Sex-biased parasitism,seasonality and sexual size dimorphism in desert rodents

We investigated seasonality of gender differences in the patterns of flea infestation in nine rodent species to test if sex-biased parasitism in terms of mean abundance, species richness, prevalence and the level of aggregation (a) varies among hosts and between seasons, and (b) is linked to sexual size dimorphism. Sexual size differences were significant in both summer and winter in Acomys cahirinus, Gerbillus pyramidum and Meriones crassus, and in winter only in Acomys russatus, Gerbillus dasyurus, Gerbillus nanus and Sekeetamys calurus. Sexual size dimorphism was male biased except for A. russatus in which it was female biased. Manifestation of sexual differences in flea infestation was different among hosts between seasons. A significant effect of sex on mean flea abundance was found in six hosts, on mean flea species richness in five hosts and on prevalence in two hosts. Male-biased parasitism was found in summer in one host only and in winter in five hosts. Female-biased parasitism occurred in winter in A. russatus. Gender differences in the slopes of the regressions of log-transformed variances against log-transformed mean abundances occurred in three hosts. No relationship was found between sexual size dimorphism and any parasitological parameter in any season using both conventional regressions and the method of independent contrasts. Our results suggest that sex-biased parasitism is a complicated phenomenon that involves several different mechanisms.     

Ectoparasitic "jacks-of-all-trades": relationship between abundance and host specificity in fleas (Siphonaptera) parasitic on small mammals

Animal species with larger local populations tend to be widespread across many localities, whereas species with smaller local populations occur in fewer localities. This pattern is well documented for free-living species and can be explained by the resource breadth hypothesis: the attributes that enable a species to exploit a diversity of resources allow it to attain a broad distribution and high local density. In contrast, for parasitic organisms, the trade-off hypothesis predicts that parasites exploiting many host species will achieve lower mean abundance on those hosts than more host-specific parasites because of the costs of adaptations against multiple defense systems. We test these alternative hypotheses with data on host specificity and abundance of fleas parasitic on small mammals from 20 different regions. Our analyses controlled for phylogenetic influences, differences in host body surface area, and sampling effort. In most regions, we found significant positive relationships between flea abundance and either the number of host species they exploited or the average taxonomic distance among those host species. This was true whether we used mean flea abundance or the maximum abundance they achieved on their optimal host. Although fleas tended to exploit more host species in regions with either larger number of available hosts or more taxonomically diverse host faunas, differences in host faunas between regions had no clear effect on the abundance-host specificity relationship. Overall, the results support the resource breadth hypothesis: fleas exploiting many host species or taxonomically unrelated hosts achieve higher abundance than specialist fleas. We conclude that generalist parasites achieve higher abundance because of a combination of resource availability and stability.     

Cell-wall lectins during winter wheat cold hardening

The polypeptide composition and functional activity of cell-wall lectins from roots of winter wheat (Triticum aestivum L., cv. Mironovskaya 808) seedlings during cold hardening were studied. Several phases of lectin activity changes were observed, which indicates their involvement in the development of general adaptation syndrome of the cell. After 0.5-h low-temperature treatment, marked alterations occurred in the profile of protein elution: lectins with mol wts of 78 and 42.5 kD disappeared and new ones with mol wts of 72, 69, 37, and 34.5 kD appeared. It was established that 17.5-and 69-kD lectins and most lectins eluted with glucose were arabinogalactan proteins (AGP), which permitted a supposition that these lectins were involved in the interaction between the cell wall and cytoskeleton. After 7-day-long hardening, total protein content reduced and lectins with mol wts of 69 and 37 kD disappeared, which corresponded to reduced lectin activity by the end of hardening. A transient appearance of 37-and 69-kD lectins, which are AGP, might indicate their involvement in the triggering the development of plant-cell defense responses.     

