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PubMed1998

A different tempo of mitochondrial DNA evolution in birds and their parasitic lice.

A phylogeny for the lice (Insecta: Phthiraptera: genus Dennyus) parasitic on swiftlets (Aves: Collocalliinae) was constructed based on mitochondrial cytochrome b DNA sequences. This phylogeny is congruent with previous phenetic analyses of morphometric data for the lice. Comparison with a previously obtained phylogeny for the hosts indicates some degree of cospeciation. These cospeciation events are used to compare relative rates of evolution in the birds and their lice for the same segment of the cytochrome b gene. Cytochrome b is evolving two to three times more rapidly in lice than in birds, and louse cytochrome b is highly divergent compared to that of most other insects. Although generation time has been suggested as an explanation for the disparity in evolutionary rates between lice and their hosts, we suggest that the small effective population sizes of lice coupled with founder events occurring during transmission to new host individuals may be an important factor.

Amino Acid Sequence↗

PubMed2000

Molecular phylogenetic analysis of the Pneumoroidea (Orthoptera, Caelifera): molecular data resolve morphological character conflicts in the basal acridomorpha.

A key transition in the evolution of the insect suborder Caelifera (Orthoptera; Insecta) was from predominantly non-angiosperm-feeding basal lineages to the modern acridomorph fauna (grasshoppers and related insects). However, because of conflicts in the distribution of several complex morphological characters, the relationships of the presumed intermediates, and in particular of the superfamily Pneumoroidea, are presently unclear. We undertook a phylogenetic study of representatives of all of the transitional acridomorph families using mitochondrial and nuclear DNA sequences. No support for pneumoroid monophyly was obtained from nonparametric bootstrap analysis. Furthermore, adopting a maximum-likelihood approach, specific hypotheses of relationships within the Pneumoroidea were firmly rejected using parametric bootstrapping and Kishino-Hasegawa tests. The results indicate that the Pneumoroidea are at best a grade. This distinction implies that the evolution of the proposed pneumoroid synapomorphies, femoro-abdominal stridulation and simple male genital structure, might previously have been misinterpreted as cases of single character gains or losses within lineages. Reconstructions of character states for the femoro-abdominal stridulation indicate that, in fact, multiple losses or gains are equally likely. An important implication of our findings is that, in grasshoppers, auditory tympana may have evolved before stridulation, supporting the argument that the original function of tympana may have been related not to conspecific communication but to predator detection. Overall, the results of this study emphasize the high information content of these minor groups (in this case, the four intermediate families under consideration contain only 0.2% of extant orthopteran species diversity). Our analyses also demonstrate the advantages of model-based methods in analyzing systematic problems and, in particular, of the importance of testing specific phylogenetic hypotheses when a priori support for groupings (e.g., from nonparametric bootstrapping) is marginal.

Animals↗

PubMed2001

One-step PCR amplification of complete arthropod mitochondrial genomes.

A new PCR primer set which enables one-step amplification of complete arthropod mitochondrial genomes was designed from two conserved 16S rDNA regions for the long PCR technique. For this purpose, partial 16S rDNAs amplified with universal primers 16SA and 16SB were newly sequenced from six representative arthropods: Armadillidium vulgare and Macrobrachium nipponense (Crustacea), Anopheles sinensis (Insecta), Lithobius forficatus and Megaphyllum sp. (Myriapoda), and Limulus polyphemus (Chelicerata). The genomic locations of two new primers, HPK16Saa and HPK16Sbb, correspond to positions 13314-13345 and 12951-12984, respectively, in the Drosophila yakuba mitochondrial genome. The usefulness of the primer set was experimentally examined and confirmed with five of the representative arthropods, except for A. vulgare, which has a linearized mitochondrial genome. With this set, therefore, we could easily and rapidly amplify complete mitochondrial genomes with small amounts of arthropod DNA. Although the primers suggested here were examined only with arthropod groups, a possibility of successful application to other invertebrates is very high, since the high degree of sequence conservation is shown on the primer sites in other invertebrates. Thus, this primer set can serve various research fields, such as molecular evolution, population genetics, and molecular phylogenetics based on DNA sequences, RFLP, and gene rearrangement of mitochondrial genomes in arthropods and other invertebrates.

