Nestedness and β‐diversity in ectoparasite assemblages of small mammalian hosts: effects of parasite affinity,host biology and scale

We asked whether (a) variation in species composition of parasite assemblages on the same host species follows a non‐random pattern and (b) if so, manifestation of this non‐randomness across space and time differs among parasites, hosts and scales. We assessed nestedness and its contribution to β‐diversity of fleas and gamasid mite assemblages exploiting small mammals across three scales: (a) within the same region across different locations; (b) within the same location across different times and (c) across distinct geographic regions. We estimated (a) the degree of nestedness (N_COL) and (b) the proportional contribution of nestedness to the total amount of β‐diversity across locations, times and regions (β_NESP). In the majority of host species, parasite assemblages were nested significantly across all three scales. In mites, but not fleas, N_COL correlated with the contribution of nestedness to the total amount of β‐diversity. In fleas, N_COL did not differ among assemblages at the two local scales, but was significantly lower at regional scale. In mites, N_COL was the highest in assemblages at local spatial scale. β_NESP was significantly higher (a) in flea than in mite assemblages at both local scales and (b) in mite than in flea assemblages at regional scale. In fleas, β_NESP was higher at both local scales, whereas in mites it was higher at both local temporal and regional scales. Sheltering habits and geographic range of a host species did not affect either N_COL or β_NESP in flea assemblages, but both metrics significantly decreased with an increase of geographic range of a host species in mite assemblages. We conclude that flea and mite assemblages across host populations at smaller and larger spatial scales and at temporal scale were characterized by nestedness which, in turn, contributed to an important degree to the total amount of β‐diversity of these assemblages.     

Aggregative structure is the rule in communities of fleas: null model analysis

We used null models to examine patterns of species co‐occurrences in 59 communities of fleas parasitic on small mammals from 4 biogeographic realms (Afrotropics, Nearctic, Neotropics, and Palaearctic). We compared frequencies of co‐occurrences of flea species across host species with those expected by chance, using a null model approach. We used 4 tests for non‐randomness to identify pairs of species (within a community) that demonstrate significant positive or negative co‐occurrence. The majority of flea communities were non‐randomly assembled. Patterns of flea co‐occurrences on the same host species indicated aggregation but not segregation of flea species (except for the flea community of Madagascar). Although only a small fraction of species pairs were associated significantly (264 of 10, 943 species pairs according to the most liberal criterion), most of these associations were positive (except for 2 negatively associated species pairs). Significantly associated pairs were represented mainly by non‐congeneric species. The degree of non‐randomness of the entire flea community was similar among biogeographic regions, but the strength of pair‐wise association varied geographically, being the highest in the Afrotropics and the lowest in the European region of the Palaearctic.     

Feeding performance of fleas on different host species: is phylogenetic distance between hosts important?

We asked if and how feeding performance of fleas on an auxiliary host is affected by the phylogenetic distance between this host and the principal host of a flea. We investigated the feeding of 2 flea species, Parapulex chephrenis and Xenopsylla ramesis, on a principal (Acomys cahirinus and Meriones crassus, respectively) and 8 auxiliary host species. We predicted that fleas would perform better (higher proportion of fleas would feed and take larger bloodmeals) on (a) a principal rather than an auxiliary host and (b) auxiliary hosts phylogenetically closer to a principal host. Although feeding performance of fleas differed among different hosts, we found that: (1) fleas did not always perform better on a principal host than on an auxiliary host; and (2) flea performance on an auxiliary host was not negatively correlated with phylogenetic distance of this host from the principal host. In some cases, fleas fed better on hosts that were phylogenetically distant from their principal host. We concluded that variation in flea feeding performance among host species results from interplay between (a) inherent species-specific host defence abilities, (b) inherent species-specific flea abilities to withstand host defences and (c) evolutionary tightness of association between a particular host species and a particular flea species.     

Morphological and physiological changes in roots of various wheat genotypes as related to cytoskeleton disruption

A depolymerizing effect of anti-microtubule drug oryzalin on the roots of three winter wheat (Triticum aestivum L.) cultivars contrasting in their frost-resistance was studied. The influence of plant cold acclimation (3°C, 7 days) and ABA treatment (30 μM) on oryzalin action was evaluated. Plant growing in the presence of 10 μM oryzalin under optimum temperature of 23°C resulted in the root-length decrease by 19–24% and root-apex swelling. All cells, especially in the root cortex, changed their radial dimensions. The cells acquired a rounded or irregular shape and increased in size. This indicates the loss of correct cell growth polarity. Most pronounced changes in the root apex diameter and most severe linear growth suppression were observed in the cultivar of moderate frost-resistance. The roots of this cultivar contained the highest amounts of actin and tubulins, as was evident from the immunoblot analysis. The effect of oryzalin on root growth and apex swelling was correlated with the content of actin in the roots of different wheat cultivars. Cold acclimation and exogenous ABA reduced (or prevented) oryzalin action on roots in a cultivar-specific manner. The conclusion was made that the bulk of the cytoskeletal net determined the efficiency of the cytoskeletal control of plant growth and morphogenesis. During autumn and winter periods, this is important for a better adaptation to temperature fluctuations of moderately frost-resistant plants, which are characterized by a high ecological plasticity.     

Abundance patterns and coexistence processes in communities of fleas parasitic on small mammals

The abundance of a given species in a community is likely to depend on both the total abundance and diversity of other species making up that community. A large number of co-occurring individuals or co-occurring species may decrease the abundance of any given species via diffuse competition; however, indirect interactions among many co-occurring species can have positive effects on a focal species. The existence of diffuse competition and facilitation remain difficult to demonstrate in natural communities. Here, we use data on communities of fleas ectoparasitic on small mammals from 27 distinct geographical regions to test whether the abundance of any given flea species in a community is affected by either the total abundance of all other co-occurring flea species, or the species richness and/or taxonomic diversity of the flea community. At all scales of analysis, i.e. whether we compared the same flea species on different host species, or different flea species, two consistent results emerged. First, the abundance of a given flea species correlates positively with the total abundance of all other co-occurring flea species in the community. Second, the abundance of any given flea species correlates negatively with either the species richness or taxonomic diversity of the flea community. The results do not support the existence of diffuse competition in these assemblages, because the more individuals of other flea species are present on a host population, the more individuals of the focal species are there as well. Instead, we propose explanations involving either apparent facilitation among flea species via suppression of host immune defenses, or niche filtering processes acting to restrict the taxonomic composition and abundance of flea assemblages.     

Extractable Microbial DNA Pool and Microbial Activity in Paleosols of Southern Urals

An evaluation of microbial DNA pools was performed using direct quantitative isolation of DNA from contemporary soils of Southern Urals and paleosols sealed under burial mounds early in the Bronze Age more than 5000 years B.P. Significant regression dependence was found between the biomass and DNA contents in these soils (R ²= 0.97). Activity and dominant ecological strategies of microbial communities of paleosols and contemporary southern black soil were compared from growth parameters obtained by analysis of respiratory curves. The ratio of maximum specific growth rates of soil microorganisms on glucose and on yeast extract was shown to provide an auxotrophy index for soil microbial communities.