Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. III. Aggregation

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticksAmblyomma hebraeum andA. variegatum, as well as mixtures of these components, extracts of prefed males and live prefed males, were tested as aggregation stimulants. In field assays, laboratory-reared unfed male and female ticks were released 20 cm downwind of CO₂/pheromone release sites; the numbers of ticks that aggregated at the release sites were recorded after 30 min. InA. variegatum, aggregation was induced by methyl salicylate,o-nitrophenol, 2,6-dichlorophenol, phenylacetaldehyde and some mixtures containing these compounds; a strong aggregation response was induced by an extract of five prefed malesA. variegatum and a weak response was induced by an extract of 50 prefed males ofA. hebraeum. InA. hebraeum, aggregation was induced by phenylacetaldehyde, mixtures of compounds that included phenylacetaldehyde, extracts of 50 prefed males ofA. hebraeum orA. variegatum and 50 live prefed males ofA. hebraeum. InA. variegatum, aggregation was inhibited if compounds that do not occur naturally in the AAP of the species were included in mixtures. InA. hebraeum, phenylacetaldehyde appeared to act as an arrestant for ticks that had been attracted to release sites by other compounds.     

A comparison of the attraction of nymphs and adults of the ticksAmblyomma hebraeum andA. variegatum to carbon dioxide and the male-produced aggregation-attachment pheromone

The attraction of nymphs of the ticksAmblyomma hebraeum andA. variegatum to CO₂ alone and CO₂ together with the male-produced aggregation-attachment pheromone (AAP) was investigated. Matching experiments on the attraction of the adults of the two species were run for comparison. Nymphs ofA. hebraeum were strongly attracted to sources of CO₂ and CO₂/AAP at distances of 10 and 15 m. At distances of 20 and 25 m significantly more nymphs were attracted to CO₂/AAP than to CO₂ alone. Adults ofA. hebraeum were not attracted to CO₂ alone at any distance; these ticks were attracted to CO₂ and AAP together for distances of up to 25 m. The patterns of attraction of nymphs and adults ofA. variegatum at 10 m were similar to those recorded inA. hebraeum.     

Comparison of the attachment rates of males of the ticksAmblyomma hebraeum andA. variegatum to cattle,sheep and rabbits in the absence of aggregation-attachment pheromone

Losses in domestic ruminants caused by heartwater (Cowdria ruminantium infection) in Zimbabwe and Mozambique are greater when the vector isAmblyomma hebraeum than when the vector isA. variegatum. It has been suggested that the epidemiology of the disease may be influenced by the rates at which unfed adults of these two tick species attach to uninfested hosts (i.e. in the absence of the male-produced aggregation-attachment pheromone [AAP]). In this study we confined unfed males ofA. hebraeum andA. variegatum on uninfested cattle, sheep and rabbits and recorded their attachment rates. Males of both species attached more rapidly on cattle than on sheep or rabbits. Males ofA. hebraeum attached more rapidly than males ofA. variegatum on all three host species. The differences in the attachment rates between the two species were much greater on sheep and rabbits than on cattle. The findings suggest that in the absence of AAP, pioneer males of both tick species may attach to cattle, and pioneer males ofA. hebraeum may also attach to sheep. The differences in the attachment rates ofA. hebraeum andA. variegatum provide a possible explanation for observed differences in the epidemiology of heartwater associated with these two vector species.     

A segment of rye chromosome 1 enhances growth and embryogenesis of calli derived from immature embryos of wheat

Summary The influence of the short arm of rye chromosome 1 (1RS) from Secale cereale var. Imperial on the growth and differentiation of callus cultures from wheat Triticum aestivum var. Chinese Spring immature embryos was analysed. This chromosome arm was found to stimulate both embryogenesis and the rate of growth of calli. Recombinant lines carrying segments of 1RS were used to delineate the regions of 1RS responsible for the tissue culture effects. The enhancement of embryogenesis and the stimulation of growth were shown to be associated with two distinct genetic regions of the chromosome arm; the former is located between the centromere and the Sec 1 locus, while the latter is situated in the immediate vicinity of the Sec 1 locus.     

Detection and quantification of triazine herbicides using algal cell fluorescence

Summary A continuous-flow system is described which, by measuring fluorescence of the unicellular alga Chlorella, is capable of measuring concentrations of the triazine herbicide, simazine, as low as 60nM (approx 12g l^-1) within 5 minutes. Further developments are suggested to achieve the desired detection limit of 0.5nM. The use of such an instrument in environmental analysis is discussed.     

