What are the consequences of ant–seed interactions on the abundance of two dry-fruited shrubs in a Mediterranean scrub?

Strong interactions between dry-fruited shrubs and seed-harvesting ants are expected in early successional scrubs, where both groups have a major presence. We have analysed the implications of the seed characteristics of two dry-fruited shrub species (Coronilla minima and Dorycnium pentaphyllum) on seed predation and dispersal mediated by harvester ants and the consequences of these processes on spatio-temporal patterns of plant abundance in a heterogeneous environment. We found that large C. minima seeds were collected much more (39%) than small D. pentaphyllum seeds (2%). However, not all of the removed seeds of these plant species were consumed, and 12.8% of the seeds were lost along the trails, which increased dispersal distances compared with abiotic dispersal alone. Seed dropping occurred among all microhabitats of the two plant species, but especially in open microhabitats, which are the most suitable ones for plant establishment. The two plant species increased their presence in the study area during the study period: C. minima in open microhabitats and D. pentaphyllum in high vegetation. The large size of C. minima seeds probably limited the primary seed dispersal of this species, but may have allowed strong interaction with ants. Thus, seed dispersal by ants resulted in C. minima seeds reaching more suitable microhabitats by means of increasing dispersal distance and redistribution among microhabitats. In contrast, the smaller size of D. pentaphyllum seeds arguably allows abiotic seed dispersal over longer distances and colonization of all types of microhabitats, although it probably also limits their interaction with ants and, consequently, their redistribution in suitable microhabitats. We suggest that dyszoochory could contribute to the success of plant species with different seed characteristics in scrub habitats where seeds are abundantly collected by seed-harvesting ants.     

What causes outbreaks of the gypsy moth in North America?

The gypsy moth has been present in North America for more than 100 years, and in many of the areas where it has become established outbreaks occur with varying degrees of periodicity. There also exists extensive spatial synchrony in the onset of outbreaks over large geographic regions. Density-dependent mortality clearly limits high-density populations, but there is little evidence for strong regulation of low-density populations. Predation by small mammals appears to be the major source of mortality affecting low-density populations, but because these are generalist predators and gypsy moths are a less preferred food item, mammals do not appear to regulate populations in a density-dependent fashion. Instead, predation levels appear to be primarily determined by small mammal abundance, which is in turn closely linked to the production of acorns that are a major source of food for overwintering predator populations. Mast production by host oak trees is typically variable among years, but considerable spatial synchrony in masting exists over large geographic areas. Thus, it appears that the temporal and spatial patterns of mast production may be responsible for the episodic and spatially synchronous behavior of gypsy moth outbreaks in North America. This multitrophic relationship among mast, predators, and gypsy moths represents a very different explanation of forest insect outbreak dynamics than the more widely applied theories based upon predator–prey cycles or feedbacks with host foliage quality. Received: September 8, 1999 / Accepted: September 20, 2000     

Are population differences in plant quality reflected in the preference and performance of two endoparasitoid wasps?

In recent years, increasing attention has been paid in exploring the role of direct plant defence, through the production of allelochemicals, on the performance of parasitoid wasps and their hosts. However, few studies have determined if parasitoids can detect differences in plant quality and thus preferentially attack hosts on which their progeny develop most successfully. In this study we examined the development and preference of two endoparasitoids, Diadegma semiclausum and Cotesia glomerata , developing in larvae of their respective hosts, Plutella xylostella and Pieris brassicae . In turn, these were reared on different wild populations of black mustard Brassica nigra originating in the Netherlands and Sicily (Italy), as well as single cultivated strains of B. nigra and brown mustard, B. juncea . Chemical analyses of foliar glucosinolates and volatile emissions by P. xylostella -damaged plants revealed large differences between B. nigra and B. juncea plants, with smaller differences among the B. nigra populations. The four mustard populations differentially affected development time and body mass of the herbivores and parasitoids. Contrasts among the means revealed significant differences mainly between B. nigra and B. juncea . Both parasitoids, however, preferred to alight on plants in which their progeny developed most successfully. In behavioural bioassays, D. semiclausum did not discriminate among the B. nigra populations and preferred to alight on B. juncea , which was the best plant population for parasitoid development. By contrast, C. glomerata females exhibited the lowest preference for Italian B. nigra populations, on which adult parasitoid size was the smallest. These results reveal that parasitoids can detect even small differences in plant quality presumably through their volatile blends and that plant preference and offspring performance in the two species are 'optimally synchronized'.     

Does freezing and dynamic flexing of frozen branches impact the cavitation resistance of Malus domestica and the Populus clone Walker?

