Body size distribution in flea communities harboured by Siberian small mammals as affected by host species,host sex and scale: scale matters the most

The distribution of body sizes of co-existing species at different scales reflects the scale-dependency of rules governing community assembly. Investigation of among-scale variation in community assembly is impeded by the methodological difficulties of establishing scale boundaries. Studying body size distribution in parasites allows us to avoid the problem of defining scale because parasite communities have clear boundaries and are represented by infracommunities (an assemblage harboured by an individual host), component communities (an assemblage harboured by a host population in a locality), and compound communities (an assemblage harboured by a host community in a locality). We studied body size distribution of fleas parasitic on small mammals in Western Siberia using null models. We asked whether body size ratios (i.e., size differences among coexisting species) in these communities demonstrate non-random segregated or aggregated patterns and whether these patterns differ between (a) host species, (b) host sexes and (c) infra-, component, and compound communities. No effect of host sex on the pattern of body size distribution was found at either scale, whereas an effect of host species was found in infracommunities only. We found a tendency of flea infracommunities toward segregation, whereas body size distributions in component and compound communities were consistently aggregated. We propose that the former could be caused by apparent competition (=?negative indirect interactions among fleas due to shared natural enemy, i.e. a host), whereas we the latter could be explained by host- and environment-associated filtering (=?factors restricting co-occurring species to a certain subset that share certain traits). We conclude that, counterintuitively, flea communities at the lowest hierarchical scale are mainly governed by evolutionary mechanisms, whereas communities at higher scale are assembled via ecological processes.     

Organization of fusicoccin receptor in higher plant plasma membrane: relationship between affinity and molecular mass

Higher plant plasma membranes carry receptors of different affinity for the phytotoxin fusicoccin. Reception of fusicoccin involves proteins belonging to the highly conserved 14-3-3 family, but the complete structure of the fusicoccin receptor (FCR) is unknown. Using radiation inactivation analysis, we estimated the molecular masses of low-affinity and high-affinity FCR at 63 +/- 7 and 130 +/- 15 kD, respectively. The dose dependences of receptor inactivation indicate that microsomal specimens contain "silent" FCRs of 420 +/- 90 kD in amounts commensurate with that of the active FCRs. Both low- and high-affinity FCRs are inactivated by hydrolytic enzymes from the outer surface of the plasma membrane, and impairment of protoplast integrity causes an irreversible transition of the low-affinity binding site into the high-affinity one. A scheme is proposed for the organization of different types of FCR in the plasma membrane, implying that the membrane affinity for fusicoccin reflects the interaction between proteins in the FCR complex.     

The dependence [correction of dependance] between the mineral content in skeletal bones and the state of periodontium in women in case of hypoestrogenemia

Women with hypoestrogenemia either through secondary amenorrhea of unknown etiology, post-menopausal period or removed ovaries due to benign tumor were studied to determine if there is a relationship between the hormone state of women and their skeletal and periodontal tissues. Results indicated that women with hypoestrogenemia showed more pronounced changes in periodontium tissue as compared to normal women. These women also showed evidence of periodontium injury. These results are discussed along with implications for treatment and preventive measures.     

Level of energy intake affects the estrous cycle in Sundevall's jird (Meriones crassus)

Effects of energy intake on the estrous cycle of the desert gerbillid, Sundevall's jird (Meriones crassus; 80 g; n=22) were studied. Females were offered either maintenance or below maintenance levels of millet seeds and ad lib. Atriplex halimus leaves and stems; drinking water was not available. Vaginal smears were used to determine sexual stage. We hypothesized that the estrous cycle ceases at low levels of energy intake and commences when sufficient energy is available. Females lost body mass linearly with a decrease in metabolizable energy intake. Estrous cycle averaged 4.46 d at maintenance energy intake but increased to an average of 7.81 d at 70% of maintenance energy intake. A cessation of the cycle occurred at an energy intake below 70% of maintenance requirements, which resulted in a body mass loss of more than 1% per day. More variability in the length of the different stages of the cycle was found with lower levels of energy intake. When offered ad lib. millet seeds and A. halimus (n=14), recovery to the normal cycle was attained within 10 d by 43% of the females and within 16 d by the rest of the females. Recovery time was longest in females that previously had the lowest energy intake. We concluded that the estrous cycle of M. crassus is sensitive to energy intake. With restricted energy intake, the estrous cycle and reproductive activities cease but can be restored with provision of adequate energy. This strategy ensures that reproduction occurs when conditions of food availability and body condition of the females are favorable.     

