insect symbioses. A cluster of bacterial symbionts, established within a broad range of insects, share high 16S rRNA similarities with the secondary symbiont of the tsetse fly (Diptera: Glossinidae), Sodalis glossinidius. Although 16S rRNA [...] Read more.
Bacteria excel in most ecological niches, including insect symbioses. A cluster of bacterial symbionts, established within a broad range of insects, share high 16S rRNA similarities with the secondary symbiont of the tsetse fly (Diptera: Glossinidae), Sodalis glossinidius. Although 16S rRNA has proven informative towards characterization of this clade, the gene is insufficient for examining recent divergence due to selective constraints. Here, we assess the application of the internal transcribed spacer (ITS) regions, specifically the ITSglu and ITSala,ile, used in conjunction with 16S rRNA to enhance the phylogenetic resolution of Sodalis-allied bacteria. The 16S rRNA + ITS regions of Sodalis and allied bacteria demonstrated significant divergence and were robust towards phylogenetic resolution. A monophyletic clade of Sodalis isolates from tsetse species, distinct from other Enterobacteriaceae, was consistently observed suggesting diversification due to host adaptation. In contrast, the phylogenetic distribution of symbionts isolated from hippoboscid flies and various Hemiptera and Coleoptera were intertwined suggesting either horizontal transfer or a recent establishment from an environmental source. Lineage splitting of Sodalis-allied bacteria into symbiotic and free-living sister groups was also observed. Additionally, we propose an ITS region as a diagnostic marker for the identification of additional Sodalis-allied symbionts in the field. These results expand our knowledge of informative genome regions to assess genetic divergence since splitting from the last common ancestor, of this versatile insect symbiont clade that have become increasingly recognized as valuable towards our understanding of the evolution of symbiosis. These facultative and recently associated symbionts may provide a novel source of traits adaptable to the dynamic ecologies encountered by diverse host backgrounds. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessCommunication Inhibition of Melanization by a Parasitoid Serine Protease Homolog Venom Protein Requires Both the Clip and the Non-Catalytic Protease-Like Domains
Insects 2011, 2(4), 509-514; doi:10.3390/insects2040509
Received: 18 October 2011 / Revised: 10 November 2011 / Accepted: 15 November 2011 / Published: 25 November 2011
Cited by 1 | PDF Full-text (207 KB) | HTML Full-text | XML Full-text
Abstract
Endoparasitoid wasps inject a variety of components into their host hemocoel at oviposition to facilitate successful development of their progeny. Among these are venom proteins which have been shown to play crucial roles in host regulation. A serine protease homolog (SPH)-like venom [...] Read more.
Endoparasitoid wasps inject a variety of components into their host hemocoel at oviposition to facilitate successful development of their progeny. Among these are venom proteins which have been shown to play crucial roles in host regulation. A serine protease homolog (SPH)-like venom protein from Cotesia rubecula was previously shown to inhibit melanization in the host hemolymph by blocking activation of prophenoloxidase to phenoloxidase, a key enzyme in melanin formation. Similar to other SPHs, Vn50 consists of a clip and a protease-like (SPL) domain. Protein modeling demonstrated that Vn50 has a very similar structure to known SPHs and functional analysis of Vn50 domains expressed in insect cells indicated that neither of the domains on its own has an inhibitory effect on melanization. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessArticle Effect of Host Genotype on Symbiont Titer in the Aphid—Buchnera Symbiosis
Insects 2011, 2(3), 423-434; doi:10.3390/insects2030423
Received: 3 August 2011 / Revised: 23 August 2011 / Accepted: 7 September 2011 / Published: 16 September 2011
Cited by 6 | PDF Full-text (362 KB) | HTML Full-text | XML Full-text
Abstract
Obligate nutritional symbioses require balance between the energetic needs of the host and the symbiont. The resident symbiont population size within a host may have major impacts on host fitness, as both host and symbiont consume and supply metabolites in a shared [...] Read more.