Polymorphism of heterochromatin C-blocks of rye genome chromosomes in rye-wheat amphidiploids and their chromosome substitution lines

Polymorphism of heterochromatin C-blocks in chromosomes of rye genome has been studied in the F1BC1 hybrids and the D/A substitution lines of rye-wheat amphidiploids (Verasen x L374, Novosibirskaya x x L246)--secalotriticum for revealing cytogenetic markers of rye chromosomes. An increase in polymorphism for the presence and value of heterochromatin blocks in chromosomes of rye genome was shown in the F1BC1 hybrids ((Verasen x L374) x L145 x L145) and unstable genotypes of the F6BC1 chromosome substitution lines (line 118 (Novosibirskaya x L246) x Reso x Reso), line 104 ((Verasen x x L374) x Garmoniya x Garmoniya) that was related to activation of mobile genetic elements present in cereals. Heterochromatin markers of all seven chromosomes in rye genome were revealed. The polymorphism system of heterochromatin blocks may serve as a marker for specificity of the linear chromosome structure during reconstruction of synthetic cereal genomes, and as a test for cytological and morphogenetic stability of hybrid polygenomes in a series of generations.     

Partitioning of metabolizable energy intake in sucking altricial and precocial rodent pups

We partitioned the metabolizable energy intake (MEI) into energy for maintenance (ME_m) and for growth (ME_g) in sucking precocial and altricial rodent pups. Each of the two components includes energy loss due to the heat increment of feeding. ME_m of precocial pups expressed as average daily energy costs or as a proportion of MEI was greater than in altricial pups of similar size and, therefore, less energy was available for growth. Consequently, the overall energy cost (via total MEI) per unit postnatal growth of precocial pups was greater than for altricial pups of similar size. We used the proportion of calculated ME_m to that predicted by body mass as an index of precociality in rodent pups. The proportion of ME_g to MEI in precocial pups was lower than in altricial pups and was inversely related to the index of precociality.     

Evolution of host specificity in fleas: is it directional and irreversible?

Evolutionary trends in the evolution of host specificity have been the focus of much discussion but little rigorous empirical testing. On the one hand, specialization is often presumed to lead irreversibly into evolutionary dead ends and little diversification; this would mean that generalists might evolve into specialists, but not vice versa. On the other hand, low host specificity may limit the risk of extinction and provide more immediate fitness benefits to parasites, such that selection may favour evolution toward a generalist strategy. Here, we test for directionality in the evolution of host specificity using a large data set and phylogenetic information on 297 species of fleas parasitic on small mammals. The analyses determined whether host specificity, measured both as the number of host species exploited and their taxonomic diversity, was related to clade rank of the flea species, or the number of branching events between an extant species and the root of the phylogenetic tree (i.e., the total path length from the root of the tree to the species). Based on regression analyses, we found positive relationships between the number of host species used and clade rank across all 297 species, as well as within one (Hystrichopsyllidae) of four large families and one of seven large genera investigated separately; in addition, we found a positive relationship between the taxonomic diversity of host species used and clade rank in another of the seven genera. These results suggest a slight evolutionary trend of decreasing host specificity. Using a much more conservative likelihood ratio test, however, a random walk, or null model, of evolution could not be discarded in favour of the directional trends in all cases mentioned above. Still, these results suggest that host specificity may have tended to decrease in many flea lineages, a process that could have been driven by the benefits of exploiting a wide range of host species.     

Cytoskeleton-induced alterations of the lectin activity in winter wheat under cold hardening and abscisic acid (ABA)

The roots and leaves of 7-day seedlings of three winter wheat cultivars differing in frost resistant were used to study changes in lectin activity under cytoskeleton modifiers (DMSO-7%; colchicine-1 m m; oryzalin-15 microm; cytochalasin B-15 microm) of non-hardened (23 degrees C) and hardened (2-3 degrees C, 3-7 day) plants. Plants were grown with ABA (30 microm) or without ABA. Pretreatment with colchicine, oryzalin [inhibitors of microtubules (MT) polymerization], cytochalasin B [inhibitor of microfilament (MF) polymerization] increased the activity of cell wall lectins, although pretreatment with DMSO (stabilizer of microtubules) decreased the activity. Both hardening and ABA decreased the effect of the cytoskeletal modifiers. These results could be explained by the appearance of tolerant MTs with less affinity. It is probable that increase in the activity of cell wall lectins may be the compensatory mechanism which stabilizes the cytoskeleton structure in conditions tending to disrupt it. The genotype with low resistance had higher sensitivity of lectin activity to cytoskeleton modifiers than the frost resistant genotype. The results suggest that leaves have more stable MTs and MFs and stronger MT-MF binding than roots.     

