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The Thaumapsylla breviceps orientalis is endemic to China and exhibits extreme host specificity (monoxenous). This study reports the first mitogenome sequenced for the family Ischnopsyllidae and provides comprehensive analysis of both the morphological characteristics and mitogenome of T. b. orientalis . The assembled mitogenome is 15,631 bp in length with a high AT content (78.5%), and its codon usage bias is predominantly shaped by natural selection. Evolutionary analysis based on evolutionary rates and nucleotide diversity across different families within Siphonaptera revealed that Pulicidae has the fastest evolutionary rate and the highest nucleotide diversity, a pattern likely driven by differences in their hosts and habitats. We observed that early-diverging flea lineages are predominantly polyxenous, whereas later-diverging lineages are primarily pleioxenous or monoxenous. Phylogenetic results indicate that the taxonomic status of the families Ctenophthalmidae, Vermipsyllidae, and Hystrichopsyllidae requires further study and revision. This research addresses a key knowledge gap in Ischnopsyllidae mitogenomics and clarifies the phylogenetic relationships within the order Siphonaptera.

We studied patterns of compositional, functional, and phylogenetic α- and β-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.

Background Insects belonging to the Siphonaptera order are obligatory ectoparasites of vertebrates, including humans. Their life cycle is marked by holometabolous development, and adults are adapted to have a bloodmeal out of their hosts. The objective of this study is to review the families occurring in Brazil with their species and report new records from fleas collected in an Atlantic Rainforest preserved area, including Rickettsia sp. monitoring. Methods Literature research was carried out, including journal articles and books available in scientific databases. The sample collection took place at Legado das Águas—Reserva Votorantim private reserve, where wild rodents, marsupials, and bats were captured and inspected for the presence of fleas. The fleas were identified, and their genetic material was extracted and subjected to two polymerase chain reactions (PCRs): an endogenous control to validate the extraction and a Rickettsia screening. Results A total of 8 families were reviewed, resulting in 63 valid species that interact with a wide range of hosts. Among the collected fleas, 7 species were identified as interacting with 19 different host genera belonging to the Rodentia, Didelphimorphia, and Chiroptera orders. We highlight the presence of 2 new locality records and 15 new host interactions. Of the collected fleas, 105 specimens were tested individually for Rickettsia bacteria, but none showed expected amplicons for the bacterium. Conclusions This study provides an extensive revision of the Siphonaptera order present in Brazil with new insights, since the last robust revision made was from 2000, along with new information regarding host association and locality based on field collections conducted by the authors, which helps understanding the host-parasite interaction and encourages new studies. Graphical Abstract

Fleas are the most important insect vectors that parasitize warm-blooded animals and are known vectors of zoonotic pathogens. A recent study showed that Stenoponia polyspina parasitizing Eospalax baileyi in Zoige County have carried Bartonella spp. and Spotted fever group Rickettsia (SFGR). Accurate identification and differentiation of fleas are essential for prevention and control of zoonotic pathogens. To understand phylogenetic relationship of the subfamily Stenoponiinae, we described morphological characteristics of S. polyspina and sequenced its mitogenome with 14,933 bp in size and high A + T content (~ 79%). The S. polyspina mitogenome retained the ancestral pattern of mitochondrial gene arrangement of arthropods without rearrangement. The start codons of 13 protein-coding genes (PCGs) are traditional ATN and the stop codons are TAA or TAG. Anticodon loops of all tRNA genes were 7 bp except for trnL 2 and trnD had anticodon loops with 9 bp and the abnormal anticodon loops may be associated with frameshifting mutation. Genetic distance and Ka/Ks ratios indicated that all 13 PCGs of S. polyspina were subjected to purifying selection, with cox1 at the slowest rate and atp8 at the fastest rate. The mitogenomes of 24 species representing 7 families in the order Siphonaptera were selected to reconstruct phylogenetic tree based on concatenated nucleotide sequences of two datasets (PCGRNA matrix and PCG12RNA matrix) using Bayesian inference (BI) and Maximum likelihood (ML) methods. Phylogenetic tree supported that the superfamilies Ceratophylloidea, Vermipsylloidea, Pulicoidea were monophyletic and the superfamily Hystrichopsylloidea was paraphyletic. The family Ctenophthalmidae was monophyletic in PCGRNA-ML (codon partition) and paraphyletic in the remain trees. S. polyspina belongs to the subfamily Stenoponiinae was closely more related to the subfamily Rhadinopsyllinae. This paper explored phylogenetic position of diverse clades within the order Siphonaptera based on morphological and mitogenome data of S. polyspina . Our research enriched NCBI database of the order Siphonaptera.

