Author: Massimo Sandal

A lesson from the Iceland walrus

One of my pet peeves is the persistent delusion, implicit in many discussions, that the ecological crisis is a recent phenomenon. Industrialization, pesticides, intensive agriculture on a massive scale would have only recently tipped the scales, while before humanity was more or less in equilibrium with the environment. That we were sustainable. Noble savages. Truth is, we’ve never been. The current Anthropocene extinctions are nothing more than the continuation of the Pleistocene extinctions, and all together they are phases of the Sixth Extinction.

There are endless stories about that, from the American or Australian megafaunas, to the dodo. But it is always interesting to have another clean-cut example. Apparently, there was a distinct populaton of walruses in Iceland, until a few centuries ago. Then they disappeared, abruptly. The killers, as suggested by a recent study  by Xenia Kéighley et al. published on Molecular Biology and Evolution (and open access, yay!), were the Norse, that colonizing Iceland found a bonanza of meat, fat, skin and ivory under the guise of long-toothed pinnipeds, and hunted them to extinction.  It is a deliciously interdisciplinary work, where you find genetic analysis of ancient DNA intertwined with the analysis of Norse sagas. So much for who wants to keep the two cultures separate.

There is a twist. Human-driven extinctions are ancient, but they are  land extinctions. Sea ecosystems were, indeed, mostly untouched until recently as far as we know. The Iceland walrus seems to be one of the earliest cases where our hand started to waste marine blood:

This is to one of the earliest examples of local extinction of a marine species following human arrival, during the very beginning of commercial marine exploitation.

A very significant event for the Sixth Extinction indeed. And the cause was, quite remarkably, capitalism, or at least its basic driver: trade.

We show that commercial hunting, economic incentives, and trade networks as early as the Viking Age were of sufficient scale and intensity to result in significant, irreversible ecological impacts on the marine environment. […]

Therefore, the extinction of the Icelandic walrus provides an exceptionally early example of hunting not driven solely for subsistence, but rather international demand for valuable trade commodities including walrus ivory, oil, and skin sold across medieval markets in Europe, the Middle East, and Asia.

In contrast to other species, the Iceland walrus did not die because the Vikings needed it. It died because they sold it. It was easy cash, until it lasted. While we have never been capable of a sustainable coexistence with many ecosystems, we live in an age of what has been called the Great Acceleration, where lots of ecological parameters skyrocket into the abyss.  And what drives this acceleration if not trade, economic growth, exploitation of resources?  To those who think that the socioeconomy of the human species has little to do with the Sixth Extinction, the Iceland walrus is a stern warning. The Invisible Hand is tainted forever with the blood of human and non human creatures.

The paper is: Xénia Keighley, Snæbjörn Pálsson, Bjarni F Einarsson, Aevar Petersen, Meritxell Fernández-Coll, Peter Jordan, Morten Tange Olsen, Hilmar J Malmquist “Disappearance of Icelandic Walruses Coincided with Norse Settlement”, Molecular Biology and Evolution, Volume 36, Issue 12, December 2019, Pages 2656–2667, https://doi.org/10.1093/molbev/msz196

 

The blind Cain

Never trust confessions, psychologists know: we are prone to confess crimes we never did. Is the Neanderthal extinction a case in point? It could be, following the suggestion of a paper recently published on PLOS One by Krist Vaesen et al: Neanderthal would have gone extinct even without us.

The way the story goes, we killed them. At the end of the Ice Age, while Neanderthals were holding Europe, a new wave of anatomically modern humans came from the south and slowly, but relentlessly, fighted with them or at least outcompeted them up to extinction -together with Denisovans and possibly other non-sapiens human species. As such they can be considered, with the rest of the Pleistocene megafauna, among the first victims of the man-made sixth mass extinction, and so I depicted them in my book. Neanderthals are our mark of Cain, the brothers whose blood still stains our hands.