Influence of inhibitors of cytoskeleton proteins on water exchange of wheat roots under the after-action of water stress

The dynamics of water molecular state and transport in winter wheat (Triticum aestivum L.) of roots different resistance cultivars was studied by a biophysical method, Nuclear Magnetic Resonance (NMR), and a physiological method, Water-Holding Capacity (WHC). The effective coefficient of water self-diffusion (D(eff)), spin-spin relaxation times (T(2)) and WHC were measured after structural modification of cytoskeleton by colchicine and cytochalasin B after the action of water stress. New information about molecular mechanisms of water state and water transport regulation determined by the influence of dynamic cytoskeleton structure has been obtained. This is very important for the development of a fundamental theory of water exchange in plants, and for the ways of its optimization under conditions of environmental stress.     

Anti-inflammatory properties of intestinal Bifidobacterium strains isolated from healthy infants

Certain Bifidobacterium strains have been shown to inhibit inflammatory responses in intestinal epithelial cells. However, the precise mechanisms of these effects, including the chemical nature of the active compounds, remain to be elucidated. Here partial characterization of the anti-inflammatory properties of Bifidobacterium strains isolated from feces of healthy infants is reported. It was found that conditioned media (CM) of all strains studied are capable of attenuating tumor necrosis factor-α (TNF-α) and lipopolysaccharide- (LPS) induced inflammatory responses in the HT-29 cell line. In contrast, neither killed bifidobacterial cells, nor cell-free extracts showed such activities. Further investigations resulted in attribution of this activity to heat-stable, non-lipophilic compound(s) resistant to protease and nuclease treatments and of molecular weight less than 3 kDa. The anti-inflammatory effects were dose- and time-dependent and associated with inhibition of IκB phosphorylation and nuclear factor-κ light chain enhancer of activated B cells (NF-κB)-dependent promoter activation. The combined treatments of cells with CMs and either LPS or TNF-α, but not with CMs alone, resulted in upregulation of transforming growth factor-β1, IκBζ, and p21(CIP) mRNAs. Our data suggest certain species-specificities of the anti-inflammatory properties of bifidobacteria. This observation should prompt additional validation studies using larger set of strains and employing the tools of comparative genomics.     

Compositional and phylogenetic dissimilarity of host communities drives dissimilarity of ectoparasite assemblages: geographical variation and scale-dependence

We tested the hypothesis that compositional and/or phylogenetic dissimilarity of host assemblages affect compositional and/or phylogenetic dissimilarity of parasite assemblages, to different extents depending on scale, using regional surveys of fleas parasitic on small mammals from 4 biogeographical realms. Using phylogenetic community dissimilarity metric, we calculated the compositional and phylogenetic dissimilarity components between all pairs of host and parasite communities within realms and hemispheres. We then quantified the effect of compositional or phylogenetic dissimilarity in host regional assemblages, and geographical distance between assemblages, on the compositional or phylogenetic dissimilarity of flea regional assemblages within a realm, respectively. The compositional dissimilarity in host assemblages strongly affected compositional dissimilarity in flea assemblages within all realms and within both hemispheres. However, the effect of phylogenetic dissimilarity of host assemblages on that of flea assemblages was mostly confined to the Neotropics and Nearctic, but was detected in both the Old and New World at the higher scale, possibly because of phylogenetic heterogeneity in flea and host faunas between realms. The clearer effect of the compositional rather than the phylogenetic component of host community dissimilarity on flea community dissimilarity suggests important roles for host switching and ecological fitting during the assembly history of flea communities.