Hello, and welcome to the Carnival of Evolution #61. For this edition, I’ve chosen to celebrate what I perceive as an inexplicably underappreciated group of animals: the Crustacea. Of the major arthropod groups, I notice that crustaceans often get the short end of the stick. Everyone can name insects and recognise spiders, but besides seafood, crustaceans seem to be a question mark with most people. Insects and spiders have movies and songs written about them; crabs are the logo for cancer, the vernacular name for an STD, and they are an astrological sign.
Insulting. Crustaceans are awesome. There may be over a million insect species, but crustaceans take the cake when it comes to disparity, or morphological diversity, a measure in which no other taxon can match them. They are so morphologically diverse that some crustaceans were traditionally classified as molluscs, annelids, or even as separate phyla. They range from ectoparasites found stuck on sensory hairs of the antennule of copepods to the 4 meter large Japanese spider crab. Euphausia superba, the Antarctic krill, have around 500 million tons in total biomass, surpassing ants and nematodes. They live from the deepest abyss of the oceans to lakes to little puddles under leaves to being fully terrestrial – very few taxa can claim to have diversified into so many habitats. Heck, if you accept the hypothesis that insects are crustaceans (more on that later), then crustaceans can also fly, leaving only outer space as an unconquered frontier.
So, in order to give crustaceans some love, following every post in this carnival edition, I will write an addendum with a relevant example from the crustacean world. That gives you double the reading to do. Enjoy!
In Bird Feeders, Pornography, and Other Evolutionary Traps, Ryan Somma at Ideonexus presents his thoughts on on a recent study on “evolutionary traps,” rapid human-induced environmental changes that trigger maladaptive behaviors in animals, and how humans fall into our own traps and how something as innocent as a bird feeder can become a trap. The post is spurred by a new paper which Carl Zimmer at The Loom also presents in Freeing Animals From Our Evolutionary Traps.
The opposite of an evolutionary trap, i.e. a good behavioural adaptation to human-induced changes, can be found in hermit crabs. Hermit crabs spend their lives living in snail shells. When they moult, they get rid of their current shell and find another bigger one (or fight another hermit crab to get his shell). The shell is basically a mobile home: it gives the hermit shelter from predation and from environmental changes. If you go to a polluted beach, you might encounter something even more peculiar: a hermit crab adopting a piece of plastic or an appropriate small glass container instead of a snail shell. This is the opposite of an evolutionary trap – assuming the debris is really as strong as a snail shell.
In Pleasure and procreation, Zen Faulkes at Neurodojo discusses a new paper on the non-existent correlation between female orgasms and reproductive rate, meaning that orgasms are not adaptive, even though they are undeniably pleasurable.
It’s rumoured that penis size has a good correlation with the pleasure experienced by the woman and induction of orgasm . I merely mention this to segue into talking about the Cirripedia – barnacles. As the picture to the left shows, there is no better demonstration of the disparity of the crustaceans than barnacles. The adult lives upside down inside those plates, which are actually the carapace, its legs sticking out of the hole. They are sessile, not able to move anywhere. At mating time, the penis is also stuck out of the hole and, much like the human penis, becomes hard and extended due to extra pressure. Unlike the human penis, the enlargement makes the penis end up being 9-10 times the size of the barnacle’s body. Truly pleasurable. It’s equipped with all sorts of sensory organs that the barnacle uses to sense the environment as it blindly taps its penis around. When it finally hits another barnacle, it ejaculates inside its house. Not so pleasurable.
In My pet theory about the human nose: breastfeeding, Bjørn Østman of Pleiotropy proposes that the human nose is shaped the way it is because of our need to feed from breasts that engulf our faces as babies. Interesting, and it should be testable.
Breasts are mammalian features, so I’m stuck with sharing a pet hypothesis about crustaceans. I have one that can easily be the subject of a research proposal, feel free to steal it (or, uh, hire me?). It involves the Oniscidea, the only fully-terrestrial group of isopod crustacean, and which all of you have encountered in your daily lives – these are the pillbugs and woodlice. Being terrestrial arthropods, they’ve converged on a tracheal system in order to breathe, much like insects and spiders have done. I hypothesise that the genetic basis for the development of the tracheal system in the oniscids is pretty much the same as the one in insects, a case of deep homology.
