Crustacean cannot adapt to survive climate change

Tigriopus californicus’ portrait offers the first modern case study to confirm paleoclimatic warnings. Species may be able to evolve around slow changes. But this warming is too fast.

Three months ago a group of Californian scientists [Philosophus cal.– not to be confused with] warned in a Nature publication that the world is already en route to the sixth mass extinction, considering present trends of species decline. And although the biodiversity crisis is caused by the cumulative effect of many different environmental threats [as perfectly illustrated by the case of CCD] climate change is often quoted as the single largest contributor.

But to prove this point we rely on comparisons over millions of years of geology to get to other periods when the Earth’s climate went through transition and Earth’s life was in distress. From fossil records we know lifeforms don’t like drastic changes to their environments – they vanish.

Here on we recently took a better look at some of these dramatic climate changes of the very distant past, in the Cryogenian and the Paleocene-Eocene Thermal Maximum (PETM), possibly connected as moments where deep sea methane hydrates melted and caused a ‘sudden’ warming.

The PETM is ‘just’ 55.8 million years away, so its prints can be studied with relative ease. [Have Cretaceous limestone outcrops nearby, with these typical ammonites? Follow them uphill till the ammonites stop – that’s (sort of) where (65.5 million years ago) the dinosaur-killing meteorite hit – and the layer on top of that could well be Paleocene (or any other Tertiary).]

The PETM is also interesting because it happened so fast, geologists say – and that’s why it killed so much marine life. ‘Fast’ in this case means – we know since last week’s Nature Geoscience – not 6 degrees in 10,000 years (as previously suggested), but 6 degrees in 20,000 years. As we are now somewhere on course for a minimal 3 degrees in one century, the current climate change happens at least 100 times faster.

That’s where the logic comes from to suggest species these days may also die out, because they won’t have enough time to evolve or adapt otherwise.

But paleostudies are easily dismissed. It’s the past, so it’s highly theoretical by nature, we feel. ‘You talk of extinctions, but when I look that far back getting born in the first place is my primary concern.’

‘And now that I live myself, I don’t feel that a little extra warming could hurt life that much.’

It’s like the frog in boiling water that fails to see the forest through the trees. We are (by definition) caught right in the midst of the Anthropocene. Species die out all around us all the time, some receive (a little) attention, many go unnoticed; always it is hard to pinpoint CO2 as the main culprit.

And to add up to this we live under false assumptions about the genetic adaptability of species around us, a new study by the University of California suggests. We are finally getting to the little shrimplike that features in Wednesday’s Proceedings of the Royal Society B.

T. californicus is a tiny crustacean that lives along the northern Pacific Ocean, on the fringes of the sea. In fact it lives just outside it, in small pools in the rocks, which are filled with ocean spray from the waves beneath.

It is a common creature – it can be found from Alaska to California, suggesting it is quite tolerant to temperature differences. That suggestion is an assumption and it is wrong. The different colonies have no contact and all have distinctly evolved genetic heat tolerance. During simulated evolution (selective breeding with those that survive slightly increasing warming) over the generations the researchers were only able to increase the heat tolerance by 0.5 degrees – in a few of the groups. In others it had hit a plateau before.

“[…]heat-tolerant phenotypes observed in low-latitude populations cannot be achieved in high-latitude populations, either through acclimation or 10 generations of strong selection. Finally, in four populations there was no increase in thermal tolerance between generations 5 and 10 of selection, suggesting that standing variation had already been depleted. Thus, plasticity and adaptation appear to have limited capacity to buffer these isolated populations against further increases in temperature. Our results suggest that models assuming a uniform climatic envelope may greatly underestimate extinction risk in species with strong local adaptation,” the researchers conclude.

The proof is only in a tiny copepod. But that copepod may not be the only organism who will find it hard to bend its genes over several degrees – within this one century. Besides that we don’t have to bring every type of crustacean to the laboratory, to investigate the effects of climate change. Studies of the deep rough ocean draw the exact same conclusion: decline.

© Rolf Schuttenhelm |

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