"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

August 24, 2015

Polysphincta boops

This is the sixth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Rebecca-Lee Puglisi about not one, but THREE spider-zombifying and how they differ in their host preference, as well as what kind of web they make their spider hosts weave (you can read the previous post on how parasites mess with the Monarch Butterfly's migration here).

Photo of Polysphincta boops by Hectonichus
We all know that the natural world is amazing, and we all know that I hate horror movies! But what if losing ones self control and being manipulated by another was actually happening today and not just something you saw in movies? Let’s set the scene here. You are minding your own business when a six legged monster jumps upon your back, stabbing and poisoning you, knocking you unconscious for a few moments. When you wake up, you're no longer yourself and under control by the monster until the day you die. This nightmare happens on a daily basis to Orb-Weaver Spiders (Araneus and Araniella) in nature thanks to parasitoid wasps (Polysphincta and Sinarachna) that use them as hosts.

A study published last year in the journal Ecological Entomology aimed to identify whether the variations in host response to manipulation is a result of differences among parasitoids or among the spiders themselves. Spiders and wasps were collected at four different locations over Europe by shaking trees and catching the spiders and wasps in large nets underneath. The researchers collected four species of spiders (Araneus diadematus, Araniella cucurbitina, Araniella displicata, and Araniella ophistographa), and three species of parasitoid wasps (Polysphincta boops, Polysphincta tuberose, and Sinarachna pallipes), and 417 spiders were collected in total and placed into a laboratory in separate arenas where different species of wasps were introduced.

They found that while Polysphincta boops only parasitised one spider species - A. ophistographa, its relative P. tuberose was less picky and parasitised three spider species - A. cucurbitina, A. opisthographa, and A. diadematus. The same goes for S. pallipes, which parasitised A. cucurbitina, A. displicata, and A. opisthographa. All these wasps sting the spiders, paralysing them to lay an egg on their abdomen. The spider awakes with the egg that then hatches and feeds on the spiders' hemolymph (its blood), and the spider continues its life as normal.
Left: Web woven by spider parasitised by Polysphincta. Right: Web woven by spider parasitised by Sinarachna
Photos from Fig. 2 of the paper 

Their experiments showed that the parasitised spider’s webs changed from a two-dimensional to a three-dimensional structure with difference in the densities of the webs and the cocoons created. The differences between the webs / cocoons are determined by the final instar larva of the wasp species when neuromodulator chemicals are injected in the host spider by the larva. The spiders parasitised by Polysphincta wasps created a high density silk web with a low density cocoon web, whereas spiders parasitised by the Sinarachna wasps created the opposite structures, with a low density silk web and a high density cocoon web.

Higher density webs and cocoons provided better protection for the developing larva. After manipulating the spider to make the web and cocoon for the wasp larva, the larva then develops into its final stage where it kills the spider host, and eats all its internal organs before retreating into the web cocoon where it will grow into adult wasp. After the it reaches maturity, it will then find a mate to start the whole cycle again. This whole process takes roughly 20-30 days.

This whole circle of life and host manipulation interactions is both amazing and horrifying! I mean, have you seen the ‘chest buster’ scene from the movie ‘Alien’? If movie writers decide to make another big blockbuster about parasitoid creatures like those wasps, but have them attack humans, I will never sleep again!

Korenko, S., Isaia, M., Satrapova, J., & Pekar, S. (2014). Parasitoid genus‐specific manipulation of orb‐web host spiders (Araneae, Araneidae). Ecological Entomology 39, 30-38.

This post was written by Rebecca-Lee Puglisi

No comments:

Post a Comment