So I got really busy and am forced to compile a month’s worth of papers into one post. Happy reading. By the way, I have made a Facebook page for the blog which you can like and follow and write on, and all the informational posts are also getting uploaded on Glipho.
[OA] indicates open access papers. For detailed discussion of any of these, feel free to request!
Must-Read Papers (unsorted):
Polyandry is when a single female mates with multiple males, a mating system that isn’t uncommon among animals. Polyandry comes in many flavours, and bears significant costs (injury, energy expended during repeated mating, predation risk) that are recouped by the reaped benefits (selecting the father, more parental care, more genetic diversity for offspring). This special issue reviews all aspects of the evolution of polyandry in the light of the latest research in ecology and evolutionary theory. Two [OA] papers.
The very common misconception of evolution having a direction or preferred goal is most commonly manifested when people ask “why aren’t all animals intelligent?”, or “why are bacteria still unicellular?”. In the latter, the thought process is that multicellularity is a trend that all “higher-evolved” organisms undergo. This is, of course, completely wrong. Multicellularity is a rarity that only has three major occurrences – plants, fungi, animals. The rest of the diversity of life – which far outnumbers the diversity of these three clades – is unicellular. Thus, the real interest in multicellularity isn’t “Why aren’t these organisms multicellular?”, but “Why are those other organisms multicellular?”. Multicellularity is the weird exception, not the trend to be followed. This paper reviews the origins of multicellularity in all organisms that express it, and answers the mechanical and molecular genetic details of this question: it’s all cell adhesion, communication, and specialisation, tissue pattern formation, and morphogenesis. If you need a review of these things, then this paper is perfect.
In the description above, the first question I mention is “Why aren’t all animals intelligent?”, with the questioner almost always defining intelligence as modern human-like intelligence. Not only is that a stupid definition, it also implicitly assumes that having a human brain is all nice and dandy. Not so. The human brain is a gigantic lump of inefficiency, the equivalent of a supercomputer built by a five year old with unlimited resources. The energy needed to grow and maintain our brain (and thus acquire and keep our intelligence) is truly immense, and this is a cost that we can bear only because of we’ve managed to get ourselves a fancy supply of constant food. This paper provides direct empirical evidence for this energy-cognition trade-off using experimental evolution on guppies: large-brained guppies end up smarter, but also produce less offspring and have smaller guts.
Another popular misconception to take down: genetics are not a blueprint. I get a surprising amount of people asking me whether spiders decide hwo their webs should be and if they can customise them. Of course they can. Phylogeny predicts the general architecture of the spider web, whether it’ll be an orb or a sheet or dragline, but only because different spider taxa have different leg and spinneret arrangements and so are physically incapable of building different web types. But the fine details of the web – how dense the threads should be and even how sticky they are – are all determined by the spider depending on its situation. This paper provides a demonstration of that, where amount of food available causes significant changes in web architecture. This is not genetically-determined, it’s just a reaction to the ecological circumstances.
A great example of experimental evolution, the researchers created a virus that has a flexible life history by selecting for multiple infection. When acting alone, the virus kills its host slowly, when others are around, it kills its host quickly. That such flexibility is exhibited by disease-causing viruses in the wild makes this research important as well as cool.
Another great experimental evolution paper, this time growing photosynthetic algae for so long in the dark that they evolve to become incapable of photosynthesis.
One of the most insightful things I learned in zoology was that there are no hard lines distinguishing symbioses, mutualisms, and parasitisms. All these interactions are on a spectrum from fully beneficial to both parties to fully detrimental to one party and fully beneficial to the other. This paper provides a case in point to the fluidity of species interactions: when two predators interact, it’s usually a kleptoparasitic interaction, with one predator stealing the other’s food. However, the researchers here show that the spider Cyrtophora unicolor allows the smaller spider Argyrodes fissifrons to get on its web and take small prey, because the shiny colour of A. fissifrons attracts moths for C. unicolor to feed on. Both predators have entered into this mutually-exploitative and mutually beneficial interaction; it may be that in the future, the interaction will shift to another side of the spectrum and one will become parasitic on the other (C. unicolor enslaving the smaller spider, or the smaller spider becoming a true kleptoparasite).
