Evolution, Ecology, and Baby Urchins

In my first post, I promised to unpack my research statement a little bit. What exactly do all these terms mean and why are they important? Today I'll focus on the first term: evolutionary ecology.

Like all compound nouns, this is really an adjective (evolutionary) combined with a noun (ecology).

Ecology, according to the dictionary definition, is the study of the interaction between organisms and their environment. How do animals and plants interact with each other, and how does the environment influence what they do?

Evolution is the study of how organisms change through time due to changes in their genes (usually changes in the sequence of their DNA).

So evolutionary ecology is the study of how evolution impacts the way organisms interact with their environment, or how interactions between organisms and environment can influence the course of evolution. Two sides of the same coin, and I find both perspectives fascinating.

Some of my favorite science stories come from the field of evolutionary ecology. Seriously, go read about how toxic newts and their garter snake predators are fighting to the death in an evolutionary arms race. Or what happens when you watch bacteria evolve for twenty-five years while changing their environment in controlled ways (that's a lot of bacterial generations!)? But there are plenty of cool questions and answers in marine evolutionary ecology as well, and that is what I spend a lot of time thinking about. Here is an example of evolutionary ecology thinking applied to a classic marine invertebrate problem.

<- This is a picture of a larval echinoderm (a heart urchin), as seen through a microscope. It will grow up to look like this, as seen not through a microscope. ->

Like any organism, a female echinoderm has a decision to make when she reproduces. (I use 'decision' here as if it were some sort of conscious choice, but since the female echinoderm doesn't have a brain, she is not making a 'decision' like you did when you wanted breakfast this morning. She just does her thing in response to cues from the environment and from her genes. Having seen my brother trying to make decisions before breakfast, he might actually be part echinoderm, but I digress.) Assuming that she has a certain amount of energy stores to make eggs, she can either use that energy to make many many tiny eggs, or a much smaller number of big, energy-rich eggs. Each choice comes with costs and benefits. Many tiny eggs make more offspring, but they may be more vulnerable out in the water. Larger eggs means fewer offspring, but because they got more energy from their mom, they are bigger and may have better chances of survival. So what is a female echinoderm to do?

I chose the example of an echinoderm here more-or-less at random. All marine invertebrate groups are faced with this 'choice.' Some species of echinoderm do one thing while other closely related species of echinoderms do the other. Some species of worms and sea slugs can do both (maybe more on that some other time). Understanding why these different strategies might evolve is the purview of evolutionary ecologists. If food is scarce, is it better for mom to make larger babies that don't need to feed themselves? and if there's lots of food for the babies to eat, is mom more likely to make tiny babies? what if the food supply changes through time in an unpredictable fashion?

My goal here is not to answer these questions (there are whole research programs devoted to them -- see the reference below for a thorough overview), but to give you a feel for the sort of questions that I study as an evolutionary ecologist of marine invertebrates. Next time I'll talk more about those invertebrates -- who are they, why should we care about them, and which ones are the absolute coolest?

Oh! and the answers to the questions about the Octopi Wall Street cartoon on the last entry. We have pictured, from left to right:
- a jellyfish (phylum Cnidaria)
- a grasshopper (phylum Arthropoda)
- a snail (phylum Mollusca)
- an octopus (phylum Mollusca)
- a sea star (phylum Echinodermata)
The sea star is our closest relative in the picture. More on that next time.

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Further reading:
The Evolutionary Ecology of Offspring Size in Marine Invertebrates (Marshall & Keough 2008, Advances in Marine Biology, 53: 1–60.)