Animals↗

PubMed2002

Hox gene sequences from the geophilomorph centipede Pachymerium ferrugineum (C. L. Koch, 1835) (Chilopoda: Geophilomorpha: Geophilidae): implications for the evolution of the Hox class genes of arthropods.

Here we report on a partial screen for Hox gene sequences from the geophilomorph centipede Pachymerium ferrugineum, resulting in 11 different sequences. All of these sequences could be homologized to specific Drosophila genes, yielding two representatives for the Dfd class and one each for the remaining classes. Phylogenetic analysis of these data with a broad sample of arthropod/onychophoran homologous sequences confirmed these results and provided further support for the monophyly of the Hox3/zen class. Conversely, the phylogenetic status of ftz-type genes remains uncertain. Our results complement the previous partial findings for two other centipedes (the scolopendromorph Ethmostigmus rubripes and the lithobiomorph Lithobius forficatus) and confirm the expectation that in myriapods, too, all Hox genes classes are present. This suggests that even the Chilopoda, with uniform trunk segments, have the same number of Hox genes as the more tagmatized Insecta.

Amino Acid Sequence↗

PubMed2000

Why and how marine-invertebrate larvae metamorphose so fast.

It is argued that larviparous development has evolved at least eight times among extant animals. A 'need for speed hypothesis' is proposed to explain profound convergence on a pattern of small larvae and rapid metamorphosis across six marine invertebrate clades. Shared selection pressures include limits to larval size, the plankton-to-benthos transition, extreme hazards on the benthos, and the profound helplessness of metamorphosing animals. The adaptive mechanisms include: (1) development of juvenile structures in larvae before they are metamorphically competent; (2) external cues trigger metamorphosis; and (3) rapid cell-to-cell conductance of the metamorphic signal to bring about rapid loss of larval structures and release of juvenile structures. Both pattern and mechanisms contrast in every regard with those of the other two major larviparous clades, Insecta and Amphibia.

Adaptation, Physiological↗

PubMed1987

Quantification and characterization of metallothioneins in tissues of lower vertebrates and invertebrates.

Metallothionein (MT) and the related metal-binding proteins in tissues of lower vertebrates and invertebrates were isolated by gel filtration chromatography (conventional liquid and high performance liquid chromatography). The metal-binding proteins including MT were detected by determining the metals bound to the proteins by atomic absorption spectrophotometry. This analytical procedure was recommendable as the first step to characterize unknown metal-binding proteins in diverse living bodies. As MT in the lower vertebrates, avian (Japanese quail), reptilian (tortoise), amphibian (8 species of frogs and 2 species of tailed amphibians) and fish MTs were isolated and characterized. The number of isoMTs was different among animals belonging not only to different classes but also to different species in the same family. One of the isoMTs in the avian, reptilian and amphibian MTs was shown to contain one histidinyl residue. Cadmium(Cd)-binding proteins were induced in three species of insect (Insecta, Arthropoda) larvae (midge, fleshfly and silkworm) by loading of Cd. Distribution of Cd in insect tissues was different among the three species though the alimentary canal was commonly the most important tissue for the storage of Cd in all species. Further, Cd in the soluble fractions was bound to inducible proteins of different molecular sizes in the three species. Cd-binding protein was also detected in the waterflea (Crustacea, Arthropoda) after loading of Cd. Cd-binding proteins induced in the earthworm (Oligochaeta, Annelida) by loading of Cd were a mixture of proteins with three different molecular sizes. One of the Cd-binding proteins with an apparent molecular size of 7,000 was shown to have characteristics of MT.

