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  • 1
    Electronic Resource
    Electronic Resource
    Faster evolutionary rates in endosymbiotic bacteria than in cospeciating insect hosts (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 727-731 
    Details
    ISSN: 1432-1432
    Keywords: Aphid ; Bacteria ; Buchnera ; Cospeciation ; Endosymbiosis ; Evolutionary rates ; Molecular clock ; Prokaryote ; Ribosomal DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hypothesis of a universal molecular clock holds that divergent lineages exhibit approximately constant rates of nucleotide substitution over evolutionary time for a particular macromolecule. We compare divergences of ribosomal DNA for aphids (Insecta) and Buchnera, the maternally transmitted, endosymbiotic bacteria that have cospeciated with aphids since initially infecting them over 100 million years ago. Substitution rates average 36 times greater for Buchnera than for their aphid hosts for regions of small-subunit rDNA that are homologous for prokaryotes and eukaryotes. Aphids exhibit 18S rDNA substitution rates that are within the range observed in related insects. In contrast, 16S rDNA evolves about twice as fast in Buchnera as in related free-living bacterial lineages. Nonetheless, the difference between Buchnera and aphids is much greater, suggesting that rates may be generally higher in bacteria. This finding adds to evidence that molecular clocks are only locally rather than universally valid among taxonomic groups. It is consistent with the hypothesis that rates of sequence evolution depend on generation time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00173152
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  • 2
    Electronic Resource
    Electronic Resource
    The Tryptophan Biosynthetic Pathway of Aphid Endosymbionts (Buchnera): Genetics and Evolution of Plasmid-Associated Anthranilate Synthase (trpEG) Within the Aphididae (1996)
    Springer
    Journal of molecular evolution 42 (1996), S. 414-421 
    Details
    ISSN: 1432-1432
    Keywords: Key words: Aphid —Buchnera aphidicola— Cospeciation — Endosymbiosis — Mutualism — Tryptophan biosynthesis —trpEG—trpB— Gene amplification — Plasmid evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The bacterial endosymbionts (Buchnera) from the aphids Rhopalosiphum padi, R. maidis, Schizaphis graminum, and Acyrthosiphon pisum contain the genes for anthranilate synthase (trpEG) on plasmids made up of one or more 3.6-kb units. Anthranilate synthase is the first as well as the rate-limiting enzyme in the tryptophan biosynthetic pathway. The amplification of trpEG on plasmids may result in an increase of enzyme protein and overproduction of this essential amino acid, which is required by the aphid host. The nucleotide sequence of trpEG from endosymbionts of different species of aphids is highly conserved, as is an approximately 500-bp upstream DNA segment which has the characteristics of an origin of replication. Phylogenetic analyses were performed using trpE and trpG from the endosymbionts of these four aphids as well as from the endosymbiont of Schlechtendalia chinensis, in which trpEG occurs on the chromosome. The resulting phylogeny was congruent with trees derived from sequences of two chromosome-located bacterial genes (part of trpB and 16S ribosomal DNA). In turn, trees obtained from plasmid-borne and bacterial chromosome-borne sequences were congruent with the tree resulting from phylogenetic analysis of three aphid mitochondrial regions (portions of the small and large ribosomal DNA subunits, as well as cytochrome oxidase II). Congruence of trees based on genes from host mitochondria and from bacteria adds to previous support for exclusively vertical transmission of the endosymbionts within aphid lineages. Congruence with trees based on plasmid-borne genes supports the origin of the plasmid-borne trpEG from the chromosomal genes of the same lineage and the absence of subsequent plasmid exchange among endosymbionts of different species of aphids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00006069
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular phylogeny of the homoptera: a paraphyletic taxon (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 211-223 
    Details
    ISSN: 1432-1432
    Keywords: Homoptera ; Heteroptera ; Hemiptera ; Paraphyletic taxon ; Phylogeny, 18S rDNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Homoptera and Heteroptera comprise a large insect assemblage, the Hemiptera. Many of the plant sap-sucking Homoptera possess unusual and complex life histories and depend on maternally inherited, intracellular bacteria to supplement their nutritionally deficient diets. Presumably in connection with their diet and lifestyles, the morphology of many Homoptera has become greatly reduced, leading to major controversies regarding the phylogenetic affiliations of homopteran superfamilies. The most fundamental question concerns whether the Homoptera as a whole are monophyletic. Recent studies based on morphology have argued that the Homoptera Sternorrhyncha (Aphidoidea, Coccoidea, Psylloidea, Aleyrodoidea) is a sister group to a group comprising the Homoptera Auchenorrhyncha (Fulgoroidea, Cicadoidea, Cercopoidea, Cicadelloidea) and the Heteroptera, making the Homoptera paraphyletic. We sequenced the 5′ 580-680 base pairs of small-subunit (18S) ribosomal DNA from a selection of Homoptera, Hemiptera, and their putative outgroups, the Thysanoptera and Psocoptera, to apply molecular characters to the problem of Homoptera phylogeny. Parsimony, distance, maximum-likelihood, and bootstrap methods were used to construct trees from sequence data and assess support for the topologies produced. Molecular data corroborate current views of relationships within the Sternorrhyncha and Auchenorrhyncha based on morphology and strongly support the hypothesis of homopteran paraphyly as stated above. In addition, it was found that Homoptera Sternorrhyncha have extra, GC-rich sequence concentrated in a variable region of the 18S rDNA, which indicates that some unique evolutionary processes are occurring in this lineage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170675
