Impact of riparian land use on stream insects of Kudremukh National Park, Karnataka state, India

The impact of riparian land use on the stream insect communities was studied at Kudremukh National Park located within Western Ghats, a tropical biodiversity hotspot in India. The diversity and community composition of stream insects varied across streams with different riparian land use types. The rarefied family and generic richness was highest in streams with natural semi evergreen forests as riparian vegetation. However, when the streams had human habitations and areca nut plantations as riparian land use type, the rarefied richness was higher than that of streams with natural evergreen forests and grasslands. The streams with scrub lands and iron ore mining as the riparian land use had the lowest rarefied richness. Within a landscape, the streams with the natural riparian vegetation had similar community composition. However, streams with natural grasslands as the riparian vegetation, had low diversity and the community composition was similar to those of paddy fields. We discuss how stream insect assemblages differ due to varied riparian land use patterns, reflecting fundamental alterations in the functioning of stream ecosystems. This understanding is vital to conserve, manage and restore tropical riverine ecosystems.

Ecology of acoustic signalling and the problem of masking interference in insects

The efficiency of long-distance acoustic signalling of insects in their natural habitat is constrained in several ways. Acoustic signals are not only subjected to changes imposed by the physical structure of the habitat such as attenuation and degradation but also to masking interference from co-occurring signals of other acoustically communicating species. Masking interference is likely to be a ubiquitous problem in multi-species assemblages, but successful communication in natural environments under noisy conditions suggests powerful strategies to deal with the detection and recognition of relevant signals. In this review we present recent work on the role of the habitat as a driving force in shaping insect signal structures. In the context of acoustic masking interference, we discuss the ecological niche concept and examine the role of acoustic resource partitioning in the temporal, spatial and spectral domains as sender strategies to counter masking. We then examine the efficacy of different receiver strategies: physiological mechanisms such as frequency tuning, spatial release from masking and gain control as useful strategies to counteract acoustic masking. We also review recent work on the effects of anthropogenic noise on insect acoustic communication and the importance of insect sounds as indicators of biodiversity and ecosystem health.

How mutualisms between plants and insects are stabilized

While the idea of cooperation between individuals of a species has received considerable attention, how mutualistic interactions between species can be protected from cheating by partners in the interaction has only recently been examined from theoretical and empirical perspectives. This paper is a selective review of the recent literature on host sanctions, partner-fidelity feedback and the concept of punishment in such mutualisms. It describes new ideas, borrowed from microeconomics, such as screening theory with and without competition between potential partners for a host. It explores mutualism-stabilizing mechanisms using examples from interactions between figs and fig wasps, and those between ants and plants. It suggests new avenues for research.

The X Chromosome of Hemipteran Insects: Conservation, Dosage Compensation and Sex-Biased Expression

Insects of the order Hemiptera (true bugs) use a wide range of mechanisms of sex determination, including genetic sex determination, paternal genome elimination, and haplodiploidy. Genetic sex determination, the prevalent mode, is generally controlled by a pair of XY sex chromosomes or by an XX/XO system, but different configurations that include additional sex chromosomes are also present. Although this diversity of sex determining systems has been extensively studied at the cytogenetic level, only the X chromosome of the model pea aphid Acyrthosiphon pisum has been analyzed at the genomic level, and little is known about X chromosome biology in the rest of the order. In this study, we take advantage of published DNA- and RNA-seq data from three additional Hemiptera species to perform a comparative analysis of the gene content and expression of the X chromosome throughout this clade. We find that, despite showing evidence of dosage compensation, the X chromosomes of these species show female-biased expression, and a deficit of male-biased genes, in direct contrast to the pea aphid X. We further detect an excess of shared gene content between these very distant species, suggesting that despite the diversity of sex determining systems, the same chromosomal element is used as the X throughout a large portion of the order.

