Irina Khokhlova - Academia.edu (original) (raw)

Papers by Irina Khokhlova

Research paper thumbnail of Effects of parasite pressure on parasite mortality and reproductive output in a rodent-flea system: inferring host defense trade-offs

Parasitology Research, 2016

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Research paper thumbnail of On the biology of Sundevall's jird (Meriones crassus Sundevall, 1842) (Rodentia : Gerbillidae) in the Negev Highlands, Israel

Mammalia, 1996

Data on the biology of Meriones crassus in the Central Negev are presented based on 3.5 years of ... more Data on the biology of Meriones crassus in the Central Negev are presented based on 3.5 years of field observations and data on mark-recapture of 392 individuals. Constant sexual differences in body mass were shown, whereas seasonal variation of body mass was observed in years with low food availability only. Reproduction was observed from January to September with peaks in February-May and August. Duration of pregnancy was 18-22 days and the litter size was 3-7 pups. Details of postnatal development are provided. The dynamics of age structure was related to the patterns of reproduction. Longevity in the field was up to two years and in captivity it was more than three years. The species is relatively low habitat-specific : it only avoids rocks and occurs in all other habitats. The highest density (up to four individuals per 1 ha) was found in sand dunes. Habitat selection is seasonally variable and is determined by different environmental factors in different seasons. Pattern of individual space use is characterized by periodical strong territorial conservatism. Observations on radio-implanted M. crassus showed that an individual remained in close vicinity of its burrow during the entire night for a relatively long period. Then, it moved to another burrow where it stayed for three-seven nights. Jirds had relatively short periods of aboveground activity (5-10 % of dark time) ; activity was restricted to the area under shrub canopy just near the burrow. All individuals were highly infested by fleas. Four flea species were recorded. The most common flea in most habitats was Xenopsylla conformis, whereas in wadis covered with loess it was replaced by Xenopsylla ramesis. Résumé.-La capture-recapture de 392 individus marqués de Meriones crassus, et 3,5 années d'observation ont permis d'obtenir des données sur la biologie de cette espèce dans le Neguev central. Il ya des différences contantes de poids du corps selon le sexe, et une variation de ce poids lorqu'il y a peu de nourriture disponible. La reproduction a été constatée de janvier à septembre, avec des pics entre février et mai, et en août. La durée de gestation a été de 18 à 22 jours et les portées comprenait 3 à 7 jeunes dont on a étudié le développement post-natal. La dynamique de la structure d'âge était liée à celle de la reproduction. La longévité dans la nature était supérieure à 2 ans, et à plus de 3 ans en captivité. L'espèce a un habitat peu spécifique : elle évite les rochers mais vit dans tous les autres habitats. La densité la plus élevée (plus de 4 individus à l'hectare) a été constatée dans les dunes. Le choix de l'habitat dépend de la saison et de facteurs environnementaux. Le type d'utilisation de l'espace individuel est caractérisé par un fort et périodique conserva

Research paper thumbnail of Trait-based and phylogenetic associations between parasites and their hosts: a case study with small mammals and fleas in the Palearctic

Research paper thumbnail of Notes on the biology of the bushy-tailed jird, Sekeetamys calurus, in the central Negev, Israel

Research paper thumbnail of Biology of Wagner's gerbil Gerbillus dasyurus (Wagner, 1842)(Rodentia: Gerbillidae) in the Negev Highlands, Israel

Research paper thumbnail of Assembly rules of ectoparasite communities across scales: Combining patterns of abiotic factors, host composition, geographic space, phylogeny and traits

Research paper thumbnail of Phylogenetic Signal in Module Composition and Species Connectivity in Compartmentalized Host-Parasite Networks

The American Naturalist, 2012

Across different taxa, networks of mutualistic or antagonistic interactions show consistent archi... more Across different taxa, networks of mutualistic or antagonistic interactions show consistent architecture. Most networks are modular, with modules being distinct species subsets connected mainly with each other and having few connections to other modules. We investigate the phylogenetic relatedness of species within modules and whether a phylogenetic signal is detectable in the within-and among-module connectivity of species using 27 mammal-flea networks from the Palaearctic. In the 24 networks that were modular, closely related hosts co-occurred in the same module more often than expected by chance; in contrast, this was rarely the case for parasites. The within-and among-module connectivity of the same host or parasite species varied geographically. However, among-module but not within-module connectivity of host and parasites was somewhat phylogenetically constrained. These findings suggest that the establishment of host-parasite networks results from the interplay between phylogenetic influences acting mostly on hosts and local factors acting on parasites, to create an asymmetrically constrained pattern of geographic variation in modular structure. Modularity in host-parasite networks seems to result from the shared evolutionary history of hosts and by trait convergence among unrelated parasites. This suggests profound differences between hosts and parasites in the establishment and functioning of bipartite antagonistic networks.