Frost damage to the xylem conduits of trees is a phenomenon of eco-physiological importance. It is often documented in terms of the percentage loss of conductivity (PLC), an indicator of air filling of the conduits. However, trees that refill their conduits in spring could be impacted more by damage to the conduits that reduce cavitation resistance, making them more susceptible to future drought events. We investigated whether ice formation, dynamic flexing of frozen branches or freeze–thaw events could reduce the cavitation resistance (cause “frost fatigue”) in first-year shoots of apple (Malus domestica) and clonal hybrid cottonwood (Walker). Frost fatigue was measured in terms of P₅₀ (the negative xylem pressure required to cause a 50 % loss of conductivity). All treatment groups showed significant frost fatigue, with the exception of the pre-flushed, constantly frozen poplar branches. The P₅₀ following freeze treatments was approximately 50 % of the pre-freeze values. The effect tended to be greater in freeze–thawed branches. Dynamic bending of the branches had no effect on either PLC or P₅₀. In three out of four cases, there was a significant correlation between P₅₀ and PLC. Frost fatigue occurred in both apple and poplar, two unrelated species with different drought and frost tolerances, suggesting that it may be a widespread phenomenon that could impact the ecophysiology of temperate forests.     

Anatomy of rodent and human livers: What are the differences?

The size of the liver of terrestrial mammals obeys the allometric scaling law over a weight range of >3 1 10⁶. Since scaling reflects adaptive changes in size or scale among otherwise similar animals, we can expect to observe more similarities than differences between rodent and human livers. Obvious differences, such as the presence (rodents) or absence (humans) of lobation and the presence (mice, humans) or absence (rats) of a gallbladder, suggest qualitative differences between the livers of these species. After review, however, we conclude that these dissimilarities represent relatively small quantitative differences. The microarchitecture of the liver is very similar among mammalian species and best represented by the lobular concept, with the biggest difference present in the degree of connective tissue development in the portal tracts. Although larger mammals have larger lobules, increasing size of the liver is mainly accomplished by increasing the number of lobules. The increasing role of the hepatic artery in lobular perfusion of larger species is, perhaps, the most important and least known difference between small and large livers, because it profoundly affects not only interventions like liver transplantations, but also calculations of liver function.     

What is the purpose of HIV antibody testing?

Considerable attention, both in the scientific literature and in the popular media, has focused recently on the accuracy of tests for HIV antibodies. Many have pointed to the dangers of falsely identifying persons as being infected, and they have stressed that the predictive power of a positive test result may be small in populations with a low prevalence of HIV infection. The purpose of this paper is to argue that the current testing/counseling protocols, which are designed to increase specificity at the expense of sensitivity, are inappropriate in high-prevalence groups.     

Diets of fruit-eating birds: what are the causes of interspecific differences?

Differences in fruit choice among the bird species of a Spanish shrubland were related to the size of fruits and to the lipid content of pulp. Lipid-rich fruits were selected by the bird species with slower food passage rates through the digestive tract. These bird species also fed frequently on insects and seeds. Bird species with faster food passage rates fed less on insects and seeds, and ate mainly fruits with pulp poor in lipids (rich in sugars and water). Studies of digestion in birds indicate that lipids require slower food passage rates for efficient digestion and intestinal transport than simple sugars. The available evidence indicates that the European bird species that show stronger preferences for lipid-rich fruits are no better as seed dispersers, from the point of view of the plants, than species choosing lipidpoor fruits. Thus, the degree of frugivory of birds, their fruit choice patterns and their effects on seed dispersal do not seem to be related to each other in the ways expected by the early models of the evolution of fleshy fruits.     

Does the strength of facilitation by nurse shrubs depend on grazing resistance of tree saplings?

Facilitation of tree regeneration by nurse shrubs that offer protection against large herbivores is an important driver of wood-pasture dynamics. Here we asked whether the response to facilitation by nurse shrubs depends on the grazing resistance of the protégé saplings. We experimentally tested the protective effects of the thorny Rosa rubiginosa on browsing frequency, survival, and biomass change of saplings of two species-groups, presumably differing in grazing resistance: the coniferous Abies alba and Picea abies and the deciduous Acer pseudoplatanus and Fagus sylvatica saplings. The saplings were planted under and outside (1.5 m) planted nurse shrubs, under zero, low and high grazing intensity. In total, 1920 young saplings were transplanted to 60 blocks and followed for 1 year.Although the number of saplings browsed did not differ between species-groups, the coniferous saplings showed lower resistance to cattle browsing (i.e. lower survival and growth rates) than the deciduous saplings. The less resistant coniferous saplings benefited significantly more from nurse shrubs than the more resistant deciduous species in terms of growth of the surviving saplings, but not in terms of overall survival. This was likely due to herbivory on the nurse shrubs causing incidental browsing on protégé saplings and differences in biomass off-take. At high grazing intensity facilitative effects of the nurse shrubs decreased, especially for the coniferous species.These results have important management implications for the endangered wood-pastures in Western Europe. For a sustainable management and conservation that allows tree recruitment, grazing intensity should remain low to best promote facilitation processes for all tree species, but in particular for the less resistant conifer saplings.     

