Phylogeny of the Dipus sagitta Species Complex by Nuclear Gene Sequences.

The northern three-toed jerboa Dipus sagitta had long been considered to be a single polytypic species. High genetic diversity of D. sagitta was earlier revealed on the basis of several mitochondrial and nuclear genes, and several separate species were hypothesized to occur within the taxon. However, the relationships between phylogenetic lineages have not been established because of the small sample size of nuclear genes. In the present work, a far larger set of nuclear DNA loci was used, and thus, a higher resolution of the phylogenetic tree was achieved for ten D. sagitta forms. The structure revealed for the species mainly confirmed the topology and relationships of the mtDNA lineages. Yet the mitochondrial and nuclear phylogenies were not completely consistent. Some of the D. sagitta genetic lineages were therefore assumed to be a product of reticular evolutionary processes. The taxon was concluded to be the diverse species complex D. sagitta sensu lato, in which long-diverged lineages are not always reproductively isolated.

Sex ratio in flea infrapopulations: number of fleas, host gender and host age do not have an effect.

This study set out to determine whether the sex ratio of fleas collected from host bodies is a reliable indicator of sex ratio in the entire flea population. To answer this question, previously published data on 18 flea species was used and it was tested to see whether a correlation exists between the sex ratio of fleas collected from host bodies and the sex ratio of fleas collected from host burrows. Across species, the female:male ratio of fleas on hosts correlated strongly with the female:male ratio of fleas in their burrows, with the slope of the regression overlapping 1. Controlling for flea phylogeny by independent contrasts produced similar results. It was also ascertained whether a host individual is a proportional random sampler of male and female fleas and whether the sex ratio in flea infrapopulations depends on the size of infrapopulations and on the gender and age of a host. Using field data, the sex ratio in infrapopulations of 7 flea species parasitic on 4 rodent species was analysed. Populations of 3 species (Nosopsyllus iranus, Parapulex chephrenis and Xenopsylla conformis) were significantly female-biased, whereas male bias was found in 1 species (Synosternus cleopatrae). In general, the sex ratio of fleas collected from an individual rodent did not differ significantly from the sex ratio in the entire flea population. Neither host gender, and age nor number of fleas co-occurring on a host affected (a) the sex ratio in flea infrapopulations and (b) the probability of an infrapopulation to be either female- or male-biased.

Relationships between parasite abundance and the taxonomic distance among a parasite's host species: an example with fleas parasitic on small mammals.

Opportunistic parasite species, capable of exploiting several different host species, do not achieve the same abundance on all these hosts. Parasites achieve maximum abundance on their principal host species, and lower abundances on their auxiliary host species. Taxonomic relatedness between the principal and auxiliary host species may determine what abundance a parasite can achieve on its auxiliary hosts, as relatedness should reflect similarities among host species in ecological, physiological and/or immunological characters. We tested this hypothesis with fleas (Siphonaptera) parasitic on small Holarctic mammals. We determined whether the abundance of a flea in its auxiliary hosts decreases with increasing taxonomic distance of these hosts from the principal host. Using data on 106 flea species from 23 regions, for a total of 194 flea-locality combinations, we found consistent support for this relationship, both within and across regions, and even after controlling for the potentially confounding effect of flea phylogeny. These results are most likely explained by a decrease in the efficiency of the parasite's evasive mechanisms against the host's behavioural and immune defences with increasing taxonomic distance from the principal host. Our findings suggest that host switching over evolutionary time may be severely constrained by the coupling of parasite success with the relatedness between new hosts and the original host.

Comparing various forms of morphological diversity by means of dispersion analysis (exemplified by studying measurable morphological traits variation in three rodent genera, Mammalia).

Dispersion analysis of variances (MANOVA) is shown to be of use in comparative analysis of different forms of morphological diversity expressed in measurable traits. This approach is exemplified by analysis of subgeneric, species, subspecies, sex, and individual forms of MD in rodent genera Allactaga, Alticola, and Spalax. Some conditions and limitations of the approach are discussed.

Searching for general patterns in parasite ecology: host identity versus environmental influence on gamasid mite assemblages in small mammals.

