Lecture 10 (6/10/09): What's Up With "Critter" Days?

I've been getting quite a few questions about these "Critter" days lately. So far, we've had exactly two of them in lecture. One Critter day consisted of 20 minutes of slides/discussion following Exam 1. The other Critter day was 60 minutes of slides/discussion following Quiz 2 today.

Now that there has been two of them, I get the sense that some of you are starting to mumble to yourselves, and to each other, the all-important question: Will anything from these Critter days be on future quizzes or exams?

Before we tackle that question, I want to tackle a related question that I was asked today after class: Exactly how are these Critter days related to the material we've been covering in recent lectures?

This is an excellent question and its one that I hope I can answer...visually.

Take a quick look back with me to an extremely important slide that Prof S showed during Lecture 9.

In hindsight, I probably should have devoted an entire Blog to the "Speciation" slide (below right) in the days leading up to Quiz 2. I (regretfully) say this because I now think I can map a whole bunch of really important terms from this course--genetic drift, reproduction isolation, allele frequencies, Hardy-Weinberg Equilibrium, etc.--onto this one diagram. And, had I done so in a Blog prior to Quiz 2, I think even more of you would have had even more success on today's quiz. Lesson learned...

So what does this diagram show? The blue arrow (ignore the green arrow) is an abstract representation of speciation. In other words, it is supposed to show one species in the process of becoming two species. If there was a single diagram in this course that could represent what today's Quiz 2 was testing your knowledge/understanding of, it's this diagram: If you knew all of the different factors required to produced a new species (i.e., if you knew how to make the blue arrow 'split'), then you likely did very well on the quiz.

Well, after you finished the Quiz 2 on speciation today, Prof S began a Power Point presentation about some "Critters." More specifically, he talked about "Eukarya," including protists, seedless plants, liverworts, hornworts, mosses, ferns, club mosses, seed plants, gymnosperms, angiosperms, etc. But after talking with a few students after class, I got the sense that they were a little bit perplexed as to how the post-quiz material was related to the pre-quiz material. A couple of students said they had a similar feeling when Prof S presented the 20 minutes of "Archea" and "Bacteria" following Exam 1.

To address these concerns, I'm going to have you do a 'thought' exercise with me. My goal in having you do this exercise is to show you how the Critter days and the material tested by Quiz 2 (i.e., speciation), are actually only a few small, easily traced, highly 'illustratable' steps away from each other!

Step One: Abstraction

I need you to do something for me. Go back up to the blue arrow in the speciation slide above, and trace the outline of the blue arrow in your mind. Once you do this, fill in the outlined arrow with black, and then make all of the other colors, arrows, words and images on the slide...disappear.

Congratulations, you've successfully performed an abstraction (which, you should know, is a skill that biologists are masters at doing). You should now see the same thing that I have drawn in the image immediately at right.




Step Two: Rotation

The next mental exercise that I need you to do is rotate the (abstracted) arrow 90 degrees...oh yeah, counterclockwise. If you're following my instructions correctly you should now have in your head the image at right: the two arrows should point 'up.'

Before we go on, it's important to remember that the upward pointing split-arrow still represents speciation! The horizontal blue arrow is still 'there,' but at the same time it's not. I know, I know: it's sort of paradoxical when someone tells you that something is 'there,' but then at the same time tells you that that same thing is 'not there.' But that's one of the powerful things about abstractions...they're like slang in spoken or written language. Nowadays, you say (or text) "OMG!" to someone and they understand exactly what's not there, "Oh My God!"


Step Three: Shrink & Multiply

This next step is easy. Shrink the upward pointing arrow from Step Two and multiply it...6 times. You should now have 7 copies of the (now shrunk) upward pointing arrows, dancing to-and-fro in your mind.

By the way, we're almost done. Just a couple of more steps to go to see how speciation (Quiz 2) connects with Prof S's Critter days. We just have to decide on how to arrange the scattered arrows currently floating in (mental) space.




Step Four: Arrangement

The task now is to arrange the 7 arrows in a very specific arrangement. They all need to be pointing up, and they need to look like they're almost 'growing' out of one another.

I know those aren't great directions, but just look at my image at right...got the picture?

