Structure of compound and component communities of fleas parasitic on small mammals in six different regions as revealed by environmental-based co-occurrence geometry analyses.

We inferred the patterns of co-occurrence of flea species in compound (across all host species) and component (across conspecific hosts) communities from six regions of the world (Mongolia, Northwest Argentina, Argentinian Patagonia, West Siberia, Slovakia, and South Africa) using the novel eigenvector ellipsoid method. This method allows us to infer structural community patterns by comparing species' environmental requirements with the pattern of their co-occurrences. We asked whether: (a) communities are characterized by species segregation, nestedness, or modularity; (b) patterns detected by the novel method conform to the patterns identified by traditional methods that search for non-randomness in community structure; and (c) the pattern of flea species co-occurrences in component communities is associated with host species traits. The results of the application of the eigenvector ellipsoid method suggested that the co-occurrence of flea species was random in all compound communities except in South Africa, where this community demonstrated a tendency to be nested. Flea species co-occurrences were random in many component communities. Species segregation was detected in the flea community of one host, whereas the flea communities of 14 hosts from different regions appeared to be nested. No indication of a modular structure in any community was found. The nestedness of flea component communities was mainly characteristic of hosts with a low relative brain mass. We concluded that the application of this novel method that combines data on species distribution and their environmental requirements allows better identification of the community structural patterns and produces more reliable results as compared with traditional methods.

Cryptic taxonomic diversity and high-latitude melanism in the glossiphoniid leech assemblage from the Eurasian Arctic.

The family Glossiphoniidae is a diverse and widespread clade of freshwater leeches, playing a significant role in functioning of aquatic ecosystems. The taxonomy and biogeography of leeches from temperate, subtropical, and tropical regions attracted much attention of zoologists, while their taxonomic richness and distribution in the Arctic are poorly understood. Here, we present an overview of the Eurasian Arctic Glossiphoniidae based on the most comprehensive occurrence and DNA sequence datasets sampled to date. This fauna contains 14 species, belonging to five genera and three subfamilies. One genus and five species are new to science and described here. The world's northernmost occurrences of glossiphoniids are situated on the Taymyr Peninsula at 72° N, although further records at higher latitudes are expected. Most Arctic leeches are characterized by broad ranges crossing several climatic zones (e.g., Glossiphonia balcanica and G. nebulosa), although the distribution of two new species may be confined to the high-latitude areas. The Taymyr Peninsula with the nearby Putorana Plateau represents the most species-rich area (totally 9 species), while the European Arctic, Iceland, Kolyma Highland, and Chukotka Peninsula house depleted faunas (2-4 species per subregion). Finally, we show that the high-latitude melanism is a common phenomenon in glossiphoniid leeches.

Pattern Without Process: Eugen Smirnov and the Earliest Project of Numerical Taxonomy (1923-1938).

The progress towards mathematization or, in a broader context, towards an increased "objectivity" is one of the main trends in the development of biological systematics in the past century. It is commonplace to start the history of numerical taxonomy with the works of R. R. Sokal and P. H. A. Sneath that in the 1960s laid the foundations of this school of taxonomy. In this article, I discuss the earliest research program in this field, developed in the 1920s by the Russian entomologist and biometrician Eugen (Evgeniy Sergeevich) Smirnov. The theoretical and methodological grounds of this program are considered based on the published works of Smirnov as well as some archival sources. The influence of Smirnov's evolutionary (mechano-Lamarckian) convictions on the development of this project of "exact systematics" is analyzed as well as the author's attempts to establish a novel concept of "mathematical essentialism" in animal taxonomy. The probable causes of the failure of Smirnov's project are viewed from both externalist and internalist perspectives, including the opposition to the use of quantitative methods in biology by some of the Lysenkoist ideologists in the USSR. A brief comparison of Smirnov's research program with that developed 40 years later by Sokal and Sneath is provided.

Dark host specificity in two ectoparasite taxa: repeatability, parasite traits, and environmental effects.

