Marker Mark and Recapture
Transit was long.
I used it to design a deeply elegant experiment — elegance is the true mark of a good experiment, where a complex problem is broken down into a simply testable idea or procedure — to address one of the most profound questions in science: Where do all of the Sharpies go on a research cruise?
The approach was simple. We would do a mark-recapture experiment to: i) estimate the total black Sharpie population on board and ii) map changes in the distribution of permanent markers as we approached the end of our pre-sampling preparatory period.
A mark-recapture is a very versatile technique. I advise readers to use it for all kinds of common questions: how many socks actually live in my house? At what rate do all of my Oreos migrate towards my roommates bedroom? Which toys does my cat move around in the night?
Essentially, you capture and count a sub-population of something (markers, fish, tigers, socks, cat toys – some of these are harder to subjugate than others) and mark them in a pretty permanent way. Then, as with all the things we love, you set them free. You wait some civilized amount of time dependent on what your question and your target population, and then set out to recapture and count them again.
The idea is that the frequency with which you encounter marked items/organisms is proportionate to the size of the total (i.e., marked and unmarked) population of items or organisms of interest. The more frequently you encounter a marked item compared to unmarked ones, the smaller your population. The less frequently, the larger. You can also map the distribution of your marked items compared to the original distribution to determine how far your target populations travel, how large their home range is, etc.
So, we broke out the Sharpies. We borrowed some delightfully red nail polish from our collaborator Gaya. We painted discrete patches of nail polish on the lids of ten markers, and then we set them free. They looked quite nice, really (Figure 1). To encourage dispersal, we left the Sharpies spread all over the benches so that any passerby would assume we had far too many, and that some should come with them. I am a little embarrassed to say that a lot of thought went into all of this.
Figure 1. A sharpie marked for recapture.
On Night One post-liberation, nothing happened. This was alarming — I had hypothesized that they all would be gone. It was so thrilling to be so wrong! For the next two days, we used the Sharpies as part of our work, but still, none left the home range of our benches.
After three days, we called it off, having made three key findings:
- Despite their famously wandering ways, markers appear to be truly sessile. Despite their high utility (many researchers were observed using Sharpies during the study period), and being laid out in a manner designed to lure a vector to help disperse the markers, no Sharpies moved. This is an incredible level of geographic staying power completely incommensurate with the established fact that Sharpies disappear all of the time.
- The distribution and population density of Sharpies is heterogeneous. On our benches, the population appears to be minimal (all markers had been captured) while marker populations in other labs and even on adjacent benches is seemingly infinite (no marked markers were found). I don’t know how many markers are on this ship, but it must be huge — essentially infinite — and especially so away from where we work.
- We really fundamentally misunderstood the dynamics of markers on a research cruise.
Taken together, we found no evidence that Sharpies migrate during research cruises, at least during pre-sampling periods. It seems likely that the loss of markers is a seasonal process: while we observed no loss during pre-sampling, perhaps their loss processes accelerate during other phases of the cruise. Repeating the experiment during our sampling period and on our transit home is almost certain to yield very different results, and reconcile the lack of loss here with the established pattern of Sharpie loss.
Finally, while it is clear that any loss of markers from our bench during the rest of the cruise would be detrimental because our own Sharpie supply is seemingly minimal, us taking markers from almost any other bench would not induce any noticeable harm on other researchers, infinitely inundated with markers as they are. Very useful indeed.
As a viral ecologist, I found this experiment to be quite enlightening. We don’t think that viruses can actively move, just like permanent markers. We think that markers need humans and that viruses need hosts to move around. However, in this experiment we couldn’t get even markers — something that people want to engage with — to move. How are viruses, those most precious of creatures, ever meant to stand a chance in a world where hosts are actively seeking to avoid them? I just don’t think that we have a good idea of what is going on here.
I came into this experiment full of the confidence of logic: ‘markers disappear, so I will design an experiment to elucidate how’. But I was wrong in some way I still don’t fully understand. The confidence of logic does that to you. It whispers answers in your ear so confidently that you don’ take the time to read or understand the whole question. It reminds me of the Bob Dylan line from the song Desolation Row ‘they’ll kill him with self-confidence after poisoning him with words’.
I’ve been turning these thoughts over in my head for days, seeking an answer for how I got so wrong. Maybe Sharpie loss processes occur on a different time scale than the days I had studied? Maybe they occur on some cruises but not others (if so, why?)? Maybe there are areas of massive marker loss and areas of complete stasis? If so, what characterizes these neighborhoods (perhaps the pace of Sharpie usage in these areas)? How many people picked up markers and then put them back? Imagine if the marked Sharpie were lethal viruses instead, and everyone who picked one up died — how would the viruses ever get around?
I never thought that I would end up drawn this deeply into marker dynamics, but honestly, this stuff is cool!! I love to be wrong. It means that there is a lot further to travel before understanding dawns. I am so glad I did this experiment.
Written by Ben Knowles