Research paper thumbnail of Ectoparasitic “Jacks‐of‐All‐Trades”: Relationship between Abundance and Host Specificity in Fleas (Siphonaptera) Parasitic on Small Mammals

The American Naturalist, 2004

All rights reserved. taxonomic distance among those host species. This was true whether we used m... more All rights reserved. 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.

Research paper thumbnail of What are the factors determining the probability of discovering a flea species (Siphonaptera)?

Parasitology Research, 2005

Our aim was to determine which of four variables (number of host species exploited by the parasit... more Our aim was to determine which of four variables (number of host species exploited by the parasite, taxonomic distinctness of these hosts, geographic range of the principal host, and year of description of this host) was the best predictor of description date of fleas. The study used previously published data on 297 flea species parasitic on 197 species of small mammals from 34 different regions of the Holarctic and one region from the Neotropics. We used both simple linear and multiple regressions to evaluate the relationships between the four predictor variables and the year of flea description, on species values as well as on phylogenetically independent contrasts. Whether or not the analyses controlled for flea phylogeny, all predictor variables correlated significantly with year of flea description when tested separately. In multiple regressions, however, the number of exploited host species was the best predictor of the date of flea description, with the geographic range of the principal host species as well as the date of its description having a lesser, though significant, influence. Overall, our results indicate that a flea species is more likely to be discovered and described early if its biological characteristics (exploitation of many host species) and those of its hosts (long-known to science, broad geographic distributions) increase its chances of being included in a collection. Because the variables we investigated only explained about 10-11% of the variation in year of description among flea species, other factors must be important, such as temporal variability in the activity of flea taxonomists.

Research paper thumbnail of How are the host spectra of hematophagous parasites shaped over evolutionary time? Random choice vs selection of a phylogenetic lineage

Parasitology Research, 2008

Among generalist parasites, some species exploit only hosts from one particular phylogenetic line... more Among generalist parasites, some species exploit only hosts from one particular phylogenetic lineage, whereas others can use a broader phylogenetic range of hosts, often seemingly using a random subset of the locally available host species. The latter type of generalist parasites should have greater opportunities to expand their geographical range and should not be restricted to stable and predictable host species because they are less prone to extinction than generalist parasites limited to a phylogenetically narrower host spectrum. We analyzed the diversity skewness of the host spectrum of 21 flea species from South Africa and 39 flea species from northern North America. Diversity skewness measures the balance in the shape of the phylogenetic tree of a set of species: the greater the skew, the more one lineage is overrepresented in an assemblage. When compared to a null expectation, i.e., random selections from the locally available pool of host species, the host spectra of most fleas was not more or less skewed than that expected by chance, though there were a few exceptions. Across South African fleas, the diversity skewness of the host spectrum was strongly negatively correlated with the size of a flea's geographic range; this relationship was not seen among North American flea species. There was no evidence among either set of fleas that average host body mass (a surrogate measure of host life span) correlated with the diversity skewness of the host spectrum. These findings are discussed with respect to the evolution of host specificity, its measurement, and historical differences between the two geographic areas considered.

Research paper thumbnail of Resource predictability and host specificity in fleas: the effect of host body mass

Parasitology, 2006

Ecological specialization is hypothesized to result from the exploitation of predictable resource... more 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.

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

Parasitology, 2008

SUMMARYThis study set out to determine whether the sex ratio of fleas collected from host bodies ... more SUMMARYThis 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 rode...

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

Parasitology, 2012

SUMMARYWe tested the hypothesis that compositional and/or phylogenetic dissimilarity of host asse... more SUMMARYWe 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 dissimila...