Crop Classification using Biologically-inspired Techniques with High Resolution Satellite Image

Remote sensing provides a lucid and effective means for crop coverage identification. Crop coverage identification is a very important technique, as it provides vital information on the type and extent of crop cultivated in a particular area. This information has immense potential in the planning for further cultivation activities and for optimal usage of the available fertile land. As the frontiers of space technology advance, the knowledge derived from the satellite data has also grown in sophistication. Further, image classification forms the core of the solution to the crop coverage identification problem. No single classifier can prove to satisfactorily classify all the basic crop cover mapping problems of a cultivated region. We present in this paper the experimental results of multiple classification techniques for the problem of crop cover mapping of a cultivated region. A detailed comparison of the algorithms inspired by social behaviour of insects and conventional statistical method for crop classification is presented in this paper. These include the Maximum Likelihood Classifier (MLC), Particle Swarm Optimisation (PSO) and Ant Colony Optimisation (ACO) techniques. The high resolution satellite image has been used for the experiments.

Trehalose Toxicity in Cuscuta refexal Correlation With low Trehalase Activity

A toxic effect of a,a-trehalose in an angiospermic plant, Cuscuta reflexa (dodder), Is described. This disaccharide and Its analogs, 2-aminotrehalose and 4-aminotbhakose, induced a raid blackening of the terminal region of the vine which is Involved in elongation growth. From the results of in vitro growth of several angkiopermic plants and determination of trehalase activity in them, it is concluded that the toxic effect of trehalose in Cucaa is because of the very low trehalas activity In the vine. As a result, trehalose accumulates In the vine and interferes with some process closely associated with growth. The growth potential of Lemma (a duckweed) in a medium containing trehalose as the carbon source was ihreversibly lost upon addition of trealosamine, an Inhibitor of trehalase activity. It is concluded that, if allowed to accumulate within the tissue, trehalose may be potentiaMly toxic or inhibitory to higher plants in generaL The presence of trhalase actvity in plants, where Its substrate has not been found to occur, is envisged to relieve the plant from the toxic effects of trehalose which it may encounter in soil or during association with fungi or insects.

Impact of Grazing, Fire and Extraction on the Bamboo (Dendrocalamus-Strictus and Bambusa-Arundinacea) Populations of Karnataka

Dendrocalamus strictus and Bambusa arundinacea are monocarpic, gregariously flowering species of bamboo, common in the deciduous forests of the State of Karnataka in India. Their populations have significantly declined, especially since the last flowering. This decline parelleis increasing incidence of grazing, fire and extraction in recent decades. Results of an experiment in which the intensities of grazing and fire were varied, indicate that while grazing significantly depresses the survival of seedlings and the recruitment of new eulms of bamboo clumps, fire appeared to enhance seedling survival, presumably by reducing competition of lass fire-resistant species. New shoots of bamboo are destroyed by insects and a variety of herbivorous mammals. In areas of intense herbivore pressure, a bamboo clump initiates the production of a much larger number of new culrm, but results in many fewer and shorter intact culms. Extraction renders the new shoots more susceptible to herbivore pressure by removal of the protective covering of branches at the base of a bamboo clump. Hence, regular and extensive extraction by the paper mills in conjuction with intense grazing pressure strongly depresses the addition of new culms to bamboo clumps. Regulation of grazing in the forest by domestic livestock along with maintenance of the cover at the base of the clumps by extracting the culms at a higher level should reduce the rate of decline of the bamboo stocks.