At this point you can see that I've not only arranged the arrows, but I've also labeled the illustration (if you click on the image it'll get larger in a new window). I've given it a time dimension in the form of a vertical line: it says "past" on the bottom and "present" on the top. I've also given it a title, "A model of the evolution of life on Earth by means of speciation."

If you've been following my mental exercise step-by-step, you'll STILL be able to 'see' the blue arrowed diagram lurking just beneath the surface of this new 'tree' of stacked black arrows. Why? Because the blue arrow is STILL there (and not there!). It's just that now the tree of stacked black arrows carries with it the blue arrow's meaning. What is this important meaning?

That's right, you guessed it, it's the concept of speciation. Abstraction can be pretty nifty, eh?

Almost done...almost there

OK, so...to start to summarize and begin to bring today's Blog to a close...The image we produced at the end of our mental/visual exercise illustrates no less than 3 important things that are relevant to your work in BS110:

(1) It illustrates an important concept in this course: It shows how, over time, multiple speciation events could explain the large diversity of life forms presently found on Earth. This happens to be an idea that is largely attributed to Charles Darwin (1809-1882). However, some historians have made persuasive arguments that a contemporary and countryman of Darwin's, Alfred Russell Wallace (1823-1913), deserves more credit for his ideas about the origin of species than have been typically attributed to him in most historical accounts.

• By the way, you wanna read a great book for non-scientists about the adventures of Wallace, Darwin, and the development of the theory of evolution? Try this one, Song of the Dodo by David Quammen. It's fantastic.
  

(2) It illustrates what Quiz 2 covered today! To the right, I have made a red circle around a single speciation event in the diagram.

This was the content, the material, the concept, the idea...whatever you want to call it...this was the 'stuff' that Prof S asked you questions about on today's quiz. My guess is that in the coming days Prof S will talk in more detail about the sum total of the ideas contained within an image like this.

(3) It answers one of the two questions that we posed at the beginning of this Blog (Exactly how are these Critter days related to the material we've been covering in recent lectures?)! Hopefully, you can now see why Prof S has been sharing groups of organisms like "Archea," "Bacteria," and "Eurkarya" with you in class. As you can see from the new image I've created (below right), these are the 3 main categories that most contemporary biologists use to talk about the present (and past) diversity of life on planet Earth!

So, when Prof S is doing his Critter days, in some ways he is sharing with you parts of the current structure of the 'tree of life.' If you click on the image to the right you will immediately recognize a couple of the names appearing in brown, red and purple colors: they are some of the groups of organisms that he discussed in the two Critter days that we've had so far.

To once again remind you of how the Critter days are not that far removed from speciation and Quiz 2, I've included a (somewhat transparent) reproduction of the stacked black arrow tree that emerged from our mental/visual exercises above (upper left corner of the image). See the resemblance between the two images? And even though the red box that showed what Quiz 2 was testing is not there anymore, can you also still 'see' it?

I thought so. You're getting the hang of this abstraction business. In addition, I guess it's official: The SCIENCE sEDiment Blog now has you seeing things that aren't even there (or are they?).

Which brings me to the other question that I promised to answer in this Blog. The one that I know you all care deeply about: Will anything from these Critter days be on future quizzes or exams?

I don't know...why doesn't one of you develop some guts...some courage...some daring...some mettle...some pluck...and ask Professor S in class on Friday.

:)

Lecture 9 (6/8/09): Getting ready for Quiz 2

I know lots of you are working hard to get ready for the quiz, so I thought I'd try to do two things in this post (I can't make it a long one tonight).

First, I want to summarize the most important points from Chapter I and Chapter II of the Biology Bedtime Story. In this summary, I want to tell you what I was doing and what I wasn't doing. Second, I want to try and put a little bit of organization around the Lecture 9 slides so that you can maximize your study time effectively. Here goes...

Did the Forts live happily ever after?

When we last left our finch population, we saw that the drought of 1977 absolutely tore them apart.

By 'tore apart,' I mean to say that they experienced one of the most severe selection pressures that Mother nature could throw at them. Was this a natural selection event? Yes it was. Absolutely.

As you'll recall from the bar graph at the bottom of the Chapter 2 Blog (also below right), the drought seemed to select against the allele combinations for the below average and average beak sizes. However, the drought also seemed to select for the allele combinations for above average beak sizes. Could this same change in the frequency of phenotypes in this Fort population have happened through genetic drift?