Research paper thumbnail of Is abundance a species attribute? An example with haematophagous ectoparasites

Oecologia, 2006

Population density is a fundamental property of a species and yet it varies among populations of ... more Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that diVer among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of Xeas ectoparasitic on small mammals. The data included samples of 548 Xea populations, representing 145 Xea species and obtained from 48 diVerent geographical regions. Abundances of the same Xea species on the same host species, but in diVerent regions, were more similar to each other than expected by chance, and varied signiWcantly among Xea species, with 46% of the variation among samples accounted by diVerences between Xea species. Thus, estimates of abundance are repeatable within the same Xea species. The same repeatability was also observed, but to a lesser extent, across Xea genera, tribes and subfamilies. Independently of the identity of the Xea species, abundance values recorded on the same host species, or in the same geographical region, also showed signiWcant statistical repeatability, though not nearly as strong as that associated with abundance values from the same Xea species. There were also no strong indications that regional diVerences in abiotic variables were an important determinant of variation in abundance of a given Xea species on a given host species. Abundance thus appears to be a true species trait in Xeas, although it varies somewhat within bounds set by species-speciWc life history traits.

Research paper thumbnail of Annual cycles of four flea species in the central Negev desert

Medical and Veterinary Entomology, 2002

Bionomics of fleas (Siphonaptera) parasitizing rodent hosts, mostly the gerbil Gerbillus dasyurus... more 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.

Research paper thumbnail of Sampling fleas: the reliability of host infestation data

Medical and Veterinary Entomology, 2004

The use of measures of host infestation as a reliable indicator of a flea population size to be u... more 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.

Research paper thumbnail of A Small Gerbil That Maximizes Intake of Energy from Low-Energy Food

Journal of Mammalogy, 1997

Research paper thumbnail of Geographical patterns of abundance: testing expectations of the ‘abundance optimum’ model in two taxa of ectoparasitic arthropods

Journal of Biogeography, 2008

Aim The 'abundance optimum' hypothesis predicts that species abundance peaks in the locality with... more Aim The 'abundance optimum' hypothesis predicts that species abundance peaks in the locality with the most favourable conditions and decreases with an increase of distance from that locality. We tested this prediction for 9 fleas and 13 gamasid mite species. Location We used published data on fleas and gamasid mites that are parasitic on small mammals throughout the Palaearctic. Methods For each ectoparasite, we computed the correlation between the relative abundance on its principal host species in a region and the distance from that region to the region of maximum abundance. Then, the correlation coefficients were used in a meta-analysis. We also made a cross-species comparison between relative abundances in localities (a) closest to and (b) furthest from the locality of maximum abundance. Results Although the relationship between the relative abundance in a region and the distance from that region to the region of maximum abundance was negative in 19 out of 22 ectoparasites, it was only statistically significant in three of them. However, a meta-analysis of coefficients of correlations across all species revealed a significant negative effect of the distance from the region of maximum abundance on relative abundance in a particular region. A cross-species comparison between relative abundances in the localities closest to and furthest from the locality of maximum abundance demonstrated that the former were significantly higher than the latter. Main conclusions A lack of strict host specificity in the ectoparasites studied, and the absence of any strong spatial correlations among the environmental variables affecting ectoparasite reproduction and abundance, may provide an explanation for the spatial independence in abundance values of most species. However, a preference for a particular host even in host-opportunistic parasites combined with species-specific environmental preferences could be the reason behind the weak, but significant, negative abundance-distance relationship across species. The contradiction between results obtained when separate species were considered and when the overall pattern was analysed across species suggests that there exists a general underlying spatial pattern that can often be masked by other factors.

Research paper thumbnail of Latitudinal gradients in niche breadth: empirical evidence from haematophagous ectoparasites

Journal of Biogeography, 2008

The most pervasive patterns in biogeography are those related to latitude. In particular, the mos... more The most pervasive patterns in biogeography are those related to latitude. In particular, the most conspicuous of these patterns, such as latitudinal gradients in species richness and geographic range size, have been extensively studied and documented (

Research paper thumbnail of Flea species richness and parameters of host body, host geography and host ‘milieu’

Journal of Animal Ecology, 2004

... Gregory, RD, Keymer, AE & Harvey, PH (1996) Helminth parasite richnes... more ... Gregory, RD, Keymer, AE & Harvey, PH (1996) Helminth parasite richness among vertebrates. ... McTier, TL, George, JE & ... University of Chicago Press, Chicago. Reiczigel, J. & Rózsa, L. (1998) Host-mediated site-segregation of ectoparasites: an individual-based simulation study ...

