Osmoregulation in anthozoan-dinoflagellate endosymbiosis

If Ambien is no longer working for you, take a hack at my Ph.D. dissertation on osmoregulation in anthozoan-dinoflagellate endosymbiosis with the late Dr. Ruth Gates. Read more about the excellent work they are doing at the Hawaii Institute of Marine Biology.

Chapter 1: Introduction (see here for the manuscript version.).

Most animals only have to balance the water in their own cells. Corals and anemones have a harder job: their cells are packed with algae that, every daylight hour, pump sugars into the cell — and those sugars change the cell's water balance. So these animals face a water-management problem almost no other animal does, and it shifts on a day/night rhythm. This chapter gathers everything known about how marine animals and algae each handle water balance separately, and shows that we know almost nothing about how the combined coral-plus-algae unit does it. It argues this gap matters for understanding coral bleaching, since the heat that triggers bleaching also throws off this delicate water balance.

Chapter 2: Gene expression protocols for dual-compartmental organisms (click here for the manuscript version.).

When scientists measure how active a coral's genes are, there's a hidden trap: the sample is really a blend of two organisms — coral plus algae — and the proportion of algae differs from sample to sample. Standard methods ignore this and can give misleading answers. Anderson built a corrected recipe: add a known reference "spike" to each sample, and use an algal headcount (estimated from a specific algal gene, HSP70) to work out how much of the signal comes from algae versus coral. He proved it worked using sea anemones deliberately stocked with different amounts of algae. The method is useful to anyone studying genes in any mixed-organism sample, not just corals.

Chapter 3 — What's "normal" over a day for a Hawaiian coral’s (Pocillopora damicornis) gastrodermal cells? (click here for manuscript version.)

You can't tell whether a coral is "stressed" from its genes unless you first know what normal looks like around the clock. He tracked three stress-signaling genes (the MAPK family) plus two commonly used "reference" genes across day and night in a Hawaiian coral. Two of the stress genes were too faint to detect; the third spiked at night — possibly the coral re-balancing its water after dark, or possibly tied to its algae multiplying (their numbers rose at night). Importantly, the two "reference" genes — which researchers often assume stay constant — actually swung up and down a lot over the day, making them unreliable baselines. A useful cautionary result for the whole field.

Chapter 4 — Do coral cells shrink at night? (proof-of-concept with the Taiwanese coral Seriatopora hystrix)(click here for manuscript version.)

This tests a neat idea: coral cells may physically swell during the day (when algae are pumping in sugars) and shrink at night (when photosynthesis stops and the pressure drops). He measured three genes for the cell's internal "scaffolding" (the cytoskeleton) that should rise and fall with cell size. All three dropped sharply at night — 4 to 7.5-fold lower than midday — consistent with cells becoming smaller and more crowded after dark. The honest caveat: the algae also grew more numerous at night (also crowding the cell), so the safest conclusion is that the coral's effective cell volume shrinks at night, whatever the exact cause.

Chapter 5 — Pulling it together (synthesis)

The overall story: coral cells likely expand by day and contract by night, driven by the algae's light-dependent sugar output and their changing numbers. Three takeaways for the field: (1) you must know a coral's natural daily rhythms before you can claim an experiment "stressed" it; (2) experiments should be designed around time-of-day and light; and (3) because the coral-plus-algae unit balances its water in a fundamentally unusual way, claims about how well corals can adapt to climate change are premature until this is accounted for. The chapter also lays out important caveats — genes aren't the same as proteins, and lab results aren't the same as the wild — and revisits how the field had been framing these questions.