The abundance and diversity of parasites vary among different populations of host species. In some host-parasite associations, much of the variation seems to depend on the identity of the host species, whereas in other cases it is better explained by local environmental conditions. The few parasite taxa investigated to date make it difficult to discern any general pattern governing large-scale variation in abundance or diversity. Here, we test whether the abundance and diversity of gamasid mites parasitic on small mammals across different regions of the Palaearctic are determined mainly by host identity or by parameters of the abiotic environment. Using data from 42 host species from 26 distinct regions, we found that mite abundances on different populations of the same host species were more similar to each other than expected by chance, and varied significantly among host species, with half of the variance among samples explained by differences between host species. A similar but less pronounced pattern was observed for mite diversity, measured both as species richness and as the taxonomic distinctness of mite species within an assemblage. Strong environmental effects were also observed, with local temperature and precipitation correlating with mite abundance and species richness, respectively, across populations of the same host species, for many of the host species examined. These results are compared to those obtained for other groups of parasites, notably fleas, and discussed in light of attempts to find general rules governing the geographical variation in the abundance and diversity of parasite assemblages.

Resource predictability and host specificity in fleas: the effect of host body mass.

Ecological specialization is hypothesized to result from the exploitation of predictable resource bases. For parasitic organisms, one prediction is that parasites of large-bodied host species, which tend to be long-lived, should specialize on these hosts, whereas parasites of small host species, which represent more ephemeral and less predictable resources, should become generalists. We tested this prediction by quantifying the association between the level of host specificity of fleas and the mean body mass of their mammalian hosts, using published data from 2 large, distinct geographical regions (South Africa and northern North America). In general, we found supporting evidence that flea host specificity, measured either as the number of host species exploited or their taxonomic distinctness, became more pronounced with increasing host body mass. There were, however, some discrepancies among the results depending on the different measures of host specificity, the geographical region studied, or whether we used the raw values or phylogenetically independent contrasts. These are discussed with respect to other forces acting on the evolution of host specificity in parasites, as well as in the context of the regions' contrasting evolutionary histories. Overall, though, our findings indicate that the exploitation of large-bodied, and therefore long-lived, host species has promoted specialization in fleas, most likely because these hosts represent predictable resources.

Abundance and distribution of fleas on desert rodents: linking Taylor's power law to ecological specialization and epidemiology.

We investigated variation in the abundance-prevalence relationships of fleas among 17 different flea-host associations as well as among different species of hosts and fleas in the Negev desert. We explored variation in the value of exponent of Taylor's power relationship with changes in flea community size and flea specialization (host specificity and seasonal pattern of activity). We tested if a simple epidemiological model can reproduce the pattern of the abundance-prevalence relationship. We confirmed aggregated distribution of fleas within a population of host species as well as across a whole host community and the existence of a positive relationship between local flea abundance and their prevalence. Prevalence, mean abundance and variance of abundance were significantly higher in host specific than host opportunistic fleas. When ecological specialization was considered, based on a seasonal pattern of activity, these parameters were higher in year-round-active than seasonal fleas. The degree of flea specialization and flea community richness affected the pattern of the relationship between mean abundance and its variance. Power law slopes decreased with increasing richness of flea community. A simple epidemiological model based on mean flea abundance and degree of aggregation, corrected for host sample size, can predict the observed pattern of prevalence. In some cases, observed flea prevalence was higher than that predicted from the epidemiological model. The discrepancy of the observed prevalence from that predicted by the model can be explained by either a relatively low negative effect of flea parasitism on a host (at least, in terms of pathology) or strong resistance of a host to flea parasitism or both.

Covariance in species diversity and facilitation among non-interactive parasite taxa: all against the host.

Different parasite taxa exploit different host resources and are often unlikely to interact directly. It is unclear, however, whether the diversity of any given parasite taxon is indirectly influenced by that of other parasite taxa on the same host. Some components of host immune defences may operate simultaneously against all kinds of parasites, whereas investment by the host in specific defences against one type of parasite may come at the expense of defence against other parasites. We investigated the relationships between the species diversity of 4 higher taxa of ectoparasites (fleas, sucking lice, mesostigmatid mites, and ixodid ticks), and between the species richness of ectoparasites and endoparasitic helminths, across different species of rodent hosts. Our analyses used 2 measures of species diversity, species richness and taxonomic distinctness, and controlled for the potentially confounding effects of sampling effort and phylogenetic relationships among host species. We found positive pairwise correlations between the species richness of fleas, mites and ticks; however, there was no association between species richness of any of these 3 groups and that of lice. We also found a strong positive relationship between the taxonomic distinctness of ecto- and endoparasite assemblages across host species. These results suggest the existence of a process of apparent facilitation among unrelated taxa in the organization of parasite communities. We propose explanations based on host immune responses, involving acquired cross-resistance to infection and interspecific variation in immunocompetence among hosts, to account for these patterns.

