Annual Survey of Horsehair Worm Cysts in Northern Taiwan, with Notes on a Single Seasonal Infection Peak in Chironomid Larvae (Diptera: Chironomidae)

Testing the efficacy of different molecular tools for parasite conservation genetics: a case study using horsehair worms (Phylum: Nematomorpha)

In recent years, parasite conservation has become a globally significant issue. Because of this, there is a need for standardized methods for inferring population status and possible cryptic diversity. However, given the lack of molecular data for some groups, it is challenging to establish procedures for genetic diversity estimation. Therefore, universal tools, such as double-digest restriction-site-associated DNA sequencing (ddRADseq), could be useful when conducting conservation genetic studies on rarely studied parasites. Here, we generated a ddRADseq dataset that includes all 3 described Taiwanese horsehair worms (Phylum: Nematomorpha), possibly one of the most understudied animal groups. Additionally, we produced data for a fragment of the cytochrome c oxidase subunit I (COXI) for the said species. We used the COXI dataset in combination with previously published sequences of the same locus for inferring the effective population size (Ne) trends and possible population genetic structure.We found that a larger and geographically broader sample size combined with more sequenced loci resulted in a better estimation of changes in Ne. We were able to detect demographic changes associated with Pleistocene events in all the species. Furthermore, the ddRADseq dataset for Chordodes formosanus did not reveal a genetic structure based on geography, implying a great dispersal ability, possibly due to its hosts. We showed that different molecular tools can be used to reveal genetic structure and demographic history at different historical times and geographical scales, which can help with conservation genetic studies in rarely studied parasites.

The return to land: association between hairworm infection and aquatic insect development

Host manipulation by parasites can shape host behaviour, community structure, and the flow of energy through food webs. A well-known example of host manipulation comes from hairworms (phylum Nematomorpha), which somehow cause their terrestrial insect definitive hosts to enter water, a phenomenon that has received lots of attention in recent years. However, little focus has been directed towards the interactions between hairworms and their aquatic insect hosts and the return of dormant hairworms from water to land. Here, we ask whether hairworm cyst infections impact, either directly or indirectly, the life history of their aquatic transport hosts. By observing the development of last-instar Olinga jeanae (Trichoptera: Conoesucidae) caddisfly larvae naturally infected with Gordius-type hairworm cysts under controlled conditions, we found that higher numbers of cysts per infected caddisfly correlated with a decrease in time to pupation. These new observations suggest that, apart from the striking host manipulation that brings the parasite from land to water, the presence of dormant hairworms is associated with changes in the development of their aquatic hosts, either through direct or indirect mechanisms, which may accelerate their transition from water to land.

Come with me if you want to live: sympatric parasites follow different transmission routes through aquatic host communities

Community composition, including the relative density of each host species, plays a vital role in the transmission of parasites or disease in freshwater ecosystems. Whereas some host species can effectively transmit parasites, others can act as dead ends (non-viable transmission routes), accumulating large numbers of parasites throughout their life, thus becoming important sinks for parasite populations. Although population sinks have been identified in certain host-parasite systems, robust field estimates of the proportions of parasites that are lost to these hosts are lacking. Here, we quantified the distribution of encysted larval hairworms (phylum Nematomorpha), common parasites in lotic ecosystems, in two subalpine stream communities of New Zealand. With parasite and host population densities calculated per m², we identified which host species most likely contributed to the transmission of three sympatric hairworm morphotypes identified in both streams, and which species acted as population sinks. We also tested for seasonal patterns and peaks in the abundance of each morphotype in the two communities over the sampling season. Finally, we tested whether hosts emerging from the streams had comparable abundances of hairworm morphotypes throughout the sampling period. For each morphotype, different key sets of host species harboured more hairworms on average (abundance) than others, depending on the stream. For one morphotype in particular, two species of hosts were found to be important population sinks that inhibited over a third of these parasites from completing their life cycle. We also observed a clear peak in abundance for another hairworm morphotype during summer. Our data suggest that hosts emerging from the streams matched their aquatic counterparts with respect to hairworm abundance, indicating no infection-dependent reduction in emergence success. Our findings suggest that, depending on relative community composition, sympatric parasites follow different host transmission pathways, some of which lead to dead ends that potentially impact overall infection dynamics. In turn, this information can help us understand the spread or emergence of disease in both freshwater and terrestrial environments, since hairworms infect terrestrial arthropods to complete their life cycle.

A new millipede-parasitizing horsehair worm, Gordius chiashanus sp. nov., at medium altitudes in Taiwan (Nematomorpha, Gordiida)

Gordiuschiashanussp. nov., a newly described horsehair worm that parasitizes the Spirobolus millipede, is one of the three described horsehair worm species in Taiwan. It is morphologically similar to G.helveticus Schmidt-Rhaesa, 2010 because of the progressively broadening distribution of bristles concentrated on the male tail lobes, but it is distinguishable from G.helveticus because of the stout bristles on the mid-body. In addition, a vertical white stripe on the anterior ventral side and areoles on the inside wall of the cloacal opening are rarely mentioned in other Gordius species. Free-living adults emerged and mated on wet soil under the forest canopy in the winter (late November to early February) at medium altitudes (1100–1700 m). Mucus-like structure covering on the body surface, which creates a rainbow-like reflection, might endow the worm with high tolerance to dehydration. Although Gordiuschiashanussp. nov. seems to be more adaptive to the terrestrial environment than other horsehair worm species, cysts putatively identified as belonging to this hairworm species found in the aquatic paratenic host, Ephemeraorientalis McLachlan, 1875, suggest the life cycle of Gordiuschiashanussp. nov. could involve water and land. The free-living adults emerged from the definitive hosts might reproduce in the terrestrial environment or enter an aquatic habitat by moving or being washed away by heavy rain instead of manipulating the behavior of their terrestrial definitive hosts.

A new orthopteran-parasitizing horsehair worm, Acutogordius taiwanensis sp. n., with a redescription of Chordodes formosanus and novel host records from Taiwan (Nematomorpha, Gordiida)

A description of a new species of horsehair worm, Acutogordius taiwanensissp. n., a redescription of Chordodes formosanus, and novel host records for the latter are provided. Acutogordius taiwanensissp. n. is morphologically similar to A. protectus with moderately flat areoles on its tail tips, but is distinguishable by small mid-body ornamentations. Despite the distinct differences in the post-cloacal crescents between 14 male samples, their conspecific status, along with that of nine female samples, was upheld by a phylogenetic comparison of partial cytochrome oxidase subunit I (COI) sequences. Chordodes formosanus is another common horsehair worm species in Taiwan, which was previously believed to specifically parasitize Hierodula mantids. However, in this study, five C. formosanus were observed emerging from an Acromantis mantid, and two long-horned grasshopper hosts (Leptoteratura sp. and Holochlora japonica). These five worms showed high degrees of similarity in COI sequences and morphology, but one of these individuals bore abnormal crowned areoles, which has never been observed in C. formosanus, and may be attributed to the incomplete development of this particular individual.