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  • 4
    Electronic Resource
    Electronic Resource
    Genetic Characterization of Plasmids Containing Genes Encoding Enzymes of Leucine Biosynthesis in Endosymbionts (Buchnera) of Aphids (1999)
    Springer
    Journal of molecular evolution 48 (1999), S. 77-85 
    Details
    ISSN: 1432-1432
    Keywords: Key words:Buchnera— Endosymbionts —Schizaphis graminum—Diuraphis noxia— Leucine biosynthesis — Plasmid amplification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The prokaryotic endosymbionts (Buchnera) of aphids are known to provision their hosts with amino acids that are limiting in the aphid diet. Buchnera from the aphids Schizaphis graminum and Diuraphis noxia have plasmids containing leuABCD, genes that encode enzymes of the leucine biosynthetic pathway, as well as genes encoding proteins probably involved in plasmid replication (repA1 and repA2) and an open reading frame (ORF1) of unknown function. The newly reported plasmids closely resemble a plasmid previously described in Buchnera of the aphid Rhopalosiphum padi [Bracho AM, Martínez-Torres D, Moya A, Latorre A (1995) J Mol Evol 41:67–73]. Nucleotide sequence comparisons indicate conserved regions which may correspond to an origin of replication and two promoters, as well as inverted repeats, one of which resembles a rho-independent terminator. Phylogenetic analyses based on amino acid sequences of leu gene products and ORF1 resulted in trees identical to those obtained from endosymbiont chromosomal genes and the plasmid-borne trpEG. These results are consistent with a single evolutionary origin of the leuABCD-containing plasmid in a common ancestor of Aphididae and the lack of plasmid exchange between endosymbionts of different aphid species. Trees for ORF1 and repA (based on both nucleotides and amino acids) are used to examine the basis for leu plasmid differences between Buchnera of Thelaxes suberi and Aphididae. The most plausible explanation is that a single transfer of the leu genes to an ancestral replicon was followed by rearrangements. The related replicon in Buchnera of Pemphigidae, which lacks leuABCD, appears to represent the ancestral condition, implying that the plasmid location of the leu genes arose after the Pemphigidae diverged from other aphid families. This conclusion parallels previously published observations for the unrelated trpEG plasmid, which is present in Aphididae and absent in Pemphigidae. Recruitment of amino acid biosynthetic genes to plasmids has been ongoing in Buchnera lineages after the infection of aphid hosts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00006447
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  • 5
    Electronic Resource
    Electronic Resource
    Consequences of reductive evolution for gene expression in an obligate endosymbiont (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 48 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The smallest cellular genomes are found in obligate symbiotic and pathogenic bacteria living within eukaryotic hosts. In comparison with large genomes of free-living relatives, these reduced genomes are rearranged and have lost most regulatory elements. To test whether reduced bacterial genomes incur reduced regulatory capacities, we used full-genome microarrays to evaluate transcriptional response to environmental stress in Buchnera aphidicola, the obligate endosymbiont of aphids. The 580 genes of the B. aphidicola genome represent a subset of the 4500 genes known from the related organism, Escherichia coli. Although over 20 orthologues of E. coli heat stress (HS) genes are retained by B. aphidicola, only five were differentially expressed after near-lethal heat stress treatments, and only modest shifts were observed. Analyses of upstream regulatory regions revealed loss or degradation of most HS (σ32) promoters. Genomic rearrangements downstream of an intact HS promoter yielded upregulation of a functionally unrelated and an inactivated gene. Reanalyses of comparable experimental array data for E. coli and Bacillus subtilis revealed that genome-wide differential expression was significantly lower in B. aphidicola. Our demonstration of a diminished stress response validates reports of temperature sensitivity in B. aphidicola and suggests that this reduced bacterial genome exhibits transcriptional inflexibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03522.x
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  • 6
    Electronic Resource
    Electronic Resource
    W.D. Hamilton, 1936–2000 (2000)
    [s.l.] : Nature America Inc.
