Mantids contaminated with horsehair worms exhibit dramatic modifications in behaviour linked to the manufacturing of parasite manipulation molecules which might be homologous to host molecules.

Hilary Hurd 10 Nov 2023

A horsehair worm. Supply: Wikipedia, attribution; Bildspende von D. Andreas Schmidt-Rhaesa, Veröffentlichung unter GNU FDL

The weird manner through which parasitic infections can alter the behaviour of their host maintain a particular fascination. These behavioural modifications typically expose the host to larger threat of predation by the parasite’s definitive host, thus enhancing the parasite’s prospect of transmission. The mechanism underlying these behavioural modifications have been the topic of a lot debate. Are they the results of so-called manipulation molecules, produced by the parasite (an instance of the prolonged phenotype idea), or the results of host engendered responses to an infection?

Horsehair worms

One group of parasites that trigger a spectacular change within the behaviour of their hosts are the nematomorphs. Often known as horsehair worms due to their form and occasional look in horse water-troughs, the adults are free dwelling and located in damp or aquatic environments, whereas the larvae infect arthropods, often bugs.

Nematomorph infections in two teams of insect hosts, the crickets and mantids, have been investigated in some element.  Crickets and mantids often shun open areas and water our bodies due to the chance of publicity to predators, Nevertheless, when contaminated with a number of horsehair worms, they wander to massive water our bodies, attracted by the horizontally polarised mild the water provides off. Right here they launch themselves into the water, probably committing suicide.

As they wrestle to remain afloat the lengthy skinny horsehair worms emerge from their our bodies and swim away. Lots of the hosts drown however, if they’ll make it to the financial institution, it has been noticed that they’ll survive the an infection and subsequent ducking. The grownup worms mate, eggs hatch within the water and the horsehair worm larvae infect aquatic insect larvae. They continue to be of their insect host till it emerges from the water and, if this contaminated insect is predated by the horsehair worm’s main host, the life cycle is accomplished (For those who’ve not come throughout these parasites earlier than I like to recommend viewing this video).

The mechanism underlying host manipulation.

In 2005, a proteomics examine of horsehair worms infecting crickets confirmed that the parasites produce molecules that alter the central nervous system of the host. Two proteins had been discovered to be homologous to proteins discovered within the cricket, suggesting a case of molecular mimicry.

This suggestion has not too long ago been bolstered by a publication from a staff from the RIKEN Heart for Biosystems Dynamics Analysis in Japan, led by Tappei Mishina. This group investigated the parasitic nematomorph, Chordodes fukuii, and its host, the narrow-winged mantis, Tenodera angustipennis.

Subject-collected mantids had been held in water. If nematomorphs emerged it was assumed that they had been mature and host manipulation could be occurring. The presence of immature nematomorphs that didn’t emerge was considered a pre-manipulation state. Nematomorphs stored for a number of days after emergence had been considered post-manipulation and uninfected mantids had been controls. Complete transcriptome evaluation was carried out on entire physique RNA collected from entire nematomorphs, and simply from the brains of mantids, at these completely different phases.

Over 3,000 up-regulated and over 1,500 down-regulated genes had been detected in nematomorphs through the manipulation part, whereas mantid brains didn’t present clear distinction between any phases. This strongly supported the speculation that nematomorphs had been producing manipulation molecules that mimic host molecules to manage features of host behaviour.

Horizontal gene switch 

Molecular mimicry may happen in two attainable methods, by convergent evolution or by horizontal gene switch. The previous would outcome within the manufacturing of proteins which have related 3D constructions to host molecules, however with genes that do not need sequence similarity. In distinction, shut sequence similarity between parasite genes and people host genes that they mimic could be seen, if horizontal gene switch had occurred.

To handle the likelihood that molecular mimicry had occurred, the researchers carried out protein and nucleotide homology searches in opposition to a number of nematomorphs and mantids. Nearly 100% identification occurred between genes from completely different species of mantid. Nevertheless, 1,420 of C. fukuii genes had been discovered to have excessive sequence homology with their mantid host, however not with different nematomorph species.

The authors cautiously conclude that a number of horizontal gene switch from mantid to nematomorph is at the very least partly liable for their potential to control host behaviour, although how they have an effect on the manipulation stays to be found.

Moreover, they counsel a common position for horizontal gene switch to have occurred within the genome evolution of different manipulative parasites and counsel the methodology used on this examine might be utilized extensively to elucidate this proposal.

As they state, there’s little or no proof of horizontal gene switch between multicellular eukaryotes. This makes they findings notably thrilling and it’s to be hoped that many extra manipulative parasite / host associations are investigated on this manner.