Well, my weekdays haven’t been too interesting (more feeding larvae and collecting butterflies), but I had a really nice weekend (Feb 18-19). On Saturday I woke up early, clambered into a van with 11 other researchers, and went to a beach about two hours away. It was quite idyllic: black sand, thatched cabanas, waves perfectly-sized for body surfing, and not a shark, jellyfish, or sharp rock in sight. I spent most of the day shredding the gnar, but also did my fair share of lounging around, eating junk food. It was, in a word, fantastic.
As you probably know, I’m posting this right around the start of Lent, which means that the past week or so in Panama has been Carnival (perhaps most famously celebrated in Brazil). We here at STRI celebrated Carnival last Sunday. Gamboa is a rather small place, and our celebration was also rather small. We divided Gamboa in half, and each “neighborhood” made a parade float out of a truck and nominated a queen to dance on the float. We had a very short, very small “culeco” around Gamboa, which is a parade with music and water fighting. The parade quickly dissolved into just a water fight, which lasted for a few hours, Then we dried off, fired up some grills, and had a massive barbecue, which evolved into a party that went late into the night.
Unfortunately for my readers, I was too busy enjoying myself to catalog these experiences with photos, so I don’t have any to post. Instead, I have something just as enthralling as pictures: science!
Science Break 1- Species
The easy way to explain what I do here in Panama is to say “I use butterflies to study evolution.” I thought I might try to expand on that with some posts that actually explain the science I’m doing. My hope is that I’ll be able to explain everything in simple enough terms that my even my readers whose high school biology classes were decades ago will be able to understand. Feel free to post questions in the comments and I can try to clarify things.
I’ll start by looking at a word that we all know and use, but don’t often think deeply about: “species.” We all know that, say, tigers and mosquitoes are different species, but hardly ever think about why that is. In evolutionary biology, “species” can be defined in a number of ways, but perhaps the most common definition is the biological species concept, which says that species are defined by whether or not populations (groups of organisms) can mate with each other and produce viable offspring. Populations that can’t interbreed are separate species. Populations that can interbreed are the same species. When populations can’t mate with each other, we also say they are “reproductively isolated.” Reproductive isolation is simply a measure of populations’ inability to mate with each other. We can apply these definitions to a real world example. Tigers and mosquitoes can’t mate with each other and produce tigsquitoes, thus they are reproductively isolated and are separate species.
Unfortunately, it’s not always as simple as the tigsquito example. Take horses and donkeys, for instance. We consider them different species, yet they can mate and produce a hybrid, mules. Are donkeys and horses part of the same species? The answer, unsurprisingly, is no. Mules are sterile, which means they aren’t “viable offspring”, and thus horses and donkeys really are separate species.
Looking at these two examples, we see that there are different levels of reproductive isolation, even between things that are definitely species. Tigers and mosquitoes are (in comparison to each other) slightly more reproductively isolated than horses and donkeys: the former can’t mate at all, while the latter can, but produce sterile offspring. Reproductive isolation, then, exists along a continuum. One pole is zero reproductive isolation: the organisms within population(s) can mate with each other and produce offspring with no problem. At the other pole, we have total reproductive isolation: the populations can't mate with each other at all. In between, things can get pretty tricky, but I won’t discuss that until my next entry, which will be on speciation: they process of creating new species.