This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Earwigs, small, elongated insects with distinctive pincers at the rear of their abdomens, have little reason to enter open water. While many earwig species are attracted to damp environments, they typically avoid open water.
Yet past studies have found that European earwigs infected with a parasitic roundworm called Mermis nigrescens tend to head toward open water. The molecular and biological reasons for this unusual behavior have not been fully uncovered. Researchers at the University of Otago in New Zealand, the New Zealand Institute for Bioeconomy Science Limited, the University of British Columbia and Brown University recently sought to shed light on the genetic processes contributing to the water-seeking behavior.
Their findings, presented in a paper published in Proceedings of the Royal Society B: Biological Sciences, suggest that the infected insects' march toward water is accompanied by changes in gene activity in both earwigs and the worms infecting them. "I have long been intrigued by the ability of some parasites to manipulate their hosts," Neil J. Gemmell, senior author of the paper, told Phys.org.
"The main inspiration came about during hikes here in New Zealand, where I would on occasion find our native wētā, a large and colorful ground insect, drowned in puddles with large hairworms erupting from their bodies. I was curious to know how the parasite exerted that power over its host that ultimately drove it to kill itself." After observing drowned wētā with parasitic worms leaving their bodies, Gemmell set out to better understand what prompted the insects to enter large puddles. His initial investigations revealed that similar behavior occurred in earwigs, which turned out to be easier to examine than wētā.
For their study, the researchers collected European earwigs and compared uninfected individuals with those at early and late stages of a Mermis nigrescens infection. They examined the insects using RNA sequencing, a technique that measures RNA molecules produced when genes are active. "We used RNA sequencing to describe the suite of genes that were expressed by both the host and the infecting parasite, to explore how the parasitic nematode Mermis nigrescens manipulates European earwigs into seeking out water," Gemmell explained.
"By comparing gene activity in both the parasite and its host at multiple stages of infection, ranging from healthy earwigs to the moment the parasite emerged, we identified coordinated changes in thousands of genes." In their analyses, the researchers detected activity from 12,876 earwig genes and 9,722 roundworm genes. Across comparisons of all sampled stages, they found that 673 earwig genes and 2,672 worm genes became more active, while the activity of 593 earwig genes and 2,293 worm genes dropped. "We found that earwigs showed increased activity in genes associated with sensory and signaling pathways during manipulation, while the nematodes activated genes involved in transport and secretion, suggesting a sophisticated molecular dialogue between host and parasite that ultimately drives the host's fatal journey to water," Gemmell said.
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