Milk-producing spider

In biology, organizing living things in categories is called taxonomy. Such categories are established based on shared characteristics of the members. These characteristics were usually visual attributes. For example, a red-footed booby (it’s a bird, silly!) is obviously different than a blue-footed booby, so we put them in different categories, which Aristotle called in Greek something like species.

Biological taxonomy is very useful, not only to provide countless hours of fight (both verbal and physical!) for biologists, but to inform us of all sorts of unexpected relationships between living things. These relationships, in turn, can give us insights into our own evolution, but also the evolution of things inimical to us, like diseases, and, perhaps, their cure. Also extremely important, it allows scientists from all over the world to have a common language, thus maximizing information sharing and minimizing misunderstandings.

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All well and good. And it was all well and good since Carl Linnaeus introduced his famous taxonomy system in the 18th Century, the one we still use today with species, genus, family, order, and kingdom. Then we figured out how to map the DNAs of things around us and this information threw out the window a lot of Linnean classifications. Because it turns out that some things that look similar are not genetically similar; likewise, some living things that we thought are very different from one another, turned out that, genetically speaking, they are not so different.

You will say, then, alright, out with visual taxonomy, in with phylogenetic taxonomy. This would be absolutely peachy for a minority of organisms of the planet, like animals and plants, but a nightmare in the more promiscuous organisms who have no problem swapping bits of DNA back and forth, like some bacteria, so you don’t know anymore who’s who. And don’t even get me started on the viruses which we are still trying to figure out whether or not they are alive in the first place.

When I grew up there were 5 regna or kingdoms in our tree of life – Monera, Protista, Fungi, Plantae, Animalia – each with very distinctive characteristics. Likewise, the class Mammalia from the Animal Kingdom was characterized by the females feeding their offspring with milk from mammary glands. Period. No confusion. But now I have no idea (nor do many other biologists, rest assured) how many domains or kingdoms or empires we have, nor even what the definition of a species is anymore.

As if that’s not enough, even those Linnean characteristics that we thought set in stone are amenable to change. Which is good, shows the progress of science. But I didn’t think that something like the definition of mammal would change. Mammals are organisms whose females feed their offspring with milk from mammary glands, as I vouchsafed above. Pretty straightforward. And not spiders. Let me be clear on this: spiders did not feature in my – or anyone’s! – definition of mammals.

Until Chen et al. (2018) published their weird article a couple of weeks ago. The abstract is free for all to see and states that the females of a jumping spider species feed their young with milk secreted by their body until the age of subadulthood. Mothers continue to offer parental care past the maturity threshold. The milk is necessary for the spiderlings because without it they die. That’s all.

I read the whole paper since it was only 4 pages of it and here are some more details about their discovery. The species of spider they looked at is Toxeus magnus, a jumping spider that looks like an ant. The mother produces milk from her epigastric furrow and deposits it on the nest floor and walls from where the spiderlings ingest it (0-7 days). After the first week of this, the spiderlings suck the milk direct from the mother’s body and continue to do so for the next two weeks (7-20 days) when they start leaving the nest and forage for themselves. But they return and for the next period (20-40 days) they get their food both from the mother’s milk and from independent foraging. Spiderlings get weaned by day 40, but they still come home to sleep at night. At day 52 they are officially considered adults. Interestingly, “although the mother apparently treated all juveniles the same, only daughters were allowed to return to the breeding nest after sexual maturity. Adult sons were attacked if they tried to return. This may reduce inbreeding depression, which is considered to be a major selective agent for the evolution of mating systems (p. 1053).”

During all this time, including during the emergence into adulthood of the offsprings, the mother also supplied house maintenance, carrying out her children’s exuviae (shed exoskeletons) and repairing the nest.

The authors then did a series of experiments to see what role does the nursing and other maternal care at different stages play in the fitness and survival of the offsprings. Blocking the mother’s milk production with correction fluid immediately after hatching killed all the spiderlings, showing that they are completely dependent on the mother’s milk. Removing the mother after the spiderlings start foraging (day 20) drastically reduces survivorship and body size, showing that mother’s care is essential for her offsprings’ success. Moreover, the mother taking care of the nest and keeping it clean reduced the occurrence of parasite infections on the juveniles.