What causes the variation of polarization degree across the emission spectrum of proteins?

A gradual decrease in fluorescence polarization across the emission spectrum on increase in wavelength has been recorded for a number of proteins and also for tryptophan, N-acetyltryptophan and glycyltryptophan. Various factors responsible for this dependence have been analyzed. It is shown that if the emission originates from both the 1La and 1Lb states, the position and form of the fluorescence spectrum polarization components as well as the slope of the dependence of the degree of polarization upon emission wavelength must always vary with the excitation wavelength. However, this condition, although necessary, is not enough to prove the participation of 1Lb in emission. The dependence of the form of the emission polarization spectrum upon excitation wavelength obtained for some proteins is explained by tyrosine residues contributing to the emission. Consequently, there are no reasons for assuming that the 1Lb oscillator participates in emission. It has been observed that for individual emitting centres, the slope of the dependence of the degree of polarization upon emission wavelength is determined by alteration of the vibrational substates, between which the transition with radiation takes place. The heterogeneity in the microenvironment properties of separate tryptophan residues in multitryptophan proteins and the existence, under certain conditions, of a correlation between the radiative lifetime of the emitting centre (determining the degree of the emission polarization) and the completeness of the microenvironment orientational relaxation (determining the emitted quantum of energy) can also affect the slope of this dependence.     

Does perianth colour affect the seed germination of two desert shrubs under different storage periods and conditions?

Haloxylon salicornicum and Salsola vermiculata (Amaranthaceae) are two perennial shrubs producing fruits with differently coloured perianths (yellow vs pink) on separate individuals. To test the impact of different storage periods (four, eight and twelve months) and temperature conditions (freezing, room temperature and natural field temperatures) on the seed germination of the two seed categories, germination tests were carried out on both species. For both species, collected from wild plants in the Arabian desert (Qatar), seed germination was tested under two photoperiods (light 12/12; dark 24 hours) at 20/30°C for winged (intact) and de‐winged seeds. For each species, all the considered factors (perianth colour, wing presence, photoperiod, storage period and storage conditions) had significant effects on seed germination (p < 0.001), while the interactions among factors varied in their level of significance depending on the species. In both species, yellow seeds germinated considerably better than the pink ones, the presence of wings slowed the germination, and both storage period and temperature conditions highly influenced their germination ability. Our results indicate that seeds from different perianth colours have different germination strategies to delay their germination and distribute the species through time by escaping germination time by imposing some kind of after‐ripening or seed dormancy. The variation in storage time and storage conditions might help in extending their germination period, where one set of seeds germinate immediately, and the other set of seeds becomes dormant and thus contributes to the formation of a soil seed bank for the long‐term recruitment of seedlings. This study highlights an ecological advantageous strategy for these two species growing in the unpredictable desert habitat.     

What is the clinical utility of DNA testing in patients with familial hypercholesterolaemia?

PURPOSE OF REVIEW: Familial hypercholesterolaemia is a common genetic disorder of lipid metabolism in which patients have a significantly elevated risk of early coronary heart disease, which can be substantially lowered by treatment with the statin class of drugs. In many countries in Europe, tracing of relatives using DNA information, once the family mutation has been identified, is being actively carried out. The present review examines the specificity and clinical utility of DNA testing in patients with familial hypercholesterolaemia. RECENT FINDINGS: Technological progress has improved the detection rate in patients with the strongest clinical suspicion of familial hypercholesterolaemia to more than 70-80%. Patients carrying a mutation have, on average, higher low-density lipoprotein cholesterol levels and greater risk of early coronary heart disease, and studies have reported the utility of DNA information in the identification of affected relatives. More than 1000 different molecular causes of familial hypercholesterolaemia are documented in the University College London database, and although more than 90% of these clearly cause familial hypercholesterolaemia, the remainder require careful interpretation. SUMMARY: DNA testing, as an adjunct to the measurement of plasma low-density lipoprotein cholesterol levels, has clinical utility in providing an unequivocal diagnosis in patients and in identifying affected relatives at an early age so that they can be offered lifestyle advice and appropriate lipid-lowering therapies. Researchers and DNA diagnostic laboratories need to interpret novel sequence changes with caution in order to avoid a false positive diagnosis.     

What causes the abnormal phenotype in a 49,XXXXY male?