We applied the concept of dark diversity (species that may potentially inhabit a locality but are absent) to the host spectrum of a parasite and defined it as dark host specificity (DHS). We studied the trait-associated and geographic patterns of dark host specificity in fleas and gamasid mites parasitic on small mammals, asking the following questions: (a) Is dark host specificity repeatable across populations of the same species? (b) Is it associated with morphological and/or ecological species traits? (c) What are the factors associated with geographical variation in the DHS among populations of the same species? The DHS was repeatable within species with a large proportion of variance among samples, accounted for by differences between species. The average DHS of fleas, but not mites, was affected by parasite traits, with the DHS being higher in fleas with larger geographic ranges, higher characteristic abundance levels, and summer reproduction peaks. In the majority of ectoparasites, the regional DHS decreased with an increase in either structural or phylogenetic host specificity. The associations between the DHS and the environmental or host-associated characteristics of a region were revealed in a few species (eight of 22 fleas and three of 12 mites). The DHS decreased with (a) an increase in air temperature in two fleas, (b) a decrease in precipitation in two fleas, and (c) an increase in regional host species richness (in three fleas and three mites). Overall, our results suggest that dark host specificity in arthropod ectoparasites is a species-specific character associated, to a large extent, with the breadth of their host-related niches, while the influences of parasite traits and local environmental conditions are minor.

Temporal variation of metacommunity structure in arthropod ectoparasites harboured by small mammals: the effects of scale and climatic fluctuations.

We applied the elements of metacommunity structure (EMS) approach and studied the temporal dynamics of metacommunity structure in arthropod ectoparasites (fleas, gamasid mites and ixodid ticks) harboured by six small mammalian hosts sampled for three decades in the same locality in Western Siberia at three hierarchical scales (inframetacommunities, component metacommunities and a compound metacommunity). All metacommunities were positively coherent. Inframetacommunity structures varied across sampling periods in all host species. The main structural pattern in an inframetacommunity of the same host varied across sampling times but was mostly characterized by clumped species distributions (Clementsian, Gleasonian and their quasi-versions). Component metacommunities in five of the six host species were characterized by either a Clementsian or a quasi-Clementsian distribution. In four of the six host species, this pattern was driven by mite distribution. The temporal structure of compound metacommunity was characterized by a Clementsian pattern. In contrast to the majority of component metacommunities, this pattern was driven by fleas, whereas the temporal structure of gamasid mite compound metacommunities demonstrated a Gleasonian distribution. The temporal gradient in infracommunity composition was not associated with temporal changes in either air temperature or precipitation, whereas the precipitation gradient was positively correlated with the structure of component (in five host species) and compound metacommunities. In conclusion, the best-fit metacommunity structure of ectoparasites varies temporally due to temporal changes in distribution patterns that can be associated with year-to-year climatic variation, affecting both hosts and parasites.

Trapped on the Roof of the World: taxonomic diversity and evolutionary patterns of Tibetan Plateau endemic freshwater snails (Gastropoda: Lymnaeidae: Tibetoradix).

The high-elevation Tibetan Plateau (western China) is inhabited by a unique, though not particularly species-rich, community of organisms. We explored the species content and evolutionary history of the Tibetan Plateau endemic freshwater snail genus Tibetoradix. Phylogenetic relationships within the genus were reconstructed based on available sequence data. We used a single-rate Poisson Tree Processes approach for species delimitation and compared putative species-level clades with already described taxa. We found that the genus consists of at least 6 species, of which we described 4 as new to science. Shell and soft body morphology was examined and the radula in Tibetoradix was described for the first time. Based on our findings, the diversification of the genus did not result in a prominent morphological differentiation and a number of species can be regarded as morphologically cryptic. Single species found in different drainage areas indicate relatively good passive dispersal abilities of the snails. The allopatric distribution of the species could result from competitive exclusion between them. The absence of Tibetoradix spp. outside the Tibetan Plateau could be explained by a scenario of an "evolutionary trap", where adaptations to high elevation conditions prevented the taxa from a successful colonization of lower elevations.

