Patterns of diversity and abundance of fleas and mites in the Neotropics: host‐related,parasite‐related and environment‐related factors

The effects of host‐related, parasite‐related and environmental factors on the diversity and abundance of two ectoparasite taxa, fleas (Insecta: Siphonaptera) and mites (Acari: Mesostigmata), parasitic on small mammals (rodents and marsupials), were studied in different localities across Brazil. A stronger effect of host‐related factors on flea than on mite assemblages, and a stronger effect of environmental factors on mite than on flea assemblages were predicted. In addition, the effects of parasite‐related factors on flea and mite diversity and abundance were predicted to manifest mainly at the scale of infracommunities, whereas the effects of host‐related and environmental factors were predicted to manifest mainly at the scale of component and compound communities. This study found that, in general, diversity and abundance of flea and mite assemblages at two lower hierarchical levels (infracommunities and component communities) were affected by host‐related, parasite‐related and environmental factors, and compound communities were affected mainly by host‐related and environmental factors. The effects of factors differed between fleas and mites: in fleas, community structure and abundance depended on host diversity to a greater extent than in mites. In addition, the effects of factors differed among parasite assemblages harboured by different host species.     

Sexual size dimorphism and sex ratio in arthropod ectoparasites: contrasting patterns at different hierarchical scales

The aims of this study were to determine whether sexual size dimorphism in fleas and gamasid mites (i) conforms to Rensch’s rule (allometry of sexual size dimorphism) and (ii) covaries with sex ratio in infrapopulations (conspecific parasites harboured by an individual host), xenopopulations (conspecific parasites harboured by a population of a given host species in a locality) and suprapopulations (conspecific parasites harboured by an entire host community in a locality). Rensch’s rule in sexual size dimorphism was tested across 150 flea and 55 mite species, whereas covariation between sexual size dimorphism and sex ratio was studied using data on ectoparasites collected from small mammalian hosts in Slovakia and western Siberia. For fleas, we controlled for the confounding effect of phylogeny. The slope of the linear regression of female size on male size was significantly smaller than 1 in fleas, but did not differ from 1 in mites. The proportion of males in flea infrapopulations significantly increased with an increase in the female-to-male body size ratio. The same was true for obligatory haematophagous mites. No relationship between sex ratio and sexual size dimorphism was found for xenopopulations of either taxon or for mite suprapopulations. However, when controlling for the confounding effect of phylogeny, a significant negative correlation between sex ratio and sexual size dimorphism was revealed for flea suprapopulations. We conclude that (i) some macroecological patterns differ between ectoparasite taxa exploiting the same hosts (allometry in sexual size dimorphism), whereas other patterns are similar (sexual size dimorphism-sex ratio relationship in infrapopulations), and (ii) some patterns are scale-dependent and may demonstrate the opposite trends in parasite populations at different hierarchical levels.     

Body size and coexistence in gamasid mites parasitic on small mammals: null model analyses at three hierarchical scales

We studied body size ratio in gamasid mites (Acari: Mesostigmata) parasitic on Palearctic small mammals at 3 hierarchical scales, namely infracommunities (an assemblage of mites harboured by an individual host), component communities (an assemblage of mites harboured by a host population), and compound communities (an assemblage of mites harboured by a host community). We used null models and asked a) whether body size distributions in these communities demonstrate non‐random patterns; b) whether these patterns indicate segregation or aggregation of body sizes of coexisting species; and c) whether patterns of body size distribution are scale‐dependent, that is, differ among infracommunities, component communities, and compound communities. In most mite assemblages, the observed pattern of body size distribution did not differ from that expected by chance. However, meta‐analyses demonstrated that component and compound communities of gamasid mites consistently demonstrated a tendency to reduced body size overlap, while we did not find any clear trend in mite body size distribution across infracommunities. We discuss reasons for scale‐dependence of body size distribution pattern in parasite communities and propose ecological and evolutionary mechanisms that allowed the reduced body size overlap in component and compound communities of ectoparasites to arise.     

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.     