In New Views on Evolution in the Reading Queue, Bradly Alicea from Synthetic Daisies reviews two recent papers on the evolution of the human brain and human cognition. The first is on the evolution of memory, the second a novel hypothesis on the evolution of the neocortex.
I will not summarise what we know of the cognitive abilities of crustaceans. What is generally accepted is that they are underestimated and more research is needed. Some examples of crustacean cognition come from the Caribbean spiny lobster, Panulirus argus, which can remember the smell of noxious foods for several days, and has the ability to construct a mental map that allows it to return home from 30+ kms away (their usual seasonal migration is over 200 km!).
Staying with humans, in Oral Bacteria and Our Health – An Evolutionary Diet Perspective, Andy The Barefoot Golfer lectures us on dental hygiene and how dietary changes during recent human evolution have consequently had an impact on our oral microbiota. It behooves us all to keep evolution in mind when it comes to our health.
Unlike weakling vertebrates, crustaceans need not fear their oral microbiome. In fact, if you go to hydrothermal vents in the deep sea, you will find a wealth of crustaceans, like the Rimicaris swarm pictured to the left, surviving solely by letting symbiotic bacteria on their mouthparts give them nutrients they produce by chemosynthesis.
Crustaceans don’t have “arms”, obviously, but there is one crustacean group where this interplay between neurology-enabled accuracy and pure biomechanics could also play a role: in the Alpheidae. These are the snapping shrimp, and they have one grossly enlarged claw that they can close very quickly to produce a jet of water and a cavitation bubble to smash prey or deter predators. This also produces a bang, loud enough that some species have earned the name of pistol shrimp. It’s a long shot (no pun intended), but the analogy to the human case is that the action requires specific morphology (arm and shoulder configuration vs. specialised claw) and the ability to predict trajectories (albeit straight-line and much shorter distances in the snapping shrimp).
In BEACON Researchers at Work: Evolving division of labor, Anya Johnson from the BEACON Center for the Study of Evolution in Action explains her research on simulating the evolution of division of labour using Avida. The evolution of division of labour is one of the most interesting questions in evolutionary biology, and such theoretical and modeling work lays the ground for experimental evolution studies, which can then complement what we find out from social animals and their natural history.
One such animal is the Synalpheus genus of alpheid, which are the only known eusocial crustaceans, i.e. they have a lifestyle similar to that of ants and termites, with extensive division of labour among different castes in their societies.
In Life Is One, Amrita Goswami at the The Mobius Strip presents her evolutionary artwork, reproduced here in tiny, as well as an article on LUCA, the last universal common ancestor.
I will not get into the muddle of crustacean phylogenetics, but with the “all is one” theme, how does the idea that insects are crustaceans sound like? As weird as that sounds, it is actually one of the leading hypotheses for the relationship between insects and crustaceans; see Regier et al. (2010). In simple words, if this Pancrustacea hypothesis is true (pretty likely), that would mean that insects are merely land-dwelling, flying shrimp. Life is one, indeed.
In New Algorithms Force Scientists to Revise the Tree of Life, Emily Singer at Wired explains Salichos & Rokas’s recent Nature paper that got some interesting results on molecular phylogenetic methodology. While it hasn’t forced us to revise the tree of life just yet, it will be interesting to see what broader impact it has on current phylogenetic hypotheses, including the Pancrustacea.
In The first Darwinian evolutionary tree, David Morrison at The Genealogical World of Phylogenetic Networks takes us on a trip through history to show us the very first evolutionary tree. There’s also mention of the good old Steinheim snails, the topic of my very first term paper when I was a student.
Since we’re in history, the picture to the left is of the first scientific mention of crustaceans as Crustata, in page 343 of Bellon’s De aquatilibus, libri duo. Click on it to see the full size and try to read. However, nomenclature rules state that nothing before Linnaeus can be cited as a first name, and because Linnaeus didn’t use the name Crustacea (he dumped crustaceans in his Insecta Aptera), the name citation for Crustacea is in page 174 of Morten Thrane Brünnich‘s 1772 Zoologiae fundamenta praelectionibus academicis accommodata; the description is on page 184. And yes, you can’t work in taxonomy without knowing Latin.