The authors analyzed the milk and it’s highly nutritious: “spider milk total sugar content was 2.0 mg/ml, total fat 5.3 mg/ml, and total protein 123.9 mg/ml, with the protein content around four times that of cow’s milk (p. 1053)”.

Speechless I am. Good for the spider, I guess. Spider milk will have exorbitant costs (Apparently, a slight finger pressure on the milk-secreting region makes the mother spider secret the milk, not at all unlike the human mother). Spiderlings die without the mother’s milk. Responsible farming? Spider milker qualifications? I’m gonna lay down, I got a headache.

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REFERENCE: Chen Z, Corlett RT, Jiao X, Liu SJ, Charles-Dominique T, Zhang S, Li H, Lai R, Long C, & Quan RC (30 Nov. 2018). Prolonged milk provisioning in a jumping spider. Science, 362(6418):1052-1055. PMID: 30498127, DOI: 10.1126/science.aat3692. ARTICLE | Supplemental info (check out the videos)

By Neuronicus, 13 December 2018

Pooping Legos

Yeah, alright… uhm… how exactly should I approach this paper? I’d better just dive into it (oh boy! I shouldn’t have said that).

The authors of this paper were adult health-care professionals in the pediatric field. These three males and three females were also the participants in the study. They kept a poop-diary noting the frequency and volume of bowel movements (Did they poop directly on a scale or did they have to scoop it out in a bag?). The researchers/subjects developed a Stool Hardness and Transit (SHAT) metric to… um.. “standardize bowel habit between participants” (p. 1). In other words, to put the participants’ bowel movements on the same level (please, no need to visualize, I am still stuck at the poop-on-a-scale phase), the authors looked – quite literally – at the consistency of the poop and gave it a rating. I wonder if they checked for inter-rater reliability… meaning did they check each other’s poops?…

Then the researchers/subjects ingested a Lego figurine head, on purpose, somewhere between 7 and 9 a.m. Then they timed how much time it took to exit. The FART score (Found and Retrieved Time) was 1.71 days. “There was some evidence that females may be more accomplished at searching through their stools than males, but this could not be statistically validated” due to the small sample size, if not the poops’. It took 1 to 3 stools for the object to be found, although poor subject B had to search through his 13 stools over a period of 2 weeks to no avail. I suppose that’s what you get if you miss the target, even if you have a PhD.

The pre-SHAT and SHAT score of the participants did not differ, suggesting that the Lego head did not alter the poop consistency (I got nothin’ here; the authors’ acronyms are sufficient scatological allusion). From a statistical standpoint, the one who couldn’t find his head in his poop (!) should not have been included in the pre-SHAT score group. Serves him right.

I wonder how they searched through the poop… A knife? A sieve? A squashing spatula? Gloved hands? Were they floaters or did the poop sink at the base of the toilet? Then how was it retrieved? Did the researchers have to poop in a bucket so no loss of data should occur? Upon direct experimentation 1 minute ago, I vouchsafe that a Lego head is completely buoyant. Would that affect the floatability of the stool in question? That’s what I’d like to know. Although, to be fair, no, that’s not what I want to know; what I desire the most is a far larger sample size so some serious stats can be conducted. With different Lego parts. So they can poop bricks. Or, as suggested by the authors, “one study arm including swallowing a Lego figurine holding a coin” (p. 3) so one can draw parallels between Lego ingestion and coin ingestion research, the latter being, apparently, far more prevalent. So many questions that still need to be answered! More research is needed, if only grants would be so… regular as the raw data.

The paper, albeit short and to the point, fills a gap in our scatological knowledge database (Oh dear Lord, stop me!). The aim of the paper was to show that ingested objects by children tend to pass without a problem. Also of value, the paper asks pediatricians to counsel the parents to not search for the object in the faeces to prove object retrieval because “if an experienced clinician with a PhD is unable to adequately find objects in their own stool, it seems clear that we should not be expecting parents to do so” (p. 3). Seems fair.