Research paper thumbnail of Effects of parasite pressure on parasite mortality and reproductive output in a rodent-flea system: inferring host defense trade-offs

Parasitology Research, 2016

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Research paper thumbnail of On the biology of Sundevall's jird (Meriones crassus Sundevall, 1842) (Rodentia : Gerbillidae) in the Negev Highlands, Israel

Mammalia, 1996

Data on the biology of Meriones crassus in the Central Negev are presented based on 3.5 years of ... more Data on the biology of Meriones crassus in the Central Negev are presented based on 3.5 years of field observations and data on mark-recapture of 392 individuals. Constant sexual differences in body mass were shown, whereas seasonal variation of body mass was observed in years with low food availability only. Reproduction was observed from January to September with peaks in February-May and August. Duration of pregnancy was 18-22 days and the litter size was 3-7 pups. Details of postnatal development are provided. The dynamics of age structure was related to the patterns of reproduction. Longevity in the field was up to two years and in captivity it was more than three years. The species is relatively low habitat-specific : it only avoids rocks and occurs in all other habitats. The highest density (up to four individuals per 1 ha) was found in sand dunes. Habitat selection is seasonally variable and is determined by different environmental factors in different seasons. Pattern of individual space use is characterized by periodical strong territorial conservatism. Observations on radio-implanted M. crassus showed that an individual remained in close vicinity of its burrow during the entire night for a relatively long period. Then, it moved to another burrow where it stayed for three-seven nights. Jirds had relatively short periods of aboveground activity (5-10 % of dark time) ; activity was restricted to the area under shrub canopy just near the burrow. All individuals were highly infested by fleas. Four flea species were recorded. The most common flea in most habitats was Xenopsylla conformis, whereas in wadis covered with loess it was replaced by Xenopsylla ramesis. Résumé.-La capture-recapture de 392 individus marqués de Meriones crassus, et 3,5 années d'observation ont permis d'obtenir des données sur la biologie de cette espèce dans le Neguev central. Il ya des différences contantes de poids du corps selon le sexe, et une variation de ce poids lorqu'il y a peu de nourriture disponible. La reproduction a été constatée de janvier à septembre, avec des pics entre février et mai, et en août. La durée de gestation a été de 18 à 22 jours et les portées comprenait 3 à 7 jeunes dont on a étudié le développement post-natal. La dynamique de la structure d'âge était liée à celle de la reproduction. La longévité dans la nature était supérieure à 2 ans, et à plus de 3 ans en captivité. L'espèce a un habitat peu spécifique : elle évite les rochers mais vit dans tous les autres habitats. La densité la plus élevée (plus de 4 individus à l'hectare) a été constatée dans les dunes. Le choix de l'habitat dépend de la saison et de facteurs environnementaux. Le type d'utilisation de l'espace individuel est caractérisé par un fort et périodique conserva

Research paper thumbnail of Trait-based and phylogenetic associations between parasites and their hosts: a case study with small mammals and fleas in the Palearctic

Research paper thumbnail of Notes on the biology of the bushy-tailed jird, Sekeetamys calurus, in the central Negev, Israel

Research paper thumbnail of Biology of Wagner's gerbil Gerbillus dasyurus (Wagner, 1842)(Rodentia: Gerbillidae) in the Negev Highlands, Israel

Research paper thumbnail of Assembly rules of ectoparasite communities across scales: Combining patterns of abiotic factors, host composition, geographic space, phylogeny and traits

Research paper thumbnail of Phylogenetic Signal in Module Composition and Species Connectivity in Compartmentalized Host-Parasite Networks

The American Naturalist, 2012

Across different taxa, networks of mutualistic or antagonistic interactions show consistent archi... more Across different taxa, networks of mutualistic or antagonistic interactions show consistent architecture. Most networks are modular, with modules being distinct species subsets connected mainly with each other and having few connections to other modules. We investigate the phylogenetic relatedness of species within modules and whether a phylogenetic signal is detectable in the within-and among-module connectivity of species using 27 mammal-flea networks from the Palaearctic. In the 24 networks that were modular, closely related hosts co-occurred in the same module more often than expected by chance; in contrast, this was rarely the case for parasites. The within-and among-module connectivity of the same host or parasite species varied geographically. However, among-module but not within-module connectivity of host and parasites was somewhat phylogenetically constrained. These findings suggest that the establishment of host-parasite networks results from the interplay between phylogenetic influences acting mostly on hosts and local factors acting on parasites, to create an asymmetrically constrained pattern of geographic variation in modular structure. Modularity in host-parasite networks seems to result from the shared evolutionary history of hosts and by trait convergence among unrelated parasites. This suggests profound differences between hosts and parasites in the establishment and functioning of bipartite antagonistic networks.