The first thing you experience as a science communicator is that most people want to be given an excuse to learn something. It must have some sort fo practical application in their lives, or it must be something they can see for themselves. While this is based on my personal experiences with public lectures, this paper confirms this in the case of global warming: if people feel like they’re “experiencing” global warming, they’re more likely to accept it’s happening. Of course, this also brings up the thorny issue of the misconceptions about global warming – the classic confusion of short-term weather patterns with long-term climate change, a blight on the popular conception of climate change.
Yet another feathered dinosaur around the early origin of flight, although Eosinopteryx here couldn’t fly, it was more a runner; I imagine it like the flightless birds of today.
Today’s echinoderms (brittlestars, sea stars, sea lillies, sea urchins, sea cucumbers) are a tiny vestige of echinoderms’ past disparity. While these extant echinoderms are characterised by pentaradial symmetry, their early fossil record shows a wealth of different body plans, including bilaterally-symmetrical ones that had sown some confusion by being thought to be a link between chordates and echinoderms. This paper describes two Cambrian localities from Morocco with well-preserved echinoderms. When combined with the knowledge we have of other Cambrian echinoderms, we get the insight from the title: the very diverse echinoderm body plans (all but one of which are now extinct) emerged very quickly, in a timespan of 10-15 million years.
A favoured “weapon” of global warming opponents is their fallacious trotting out of geology to point out that Earth’s climate has always varied, so why raise the alarm over a couple of degrees of warming. This is a fallacy because we don’t care about the Earth, we care about ourselves and our future survival. The Earth isn’t affected by global warming, or anything else we do for that matter (unless we start messing around with the core, or install a giant rocket booster and push the Earth into the Sun). And what geology tells us is that climate forcing has always had drastic impacts on both geomorphology and the biotic sphere. This paper shows how CO2 levels in the past 40 years have affected sea level, and predicts that even if we keep CO2 levels as they are now, we have a 68% chance of getting a 9+m rise in sea level. That’s a lot of major cities and little islands drowned (and even some mainland countries too, like most of Bangladesh).
Record-breaking temperatures followed by record-breaking phenological changes. I’d tell you to expect more papers showing changes in insects, but there’s already a ton of them…
… like this one.
Humans aren’t the only animals who clean their food.
Bed bugs go even further and keep their sperm germ-free.
While this paper isn’t a must-read itself – it’s just a reporting of three new genomes – I consider this an important step, sicne these genomes can now be incorporated into a new phylogenomics analysis of the animals, which might prove fruitful. I do have one qualm though: the organisms they picked are model organisms, but like with most model organisms, they’re not really basal within their own clades, making their utility for phylogenetics that much more limited. Still, better than nothing, I suppose.
Must-read only in the sense that this makes an excellent journal club paper to be dissected, an activity I did with a colleague’s class via Skype. Read it to sharpen your skepticism and critiquing skills. (Technically, that’s how you should treat every single paper, but some are more amenable to such things…)
The way birds can use the magnetic field for naviation is always fascinating, although I profess a casual ignorance of the details. All I knew prior to this paper is that they have magnetic pigments in one fo their eyes that allow them to “see” the magnetic field, but apparently it’s much more complex as this review shows. It concentrates on the beak and its innervation, showing that the magnetic receptors there record the strength of the magnetic field.
One of my biggest pet peeves is the conflation of evolutionary altruism (where helping and selfishness are defined purely from the consequences on allele frequencies) and social altruism, which is a behavioural, cultural, sociological thing that, in my opinion, has nothing to do with the altruism of evolutionary theory. This paper dissects the various uses of “altruism” in different disciplines, and gives them a neat descriptive adjective to help us all not talk at cross-purposes. I like it, although I know many who will scoff at these separations (they’re the same people who trigger my pet peeve).
They’re elevated… but still nowhere near being significant for human health. The anti-nuclear crowd really has their work cut out for them.
