Evolutionary Oceanography
John Wares
It is amazing how much of the world we know is actually practically invisible. We all know that the surface of the
Earth is seven-tenths water, of course*. And in that, mostly ocean, there are tunas and sea turtles and corals and barnacles. But really, what is important it seems is the small stuff. The stuff that is
so abundant, that despite the tiny size there is enough to feed a lot of blue whales.
What I'm talking about are the plankton. There are two types (I think): plant (phytoplankton) and animal (zooplankton). Yes, there are protists, and viruses, and other microbes in the sea, and they get digested with the whole mass of stuff that gets mashed against the baleen of a whale to make a nutrient smoothie. But we are going to focus on the multicellular fun of the ocean, and how it moves around, and mostly how we don't know that well about how it moves around.
There are three components, none of which we understand all that well. At least, to my liking.
- The life history of the plankton. Understanding this first involves separating alga from animal, and then a number of factors including size, and temperature during development, and what this thing eats or needs, come into the equation. Basically, though, what we generally know little about, and have a lot of uncertainty about, is why it develops in the length of time that it does from zygote to adult, what it needs, to what extent it is a passive floating particle in the ocean or an active swimmer with behavior that is important to its survival, and where it goes while it is developing from a small number of cells to a large number of cells with distinct function.
- Where it goes while it is developing depends not so much on behavior - but that is important - as on the movement of water in the ocean. The viscosity of fluids is important when you are small, and most of these plankton are on the order of a few hundreds of micrometers at their largest. That means that where the water moves, they get carried along. This is important in a lot of ways.
- At a certain scale - I'm talking about time scale as well as spatial scale - the movement of individuals within populations of larvae (another way to think about plankton, in many animals they are the young versions of adults we find on the seafloor) influences how the distinct architecture created by environmental and genetic influences (note the double-usage of "influence", each time suggesting uncertainty) can be associated with its place of origin, of development, of maturation, of existence as an adult. That is a long sentence that leads us to think about how individuals can be adapted to a particular environment, and that is a pretty complex subject.
- Finally, that environment is changing. Has changed. Of course, I'm talking about climate change, but it is so much deeper than the "global warming" phrase; climate change encompasses how chemical change in the atmosphere and ocean lead to increased sea surface temperature, ocean acidification, altered weather and climate patterns, and many other effects.
I just listed four things that all interact - or are they four different ways of describing the same phenomenon? - but all have a great deal of uncertainty surrounding each topic. Here is the key question: how does each one interact in a way that, by informing each other, we reduce that uncertainty enough to understand the whole problem, and what to do or what to study next?
This is evolutionary oceanography. It is the study of how variance, and uncertainty, in the description of many interacting things, lets us understand better what the ocean is, biologically, what it is doing, and what it will become. I am exploring this topic on the web, using a wiki, because that lets me pull together the resources that are visual, data-rich, and correct as quickly as possible. Here is my outline:
- What's Larvae Got To Do With It?
- The Motion of the Ocean
- The Marine Synthesis
- Wish I'd Paid More Attention in Biochem
What's Larvae Got To Do With It?
Of course, I'll start off first by thanking my colleague Peter Marko. Not only have I blatantly ripped off
one of the best titles for a scientific paper ever, but Peter is one my colleagues who pushed me to think about how larvae are not just larvae, but eventual adults. Remember, we are talking about marine organisms, and most marine creatures have a biphasic life cycle. Here I am using "creatures" loosely: always keep in mind there are unicellular beasts, kelp that are simple but could be laid out along a soccer field an impressive distance, and metazoan life that moves slowly but still fulfills the basic tenets of ecology: eat or be eaten. Even among the top predators of the marine invertebrate world (I'm leaving the fish aside here, charismatic, quick-moving, and tasty though they are), there are top-top predators like
Pycnopodia seastars willing to eat anything in their path, including other seastars.
So anyway, these larvae - that become adults - have an ecology. They have behavior. They are individuals. They, my friend, are corporations, as former presidential candidate Mitt Romney said. Wait. Something is backwards. But it works, still. Every individual is a member of a population, which is part of a species; and every individual is incorporated (
Merriam Webster,
united in one body) through proteins and associated cellular complexes, generated by the genetic architecture of that organism, and that involves genes, which involves different mutations.... it gets complicated. We will get there soon enough.
