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PubMed2002

Genetic engineering in insects of agricultural importance.

The past five years have witnessed the extension of genetic transformation techniques into 11 insect species covering four orders within the Insecta. While the robustness of these transformation systems can be improved, there is now a highly likely probability that transformation of a given insect species will ensue, provided transposable element-containing plasmid DNA can be effectively delivered to the embryo or some other life stage. These developments have shifted emphasis to concerns of transgene stability and the regulation of the rearing and release of these transgenic insects. They have also led to some elegant demonstrations of genetic sexing mechanisms in Drosophila melanogaster with the expectation that similar systems be extended into pest insect species. These developments and issues are discussed in this short review.

Animals↗

PubMed2003

Comparison of fatty acid composition in major lipid classes of the dominant benthic invertebrates of the Yenisei river.

The composition and content of fatty acids (FAs) in total lipids, triacylglycerols (TAG) and polar lipids (PL) in dominant groups of benthic invertebrates: gammarids (Gammaridae, Amphipoda), chironomid larvae (Chironomidae, Diptera), caddisfly larvae (Trichoptera) and mayfly larvae (Ephemeroptera) were studied in the Yenisei river. For the first time data on the FA composition of species belonging to Trichoptera (Insecta) are presented. The groups of aquatic insect larvae and gammarids weakly differed in total content of essential polyunsaturated fatty acids (PUFAs). Hence, the strong invasion of gammarids which occurred in the last decades in the Yenisei river should not result in a decrease in potential yield of essential PUFA in the ecosystem and corresponding decrease in food resource quality for fish in respect to PUFA content. Significant differences in biomarker FAs in TAG were found which correlated to specific food sources. Different levels of long-chain PUFA in PL of the invertebrates are discussed in relation to the genetic ability of particular taxa to form these FAs.

Analysis of Variance↗

PubMed2002

Species diversity enhances ecosystem functioning through interspecific facilitation.

Facilitation between species is thought to be a key mechanism by which biodiversity affects the rates of resource use that govern the efficiency and productivity of ecosystems; however, there is no direct empirical evidence to support this hypothesis. Here we show that increasing the species diversity of a functional group of aquatic organisms induces facilitative interactions, leading to non-additive changes in resource consumption. We increased the richness and evenness of suspension-feeding caddisfly larvae (Insecta, Trichoptera) in stream mesocosms and found that the increased topographical complexity of the benthic habitat alters patterns of near-bed flow such that the feeding success of individuals is enhanced. Species diversity reduces 'current shading' (that is, the deceleration of flow from upstream to downstream neighbours), allowing diverse assemblages to capture a greater fraction of suspended resources than is caught by any species monoculture. The fundamental nature of this form of hydrodynamic facilitation suggests that it is broadly applicable to freshwater and marine habitats; in addition, it has several analogues in terrestrial ecosystems where fluxes of energy and matter can be influenced by biophysical complexity. Thus, changes in species diversity may alter the probability of positive species interactions, resulting in disproportionately large changes in the functioning of ecosystems.

Animals↗

PubMed2006

Evolution of insect P450.

The first fully sequenced insect genomes were those of the fruitfly and the mosquito, both from the order Diptera. Now, with an increasing number and diversity of insect genomes becoming available, the diversity of insect P450 genes can be better appreciated and tentative ideas about the evolution of the CYP (cytochrome P450) superfamily in insects can be proposed. There are four large clades of insect P450 genes that existed before the divergence of the class Insecta and that are also represented by CYP families in vertebrates: the CYP2 clade, the CYP3 clade, the CYP4 clade and the mitochondrial P450 clade. P450s with known or suspected physiological functions are present in each of these clades and only a dozen genes appear to have orthologues or very close paralogues in each insect genome. P450 enzymes from each of these clades have been linked to insecticide resistance or to the metabolism of natural products and xenobiotics. In particular, insects appear to maintain a repertoire of mitochondrial P450 paralogues devoted to the response to environmental challenges.

Amino Acid Sequence↗

PubMed2001

Genetic differentiation of Baetis alpinus Pictet (Ephemeroptera: Baetidae) in fragmented alpine streams.

The interpretation of low FST values as evidence of high levels of gene flow among habitat fragments may be confounded by population genetic structures that are indicative of historical rather than present-day levels of gene flow. We examined the genetic structure of 23 populations of Baetis alpinus (Insecta: Ephemeroptera) living in alpine streams fragmented by lakes ( approximately 10 000 years old), reservoirs ( approximately 100 years old), and in nonfragmented streams, to examine if lakes act as barriers to gene flow and to investigate the temporal resolution of allozyme markers. Estimates of gene flow indicated little or no genetic divergence along four nonfragmented reference streams and across two lakes and two reservoirs (FST=0.004-0.041), but marked differentiation across four lakes (FST=0.092-0.362) and across one reservoir that was a lake enlarged by a dam (FST=0.075). Differentiation was unrelated to distance between fragments, but occurred only in lakes found in valleys that have been ice-free throughout the Holocene. We suggest that standing water bodies act as barriers to gene flow in B. alpinus and that low FST values observed between fragments separated by reservoirs do not indicate high levels of gene flow but rather show that genetic differentiation was not detectable within the first 100-1000 years of habitat fragmentation.