Obligate nutritional symbioses require balance between the energetic needs of the host and the symbiont. The resident symbiont population size within a host may have major impacts on host fitness, as both host and symbiont consume and supply metabolites in a shared metabolite pool. Given the massive genome degradation that is a hallmark of bacterial endosymbionts of insects, it is unclear at what level these populations are regulated, and how regulation varies among hosts within natural populations. We measured the titer of the endosymbiont Buchnera aphidicola from different clones of the pea aphid, Acyrthosiphon pisum, and found significant variation in titer, measured as Buchnera genomes per aphid genome, among aphid clones. Additionally, we found that titer can change with the age of the host, and that the number of bacteriocytes within an aphid is one factor likely controlling Buchnera titer. Buchnera titer measurements in clones from a sexual cross indicate that the symbiont genotype is not responsible for variation in titer and that this phenotype is likely non-heritable across sexual reproduction. Symbiont titer is more variable among lab-produced F1 aphid clones than among field-collected ones, suggesting that intermediate titer is favored in natural populations. Potentially, a low heritability of titer during the sexual phase may generate clones with extreme and maladaptive titers each season. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
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Review

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Open AccessReview Ecological and Evolutionary Determinants of Bark Beetle —Fungus Symbioses
Insects 2012, 3(1), 339-366; doi:10.3390/insects3010339
Received: 16 February 2012 / Revised: 1 March 2012 / Accepted: 15 March 2012 / Published: 22 March 2012
Cited by 33 | PDF Full-text (2853 KB) | HTML Full-text | XML Full-text
Abstract
Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can [...] Read more.
Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can be associated with many. In addition, most of these symbioses are multipartite, with the host beetle associated with two or more consistent partners. Mycangia, structures of the beetle integument that function in fungal transport, have evolved numerous times in the Scolytinae. The evolution of such complex, specialized structures indicates a high degree of mutual dependence among the beetles and their fungal partners. Unfortunately, the processes that shaped current day beetle-fungus symbioses remain poorly understood. Phylogeny, the degree and type of dependence on partners, mode of transmission of symbionts (vertical vs. horizontal), effects of the abiotic environment, and interactions among symbionts themselves or with other members of the biotic community, all play important roles in determining the composition, fidelity, and longevity of associations between beetles and their fungal associates. In this review, I provide an overview of these associations and discuss how evolution and ecological processes acted in concert to shape these fascinating, complex symbioses. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessReview Modification of Insect and Arachnid Behaviours by Vertically Transmitted Endosymbionts: Infections as Drivers of Behavioural Change and Evolutionary Novelty
Insects 2012, 3(1), 246-261; doi:10.3390/insects3010246
Received: 29 January 2012 / Revised: 17 February 2012 / Accepted: 21 February 2012 / Published: 29 February 2012
Cited by 12 | PDF Full-text (134 KB) | HTML Full-text | XML Full-text
Abstract
Vertically acquired, endosymbiotic bacteria such as those belonging to the Rickettsiales and the Mollicutes are known to influence the biology of their arthropod hosts in order to favour their own transmission. In this study we investigate the influence of such reproductive parasites [...] Read more.
Vertically acquired, endosymbiotic bacteria such as those belonging to the Rickettsiales and the Mollicutes are known to influence the biology of their arthropod hosts in order to favour their own transmission. In this study we investigate the influence of such reproductive parasites on the behavior of their insects and arachnid hosts. We find that changes in host behavior that are associated with endosymbiont infections are not restricted to characteristics that are directly associated with reproduction. Other behavioural traits, such as those involved in intraspecific competition or in dispersal may also be affected. Such behavioural shifts are expected to influence the level of intraspecific variation and the rate at which adaptation can occur through their effects on effective population size and gene flow amongst populations. Symbionts may thus influence both levels of polymorphism within species and the rate at which diversification can occur. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessReview Insect Sex Determination Manipulated by Their Endosymbionts: Incidences, Mechanisms and Implications
Insects 2012, 3(1), 161-199; doi:10.3390/insects3010161
Received: 25 November 2011 / Revised: 14 January 2012 / Accepted: 2 February 2012 / Published: 10 February 2012
Cited by 21 | PDF Full-text (355 KB) | HTML Full-text | XML Full-text
Abstract
The sex-determining systems of arthropods are surprisingly diverse. Some species have male or female heterogametic sex chromosomes while other species do not have sex chromosomes. Most species are diploids but some species, including wasps, ants, thrips and mites, are haplodiploids (n in [...] Read more.