Background The great gerbil ( Rhombomys opimus ), whose ectoparasitic fleas significantly influence the transmission and prevalence of plague, was the dominant rodent species in the Junggar Basin in Northwestern China. However, the distribution pattern of fleas parasitizing the great gerbils and whether that pattern affected the intensity of plague prevalence in different regions remains unclear. Methods A total of 17,780 fleas were collected from 2258 great gerbils throughout 90 investigations. This study focused on analyzing the rate of flea infestation and the flea indices of species that parasitized the great gerbils. The aggregation patterns of fleas parasitizing the great gerbils were measured using the parameter b of Taylor’s power law, and the differences in the aggregation index of plague epidemic areas were compared. Results We observed an aggregated distribution of ectoparasitic fleas in the great gerbils. The aggregation degree of combined fleas was higher ( P  > 0.05) in the eastern area of the Junggar Basin than in the western area. The primary species of ectoparasitic fleas of the great gerbils were Xenopsylla skrjabini , Xenopsylla minax , Xenopsylla hirtipes , and Nosopsyllus laeviceps laiveceps . X. skrjabini exhibited the highest ( P < 0.01) degree of aggregation in the eastern zone (III), with an aggregation index of 1.61. In addition, in the middle zone (II), the aggregation index of X. minax and X. hirtipes reached their peak, with values of 1.53 and 1.56, respectively. Conversely, the degree of aggregation of N. laeviceps was more pronounced in the eastern zone than in the western zone of the Junggar Basin. Notably, the aggregation degree of the combined fleas of the great gerbils during the low-intensity plague epidemic period, with an index of 1.93, was significantly higher ( P  < 0.001) than during the high-intensity epidemic period, with an index of 1.50. Conclusions Fleas exhibited an aggregated distribution within the great gerbil population. The levels of flea aggregation varied across zones characterized by differing intensities of plague epidemics. In addition, the degree of flea aggregation was significantly correlated with the intensity of plague prevalence. Graphical Abstract

Fleas, which are ubiquitous small wingless parasitic insects, have a significant impact on human and animal health globally. In this study, we sequenced and analyzed the complete mitochondrial genomes of Paradoxopsyllus custodis and Stenischia montanis yunlongensis . The lengths of these genomes were 15,375 bp and 15,651 bp respectively, encompassing a total of 37 genes. Notably, all nucleotide combinations displayed a marked AT preference, with ATN as start codon for all 13 protein-coding genes in both species. Furthermore, only two genes in Paradoxopsyllus custodis were terminated with an incomplete stop codon T(AA). The five most frequently utilized codons among the 13 PCGs in both species ended with A / U, and their relative synonymous codon usage values surpassed 2. Phylogenetic relationships among fleas were assessed using maximum likelihood (ML) and Bayesian inference (BI), providing support for the paraphyletic of Leptopsyllidae. This study not only enhances our understanding of the mitochondrial genome within the genera Paradoxopsyllus and Stenischia , but also offers valuable genetic markers for the taxonomic identification and phylogenetic evolution within the order Siphonaptera.

The “host-diversity-begets-parasite-diversity” (HDBPD) pattern has been demonstrated for traditional metrics of functional diversity. We applied the decomposition of functional alpha (functional diversity structure; FDS) and beta (functional resemblance; FR) diversity into (a) Simpson’s dominance, functional redundancy, and functional diversity and (b) taxonomic similarity, functional dissimilarity, and beta redundancy, respectively, coupled with ternary diagrams, to test whether the HDBPD rule also holds for FDS and FR and their separate components for communities of fleas and small mammals from different biomes of the Palearctic. We compared patterns of FDS and FR and their components within and between fleas and hosts within and between biomes and tested for correlation of separate components of functional alpha and beta diversities between fleas and hosts. Differences in FR between biomes were detected for both fleas and hosts (due to differences in each FR component), but not in FDS. Within biomes, fleas and hosts demonstrated marginally significant differences in FDS in steppes and temperate forests due to differences in the functional diversity component. Differences in FR between fleas and hosts were found in four of five biomes (due to differences in one or two FR components). Values of each of the three separate components of the flea FDS correlated positively with values of the respective components of the host FDS suggesting the effect of functional alpha diversity of hosts on that of fleas. No correlation between separate components of the flea and host FR was found implying no link between host and flea functional beta diversity. We conclude that the HDBPD rule, when applied to functional beta diversity, is not as universal as it was previously thought to be.