Or maybe, not. J.L.Borges used to say that the proofs of death are mere statistics: and indeed statistics is enough to prove that extinction is, under reasonable circumstances, almost inevitable in the long run. If members of a population are born and die with more or less the same frequency, the population oscillation will sooner or later hit a descending phase by mere chance, until it gets to zero. It might take a long time but it is almost assured it will happen. The smaller the population, the easier it is to happen. Neanderthals had small populations, and scattered. This is enough to doom any species.

This is the crudest model; better models are possible and the one of the study takes into account, for example, the so-called Allee effect, that correlates the population size/density to the individual fitness. In other words, in group there is strengths. There are a myriad reasons for that: a more diverse genetic pool, the ability of flocking or schooling for defense, less energy to spend finding a sexual partner, and so on. This is important to keep in mind even today, since it means many species become basically a lost cause even when hundreds or thousands of individuals are still alive.

The Neanderthals apparently were never many, and never very dense. We have to imagine them as small scattered tribes of hardy lonely wanderers. And so, according to the study, they could have just died by themselves, even if the modern humans (us) never appeared on the scene.

Does this mean we are absolved? Not really. I am not capable of judging the mathematical model now. But even if perfect (and such models never are) it only means it could have happened anyway. It does not mean we were not involved. We did interact with Neanderthals. We interbred with them, so much fragments of their genome survive in ours. According to other models, for example, we shared diseases. Our history and the history of Neanderthals are robustly tied together.

But it is an interesting reminder of how we tend to weave stories into the patterns of life. Our brothers on this planet all died, only us standing. It is easy to find pride in this, and dissimulate it as guilt: it becomes a fascinating story. But fascinating stories are fictions of our brains. The reality of the world is made of chaos and impersonal forces, and under their gale we live and die. It could be mere statistics, it could be us, it does not matter for the Neanderthal bones, every day a bit less forgotten, yet no less cold.

 

 

Hope for the bugs?

It is so hard to find good news from the ongoing sixth extinction that, when this happens, one can be forgiven for disbelief. But a new paper by Macgregor et al. published on Nature Ecology and Evolution seems to cast doubt on the ongoing narrative of insectageddon, the apparent catastrophic decline in insect population.

The trick? Most papers observing a decline in the insect populations don’t go back in time much beyond year 1980. Can we grasp what happened before that, and how do data look like in this larger context? Macgregor et al. do exactly that: they found a thick dataset on British moth populations going back up to 1967, from 34 sites – the Rothamsted Insect Survey. These are mostly light traps that are counted daily, since more than 40 years. The very fact there is such a monitoring, while most of insect populations worldwide are so poorly known, is amazing.

Are moths declining? Yes – but only since 1982-ish. Before that, they were increasing. So much that today in Britain we still have more moth biomass than in 1967 -more than double, actually.

My former scientist self twitches a bit at seeing these graphs fitted with two straight lines with an arbitrary inflection point, but we can forgive this: it seems indeed in most cases the population is rising up to to the late ’70s and then plateauing or declining (Moth family Erebidae seems to just rise, however).

Another interesting thing of their dataset is that they sample urban and arable land, while other studies, like the ones from Germany, sample only protected areas. They see the population trends are different, with arable lands showing no decline, and woodlands showing the sharpest.

So, what does it mean? Is the current decline of insects a blip of a simply larger fluctuation trend? Callum Macgregor, first author of the paper, does not think we can go back to sleep, as he states on The Guardian:

“It’s absolutely not the case that everything is fine,” said Dr Callum Macgregor. “We do know that insects are in long-term decline as a whole, and also that the majority of insect species are declining.

“The concerning thing about the decline is that it’s over a 35-year period and there’s no real sign that that long-term declining trend is reversing.

“Having said that, the implication of a phrase like ‘insect Armageddon’ is that it’s an end-of-days scenario and it’s almost hopeless, and I don’t think it is hopeless. There is still time and opportunity for us to turn things around and make positive changes in the way we use our land.”

So, what was going on (apart from the birth of punk rock)? Hard to say, the author hypothesize perhaps yearly weather fluctuations such as droughts made the population oscillate, before the ongoing decline -mapping very well with the one measured elsewhere- took place.

