Geographic variation for climatic stress resistance traits in the springtail Orchesella cincta

Multiple traits of stress resistance were investigated in the epedaphic springtail Orchesella cincta. Second generation adults from five laboratory populations were compared with respect to resistance to extreme temperatures and desiccation, and traits relevant to climatic adaptation. Populations were collected along a 2000-km latitudinal gradient ranging from Denmark to southern Italy and reared under the same standard laboratory conditions. Traits investigated were resistance to high and low temperature, desiccation resistance, body size and water loss rate (WLR). Results showed genetically based differences in resistance to high and low temperature, desiccation, WLR, water pool and body size between populations. Individuals from the most northern population had the highest desiccation-and cold shock resistance, and the lowest heat shock resistance. Females were significantly more desiccation resistant than males. The results of cold shock resistance showed a positive increase with lowest environmental temperature recorded at the sites of population origin, whereas heat shock resistance showed a positive increase with highest recorded temperature at the sites of population origin. Desiccation resistance increased towards the most southern and northern population, suggesting that both low and high temperature extremes affect desiccation resistance. Body mass, water pool and WLR showed interpopulation as well as sex specific variation. This provides evidence for geographical variation in stress resistance of springtails related to climatic conditions.     

Genetic variation in fitness parameters associated with resistance to Bacillus thuringiensis in male and female Trichoplusia ni

Resistance of insects to insecticides is often associated with reduced fitness in the absence of selection. We examined fitness trade-offs associated with resistance to the microbial insecticide, Bacillus thuringiensis (Bt), across full-sib families in a resistant population of Trichoplusia ni. Significant genetic variation in and heritability of susceptibility to Bt occurred among the full-sib families. Male pupal weight was positively correlated with Bt susceptibility, indicating a potential fitness cost, but no such correlation occurred for females. Significant heritability for pupal weight was present for males but not females. A significant negative genetic correlation existed between development time and Bt susceptibility, indicating that resistant larvae developed more slowly than susceptible larvae. Selection for Bt resistance in T. ni resulted in changes in life-history traits that affected males more than females.     

Protozoan and intracellular fungal gut endosymbionts in Drosophila: prevalence and fitness effects of single and dual infections

We report on the effect of single and mixed infections with two gut symbionts, trypanosomatids and the intracellular fungus Coccidiascus legeri, on the life history of their host, Drosophila melanogaster. We also provide the first report on the prevalence of C. legeri in natural populations of Drosophila. Prevalence overall was low (3.4%), and differed with host species, but persisted from the first to the second year of our survey. We documented delayed pupation in flies exposed to trypanosomatids, but larvae exposed to the fungus eclosed more quickly than controls. Larvae exposed to mixed infections pupated more slowly, but eclosed more quickly than controls.     

Genetic diversity analysis of Zingiber Officinale Roscoe by RAPD collected from subcontinent of India

The present investigation was undertaken for the assessment of 12 accessions of Zingiber officinale Rosc. collected from subcontinent of India by RAPD markers. DNA was isolated using CTAB method. Thirteen out of twenty primers screened were informative and produced 275 amplification products, among which 261 products (94.90%) were found to be polymorphic. The percentage polymorphism of all 12 accessions ranged from 88.23% to 100%. Most of the RAPD markers studied showed different levels of genetic polymorphism. The data of 275 RAPD bands were used to generate Jaccard’s similarity coefficients and to construct a dendrogram by means of UPGMA. Results showed that ginger undergoes genetic variation due to a wide range of ecological conditions. This investigation was an understanding of genetic variation within the accessions. It will also provide an important input into determining resourceful management strategies and help to breeders for ginger improvement program.     