Is Human-X Chromosome Inactivation A Sex-Determining Device

The evolutionary function of X chromosome inactivation is thought to be dosage compensation. However, there is, at present, little evidence to suggest that most X chromosome-linked genes require such compensation. Another view--that X chromosome inactivation may be related to sex determination--is examined here. Consider a hypothetical DNA sequence regulating a major structural gene concerned with the determination of maleness. If this regulatory sequence occurs in both X and Y chromosomes and if its copy number in the Y chromosome is significantly greater than in the X chromosome, then the male-determining properties of the Y chromosome could be attributed to this higher copy number. On the other hand, if the Y chromosome has the same copy number of this sequence as the X chromosome, it is difficult to see how determination of two sexes would occur under such circumstances because XX and XY genomes would then be indistinguishable in this regard. Such a situation seems to occur in the human species with respect to the banded krait minor satellite, a repetitious DNA sequence associated with sex determination. This apparent difficulty may be resolved if X chromosome inactivation renders regulatory as well as structural genes nonfunctional and thereby brings about a significant reduction in the effective copy number of X chromosome-linked DNA sequences concerned with sex determination. It is suggested that X chromosome inactivation brings about, in this manner, a critical inequality between XX and XY embryos and that sex determination in humans is a consequence of this inequality. An analogous situation appears to exist in certain insects in which inactivation of a haploid set of chromosomes (and presumably, therefore, a 50% reduction in the effective copy number of most genes) is associated with maleness. If this line of reasoning is correct, it would suggest that sex determination may be the primary function of X chromosome inactivation.

Social evolution - Has nature ever rewound the tape?

Social insects such as ants, bees, wasps and termites exhibit extreme forms of altruism where some individuals remain sterile and assist other individuals in reproduction. Hamilton's inclusive fitness theory provides a powerful framework for investigating the evolution of such altruism. Using the paper wasp Ropalidia marginata, we have quantified and delineated the role of ecological, physiological, genetic and demographic factors in social evolution. An interesting feature of the models we have developed is their symmetry so that either altruism or selfishness can evolve, depending on the numerical values of various parameters. This suggests that selfish/solitary behaviour must occasionally re-emerge even from the eusocial state, It is useful to contemplate expected intermediate states during such potential reversals. We can perhaps envisage three successive steps in such a hypothetical process: i) workers revolt against the hegemony of the queen and challenge her status as the sole reproductive, ii) workers stop producing queens and one or more of them function as egg layers (functional queen/s) capable of producing both haploid as well as diploid offspring and iii) social evolution reverses completely so that a eusocial species becomes solitary, at least facultatively. It appears that the third step, namely transition from eusociality to the solitary state, is rare and has been restricted to transitions from the primitively eusocial state only. The absence of transitions from the highly eusocial state to the solitary state may be attributed to a number of 'preventing mechanisms' such as (a) queen control of workers (b) loss of spermathecae and ability to mate (c) morphological specialization (d) caste polyethism and (e) homeostasis, which must each make the transition difficult and, taken together, perhaps very difficult. However, the discovery of a transition from the highly eusocial to the solitary state can hardly he ruled out, given that little or no effort has gone into its detection. In this paper I discuss social evolution and its possible reversal and cite potential examples of stages in the transition from the social to the solitary.

Lipid composition of the silkworm Bombyx mori L

The constituents of silkworm fat were studied in detail. An unsaturated fat with a high concentration of phospholipid was generally observed. Its iodine value increased during metamorphosis. The free fatty acid concentration likewise increased from the spinning larvae to the moth stage. Analyses of silkworm organs revealed that the fat body had the most fat and the least free fatty acids, whereas haemolymph contained the least fat. Silk glands contained the maximum phospholipid percentage. Stearic acid predominated in those tissues that had a high percentage of phospholipid. Stearic acid was the predominant saturated fatty acid in both the phospholipids and lecithin, and it accounted for 35–50 per cent of the free fatty acids of all the tissues. Q10 was the ubiquinone present; also found were ubichromenol and tocopherol. Results show that silkworm sterol may be cholesterol. Intestines contained the maximum quantities of sterol, ubiquinone, ubichromenol, and tocopherol. The composition of silkworm phospholipids varies considerably from those of other insects, but lecithin is comparable in its composition with lecithins of other animals. The phospholipids had with them a highly complexed protein along with a polysaccharide. In experiments with snake venoms unsaturated fatty acids were found to be predominantly released from silkworm lecithin.