Can we breathe? Hardly. We know that humans are causing a mass extinction since ages -at least, since we wiped out the Pleistocene megafauna. There is little doubt on that. Still, the data of Macgregor et al. are a interesting reminder that data only make sense in context, including the context of other data. Wild populations can oscillate, indeed, wildly, and long-term trends will be always superimposed on local phenomena. It’s a shame there are probably not many more long-term population data in the past to understand what is going on with insects worldwide. For now, I’m still not optimistic -but if the British moths teach us something, is that yes, there might be still time to reverse trends, since it was worse recently and ecosystems still did not collapse. But this time is not much. This is a reminder to hurry, not to relax.

The paper is: Macgregor, C. J., Williams, J. H., Bell, J. R., & Thomas, C. D. (2019). Moth biomass increases and decreases over 50 years in Britain. Nature Ecology & Evolution. doi:10.1038/s41559-019-1028-6

 

 

Lice wandering in Paleocene feathers

I have a fondness for parasites. Not on my body, of course, but as biological entities go, they’re among the most remarkable examples of specialization, adaptation and bodyplan plasticity. Parasites can go very far in becoming unrecognizable members of their own group, as Sacculina or pentastomids demonstrate… but I digress.

Parasites are also useful to understand life history and evolution. A nice factoid is that we have an idea of when humans started to use clothes thanks to lice. Body lice need clothes to survive (that’s where they nest), and we know they split from head lice 170.000-83.000 years ago. Thus probably clothing can’t be younger than that.

Now, what happens to parasites when their host goes extinct? They tend to go extinct as well, since most parasites are incredibly specific. This is a hidden biodiversity loss that we tend to overlook, but with each extinction of a free living species we lose also the whole parasitic ecosystem focused on that species -from viruses and bacteria to bugs and worms. Species do rarely die alone.

Viceversa, what happens to parasites after a mass extinction, when survivors start to diversify, often explosively, and reoccupy an empty world? A clue comes from a paper published on Communications Biology by Robert de Moya et al. that examines the diversification of bird feather lice after the K/T event. The answer is: they move around a lot.

The three groups of living birds -paleognaths (ostrichs, kiwis, tinamous, moa…) , Galloanserae (hen and ducks) and Neoaves (everything else)- diverged before the K/T event. We know that because we know at least a member of Galloanserae, the duck-ish bird Vegavis iaai, from before the end of the Cretaceous.  If lice followed loyally their hosts, we should expect that they would have diversified also before K/T. Paleognath-loving lice on paleognaths, galloanserae-loving lice on ducks and hens, and so on.

But it is not so. de Moya et al. show genomic evidence that bird feather lice diversified about 50 millions of years ago, after the end-Cretaceous mass extinction:

Using the louse phylogenomic data set, we also conducted a dating analysis using calibration points external to the clade of feather lice. These dating analyses indicate that feather lice began radiating around 50 Mya, somewhat after the K-Pg boundary (Fig. 2), which is similar to previously published studies4. Thus, feather lice began to diversify following the origin of most modern avian orders1,2. […] Rather, overall the cophylogenetic analyses suggested that multiple host-switches have taken place by lice among modern groups of birds. The results of Jane7 cophylogenetic analyses indicated that the ancestral host of feather lice was the common ancestor of the Galloanserae

So, all living birds must thank ducks, hens and their relatives if they suffer feather lice. The ancestors of modern paleognats and Neoaves must have had their own lice, but they disappeared for some reason after the K/T event. The jumps were multiple and complex, apparently:

Cophylogenetic analyses suggest host-switching occurred from other birds to palaeognaths at least three times (Supplementary Tables 1 and 2, Supplementary Fig. 2) depending on the host tree evaluated (three host-switches in comparison with the Jarvis et al. tree1 and four host-switches in comparison with the Prum et al. tree2). All analyses indicate one of these host-switches to Palaeognathae was from an ancestor within Galloanserae to the ancestor of emus. Furthermore, two consistent host-switches to palaeognaths originated from the ancestors of frogmouths and potoos, two early diverging lineages of Neoaves.