Determinants of ectoparasite assemblage structure on rodent hosts from South American marshlands: the effect of host species,locality and season

The relative effects of host species identity, locality and season on ectoparasite assemblages (relative abundances and species richness) harboured by four cricetid rodent hosts (Akodon azarae, Oligoryzomys flavescens, Oxymycterus rufus and Scapteromys aquaticus) were assessed across six closely located sites in Buenos Aires province, Argentina. Relative abundances of ectoparasites (14 species including gamasid mites, an ixodid tick, a trombiculid mite, lice and fleas), as well as total ectoparasite abundance and species richness, were determined mainly by host species and to a lesser extent by locality (despite the small spatial scale of the study), whereas seasonal effect was weak, albeit significant. The abundances of some ectoparasites were determined solely by host, whereas those of other ectoparasites (sometimes belonging to the same higher taxon) were also affected by locality and/or season. In gamasids, there was a significant effect of locality for some species, but not for others. In fleas and lice, the effect of locality was similar in different species, suggesting that this effect is related to the characteristic life history strategy.     

Decay of similarity of gamasid mite assemblages parasitic on Palaearctic small mammals: geographic distance, host-species composition or environment

Aim The similarity between parasite assemblages should decrease with increasing geographic distance between them, increasing dissimilarity in environmental conditions, and/or increasing dissimilarity of the local host fauna, depending on the dispersal abilities of the parasites and the intimacy of their associations with the host. We tested for a decay in the similarity of gamasid mite assemblages parasitic on small mammals with increasing geographic, ‘environmental’ and ‘host faunal’ (= ‘host’) distances. Location We used data on assemblages of haematophagous gamasid mites (superfamily Dermanyssoidea) parasitic on small mammals (Insectivora, Lagomorpha and Rodentia) from 26 different regions of the northern Palaearctic. Methods Similarity in mite assemblages was investigated at the compound community level across all regions, and at the component community level, across populations of the same host species for each of 11 common host species. Similarity between pairs of mite communities was estimated using both the Jaccard and the Sorensen indices. Environmental distance was estimated as the dissimilarity between locations in a composite measure of climatic variables, and host faunal distance was simply taken as the reciprocal of indices of similarity between the composition of host faunas in different locations. Generalized Linear Models (GLM) and Akaike's Information Criterion were used to select the best model of decay in similarity as a function of geographic, ‘environmental’ and ‘host faunal’ distances. Results Overall, despite slight differences among host species, the similarity in mite assemblages decreased with both increasing ‘environmental’ distance and increasing ‘host faunal’ distance, but was generally unaffected by geographic distance between regions. The similarity of component communities of gamasid mites among host populations was determined mainly by similarity in the physical environment, whereas that of compound communities varied mainly with host‐species composition. Main conclusions Our results indicate that the general decay in community similarity with increasing geographic distances does not apply to assemblages of gamasid mites; it is possible that they can overcome great distances by means of passive dispersal (either by phoresy or wind‐borne), or more likely they occur wherever their hosts are found as a result of tight cospeciation in the past. Mite assemblages on small mammalian hosts seem to be affected mainly by local environmental conditions, and, to a much lesser extent, by the species composition of local host communities.     

Beta-diversity of ectoparasites at two spatial scales: nested hierarchy,geography and habitat type

Beta-diversity of biological communities can be decomposed into (a) dissimilarity of communities among units of finer scale within units of broader scale and (b) dissimilarity of communities among units of broader scale. We investigated compositional, phylogenetic/taxonomic and functional beta-diversity of compound communities of fleas and gamasid mites parasitic on small Palearctic mammals in a nested hierarchy at two spatial scales: (a) continental scale (across the Palearctic) and (b) regional scale (across sites within Slovakia). At each scale, we analyzed beta-diversity among smaller units within larger units and among larger units with partitioning based on either geography or ecology. We asked (a) whether compositional, phylogenetic/taxonomic and functional dissimilarities of flea and mite assemblages are scale dependent; (b) how geographical (partitioning of sites according to geographic position) or ecological (partitioning of sites according to habitat type) characteristics affect phylogenetic/taxonomic and functional components of dissimilarity of ectoparasite assemblages and (c) whether assemblages of fleas and gamasid mites differ in their degree of dissimilarity, all else being equal. We found that compositional, phylogenetic/taxonomic, or functional beta-diversity was greater on a continental rather than a regional scale. Compositional and phylogenetic/taxonomic components of beta-diversity were greater among larger units than among smaller units within larger units, whereas functional beta-diversity did not exhibit any consistent trend regarding site partitioning. Geographic partitioning resulted in higher values of beta-diversity of ectoparasites than ecological partitioning. Compositional and phylogenetic components of beta-diversity were higher in fleas than mites but the opposite was true for functional beta-diversity in some, but not all, traits.     

