Month: November 2019

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