The role of muscarinic cholinoreceptors in the retrieval of the instrumental food conditioned reflex in cats

It was demonstrated in cat experiments that impairment of the retrieval of appetitive instrumental conditioning observed after systemic administration of antagonists of muscarinic central cholinoreceptors scopolamine (a nonselective M1 antagonist) and trihexyphenidyl (relatively selective M1 antagonist) could be connected with central and peripheral side effects of these antagonists. It was established that in case of the absence of side effects (low doses of trihexyphenidyl, 1 mg/kg) the blockade of M1-cholinoreceptors led either to selective fall-off of the motor instrumental reaction with in the presence of contextual behavior and other conditioned reactions or the appearance of errors that seemingly was indicative of the disturbance of triggering and realization of the motor program as the most important component of conditioning performance. The systemic injection of trihexyphenidyl (10 mg/kg), scopolamine (0.03 and 0.06 mg/kg) and nonselective peripheral antagonist methylscopolamine (0.03 mg/kg) led to changes in the general functional state (disorders in the emotional and motivational sphere), the expression of which depended on the individual sensitivity to anticholinergic drugs. The disturbance of CR retrieval observed in parallel with side reactions was characterized by a complete cessation of conditioning and apparently was not associated with memory deterioration.     

Interaction of SecB and SecA with the N-Terminal Region of Mature Alkaline Phosphatase on Its Secretion in Escherichia coli

Export-specific chaperone SecB and translocational ATPase SecA catalyze the cytoplasmic steps of Sec-dependent secretion in Escherichia coli. Their effects on secretion of periplasmic alkaline phosphatase (PhoA) were shown to depend on the N-terminal region of the mature PhoA sequence contained in the PhoA precursor. Amino acid substitutions in the vicinity of the signal peptide (positions +2, +3) not only dramatically inhibited secretion, but they also reduced its dependence on SecB. Immunoprecipitation reported their impaired binding with mutant prePhoA. The results testified that SecB and SecA interact with the mature PhoA region located close to the signal peptide in prePhoA.     

Cooperative activity of motor and frontal cortex neurons in trained cats systemically administered M-cholinoreceptor blockers]

It was shown previously that peripherally administered antagonists of the central 1 M-cholinoreceptors led to a selective impairment of bar-pressing response in a food-reinforced operant conditioned task but did not alter contextual behavior and functions such as motivation, perception, and locomotion. To obtain information about the central mechanisms of the conditioning impairment, we recorded simultaneously the extracellular multiunit activity from the frontal and motor neocortical areas of five cats trained to acquisition criteria in a food-reinforced operant conditioning task. Multiunit recordings were performed drur 1) normal conditioning; 2) conditioning during subcutaneous administration of muscarinic antagonists scopolamine (0.03 mg/kg), trihexyphenidyl (1 mg/kg), and methylscopolamine (0.03 mg/kg). Autocorrelation analysis showed that scopolamine and trihexyphenidyl but not methylscopolamine led to a significant increase in the tendency of cortical cells to fire in a cyclic way (i.e., the shift of the firing pattern from a single-spike discharge to burst, rhythmic, or rhythmic-burst discharge) both in the motor and frontal areas. Cross-correlation analysis showed that the bursting and rhythmic-bursting cells synchronized their activity within and (in a number of cases) between the cortical areas. These changes in the neuronal activity within the motor cortex and frontal cortex were accompanied by a significant decrease in the functional connectivity both inside and between the cortical areas in parallel with selective impairment of the conditioned response.     

Species co-occurrences in ectoparasite infracommunities: Accounting for confounding factors associated with space,time, and host community composition

1. We explored patterns of co-occurrence of ectoparasite species on individual hosts from Central Europe (Slovakia) and South America (Argentina) within and between higher taxa while controlling for confounding factors associated with variation between host individuals and host species, as well as spatial and temporal variation. We used a recently developed statistical approach, the hierarchical modelling of species communities. 2. Although the probability of pairwise associations of the majority of species in both regions did not differ from random, all significant species associations in Slovakia were positive, whereas the only three significant species associations in Argentina were negative. On average, associations between ectoparasite species belonging to different higher taxa were positive in Slovakia and negative in Argentina. 3. At the host species level, both positive and negative associations between species were detected in all higher taxa. This was also true for ectoparasite co-occurrences in the same site, habitat, or year; although the number of co-occurring species pairs with high posterior probability was much greater in Slovakia than in Argentina. 4. We conclude that consideration of species co-occurrences across the entire multi-host assemblage and control for confounding spatial and temporal factors provided important insights into parasite community structure.