Co-occurrence of ectoparasites on rodent hosts: null model analyses of data from three continents

We studied patterns of species co-occurrence in communities of ectoparasitic arthropods (ixodid ticks, mesostigmate mites and fleas) harboured by rodent hosts from South Africa ( Rhabdomys pumilio ), South America ( Scapteromys aquaticus and Oxymycterus rufus ) and west Siberia ( Apodemus agrarius , Microtus gregalis , Microtus oeconomus and Myodes rutilus ) using null models. We compared frequencies of co-occurrences of parasite species or higher taxa across host individuals with those expected by chance. When non-randomness of parasite co-occurrences was detected, positive but not negative co-occurrences of parasite species or higher taxa prevailed (except for a single sample of mesostigmate mites from O. rufus ). Frequency of detection of non-randomness of parasite co-occurrences differed among parasite taxa, being higher in fleas and lower in mites and ticks. This frequency differed also among host species independent of parasite taxon, being highest in Microtus species and lowest in O. rufus and S. aquaticus . We concluded that the pattern of species co-occurrence in ectoparasite communities on rodent hosts is predominantly positive, depends on life history of parasites and may be affected to a great extent by life history of a host.     

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.     

Aggregation and species coexistence in fleas parasitic on small mammals

The aggregation model of coexistence states that species coexistence is facilitated if interspecific aggregation is reduced relative to intraspecific aggregation. We investigated the relationship between intraspecific and interspecific aggregation in 17 component communities (the flea assemblage of a host population) of fleas parasitic on small mammals and hypothesized that interspecific interactions should be reduced relative to intraspecific interactions, facilitating species coexistence. We predicted that the reduction of the level of interspecific aggregation in relation to the level of intraspecific aggregation would be positively correlated with total flea abundance and species richness of flea assemblages. We also expected that the higher degree of facilitation of flea coexistence would be affected by host parameters such as body mass, basal metabolic rate (BMR) and depth and complexity of burrows. Results of this study supported the aggregation model of coexistence and demonstrated that, in general, a) conspecific fleas were aggregated across their hosts; b) flea assemblages were not dominated by negative interspecific interactions; and c) the level of interspecific aggregation in flea assemblages was reduced in relation to the level of intraspecific aggregation. Intraspecific aggregation tended to be correlated positively to body mass, burrow complexity and mass-independent BMR of a host. Positive interspecific associations of fleas tended to occur more frequently in species-rich flea assemblages and/or in larger hosts possessing deep complex burrows. Intraspecific aggregation increased relative to interspecific aggregation when species richness of flea infracommunities (the flea assemblage of a host individual) and component communities increased. We conclude that the pattern of flea coexistence is related both to the structure of flea communities and affinities of host species.     

Similarity in ectoparasite faunas of Palaearctic rodents as a function of host phylogenetic, geographic or environmental distances: Which matters the most?

Different host species harbour parasite faunas that are anywhere from very similar to very different in species composition. A priori, the similarity in the parasite faunas of any two host species should decrease with increases in either the phylogenetic distance, the distinctness of the environments occupied or the geographical distance between these hosts. We tested these predictions using extensive data on the faunas of fleas (Insecta: Siphonaptera) and gamasid mites (Acari: Parasitiformes) parasitic on rodents across the Palaearctic. For each pair of host species, we computed the similarity in parasite faunas based on both species composition as well as the phylogenetic and/or taxonomic distinctness of parasite species. Phylogenetic distances between hosts were based on patristic distances through a rodent phylogeny, geographic distances were computed from geographic range data, and environmental dissimilarity was measured from the average climatic and vegetation scores of each host range. Using multiple regressions on distance matrices to assess the separate explanatory power of each of the three dependent variables, environmental dissimilarity between the ranges of host species emerged as the best predictor of dissimilarity between parasite faunas, especially for fleas; in the case of mites, phylogenetic distance between host species was also important. A closer look at the data indicates that the flea and mite faunas of two hosts inhabiting different environments are always different, whilst hosts living in similar environments can have either very similar or dissimilar parasite faunas. Additional tests showed that dissimilarity in flea or mite faunas between host geographic ranges was best explained by dissimilarity in vegetation, followed by dissimilarity in climatic conditions. Thus, external environmental factors may play greater roles than commonly thought in the evolution of host-parasite associations.     

