Ben Hanelt

Mounting evidence supports the assertion that Earth is undergoing a sixth mass extinction event, driven exclusively by human activity. Among the many taxa at risk are parasitic organisms, which are often overlooked in biodiversity assessments. Parasites, particularly those with complex life cycles like gordiids (hairworms), are highly susceptible to extinction through mechanisms including host loss, habitat alteration, and climate-induced phenological mismatches. Gordiids, freshwater parasitic worms requiring both aquatic and terrestrial insect hosts, are widely distributed but largely understudied, with over 80% of species diversity yet to be described. In the southwestern United States, a region disproportionately affected by climate change, endemic gordiid species face unprecedented threats, including prolonged droughts, reduced streamflow, insect host declines, and increasingly frequent and severe wildfires. These changes negatively impact the availability and synchrony of hosts required to complete the gordiid life cycle, while wildfires additionally increase post-burn erosion that may flush parasite stages downstream and out of suitable habitats. Recent studies have documented apparent extinctions of several gordiid species with restricted ranges in the Sky Islands and Rocky Mountains, including Paragordius amicus, Gordius sp., and Gordionus lokeri, each known from single localities before devastating megafires. Cryopreservation offers a promising long-term strategy, as gordiid larvae can be frozen and reanimated even after more than a decade, introducing the idea of “seed banking” to parasites and the possibility of reintroducing extinct species. Our findings underscore the urgent need to integrate parasitic taxa into conservation strategies and biodiversity assessments.

The 19 genera within the phylum Nematomorpha contain approximately 350 species. The cosmopolitan genus Gordionus Müller, 1926 contains about 58 species, 6 of which occur in the contiguous United States of America. Recently, 2 new Gordionus species were described from high-altitude streams within the southern Rocky Mountains, near Santa Fe, New Mexico. Here we describe another new Gordionus species, from a high-altitude stream in the southern Rocky Mountains, from near Taos, New Mexico. The sites consisted of temporary puddles and a small human-made stream at 3,175–3,250-m altitude in aspen/pine woodland. Gordionus lokeri n. sp. has 1 areole type, which varies in shape and size between and within body regions. Midbody areoles are elongated, polygonal, or triangular, shingled, with the raised side of the areole serrated. The interareolar space is narrow, containing few bristles. The male cloacal opening is surrounded inside and outside by narrow branching bristles that bifurcate or trifurcate deeply; the furcae then subdivide several times terminally. Adhesive warts are lacking. Genetic data, consisting of partial cytochrome c oxidase subunit I (COI) gene sequences, clearly separated G. lokeri n. sp. from other Nearctic species. This is the third Gordionus species described from high-elevation streams in the Rocky Mountains. It appears that this high-altitude habitat represents the preferential niche for numerous species of this genus, and thus future work should focus on describing gordiid diversity in other parts of the Rocky Mountains.

