Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
My Okinawa correspondent sends a happier picture than last time, this one of a living longhorn beetle, a member of the family Cerambycidae. Note the very long antennae, and the impressive tarsi. Cerambycids are often brightly or contrastingly colored.
An Okinawan longhorn beetle, 30.iii.2016.
Normally I’d have no idea what particular genus or species an Okinawan insect would be– I was happy I recognized the order and family!– but this seems to be an Asian longhorned beetle, Anoplophora glabripennis, which has become an invasive species in the US, Canada, Trinidad, and several European countries. The larvae feed on the sapwood of maples, elms, and other trees. If a reader more knowledgeable about Okinawan or East Asian insects has an opinion, please weigh in.
Richard ‘Dick’ Levins, the John Rock Professor of Population Sciences at the Harvard School of Public Health, died on January 19 of this year. He was one of the most influential population biologists of the 20th century, and a close colleague and associate of Dick Lewontin, Jerry’s doctoral advisor.
Richard Levins, 1930-2016
Levins was an early and active participant in the group of biologists that, in the early 1960s, worked to unite ecology, evolutionary biology, and genetics into a unified and theoretically-rich science of the biology of populations. Included among this group was Dick Lewontin, Larry Slobodkin, E.O. Wilson, and, perhaps most saliently for Levins, Robert MacArthur.
Both Levins and MacArthur were skilled in mathematical theory, and both wanted to develop a unified, general, and realistic theory of ecology and evolution. They collaborated on a number of seminal papers, and Levins (1966) wrote an important exposition and defense of the style of modeling that he and MacArthur favored, and which proliferated throughout population biology. The self-conscious unification of ecology and evolutionary biology in which Levins participated was an important event in the history of the field, but it has received little attention from historians. Sharon Kingsland touches on it in her Modeling Nature, but the most extensive treatment I know of is in E.O. Wilson’s memoir, Naturalist (though see note below.)
Wilson had a spectacular falling out with Levins and Lewontin in the 70s, so other accounts would be welcome. Some flavor of the movement, its goals, and participants, can be found in the 1968 symposium volume Population Biology and Evolution, edited by Lewontin, which included contributions by Levins, MacArthur, and Slobodkin, and which was favorably reviewed by Wilson in Science.
Though both Levins and MacArthur were accomplished theoreticians, both also had a natural-historical side (MacArthur, famously, “really knew his warblers“), and it is in fact Levins’ empirical side that first attracted my attention. Levins had a farm in Puerto Rico, and later was professor at the University of Puerto Rico. While there, he had a collaboration of many years with Harold Heatwole, documenting the biogeography of the biota of Puerto Rico and the nearby Virgin Islands, which involved substantial field work.
Levins was most interested in the insects, while Heatwole is a herpetologist. As Heatwole put it, this field work taught Dick “to love ants for themselves.” (There is no good online list of Levins’ papers, but those written with Heatwole are listed at the latter’s website.)Their 1981 paper with Michael Byer is rich in data and modestly synthetic, with a good bibliography. Their work was of great interest to me, as my dissertation field work was concentrated in the Virgin Islands, and my 2012 paper cited below is basically an update of the herpetological data parts of their 1981 paper.
But there was also one important theoretical paper, “On the distribution of organisms on islands”, that came out of their island collaboration. Published in 1963 in the Caribbean Journal of Science, it contains, in capsule form, the equilibrium theory of island biogeography, deriving the species species richness of an island biota from the balance of extinction and colonization.
This is of course, the theory made famous by, and now universally associated with, MacArthur and Wilson, who also first published on it in 1963, but in the more prestigious journal Evolution. The Levins and Heatwole paper has been almost universally overlooked. (Ilkka Hanski and I have cited it.) This could be a lesson in choosing your publication outlets wisely, but, in fairness to MacArthur and Wilson, their paper was more comprehensive, and explored more ramifications. Given the close connections among Levins and the latter two, it would be interesting to know how the ideas developed so as to result in near simultaneous publication of the same basic idea.