In George Williams contradicts Red Queen hypothesis, Joachim at the Mousetrap recounts a disagreement the venerable George C. Williams had with one of the equally-venerable William D. Hamilton’s ideas about the evolution of sex. See also Part 2.
I can’t think of a crustacean example that is 100% relevant to Williams’s disagreement, but Williams’s issue is more fully explored in his classic 1975 book, Sex and Evolution. One of the related themes in that book was parthenogenesis and its evolution and maintenance, and the Darwinulidae are a very useful model system in the investigation of parthenogenesis which Williams would have found useful (I don’t recall him ever mentioning them in a book or paper). Darwinulids are a family of ostracod, and they’ve been parthenogenic for over 100 million years, which is very remarkable considering that parthenogenesis isn’t expected to be all that common or successful except under unique circumstances.
In The maintenance of sex and group selection, Joachim at the Mousetrap shares a video of the also-venerable John Maynard Smith talking about group selection.
Group selection is a contentious topic for silly reasons. I say that because it really should not be such a thorny issue – just run a proper experimental program for it instead of building ever-more-theoretical models, gather real empirical data, and the answers will fall out. Michael Wade did this way back in the 1970s (Wade, 1977), using the red flour beetle. Daphnia would be a more-than-ideal candidate for a model organism for such a program. These are tiny aquatic Cladocera, commonly called water fleas. Daphnia are numerous in the wild, are easily reared in the lab, reproduce quickly and with a large number of offspring, and come with a variety of reproductive modes. All it would need is some proper coordination and a large number of students, and a comprehensive experimental program can be set-up to test all the issues people have with group selection. I wish I thought of this before writing up the carnival…
Daphnia is already used as a model system, but for another topic: phenotypic plasticity in response to environmental changes. Peter Conlin writes about Daphnia‘s plasticity before moving on to his own research using yeast at the BEACON Center, in BEACON Researchers at work: Changing environments / changing organisms.
In Academic dispersal, close-to-be-newly-minted-Dr. Ben Haller (congratulations!) at Eco-evolutionary dynamics summarises every chapter of his Ph.D. thesis, a series of studies that are definitely very interesting. In a nutshell, they deal how certain ecological factors (landscape complexity, species interactions) influence how evolution proceeds.
My biological intuition says that there is definitely an extension to be made to this research using diapausing organisms, such as the Anostraca (fairy shrimp). Maybe it’s just because I work with them though. Pictured to the left is a pregnant one from a vernal pond, with a full load of eggs. Those eggs are drought-resistant, and are laid as the pond is drying out in order for the population to survive the summer season, a metapopulation getting reborn the next winter. However, it’s not as simple as “add water, hatch”. The amount of ecological factors at play is incredibly high, and the process not at all clear. Given that every single vernal pond is different, this can lead to ecological isolation, and a variation in selection regimes between the populations of different vernal ponds (and, from personal observation, even within the same pond, if it’s structurally complex enough). Feel free to make of this ramble what you will, steal the idea and run with it (or, uh, hire me?).
In More people means more ideas AND mutations, Jason Collins at Evolving Economics points out one of the ways in which economics and evolution are similar. Personally, I view such interdisciplinary comparisons as very useful, as the thinking and methodologies behind evolutionary research can inform other fields, similar to how linguistics uses phylogenetic methods. It also works ther other way around: evolution coopted game theory from economics.
Carcinology (the study of crustaceans) and economics also intersect, given that crustaceans make up a significant portion of a seafood diet. Crustaceans are cultured and fished, all to keep up the supply for an ever-increasing demand. Why yes, “supply and demand” is the only principle of economics I know about.
In Clever microbes: bacterial sensors and signals, S.E. Gould at Lab Rat explains the findings of a 2011 paper on the phase shock response of bacteria, in other words how bacteria respond to pathogenic threats, i.e. how their immune system works.
The Penaeidae are the most cultured shrimp worldwide, given their ubiquity as seafood – most of the shrimps and prawns that you buy and eat are penaeids. As with any agricultural system, disease plays a big factor, with many aquacultural losses happening due to infection, so the immune system of penaeids is under constant research. They have an innate immune system enabled by the hemocytes coursing through the circular system. These are analogous to white blood cells in vertebrates, dispatching intruding microcritters on encounter by phagocytosis or by encapsulating them in nodules. They also have a range of pathogen-specific biochemical responses in which antifungal and antimicrobial chemicals are produced, e.g. AMPs and lysozymes. In addition, they respond well to innoculation, exhibiting better survival rates to a second wave of the same infection, meaning their immune system is adaptive.