Background: The full scope of the genes expressed by schistosomes during intramolluscan development has yet to be characterized. Understanding the gene products deployed by larval schistosomes in their snail hosts will provide insights into their establishment, maintenance, asexual reproduction, ability to castrate their hosts, and their prolific production of human-infective cercariae. Using the Illumina platform, the intramolluscan transcriptome of Schistosoma mansoni was investigated in field-derived specimens of the prominent vector species Biomphalaria pfeifferi at 1 and 3 days post infection (d) and from snails shedding cercariae. These S. mansoni samples were derived from the same snails used in our complementary B. pfeifferi transcriptomic study. We supplemented this view with microarray analyses of S. mansoni from B. glabrata at 2d, 4d, 8d, 16d, and 32d. Principal Findings: Transcripts representing at least 7,740 (66%) of known S. mansoni genes were expressed during intramolluscan development, with the greatest number expressed in snails shedding cercariae. Many transcripts were constitutively expressed throughout development featuring membrane transporters, and metabolic enzymes involved in protein and nucleic acid synthesis and cell division. Several proteases and protease inhibitors were expressed at all stages, including some proteases usually associated with cercariae. Transcripts associated with G-protein coupled receptors, germ cell perpetuation, and stress responses and defense were well represented. We noted transcripts homologous to planarian anti-bacterial factors, several neural development or neuropeptide transcripts including neuropeptide Y, and receptors that may be associated with schistosome germinal cell maintenance and that could also impact host reproduction. In at least one snail the presence of larvae of another digenean species (an amphistome) was associated with repressed S. mansoni transcriptional activity. Conclusions/Significance: This in vivo study, particularly featuring field-derived snails and schistosomes, provides a distinct view from previous studies of development of cultured intramolluscan stages from lab-maintained organisms. We found many highly represented transcripts with suspected or unknown functions, with connection to intramolluscan development yet to be elucidated. AUTHOR SUMMARY: Schistosoma mansoni is one of the most important schistosome species causing the neglected tropical disease human intestinal schistosomiasis. By focusing on S. mansoni in vivo with its broadly distributed sub-Saharan African snail intermediate host, Biomphalaria pfeifferi , we uncover new insights and basic knowledge of this host-parasite relationship that are critical for understanding schistosomiasis transmission. We show that in vivo studies, particularly using field-derived specimens, provides a distinct view from the uniformed transcriptional responses traditionally seen from in vitro studies on S. mansoni and Biomphalaria snails. With the growing consensus that we need to supplement chemotherapy with other control methods, understanding how S. mansoni interacts with its obligatory snail host becomes integral for future planning of control programs. The data provided within provides specific analysis on how the schistosomes successfully protect themselves from host defenses and the necessary transcriptional responses required for its amplifying asexual proliferation that result in human-infective cercariae.

Gordiids, or freshwater hairworms, are members of the phylum Nematomorpha that use terrestrial definitive hosts (arthropods) and live as adults in rivers, lakes, or streams. The genus Paragordius consists of 18 species, one of which was described from the Nearctic in 1851. More than 150 years later, we are describing a second Paragordius species from a unique habitat within the Nearctic; the Madrean Sky Island complex. The Madrean Sky Islands are a series of isolated high mountains in northern Mexico and the southwestern United States (Arizona and New Mexico), and are well known for their high diversity and endemicity. The new species is described based on both molecular data (COI barcoding) and morphological characters of the eggs, larvae, cysts, and adults. Adult females have unique small oblong mounds present on the interior of the trifurcating lobes with randomly dispersed long hairs extending from the furrows between the mounds. Marked genetic differences support observed morphological differences. This species represents the second new hairworm to be described from the Madrean Sky Islands, and it may represent the first endemic hairworm from this biodiversity hotspot.

The host-parasite associations between ground beetles (Coleoptera: Carabidae) and hairworms (Nematomorpha: Gordiida) collected from the arctic (an understudied and ecologically important region) is described. Carabids and their parasites were collected from 12 sites spanning the 3 northernmost ecoclimatic zones of Canada (north boreal, subarctic and high arctic) using standardized methods. The beetles and hairworms were identified using traditional morphological approaches. Seven beetle species are recorded as hosts: Amara alpina, Pterostichus caribou, P. brevicornis, P. tareumiut, P. haematopus, Patrobus septentrionis, and Notiophilus borealis. All represent new host records (increasing the known North American host list from 14 to 21), and this is the first record of hairworm infection in the genus Notiophilus. Beetles from Banks Island, Northwest Territory, were infected in high numbers (11-19% per sampling period) and were used as an ecological case study. There was no significant r...

In this study, we sampled aquatic snails for the presence of hairworm cysts from 46 streams in Payne County, Oklahoma. Gordiid cysts were found at 70 % (32/46) of sites examined. Based on cyst morphology, we were able to identify three morphological types of gordiid cysts, including Paragordius, Gordius, and Chordodes/Neochordodes. Using our gordiid cyst presence data in conjunction with environmental variables, we developed an ecological niche model using Maxent to identify areas suitable for snail infections with gordiids. The model successfully predicted all presence localities of gordiid cysts in snails over a geographic area of 1,810 km2. We used this information, along with arthropod host infections and crowdsourcing, citizen scientists sampling for adult free-living worms during peak emergent times in areas predicted suitable by the model, to document Paragordius varius, Chordodes morgani, and a new species of gordiid (Gordius n. sp.). To our knowledge, this is the first ecological niche model attempted on such a narrow geographic scale (county level) that recovered known locations successfully. We provide new scanning electron micrographs and molecular data for these species. Our field data and ecological niche model clearly indicate that gordiid cysts are easy to detect in the environment and together these sampling techniques can be useful in discovering new species of gordiids, even in relatively well sampled areas for these cryptic parasites.