Amphibians↗

PubMed1995

Molecular evolution of the nicotinic acetylcholine receptor: an example of multigene family in excitable cells.

An extensive phylogenetic analysis of the nicotinic-acetylcholine-receptor subunit gene family has been performed by cladistic and phenetic methods. The conserved parts of amino acid sequences have been analyzed by CLUSTAL V and PHYLIP software. The structure of the genes was also taken in consideration. The results show that a first gene duplication may have occurred before the appearance of Bilateria. Three subfamilies then appeared: I--the neuronal alpha-bungarotoxin binding-site subunits (alpha 7, alpha 8); III--the neuronal nicotinic subunits (alpha 2-alpha 6, beta 2-beta 4), which also contain the muscle acetylcholine-binding subunit (alpha 1); and IV--the muscle non-alpha subunits (beta 1, gamma, delta, epsilon). The Insecta subunits (subfamily II) could be orthologous to family III and IV. Several tissular switches of expression from neuron to muscle and the converse can be inferred from the extant expression of subunits and the reconstructed trees. The diversification of the neuronal nicotinic subfamily begins in the stem lineage of chordates, the last duplications occurring shortly before the onset of the mammalian lineage. Such evolution parallels the increase in complexity of the cholinergic systems.

Amino Acid Sequence↗

PubMed1983

Ultrastructural and immunocytochemical investigation of ecdysteroid secretion by the prothoracic gland of the waxmoth Galleria mellonella.

The formation and secretion of ecdysteroid by the prothoracic gland cells of Galleria mellonella (Insecta, Lepidoptera) were investigated electron microscopically and immunocytochemically. The moulting hormone ecdysone becomes first evident in vesicles and tubules of the smooth endoplasmic reticulum (SER). The SER forms secretory granules in which ecdysone was shown immunocytochemically. The Golgi apparatus seems not to be directly involved in ecdysone secretion. The secretory granules are released from the cells by exocytosis.

Animals↗

PubMed1995

FMRFamide-like and allatostatin-like immunoreactivity in the lateral heart nerve of Periplaneta americana: colocalization at the electron-microscopic level.

Both allatostatin immunoreactivity (AS-IR) and FMRFamide immunoreactivity (FMRFa-IR) have been demonstrated light-microscopically in the lateral heart nerve of Periplaneta americana. The identical labeling of some fibers suggests the coexistence of the two antigens. Electron-microscopically, six granule types in the peripheral part of the lateral heart nerve can be distinguished according to their size and density (types 1-6). These granule types can be subdivided immunocytochemically by means of a new mirror-section technique. Granules of types 4 and 5 always exclusively show FMRFa-IR. In the populations of fibers containing granules of types 1 and 6, axon profiles can be found that contain granules colocalizing FMRFa-IR and AS-IR. Other axon profiles of these populations only contain immunonegative granules of the same ultrastructure. Granules of type 2 can be differentiated immunocytochemically in three forms in the same section: In some fibers, they are nonreactive; in other fibers of the same section, they show FMRFa - IR, whereas in a third fiber type, granules show AS - IR. Finally, granules of type 3 can be observed with FMRFa-IR. In other fibers, they occur with the same ultrastructure but exhibit no immunoreactivity. Two soma types occur in the lateral heart nerve. Soma type I is characterized by the production of electron-dense granules that show FMRFa-IR. Type II is in close contact with various fibers, forming different types of axosomatic synapses, hitherto unknown in Insecta.

Amino Acid Sequence↗

PubMed1985

The fine structure of euchromatin and centromeric heterochromatin in Tenebrio molitor chromosomes.

