Avoidance of the host immune response by a generalist parasitoid, Compsilura concinnata Meigen

Abstract.  1. Ecological interactions between parasitoids and their hosts are extremely strong as parasitoid offspring rely entirely on an individual host to complete development. The ability of a parasitoid to use a host is influenced directly by the degree to which the parasitoid can overcome host defences and grow within the host.
2. Hymenopteran parasitoids have evolved different host-specific strategies to defeat the host immune system, such as the use of venom, endosymbiont virus, or mimicking the host tissue. Dipteran parasitoids from the Tachinidae family do not use these subterfuges and rely mainly on avoiding the host immune system by hiding in specific tissues.
3. Little is known of the effect of this strategy on the host immune system, the absorption of nutrients by the parasitoid larvae, or the implications for parasitoid host range.
4. In this study, the impact of a polyphagous tachinid parasitoid Compsilura concinnata Meigen on a pest lepidopteran Trichoplusia ni Hübner are assessed. Phenoloxidase levels and haemolymph proteins were measured in parasitised T. ni as a function of host immune response.
5. Haemolymph phenoloxidase in the host did not vary with parasitisation but was triggered when a piece of monofilament was implanted in the haemocoel. Haemolymph proteins were depleted in heavily parasitised T. ni .
6. These results indicate that C. concinnata has a strategy that avoids the host immune system, and accesses the necessary nutrients for larval growth. This strategy could explain the success of this tachinid and its wide host range.     

Resource choice in orchard populations of Drosophila

Three capture-recapture experiments were performed on natural populations of Drosophila from orchards in California. Two of the experiments investigated choice between known breeding substrates: oranges v. grapefruits and figs v. peaches. The third involved choice between citrus baits in a citrus orchard and both banana and citrus baits in an adjacent almond orchard. Drosophila pseudoobscura showed no fidelity to the bait or area of initial capture. However, a statistically significant but low level of resource fidelity was displayed by D. melanogaster/D. simulans. An index of differential choice is used to compare our results to those of previous studies. Possible biological bases of choice behaviour are discussed.     

Thermal Dependence of Air Convection Requirement and Blood Gases in the Snake Coluber constrictor

In this report I discuss ventilatory and circulatory adjustmentsthat prov for increased O₂transport associated with increasedbody temperature in the snake Coluber constrictor. Also includedis the effect of temperature upon acid-base status. Minute ventilationincreases with rising body temperature but does not keep pacewith the increment in resting O₂ consumption. The decrease inair convection requirement (i.e., ventilation ÷ oxygenconsumption) causes lung pO₂ and arterial oxygen contentto falland lung pCO₂ to rise. With the rise in lung pCO₂, systemicarterial pCO₂ and H⁺; concentration increase while plasma bicarbonateconcentration does not change. The effect of temperature uponair convection requirement, arterial pCO₂, and pH are most pronouncedat body temperatures above about 27°C whereColuber behavesapproximately as an alphastat pH regulator. Despite the inverserelationship between temperature and lung pO₂, systemic arterialpO₂ is about 80 torr lower at 15°C than at 35°C. Thisdecline in arterial pO₂ as temperature falls is explained byleft shifting the oxygen dissociation curve in the presenceof aconstant right-to-left intracardiac shunt.     

Ecological Bases of Hormone--Behavior Interactions: The "Emergency Life History Stage"

SYNOPSIS. Superimposed upon seasonal changes in morphology,physiology and behavior, are facultative responses to unpredictableevents known as labile (i.e., short-lived) perturbation factors(LPFs). These responses include behavioral and physiologicalchanges that enhance survival and collectively make up the "emergency"life history stage. There is considerable evidence that glucocorticosteroids,and other hormones in the hypothalamo—pituitary—adrenal(HPA) cascade, initiate and orchestrate the emergency life historystage within minutes to hours. This stage has a number of sub—stagesthat promote survival and avoid potential deleterious effectsof stress that may result from chronically elevated levels ofcirculating glucocorticosteroids over days and weeks. Thesesub—stages may include: redirection of behavior from anormal life history stage to increased foraging, irruptivetypemigration during the day, enhanced restfulness at night, andelevated gluconeogenesis. Once the perturbation passes, glucocorticosteroidsmay also promote recovery. Additional evidence from birds indicatesthat glucocorticosteroid responses to a standardized capture,handling and restraint protocol are modulated both on seasonaland individual levels. Field work reveals that these changesin responsiveness to LPFs have ecological bases, such as reproductivestate, body condition etc., that in turn indicate differenthormonal control mechanisms in the HPA cascade.     