Summary The chromosome replication pattern of a man with 49,XXXXY was analyzed using ³H-thymidine and autoradiography as well as BrdU and acridine orange. The former technique showed a highly irregular replication pattern; the latter revealed one early replicating X chromosome, and the other three more or less asynchronously replicating. Two hypotheses seem to explain best the abnormal phenotype of males with an XXXXY sex chromosome constitution: (1) The number of the always active regions (tip of Xp) and of the possibly always active regions (the Q-dark regions on both sides of the centromere) is increased from one to four. (2) The replication pattern of the late-replicating X chromosomes is highly asynchronous, which might affect the phenotype. The possibility that more than one X chromosome might remain active in some cells, an even more abnormal and obviously deleterious situation, is still open.     

Virulence and resistance in malaria: who drives the outcome of the infection?

Theoretical and experimental studies have established the dynamic nature of virulence and that, like all traits, it has evolved. Understanding parasite evolution offers a conceptual framework for diverse fields and can contribute greatly to decision-making in disease control. Recently, Grech et al. investigated the effects of host genotype-by-parasite genotype interactions on the expression of virulence in an artificial rodent-malaria system. They found that both parasite and host effects explained most of the variance in the virulence, resistance and transmission potential. These findings are a major contribution to the emerging debate on the pros and cons of a coevolutionary approach of virulence evolution; they also hold great potential for more effective control strategies.     

Are symplast tolerance to intense drought conditions and xylem vulnerability to cavitation coordinated? An integrated analysis of photosynthetic,hydraulic and leaf level processes in two Mediterranean drought-resistant species

In the last decades, plant resistance to drought conditions has been studied intensively both at whole-tree level and at tissue level. These studies have highlighted the role of xylem cavitation in the global resistance of plants to drought. In this paper, we investigate the coordination among several symplastic variables during intense drought conditions and its relationship to resistance to xylem cavitation. We selected 2-year-old seedlings of Pistacia lentiscus L. and Quercus coccifera L., two Mediterranean drought-resistant species with differences in both xylem vulnerability to cavitation and survival rates under field conditions. Drought provoked large decreases in photosynthetic rates and predawn F_v/F_m ratios, as well as less marked decreases in actual PSII efficiency (due to decreases in both intrinsic PSII efficiency and photochemical quenching). Photosynthetic pigment composition remained fairly unchanged down to water potentials of −8 MPa, despite inter-conversions within the xanthophyll cycle in both species. Cell membrane injury and proline accumulation followed similar patterns, and were much more intense in P. lentiscus than in Q. coccifera. Comparisons between variables revealed that both species: (i) followed a drought avoidance strategy, (ii) were very resistant to drought conditions at symplastic level, and (iii) showed an overall good relationship between apoplast (xylem cavitation) and symplast resistance (membrane stability, PSII functionality, proline accumulation and pigment composition). Differences between species in functional symplastic and apoplastic characteristics are discussed.     

What are causes and treatment strategies for patellar-tendinopathy in female runners?

Patellar-tendinopathy (PT) is a common overuse injury in long distance runners, especially in women. Until today, no definite combinations of clinical, biomechanical, or training variables, or causative factors in the development of PT have been found. This study focused on assessing the differences in biomechanical characteristics between healthy runners (CO) and runners with PT only. We examined a total of 42 women. 21 CO and 21 PT. 3D kinematics of barefoot running was used in the biomechanical setup. Both groups were matched with respect to height and weight. After determining dropouts due to forefoot running, poor quality of data and lack of matching subjects in CO in terms of body height and weight, the final population comprised 24 subjects (CO=12, PT=12). Biomechanical evaluations indicate eccentric overloading of the quadriceps muscle group (knee extensors), increased pronation velocity as well as a lack of joint coordination as major etiological factors in the development of PT. We assume that eccentric strengthening of the knee extensors, as well as reduction of pronation velocity through orthotics, proper running shoes, and balance training will help treat and possibly prevent PT.     

Population dynamics in the Grey Bush Cricket Platycleis albopunctata (Orthoptera: Tettigoniidae) – What causes interpopulation differences?

We found sharply differing population dynamics in Platycleis albopunctata at two one-hectare study sites differing in vegetation cover and inclination of slopes. At one site, the population remained relatively constant (about 600 individuals) over the period observed, while at the other site the population size varied during the observation period between more than 3000 and less than 100 individuals. This field observation was analysed by an experimental study of embryonic development and reproduction, both of which are expected to largely influence population dynamics. These experiments revealed a close correlation between the temperature and the duration of egg development on the one hand and fecundity on the other. We concluded that the temperature dependence of development and reproduction is responsible for the weather dependence of population dynamics. Based on our results, we developed a hypothesis to explain the striking differences in the dynamics of the two study sites which attributes them to differences in microclimate and primary production. Additionally, we applied a simulation model to investigate the weather dependence of the population dynamics. Finally, we discuss the consequences of different population dynamics for conservation: (a) the example stresses the difficulties that arise when using demographic data of any population for the prognosis of the extinction risk of a population under study; (b) the dependence of population dynamics on habitat parameters means they can be influenced by management.