The fine structure of constitutive heterochromatin and euchromatin was compared in electron microscope whole-mount preparations of Tenebrio molitor (Insecta, Coleoptera) spermatocyte nuclei. Tenebrio molitor pachytene chromosomes display extended segments of centromeric heterochromatin and thus are especially suitable for this purpose. When nuclei were incubated in solutions containing different concentrations of NaCl or of MgCl2, two levels of chromatin fine structures were observed in the euchromatic segments: nucleosome fibers (0.1 mM-20 mM NaCl) and supranucleosomal fibers with 28 nm in diameter (40 mM-100 mM NaCl, 0.2 mM-1.0 mM MgCl2). The fine structure in the heterochromatic segments was the same as that in the euchromatic segments in all NaCl concentrations and in MgCl2 concentrations up to 0.4 mM. In higher MgCl2 concentrations the heterochromatin remained more compact than the euchromatin and consisted of 37-nm-thick fibers in 0.6 mM MgCl2 and of 65-nm-thick fibers in 1.0 mM MgCl2. After the 37-nm and the 65-nm fibers had been dispersed in Mg2+-free solutions they could be recondensed by incubation in 0.6 mM and 1.0 mM MgCl2, respectively. It is concluded that a Mg2+-sensitive component of the heterochromatin is responsible for the folding of the nucleosome chain to heterochromatin-specific supranucleosomal structures.

Animals↗

PubMed1994

Biochemical genetic studies on wild populations of three species of green leafhoppers, Nephotettix, from Peninsular Malaysia.

Nine populations of three species of Nephotettix (Insecta: Hemiptera) from Peninsular Malaysia were analysed for nine enzymes comprising 11 loci. Nei's (Genetics 89, 583, 1978) genetic distance, D, between N. virescens and N. malayanus was 0.181, that between N. virescens and N. nigropictus was 0.283, and that between N. malayanus and N. nigropictus was 0.203. The genetic distance between N. nigropictus from rice plant and from the weed-grass L. hexandra at Universiti Pertanian Malaysia was 0.004 and their genetic identity was 0.996, thus indicating that this insect species fees on both host plants. The proportion of polymorphic loci and the observed heterozygosities were higher in N. nigropictus, with a wider range of host plants, than in N. virescens and N. malayanus, restricted to rice and L. hexandra, respectively.

Alleles↗

PubMed1994

Genetic, molecular and developmental analysis of the glutamine synthetase isozymes of Drosophila melanogaster.

The glutamine synthetase isozymes of Drosophila melanogaster offer an attractive model for the study of the molecular genetics and evolution of a small gene family encoding enzymatic isoforms that evolved to assume a variety of specific and sometimes essential biological functions. In Drosophila melanogaster two GS isozymes have been described which exhibit different cellular localisation and are coded by a two-member gene family. The mitochondrial GS structural gene resides at the 21B region of the second chromosome, the structural gene for the cytosolic isoform at the 10B region of the X chromosome. cDNA clones corresponding to the two genes have been isolated and sequenced. Evolutionary analysis data are in accord with the hypothesis that the two Drosophila glutamine synthetase genes are derived from a duplication event that occurred near the time of divergence between Insecta and Vertebrata. Both isoforms catalyse all reactions catalysed by other glutamine synthetases, but the different kinetic parameters and the different cellular compartmentalisation suggest strong functional specialisation. In fact, mutations of the mitochondrial GS gene produce embryo-lethal female sterility, defining a function of the gene product essential for the early stages of embryonic development. Preliminary results show strikingly distinct spatial and temporal patterns of expression of the two isoforms at later stages of development.

Animals↗

PubMed1988

An evolutionary tree for invertebrate globin sequences.