Revealing the stygobiont and crenobiont Mollusca biodiversity hotspot in the Caucasus: Part III. Revision of stygobiont microsnails (Mollusca: Gastropoda: Hydrobiidae) from the Russian part of Western Transcaucasia, with the description of new taxa.

A taxonomic revision of the stygobiont microsnails from north-western Transcaucasia (Krasnodar Krai, Russia) is presented. Two new generaSchapsugia gen. n. and Tachira gen. n. are established. It is shown that the genus Paladilhiopsis does not occur in this area, and the snails previously assigned to this genus belong to Schapsugia gen. n. Two nominal species Paladilhiopsis orientalis Starobogatov, 1962, and P. subovata Starobogatov, 1962 are considered junior synonyms of Sch. pulcherrima (Starobogatov, 1962), based on a re-examination of their conchological variation. In addition, two more species of Schapsugia are described: Sch. kudepsta sp. nov. and Sch. occultata sp. nov. The anatomical structure of another species, Geyeria valvataeformis Starobogatov, 1962 was studied for the first time. It is revealed that it should be placed in a separate genus (Tachira gen. n.). Thus, the previously proposed placement of the microsnails from north-western Transcaucasia in hydrobiid genera from the Balkan Peninsula (Geyeria, Paladilhiopsis) is rejected.

Decline of unique Pontocaspian biodiversity in the Black Sea Basin: A review.

The unique aquatic Pontocaspian (PC) biota of the Black Sea Basin (BSB) is in decline. The lack of detailed knowledge on the status and trends of species, populations, and communities hampers a thorough risk assessment and precludes effective conservation. This paper reviews PC biodiversity trends in the BSB (Bulgaria, Romania, Moldova, Ukraine, and Russia) using endemic mollusks as a model group. We aim to assess changes in PC habitats, community structure, and species distribution over the past century and to identify direct anthropogenic threats. The presence/absence data of target mollusk species were assembled from literature, reports, and personal observations. Pontocaspian biodiversity trends in the northwestern BSB coastal regions were established by comparing 20th- and 21st-century occurrences. The direct drivers of habitat and biodiversity change were identified and documented. We found that a pronounced decline of PC species and communities is driven by (a) damming of rivers, (b) habitat modifications that disturbed previous natural salinity gradients and settings in the studied area, (c) pollution and eutrophication, (d) invasive alien species, and (e) climate change. Four out of the 10 studied regions, namely, the Danube Delta-Razim Lake system, Dniester Liman, Dnieper-Bug estuary, and Taganrog Bay-Don Delta, contain favorable ecological conditions for PC communities and still host threatened endemic PC mollusk species. Distribution data are incomplete, but the scale of deterioration of PC species and communities is evident from the assembled data, as are major direct threats. Pontocaspian biodiversity in the BSB is profoundly affected by human activities. Standardized observation and collection data as well as precise definition of PC biota and habitats are necessary for targeted conservation actions. This study will help to set the research and policy agenda required to improve data collection to accommodate effective conservation of the unique PC biota.

Spatial and temporal variation of compositional, functional, and phylogenetic diversity in ectoparasite infracommunities harboured by small mammals.

We studied patterns of compositional, functional, and phylogenetic α- and ß-diversity in flea and gamasid mite infracommunities of small Siberian mammals, taking into account host-associated (species) and environmental (biome or sampling period) factors. We asked: (a) How do these factors and their interactions affect infracommunity diversity? (b) Does infracommunity composition, in terms of species, traits, and phylogenetic lineages, deviate from random? (c) Are species, traits, and phylogenetic lineages in infracommunities clustered or overdispersed?, and (d) Do patterns of diversity differ between the three diversity facets and/or the two ectoparasite taxa? We found that the α-diversity of infracommunities was strongly affected by host species, biome, and sampling period. The highest proportion of infracommunity diversity in both taxa was associated with the interaction between either host species and biome or host species and sampling period. Infracommunities of both taxa within, as well as between, host species, biomes, and sampling periods were characterized by the clustering of species, traits and lineages. The patterns of the effects of host species, biome, and sampling period on infracommunity diversity were congruent among the three diversity facets in both fleas and mites. We conclude that the assembly patterns in ectoparasite infracommunities mirror those characteristics of component and compound communities.

