It is all about the question. Without a solid question all the data in the world won’t make sense. There has even been recent debate as to whether or not the recent boom in DNA sequencing technology is actually helping the field of parasitology for similar reasons; its data but it is not helping to answer the fundamental questions surrounding parasite biology. I tend to disagree with this point of view but I am reminded of the importance of the question each time I am involved with the teaching of the University of Lethbridge field biology course.
In this course students spend a week in the Cypress Hills Interprovincial Park learning the basics of field biology/ecology. Mainly, how to take an observation made in the field and develop a question to test the basis of that observation in a scientifically sound manner, i.e. using replicates and randomization to ensure good data. There is also a great deal of” McGuiverness” also required because often the equipment that can be feasibly brought to and still function in the field is limited and fairly basic. One project carried out this year really shows how asking a simple question and devising a simple experiment can provide data and insight into some very relevant and interesting biological and ecological aspects of the Dicrocoelium manipulated behaviour system. From there we’ll speculate on how to further bring this into the lab, hopefully showing how the field and lab need each other despite what each may say of the other.
In this project the students asked the question of the Dicrocoelium infected ants found in the Cypress Hills Park, will they return to the same plant they were clinging to if given the choice of another plant. Check out the About page for more background on Dicrocoelium and its effect on its ant hosts but in brief the parasite causes ants to cling to vegetation when the temperature is cool. The parasites do this in order to put themselves in the path of grazing mammals that accidently ingests the infected ants clinging to the vegetation. The important thing here is that the parasite relinquishes control of the ant when the temperature gets to warm whereby the ant may die. Ok, so back to the question. If we raise the temperature and the ants stop clinging and then lower the temperature will the ant return to the same flower if given another plant of the same species to cling to as well? In order to test this, plants with a single infected ant were clipped and placed into a container with another flower head of the same species. The containers were then placed in a lit area until the ant inside released from the plant. The container was then placed in a shaded area to decrease the temperature and it was observed whether the ant returned to the plant, went to the new one or never returned to cling. If they do consistently return, this would indicate that they somehow know or are attracted to the original plant they clung to. Why would they do this? How do they know which plant they were on, good memory, a chemical cue perhaps? We can’t really answer how they would know here but this may lead us to a plausible explanation of why.
If infected ants left some sort of a clue as to where they had visited and where more likely to return, not only would they be more inclined to return to their original site of clinging but other infected ants may too be attracted to come and join them and this may be of advantage for the parasite. The parasite driving this clinging behaviour has the ultimate goal of getting into the final host that eats it off the plant. Once in that host it will then need to find a mate to reproduce with so, if there are lots of ants each with parasites inside all clinging in the same area, or flower it would seem likely that they would all get ingested at the same time. Then they would all end up in the same host with more potential mates. It was this line of thought that led to the second part of the field experiment.
Using the same set up as before, the containers (clinging arenas) with flower heads in them, the students set up an experiment to test the question: if four infected ants are made not to cling and then given a choice of four plants of the same species will they tend to cling in groups on the same flower or each choose a different one? By first asking if they would go to the same plant, indicating some sort of a memory or physical cue leading them back to the same plant a theory explaining why this may be biologically relevant was born, leading to a second experiment to further test that theory. Now I do not have the students’ data and will wait for their report in order to say if we got a reasonable answer to this question but let us imagine taking this to the molecular biology lab to find further justification for the nice little theory devised here.
Inside of each ant there are multiple parasite individuals, this number can vary from one to hundreds. From a parasite perspective then depending on how many other individuals are in the same ant the chances of finding a mate can be good or bad. Now this isn’t in the parasites control, so as we have mentioned, getting all the other infected ants to hang out and get eaten together would be in your best interest for this reason alone. However it may be of further importance from a genetic standpoint. Species that use sexual reproduction do so in order to recombine genetic material and create new and better combinations of genes. They are maximising genetic diversity. One of the ways to do this is by mating with individuals that are not genetically similar to you. This adds an extra level of consideration that now must be taken into account by the parasites within these ants. Are parasites infecting a single ant more or less likely to be related to each other than they are to parasites infecting another ant? This is a question that can be answered with molecular biology.
By using molecular biology techniques we can, in theory, determine the genetic relatedness of the individuals within each ant. This will not only provide evidence for or against the idea that the parasite wants to get as many ants as possible to be ingested together it can also shed light onto how the parasites are being transmitted to the ant, remember they get infected by snails, but we won’t even start speculating on that part of the life cycle.
The point of all this was to show firstly the importance of having a concise testable question not only for field research but all research and secondly how field work can lead to lab work. Using fancy lab techniques can often be regarded as the “better” of the two options but without observations and data from the field, sometimes the practical meaning behind the genetic data may get lost. Plus a whole summer inside a lab can get quite dreary.
Brad van Paridon