Deconstructing spatial patterns in species composition of ectoparasite communities: the relative contribution of host composition,environmental variables and geography

Aim We determined whether dissimilarity in species composition between parasite communities depends on geographic distance, environmental dissimilarity or host faunal dissimilarity, for different subsets of parasite species with different levels of host specificity. Location Communities of fleas parasitic on small mammals from 28 different regions of the Palaearctic. Method Dissimilarities in both parasite and host species composition were computed between each pair of regions using the Bray–Curtis index. Geographic distances between regions were also calculated, as were measures of environmental dissimilarity consisting of the pairwise Euclidean distances between regions derived from elevation, vegetation and climatic variables. The 136 flea species included in the dataset were divided into highly host‐specific species (using 1–2 host species per region, on average), moderately host‐specific species (2.2–4 hosts per region) and generalist species (>4 hosts per region). The relative influence of geographic distance, host faunal dissimilarity and environmental dissimilarity on dissimilarity of flea species composition among all regions was analysed for the entire set of flea species as well as for the three above subsets using multiple regressions on distance matrices. Results When including all flea species, dissimilarity in flea species composition was affected by all three independent variables, although the pure effect of dissimilarity in host species composition was the strongest. Results were different when the subsets of fleas differing in host specificity were treated separately. In particular, dissimilarity in species composition of highly host‐specific fleas increased solely with environmental dissimilarity, whereas dissimilarity for both moderately specific and non‐specific fleas increased with both geographic distance and dissimilarity in host species composition. Main conclusions Host specificity seems to dictate which of the three factors considered is most likely to affect the dissimilarity between flea communities. Counter‐intuitively, environmental dissimilarity played a key role in determining dissimilarity in species composition of highly host‐specific fleas, possibly because, although their presence in a region relies on the occurrence of particular host species, their abundance is itself mostly determined by climatic conditions. Our results show that deconstructing communities into subsets of species with different traits can make it easier to uncover the mechanisms shaping geographic patterns of diversity.     

Functional and phylogenetic uniqueness of helminth and flea assemblages of two South African rodents

The loss of a particular species from a community may have different effects on its functioning, depending on the presence or absence of functionally similar or phylogenetically close species in that community (redundancy). Redundancy is thus defined as the fraction of species diversity not expressed by functional or phylogenetic diversity. We assessed functional and phylogenetic alpha- and beta-redundancy in helminth and flea assemblages of two species of South African rodents, Rhabdomys dilectus and Rhabdomys pumilio, using community uniqueness as the inverse indicator of redundancy. We asked whether patterns of functional and phylogenetic alpha- and beta-uniqueness differed between (i) parasite groups (endo- versus ectoparasites), (ii) host species within parasite groups, and (iii) biomes within host species. We found differences between the two hosts in the functional and phylogenetic alpha-uniqueness (but not beta-uniqueness) of flea, but not helminth, assemblages. Significant correlations between the alpha-uniqueness of parasite assemblages and the total parasite prevalence were found only for phylogenetic uniqueness and only in helminths. Pairwise site-by-site dissimilarities in uniqueness (beta-uniqueness) and pairwise dissimilarity in prevalence were significantly associated (positively) in helminths but not in fleas. A between-biome difference in functional (but not phylogenetic) alpha-uniqueness was found in both helminth and flea assemblages harboured by R. pumilio. We conclude that the resilience of parasite assemblages in terms of the effect on hosts depends not only on their transmission strategy but also on traits of host species and environmental factors.     