An annotated catalogue of the gamasid mites associated with small mammals in Asiatic Russia. The family Hirstionyssidae (Acari: Mesostigmata: Gamasina).

This article represents the third (and last) part of the catalogue of ectoparasitic gamasid mites associated with small mammals in Asiatic Russia (Siberia and the Russian Far East). A total of 19 species of the genus Hirstionyssus Fonseca, 1948 are indexed, with data on their taxonomic position, nomenclature, host range, and distribution within the region. As a conclusion, a brief overview of fauna of ectoparasitic gamasid mites parasitising Micromammalia (except bats) of Asiatic Russia is given. In total, 71 mite species belonging to nine genera of three families (Haemogamasidae, Hirstionyssidae, Laelapidae) are recorded and divided among taxonomic and ecological groupings.

The Pleistocene-Holocene aquatic molluscs as indicators of the past ecosystem changes in Transbaikalia (Eastern Siberia, Russia).

Data on the historical change of the Transbaikalian malacofauna in the Neopleistocene and Holocene is presented. Aquatic mollusc shells from archaeological excavations of the ancient settlements dating from the Neolithic period to Medieval and also from a drill hole of the Neopleistocene alluvial deposits were collected. In total eight species of bivalve molluscs from the families Margaritiferidae, Unionidae, Lymnocardiidae, Glycymerididae [marine], and two gastropod species from families Viviparidae and Planorbidae were identified. These species were aged using radiocarbon dating. It was found that the species ranged in age from more than 50.000 to 2.080-1.210 years BP. Five species inhabited the Transbaikal region which are locally extirpated today. Their disjunctive ranges in the past included southern Europe and Western and Eastern Siberia to Transbaikalia and in the east to Far East and Primorye Territory of Russia. A remarkable finding is that of the bivalve genus Monodacna, which was found very far from its native range, the Ponto-Caspian region. The time of existence and extirpation of the thermophilic species of genera Monodacna, Planorbis, Lanceolaria and Amuropaludina corresponds to cycles of the warming and cooling in Pleistocene and Holocene according to regional climate chronological scales. These species can be used as palaeoclimate indicators. Change of the regional malacofaunal species composition is connected with the natural climatochron cycles in the Pleistocene and Holocene resulting in evidence for succession. In the course of this succession, these stenothermal species became extirpated on a regional level, decreasing their global ranges.

Spatial and temporal turnover of parasite species and parasite-host interactions: a case study with fleas and gamasid mites parasitic on small mammals.

We studied patterns of ectoparasite species turnover and pairwise ectoparasite-host interactions across space and time in fleas and mites harboured by small mammals using a novel metric, zeta diversity (similarity between multiple communities). We asked whether the zeta diversity of parasites and their interactions with hosts follow a similar spatial or temporal trend. We found substantial differences in some (zeta decline and retention rate) but not in other (zeta decay) spatial patterns of zeta diversity between species and interactions, whereas the differences between the patterns of the temporal species versus interaction zeta diversity occurred to a much lesser extent. In particular, the parametric form of zeta decline suggested that the distribution of ectoparasite species across localities is driven mainly by niche-based processes, whereas the spatial distribution of flea-host and mite-host interactions is predominantly stochastic. We also found much stronger variation in the number of shared species and interactions over space than over time. Parasite community composition, in terms of species, appeared to be much more temporally stable than that in terms of parasite-host interactions. The parametric form of temporal zeta decline indicated that both parasite communities and parasite-host networks are assembled over time via niche-based processes.