Apparently, jumps between hosts were favoured by a common environment -not surprising, but nice to see that popping out of the analysis:

For example, both of the recent avian phylogenomic studies recovered a large group (Aequorlitornithes) of water associated birds1,2. We also found that the feather lice of these birds tended to be closely related. However, feather lice from some other birds associated with water, such as ducks and cranes, also fall within this clade of lice. Cophylogenetic reconstruction (Supplementary Fig. 2) suggests that ducks and cranes acquired their feather lice through host-switching from an ancestral flamingo8 (a member of the Aequorlitornithes). Thus, host-switching in these cases might have been facilitated by a shared aquatic habitat. We also reconstructed the acquisition of feather lice from two main lineages of predatory birds, hawks and falcons, as being the result of host-switching from other avian lineages (Supplementary Fig. 2). Hawks, for example, sometimes acquire feather lice from their prey9. Thus, predation on other birds may facilitate host-switching by feather lice to raptors10.

It seems that feather lice have an advantage on mammalian lice: they do not elicit an immune response from their host, which is probably a significant factor that makes it hard for them to change hosts (you have to re-adapt to a new host that will mount a significant immune response to you). But they also note an intriguing coincidence:

Numerous accounts have documented the ability of feather lice to attach to winged hippoboscid flies (louse flies, Diptera) and disperse between hosts via phoretic hitch-hiking11,12. The divergence of avian feeding hippoboscid flies is estimated to have occurred up to around 52 Mya13 providing opportunities for ancient host-switching via phoresis.

Whoa. Parasitic bugs acting as carriers of other parasitic bugs, this I did not know. And these carriers evolved roughly when the feather lice started to disperse. I wouldn’t bet on this being the reason all this host shuffling mess happened, but it surely it makes me scratch my feath…erm, head.

In summary, it is interesting to see how the diversification of birds and their parasites was all but monotonous. Birds diversified, lice of a lineage started jumping around and moved the other lice away (again, an extinction of parasites we will never know much about), perhaps the emergence of other parasites helping around. Birds, like any other being, are actually environments hosting an ecosystem, and species can move between these environments, forget their previous environment and evolve to occupy a new one.

After all, what loyalty can you expect from parasites?

The paper is: Moya, R.S., Allen, J.M., Sweet, A.D. et al. Extensive host-switching of avian feather lice following the Cretaceous-Paleogene mass extinction event. Commun Biol 2, 445 (2019) doi:10.1038/s42003-019-0689-7

The hidden bombardment

Earth is very good at cosmetics: it quickly and efficiently covers its scars. The Chicxulub impact that wiped out the Cretaceous was one of the largest impact events in the last hundred million years in the Solar System, and yet it left no visible trace today, save for an arc of carsic structures known as cenotes in the Yucatan Peninsula. We had to dig deep and hard to find it. So it is no surprise that new impact events are still being found. Nozaki et al. now declare on Scientific Reports to have found 11 million years old ejecta in the sediments of the North Pacific. Ejecta, mind you, not the crater. That is unknown yet.

We managed to link only one mass extinction to asteroid impact. That might be the case. But impacts have been (and will be) a constant in Earth history. While globally catastrophic impacts are rare, what about locally catastrophic ones? They must have had important ecological consequences. A region-devastating impact can still alterate weather patterns and radically steer the direction of life history. A promising but localized lineage can be wiped off, a destroyed area can be re1populated and lead to speciation, and so on. Our past must have been sculpted by many more fatal days than the one at Chicxulub, and we still have almost no idea.

Coal knew, and the Climate Christ

The atmospheric greenhouse effect is known since more than a century, thanks to several scientists including Eunice Newton Foote and Arrhenius. It is thus pretty pleonastic, but still worthy of attention, that the coal industry knew of the issue since at least 1966 as documented digging an issue of the Mining Congress Journal. And of course they covered it up and continue peddling climate negationism, pumping millions into nefarious (un)think-tanks such as the Heartland Institute.