Does investment into ��expensive�� tissue compromise anti-parasitic defence? Testes size, brain size and parasite diversity in rodent hosts

Species richness of parasite assemblages varies among host species. Earlier studies that searched for host-related determinants of parasite diversity mainly considered host traits that affect the probability of host encounter with parasites, whereas host traits related to defensibility against parasites have rarely been investigated. From the latter perspective, evolutionary investment in ??expensive?? tissue or organs (like testes or brain) may trade off against energetically costly anti-parasitic defences. If so, richer parasite assemblages are expected in hosts with larger testes and brains. We studied the relationships between testes and brain size and diversity of parasites (fleas, gamasid mites and helminths) in 55 rodent species using a comparative approach and application of two methods, namely the method of independent contrasts and generalized least-squares (GLS) analysis. Both phylogenetically correct methods produced similar results for flea and helminth species richness. Testes size positively correlated with flea and helminth species richness but not gamasid mite species richness. No correlation between brain size and species richness of any parasite group was found by the method of independent contrasts. However, GLS analysis indicated negative correlation between brain size and mite species richness. Our results cast doubt on the validity of the expensive tissue hypothesis, but suggest instead that larger testes are associated with higher parasite diversity via their effect on mobility and/or testosterone-mediated immunosuppression.     

Biogeography of parasite abundance: latitudinal gradient and distance decay of similarity in the abundance of fleas and mites,parasitic on small mammals in the Palearctic,at three spatial scales

We tested whether biogeographic patterns characteristic for biological communities can also apply to populations and investigated geographic patterns of variation in abundance of ectoparasites (fleas and mites) collected from bodies of their small mammalian hosts (rodents and shrews) in the Palearctic at continental, regional and local scales. We asked whether (i) there is a relationship between latitude and abundance and (ii) similarity in abundance follows a distance decay pattern or it is better explained by variation in extrinsic biotic and abiotic factors. We analysed the effect of latitude on mean intraspecific abundance using general linear models including proportional abundance of its principal host as an additional predictor variable. Then, we examined the relative effect of geographic distance, biotic and abiotic dissimilarities among regions, subregions or localities on the intraspecific dissimilarity in abundance among regions, subregions or localities using Generalized Dissimilarity Modelling. We found no relationship between latitude and intraspecific flea or mite abundance. In both taxa, environmental dissimilarity explained the largest part of the deviance of spatial variation in abundance, whereas the effect of the dissimilarity in the principal host abundance was of secondary importance and the effect of geographic distance was minor. These patterns were generally consistent across the three spatial scales, although environmental variation and dissimilarity in principal host abundance were equally important at the local scale in fleas but not in mites. We conclude that biogeographic patterns related to latitude and geographic distance do not apply to spatial variation of ectoparasite abundance. Instead, the geographic distribution of abundance in arthropod ectoparasites depends on their responses, mainly to the off-host environment and to a lesser extent the abundance of their principal hosts.     

中国云南小兽寄生革螨的群落结构和空间分布

寄生在小兽体表的革螨可能是传播肾综合征出血热和立克次体痘等人兽共患病的媒介。本文报道了云南省28个县(市)小兽体表革螨的野外调查结果, 运用物种数、平均丰富度和Shannon多样性指数对小兽寄生革螨的群落特征和沿环境梯度的空间分布进行了研究, 并用系统聚类分析法 (SPSS 16.0软件)对18种主要小兽的革螨群落相似性进行了比较。在云南省28个县(市)共捕获到小兽14 544头, 隶属于5目（啮齿目、食虫目、攀鼩目、兔形目、食肉目）10科35属67种, 在捕获的小兽体表采集到革螨80 791头, 经鉴定属于10科33属112种。结果分析表明: 主要的宿主动物为黄胸鼠 Rattus tanezumi、齐氏姬鼠Apodemus chevrieri和大绒鼠Eothenomys miletus;纳氏厉螨Laelaps nuttalli、毒厉螨L. echidninus和贵州厉螨L. guizhouensis为革螨的优势种。齐氏姬鼠A. chevrieri、社鼠N. confucianus和黄胸鼠R. tanezumi体表寄生的革螨种类最多;臭鼩鼱Suncus murinus、齐氏姬鼠A. chevrieri和灰麝鼩Crocidura attenuata的革螨群落多样性最高。聚类分析结果表明, 大部分革螨群落的相似程度与相应小兽的亲缘关系及所处生态环境的相似性是基本一致的, 分类地位和生境选择相似的小兽, 它们的革螨群落也被聚为一类。革螨物种数沿纬度梯度的水平分布呈现两个峰值, 最大峰值出现在25°~26°N之间;沿海拔梯度的垂直分布呈单峰分布格局, 峰值在海拔2 000~2 500 m之间。革螨和小兽的多样性沿纬度梯度和海拔梯度的空间分布趋势也均表现出随着纬度和海拔的升高而先升高后降低的单峰型分布格局, 峰值分别出现在北纬25°~27°N和海拔2 000~2 500 m之间。结果提示云南革螨群落种类丰富, 多样性高。云南革螨物种数和多样性的分布格局可能直接受到古北和东洋两区系边缘效应的影响。     