Role of juvenile hormone in the synthesis and sequestration of vitellogenins in the red cotton stainer, Dysdercus koenigii (Heteroptera : Pyrrhocoridae)

Investigations were carried out to determine the role of juvenile hormone (JH) and 20-hydroxy ecdysone in the synthesis and uptake of vitellogenins, which were earlier identified, purified and characterised, in Dysdercus koenigii. The concentration(s) of vitellogenin(s) in fat body, haemolymph and that of vitellin(s) in ovary were significantly lower after chemical allatectomy at eclosion. In addition, at 70 h after emergence, chemical allatectomy reduced ovarian vitellin concentration, but vitellogenin levels remained normal in the fat body and haemolymph. The haemolymph vitellogenins were not incorporated into oocytes in such insects. Administration of JH-III at 20 h after allatectomy restored vitellogenin levels in the fat body and haemolymph, but the ovary failed to incorporate the available vitellogenins from haemolymph in such insects. However, when JH-III was administered twice, one at 20 h and then at 70 h after allatectomy, vitellogenin concentrations in fat body and haemolymph and also vitellin concentrations in ovary approached control levels. It is suggested that JH has two separate roles, one in vitellogenin synthesis and the other in uptake. 20-hydroxy ecdysone had no apparent role in either vitellogenin synthesis or uptake in D. koenigii. (C) 2000 Elsevier Science Inc. All rights reserved.

How do heterogametic females survive without gene dosage compensation?

When the male is the heterogametic sex (XX♀-XY♂ or XX♀-XO♂), as inDrosophila, orthopteran insects, mammals andCaenorhabditis elegans, X-linked genes are subject to dosage compensation: the single X in the male is functionally equivalent to the two Xs in the female. However, when the female is heterogametic (ZZ♂-ZW♀), as in birds, butterflies and moths, Z-linked genes are apparently not dosage-compensated. This difference between X-linked and Z-linked genes raises fundamental questions about the role of dosage compensation. It is argued that (i) genes which require dosage compensation are primarily those that control morphogenesis and the prospective body plan; (ii) the products of these genes are required in disomic doses especially during oogenesis and early embryonic development; (iii) heterogametic females synthesize and store during oogenesis itself morphogenetically essential gene products - including those encoded by Z-linked genes — in large quantities; (iv) the abundance of these gene products in the egg and their persistence relatively late into embryogenesis enables heterogametic females to overcome the monosomic state of the Z chromosome in ZW embryos. Female heterogamety is predominant in birds, reptiles and amphibians, all of which have megalecithal eggs containing several thousand times more maternal RNA and other maternal messages than eggs of mammals,Caenorhabditis elegans, orDrosophila. This increase in egg size, yolk content and, concomitantly, the size of the maternal legacy to the embryo, may have facilitated female heterogamety and the absence of dosage compensation.

Sociobiology in turmoil again

Altruism is defined as any behaviour that lowers the Darwinian fitness of the actor while increasing that of the recipient. Such altruism (especially in the form of lifetime sterility exhibited by sterile workers in eusocial insects such as ants, bees, wasps and termites) has long been considered a major difficulty for the theory of natural selection. In the 1960s W. D. Hamilton potentially solved this problem by defining a new measure of fitness that he called inclusive fitness, which also included the effect of an individual's action on the fitness of genetic relatives. This has come to be known as inclusive fitness theory, Hamilton's rule or kin selection. E. O. Wilson almost single-handedly popularized this new approach in the 1970s and thus helped create a large body of new empirical research and a large community of behavioural ecologists and kin selectionists. Adding thrill and drama to our otherwise sombre lives, Wilson is now leading a frontal attack on Hamilton's approach, claiming that the inclusive fitness theory is not as mathematically general as the standard natural selection theory, has led to no additional biological insights and should therefore be abandoned. The world cannot but sit up and take notice.