Temperature Response Pattern during Afterripening of Achenes of the Winter Annual Krigia oppositifolia (Asteraceae)

Abstract Freshly-matured achenes of Krigia oppositifolia Raf. were buried in soil at near-natural temperatures for 0–35 months and then exhumed and tested in light and darkness at (12/12 hr) daily thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20°C. Achenes required light for germination and exhibited an annual dormancy/nondormancy cycle, being dormant in spring and nondormant in autumn. High summer temperatures (30/15, 35/20°C) fully promoted afterripening, whereas low temperatures (5, 15/6°C) prevented it. As buried seeds came out of dormancy in summer, they first germinated at medium temperatures (20/10, 25/15°C), but with additional afterripening the maximum and minimum temperatures for germination increased and decreased, respectively. Thus, during afterripening, achenes exhibit type 3 temperature responses, which otherwise are known only in two perennial Asteraceae and one perennial Liliaceae. The physiological responses of achenes of K. oppositifolia are unlike those of most winter annuals, which have type 1 responses—i.e., the maximum temperature for germination increases during afterripening. Also, they are unlike the majority of Asteraceae, which have type 2 responses—i.e., the minimum temperature for germination decreases during afterripening. Type 1 responses, typical of most winter annuals, have yet to be reported in the Asteraceae.     

WRITING AMISH CULTURE INTO GENES: BIOLOGICAL REDUCTIONISM IN A STUDY OF MANIC DEPRESSION

Critical realism is used to explore the problem of reductionism in a classic (the Amish Study) andwidely-cited study of manic depression. Along withrelated ideas drawn from the works of R.C.Lewontin, Arthur Kleinman, and Byron Good, it isshown that natural and social scientists deployatomistic and holistic reductionism; this, in turn,leads to the construction of artificially closedsystems' through the control of variables orexogenous forces. The psychiatric genetic studies ofthe Amish were predicated on the assumption thatAmish society is homogeneous and unchanging and,therefore, closed. We conclude by arguing thatinteractions between behaviors and genes, where theyexist, take place only within open systems, characterizedby multiple mechanisms – social andbiological – that together co-determineany event. To move forward, it is argued, behavior and generesearch requires recognition and resolution of thephilosophical conundrums that accompany reductionism.     

Photosynthate partitioning into leaf starch as affected by daily photosynthetic period duration in six species

Starch accumulation rates increased up to five-fold in the leaves of five out of six species examined when plants were shifted from a long (12 or 14-h) to a short (7-h) photosynthetic period. The five species that responded were corn (Zea mays L.), pangola (Digitaria decumbens Stent.), soybean (Glycine max L.) Merr.), spinach (Spinacia oleracea L.), and sugarbeet (Beet vulgaris L.) However, the rate of starch accumulation in alfalfa (Medicago sativa L.) was unaltered following a shift from a long to a short photosynthetic period. We conclude that photosynthate partitioning into chloroplast starch, at least in a wide variety of species, is a programmable process that can be manipulated by altering the length of the daily photosynthetic period.     

Nutrient availability effects on vesicular-arbuscular mycorrhizal bell pepper (Capsicum annuum) seedlings and transplants

Pepper (Capsicum annuum) seeds were sown in nutrient-poor sand or nutrient-rich peat/vermiculite amended or not amended with Glomus macrocarpum. The vesicular-arbuscular mycorrhizal (VAM) seedlings were irrigated with three levels of nutrient solution, and transplanted into four levels of P-amended soil, each of which was irrigated with two levels of nutrient solution minus P. Mycorrhizal seedlings in sand were responsive to increasing nutrient levels; in nutrient-rich peat the seedlings did not respond to additional fertilisation. The greatest seedling development accompanied by good fungus colonisation was in nutrient-poor medium irrigated with the highest nutrient solution tested (18 mM N, 1.2 mM P, and 7 mM K). Non-VAM plants almost ceased growing between the weeks 4 and 5, whereas VAM plants increased in weight by 41–188%. After transplanting, sand-grown seedlings benefited from VAM when 300 mg P/kg or more was added to the soil but peat-grown plants did not. Fruit development was delayed in all non-VAM plants compared with VAM ones.