Geographical variation in host specificity of fleas (Siphonaptera) parasitic on small mammals: the influence of phylogeny and local environmental conditions

The evolution of host specificity remains a central issue in the study of host‐parasite relationships. Here we tackle three basic questions about host specificity using data on host use by fleas (Siphonaptera) from 21 geographical regions. First, are the host species exploited by a flea species no more than a random draw from the locally available host species, or do they form a taxonomically distinct subset? Using randomization tests, we showed that in the majority of cases, the taxonomic distinctness (measured as the average taxonomic distances among host species) of the hosts exploited by a flea is no different from that of random subsets of hosts taken from the regional pool. In the several cases where a difference was found, the taxonomic distinctness of the hosts used by a flea was almost always lower than that of the random subsets, suggesting that the parasites use hosts within a narrower taxonomic spectrum than what is available to them. Second, given the variation in host specificity among populations of the same flea species, is host specificity truly a species character? We found that host specificity measures are repeatable among different populations of the same flea species: host specificity varies significantly more among flea species than within flea species. This was true for both measures of host specificity used in the analyses: the number of host species exploited, and the index measuring the average taxonomic distinctness of the host species and its variance. Third, what causes geographical variation in host specificity among populations of the same flea species? In the vast majority of flea species, neither of our two measures of host specificity correlated with either the regional number of potential host species or their taxonomic distinctness, or the distance between the sampled region and the center of the flea's geographical range. However, in most flea species host specificity correlated with measures of the deviation in climatic conditions (precipitation and temperature) between the sampled region and the average conditions computed across the flea's entire range. Overall, these results suggest that host specificity in fleas is to a large extent phylogenetically constrained, while still strongly influenced by local environmental conditions.     

Taphonomy and compositional fidelity of Quaternary fossil assemblages of terrestrial gastropods from carbonate-rich environments of the Canary Islands

Quaternary aeolian deposits of the Canary Islands contain well‐preserved terrestrial gastropods, providing a suitable setting for assessing the taphonomy and compositional fidelity of their fossil record over ~13 kyr. Nine beds (12, 513 shells) have been analysed in terms of multivariate taphonomic and palaeoecological variables, taxonomic composition, and the stratigraphic and palaeontological context. Shells are affected by carbonate coatings, colour loss and fragmentation. Shell preservation is size‐specific: juveniles are less fragmented and show colour preservation more commonly than adults. In palaeosols, the adult shell density correlates negatively with the proportion of fragmented adults, negatively with the proportion of juveniles, and positively with the proportion of adults with coatings. High bioturbation intensity in palaeosols is associated with low shell fragmentation and high proportion of shells with coatings. These relationships imply that high adult density in palaeosols was driven by an increase in shell production rate (related to a decrease in predation rates on adults and a decrease in juvenile mortality) and a decrease in shell destruction rate (related to an increase in durability enhanced by carbonate precipitation). In dunes, the relationships between taphonomic alteration, shell density and bioturbation are insignificant. However, dune assemblages are characterized by a lower frequency of shells with coatings and higher rates of colour loss, indicating lower shell durability in dunes than in palaeosols. Additionally, non‐random differences in the coating proportion among palaeosols imply substantial temporal variation in the rate of carbonate crust formation, reflecting long‐term changes in bioturbation intensity that covaries positively with shell preservation. Dunes and palaeosols do not differ in species abundances despite differences in the degree of shell alteration, suggesting that both weakly and strongly altered assemblages offer data with a high compositional fidelity. Carbonate‐rich terrestrial deposits originating in arid conditions can enhance the preservation of gastropods and result in fossil assemblages that are suitable for palaeoecological and palaeoenvironmental studies of terrestrial ecosystems.     

Somatic maturation and sensorimotor development of C57BL/6 mice prenatally exposed to cytosine arabinoside

The topical problem of experimental neurobiology is the development of pharmacological models to search for correlation between induced brain pathology and changes in behavioral phenotype. Cytosine arabinoside (Ara-c) is an antiproliferative agent, exposure to which in the critical period of the embryonic formation of the cortex results in the abnormality of its development. This study was aimed at estimation of the somatic and sensorimotor aspects of the early postnatal maturatrion of behavioral acts in mice with developmental abnormalities of the cortex induced by Ara-c. Pregnant C57BL/6 mice were injected with the substance on the 12.5th 13.5th gestation days. Offspring behavior was studied using a modified Fox battery on the 1st-21st postnatal days. Severe disorders of the sensorimotor development with slight somatic changes were revealed in the offsprings of Ara-c-treated mice. Features of these pathological changes point to a correlation between the developmental changes in behavioral phenotype and irregularities of the cortex formation. This experimental model can be applied to neurobiological and pharmacological studies.     