In Episode 62: Earth Day ExTREEvaganza, Randall from Variation, Selection, Inheritance shares a podcast that goesthrough the tymology of the word ent (yes, from LotR), but there’s also some discussion on plants’ communication abilities. Plant physiology is a fascinating topic – unlike animals, plants can’t move around and run away, so their physiology has evolved to cope with constant and inescapable changes in the environment. Communication skills are part of this, for example using volatile chemicals to “warn” other plants when there are herbivores flying around.
There is an entire book edited by Breithaupt & Thiel on Chemical Communication in Crustaceans, from which this account derives from. A cool case of chemical communication in crustaceans comes from some copepods. These are the dominant zooplankton in most marine and aquatic habitats, they’re found everywhere (I once found them in a small puddle under some leaves in a forest!) and have an incredible diversity in form, as the illustration above shows. These copepods live in areas where water flow is stable – not producing eddies or vortices. When mating time is reached, the female swims in such a manner as to leave a characteristic wake behind it. She deposits gradually higher concentrations of pheromones in this wake. The male picks up the distrubance of the water, and then follows the pheromones like a trail to reach the female, even though she can be pretty far away.
In Evolution’s got a P.R. Problem, Holly Dunsworth at The Mermaid’s Tale goes through a laundry list of many factors that play into the general ignorance about evolution – even among those who claim to be into science. Nobody is spared. And that’s good. Also includes several nice posters.
You know who else has a P.R. problem? Bathynomus giganteus, the cymothoid isopod pictured above. As the name suggests, it’s gigantic (see here for why). And people on the internet are digusted by it – I get WTF messages about it weekly. Don’t worry. It’s completely harmless. In fact, it’s quite tasty when cooked right. Some of its cymothoid cousins are a bit worrisome though, replacing the tongues of fish so they can steal food…
In Meyer’s Hopeless Monster, Part II, Nick Matzke at The Panda’s Thumb reviews and completely demolishes the latest senseless creationist screed by Discovery Institute lackey Stephen C. Meyer (also known from the equally-stupid 2009 book, Signature in the Cell). His latest masterpiece is about the Cambrian Radiation and seems to be a compendium of every single debunked “argument” that has been parroted by creationists since the dawn of time. Matzke’s takedown is masterful and goes to incredible depth. Kudos for the Goldschmidt reference in the title too. If you want to read some more, I wrote a 30-minute distillation of my 6-hour Cambrian Radiation course here, as part of a broader public lecture on the origin and early evolution of animals (Snowball Earth to Devonian).
I could dig up some case of creationists screwing up information about crustaceans, but to round off this carnival, I want to wax poetic on creationists. Pictured above is a copepod… with a microscopic tantulocarid larva attached to it (see arrow). Notice the scale bar – that thing is barely 100µm. This stage is called the tantulus larva, the infectuous stage. Instead of a mouth, it has a suction cup to attach itself to the host. With the help of a stylet in the head, the larva drills a hole in the host’s integument for feeding, and remains permanently on the host, only detaching when sexual maturity is reached.
This reminds me of the relationship of modern creationism to evolutionary biology. Evolution is the copepod, swimming around in the ocean of knowledge, feeding and growing larger. Creationism is the tantulus larva, an unwanted yet barely-noticeable parasite on evolution. It affects nothing, existing only by taking evolution’s hard work and using it for its own useless purposes, not contributing either to evolution nor to the ocean of knowledge. Yet as long as its host is there, it will probably not go extinct. It’s here to stay.
Or so my experiences lead me to hypothesise. And on that pessimistic note, we reach the end of this edition. Good job for slogging through the whole thing, hopefully you’ve learned new things, got introduced to novel concepts, and have gained a small appreciation for the diversity of the Crustacea.
Be sure to like the Carnival on Facebook, follow it on Twitter, and subscribe to the blog so you don’t miss the next edition in August, over at the Mousetrap. Submit articles for it on the Blog Carnival website. The more, the merrier!