Accurate differentiation and identification of flea species are essential for both basic and applied research on fleas, as well as for the diagnosis of flea-borne diseases. However, distinguishing between flea species can be challenging, especially among those with minimal morphological differences. Therefore, some scholars have suggested the necessity of comprehensive revisions to the classification of fleas, incorporating morphological, molecular, and phylogenetic data. In this study, we focused on classifying the rodents’ parasitic fleas in southeastern China and provided molecular and phylogenetic data. We also described a new subspecies Ctenophthalmus breviprojiciens fujiansis n. ssp. A total of 392 fleas were collected from 8 species of rodents in 10 counties. Morphologically, they belonged to 10 species, 9 genera and 5 families. Barcode identification based on COI gene and phylogenetic analysis based on five genetic markers ( 18S rDNA , 28S rDNA , EF-1a , COI , COII ) revealed that the molecular and morphological identification of Xenopsylla cheopis , Aviostivalius klossi bispiniformis , Leptopsylla segnis , Monopsyllus anisus and Ctenocephalides felis felis were consistent. The taxonomic status of Neopsylla specialis minpiensis and Peromyscopsylla himalaica sinica as subspecies is questionable due to significant intraspecific genetic distance, and further morphological and molecular data are required to determine if they should be elevated to species level. The molecular identification of C. breviprojiciens n. ssp., N. dispar fukienensis , and Nosopsyllus nicanus could not be completed at this time due to a lack of sequences for related species in existing GenBank databases. Additionally, phylogenetic relationships of 31 species from 9 genera and 5 families of Siphonaptera were inferred based on five molecular markers ( 18S rDNA , 28S rDNA , EF-1a , COI and COII ) using Maximum Likelihood analyses. The analyses revealed that various taxa of Siphonaptera are monophyletic at the subspecies, species, and genus levels. However, at the family level, Leptopsyllidae, Ceratophyllidae, Pulicidae, and Pygiopsyllidae are all monophyletic, while Ctenophthalmidae is paraphyletic. we support the view of some authors that revising the catchall group Ctenophthalmidae and elevating each of its constituent subfamilies to family status.

Ideal disease mitigation measures for wildlife are safe and benign for target species, non-target organisms, the environment, and humans. Identifying collateral (i.e., unintended) effects is a key consideration in implementing such actions. Deltamethrin dust and fipronil-laced baits represent a group of insecticides that target fleas (pulicides) and are used to control flea (Siphonaptera) vectors of the plague bacterium Yersinia pestis to protect prairie dogs ( Cynomys spp.) and their plague-susceptible obligate predators, endangered black-footed ferrets ( Mustela nigripes ). A variety of animals use prairie dog burrows as refuge, which potentially exposes them to deltamethrin, and to fipronil and its metabolites in fecal pellets excreted by prairie dogs and other mammals that have eaten fipronil baits. We assessed the potential effects of deltamethrin and fipronil residues on survival, body mass, and activity of western tiger salamanders ( Ambystoma mavortium ), a burrow-inhabiting amphibian. Pulicides were applied at realistic concentrations in mesocosms mimicking burrows. Treatments included (1) deltamethrin dust and non-treated prairie dog fecal pellets, (2) prairie dog fecal pellets containing fipronil and fipronil sulfone, and (3) un-treated prairie dog fecal pellets as controls. All 29 salamanders survived the experiment. We did not detect pulicide residues in any control salamanders. Fipronil sulfone was detected in tissues from 3 of 10 salamanders in the fipronil treatment and deltamethrin was detected in tissues from 9 of 11 salamanders in the deltamethrin treatment. Salamanders were observed outside of burrows more frequently after treatments than before. Deltamethrin concentrations in whole body samples correlated positively with the amount of time salamanders were inside burrows. Acute, lethal effects were not detected, but uptake of deltamethrin and, to a lesser extent fipronil sulfone, into salamander tissues indicated the potential for long-term effects on this non-target species. Identifying potential collateral effects is an important aspect of evaluating mitigation actions implemented to protect endangered species.

Yersinia pestis is transmitted from fleas to rodents when the bacterium develops an extensive biofilm in the foregut of a flea, starving it into a feeding frenzy, or, alternatively, during a brief period directly after feeding on a bacteremic host. These two transmission modes are in a trade-off regulated by the amount of biofilm produced by the bacterium. Here by investigating 446 global isolated Y. pestis genomes, including 78 newly sequenced isolates sampled over 40 years from a plague focus in China, we provide evidence for strong selection pressures on the RNA polymerase ω-subunit encoding gene rpoZ . We demonstrate that rpoZ variants have an increased rate of biofilm production in vitro, and that they evolve in the ecosystem during colder and drier periods. Our results support the notion that the bacterium is constantly adapting—through extended phenotype changes in the fleas—in response to climate-driven changes in the niche. Yersinia pestis , the causative agent of plague, can change its biofilm production to influence the dynamics of flea-borne transmission. Here, the authors sequence Y. pestis isolates sampled over 40 years in China and show evidence for climate-associated selection on rpoZ to increase biofilm production.