A phylogenetic tree was constructed from 245 globin amino acid sequences. Of the six plant globins, five represented the Leguminosae and one the Ulmaceae. Among the invertebrate sequences, 7 represented the phylum Annelida, 13 represented Insecta and Crustacea of the phylum Arthropoda, and 6 represented the phylum Mollusca. Of the vertebrate globins, 4 represented the Agnatha and 209 represented the Gnathostomata. A common alignment was achieved for the 245 sequences using the parsimony principle, and a matrix of minimum mutational distances was constructed. The most parsimonious phylogenetic tree, i.e., the one having the lowest number of nucleotide substitutions that cause amino acid replacements, was obtained employing clustering and branch-swapping algorithms. Based on the available fossil record, the earliest split in the ancestral metazoan lineage was placed at 680 million years before present (Myr BP), the origin of vertebrates was placed at 510 Myr BP, and the separation of the Chondrichthyes and the Osteichthyes was placed at 425 Myr BP. Local "molecular clock" calculations were used to date the branch points on the descending branches of the various lineages within the plant and invertebrate portions of the tree. The tree divided the 245 sequences into five distinct clades that corresponded exactly to the five groups plants, annelids, arthropods, molluscs, and vertebrates. Furthermore, the maximum parsimony tree, in contrast to the unweighted pair group and distance Wagner trees, was consistent with the available fossil record and supported the hypotheses that the primitive hemoglobin of metazoans was monomeric and that the multisubunit extracellular hemoglobins found among the Annelida and the Arthropoda represent independently derived states.

Amino Acid Sequence↗

PubMed1998

Similarity of structural features and evolution of satellite DNAs from palorus subdepressus (Coleoptera) and related species

A novel highly abundant satellite DNA comprising 20% of the genome has been characterized in Palorus subdepressus (Insecta, Coleoptera). The 72-bp-long monomer sequence is composed of two copies of T2A5T octanucleotide alternating with 22-nucleotide-long elements of an inverted repeat. Phylogenetic analysis revealed clustering of monomer sequence variants into two clades. Two types of variants are prevalently organized in an alternating pattern, thus showing a tendency to generate a new complex repeating unit 144 bp in length. Fluorescent in situ hybridization revealed even distribution of the satellite in the region of pericentric heterochromatin of all 20 chromosomes. P. subdepressus satellite sequence is clearly species specific, lacking similarity even with the satellite from congeneric species P. ratzeburgii. However, on the basis of similarity in predicted tertiary structure induced by intrinsic DNA curvature and in repeat length, P. subdepressus satellite can be classified into the same group with satellites from related tenebrionid species P. ratzeburgii, Tenebrio molitor, and T. obscurus. It can be reasonably inferred that repetitive sequences of different origin evolve under constraints to adopt and conserve particular features. Obtained results suggest that the higher-order structure and repeat length, but not the nucleotide sequence itself, are maintained through evolution of these species.

Journal Article↗

PubMed2005

Long inversely oriented subunits form a complex monomer of Tribolium brevicornis satellite DNA.

Highly abundant satellite DNA named TBREV is detected and characterized in the beetle Tribolium brevicornis (Insecta: Coleoptera). An outstanding peculiarity of the TBREV satellite monomer is its complex structure based on the two approximately 470-bp-long subunits, inversely oriented within a 1061-bp-long monomer sequence. The proposed evolutionary history demonstrates a clear trend toward increased complexity and length of the TBREV satellite monomer. This tendency has been observed on three levels: first as direct and inverted duplications of short sequence motifs, then by inverse duplication of the approximately 470-bp sequence segment, and, finally, by spread of inversely duplicated elements in a higher-order register and formation of extant monomers. Inversely oriented subunits share a similarity of 82% and have a high capacity to form a thermodynamically stable dyad structure that is, to our knowledge, the longest ever described in any satellite monomer. Analysis of divergences between inversely oriented subunits shows a tendency to a further reduction in similarity between them. Except in its centromeric localization, the TBREV satellite does not show similarity to other known Tribolium satellites, either in nucleotide sequence or in monomer length and complexity. However, TBREV shares common features of other Tribolium satellites that might be under functional constraints: nonconstant rate of evolution along the monomer sequence, short inverted repeats in the vicinity of an A+T tract, nonrandom distribution of A or T >/=3 tracts, and CENP-B box-like motifs. Although long inverted subunits might reinforce structural characteristics of the satellite monomer, their nucleotide sequence does not seem to be under constraints in order to preserve the dyad structure.

