Plant stress and larval performance of a dipterous gall former

According to the plant vigour hypothesis, galling insects should respond positively and perform better on vigorous plants or plant parts, the opposite of the predictions of the plant stress hypothesis. I carried out field experiments to analyse the effects of sustained abiotic stress on the interactions between the common reed (Phragmites australis) and a gall-forming fly (Lipara lucens). The reed shoot diameter (a measure of plant vigour) is strongly affected by environmental conditions, where dry and/or nutrient-poor habitats produce thinner (stressed) shoots. L. lucens gall density is negatively correlated with shoot diameter. In a survival experiment with a wide range of shoot diameters, larval mortality was also highly correlated with shoot quality. Gall formation was higher on thinner, stressed shoots. An analysis of the gall tissues revealed that galls induced by L. lucens contain a high amount of a nutrient-rich feeding tissue. The impact of L. lucens is higher on thinner shoots. The results of this study showed that L. lucens performs better on stressed hosts, which contradicts the plant vigour hypothesis for galling insects. The low nutrient availability in the stressed shoots can be compensated by the production of galls with a nutrient-rich feeding tissue.     

Lethal and sublethal costs of autotomy and predator presence in damselfly larvae

We studied the costs of lamellae autotomy with respect to growth and survival of Lestes sponsa damselfly larvae in field experiments. We manipulated predation risk by Aeshna cyanea dragonfly larvae and lamellae status of L. sponsa larvae in field enclosures and compared differences in numbers, size and mass of survivors among treatments. In the absence of a free-ranging A. cyanea larva, about 29% of the L. sponsa larvae died. This was probably due to cannibalism. The presence of a free-ranging A. cyanea reduced larval survival by 68% compared to treatments in which it was absent or not permitted to forage on L. sponsa damselflies. Across all predator treatments, lamellae autotomy reduced survival by about 20%. The mean head width and mass of survivors was lower in the enclosures with a free-ranging A. cyanea compared to the other two predator treatments. This suggested that larvae grew less in the presence of a free-ranging predator, indicating that increased antipredator behaviours were more important in shaping growth responses than reduced population density. Mass, but not head width, of survivors was also reduced after autotomy. The fitness consequences of these effects for the adults may be pronounced. In general, these field data strongly suggest that lamellae autotomy affects population regulation of damselflies. Received: 1 February 1999 / Accepted: 22 March 1999     

DIPHTHERIA: THE PRESENT-DAY PROBLEM

The importance of diphtheria today is made evident not only by the continued frequency of its occurrence but also by its tendency to attack the older adult population. The high mortality and complication rate can be attributed in part to this shift in age incidence, as well as to delayed recognition and treatment.     

The small GTPase Rap1 is activated by turbulence and is involved in integrin [alpha]IIb[beta]3-mediated cell adhesion in human megakaryocytes

The small GTPase Rap1, which is activated by a large variety of stimuli, functions in the control of integrin-mediated cell adhesion. Here we show that in human megakaryocytes and several other commonly used hematopoietic cell lines such as K562, Jurkat, and THP-1, stress induced by gentle tumbling of the samples resulted in rapid and strong activation of Rap1. This turbulence-induced activation could not be blocked by inhibitors previously shown to affect Rap1 activation in human platelets, such as the intracellular calcium chelator BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) and various protein kinase C inhibitors. Also inhibition of actin cytoskeleton dynamics did not influence this activation of Rap1, suggesting that this activation is mediated by cell surface receptors. Human platelets, however, were refractory to turbulence-induced activation of Rap1. To determine the consequences of Rap1 activation we measured adhesion of megakaryocytes to fibrinogen, which is mediated by the integrin alphaIIbbeta3, in the presence of inhibitors of Rap1 signaling. Introduction of both Rap1GAP and RalGDS-RBD in the megakaryoblastic cell line DAMI strongly reduced basal adhesion to immobilized fibrinogen. This inhibition was partially rescued by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate but not by alpha-thrombin. From these results we conclude that in megakaryocytes turbulence induces Rap1 activation that controls alphaIIbbeta3-mediated cell adhesion.     

Age-related reproductive variation in a wild marine mammal population

Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximize reproduction and survival. In this study, we use three reproductive performance measures, maternal expenditure, offspring weaning mass, and first-year survival, to investigate the role that maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island’s southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age-related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n = 29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn, first-year pup return rates (as a proxy for survival) were assessed through the intensive mark–recapture program. Pup survival increased with female age and weaning mass. Pups of young females aged 3–6 years have a lower first-year survival probability compared with pups of older and larger females.     

Who’s the boss? Giant petrel arrival times and interspecific interactions at a seal carcass at sub-Antarctic Marion Island

Most northern giant petrels Macronectes halli arrived before southern giant petrels Macronectes giganteus at a seal carcass at sub-Antarctic Marion Island and left earlier. In interspecific interactions, southern giant petrels initiated and dominated encounters. Level of aggression may be related to the degree of satiation. Dominance by southern giant petrels at seal carcasses may help explain why northern giant petrels commence breeding earlier than southern giant petrels in sympatric situations.