How We Think About Clam Poo: Ideas Matter

Wood-boring bi-valves

Xylophaga wood sample

This is the third in a series of posts by Associate Curator of Invertebrate Zoology Janet R. Voight as she heads out on an expedition to Norway. There, she and colleagues will look for a wood-boring clam, Xylophaga dorsalis, to study its, well, poo. Read the first post and stay tuned for upcoming posts to find out what they discover.

Should you eat that expired food? Making hypotheses in daily life

When your goal is to understand what is going on with an animal that bores head-first into solid wood and then fills in the space around it with its own feces, you start with some basic questions.  For a scientist, that means making a hypothesis: a guess about what might be happening. A good hypothesis leads to testable predictions. People do this every day, so it isn’t a big deal. Let’s say you find something in the refrigerator that is just past its “sell by” date. You hypothesize that it is still edible (you’re hungry!). If that hypothesis is true, it predicts that it won’t smell bad and it will look okay. So you sniff it. If it smells fine, you hypothesize that if you eat it, you won’t get sick. But what if you notice that the color is wrong, like if it is meat and it’s green? Then, you’d reject the hypothesis that it is okay to eat. The basic idea is that to test the hypothesis, you check out whether the predictions that it smells okay and looks okay are true before you accept the hypothesis and eat it.

Many ways to test an idea

So, how does this relate to the wood-boring clams we’re studying in Norway? Here, we are hypothesizing about a process, so it isn’t a yes or no issue; we want to test as many hypotheses as we can to make the most out of the our efforts and make sure we know what is going on. This means we need to think of other potential explanations for what’s going on (called alternate hypotheses). Each one has to have testable predictions that are unique.

Our hypotheses (so far, we may come up with more):

1) The clam feces in the borehole sustain microbes, essentially culturing bacteria that turn sulfide into sulfate—so these bacteria help feed the clam!  

2) The opposite of hypothesis #1: the feces, because they are bound together by mucus the clam secretes, keep the sulfide away from the clam (it’s toxic, after all!). It gets turned into sulfate without involving the clam.   

3) Our third alternative hypothesis is that the feces carry a chemical that softens the wood and therefore makes it easier for the clam to bore into wood.

4) Our final hypothesis is a traditional one. We always must consider that sometimes a character or behavior is just there, it doesn’t do anything for anybody. This is our default.  

Think about how you would go about testing which of these (if any) is correct. I have thought about it a lot and will share what I think, and why, later on.

Read on in Part 4: Bacteria Save the Day...Maybe

Funding for this project was provided by the Robert A. Pritzker Center for Meteoritics and Polar Studies established by a grant from the Tawani Foundation.