Effects of spines and thorns on Australian arid zone herbivores of different body masses

Summary We investigated the effects of thorns and spines on the feeding of 5 herbivore species in arid Australia. The herbivores were the rabbit (Oryctolagus cuniculus), euro kangaroo (Macropus robustus), red kangaroo (Macropus rufus), sheep (Ovis aries), and cattle (Bos taurus). Five woody plants without spines or thorns and 6 woody plants with thorns were included in the study. The spines and thorns were not found to affect the herbivores' rates of feeding (items ingested/min), but they did reduce the herbivores' rates of biomass ingestion (g-dry/item). The reduction in biomass ingested occurred in two ways: at a given diameter, twigs with spines and thorns had less mass than undefended plants, and the herbivores consumed twigs with smaller diameters on plants with spines and thorns. The relative importance of the two ways that twigs with spines and thorns provided less biomass varied with herbivore body mass. Reduced twig mass was more important for small herbivores, while large herbivores selected smaller diameters. The effectiveness of spines and thorns as anti-herbivore defenses did not vary with the evolutionary history of the herbivores (i.e. native vs. introduced). Spines and thorns mainly affected the herbivores' selection of maximum twig sizes (reducing diameter and mass), but the minimum twig sizes selected were also reduced.     

Effects of rutin-fed caterpillars on an invertebrate predator depend on temperature

Summary A factorial experiment examined the effects of varying concentrations of the allelochemical rutin in caterpillars and the length of time the caterpillars had fed on the behavioral interactions of predatory stinkbugs (Podisus maculiventris) and their prey (Manduca sexta). Diet had no significant effect on defensive behavior of the caterpillars. The length of time that the caterpillars had fed (1 vs. 24 h) only influenced the frequency of caterpillars knocking the attacking stinkbugs away, with caterpillars knocking the stinkbugs away more often after 24 h of feeding. A second experiment tested the effects of diet (prey fed various concentrations of rutin), temperature (18° C and 28° C) and gender on consumption and growth parameters of fifth instar stinkbugs. At the cooler temperature, the bugs ate more, gained more weight but took twice as long to complete the stadium and consequently had reduced relative consumption and relative growth rates. Diet had no significant effect on biomass gained or stadium duration, but rutin-fed caterpillars did depress the stinkbugs' relative consumption rates. The effect of food quality on relative growth rate (RGR) was temperature dependent; rutin had no significant effect at the cooler temperature, but a high dose of rutin reduced RGR at the warmer temperature. Rutin had a greater negative impact on the females than the males. The effect of rutin on these predators was different than the effect on their prey (this study compared to Stamp (1990, 1992)): the negative effects of rutin seem to impact on the stinkbug's growth rather than on molting.     

Functional mapping of the surface of Escherichia coli ribose-binding protein: mutations that affect chemotaxis and transport.

Ribose-binding protein is a bifunctional soluble receptor found in the periplasm of Escherichia coli. Interaction of liganded binding protein with the ribose high affinity transport complex results in the transfer of ribose across the cytoplasmic membrane. Alternatively, interaction of liganded binding protein with a chemotactic signal transducer, Trg, initiates taxis toward ribose. We have generated a functional map of the surface of ribose-binding protein by creating and analyzing directed mutations of exposed residues. Residues in an area on the cleft side of the molecule including both domains have effects on transport. A portion of the area involved in transport is also essential to chemotactic function. On the opposite face of the protein, mutations in residues near the hinge are shown to affect chemotaxis specifically.     

Single channel and monolayer studies of acylated gramicidin A: influence of the length of the alkyl group

Three different gramicidin A analogues bearing acyl chains of various length on the ethanolamine moiety have been studied by investigating their single channel behaviour and their monolayer properties. It is shown that the single channel conductance does not depend on the substitution of the ethanolamine OH group and that the channel lifetime is roughly proportional to the length of the alkyl chain. The monolayer study indicates that acylation of gramicidin A produces compounds which have medium-dependent conformations. These acylated compounds are miscible with lipids, while GA is not, and the surface potential is not modified by the esterification of the alcohol group. Offprint requests to: F. Heitz     