Research paper thumbnail of Ectoparasitic “Jacks‐of‐All‐Trades”: Relationship between Abundance and Host Specificity in Fleas (Siphonaptera) Parasitic on Small Mammals

The American Naturalist, 2004

All rights reserved. taxonomic distance among those host species. This was true whether we used m... more All rights reserved. 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.

Research paper thumbnail of What are the factors determining the probability of discovering a flea species (Siphonaptera)?

Parasitology Research, 2005

Our aim was to determine which of four variables (number of host species exploited by the parasit... more Our aim was to determine which of four variables (number of host species exploited by the parasite, taxonomic distinctness of these hosts, geographic range of the principal host, and year of description of this host) was the best predictor of description date of fleas. The study used previously published data on 297 flea species parasitic on 197 species of small mammals from 34 different regions of the Holarctic and one region from the Neotropics. We used both simple linear and multiple regressions to evaluate the relationships between the four predictor variables and the year of flea description, on species values as well as on phylogenetically independent contrasts. Whether or not the analyses controlled for flea phylogeny, all predictor variables correlated significantly with year of flea description when tested separately. In multiple regressions, however, the number of exploited host species was the best predictor of the date of flea description, with the geographic range of the principal host species as well as the date of its description having a lesser, though significant, influence. Overall, our results indicate that a flea species is more likely to be discovered and described early if its biological characteristics (exploitation of many host species) and those of its hosts (long-known to science, broad geographic distributions) increase its chances of being included in a collection. Because the variables we investigated only explained about 10-11% of the variation in year of description among flea species, other factors must be important, such as temporal variability in the activity of flea taxonomists.

Research paper thumbnail of How are the host spectra of hematophagous parasites shaped over evolutionary time? Random choice vs selection of a phylogenetic lineage

Parasitology Research, 2008

Among generalist parasites, some species exploit only hosts from one particular phylogenetic line... more Among generalist parasites, some species exploit only hosts from one particular phylogenetic lineage, whereas others can use a broader phylogenetic range of hosts, often seemingly using a random subset of the locally available host species. The latter type of generalist parasites should have greater opportunities to expand their geographical range and should not be restricted to stable and predictable host species because they are less prone to extinction than generalist parasites limited to a phylogenetically narrower host spectrum. We analyzed the diversity skewness of the host spectrum of 21 flea species from South Africa and 39 flea species from northern North America. Diversity skewness measures the balance in the shape of the phylogenetic tree of a set of species: the greater the skew, the more one lineage is overrepresented in an assemblage. When compared to a null expectation, i.e., random selections from the locally available pool of host species, the host spectra of most fleas was not more or less skewed than that expected by chance, though there were a few exceptions. Across South African fleas, the diversity skewness of the host spectrum was strongly negatively correlated with the size of a flea's geographic range; this relationship was not seen among North American flea species. There was no evidence among either set of fleas that average host body mass (a surrogate measure of host life span) correlated with the diversity skewness of the host spectrum. These findings are discussed with respect to the evolution of host specificity, its measurement, and historical differences between the two geographic areas considered.

Research paper thumbnail of Resource predictability and host specificity in fleas: the effect of host body mass

Parasitology, 2006

Ecological specialization is hypothesized to result from the exploitation of predictable resource... more 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.

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

Parasitology, 2008

SUMMARYThis study set out to determine whether the sex ratio of fleas collected from host bodies ... more SUMMARYThis 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 rode...

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

Parasitology, 2012

SUMMARYWe tested the hypothesis that compositional and/or phylogenetic dissimilarity of host asse... more SUMMARYWe 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 dissimila...

