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At least 253 records · Page 14Linked to original sources
PubMed1980

Biochemical basis for the continuous copulation of female Schistosoma mansoni.

Sexual dimorphism in blood flukes of the family Schistosomatidae is marked, and until the male clasps the female in the gynaecophoric canal the female cannot attain sexual maturity or migrate out of the liver. When previously-paired egg-producing females are transferred to a new host without males, the vitelline cells necessary for egg production degenerate. By means of sensitive fluorographic analysis of electrophoresed polypeptides, we have now found molecular evidence of an obligatory continuous relationship between the sexes in Schistosoma mansoni. The male worm retains little of the protein it produces in greatest abundance, and this protein is electrophoretically identical to the most abundant protein found in, but not synthesised by, the female.

Animals↗
PubMed1998

Nitric oxide production is increased in the paraventricular nucleus of the hypothalamus of male rats during non-contact penile erections and copulation.

Male rats put in the presence of a receptive female rat that they can see, hear and smell, but cannot touch, show penile erection episodes. These non-contact erections occur concomitantly with an increase in nitric oxide production in the paraventricular nucleus of the hypothalamus, as detected by the increase in the NO2- and NO3- concentration in the paraventricular dialysate obtained from these males by in vivo microdialysis. NO2- concentration increased from 0.81+/-0.12 to 2.51+/-0.43 microM and that of NO3- from 4.50+/-0.73 to 8.31+/-2.3 microM. The NO2- increase was prevented by the nitric oxide synthase inhibitor NG-nitro-L-arginine methylester (20 microg) given unilaterally in the paraventricular nucleus, which also prevented non-contact erections. In contrast, the nitric oxide scavenger haemoglobin (20 microg) prevented the NO2- increase, but not non-contact erections; while the guanylate cyclase inhibitor methylene blue (20 microg) was ineffective on either response. NO2-and NO3- concentration was also increased in the paraventricular dialysate of male rats during in copula penile erections, that is, when sexual activity was allowed with the receptive females. As found with non-contact erections, NG-nitro-L-arginine methylester prevented NO2- increase and impaired copulatory behaviour; haemoglobin prevented NO2- increase only; and methylene blue was ineffective on either response. The present results confirm that nitric oxide is a physiological mediator of penile erection at the level of the paraventricular nucleus of the hypothalamus.

Animals↗
PubMed2002

Copulation corrupts immunity: a mechanism for a cost of mating in insects.

There are well documented costs of mating in insects but little evidence for underlying mechanisms. Here, we provide experimental evidence for a hormone-based mechanism that reduces immunity as a result of mating. We examined the mealworm beetle Tenebrio molitor and show that (i) mating reduces a major humoral immune effector-system (phenoloxidase) in both sexes, and (ii) that this down-regulation is mediated by juvenile hormone. Because both juvenile hormone and phenoloxidase have highly conserved functions across all insects, the identified mechanism is similarly likely to be highly conserved. The positive physiological function of mating-induced juvenile hormone secretion is gamete and accessory gland production: we propose that its negative effects on immune function are the consequence of physiological antagonism. Therefore, we have identified a physiological tradeoff between mating and immunity. Our results suggest that increasing mating success can result in increasing periods of immune suppression, which in turn implies that reproductively successful individuals may be more vulnerable to infection by, and the negative fitness effects of, pathogens.

Animals↗
PubMed2006

The cost of mating rises nonlinearly with copulation frequency in a laboratory population of Drosophila melanogaster.

Previous studies of Drosophila melanogaster have demonstrated a cost to females from male courtship and mating, but two critically important parameters remain unresolved: (i) the degree to which harm from multiple-mating reduces lifetime fitness and (ii) how harm from mating might change with successive matings (rematings). Here we use 'laboratory island analysis' to quantify the costs that females incur with each remating, in the currency of lifetime fitness and under conditions that closely match those to which the flies have adapted for hundreds of generations. We experimentally manipulated the number of female matings by varying the order of daily 2-h exposures of females to either sperm-less males (XO) or intact males (XY). Females that mated more often had substantially reduced lifetime fecundity, and importantly, the fitness cost from remating rapidly accelerated.

Animals↗