Animals↗

PubMed2005

Preservation and high sequence conservation of satellite DNAs suggest functional constraints.

Due to a high evolutionary turnover many satellite DNAs are restricted to a group of closely related species. Here we demonstrate that the satellite DNA family PSUB, abundant in the beetle Palorus subdepressus, is distributed in a low number of copies among diverse taxa of Coleoptera (Insecta), some of them separated for an evolutionary period of up to 60 Myr. Comparison of PSUB cloned from the species Tribolium brevicornis with the PSUB family previously characterized in Palorus subdepressus revealed high sequence conservation and absence of fixed species-specific mutations. The most polymorphic sites are those with ancestral mutations shared among clones of both species. Since the ancestral mutations contribute significantly to overall diversity, it could be proposed that a similar mutational profile already existed in an ancestral species. The pattern of variability along the satellite monomer is characterized by the presence of conserved and variable regions. The nonrandom pattern of variability as well as the absence of sequence divergence is also discerned for PRAT satellite DNA, cloned previously from two Palorus species and a distantly related Pimelia elevata. Since PRAT and PSUB are present in parallel in diverse taxa of Coleoptera, we propose that their long evolutionary preservation suggests a possible functional significance. This indication is additionally supported not only by the high evolutionary conservation of the sequences, but also by the presence of significantly conserved and variable regions along the monomers.

Animals↗

PubMed2004

Nitrification in freshwater sediments as influenced by insect larvae: quantification by microsensors and fluorescence in situ hybridization.

Sediment-reworking macrofauna can stimulate nitrification by increasing the O(2) penetration into sediments or it can reduce nitrification by grazing on nitrifying bacteria. We investigated the influence of Chironomus riparius larvae (Insecta: Diptera) on the in situ activity, abundance, and distribution of NH4+-oxidizing (AOB) and NO2--oxidizing bacteria (NOB) in two freshwater sediments with microsensors and fluorescence in situ hybridization. In organic-poor sediment, nitrification activity was reduced by the presence of C. riparius larvae, whereas no such effect was detected in organic-rich sediment. We explain this difference with the variable larval burrowing and grazing behavior in the two sediment types: In organic-poor sediment larval activities were intense and evenly distributed across the whole sediment surface, whereas in organic-rich sediment larval activities were locally restricted to the microenvironment of animal burrows. Surprisingly, the animals did not cause any significant change of the abundance of AOB and NOB. This implies that the observed reduction of nitrification activity was not density-regulated, but rather was due to the lowered metabolic activity of the nitrifiers. Partial digestion and redeposition of particle-associated bacteria by C. riparius larvae are believed to have caused this loss of metabolic activity.

Animals↗

PubMed1998

Plasmid-mediated gene transfer between insect-resident bacteria, Enterobacter cloacae, and plant-epiphytic bacteria, Erwinia herbicola, in guts of silkworm larvae.

Five strains of Enterobacter cloacae isolated from several species of plants and insects were able to grow in the guts of silkworm larvae. A much larger population of Ent. cloacae strains was detected in the insect guts and feces collected 3 and 6 days than in samples collected 1 day after feeding artificial diets contaminating these bacteria. Furthermore, insect-origin strains of Ent. cloacae were mated with a donor strain, epiphytic Erwinia herbicola, harboring RSF1010 and pBPW1::Tn7 plasmids in the insect guts by introducing these bacteria through separate artificial diets administered at different times. A number of transconjugants, Ent. cloacae strains which had acquired RSF1010 plasmid, were detected from guts and fecal samples at transfer frequencies of 10(-2) to 10(-3) per recipient. Thus, gene transfer between epiphytic Er. herbicola and insect-resident Ent. cloacae strains in the insect guts was confirmed. These findings may provide significant information about the role of "in insecta mating" in the evolution of these bacteria.

Animals↗