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Predators and parasites

Some parasites manipulate their hosts (who they infect) in some way in order to be eaten by their end host, who they will reproduce in. For example, liver flukes reproduce in sheep and cattle, but use a number of intermediate hosts, such as ants and snails, in order to reach their final host. However, not all parasites use this method as some only require a single host to reproduce but if this host is killed then the parasite will die too.

This is the kind of parasite that I work on. I'm currently in the third year of my PhD working on the nematode (parasitic worm) Heterorhabditis bacteriophora which only requires one host to reproduce. However, this parasite uses a range of defences to ensure that the host it has infected is not eaten by predators. It does this in a number of ways: it changes the colour of the host, with most insect larvae becoming red in colour, it bioluminesces (glows-in-the-dark), produces a foul-smelling odour and makes the host taste bad.

What I'm interested in is how this affects different predators' behaviour and how this is affected by different stages of infection. In the laboratory at the main university campus I set up infections using the parasite and soft-bodied, slow moving waxworm larva. After two days the larvae die and start to turn the red colour, which gradually builds up and darkens over time.

My experiments at Ness Gardens have examined the effect of different infection stages, hence differing red colouration, on predation by birds. Over the past few years I have been training birds to come down to a set of trays to feed at regular times which involved a lot of porridge! I would then place out a range of infected prey, including uninfected prey (normally white in colour) and observe the birds for two hours to see which they would take. My experiments support the idea that the red colouration seems to act as a warning signal to stop predation as birds would avoid the infected prey, especially the latter stage, dark red infected prey. They would tend to only eat the uninfected prey and throw the infected prey away once they tasted it.

This year I am now trying to see how birds respond to prey which are already quite dark in colour, such as mealworms, to see how the prey look once infected i.e. do they still turn red, and do birds respond to this in the same way as the waxworms. I am therefore running the same experiment but looking at how birds respond to infected mealworms at different infection stages, rather than waxworms. So far the experiment has been running well and is showing similar results to those with the waxworms but you'll have to watch this space!

As you walk round near the pine woods, keep an eye out for my feeding stations and feel free to come and chat to me!!!

 

Rebecca Jones, PhD student, Evolution, Ecology and Behaviour, IIB, University of Liverpool