Patterns of zeta diversity in ectoparasite communities harboured by small mammals at three hierarchical scales: taxon-invariance and scale-dependence.

We studied compositional turnover in communities of fleas and mites harboured by small mammals using zeta diversity metric (similarity between multiple communities) and asked whether the patterns of zeta diversity decline with an increase in the number of communities differ between taxa and hierarchical scales [infracommunities (parasite assemblages on individual hosts), component communities (parasite assemblages harboured by host populations), and compound communities (all parasite species in a locality)]. The average number of shared species declined with an increasing number of communities (zeta order). It attained zero at higher orders in infracommunities of both taxa with the shape of the zeta decline being best fitted by the negative exponential function, and the retention rate curves being modal. In contrast, zeta diversity values for compound communities of mites and fleas did not attain zero at higher zeta orders, and the form of the zeta decline was best fitted by the power-law function, whereas the retention rate curves were asymptotic. In component communities, the form of zeta decline was best fitted by either exponential or power-law function in dependence of whether communities were considered within a host across localities or across hosts within a locality and whether ubiquitous species were taken into account. Our main conclusions are that (a) the rules governing compositional turnover in parasite communities for the lowest and the highest hierarchical scales are taxon-invariant but scale-dependent and (b) species composition of infracommunities is mainly driven by stochastic assembly processed, whereas that of compound communities is mainly driven by niche-based processes.

Integrative taxonomy, biogeography and conservation of freshwater mussels (Unionidae) in Russia.

Freshwater mussels are ecosystem engineers and keystone species in aquatic environments. Unfortunately, due to dramatic declines this fauna is among the most threatened globally. Here, we clarify the taxonomy and biogeography of Russian Unionidae species based on the most comprehensive multi-locus dataset sampled to date. We revise the distribution and assess the conservation status for each species. This fauna comprises 16 native species from 11 genera and 4 tribes: Anodonta, Pseudanodonta (Anodontini); Amuranodonta, Beringiana, Buldowskia, Cristaria, Sinanodonta (Cristariini); Middendorffinaia, Nodularia, Unio (Unionini); and Lanceolaria (Lanceolariini). No country-level endemic species are known in Russia, except for Buldowskia suifunica that may also occur in China. Sinanodonta woodiana, a non-native species, was introduced from China. Russia comprises the northern parts of Western and Eastern Palearctic subregions. The first subregion with six species encompasses a huge area from the western boundary of Russia to the Lena Basin in Siberia. The second subregion with 10 species covers the Amur Basin, rivers east of the Lena Basin, coastal basins of the Japan Sea, and the North Pacific Islands. The fauna of Russia primarily includes widespread generalist species that are here considered Least Concern (LC). However, Buldowskia suifunica and Sinanodonta lauta have restricted distributions and are assessed here as Vulnerable (VU) and Endangered (EN), respectively.

Roots of the taxonomic impediment: Is the "integrativeness" a remedy?

The use of the "integrative approach" for classification of organisms since its formal establishment in 2005 has become a recurrent theme of zoosystematics. A bibliometric survey of the publications on integrative taxonomy of animals, which is aimed at exploring the most popular areas of research and characterizing the practical systematists' attitudes to this new approach, is presented. An analysis of 582 papers, which appeared between 2005 and 2017 in journals indexed by Scopus and the Web of Science Core Collection, has illustrated the gradual growth of the popularity of integrative taxonomy as well as some biases in the representation of higher taxa in "integrated" studies. It has been shown that the "integrative" papers have more chance of appearing in a top-ranking journal and gain relatively more citations as compared with non-integrative papers. The obtained results are discussed in the context of the "taxonomic impediment" problem thought to be a consequence of the institutional crisis of traditional taxonomy, which has been vividly debated over the past decades.

Freshwater mussels house a diverse mussel-associated leech assemblage.