Phorbol ester receptors in cerebral cortex of cats with GM1 gangliosidosis

The pathogenesis of neuronal dysfunction in the gangliosidoses is poorly understood. Studies of the feline gangliosidoses and in vitro experiments implicate ganglioside inhibition of protein kinase C (PKC) in the pathogenesis of these neurological diseases. Therefore, in the present study, the binding of [³H]phorbol-12, 13 dibutyrate was measured to determine the levels of PKC in cerebral cortex of cats with GM₁ gangliosidosis (mutant) and age matched normal siblings. This binding of ([³H]PDB) to cerebral cortex homogenates in both normal and mutant cats was highly specific. The specificity of receptors was ascertained also from displacement studies using nonradioactive phorbol ester analogues to displace [³H]PDB bound to its receptors. In both mutant and normal cat brain, phorbol 12, 13-dibutyrate (PDB), 4--phorbol 12,13-didecanoate (-PDA) and 4--phorbol 12,13-dibenzoate (-PDBz) were highly potent (approximately to same degree) and effective in displacing [³H]PDB. On the other hand, 4- phorbol 12,13-diacetate (-PDA) was a weak displacer and 4--phorbol did not displace the bound [³H]PDB in either normal or mutant brain. Scatchard analysis of the binding data indicated a homogenous single class of binding sites in normal and mutant brain (Normal: K_d=1.42×10^–7 M, B_max=8.40 pmoles/mg protein. Mutant: K_d=1.60×10^–7 M, B_max=10.00 pmoles/mg protein). Sphingosine inhibited the binding to approximately the same extent in normal and mutant cortex. These studies demonstrate the presence of highly specific, homogenous, single type phorbol ester receptors in cerebral cortex of cats with GM₁ gangliosidosis which are qualitatively and quantitatively similar to normal cat brain.     

Chrysoperla carnea predation on Heliothis virescens larvae parasitized by Microplitis croceipes

Predation by third instar larvae of Chrysoperla (=Chrysopa) carnea (Stephens) (Chrysopidae) did not alter the ratio of unparasitized Heliothis virescens (F.) (Noctuidae) larvae to H. virescens larvae parasitized by Microplitis croceipes (Cresson) (Braconidae) when these second instar larvae were exposed together to the predator on cotton (Gossypium hirsutum L., Malvaceae) in field cages. This indicates that C. carnea larvae did not prefer either parasitized or unparasitized larvae.

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Prédation par Chrysopa carnea des chenilles d'Heliothis virescens parasitées par Microplitis croceipes

Résumé Les prédations de chenilles d'Heliothis virescens, parasitées ou saines, élevées sur coton (Gossypium hirsutum L.), de la variété Stoneville 213, ont été comparées, dans des cages de 10 m² chacune placées dans la nature. Des chenilles du second stade ont été placées sur des pieds de coton dans 10 cages, à raison de 160 chenilles préalablement exposées à M. croceipes pendant leur premier stade et 40 chenilles saines par cage. Des larves du troisième stade de Chrysopa carnea ont été ajoutées dans 6 cages, à raison de 500/cage, et 4 cages ont servi de témoins pour évaluer les autres causes de mortalité. L'expérience a été répétée 2 fois. Les chenilles d'H. virescens ont été retirées au bout d'un jour dans une expérience et au bout de 2 jours dans l'autre. C. carnea n'a fait aucun choix entre chenilles parasitées ou non; la fréquence moyenne de chenilles parasitées n'a pas présenté de différence significative entre les cages avec ou sans C. carnea. Qui qu'il en soit, C. carnea a réduit significativement la survie des chenilles d'H. virescens parasitées ou non.

     

Population differences in larval hostplant use in the checkerspot butterfly, Euphydryas chalcedona

Larvae from two populations of Euphydryas chalcedona Doubleday & Hewitson (Nymphalidae) were reared on their own hostplant and that of the other population, in both pre-diapause and post-diapause instars. One population, Chico, uses Penstemon breviflorus Lindl. (Scrophulariaceae), and the other, Echo Lake, uses P. newberryi Gray. Growth rate and survival were determined for pre-diapause and post-diapause larvae from both populations on both plant species; and digestive efficiencies were calculated during the prediapause instars. The results showed that larvae from the two populations differed in their responses to the two plant species. Pre-diapause larvae from Chico performed equally well on both plant species—survival and digestive indices were not significantly different for two Penstemon species. In contrast, pre-diapause larvae from Echo Lake performed significantly worse on the non-hostplant—growth and survival were significantly lower on the non-host, P. breviflorus. In addition, comparison of digestive efficiencies for the two plants showed that larvae from Echo Lake digested P. breviflorus better than P. newberryi, but were significantly less able to convert P. breviflorus to body mass. In the post-diapause instars, larvae from Chico grew faster on the host than on the non-host. Larvae from Echo Lake grew quite slowly on both plant species and significantly more of the Echo Lake larvae returned to diapause instead of completing development.