It is well established that parasites in the phylum Nematomorpha induce suicide behavior of their insect hosts to bring adult worms to the appropriate habitat for emergence. It is not well established, however, whether other nematomorph-induced behavioral alterations occur before worm emergence. The purpose of our study was to evaluate the effect of the nematomorph Paragordius varius on the calling behavior of the male house cricket Acheta domesticus . We hypothesized that cricket calling, an energetically expensive and risky behavior, would be a potential target for nematomorph-induced behavioral alterations. We assessed if and how infection with P. varius affects A. domesticus calling behavior and whether the presence of wings at time of exposure to P. varius influenced changes in calling behavior. We recorded the calling behavior of male A. domesticus over the course of their infection after exposure to P. various before or after wing development. Additionally, we assessed whether winged crickets were "callers" or "noncallers" before exposure. We found that regardless of cricket developmental stage (or age) at time of infection, infected crickets spent significantly less time calling than their uninfected counterparts but only during the later stages of infection. Developmental stage at infection did affect whether crickets became callers: when infected before wing development significantly more uninfected crickets initiated calling; there was no difference between infected and uninfected crickets when infected as winged adults. Infection was a factor in whether callers stopped calling, with more infected crickets ceasing to call than uninfected crickets. This is the first study to show that infection with nematomorphs affects calling behavior of their insect host. Cricket calling behavior is immensely complex and although it was difficult to elucidate the adaptive nature of these parasite-induced behavioral changes, this study lays the groundwork for future studies to begin teasing out the factors that will help make the determination between side effect of infection or parasite/host adaptation.

Small RNA pathways act at the front line of defence against transposable elements across the Eukaryota. In animals, Piwi interacting small RNAs (piRNAs) are a crucial arm of this defence. However, the evolutionary relationships among piRNAs and other small RNA pathways targeting transposable elements are poorly resolved. To address this question we sequenced small RNAs from multiple, diverse nematode species, producing the first phylum-wide analysis of how small RNA pathways evolve. Surprisingly, despite their prominence in Caenorhabditis elegans and closely related nematodes, piRNAs are absent in all other nematode lineages. We found that there are at least two evolutionarily distinct mechanisms that compensate for the absence of piRNAs, both involving RNA-dependent RNA polymerases (RdRPs). Whilst one pathway is unique to nematodes, the second involves Dicer-dependent RNA-directed DNA methylation, hitherto unknown in animals, and bears striking similarity to transposon-control mechanisms in fungi and plants. Our results highlight the rapid, context-dependent evolution of small RNA pathways and suggest piRNAs in animals may have replaced an ancient eukaryotic RNA-dependent RNA polymerase pathway to control transposable elements. Transposable elements are segments of DNA that have the ability to copy themselves independently of the host genome and thus pose a severe threat to the integrity of the genome. Organisms have evolved mechanisms to restrict the spread of transposable elements, with small RNA molecules being one of the most important defense mechanisms. In animals, the predominant small RNA transposon-silencing mechanism is the piRNA pathway, which appears to be widely conserved. However, little is known about how small RNA pathways that target transposons evolve. In order to study this question we investigated small RNA pathways across the nematode phylum, using a well-studied model organism—the nematode Caenorhabditis elegans—as the starting point. Surprisingly we found that the piRNA pathway has been completely lost in all groups of nematodes bar those most closely related to C. elegans. This finding raises the intriguing question of how these nematodes are able to control transposable element mobilization without piRNAs. We discovered that there are other small RNA pathways that target transposable elements in these nematodes, employing RNA-dependent RNA polymerases in order to make small RNAs antisense to transposable elements. Intriguingly, the most ancient of these mechanisms, found in the most basal nematodes, is a Dicer-dependent RNA-directed DNA methylation pathway. This pathway shares strong similarity to transposon-silencing mechanisms in plants and fungi, suggesting that it might have been present in an ancient common ancestor of all eukaryotes. Our results highlight the rapid evolution of small RNA pathways and demonstrate the importance of examining molecular pathways in detail across a range of evolutionary distances.