    Nature medicine 6 (2000), S. 367-367 
    Details
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] William Donald Hamilton was one of the leading evolutionary biologists of our time. His theory of inclusive fitness (‘kin selection’) transformed the study of social behavior by demonstrating how altruistic and selfish tendencies are expected to be modulated by genetic relatedness. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/74607
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  • 7
    Electronic Resource
    Electronic Resource
    Snapping social swimmers (1996)
    [s.l.] : Nature Publishing Group
    Nature 381 (1996), S. 473-474 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE ants of Death Valley (elevation -86 m) remain the lowest expression of eusociality on Earth, but on page 512 of this issue1 J. E. Duffy describes eusocial colony organization in a snapping shrimp, Synalpheus regalis, which takes "the apex of animal social organization" to depths of a novel ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/381473a0
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  • 8
    Electronic Resource
    Electronic Resource
    How nutritionally imbalanced is phloem sap for aphids? (1999)
    Springer
    Entomologia experimentalis et applicata 91 (1999), S. 203-210 
    Details
    ISSN: 1570-7458
    Keywords: phloem sap ; proteins ; amino acids ; aphids ; symbionts ; Buchnera ; nutrition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aphids harbour intracellular symbionts (Buchnera) that provide their host with amino acids present in low amounts in their diet, phloem sap. To find out the extent to which aphids depend on their symbionts for synthesis of individual essential amino acids, we have evaluated how well phloem sap amino acid composition matches the aphids' needs. Amino acid compositions of the ingested phloem sap were compared to amino acids in aphid body proteins and also to available information about optimal diet composition for other plant feeding insects. Phloem sap data from severed stylets of two aphid species, Rhopalosiphum padi (L.) (Homoptera: Aphididae) feeding on wheat, and Uroleucon sonchi (L.) (Homoptera: Aphididae) feeding on Sonchus oleraceus (L.), together with published information on phloem sap compositions from other plant species were used. Phloem sap has in general only around 20% essential amino acids, with a range from 15–48%. Aphid body proteins and optimal diets for two other plant feeding insects have around 50%. The phloem sap of early flowering S. oleraceus ingested by U. sonchi contained 48%, which seems to be exceptional. Aphids feeding on different plants appear to be very differently dependent on their symbionts for their overall essential amino acid synthesis, due to the large variation in proportion of essential amino acids in phloem sap from different plants. The profile of the essential amino acids in phloem sap from different plant species corresponds rather well to profiles of both aphid body proteins and optimal diets determined for plant feeding insects. However, methionine and leucine in phloem sap are in general low in these comparisons, suggesting a higher dependence on the symbiont for synthesis of these amino acids. Concentrations of several essential amino acids in phloem from different plant species seem to vary together, suggesting that levels of symbiont provisioning of different amino acids are adjusted in parallel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003605508487
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  • 9
    Electronic Resource
    Electronic Resource
    Feeding damage by Diuraphis noxia results in a nutritionally enhanced phloem diet (1999)
    Springer
    Entomologia experimentalis et applicata 91 (1999), S. 403-412 
    Details
    ISSN: 1570-7458
    Keywords: aphid ; Diuraphis noxia ; Triticum aestivum ; endosymbiont ; insect-plant interactions ; phloem ; amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The feeding behavior of Diuraphis noxia Mordvilko (Homoptera: Aphididae) on susceptible hosts causes both ultrastructural and tissue level damage which may affect phloem composition. Genetic evidence suggests that endosymbiotic bacteria in most aphids overproduce limiting amino acids to benefit hosts but that D. noxia depends less on endosymbionts for these nutrients, possibly due to an enriched diet. To determine whether D. noxia feeding damage results in higher concentrations of essential amino acids, stylet exudates were analyzed from wheat (Triticum aestivum) damaged to different degrees. Comparison of samples from undamaged and damaged susceptible wheat revealed changes in amino acid composition and an increase in levels of essential amino acids, indicating a nutritionally enhanced ingesta. The changes in stylet exudates paralleled changes in leaf exudates, indicating that the effects are systemic. Feeding damage is not observed on a resistant wheat host, var. Halt, and leaf exudates from infested Halt did not show changes in amino acid composition. Mean relative growth of nymphs was significantly lower on Halt than on susceptible Arapahoe, indicating that Halt is a less suitable host. Both varieties show similar amino acid levels in non-infested samples, suggesting that D. noxia infestation does not enhance the phloem environment in Halt. This study provides evidence that aphid feeding can generate a nutritionally enhanced phloem diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003617523820
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  • 10
    Electronic Resource
    Electronic Resource
    Non-cultivable microorganisms from symbiotic associations of insects and other hosts (1997)
    Springer
    Antonie van Leeuwenhoek 72 (1997), S. 39-48 
    Details
    ISSN: 1572-9699
    Keywords: Buchnera ; cospeciation ; endosymbionts ; rRNA phylogeny ; symbiosis ; tryptophan biosynthesis ; leucine biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many symbiotic associations involve microorganisms which cannot be cultivated on laboratory media. These organisms remained little known until the recent advent of methods of recombinant DNA analysis and molecular phylogenetics. Applications of these methods to endosymbionts have resulted in substantial new insights concerning the genetics and evolution of these organisms. This communication provides a listing of recently studied associations involving non-cultivable symbionts. The associations involve a diverse set of host taxa and a wide range of effects, both favorable and deleterious, on host biology. Among beneficial endosymbionts, a variety of nutritional interactions have been documented. One type of association has been demonstrated for a number of animal hosts, namely endosymbioses that result from a single infection of an ancestral host by a prokaryote. In these associations, endosymbionts are transmitted maternally and are not exchanged between host lineages, resulting in a long-term pattern of codiversification of hosts and endosymbionts. The association between aphids and non-cultivable prokaryotic endosymbionts is a well studied example of such a symbiosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000239108771
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