Freshwater mussels (Unionida) are one of the most imperiled animal groups worldwide, revealing the fastest rates of extinction. Habitat degradation, river pollution and climate change are the primary causes of global decline. However, biological threats for freshwater mussels are still poorly known. Here, we describe a diverse ecological group of leeches (Hirudinea: Glossiphoniidae) inhabiting the mantle cavity of freshwater mussels. So far, examples of mussel-associated leech species are recorded from East Asia, Southeast Asia, India and Nepal, Africa, and North America. This group comprises a dozen glossiphoniid species with a hidden life style inside the mantle cavity of their hosts largely overlooked by researchers. We show that the association with freshwater mussels evolved independently in three leech clades, i.e. Batracobdelloides, Hemiclepsis, and Placobdella, at least since the Miocene. Seven mussel-associated leech species and two additional free-living taxa are described here as new to science.

The effects of environment, hosts and space on compositional, phylogenetic and functional beta-diversity in two taxa of arthropod ectoparasites.

We studied the effects of variation in environmental, host-associated and spatial factors on variation in compositional, phylogenetic/taxonomic and functional facets of beta-diversity in fleas and gamasid mites parasitic on small mammals and asked whether (a) the importance of these factors as drivers of beta-diversity differs among its multiple facets and (b) the effects of variation in environment, hosts and space on beta-diversity variation differ between the two ectoparasite taxa. To understand the relative effects of each group of predictors, we used a distance-based redundancy analysis and variation partitioning. The greatest portions of variation in the compositional beta-diversity of fleas were equally explained by host-associated and spatial predictors, whereas variation in host species composition contributed the most to variation in the compositional beta-diversity of mites. Variation in the phylogenetic (i.e. based on phylogenetic tree) beta-diversity of fleas was mainly due to variation in the phylogenetic composition of host communities, while the taxonomic (i.e. based on Linnean taxonomy) beta-diversity of mites was influenced by environmental variation. Unique contributions of spatial and environmental variation explained most of the variation in functional beta-diversity and its species replacement (= turnover) component (i.e. beta-diversity explained by replacement of species alone) in fleas and mites, respectively. Variation in the richness difference component (i.e. beta-diversity explained by species loss/gain alone) of functional beta-diversity was mainly affected by either variation in the functional composition of host assemblages (fleas) or its joint action with environmental variables (mites). We conclude that the pattern of the relative effects of environmental, host-associated and spatial factors on beta-diversity is context-dependent and may differ among different facets of beta-diversity, among different beta-diversity components and also among taxa dependent on biological affinities.

Do the pattern and strength of species associations in ectoparasite communities conform to biogeographic rules?

We tested whether biogeographic patterns characteristic of species diversity and composition may also apply to community assembly by investigating geographic variation in the pattern (PSA) (aggregation versus segregation) and strength of species associations (SSA) in flea and mite communities harbored by small mammalian hosts in Western Siberia. We asked whether (a) there is a relationship between latitude and PSA or SSA and (b) similarities in PSA or SSA follow a distance decay pattern or if they are better explained by variation in environmental factors (altitude, amount of vegetation, precipitation, and air temperature). We used a sign of a co-occurrence metric (the C-score) as an indicator of PSA and its absolute standardized value as a measure of SSA. We analyzed data using logistic and linear models, generalized dissimilarity modeling (GDM), and a logistic version of the multiple regression on distance matrices (MRM). The majority of the C-scores of the observed presence/absence matrices indicated a tendency to species aggregation rather than segregation. No effect of latitude on PSA or SSA was found. The dissimilarity in PSA was affected by environmental dissimilarity in mite compound communities only. A relatively large proportion of the deviance of spatial variation in SSA was explained by the GDMs in infracommunities, but not component communities, and in only three (of seven) and two (of eight) host species of fleas and mites, respectively. The best predictors of dissimilarity in SSA in fleas differed between host species, whereas the same factor (precipitation) was the best predictor of dissimilarity in SSA in mites. We conclude that PSA and SSA in parasite communities rarely conform to biogeographic rules. However, when a biogeographic pattern is detected, its manifestation differs among hosts and between ectoparasite taxa.

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.

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.