On the coordination of motor output during visual flight control of flies

Summary In tethered flying houseflies (Musca domestica), the yaw torque produced by the wings is accompanied by postural changes of the abdomen and hindlegs. In free flight, these body movements would jointly lead to turning manoeuvres of the animal. By recording the yaw torque together with the lateral deflections of either the abdomen or the hindlegs, it is shown that these motor output systems act in a highly synergistic way during two types of visual orientation behavior, compensatory optomotor turning reactions and orientation turns elicited by moving objects. This high degree of coordination is particularly conspicuous for the pathway activated by moving objects. Here, orientation responses either may be induced or may fail to be generated always simultaneously in all three motor output systems. This suggests that the pathway mediating orientation turns towards objects is gated before it segregates into the respective motor control systems of the wings, the abdomen and the hindlegs.     

Habitat selection and subsequent reproductive success in the beaugregory damselfish

Synopsis Male beaugregory damselfish,Stegastes leucostictus, were provided with three types of artificial breeding structures to determine if they change habitats based on past or future reproductive payoffs. All three site types quickly lured males away from their natural sites. In comparison to those living on natural sites, those using artificial sites were less likely to move to different areas and had a higher reproductive success. When given no choice, male reproductive success was correlated to structural type. A second experiment provided males with an additional structure after using the intermediate quality type for 2 months. Males would often initially use both sites but would eventually shift their spawning activity to the new site if it was of the same quality or better than the old one. However, males would not move if the new site was of inferior quality. When given a new site identical to the initial one, approximately half of the males shifted to the new site. There was no evidence that reproductive performance influenced a male's decision to use a new site.     

Model studies of low-temperature optical transitions of photosynthetic reaction centers A-, LD-, CD-, ADMR- and LD-ADMR-spectra for Rhodopseudomonas viridis

The optical spectra of the reaction center (RC) of Rhodopseudomonas viridis including absorption (A), linear dichrosism (LD), circular dichroism (CD), absorption-detected magnetic resonance (ADMR) and its linear dichroism (LD-ADMR) are simulated by an exciton model. It involves the Q_y transitions of six prosthetic groups: four (bacteriochlorophyll-b molecules, two bacteriopheophytin-b molecules and the Soret bands B_y of the special-pair pigments, which couple most strongly with the corresponding Q_y transitions. For the ADMR-spectra additional excitations of the special-pair triplet are introduced. While interactions between the Q_y transitions and the B_y transitions are in principle determined from the structural arrangement of the pigments, the interactions to the other states are adjusted to fit the spectral features for the various transitions. The interaction of the newly introduced states are interpreted in terms of a simple model.     

Enhanced formation of mouse hybridomas without hat treatment in a serum-free medium

Summary A newly developed, serum-free medium (NYSF-404) selects for antibody-producing hybridomas after fusion of antigen-sensitized mouse spleen cells with myeloma cell lines P3-X63-Ag8-U1 (P3-U1), P3-X63-Ag8-6.5.3 (Ag8.653), or P3-NSI/1-Ag4-1 (NS-1). Without the need for hypoxanthine-aminopterinthymidine (HAT) selection of hybrid cells, frequency of hybridoma formation in medium NYSF-404 is higher (twice) than that in serum- and HAT-containing medium. Colonies developed upon limiting dilution in the presence of the mortal parent myeloma cells in medium NYSF-404 and pure culture of antibody-secreting cells could be subsequently established. The results suggest that fusions can be done in serum-free medium and that the clonal growth of hybridomas is dependent on factors produced by parent myeloma cells under serum-free culture conditions. Such factors seem deficient in serum- and HAT-containing medium or are masked by serum.     