Research paper thumbnail of Is abundance a species attribute? An example with haematophagous ectoparasites

Oecologia, 2006

Population density is a fundamental property of a species and yet it varies among populations of ... more Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that diVer among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of Xeas ectoparasitic on small mammals. The data included samples of 548 Xea populations, representing 145 Xea species and obtained from 48 diVerent geographical regions. Abundances of the same Xea species on the same host species, but in diVerent regions, were more similar to each other than expected by chance, and varied signiWcantly among Xea species, with 46% of the variation among samples accounted by diVerences between Xea species. Thus, estimates of abundance are repeatable within the same Xea species. The same repeatability was also observed, but to a lesser extent, across Xea genera, tribes and subfamilies. Independently of the identity of the Xea species, abundance values recorded on the same host species, or in the same geographical region, also showed signiWcant statistical repeatability, though not nearly as strong as that associated with abundance values from the same Xea species. There were also no strong indications that regional diVerences in abiotic variables were an important determinant of variation in abundance of a given Xea species on a given host species. Abundance thus appears to be a true species trait in Xeas, although it varies somewhat within bounds set by species-speciWc life history traits.

Research paper thumbnail of Annual cycles of four flea species in the central Negev desert

Medical and Veterinary Entomology, 2002

Bionomics of fleas (Siphonaptera) parasitizing rodent hosts, mostly the gerbil Gerbillus dasyurus... more 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.

Research paper thumbnail of Sampling fleas: the reliability of host infestation data

Medical and Veterinary Entomology, 2004

The use of measures of host infestation as a reliable indicator of a flea population size to be u... more 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.

Research paper thumbnail of A Small Gerbil That Maximizes Intake of Energy from Low-Energy Food

Journal of Mammalogy, 1997

Research paper thumbnail of Geographical patterns of abundance: testing expectations of the ‘abundance optimum’ model in two taxa of ectoparasitic arthropods

Journal of Biogeography, 2008

Aim The 'abundance optimum' hypothesis predicts that species abundance peaks in the locality with... more Aim The 'abundance optimum' hypothesis predicts that species abundance peaks in the locality with the most favourable conditions and decreases with an increase of distance from that locality. We tested this prediction for 9 fleas and 13 gamasid mite species. Location We used published data on fleas and gamasid mites that are parasitic on small mammals throughout the Palaearctic. Methods For each ectoparasite, we computed the correlation between the relative abundance on its principal host species in a region and the distance from that region to the region of maximum abundance. Then, the correlation coefficients were used in a meta-analysis. We also made a cross-species comparison between relative abundances in localities (a) closest to and (b) furthest from the locality of maximum abundance. Results Although the relationship between the relative abundance in a region and the distance from that region to the region of maximum abundance was negative in 19 out of 22 ectoparasites, it was only statistically significant in three of them. However, a meta-analysis of coefficients of correlations across all species revealed a significant negative effect of the distance from the region of maximum abundance on relative abundance in a particular region. A cross-species comparison between relative abundances in the localities closest to and furthest from the locality of maximum abundance demonstrated that the former were significantly higher than the latter. Main conclusions A lack of strict host specificity in the ectoparasites studied, and the absence of any strong spatial correlations among the environmental variables affecting ectoparasite reproduction and abundance, may provide an explanation for the spatial independence in abundance values of most species. However, a preference for a particular host even in host-opportunistic parasites combined with species-specific environmental preferences could be the reason behind the weak, but significant, negative abundance-distance relationship across species. The contradiction between results obtained when separate species were considered and when the overall pattern was analysed across species suggests that there exists a general underlying spatial pattern that can often be masked by other factors.

Research paper thumbnail of Latitudinal gradients in niche breadth: empirical evidence from haematophagous ectoparasites

Journal of Biogeography, 2008

The most pervasive patterns in biogeography are those related to latitude. In particular, the mos... more The most pervasive patterns in biogeography are those related to latitude. In particular, the most conspicuous of these patterns, such as latitudinal gradients in species richness and geographic range size, have been extensively studied and documented (

Research paper thumbnail of Flea species richness and parameters of host body, host geography and host ‘milieu’

Journal of Animal Ecology, 2004

... Gregory, RD, Keymer, AE & Harvey, PH (1996) Helminth parasite richnes... more ... Gregory, RD, Keymer, AE & Harvey, PH (1996) Helminth parasite richness among vertebrates. ... McTier, TL, George, JE & ... University of Chicago Press, Chicago. Reiczigel, J. & Rózsa, L. (1998) Host-mediated site-segregation of ectoparasites: an individual-based simulation study ...