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.     

Trait‐based and phylogenetic associations between parasites and their hosts: a case study with small mammals and fleas in the Palearctic

We investigated the associations between ecological (density, shelter structure), morphological (body mass, hair morphology) and physiological traits (basal metabolic rate) of small mammals and ecological (seasonality of reproduction, microhabitat preferences, abundance, host specificity) and morphological (presence and number of combs) traits of their flea parasites that shape host selection processes by fleas. We adapted the extended version of the three‐table ordination and linked species composition of flea assemblages of host species with traits and phylogenies of both hosts and fleas. Fleas with similar trait values, independent of phylogenetic affinities, were clustered on the same host species. Fleas possessing certain traits selected hosts possessing certain traits. Fleas belonging to the same phylogenetic lineage were found on the same host more often than expected by chance. Certain phylogenetic lineages of hosts harbored certain phylogenetic lineages of fleas. The process of host selection by fleas appeared to be determined by reciprocal relationships between host and flea traits, as well as between host and flea phylogenies. We concluded that the connection between host and flea phylogenies, coupled with the connection between host and flea traits, suggests that the species compositions of the host spectra of fleas were driven by the interaction between historical processes and traits.     

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.     

Are ectoparasite communities structured? Species co-occurrence, temporal variation and null models

1. We studied temporal variation in the structure of flea communities on small mammalian hosts from eastern Slovakia using null models. We asked (a) whether flea co-occurrences in infracommunities (in the individual hosts) in different hosts as well as in the component communities (in the host species) demonstrate a non-random pattern; (b) whether this pattern is indicative of either positive or negative flea species interactions; (c) whether this pattern varies temporally; and (d) whether the expression of this pattern is related to population size of either fleas or hosts or both. 2. We constructed a presence/absence matrix of flea species for each temporal sample of a host species and calculated four metrics of co-occurrence, namely the C-score, the number of checkerboard species pairs, the number of species combinations and the variance ratio (V-ratio). Then we compared these metrics with the respective indices calculated for 5000 null matrices that were assembled randomly using two algorithms, namely fixed-fixed (FF) and fixed-equiprobable (FE). 3. Most co-occurrence metrics calculated for real data did not differ significantly from the metrics calculated for simulated matrices using the FF algorithm. However, the indices observed for 42 of 75 presence/absence matrices differed significantly from the null expectations for the FE models. Non-randomness was detected mainly by the C-score and V-ratio metrics. In all cases, the direction of non-randomness was the same, namely the aggregation, not competition, of flea species in host individuals and host species. 4. The inclusion or exclusion of the uninfested hosts in the FE models did not affect the results for individual host species. However, exclusion of the uninfested host species led to the acceptance of the null hypothesis for only six of 13 temporal samples of the component flea communities for which non-randomness was detected when the uninfested hosts were included in the analysis. 5. In most host species, the absolute values of the standardized size effect of both the C-score and V-ratio increased with an increase in host density and a concomitant decrease in flea abundance and prevalence. 6. Results of this study demonstrated that (a) flea assemblages on small mammalian hosts were structured at some times, whereas they appeared to be randomly assembled at other times; (b) whenever non-randomness of flea co-occurrences was detected, it suggested aggregation but never segregation of flea species in host individuals or populations; and (c) the expression of structure in flea assemblages depended on the level of density of both fleas and hosts.