My interest in temperature-oxygen interactions traces to research I did as a graduate student at The Friday Harbor Labs. Tnere I met and fell in love with a species of egg-mass-laying bubble snails called Melanochlamys diomedea. These snails are common in some sandy intertidal zones around San Juan Island, including False Bay. Using False Bay snails I did my first publishable set of experiments, on salinity tolerance of embryos. For a later symposium, at an SICB meeting, I wrote a paper (Woods 1999) on what turned out to be a main thread of my subsequent research (which I didn't expect at the time). That paper developed the idea that variable temperatures alter relative rates of oxygen consumption by, and supply to, biological structures, especially those (like egg masses and insect eggs) for which oxygen enters by diffusion.
Since then I have collaborated with two other biologists on the physiology and ecology of marine-invertebrate egg masses. With Bob Podolsky (College of Charleston), I have done additional work on egg masses of M. diomedea and several other species near FHL. We have focused on how oxygen concentrations in egg masses are shaped by egg-mass size, deposition site, and degree of diatom growth in egg-mass gel. We discovered, for example, that egg masses laid on subtidal macrophytes (algae, eelgrass) undergo enormous changes in oxygen levels. Those changes are driven by diurnal oxygen production by their macrophytic substrates. In addition, egg masses not laid on macrophytes often house, within their gel, high concentrations of diatoms and other unicellular photosynthesizers, which can drive rapid changes in oxygen levels.
In a related project, Amy Moran (Clemson University) I are working on the structure and function of egg masses laid by species in temperate and Antarctic waters. Yes, Antarctica! This project uses nudibranch egg masses to test mechanistic ideas about the factors underlying polar gigantism--the tendency of taxa at the poles (in polar seas) to be larger-bodied than closely related species elsewhere in the world. In particular, we have focused on the so-called oxygen hypothesis of polar gigantism (first crystallized by Chapelle and Peck, 1999), which posits that large body size is an evolutionarily allowable outcome in polar waters because (i) cold temperatures depress metabolic demand for oxygen, and (ii) cold water contains lots of oxygen. Together those characteristics of polar waters should free organisms from size-related constraints on oyxgen delivery and may allow the evolution of large body size.
We were funded by NSF's Office of Polar Programs for two field seasons at McMurdo Station to work on nudibranch egg masses, and we went to the ice with 5-person teams in both 2006 and 2007. We collected nudibranchs and their egg masses by SCUBA from the benthos of McMurdo Sound (unparalled diving--see slide show [coming soon]) and brought them back to the Crary Labs on station. There we measured embryo and egg mass size, metabolic rates of embryos held at different temperatures, and oxygen distributions inside egg masses. All measurements were integrated into a newly-developed mathematical model of oxygen distributions in egg masses. The results in a nutshell (see our two JEB papers, 2008a and 2008b, for more meat): egg masses in Antarctica are larger than related egg masses from temperate waters but our model suggests that they could be quite a bit larger still (= partial support for the oxygen hypothesis of gigantism). We also did a side-project on pycnogonids (sea spiders), which are a kind of biological poster-child for polar gigantism: some Antarctic sea spiders are the size of dinner plates! In this experiment, we collected large and small sea spiders from McMurdo Sound and measured their performance in seawater containing different levels of oxygen; this test showed no effect of body size on oxygen sensitivity, which we interpreted as a rather strong rejection of the oxygen hypothesis.
Highlights of our Antarctic research in a 2008 issue of Research View, a UM research magazine.