An amusing quote:

“Every time you turn your car on and you burn fossil fuels and you put CO2 into the air, you’re doing the work of the Lord,” Palmer told a Danish documentary team in 1997. “That’s the ecological system we live in.”

And I agree, it is the work of the Lord indeed, who told us in the Bible to exploit the Earth to the very end. But, you know, the Lord also planned this experiment of the Earth to end quickly. I wonder if there is some Hollywood script somewhere where one discovers that the global ecological crisis is just a prodrome of the Second Coming. Christian Conservatives would love it: they would not need to deny the role of fossil fuels, they would embrace it. Let carbon dioxide guide us to the Rapture, brethren!

At war with chimps

For all our prehistory and history, we clashed and fighted with other species. Sometimes they fight back: David Quammen reports on National Geographic of an ongoing and bloody conflict with chimps in rural Uganda. The details are gruesome, but it’s us who started:

The main driver of the conflicts, it seems, is habitat loss for chimps throughout areas of western Uganda, forested lands outside of national parks and reserves, which have been converted to agriculture as the population has grown. The native forest that once covered these hillsides is now largely gone, much of it cut during recent decades for timber and firewood, and cleared to plant crops.

It is a cautionary and worrying tale. The more we occupy habitats and resources of other species, the more we risk direct conflict with them -and so, the more these species will be further jeopardized. Climate change for example will probably add further competition with the rest of the biosphere, humans and non-humans clinging to land and water. Bleak times are ahead.

Baked Alaska, or a more complex Permian extinction

The Permian extinction lies in the twilight of deep time: not so remote we cannot fathom what was going on, not close enough to get a clear view. Getting a reasonable idea of what went on during the K/T event was no easy exercise, despite the (now) obvious clues such as a giant crater buried in the north Atlantic or an iridium peak at the K/T boundary. The Permian extinction, that happened almost 200 million years earlier and had no obvious silver bullet, is a much harder headache. The narrative I bought and published in my book was that of a relatively sudden global warming triggered by massive volcanism such as the Siberian Traps, but there are devilish details. Now Zhicai Zhu et al. report on Scientific Reports evidence of an abrupt change of regime from meandering to braided rivers and aeolian deposits in China. Such rapid changes in hydrology are also documented from other sites such as the Karoo Basin in Africa or Russia, but their interpretation was (and is) unclear. According to Zhu et al.:

The synchronous dramatic negative excursion in δ13C and δ18O in the uppermost Sunjiagou Formation provide reliable evidence for reduced weathering, coolness, aridification, and anoxia.

The keyword here is coolness. What coolness? Isn’t the end-Permian extinction event a period of catastrophic warming? A possible scenario is laid on:

Our study indicates a relatively cool temperature across the PTB, which was supported by some previous studies74,75,76,77 though it is different from most views that indicate a rapid increase in palaeotemperature across the PTB. However, in models for the outcomes of a massive volcanic eruption, such as that of the Siberian Traps, release of massive volumes sulphur dioxide when mixed with atmospheric water may produce a transient cooling phase before the warming, driven by CO2, methane and water vapour. Such cooling can be localised around the volcanic source, or can spread worldwide and last for 1–2 years78. Whether the conflicting findings of either global warming or cooling following the PTB eruptions can be explained by these differing consequences of the eruption, perhaps acting in sequence, or whether these differing temperature changes reflect latitudinal or regional regional effects cannot at this stage be determined.

It makes sense. A sudden warming might be catastrophic, but imagine a sudden cooling followed by sudden warming. That would really kick a biosphere off: the few that were cold-adapted enough to survive a bout of icy temperatures find then themselves at the mercy of a spike of heat. No wonder only very few beings would survive such climatic swings. We still have no idea if this is true or not, but we must be wary of using the past extinctions are strict proxies for our present crisis. Every extinction event teaches us lessons, but is also unique, no less than the species they wipe off the Earth.

The paper is: Zhu, Z., Liu, Y., Kuang, H. et al. Altered fluvial patterns in North China indicate rapid climate change linked to the Permian-Triassic mass extinction. Sci Rep 9, 16818 (2019) doi:10.1038/s41598-019-53321-z