Fixed action patterns and neural Darwinism

Summary The stereotopy of the Fixed Action Pattern of classical ethology is customarily attributed to hard wiring. We submit that this explanation is akin to the 17th century use of the homunculus to explain development. We propose extendingEdelman's notions of neural Darwinism to explain the emergence of species-characteristic (innate) motor patterns.

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Angeborene, Stereotype Verhaltensweisen und Neuraler Darwinismus

Zusammenfassung Die in der klassischen Ethologie beschriebenen angeborenen Verhaltensweisen (sensuLorenz &Tinbergen) wurden meist durch die Annahme erklärt, daß bestimmte genetisch bedingte Nervennetze die stereotypen Bewegungen in reflektorischer Weise bestimmen. Im Computerjargon heißt das hard wiring. Wir meinen, daß diese Formulierung eher einer modernen Form des Homunculus des 17. Jh. als einer echten Erklärung entspricht, weil sie nicht erklären kann, wie das exakt reproduzierbare Nervennetz entsteht. Außerdem ist bekannt, daß dasselbe Verhalten auch bei enormen Unterschieden in der Neuralanatomie auftreten kann; stereotype Bewegungen brauchen keine spezifischen Nervennetze.G. Edelmann hat bereits vorgeschlagen, daß Nervennetze für angeborene Auslösemechanismen durch eine darwinistische Auslese von Neuronen entstehen können. Wir schlagen vor, dieses Prinzip auch zur Erklärung der Entwicklung stereotyper, artspezifischer Verhaltensweisen heranzuziehen und dadurch die sogenannte hard wiring-Erklärung abzulösen.

     

Human Ovarian Function and Reproductive Ecology: New Hypotheses

A series of eight hypotheses is presented, based on the results of current research, concerning the responsiveness of the human ovary to constitutional and environmental variables. These hypotheses are motivated by a theoretical position that seeks to understand human reproductive physiology as the product of natural selection. The hypotheses are: (1) Ovarian responsiveness occurs along a graded continuum. (2) The graded continuum of response forms a final common pathway for various "stresses." (3) Ovarian function tracks energy balance, not simply nutritional status. (4) Ovarian function tracks aerobic activity independently of energy balance. (5) Additive interactions characterize the interaction of constitutional and environmental factors modulating ovarian function. (6) Reproductive maturation is synchronized with skeletal maturation, especially of the pelvis. (7) Peak ovarian function is not ordinarily achieved until the early twenties. (8) Late reproductive maturation is associated with a slower rise in indices of ovarian function with age, and a lower level of ovarian function in adulthood. Together, these hypotheses provide for two, non-exclusive theories of facultative modulation of female reproductive effort. One theory views ovarian function as responsive to the prospects for positive reproductive outcome as these may be affected by maternal age, maturation, energy balance, and activity level. The second theory views ovarian function as responsive in a similar way to the need to maintain long-term maternal energy balance.     

Oxygenation of malignant tumors after localized microwave hyperthermia

Summary The oxyhemoglobin saturation (HbO₂) of single red blood cells within tumor microvessels (diameter: 3–12 µm) of DS-Carcinosarcoma was studied using a cryophotometric micromethod. In untreated control tumors (mean tissue temperature approx. 35° C) the measured values scattered over the whole saturation range from zero to 100 sat.%, the mean being 51 sat.%. Upon heating at 40° C for 30 min, the oxygenation of the tumor tissue significantly improved as compared with control conditions. After 40° C-hyperthermia a mean oxyhemoglobin saturation of 66 sat.% was obtained. In contradistinction to this, after 43° C-hyperthermia the tumor oxygenation was significantly lower and reached a mean HbO₂ saturation value of 47 sat.%. A further temperature rise to 45° C caused the oxygenation to drop drastically (mean oxyhemoglobin saturation value: 24 sat.%). This is due to a severe restriction of nutritive blood flow.The changes in tumor oxygenation after hyperthermia seem to be predominantly mediated through changes in tumor blood flow, including tumor microcirculation, which showed a similar temperature dependence. Metabolic effects probably play a minor role in the oxyhemoglobin saturation distribution within tumor microvessels.Supported by the Deutsche Forschungsgemeinschaft (Va 57/2-1). Presented in part at the International Symposium on Biomedical Thermology, June 30 to July 4, 1981, Strasbourg, France