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REFERENCE: Tagg, A., Roland, D., Leo, G. S., Knight, K., Goldstein, H., Davis, T. and Don’t Forget The Bubbles (22 November 2018). Everything is awesome: Don’t forget the Lego. Journal of Paediatrics and Child Health, doi: 10.1111/jpc.14309. ARTICLE

By Neuronicus, 27 November 2017

Raising a child costs 13 million calories

That’s right. Somebody actually did the math on that. Kaplan in 1994, to be exact.

The anthropologist and his colleague, Kate Kopischke, looked at how three semi-isolated populations from South America live. Between September 1988 and May 1989, the researchers analyzed several variables meant to shed light mainly on fertility rate and wealth flow. They measured the amount of time spent taking care of children. They estimated the best time to have a second child. They weighed the food of these communities. And then they estimated the caloric intake and expenditure per day per individual.

Human children are unable to provision for themselves until about the age of 18. So most of their caloric intake requirements are provided by their parents. Long story (39 pages) short, Kaplan (1994) concluded that a child relies on 13 million calories provided by the adults. Granted, these are mostly hunter-gatherer communities, so the number may be a bit off from your average American child. The question is: which way? Do American kids “cost” more or less?

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P.S. I was reading a paper, Kohl (2018), in the last week’s issue of Science that quoted this number, 13 million. When I went to the cited source, Hrdy (2016), that one was citing yet another one, the above-mentioned Kaplan (1994) paper. Luckily for Kohl, Hrdy cited Kaplan correctly. But I must tell you from my own experience, half of the time when people cite other people citing other people citing original research, they are wrong. Meaning that somewhere in the chain somebody got it wrong or twisted the original research finding for their purposes. Half of the time, I tell you. People don’t go for the original material because it can be a hassle to dig it out, or it’s hard to read, or because citing a more recent paper looks better in the review process. But that comes to the risk of being flat wrong. The moral: always, always, go for the source material.

P.P.S. To be clear, I’m not accusing Kohl of not reading Kaplan because accusing an academic of citing without reading or being unfamiliar with seminal research in their field (that is, seminal in somebody else’s opinion) is a tremendous insult not be wielded lightly by bystanders but to be viciously used only for in-house fights on a regular basis. No. I’m saying that Kohl got that number second-hand and that’s frowned upon. The moral: always, always, go for the source material. I can’t emphasize this enough.

P.P.P..S. Ah, forget it. P.S. 3. Upon reading my blog, my significant other’s first question was: “Well, how much is that in potatoes?” I had to do the math on a Post-It and the answer is: 50,288 large skinless potatoes, boiled without salt. That’s 15,116 Kg of potatoes, more than 15 metric tones. Here you go. Happy now? Why are we talking about potatoes?! No, I don’t know how many potatoes would fit into a house. Jeez!

REFERENCE: Kaplan, H. (Dec. 1994). Evolutionary and Wealth Flows Theories of Fertility: Empirical Tests and New Models. Population and Development Review, Vol. 20, No. 4, pp. 753-791. DOI: 10.2307/2137661. ARTICLE

By Neuronicus, 22 October 2018

The oldest known anatomically modern humans in Europe

A couple of days ago, on December 1st, was the National Day of Romania, a small country in the South-East of Europe. In its honor, I dug out a paper that shows that some of the earliest known modern humans in Europe were also… dug out there.

Trinkaus et al. (2003) investigated the mandible of an individual found in 2002 by a Romanian speological expedition in Peștera cu Oase (the Cave with Bones), one of the caves in the SouthWest of the country, not far from where Danube meets the Carpathians.

First the authors did a lot of very fine measurement of various aspects of the jaw, including the five teeth, and then compared them with those found in other early humans and Neanderthals. The morphological features place the Oase 1 individual as an early modern human with some Neanderthal features. The accelerator mass spectrometry radiocarbon (14C) direct dating makes him the oldest early modern human discovered to that date in Europe; he’s 34,000–36,000 year old. I’m assuming is a he for no particular reason; the paper doesn’t specify anywhere whether they know the jaw owner’s gender and age. A later paper (Fu et al., 2015) says Oase 1 is even older: 37,000–42,000-year-old.