Myoblast fusion in Drosophila

The body wall musculature of a Drosophila larva is composed of an intricate pattern of 30 segmentally repeated muscle fibers in each abdominal hemisegment. Each muscle fiber has unique spatial and behavioral characteristics that include its location, orientation, epidermal attachment, size and pattern of innervation. Many, if not all, of these properties are dictated by founder cells, which determine the muscle pattern and seed the fusion process. Myofibers are then derived from fusion between a specific founder cell and several fusion competent myoblasts (FCMs) fusing with as few as 3-5 FCMs in the small muscles on the most ventral side of the embryo and as many as 30 FCMs in the larger muscles on the dorsal side of the embryo. The focus of the present review is the formation of the larval muscles in the developing embryo, summarizing the major issues and players in this process. We have attempted to emphasize experimentally-validated details of the mechanism of myoblast fusion and distinguish these from the theoretically possible details that have not yet been confirmed experimentally. We also direct the interested reader to other recent reviews that discuss myoblast fusion in Drosophila, each with their own perspective on the process [1], [2], [3] and [4]. With apologies, we use gene nomenclature as specified by Flybase (http://flybase.org) but provide Table 1 with alternative names and references.     

Identification of RAPD and SCAR markers associated with yield traits in the Indian tropical tasar silkworm Antheraea mylitta drury

The tropical tasar silkworm, Antheraea mylitta, is a semi-domesticated vanya silk-producing insect of high economic importance. To date, no molecular marker associated with cocoon and shell weights has been identified in this species. In this report, we identified a randomly amplified polymorphic DNA (RAPD) marker and examined its inheritance, and also developed a stable diagnostic sequence-characterized amplified region (SCAR) marker. Silkworms were divided into groups with high (HCSW) and low (LCSW) cocoon and shell weights, and the F₂ progeny of a cross between these two groups were obtained. DNA from these silkworms was screened by PCR using 34 random primers and the resulting RAPD fragments were used for cluster analysis and discriminant function analysis (DFA). The clustering pattern in a UPGMA-based dendogram and DFA clearly distinguished the HCSW and LCSW groups. Multiple regression analysis identified five markers associated with cocoon and shell weights. The marker OPW16_{905 bp} showed the most significant association with cocoon and shell weights, and its inheritance was confirmed in F₂ progeny. Cloning and sequencing of this 905 bp fragment showed 88% identity between its 134 nucleotides and the Bmc-1/Yamato-like retroposon of A. mylitta. This marker was further converted into a diagnostic SCAR marker (SCOPW 16_{826 bp}). The SCAR marker developed here may be useful in identifying the right parental stock of tasar silk-worms for high cocoon and shell weights in breeding programs designed to enhance the productivity of tasar silk.     

Density-mediated carry-over effects explain variation in breeding output across time in a seasonal population

In seasonal environments, where density dependence can operate throughout the annual cycle, vital rates are typically considered to be a function of the number of individuals at the beginning of each season. However, variation in density in the previous season could also cause surviving individuals to be in poor physiological condition, which could carry over to influence individual success in the following season. We examine this hypothesis using replicated populations of Drosophila melanogaster, the common fruitfly, over 23 non-overlapping generations with distinct breeding and non-breeding seasons. We found that the density at the beginning of the non-breeding season negatively affected the fresh weight of individuals that survived the non-breeding season and resulted in a 25% decrease in per capita breeding output among those that survived to the next season to breed. At the population level, per capita breeding output was best explained by a model that incorporated density at the beginning of the previous non-breeding season (carry-over effect, COE) and density at the beginning of the breeding season. Our results support the idea that density-mediated COEs are critical for understanding population dynamics in seasonal environments.     

A critical role of teashirt for patterning the ventral epidermis is masked by ectopic expression of tiptop, a paralog of teashirt in Drosophila

The teashirt gene encodes a protein with three widely spaced zinc finger motifs that is crucial for specifying trunk identity in Drosophila embryos. Here, we describe a gene called tiptop, which encodes a protein highly similar to Teashirt. We have analyzed the expression patterns and functions of these two genes in the trunk of the embryo. Initially, teashirt and tiptop expressions are detected in distinct domains; teashirt in the trunk and tiptop in parts of the head and tail. In different mutant situations, we show that, in the trunk and head, they repress each other's expression. Unlike teashirt, we found that deletion of tiptop is homozygous viable and fertile. However, embryos lacking both gene activities display a more severe trunk phenotype than teashirt mutant embryos alone. Ectopic expression of either gene produces an almost identical phenotype, indicating that Teashirt and Tiptop have, on the whole, common activities. We conclude that Teashirt and Tiptop repress each other's expression and that Teashirt has a crucial role for trunk patterning that is in part masked by ectopic expression of Tiptop.     