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Résumé Des chenilles de deux populations d'E. chalcedona ont été élevées sur leur propre plante-hôte et sur celle de l'autre population, aux stades avant et après diapause. Les deux populations s'alimentent sur différentes espèces de Penstemon (Scrophulariaceae), et une population—Echo Lake—est monophage sur P. newberry, tandis que l'autre—Chico—utilise d'abord P. breviflorus, mais les chenilles après diapause sont trouvées sur au moins deux autres espèces de plantes. Les taux de croissance et de survie ont été déterminés pour des chenilles avant et après diapause pour les deux populations sur les deux plantes; les efficacités digestives ont été calculées sur les chenilles avant diapause.Les résultats ont montré que les chenilles des deux populations différaient par leur degré de spécialisation digestive sur leur plante hôte normale: les chenilles de Chico ont utilisé aussi bien les deux plantes, tandis que celles d'Echo Lake le faisaient significativement moins bien sur la plante non-hôte, par suite de l'inaptitude à la digérer. Ainsi la population oligophage est alimentairement moins spécialisée et plus capable de se débrouiller avec une plante non-hôte. Après diapause, les chenilles de Chico s'alimentaient significativement mieux sur plante hôte que non-hôte, ce qui était le cas aussi pour la population monophage. Dans l'ensemble, les chenilles de la population monophage semblaient moins capables de se débrouiller dans des conditions défavorables ou moins avantageuses.

     

Spin probe clustering in human erythrocyte ghosts

Summary A model has been developed for 5-nitroxide stearate, I(12,3), distribution in human erythrocyte ghosts which accurately predicts ESR spectral alterations observed with increased probe/total lipid (P/L) at 37°C. This spin probe occupies a class of high-affinity, noninteracting sites at low loading. Saturation occurs with increasing probe concentration, and, at higher loading, the probe inserts itself at initially dilute sites to form membranebound clusters of variable size. No low probe remains at high P/L where all I(12,3) clusters in a concentrated phase. This model allows determination of the dilute/clustered probe ratio, and shows that I(12,3) segregates in erythrocytes at what might otherwise be considered low P/L (e.g., 1/359). These findings validate the earlier use of empirical parameters to estimate probe sequestration in biological membranes.     

Aspects of the numerical and functional respones of the aphid parasite, Aphidius sonchi, in the laboratory

The fecundity, reproductive rates, and adult survival of Aphidius sonchi Marshall (Hymenoptera: Aphidiidae) parasitizing second and third instar nymphs of the sowthistle aphid, Hyperomyzus lactucae (L.) (Homoptera: Aphididae) were measured at six different host densities under constant laboratory conditions. At host densities of less than 50 aphids per flowering shoot per female per day, oviposition constraints resulting from the lack of hosts reduced the number of eggs laid, enhanced the extent of superparasitization and, as a result, effectively lowered the fecundity and reproductive rates of the parasites. Above this host density the parasites laid on average 220–230 eggs, but the effective fecundity and reproductive rates continued to increase with the host density. By contrast, the survivorship of the parasites seemed unaffected by host density, with an average adult life span of 4–5 days at all densities. Analysis of the data showed that the intrinsic rate of increase (r_m) of the parasite varied with the host density and could reach values higher than that of the host under identical conditions. The response of r_m to changes in host density and parasite sex ratio is illustrated.Overall, A. sonchi showed a typical convex functional response, to host density. However, the response showed obvious changes through the parasite's adult life and, furthermore, the rates of changes were not consistent at all host densities. The frequency distributions of parasite eggs were generally indistinguishable from random, and the number of hosts parasitized were predicted satisfactorily by the random oviposition equation.

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Résumé L'étude a porté sure l'influence de 6 densités différentes d'Hyperomyzus lactucae (L.) (Homoptera: Aphididae), en conditions constantes de laboratoire, sur la fécondité, le taux de reproduction et la survie des adultes d'Aphidius sonchi Marshall (Hym. Aphidiidae, parasite des larves de 2e et 3e stades. A des densités inférieures à 50 pucerons par tige fleurie de Sonchus oleraceus L, par femelle et par jour, la limitation de la ponte due à l'absence d'hôtes a réduit le nombre d'oeufs émis, élevé le taux de superparasitisme et, en conséquence, diminué la fécondité et le taux de reproduction des parasites. Aux densités d'hôtes supérieures, les parasites ont pondu, en moyenne, 220 à 230 oeufs, mais la fécondité réelle et les taux de reproduction ont continué à augmenter avec la densité des pucerons. Par contre, la longévité des parasites n'a pas été affectée par la densité des hôtes, avec une durée moyenne de vie de 4 à 6 jours. L'analyse des données a montré que le taux d'accroissement intrinsèque (r_m) du parasite a changé avec la densité des hôtes, et pourrait atteindre des valeurs supérieures à celles de l'ôte sous des conditions identiques. Les réponses de r_m aux changements de densité des hôtes et au taux sexuel du parasite sont expliquées.Globalement, A. sonchi a présenté une réponse fonctionnelle convexe typique à la densité des hôtes. Cependant, cette réponse a changé au cours de la vie des images et, de plus, les taux de changement ne sont pas logiques à toutes les densités d'hôtes La fréquence de distribution des oeufs n'est généralement pas séparable d'une distribution au hasard, et le nombre d'hôtes parasites peut être prédit d'une façon satisfaisante en utilisant une équation de ponte au hasard.