After this paper it seemed to be a race to see what country can boast to have the oldest human remains on its territory. Italy and UK successfully reassessed their own previous findings thusly: UK has a human maxilla that was incorrectly dated in 1989 but new dating makes it 44,200–39,000 year old, carefully titling their paper “The earliest evidence for anatomically modern humans in northwestern Europe” (Higham et al., 2011) while Italy’s remains that they thought for decades to be Neanderthal turned out to be 45,000-43,000 years old humans, making “the Cavallo human remains […] the oldest known European anatomically modern humans” (Benmazzi et al., 2011).

I wonder what prompted the sudden rush in reassessing the old untouched-for-decades fossils… Probably good old fashioned national pride. Fair enough. Surely it cannot have anything to do with the disdain publicly expressed by some Western Europe towards Eastern Europe, can it? Surely scientists are more open minded than some petty xenophobes, right?

Well, the above thought wouldn’t have even crossed my mind, nor would I have noticed that the Romanians’ discovery has been published in PNAS and the others in Nature, had it not been for the Fu et al. (2015) paper, also published in Nature. This paper does a genetic analysis of the Oase 1 individual and through some statistical inferences that I will not pretend to fully understand they arrive to two conclusions. First, Oase 1 had a “Neanderthal ancestor as recently as four to six generations back”. OK. Proof of interbreeding, nothing new here. But the second conclusion I will quote in full: “However, the Oase individual does not share more alleles with later Europeans than with East Asians, suggesting that the Oase population did not contribute substantially to later humans in Europe.”

Now you don’t need to know much about statistics or about basic logic either to know that from 1 (one) instance alone you cannot generalize to a whole population. That particular individual from the Oase population hasn’t contributed to later humans in Europe, NOT the entire population. Of course it is possible that that is the case, but you cannot scientifically draw that conclusion from one instance alone! This is in the abstract, so everybody can see this, but I got access to the whole paper, which I have read in the hopes against hope that maybe I’m missing something. Nope. The authors did not investigate any additional DNA and they reiterate that the Oase population did not contribute to modern-day Europeans. So it’s not a type-O. From the many questions that are crowding to get out like ‘How did it get past reviewers?’, ‘Why was it published in Nature (interesting paper, but not that interesting, we knew about interbreeding so what makes it so new and exciting)?’, the one that begs to be asked the most is: ‘Why would they say this, when stating the same thing about the Oase 1 individual instead about the Oase population wouldn’t have diminished their paper in any way?’ .

I must admit that I am getting a little paranoid in my older age. But with all the hate that seems to come out and about these days EVERYWHERE towards everything that is “not like me” and “I don’t want it to be like me”, one cannot but wonder… Who knows, maybe it is really just as simple as an overlooked mistake or some harmless national pride so all is good and life goes on, especially since the authors of all four papers discussed above are from various countries and institutions all across the Globe. Should that be the case, I offer my general apologies for suspecting darker motives behind these papers, but I’m not holding my breath.

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References:

1) Trinkaus E, Moldovan O, Milota S, Bîlgăr A, Sarcina L, Athreya S, Bailey SE, Rodrigo R, Mircea G, Higham T, Ramsey CB, & van der Plicht J. (30 Sep 2003, Epub 22 Sep 2003). An early modern human from the Peştera cu Oase, Romania. Proceedings of the National Academy of Sciences U S A,  100(20):11231-11236. PMID: 14504393, PMCID: PMC208740, DOI: 10.1073/pnas.2035108100. ARTICLE  | FREE FULLTEXT PDF

 2) Higham T, Compton T, Stringer C, Jacobi R, Shapiro B, Trinkaus E, Chandler B, Gröning F, Collins C, Hillson S, O’Higgins P, FitzGerald C, & Fagan M. (2 Nov 2011). The earliest evidence for anatomically modern humans in northwestern Europe. Nature. 479(7374):521-4. PMID: 22048314, DOI: 10.1038/nature10484. ARTICLE | FULLTEXT PDF via ResearchGate