Drosophila homologue of the Rothmund-Thomson syndrome gene: essential function in DNA replication during development

Members of the RecQ family play critical roles in maintaining genome integrity. Mutations in human RecQL4 cause a rare genetic disorder, Rothmund-Thomson syndrome. Transgenic mice experiments showed that the RecQ4 null mutant causes embryonic lethality. Although biochemical evidence suggests that the Xenopus RecQ4 is required for the initiation of DNA replication in the oocyte extract, its biological functions during development remain to be elucidated. We present here our results in establishing the use of Drosophila as a model system to probe RecQ4 functions. Immunofluorescence experiments monitoring the cellular distribution of RecQ4 demonstrated that RecQ4 expression peaks during S phase, and RecQ4 is expressed only in tissues active in DNA replication, but not in quiescent cells. We have isolated Drosophila RecQ4 hypomorphic mutants, recq^EP and recq4²³, which specifically reduce chorion gene amplification of follicle cells by 4-5 fold, resulting in thin and fragile eggshells, and female sterility. Quantitative analysis on amplification defects over a 14-kb domain in chorion gene cluster suggests that RecQ4 may have a specific function at or near the origin of replication. A null allele recq4¹⁹ causes a failure in cell proliferation, decrease in DNA replication, chromosomal fragmentation, and lethality at the stage of first instar larvae. The mosaic analysis indicates that cell clones with homozygous recq4¹⁹ fail to proliferate. These results indicate that RecQ4 is essential for viability and fertility, and is required for most aspects of DNA replication during development.     

A comparison of low temperature tolerance traits between closely related aphids from the tropics, temperate zone, and Arctic

The survival of aphids exposed to low temperatures is strongly influenced by their ability to move within and between plants and to survive exposure to potentially lethal low temperatures. Little is known about the physiological and behavioural limitations on aphid movement at low temperatures or how they may relate to lethal temperature thresholds. These questions are addressed here through an analysis of the thermal ecology of three closely related aphid species: Myzus persicae, a ubiquitous temperate zone pest, Myzus polaris, an arctic species, and Myzus ornatus, a sub-tropical species. Lower lethal temperatures (LLT₅₀) of aphids reared at 15 °C were similar for M. persicae and M. polaris (range: −12.7 to −13.9 °C), but significantly higher for M. ornatus (−6.6 °C). The temperature thresholds for activity and chill coma increased with rearing temperature (10, 15, 20, and 25 °C) for all clones. For M. polaris and M. ornatus the slopes of these relationships were approximately parallel; by contrast, for M. persicae the difference in slopes meant that the difference between the temperatures at which aphids cease walking and enter coma increased by approximately 0.5 °C per 1 °C increase in rearing temperature. The data suggest that all three species have the potential to increase population sizes and expand their ranges if low temperature limitation is relaxed.     

Nutrient dynamics in 3 morphological different tropical seagrasses and their sediments

Seasonality of nutrient dynamics in three morphologically different seagrass species and their sediments was examined for 1 year between November 2006 and November 2007 at four sites in the Andaman Sea, Thailand. The smaller species, Cymodocea serrulata and Halophila ovalis, showed major seasonal variation in shoot density, above- and belowground biomass, much more than expected from seasonal changes in water temperature and light conditions. All parameters showed minimum values in the dry season due to desiccation during neap tides. In contrast Enhalus acoroides showed less seasonal variation. Only limited seasonality was found in tissue N content of all species, whereas tissue P content responded to the low P concentration in the water column during the wet season. There were no differences in sediment conditions among species, and nutrient pools were generally low. Furthermore there were no significant spatial differences in seagrass and sediment nutrient dynamics, despite varying anthropogenic activity at the study sites, reflecting the oligotrophic conditions in this region.     