Effect of export-specific cytoplasmic chaperone, protein SecB, on secretion of Escherichia coli alkaline phosphatase

The efficiency of secretion of Escherichia coli alkaline phosphatase depends on the presence in cells of a cytoplasmic chaperone—protein SecB. Secretion increases in the presence of this chaperone at 30°C, which is the most favorable for the interaction of SecB with the export-initiation domain found previously in the N-terminal region of the mature enzyme. This interaction most likely occurs in the region of the export domain, which is located close to the signal peptide and in complex with a translocational ATPase—protein SecA.     

Applications of nanoparticles in biology and medicine

Nanomaterials are at the leading edge of the rapidly developing field of nanotechnology. Their unique size-dependent properties make these materials superior and indispensable in many areas of human activity. This brief review tries to summarise the most recent developments in the field of applied nanomaterials, in particular their application in biology and medicine, and discusses their commercialisation prospects.     

Development rates of two Xenopsylla flea species in relation to air temperature and humidity

The rate of development of immature fleas, Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) was studied in the laboratory at 25 degrees C and 28 degrees C with 40, 55, 75 and 92% relative humidity (RH). These fleas are separately associated with the host jird Meriones crassus Sundevall in different microhabitats of the Ramon erosion cirque, Negev Highlands, Israel. This study of basic climatic factors in relation to flea bionomics provides the basis for ecological investigations to interpret reasons for paratopic local distributions of these two species of congeneric fleas on the same host. Both air temperature and RH were positively correlated with duration of egg and larval stages in both species. Change of humidity between egg and larval environments did not affect duration of larval development at any temperature. At each temperature and RH, the eggs and larvae of X. ramesis did not differ between males and females in the duration of their development, whereas female eggs and larvae of X. conformis usually developed significantly faster than those of males. For both species, male pupae developed slower than female pupae at the same air temperature and RH. Air temperature, but not RH, affected the duration of pupal development. At each humidity, duration of the pupal stage was significantly longer at 25 degrees C than at 28 degrees C: 15.3+/-1.7 vs. 11.7+/-1.2 days in X. conformis; 14.1+/-2.0 vs. 11.5+/-1.7 days in X. ramesis, with a significantly shorter pupal period of the latter species at 25 degrees C. These limited interspecific bionomic contrasts in relation to basic climatic factors appear insufficient to explain the differential habitat distributions of X. conformis and X. ramesis.     

Density-dependent host selection in ectoparasites: An application of isodar theory to fleas parasitizing rodents

Parasites should make the same decisions that every animal makes regarding fitness reward. They can maximize reproductive success by selection of those habitats that guarantee the greatest fitness output. We consider the host population as a habitat of a parasite population. Consequently, hosts (=habitats) that differ quantitatively or qualitatively will support different numbers of parasites. The nature of habitat selection can be detected by isodars, lines along which habitat selection yields equivalent fitness reward. We applied this approach to study host selection of five fleas, each infesting two desert rodents. Xenopsylla conformis, Xenopsylla ramesis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis parasitize Gerbillus dasyurus and Meriones crassus. Synosternus cleopatrae pyramidis parasitizes Gerbillus andersoni allenbyi and Gerbillus pyramidum. Three fleas ( X. conformis, X. ramesis and S. c. pyramidis) were able to perceive quantitative (amount of the resource; e.g. organic matter in the nest for flea larvae) and/or qualitative (pattern of resource acquisition; e.g. host defensiveness) differences between hosts. Two other fleas did not perceive between-host differences. X. conformis was a density-dependent host selector that showed sharp selectivity at low density. X. ramesis and S. c. pyramidis were density-independent host selectors with a direct correspondence of density with habitat quality. N. i. theodori and S. t. medialis were non-selectors with no relationship at all between density and host quality. The results of the application of the isodar theory suggest that ectoparasites, like other animals, behave as if they are able to make choices and decisions that favour environments in which their reproductive benefit is maximized.     

Interaction between neurons of the frontal cortex and hippocampus during the realization of choice of food reinforcement quality in cats

Six cats were subjected to the procedure of appetitive instrumental conditioning (with light as a conditioned stimuls) by the method of the "active choice" of reinforcement quality. Short-delay conditioned bar-press responses were rewarded with bread-meat mixture, and the delayed responses were reinforced by meat. The animals differed in behavior strategy: four animals preferred the bar-pressing with a long delay (the so-called "self-control" group), and two cats preferred the bar-pressing with a short delay (the so-called "impulsive" group). Multiunit activity in the frontal cortex and hippocampus (CA3) was recorded via chronically implanted nichrome wire semimicroelectrodes. An interaction between the neighboring neurons in the frontal cortex and hippocampus (within local neural networks) and between the neurons of the frontal cortex and hippocampus (distributed neural networks in frontal-hippocampal and hippocampal-frontal directions) was evaluated by means of statistical crosscorrelation analysis of spike trains. Crosscorrelations between neuronal spike trains in the delay range of 0-100 ms were explored. It was shown that the number of crosscorrelations between the neuronal discharges both in the local and distributed networks was significantly higher in the "self-control" cats. It was suggested that the local and distributed neural networks of the frontal cortex and hippocampus are involved in the system of brain structures which determine the behavioral strategy of animals in the "self-control" group.     

