Today, it was time to leave microevolution behind, and talk about how new species form. Now that they understand how adaptations and natural selection cause populations to change, it’s an easy step to understanding how this can lead to speciation. To drive that concept home, I put together a speciation activity based on this cool online natural selection simulation: http://sepuplhs.org/high/sgi/teachers/evolution_act11_sim.html.
The simulation tracks populations of birds on an island, to see how natural selection and mutations can cause phenotypic changes. You start with 3 populations of 300 birds each, and follow them through 1,000,000 years of evolution. Throughout this time, the simulation makes a notification any time a mutation takes place, along with the overall effect – was it positive or negative? Did it help to increase, or decrease the population?
The instructions on the website call for starting with three phenotypically different populations of birds, to see how they respond differently to the various selective forces. But since I was interested in speciation from common ancestors, I had my students do things a little bit differently. They started out with three identical populations of birds, with all birds having intermediate phenotypes for all characters (medium size, rather than small or large; medium beak length and curvature, and brown plumage). This way, they could get a feeling for how both selective and random forces can affect populations.
The simulation takes place in two rounds: the first, you follow birds in a single location for 500,000 years. Then, the populations disperse to different habitats on the island, and you can then witness another 500,000 years of evolution, under different selective forces. Since we were modeling speciation, I specified that, by the end of the simulation, any populations that differed in at least two characters would be considered separate species.
We didn’t see a whole lot of change after the first 500,000 years, which makes sense since all birds experienced the same conditions. But once they dispersed to different habitats, WHOA they started differentiating quite a bit. On the whole, I was pleased with the way the activity went, and the students seemed to really enjoy it. I would definitely use this activity again in the future.
After the activity, we watched a film: the Nova Origins, “How Life Began,” featuring Neil Degrasse Tyson. This is a great introduction to our next unit: diversity of life on Earth. In the film, he talks about how life might have emerged out of the chemical constituents and conditions that were present on early Earth. I mostly like it because there’s lot of volcano eruptions, and cool stuff like that. Also, I think Neil D.T. is fantastic.
After lunch, I dove right into diversity. I tend to spend more time on this part of the course than anyone else I’ve spoken with about this non-majors curriculum, and there are a couple of reasons for this. First, the amazing variety of life on Earth is one of the things that caught my interest in science at a very early age, so I absolutely love sharing my enthusiasm with students about all the cool organisms that surround us. One of my dreams is to be able to teach a dedicated zoology class one of these days (honestly, that is the class I was BORN to teach haha). If it was just about my enjoyment, however, I would try and rein myself in, but invariably, I have students who tell me this is their favorite part of the course. So, I spend a fairly substantial amount of time on diversity.
Today, we started out with mostly teeny tiny things: prokaroyotes (bacteria and archaea), and protists (mostly eukaryotic microbes, but also including some larger things like algae). I walked through the basics in lecture, and then the fun started: MICROSCOPY LAB!
In the past, I arranged to have prepared cultures of little critters on hand – things like Euglena, Parameciums, Volvox, blue-green algae. This time around, I’d thought we’d try something different. Instead of providing samples, I took the class out to the campus lake, so they could collect their own water samples, focusing more on discovery, rather than studying any particular organisms. (Along the way, we also visited the nifty fungus we’d found back on the first day of class).
On the way back from the ponds, we stopped for a little adventure. Transfer orientation was going on that week, and there were all sorts of booths set up for the new students. We tried to get some free t-shirts, but failed (they were for incoming students only), but they did take this fabulous picture of us, pond water samples at all:
Back in the classroom, we pulled out the compound microscopes, along with some glass slides and methylcellulose quieting solution (to slow down how fast they swim), and I showed them how to make wet mounts from their samples.
So, how did it work out?
IT WAS AWESOME! WE FOUND THE COOLEST STUFF!!!!!!! Here are some photos and videos, taken with my microscope camera (I have a microscope similar to this one, but I usually just remove the camera, and insert it into the eyepiece of one of the school’s microscopes, as they have better quality optics).
To be honest, although this was supposed to be the protist lab, most of the things we found were actual animals. We did find a few protists, though, like this algae:
Another protist: Halteria grandinella
I think these might be Tetrahymena:
We found an insect, and a few crustaceans, including what I think is an Alona sp (shown in the videos):
But I think the star of the show today was this lovely critter: a HYDRA! (No, not the multi-headed dragon kind. This one is a Cnidarian, closely related to jellyfish and corals):
We ended up spending the rest of class time looking through the microscopes, and I’m pretty sure everyone found something cool in the water sample they’d collected. There’s just something very satisfying, and a bit mind-blowing, about finding all these things living in the lake we walk by every day.
Seriously, microscopy is the best.