Associations of esterase 6 allozyme and activity variation with reproductive fitness inDrosophila melanogaster

Previous studies have shown that the esterase 6 (EST6) enzyme ofD. melanogaster is mainly produced in the sperm ejaculatory duct of the adult male and comparisons of wild-type males with laboratory null mutants have suggested that the enzyme plays a role in reproductive fitness. In this study we have compared 18 field-derived lines each isoallelic forEst6 for differences in five components of male reproductive fitness. No consistent fitness differences were found among lines differing in respect of the two major allozyme classes EST6-F and EST6-S, despite other evidence that these two classes are not selectively equivalent in the field. However, differences in reproductive fitness were found among lines differing in the minor mobility variants that segregate within EST6-F and EST6-S. A failure to distinguish among these minor forms may explain the discrepancies in previous studies on the effects of the major EST6 allozymes on reproductive fitness. The most significant associations we have found between EST6 and reproductive fitness were due to variation in EST6 activity levels. Male EST6 activity levels were found to be positively correlated with their time to first mating, negatively correlated with the numbers of eggs laid and progeny produced by their mates, and negatively correlated with the frequency with which their mates remate. We conclude that some EST6 variants differ in components of male reproductive fitness operative in laboratory cultures. However, the evidence for fitness differences is stronger for variants affecting the amount, rather than the structure of the enzyme, and the direction of the differences varies between some of the fitness components tested.     

Spatial and temporal regulation of the homeotic selector gene Antennapedia is required for the establishment of leg identity in Drosophila

Antennapedia is one of the homeotic selector genes required for specification of segment identity in Drosophila. Dominant mutations that ectopically express Antennapedia cause transformation of antenna to leg. Loss-of-function mutations cause partial transformation of leg to antenna. Here we examine the role of Antennapedia in the establishment of leg identity in light of recent advances in our understanding of antennal development. In Antennapedia mutant clones in the leg disc, Homothorax and Distal-less are coexpressed and act via spineless to transform proximal femur to antenna. Antennapedia is negatively regulated during leg development by Distal-less, spineless, and dachshund and this reduced Antennapedia expression is needed for the proper development of distal leg elements. These findings suggest that the temporal and spatial regulation of the homeotic selector gene Antennapedia in the leg disc is necessary for normal leg development in Drosophila.     

Chemosystematic investigations of irregular diterpenes in Anisotome and related New Zealand Apiaceae

A chemosystematic HPLC-UV and HPLC-MS investigation of New Zealand members of the Apiaceae was performed. Diterpenes were identified and quantified in methanolic extracts from subaerial parts of 28 taxa and 54 samples of Aciphylla, Anisotome, Apium, Gingidia, Lignocarpa, Oreomyrrhis, and Scandia. Six diterpenes (1-2, 4-7) and four polyacetylenes (8-11) were identified. The known compounds were the diterpenes anisotomenoic acid 1, anisotomene-1-ol 2, 16-acetoxyanisotomenoic acid 4 and anisotomene-1,12-diol 5; and the polyacetylenes falcarinol 8, falcarindiol 9, (+)-9(Z),17-octadecadiene-12,14-diyne-1,11,16-triol 10, and (+)-9(Z),17-octadecadiene-12,14-diyne-1,11,16-triol 1-acetate 11. New irregular diterpenes 13,14-dihydroanisotom-12E-ene-1,14-diol 6 and 14-methoxy-13,14-dihydroanisotom-12E-ene-1-ol 7 were isolated from A. haastii. Isomers of the new semi-synthetic diterpene 16-hydroxyanisotomenoic acid 3 were detected in extracts of Anisitone flexuosa. Structure elucidation was performed by HR mass spectrometry and 1D and 2D NMR spectroscopy. In crude extracts, compounds were identified by their HPLC retention times and their on-line HPLC-UV and MS spectra. Anisotomene diterpenes occurred in eight out of 16 species of the genus Anisotome, but were not detected in any of the other genera. In contrast, polyacetylenes were present in all the genera investigated.