Differential winter mortality and seasonal selection in the polymorphic ladybird Adalia bipunctata (L) in the Netherlands

Seasonal selection acting on the melanic polymorphism in the two-spot ladybird Adalia bipunctata was investigated in The Netherlands. An increase in melanic frequency over the spring-summer reproductive period was quantified. The selective advantage gained by melanics averaged 9%, but significant heterogeneity occurred between populations. Adult hibernation behaviour is described. The beetles when outdoors show a highly clumped distribution both between and within trees. The distribution of the morph classes between aggregations is random. Survivorship in a hibernating cohort (initial n= 1898) on a grid of 70 lime trees near Utrecht was monitored by making three counts over the winter of 1981–1982. Intense selection favouring each melanic morph occurred during December and January. The relative fitness of non-melanics was 0.55 (melanics =1). The discovery of dead beetles in late January (about 5% of total losses) and the absence of spatially density-dependent mortality were consistent with a climatic stress rather than selective predation. The period of selection was associated with very cold temperatures averaging up to 4°C below normal and an overall mortality of nearly 75%. There was no change in morph frequency, near normal temperatures and a lower mortality from February to early April. Examination of groups of nearby trees in late January strongly suggested that similar differential mortality had occurred except on some willows. This difference was probably due to the more protected hibernation sites available on these trees. Samples of hibernating cohorts at three other sites showed no evidence of differential mortality. Laboratory experiments with hibernating beetles found no difference in survivorship or rate of weight loss between starved non-melanics and melanics in temperature regimes with and without periods of adult activity. It is concluded that the intense winter selection on the study limes is probably exceptional. Examination of changes in morph frequency through the annual cycle suggests that at some sites the selection favouring melanics during reproduction is counterbalanced by selection against melanics in late summer or early autumn. The results are discussed in relation to mathematical models of cyclical selection and to other field studies including that of Timoféeff-Ressovsky (1940), who found large decreases in melanic frequency during hibernation in Berlin.     

Food selection by locusts: The rôle of learning in rejection behaviour

The food selection behaviour of male fifth instar nymphs of Locusta migratoria was monitored on the host plant wheat and on the non-host plants Senecio vulgaris, S. jacobaea and Brassica oleracea. The non-hosts were rejected, but the mode of rejection altered with time in a way which suggested associative learning. This hypothesis was tested and the results discussed in relation to classical theories of learning.

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La sélection des aliments chez les criquets: Le rôle de l'apprentissage dans le comportement de rejet

Résumé Des larves mâles de cinquième stade de Locusta migratoria ont été placées dans des cages avec des végétaux qui pouvaient être changées sans troubler les insectes. Le contact avec des pieds de blé entraînait généralement une palpation suivie de morsures et alors d'alimentation continue. Les plantes non-hôtes Senecio vulgaris, S. jacobaea et Brassica oleracea étaient rejetées, d'abord après morsures suivant la palpation, mais ultérieurement par palpation seule. Nous avons vérifié l'hypothèse que la sensation obtenue par palpation était initialement inadéquate pour provoquer le rejet, ce qui était assuré par les morsures ultérieures mais qu'avec l'expérience l'insecte apprenait à lier la sensation de palpation avec celle de morsures et progressivement rejetait après palpation seule. Ainsi les 8 premiers contacts avec des aliments désagréables ont été observés, soit quant S. vulgaris était présenté continuellement, soit quand S. vulgaris était remplacé par une autre plante désagréable après 4 contacts. Une analyse mathématique des résultats révèle une tendance au rejet par palpation seule à travers les contacts successifs, et que cette tendance est interrompue et se restaure quand l'espace végétal est changé. Ces résultats sond discutés dans le contexte des théories de l'apprentissage et on en a conclu que le phénomène observé est le résultat d'un apprentissage associatif.