Cytoskeleton-Dependent Changes in the Structural Organization of Reticuloplasmins in Triticum aestivum Cells during Cold Acclimation and Treatment with Abscisic Acid

We studied the effects of the anti-microtubule drug, oryzalin, on the content and spatial organization of reticuloplasmins (Ca²⁺-binding marker proteins of the endoplasmic reticulum) in winter wheat seedlings after their cold acclimation (3°C, 7 days) and treatment with ABA (30 M). For identification and visualization of reticuloplasmins, we applied one-dimensional SDS-PAGE with subsequent Western blotting and indirect fluorescent microscopy. We used polyclonal HSP70 and CRH antibodies against BiP and calreticulin (Cal), respectively. On immunoblots, the brightest bands corresponded to polypeptides with mol wts of 58 kD (calreticulin) and 79 kD (BiP). The content of calreticulins in roots was shown to be higher than in leaves. Cold acclimation enhanced, and ABA treatment reduced, the concentration of calreticulins in root cells. Both treatments increased the BiP concentration in roots. Oryzalin (10 M, treatment for 3 h) did not affect the level of reticuloplasmins in roots of unhardened, cold acclimated, treated with ABA and with a combination of cold and ABA plants. However, both oryzalin and low-temperature treatments resulted in the accumulation of reticuloplasmins in the two spherical structures in the vicinity of the plasmalemma and nuclear envelope. After the combined action of oryzalin and low temperature, the cortical sphere of BiP proteins was shifted into the endoplasm and calreticulins appeared in the nuclear matrix. We believe that these changes in the reticuloplasmin localization are related to the rearrangement of the endoplasmic reticulum determined by the cytoskeleton modification. They result in the improved capacity of reticuloplasmins to control Ca²⁺ behavior and/or to the function as chaperones. The results obtained permit the conclusion that cytoskeletal proteins interact with reticuloplasmins, and this interaction might be involved in the transduction of the external and internal signals.     

Oryzalin-Induced Changes in Water Status and Cytoskeleton Proteins of Winter Wheat Seedlings upon Cold Acclimation and ABA Treatment

The effect of oryzalin (a specific inhibitor of tubulin polymerization in plant cells) on water retention by the leaves and roots of winter wheat (Triticum aestivum L.) seedlings was studied. The cultivars differing in their frost resistance were compared after their acclimation to low temperature (3°C for 3 or 7 days) and after treatment with ABA. In control untreated plants, oryzalin reduced the water-retaining capacity (WRC) of leaves and roots. Both hardening and ABA lowered the effect of the inhibitor on WRC in leaves, whereas their effects on water retention by roots were opposite, i.e., hardening weakened and ABA intensified the effect of oryzalin. Oryzalin-induced reduction of WRC decreased in the following sequence of cultivars: weakly frost resistant moderately frost resistant highly frost resistant. It was more pronounced in the leaves than in the roots, the latter being characterized by the lower WRC and lower frost resistance. After three-day-long hardening of plants, an additive effect of hypothermia and ABA on oryzalin-induced decrease in WRC of leaves and the lack of such effect in the roots were observed. The immunochemical analysis of the composition and content of cytoskeletal proteins with Western blotting showed that in the leaves the actin/tubulin ratio was higher than in the roots. The treatment of nonacclimated plants with ABA lowered the content of - and -tubulins and actin in roots but did not affect the level of actin in leaves. Hardening negated the effects of ABA on cytoskeletal proteins. Oryzalin produced the greatest inhibitory effect on WRC and an increase in frost resistance in ABA-treated plants in the experiments with leaves of the weakly frost resistant cultivar before and after hardening. Organ- and cultivar-specific and ABA-mediated dependence of WRC on cytoskeletal proteins and microtubules and microfilaments formed by them is supposed to result from their effect on the state of intracellular water and water permeability of the plasma membrane. In the course of cold acclimation of plants and upon their treatment with ABA, this dependence was more distinctly expressed in leaves than in roots, and especially in the plants of the weakly frost resistant cultivar.