Animals↗

PubMed2000

Spermatozoa of the 'primitive type' in Scutigerella (Myriapoda, Symphyla).

The myriapod class Symphyla is of interest in that insects generally are assumed to be derived from symphylan-like ancestors. Male Symphyla form spermatophores that are picked up by the female. Both euspematozoa and paraspermatozoa are formed. In spite of the mode of fertilization their euspermatozoa were found to be of a kind that is typical of aquatic animals, so called 'primitive spermatozoa;' these are characterized by a short sperm head with a bilayered acrosome, a midpiece containing a few unmodified mitochondria, and a 9 + 2 flagellum. Scutigerella are unique among terrestrial arthropods in having 'primitive spermatozoa'; and together with horseshoe crabs they are only the second case in Arthropoda. Two further sperm plesiomorphies not found in other myriapods or insects are (1) the presence of a cytoplasmic canal housing the proximal flagellum and (2) the existence of microtubular triplets in centrioles, one of which acts as a basal body. Symphyla and Diplopoda both have a striated structure in the center of the subacrosomal material. The paraspermatozoa lack acrosome and nucleus but have a prominent crystal, a single mitochondrion, and two membrane systems. The structure of Scutigerella euspermatozoa is consistent with Symphyla being close to the stem group of Myriapoda plus Insecta.

Animals↗

PubMed1991

Retrotransposable elements R1 and R2 interrupt the rRNA genes of most insects.

A large number of insect species have been screened for the presence of the retrotransposable elements R1 and R2. These elements integrate independently at specific sites in the 28S rRNA genes. Genomic blots indicated that 43 of 47 insect species from nine orders contained insertions, ranging in frequency from a few percent to greater than 50% of the 28S genes. Sequence analysis of these insertions from 8 species revealed 22 elements, 21 of which corresponded to R1 or R2 elements. Surprisingly, many species appeared to contain highly divergent copies of R1 and R2 elements. For example, a parasitic wasp contained at least four families of R1 elements; the Japanese beetle contained at least five families of R2 elements. The presence of these retrotransposable elements throughout Insecta and the observation that single species can harbor divergent families within its rRNA-encoding DNA loci present interesting questions concerning the age of these elements and the possibility of cross-species transfer.

Amino Acid Sequence↗

PubMed2000

It's a bug's life.

Although the mechanisms of anterior-posterior axis formation are well understood in Drosophila, both embryological and molecular studies suggest significant variation in the mechanisms generating this axis within the Insecta class as a whole.

Animals↗

PubMed2004

Aligned 18S and insect phylogeny.

The nuclear small subunit rRNA (18S) has played a dominant role in the estimation of relationships among insect orders from molecular data. In previous studies, 18S sequences have been aligned by unadjusted automated approaches (computer alignments that are not manually readjusted), most recently with direct optimization (simultaneous alignment and tree building using a program called "POY"). Parsimony has been the principal optimality criterion. Given the problems associated with the alignment of rRNA, and the recent availability of the doublet model for the analysis of covarying sites using Bayesian MCMC analysis, a different approach is called for in the analysis of these data. In this paper, nucleotide sequence data from the 18S small subunit rRNA gene of insects are aligned manually with reference to secondary structure, and analyzed under Bayesian phylogenetic methods with both GTR+I+G and doublet models in MrBayes. A credible phylogeny of Insecta is recovered that is independent of the morphological data and (unlike many other analyses of 18S in insects) not contradictory to traditional ideas of insect ordinal relationships based on morphology. Hexapoda, including Collembola, are monophyletic. Paraneoptera are the sister taxon to a monophyletic Holometabola but weakly supported. Ephemeroptera are supported as the sister taxon of Neoptera, and this result is interpreted with respect to the evolution of direct sperm transfer and the evolution of flight. Many other relationships are well-supported but several taxa remain problematic, e.g., there is virtually no support for relationships among orthopteroid orders. A website is made available that provides aligned 18S data in formats that include structural symbols and Nexus formats.

Animals↗

PubMed2003

Rates of gene rearrangement and nucleotide substitution are correlated in the mitochondrial genomes of insects.