If you read my revised entry about genetic drift in the Chapter II Blog, then your answer should be, "Yes." It is possible that even without a natural selection event like a drought the beak phenotypes could change simply because of which birds happen to mate, and which gametes randomly join together in that process. This situation, however, even though it might result in a similar re-distribution of beak phenotypes, would not be considered natural selection.

So, my story about the Forts on the island of Daphne Major was meant to illustrate a natural selection event. Nature, in the form of a drought, selected certain phenotypes to surive the 18 month drought that started in 1977. Some of you may be wondering why those Forts with the above average beaks survive.

Well, once the drought began many of the plants on the island began to decrease their seed production. The Forts, in competition with each other as well as the other ground finches on the island, began looking around the soil and under rocks for any seeds they could find. Just like you and your friends when you are given a bowl of pistachios, the Forts cracked open and ate all of the seeds that were easiest to crack.

After a while, only the difficult seeds were left to eat! Peter and Rosemary Grant took pictures of the one seed that none of the birds seemed to want to eat, but they had to once all the rest of the seeds on the island were gone. Here it is at right. It's called a Tribulus seed and it comes from a caltrop plant. Nasty buggers, arent' they? Believe it or not there's small round seeds housed inside each of those spiky, woody sections which fit together sort of like a pinwheel.

Are you surprised that it was the Forts with the largest beak size/strength that had the most success opening these seeds during the drought? I suspect you aren't. The thing that might surprise you, however, is the difference in beak length/depth between those Forts that survived and those Forts that died. Are you ready for this? It turns out that the average difference was only about 1 mm. Those Forts that survived the drought had beak lengths/depths that were on average about 1 mm longer/deeper than those that died.

Was this a speciation event?

One thing I was to make clear is that my story was meant to illustrate a natural selection event, NOT the creation of a new species. In my story, as I explained in Chapter II, we saw a case of directional selection (you should know about the other types of selection too), but I said nothing about the creation of a new species. After the 1977 drought we still only had one species, Forts. The frequency of their phenotypes had changed, but there wasn't a new species of finch after the drought. The above average beak Forts could still reproduce with the below average and average beak Forts and produce viable, fertile offspring.

So this leads us directly to Lecture 9, in which Prof S spent nearly the entire period talking to you about what it takes to make a new species. He called this "speciation."

I'm not going to go into the details of what counts as a new species mostly because I talked a little bit about 2 species concepts in the Chapter I Blog (I talked about the Biological Species Concept & Ecological Species Concept). Plus, Prof S went over 4 species concepts in class and I don't really think there's anything tricky about them. What I do think is important is that you understand the Biological Species Concept (BSC) the best. That concept seems to me the one that Prof S favored in all of the disussions we've had thus far about species. So, according to the Biological Species Concept, how can you create a new species?

Well, according to the BSC you would have to create (at minimum) two populations from a single population. In addition, the two populations would have to lose the ability to produce viable, fertile offspring with each other.

So how does nature pull off something like this?

In Lecture 9, Prof S gave you two terms that had the word "speciation" in it: allopatric speciation and sympatric speciation. Using both your lecture notes and your textbook or other resources, my advice to you would be to get to know how these two types of speciation operate. How are they similar? How are they different? What conditions are necessary for each of them to occur? You should be able to talk through these two types of speciation pretty fluidly. The lecture slides in which these two terms appeared are copied below:

One thing I would like to point out, however, is that the order of the Lecture 9 slides may have confused you a little bit. Notice that the top of the slides above ask the question: How do these barriers arise? The "barriers" that Prof S was talking about in these two slides are the prezygotic and postzygotic barriers to gene flow (you should know the differences between these two types of barriers--Prof S spent a good deal of time on them in class--6 of 16 slides, in fact).

I want to make it clear that what Prof S was saying with these two slides is that allopatric speciation is one way that prezygotic and/or postzygotic barriers can arise. Sympatric speciation is another. Some of you may have been confused that the 'effects' (the two types of barriers to gene flow) were discussed first and the 'causes' (the two types of speciation) were discussed second.

That's all I have time to discuss now...