Adaptation to a novel host and performance trade-off in host-generalist and host-specific insect ectoparasites

HOST TRAITS EXPLAIN MORE VARIATION IN OCCUPANCY OF GENERALISTS THAN SPECIALISTS DUE TO STRONG HOST PREFERENCES AMONG GENERALISTS

The range of hosts a parasite can successfully occupy is partially determined by the niche breadth, that is, the set of environmental conditions necessary to maintain a stable population. Niche breadth is often quantified using host specificity, which encompasses the number of host species a parasite can exploit and the parasite's distribution among its hosts. Parasites with a wider niche breadth can potentially occupy more host species and are often more evenly distributed among hosts than parasites with a narrower niche breadth. However, parasites interact with potential hosts within the context of a geographic locality and the set of environmental characteristics associated with it. The extent to which environmental filters associated with host individuals and the geographic context explain variation in occupancy of parasites, and the extent to which variation in occupancy is associated with host range and specificity, is poorly understood. Using data from small mammals and ectoparasites in Vermont, I used a multiscale, multispecies occupancy model (MSOM) to (1) estimate ectoparasite occupancy at 10 geographic sites and on individual hosts within each site, (2) quantify the variation in occupancy explained by the site and host levels of the model using Bayesian R2, and (3) evaluate associations between explained variation and host range of ectoparasites. For ectoparasites collected from at least 4 different host species, I calculated structural specificity to determine the distribution of these parasites across the hosts, and β-specificity to evaluate changes in host use across habitats. Host range was significantly associated with host-level Bayesian R2: generalist parasites had more variation in occupancy explained by host-level covariates than specialist parasites. This result may be explained by differences in structural specificity: many generalists disproportionally occurred on a single-host species, suggesting that host characteristics act as habitat filters for these parasites. There were no significant associations between site-level Bayesian R2 and host specificity. However, some generalists demonstrated high β-specificity, suggesting these parasites may "switch" hosts, depending on host availability. These results highlight that the terms specialist and generalist are context dependent and may not accurately describe the niche breadth of parasite taxa. Understanding variation in host specificity as it pertains to potential habitat filters may be important for predicting which parasites can bypass host filters and "jump" to a novel host, which has implications for the surveillance and management of vector-borne diseases.

Genomic and ecological factors shaping specialism and generalism across an entire subphylum

Organisms exhibit extensive variation in ecological niche breadth, from very narrow (specialists) to very broad (generalists). Paradigms proposed to explain this variation either invoke trade-offs between performance efficiency and breadth or underlying intrinsic or extrinsic factors. We assembled genomic (1,154 yeast strains from 1,049 species), metabolic (quantitative measures of growth of 843 species in 24 conditions), and ecological (environmental ontology of 1,088 species) data from nearly all known species of the ancient fungal subphylum Saccharomycotina to examine niche breadth evolution. We found large interspecific differences in carbon breadth stem from intrinsic differences in genes encoding specific metabolic pathways but no evidence of trade-offs and a limited role of extrinsic ecological factors. These comprehensive data argue that intrinsic factors driving microbial niche breadth variation.

Revisiting the sialome of the cat flea Ctenocephalides felis

The hematophagous behaviour emerged independently in several instances during arthropod evolution. Survey of salivary gland and saliva composition and its pharmacological activity led to the conclusion that blood-feeding arthropods evolved a distinct salivary mixture that can interfere with host defensive response, thus facilitating blood acquisition and pathogen transmission. The cat flea, Ctenocephalides felis, is the major vector of several pathogens, including Rickettsia typhi, Rickettsia felis and Bartonella spp. and therefore, represents an important insect species from the medical and veterinary perspectives. Previously, a Sanger-based sialome of adult C. felis female salivary glands was published and reported 1,840 expressing sequence tags (ESTs) which were assembled into 896 contigs. Here, we provide a deeper insight into C. felis salivary gland composition using an Illumina-based sequencing approach. In the current dataset, we report 8,892 coding sequences (CDS) classified into 27 functional classes, which were assembled from 42,754,615 reads. Moreover, we paired our RNAseq data with a mass spectrometry analysis using the translated transcripts as a reference, confirming the presence of several putative secreted protein families in the cat flea salivary gland homogenates. Both transcriptomic and proteomic approaches confirmed that FS-H-like proteins and acid phosphatases lacking their putative catalytic residues are the two most abundant salivary proteins families of C. felis and are potentially related to blood acquisition. We also report several novel sequences similar to apyrases, odorant binding proteins, antigen 5, cholinesterases, proteases, and proteases inhibitors, in addition to putative novel sequences that presented low or no sequence identity to previously deposited sequences. Together, the data represents an extended reference for the identification and characterization of the pharmacological activity present in C. felis salivary glands.

Integrated analysis of the sialotranscriptome and sialoproteome of the rat flea Xenopsylla cheopis

Over the last 20 years, advances in sequencing technologies paired with biochemical and structural studies have shed light on the unique pharmacological arsenal produced by the salivary glands of hematophagous arthropods that can target host hemostasis and immune response, favoring blood acquisition and, in several cases, enhancing pathogen transmission. Here we provide a deeper insight into Xenopsylla cheopis salivary gland contents pairing transcriptomic and proteomic approaches. Sequencing of 99 pairs of salivary glands from adult female X. cheopis yielded a total of 7432 coding sequences functionally classified into 25 classes, of which the secreted protein class was the largest. The translated transcripts also served as a reference database for the proteomic study, which identified peptides from 610 different proteins. Both approaches revealed that the acid phosphatase family is the most abundant salivary protein group from X. cheopis. Additionally, we report here novel sequences similar to the FS-H family, apyrases, odorant and hormone-binding proteins, antigen 5-like proteins, adenosine deaminases, peptidase inhibitors from different subfamilies, proteins rich in Glu, Gly, and Pro residues, and several potential secreted proteins with unknown function. SIGNIFICANCE: The rat flea X. cheopis is the main vector of Yersinia pestis, the etiological agent of the bubonic plague responsible for three major pandemics that marked human history and remains a burden to human health. In addition to Y. pestis fleas can also transmit other medically relevant pathogens including Rickettsia spp. and Bartonella spp. The studies of salivary proteins from other hematophagous vectors highlighted the importance of such molecules for blood acquisition and pathogen transmission. However, despite the historical and clinical importance of X. cheopis little is known regarding their salivary gland contents and potential activities. Here we provide a comprehensive analysis of X. cheopis salivary composition using next generation sequencing methods paired with LC-MS/MS analysis, revealing its unique composition compared to the sialomes of other blood-feeding arthropods, and highlighting the different pathways taken during the evolution of salivary gland concoctions. In the absence of the X. cheopis genome sequence, this work serves as an extended reference for the identification of potential pharmacological proteins and peptides present in flea saliva.