A number of studies indicated that lineages of animals with high rates of mitochondrial (mt) gene rearrangement might have high rates of mt nucleotide substitution. We chose the hemipteroid assemblage and the Insecta to test the idea that rates of mt gene rearrangement and mt nucleotide substitution are correlated. For this purpose, we sequenced the mt genome of a lepidopsocid from the Psocoptera, the only order of hemipteroid insects for which an entire mtDNA sequence is not available. The mt genome of this lepidopsocid is circular, 16,924 bp long, and contains 37 genes and a putative control region; seven tRNA genes and a protein-coding gene in this genome have changed positions relative to the ancestral arrangement of mt genes of insects. We then compared the relative rates of nucleotide substitution among species from each of the four orders of hemipteroid insects and among the 20 insects whose mt genomes have been sequenced entirely. All comparisons among the hemipteroid insects showed that species with higher rates of gene rearrangement also had significantly higher rates of nucleotide substitution statistically than did species with lower rates of gene rearrangement. In comparisons among the 20 insects, where the mt genomes of the two species differed by more than five breakpoints, the more rearranged species always had a significantly higher rate of nucleotide substitution than the less rearranged species. However, in comparisons where the mt genomes of two species differed by five or less breakpoints, the more rearranged species did not always have a significantly higher rate of nucleotide substitution than the less rearranged species. We tested the statistical significance of the correlation between the rates of mt gene rearrangement and mt nucleotide substitution with nine pairs of insects that were phylogenetically independent from one another. We found that the correlation was positive and statistically significant (R2 = 0.73, P = 0.01; Rs = 0.67, P < 0.05). We propose that increased rates of nucleotide substitution may lead to increased rates of gene rearrangement in the mt genomes of insects.

Animals↗

PubMed2002

An insect molecular clock dates the origin of the insects and accords with palaeontological and biogeographic landmarks.

A unified understanding of >390 Myr of insect evolution requires insight into their origin. Molecular clocks are widely applied for evolutionary dating, but clocks for the class Insecta have remained elusive. We now define a robust nucleotide and amino acid mitochondrial molecular clock encompassing five insect orders, including the Blattaria (cockroaches), Orthoptera (crickets and locusts), Hemiptera (true bugs), Diptera, and Lepidoptera (butterflies and moths). Calibration of the clock using one of the earliest, most extensive fossil records for insects (the early ancestors of extant Blattaria) was congruent with all available insect fossils, with biogeographic history, with the Cambrian explosion, and with independent dating estimates from Lepidopteran families. In addition, dates obtained from both nucleotide and amino acid clocks were congruent with each other. Of particular interest to vector biology is the early date of the emergence of triatomine bugs (99.8-93.5 MYA), coincident with the formation of the South American continent during the breakup of Gondwanaland. More generally, we reveal the insects arising from a common ancestor with the Anostraca (fairy shrimps) at around the Silurian-Ordovician boundary (434.2-421.1 MYA) coinciding with the earliest plant megafossil. We explore Tilyard's theory proposing that the terrestrial transition of the aquatic arthropod ancestor to the insects is associated with a particular plant group (early vascular plants). The major output of the study is a comprehensive series of dates for deep-branching points within insect evolution that can act as calibration points for further dating studies within insect families and genera.

Animals↗

PubMed2000

The complete sequence of the mitochondrial genome of the crustacean Penaeus monodon: are malacostracan crustaceans more closely related to insects than to branchiopods?

The complete sequence of the mitochondrial genome of the giant tiger prawn, Penaeus monodon (Arthropoda, Crustacea, Malacostraca), is presented. The gene content and gene order are identical to those observed in Drosophila yakuba. The overall AT composition is lower than that observed in the known insect mitochondrial genomes, but higher than that observed in the other two crustaceans for which complete mitochondrial sequence is available. Analysis of the effect of nucleotide bias on codon composition across the Arthropoda reveals a trend with the crustaceans represented showing the lowest proportion of AT-rich codons in mitochondrial protein genes. Phylogenetic analysis among arthropods using concatenated protein-coding sequences provides further support for the possibility that Crustacea are paraphyletic. Furthermore, in contrast to data from the nuclear gene EF1alpha, the first complete sequence of a malacostracan mitochondrial genome supports the possibility that Malacostraca are more closely related to Insecta than to Branchiopoda.

Animals↗

PubMed1991

Why don't all termite species have a sterile worker caste?

No general theory explains why a sterile worker caste is not found in all species of both Hymenoptera and Isoptera (Insecta). Recent empirical finding show that, in the termites (Isoptera), feeding outside the nest correlates well with the evolution of the sterile (true) worker caste from the non-sterile (false) worker caste. Here we explain the connection between food-nest separation and true worker evolution in termites, providing a general theory on the restricted distribution of the sterile worker caste in the Isoptera. A cost-benefit model suggests that there is a critical level of nest stability above which natural selection favours true workers over false workers, irrespective of genetical relatedness. Because food-nest separation tends to increase nest stability, this theoretical result implies that the less a termite species consumes its nest as food, the more likely is its nest stability to fall above the critical level and a true worker caste will evolve.