It’s rare for any extinction to be sudden – the majority of extinctions are culminations of increasing stresses, or they’re the combinations of many local pulses of extinction that geology compresses into one major event. The Permian-Triassic extinction is the latter, with detailed dissections of earliest Triassic localities from around the world showing wildly different patterns of recovery and extinction. This paper is also a demonstration of this, by showing that there was no gradual trend of recovery from the P-T. Instead, recovery took place in quick, local bursts that repeatedly got stamped out by local extinctions. When you zoom out, it appears as though the earliest Triassic was dead; but when you zoom in, it was a boom-and-bust cycle.
A good review for those interested on the effect of climate change on the biosphere.
Oldest anything deserves a mention, so here’s the oldest finding of a rugose coral to date, from the Mid-Ordovician of Iran.
While technically an opinion piece, not a research or review paper, I think this must be read by everyone, because it summarises why evolutionary biology is important and some of the upcoming research directions that we evolutionary biologists are getting into. It gets many kudos from me for including the importance of natural history collections (critical in a time when museums are facing unprecedented budget cuts) and for reminding everyone of the utility of the fossil record. Definitely a teaching piece as well. Read it now.
Another good paper for teaching, consider this a “community ecology for dummies” primer. If you’ve always been interested in what community ecology is and what the main fights in it are, then read through this paper.
Hox genes are wellknown as master genes, responsible for deciding where body parts go on the body (you can make flies with antennas for legs by changing Hox gene expression, for example). So they’re naturally considered very important for the evolution of body plans, so their evolution is always getting studied. This research looks at one particular Hox gene, fushi tarazu (ftz), which is not involved in patternign the body, but is instead involved in the formation of the central nervous system, only being expressed in neural cells. This unique function it got was a cooption from its ancestral role, whatever that was, showing that even these master genes are subject to the same forces as other genes.
An overview of biofilms and microbial mats and their presence in palaeontology.
Speaking of microbial mats, their most useful role in palaeontology is as a cause for exceptional fossil preservation. A lot of soft tissue preservation in the fossil record is caused by the action of microbial mats conquering carcasses and depositing hardy minerals while digesting the tissues. Pyritisation is the most famous case. Even when they don’t directly cause soft tissue preservation, they may delay decay until appropriate conditions set in, or even form a coffin around the carcass where the appropriate conditions for soft tissue preservation prevail. The latter case is what is shown in this paper using Recent fish.
Speaking of exceptional fossil preservation, how about some fossil parasitism? Everyone should know tapeworms: they reside in vertebrate guts and release loads of eggs to be shat out. In this cae, the vertebrate victim was a shark, and its feces kept them entombed for 270 million years – the earliest cestode fossil to date.
Just some more mindblowing preservation.
I wrote a post about the Myxozoa here, mentioning that there is absolutely no solid hypothesis for their phylogenetic placement within the animals. We now have a reasonably-evidenced hypothesis presented in this paper: myxozoans as cnidarians, close relatives to the Medusozoa. The tree is solid, but I really have doubts from a zoological perspective. Parasites are notorious for their ability to baffle morphologists like myself, but a loss of all cnidarian traits is a bit too much for me to swallow, so I’ll wait for someone to find some vestige of a cnida before hopping on board this train.
I find the atmospheric biome to be fascinating to imagine – loads of bacteria floating around in air currents, under extreme conditions (cold, radiation) and acting as nucleation centers for cloud formation. It’s pretty wacky. This paper looks at the biogeochemistry of hailstones and even manages to culture bacteria from them.
A great methodological paper, but I cannot for the life of me understand why this is published in Science, which provides no room for proper exploration of such data-rich papers. A proper monograph is hopefully in the works.
Epigenetics is commonly trotted out in popular science as the Great New Thing that will supersede evolution and explain everything that we can’t explain already, especially when it comes to behaviour. If you want to go past these bullshit overstatements, this paper is a good start.
One of the goals most looked forward to in synthetic biology is the replication of photosynthesis. I don’t really see why – photosynthesis is really not an efficient process, so I don’t see the point of trying to replicate it. But then again, I’m not a synthetic biologist, so what do I know. In any case, this paper outlines the state of the art.
The peppered moth is the classic example used for teaching natural selection – see my natural selection post as an example. This paper reviews all its aspects, right down to the genetics and the missing pieces of knowledge. Highly-recommended. See also this related paper from the same issue.
A summary of the geological background necessary for the evolution of life. Read the rest of this entry »