The difficulty in studying marine life is that it cannot be counted accurately; there are too many individuals, and most are very small, and all of it is underwater most or all of the time. It also cannot be tracked easily, again because of size and number and the difficulty of the environment. We try, oh man we try. What this paper is about, essentially, is how we handle the uncertainty in answers we get from these attempts. It is almost maddening that, after hundreds of years of organized and diligent biological research, there are still enormous numbers of species (we don't know how many species exist, even if you can get biologists to agree on what a species is) for which we don't know:
- what do they eat?
- when and how do they reproduce?
- where are they, most of the time?
Think about that. There are some species we know pretty well, of course: the ones we eat. We have come to know an imperfect but immense amount of facts about salmon, for example. We generally agree on how many species there are, what rivers these anadromous fish return to, what habitat they need to spawn,
what nutrients they need in the ocean in order to develop, and
what eats them. We know pretty well where to find oysters (it helps that they are largely found in shallow and intertidal locations), we know when and how they reproduce (we can even help them out in that case), and we know that they are filtering microbes and plankton from the water, part of their ecology as well as survival.
However, biologists are interested in cataloguing and understanding much more about the diversity in the seas. At a very basic level, this is pragmatic: only in seeing how the whole system works can we know how to manage the resources we directly use. The truth, of course, is that most biologists only vaguely give a damn about the human interaction: we just find seastars, barnacles, and comb jellies to be gorgeous and intriguing.
Sources of error in larval biology
Measurement error (how closely do we measure the size of the copepod? how closely can we measure the rate at which a nauplius migrates vertically?), sampling error (how many individuals, from how many locations or populations, from how many species, leads us to generality?), experimental bias (does the development rate of an individual larva in a controlled, measurable environment approximate its development rate in the ocean?).
The Motion of the Ocean
The field of biological oceanography, from which this work is derivative, is expansive and a good textbook generally starts first with a discussion of water. What are its properties, and how do these properties (viscosity, clarity, salinity, and so on) influence the development and ecology of organisms? I can't begin to recapitulate this work here, but point you to Miller & Wheeler's Biological Oceanography. One of the more interesting and surprising components of understanding water in the ocean, and the organisms living in it, is that it is not a large uniform bathtub of water. There are pockets and patches and density gradients that are in constant flux; some factors fluctuate only slightly over time (though, with anthropogenic input, generally in one direction). Other factors change daily, seasonally, or with El Niño events, for example. Understanding this variation, and the trends underlying this variation, makes biological oceanography an inherently mathematical and computational field.
The Marine Synthesis
blah blah, remember that the ocean is what it is, the larvae are what they are, as are the adults. they are truths with a lot of uncertainty. what we talk about next is inference about those truths, and the inference itself has uncertainty built in. but really this applies to all 3 things, the truth is there and we can only measure in very dissatisfactory ways.
effective population size is a big concept. how it is measured. what it means when different approaches tell different htings, and why the ratio of inbreeding effective size and coalescent effective size is underutilized but powerful in documenting change in our planet, and documenting when things are features of an organism rather than a defect (e.g. get to red drum stuff).
to what extent does a strategy of larval waste lead to sweepstakes e.g. Ne/N ratio should be low, it would be a spatiotemporal nest-site model? to what extent does this become a non-neutral process, e.g. what is the heritability for traits such as timing of larval release, or other larval parameters? they get at this just a bit in this paper.
Trends in Ecology & Evolution
Don't get too fancy.
Biological Oceanography
encompasses much of what you are talking about, though I think your ideas on how these 3 components interact is useful. Bear in mind that the difference between pop gen and, say, otolith measurements, is that we think as pop gen people that we are integrating the biology and the movement. But of course otolith chemistry or stable isotope data may be thought of as also tracing something back to the origin.
Wish I'd Paid More Attention in Biochem
here the climate change part: Morgan Kelly, Melissa Pespeni, the effect of Ne on adaptation, noting that this will shape the larval ecology and shape the ocean currents as well, the genetics will continue to be a way to document and glue these together, but coalescent approaches become less useful than population genetic approaches for moving forward: (1) how do pop gen stats of baseline populations and changed populations compare with coalescent stats? (2) experimental work like Pespeni, Morgan Kelly, Jen Sunday becomes more important than demography
*never mind what some editors at big fancy journals have told me about the "generality" of work I've done with colleagues on marine biodiversity, evolution, et cetera
Evolution and Climate Change in the Oceans
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