Animals↗

PubMed2001

Stand tall and they still get you in your Achilles foot-pad.

The free-living first-instar larvae of Strepsiptera (Insecta) are the infective stage of the parasitoid. They normally enter the host via the abdominal cuticle, and there have also been reports of entry via the egg of the host. The first-instar larvae of Stichotrema dallatorreanum Hofeneder in Papua New Guinea were found to enter the host orthopteran via the tarsi. This is, to my knowledge, the first report of entry of first-instar larvae of Strepsiptera via the attachment pads (euplantulae) of the host.

Animals↗

PubMed2002

Simulating species loss following perturbation: assessing the effects on process rates.

We removed stream-living macroinvertebrate shredder species in the sequences in which they are predicted to disappear, in response to two common types of anthropogenic disturbances: acidification and organic pollution, and analysed the effects on leaf breakdown rates. The experiment was performed in field microcosms using three shredder species. Species identity significantly affected leaf breakdown rates, while species richness per se was non-significant. The simulated sequential species loss showed large effects on leaf breakdown rates, with observed rates being significantly higher than expected from single-species treatments in two, out of four, two-species, and in all four three-species treatments. The invertebrates used in this study were taxonomically distinct (Insecta: Plecoptera and Trichoptera; Crustacea: Amphipoda), and of different sizes, hence a high degree of complementarity was probably present. A method to study the effects of species loss, characteristic of perturbation type, could be more useful than a random approach when investigating the impact of perturbation. Our results may have general applicability for investigations on the effects of diversity loss on ecosystem functioning in any ecosystem exposed to human perturbations, given that the order of extinction is known or can easily be assessed.

Amphipoda↗

PubMed1996

Phylogenetic relationship among termite families based on DNA sequence of mitochondrial 16S ribosomal RNA gene.

Termites (Order Isoptera: Class Insecta), are comprised of a complex assemblage of species, with considerable variation in life history, morphology, social behaviour, caste development and ecology. At present, isoptera is divided into seven families, fourteen subfamilies, approximately 270 genera and over 2000 species. Phylogenetic hypotheses currently available for termite families and genera are based on a limited number of morphological characters and lack rigorous cladistic analysis. In this paper we report on phylogenetic relationships among ten termite genera of five families based on a DNA sequence analysis of a portion of the mitochondrial 16S rRNA gene. Parsimony and distance analysis of DNA sequences supported the existing hypothesis that Mastotermitidae is the basal lineage among extant termites. Kalotermitidae was not found to be a sister taxon of Mastotermitidae as existing hypotheses suggest, but was most closely related to Rhinotermitidae and Termitidae. Representatives of Termopsidae were more basal relative to those of Kalotermitidae. The utility of 16S rRNA nucleotide sequence analysis for inferring phylogenetic relationships among termite families, subfamilies and genera is discussed.

Animals↗

PubMed1994

Flies in the group Cyclorrhapha use (3S)-3-hydroxyretinal as a unique visual pigment chromophore.

In the class Insecta, retinal and 3-hydroxyretinal are used as chromophores of visual pigments, but the absolute structure of the 3-hydroxyretinal chromophore has yet to be clarified. This study investigates the chirality of 3-hydroxyretinal in the compound eyes of five representative orders of insects. In the orders Odonata, Hemiptera, Neuroptera and Lepidoptera, and suborders Nematocera and Brachycera of the Diptera, only (3R)-3-hydroxyretinal isomers were detected, but dipterans of the suborder Cyclorrhapha (higher flies) had the (3S)-11-cis enantiomer and a mixture of (3R)-all-trans and (3S)-all-trans 3-hydroxyretinal enantiomers; the ratio of the (3R) enantiomer to the sum of both enantiomers of the all-trans isomer was in the range 9-32%. Despite differences in feeding habits, including one species that is a butterfly parasite, all higher flies analysed to date share the same pattern of 3-hydroxyretinal enantiomers, making them a unique group with regard to the nature of the visual pigment chromophore.

Animals↗

PubMed1960

Species differentiation of insects by hemolymph electrophoresis.

By means of microclectrophoresis in agar gel, we studied the hemolymph proteins of different species of the family Triatomidae (class Insecta) and different species of the families Ixodidae and Argasidae (clalss Arachnoidea). The results show a specific electrophoretic pattern for each species. Insects infected with pathogenic organisms have the same pattern as normal insects.

Animals↗