3) Benazzi S, Douka K, Fornai C, Bauer CC, Kullmer O, Svoboda J, Pap I, Mallegni F, Bayle P, Coquerelle M, Condemi S, Ronchitelli A, Harvati K, & Weber GW. (2 Nov 2011). Early dispersal of modern humans in Europe and implications for Neanderthal behaviour. Nature, 479(7374):525-8. PMID: 22048311, DOI: 10.1038/nature10617. ARTICLE | FULLTEXT PDF via ResearchGate

4) Fu Q, Hajdinjak M, Moldovan OT, Constantin S, Mallick S, Skoglund P, Patterson N, Rohland N, Lazaridis I, Nickel B, Viola B, Prüfer K, Meyer M, Kelso J, Reich D, & Pääbo S. (13 Aug 2015, Epub 22 Jun 2015). An early modern human from Romania with a recent Neanderthal ancestor. Nature. 524(7564):216-9. PMID: 26098372, PMCID: PMC4537386, DOI:10.1038/nature14558. ARTICLE | FREE FULLTEXT PDF

By Neuronicus, 3 December 2016

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Lucy’s 9 vertebrae are actually 8

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Lucy. Left: picture of the real skeleton. Middle and Right: reconstructions. Courtesy of Wikipedia

As Google reminded us, today is the 41st anniversary of the finding of Lucy, the first discovered member of the species Australopithecus afarensis. Lucy lived in Ethiopia about 3.2 million years ago and the most extraordinary fact about her is that her fossil represents the first evidence of bipedalism in a hominin (we are also hominins).

Lucy is one “missing link” (not ‘missing’ anymore, obviously) between the common ancestor of humans and chimpanzees and humans because she has ape-like features (jaw, forehead, long arms, small cranium) and human-like features (knee, ankle, lumbar curve, pelvic bones) and walked upright.

Meyer et al. (2015) wanted to do a comprehensive reconstruction of Lucy for display at the American Museum of Natural History in New York. During this work they noticed that one vertebrae of the total of nine found is kindda small compared to the other ones. So they set to measure vertebrae form all sorts of other species, alive and extinct, and after some factor analysis they concluded that out of Lucy’s nine found vertebrae, the little one is not actually hers, but belongs to a different species from the genus Theropithecus (a baboon ancestor).

This finding is functionally uninformative and their “work does not refute previous work on Lucy or its importance for human evolution, but rather highlights the importance of studying original fossils, as well as the efficacy of the scientific method.” In other words, give the poor anthropologists not reconstructions but the original fossils to work with (most people worked with Lucy’s reconstructions which missed some details, thus allowing this pesky vertebra to remain miss-cataloged for 40 years).

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The new alignment from doi: 10.1016/j.jhevol.2015.05.007

This is the first paper of pure anthropology that I have read in full and let me tell you that I found a lot of curious things, unrelated to Lucy. Like, for example, from an anthropologist’s point of view, an adult is someone with the third molar completely erupted. We should then look into the people’s mouths before giving them the keys to the wine cellar, because some 21-year olds are definitely not adults. Also, instead of a medical doctor, get an anthropologist to teach anatomy, because oh boy do these people know their skeletons! Here is an excerpt from the Methods section: “The overall size of the A.L. 288-1am partial vertebra was calculated as the geometric mean of six linear dimensions: lamina superoinferior height and dorsoventral thickness, pars interarticularis width, interarticular facet height, and superior and inferior articular interfacet maximum transverse widths. The pars interarticularis geometric mean includes three variables from the pars interarticularis: lamina superoinferior height and dorsoventral thickness, and pars interarticularis width” (p. 175).

All in all, nice!

Reference: Meyer MR, Williams SA, Smith MP, Sawyer GJ (August 2015, Epub 6 Jun 2015). Lucy’s back: Reassessment of fossils associated with the A.L. 288-1 vertebral column. Journal of Human Evolution, 85:174-80. doi: 10.1016/j.jhevol.2015.05.007. Article | FREE FULLTEXT PDF

By Neuronicus, 24 November 2015