[The taxonomic status of the Tuva vole Alticola (A.) tuvinicus Ognev (Mammalia: Arvicolinae)]. / Taksonomicheskii status tuvinskoi polevki Alticola (A.) tuvinicus Ognev (Mammalia: Arvicolinae).

Some forms united under species Alticola tuvinicus s. lato (4 samples), A. semicanus (1 sample), A. argentatus (8 samples) are compared by 16 characters by means of principal component method and canonical analysis. Species distinctness of A. semicanus is confirmed. Specific status of the form olchonensis is supposed. The results concerning tuvinicus s. str. and kosogol are not clear-cut: these forms may be well differentiated subspecies within either A. tuvinicus s. lato or A. argentatus.

Sampling fleas: the reliability of host infestation data.

The use of measures of host infestation as a reliable indicator of a flea population size to be used in interspecific comparisons was considered. The abundance of fleas collected from host bodies and collected from host burrows was compared among 55 flea species, controlling for the effect of flea phylogeny. The mean number of fleas on host bodies correlated positively with the mean number of fleas in host burrows/nests both when the entire data pool was analysed and for separate subsets of data on 'fur' fleas and 'nest' fleas. This was also true for a within-host (Microtus californicus) between-flea comparison. The results of this study demonstrate that, in general, the index of host body infestation by fleas can be used reliably as an indicator of the entire population size.

Annual cycles of four flea species in the central Negev desert.

Bionomics of fleas (Siphonaptera) parasitizing rodent hosts, mostly the gerbil Gerbillus dasyurus (Wagner) and the jird Meriones crassus Sundevall (Gerbillidae), were investigated in the central Negev desert of Israel. Populations were sampled weekly (by Sherman trapping of hosts) from August 2000 to July 2001. Among 1055 fleas of nine species captured, four species predominated (94%). Two species of Pulicidae, Xenopsylla dipodilli Smit and X. ramesis (Rothschild), reproduced perennially, whereas adults of Nosopsyllus iranus theodori Smit (Ceratophyllidae) and Stenoponia tripectinata medialis Jordan (Hystrichopsyllidae) occurred only in cool months (October-March). During their main activity season on the most infested host species (estimated from > 300 trap-nights/month), prevalence of these four flea species reached 40-70%, 20-30%, 100% and 50-70%, respectively, with infestation intensities of 2-2.7, 7-12, 2-3.5 and 2.5-7 fleas per infested rodent, respectively. Xenopsylla dipodilli oviposition peaked during autumn with parous rate > 80% by September-October. During December-April, the majority of X. dipodilli females were immature and/or nulliparous (defined as having mature ovaries but no follicular relics). In contrast, X. ramesis had two reproductive peaks, in mid-spring and autumn, evidenced by the influx of immature females in late spring and summer (30-40%) and in winter (20-30%) after maximal parous rates: 80-100% in March-April and 95-100% in October-November. Nosopsyllus iranus theodori and Stenoponia tripectinata medialis adults occurred only during cool months. At the beginning of activity, during October-November, the sex ratio of N. i. theodori was strongly biased to females (86%) that were immature and/or nulliparous. In winter, adult females were 52-65% parous and 10-32% immature. In March, as the adult population of N. i. theodori declined, 78% of females were parous and 12% immature. Seasonal activity of S. t. medialis (November-March) was shorter than for the other three species; females were predominantly nulliparous in November (80%), after which the proportion of parous females increased gradually to 84% in February. Two females of S. t. medialis collected in March were mature but nulliparous, suggesting that this species of flea might 'oversummer' (as pupae or teneral adults) in the cocooned stage.

Host-habitat relations as an important determinant of spatial distribution of flea assemblages (Siphonaptera) on rodents in the Negev Desert.

We studied flea assemblages on rodents in different habitats of the Ramon erosion cirque in the Negev Desert to examine whether host-habitat relations influence flea spatial distribution. Eleven flea species parasitizing 12 rodent species were recorded. There was significant positive relationship between flea species richness and body mass of the host species; no relationships were found between relative richness of flea assemblage and either the number of habitats occupied by the host species or the size of host geographical range. The differences in pattern of flea parasitism among habitat types within host species were determined by both environmental features of a habitat and the specific pattern of habitat use by rodents. There was replacement of Xenopsylla conformis by Xenopsylla ramesis on Meriones crassus and Gerbillus dasyurus among different habitats. The results of ordination of the flea collections from each individual host demonstrated that the flea assemblages were segregated mainly along 4 axes, which explained 86% of total variance. Each of the ordination axes corresponded with a change in flea species composition. The directions of these changes were (1) among-hosts within a habitat and (2) among-habitats within a host.