     

The effect of phytoplankton and suspended sediment on the growth of Corbicula fluminea (Bivalvia)

Juvenile Corbicula fluminea Müller (1774) were cultured at 15.3 °C in the laboratory on eight combinations of suspended sediment and phytoplankton. Sediment concentrations were 2.6, 25, 50, and 150 mg l^–1. Chlorophyll a levels were 15.6 and 62.5 µg l^–1. Clam tissue growth was found to be independent of silt concentration but increased at the higher chlorophyll level (p < 0.05). The growth experiment was repeated at 24 °C with chlorophyll a concentrations of 18.9 and 112.6 µg l^–1. Growth was again greater at the higher phytoplankton level (p < 0.05). These results demonstrate that Asiatic clam populations are food-limited most of the growing season in the Northern and Western portions of California's eutrophic Sacramento-San Joaquin Delta where chlorophyll a levels average less than the lower of these values. Comparisons of clam growth in the laboratory and estuary support the food limitation hypothesis as at the higher food concentration laboratory tissue growth was 2.3 and 3.8 times greater during the high and low temperature evaluations than in the estuary.     

Some aspects of the natural history and food selection ofAvahi laniger

Two groups ofAvahi laniger were studied in the Forêt de Analamozoatra near Perinet in the eastern rainforest of Madagascar from August to October 1984. Overlap between the home ranges of neighbouring groups ofA. laniger was minimal. Group size ranged from one to four individuals with a median group size of two. In four out of ten groups a baby was born between August and September.A. laniger were most active after dusk and before dawn. They had an extended resting period around midnight. Their diet consisted mostly of leaves from at least 17 different plant species. They also ate flowers. Fruit eating was recorded twice. Leaves eaten had high contents of protein and sugar but did not contain alkaloids. The concentration of condensed tannins did not differ between food items and non-food items. There was no indication of competition with other prosimians that might explain their nocturnality.     

The flagellar apparatus of the golden algaSynura uvella: Four absolute orientations

Summary Flagellated vegetative cells of the colonial golden algaSynura uvella Ehr, were examined using serial sections. The two flagella are nearly parallel as they emerge from a flagellar pit near the apex of the cell. The photoreceptor is restricted to swellings on the flagella in the region where they pass through the apical pore in the scale case and the swellings are not associated with the cell membrane or an eyespot. A unique ring-like structure surrounds the axonemes of both flagella at a level just above the transitional helix. The basal bodies are interconnected by three striated, fibrous bands. Four short (<100 nm) microtubules lie between the basal bodies at their proximal ends. Two rhizoplasts extend down from the basal bodies and separate into numerous fine striated bands which lie over the nucleus. Three- and four-membered microtubular roots arise from the rhizoplasts and extend apically together. As the roots reach the cell anterior, the three-membered root bends and curves clockwise to form a large loop around the flagella; the four-membered root bends anticlockwise and terminates under the distal end of the three-membered root as it completes the loop. There are four absolute orientations, termed Types 1–4, in which the flagellar apparatus can occur. With each orientation type the positions of the Golgi body, nucleus, rhizoplasts, chloroplasts and microtubular roots change with respect to the flagella, basal bodies and photoreceptor. Two new basal bodies appear in pre-division cells, and three short microtubules appear in a dense substance adjacent to each new basal body. Based upon the positions of new pre-division basal bodies, a hypothesis is proposed to explain why there are four orientations and how they are maintained through successive cell divisions.     

Large scale selection of aluminum-resistant mutants from plant cell culture: expression and inheritance in seedlings

Summary A large number of aluminum-resistant variants, selected from non-mutagenized homozygous diploid cell cultures of Nicotiana plumbaginifolia Viv., are characterized. Of 115 variants cloned and reselected from single cells, 67 retained Al resistance in callus cultures after 6–9 months of growth in the absence of Al. There was no association between Al resistance and callus growth in the absence of Al, suggesting that the Al-resistant phenotype is not detrimental in the absence of Al challenge and that Al resistance is not the result of increased vigor. Plants regenerated from initially resistant callus lines that subsequently lost their resistance failed, with one exception, to transmit resistance to their seedling progeny. Fertile plants were regenerated from 40 of the 67 variants that retained stable Al resistance in callus culture. All 40 transmitted Al resistance to their seedling progeny (selfed and backcrossed) in segregation ratios expected for a single dominant mutation. The selfed progeny of many variants also segregated for recessive lethal mutations which were attributed to independent mutations that occurred during cell culture.