The sex-determining systems of arthropods are surprisingly diverse. Some species have male or female heterogametic sex chromosomes while other species do not have sex chromosomes. Most species are diploids but some species, including wasps, ants, thrips and mites, are haplodiploids (n in males; 2n in females). Many of the sexual aberrations, such as sexual mosaics, sex-specific lethality and conversion of sexuality, can be explained by developmental defects including double fertilization of a binucleate egg, loss of a sex chromosome or perturbation of sex-determining gene expression, which occur accidentally or are induced by certain environmental conditions. However, recent studies have revealed that such sexual aberrations can be caused by various groups of vertically-transmitted endosymbiotic microbes such as bacteria of the genera Wolbachia, Rickettsia, Arsenophonus, Spiroplasma and Cardinium, as well as microsporidian protists. In this review, we first summarize the accumulated data on endosymbiont-induced sexual aberrations, and then discuss how such endosymbionts affect the developmental system of their hosts and what kinds of ecological and evolutionary effects these endosymbionts have on their host populations. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessReview Polydnaviruses of Parasitic Wasps: Domestication of Viruses To Act as Gene Delivery Vectors
Insects 2012, 3(1), 91-119; doi:10.3390/insects3010091
Received: 22 November 2011 / Revised: 7 January 2012 / Accepted: 16 January 2012 / Published: 31 January 2012
Cited by 13 | PDF Full-text (541 KB) | HTML Full-text | XML Full-text
Abstract
Symbiosis is a common phenomenon in which associated organisms can cooperate in ways that increase their ability to survive, reproduce, or utilize hostile environments. Here, we discuss polydnavirus symbionts of parasitic wasps. These viruses are novel in two ways: (1) they have [...] Read more.
Symbiosis is a common phenomenon in which associated organisms can cooperate in ways that increase their ability to survive, reproduce, or utilize hostile environments. Here, we discuss polydnavirus symbionts of parasitic wasps. These viruses are novel in two ways: (1) they have become non-autonomous domesticated entities that cannot replicate outside of wasps; and (2) they function as a delivery vector of genes that ensure successful parasitism of host insects that wasps parasitize. In this review we discuss how these novelties may have arisen, which genes are potentially involved, and what the consequences have been for genome evolution. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)
Open AccessReview The Evolutionary Innovation of Nutritional Symbioses in Leaf-Cutter Ants
Insects 2012, 3(1), 41-61; doi:10.3390/insects3010041
Received: 3 December 2011 / Revised: 16 December 2011 / Accepted: 20 December 2011 / Published: 6 January 2012
Cited by 12 | PDF Full-text (296 KB) | HTML Full-text | XML Full-text
Abstract
Fungus-growing ants gain access to nutrients stored in plant biomass through their association with a mutualistic fungus they grow for food. This 50 million-year-old obligate mutualism likely facilitated some of these species becoming dominant Neotropical herbivores that can achieve immense colony sizes. [...] Read more.
Fungus-growing ants gain access to nutrients stored in plant biomass through their association with a mutualistic fungus they grow for food. This 50 million-year-old obligate mutualism likely facilitated some of these species becoming dominant Neotropical herbivores that can achieve immense colony sizes. Recent culture-independent investigations have shed light on the conversion of plant biomass into nutrients within ant fungus gardens, revealing that this process involves both the fungal cultivar and a symbiotic community of bacteria including Enterobacter, Klebsiella, and Pantoea species. Moreover, the genome sequences of the leaf-cutter ants Atta cephalotes and Acromyrmex echinatior have provided key insights into how this symbiosis has shaped the evolution of these ants at a genetic level. Here we summarize the findings of recent research on the microbial community dynamics within fungus-growing ant fungus gardens and discuss their implications for this ancient symbiosis. Full article
(This article belongs to the Special Issue Symbiosis: A Source of Evolutionary Innovation in Insects)

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