Levins did later develop some of the theory from his and Heatwole’s paper into the theory of metapopulations, which looks at a species’ distribution over a region as a “population of populations”– some populations going extinct, while new ones form by colonization, leading to a dynamic landscape of the species’ presence and absence. In fact, the basic metapopualtion model is to this day called the “Levins Model”.
When I was a graduate student, including doing some work in Lewontin’s lab in the Museum of Comparative Zoology, Levins had students based with Lewontin at the MCZ, but, being across the Charles River at the School of Public Health himself, I rarely saw him, and never discussed with him either his field work in Puerto Rico and the Virgin Islands, or the circumstances surrounding the development and publication of his and Heatwole’s version of the equilibrium theory of island biogeography, a failing which, to this day, I regret.
Levins was a lifelong communist, which was evident in his activities with groups such as Science for the People, and his affinity for Cuba and North Vietnam. I could not detect any hint of his political philosophy in his biological work, but John Maynard Smith, perhaps the greatest British evolutionary biologist of the second half of the 20th century, and himself an ex-Marxist who became disillusioned by communism, thought otherwise:
Levins was a Marxist before he was a biologist, and all his work shows it. His book Evolution in a Changing Environment, although it avoids the usual jargon, is the work of a conscious Marxist. I also think that it was a major contribution to ecology…. It is perhaps ironic that he made extensive use of mathematical techniques borrowed from capitalist economic theory: I cannot criticise because I have done the same. Since that time, he has worked more on applications of ecological theory. The essays in this book [The Dialectical Biologist] on pesticides, on Latin community health, and on applied biology in the Third World, reflect these interests. They illustrate the power of Marxism in the right hands. I have long thought of Levins as a rare example of a scientist whose work has been strengthened by adherence to a philosophy – Marxism or any other – and this book has confirmed that view.
Like Ernst Mayr before him– a synthesist of an earlier generation– Levins was able to participate in a symposium and celebration of his life’s achievements– “The Truth is the Whole”– organized at Harvard by his colleagues and students in the year before his death. Reminiscences by a number of his colleagues have been posted at the symposium website.
Dick Levins in Maricao, Puerto Rico, in the early 1950s (from radicalismojudio.org).
Heatwole, H. R. Levins and M.D. Byer. 1981. Biogeography of the Puerto Rican Bank. Atoll Research Bulletin 251. pdf
Kingsland, S. 1985. Modeling Nature. University of Chicago Press, Chicago.
Levins, R. 1966. The strategy of model building in population biology. American Scientist 54:421-431. pdf
Levins, R. 1968. Evolution in Changing Environments. Princeton University Press, Princeton, N.J.
Levins, R. and H. Heatwole. 1963. On the distribution of organisms on islands. Caribbean Journal of Science 3:173-177.
Levins, R. and R.C. Lewontin. 1985. The Dialectical Biologist. Harvard University press, Cambridge, Mass.
Levins, R., and R.H. MacArthur. 1966. The maintenance of genetic polymorphism in a spatially heterogeneous environment: variations on a theme by Howard Levene. American Naturalist 100:585–589.
Lewontin, R.C., ed. 1968. Population Biology and Evolution. Syracuse University Press, Syracuse, N.Y.
MacArthur, R.H., and R. Levins. 1967. The limiting similarity, convergence and divergence of coexisting species. American Naturalist 101:377–385.
Mayer, G.C. 2012. Island lists of West Indian amphibians and reptiles. Puerto Rico and the Virgin Islands. Bulletin of the Florida Museum of Natural History 51:136-147. pdf
Maynard Smith, J. 1986. Molecules are not enough [review of The Dialectical Biologist]. London Review of Books 8(2):8-9. link
Wilson, E.O. 1994. Naturalist. Warner Books, New York.
Wilson, E.O. 1969. The new population biology [review of Population Biology and Evolution]. Science 163:1184-1185.
* N.B. This book– Slack, N.G. 2010. G. Evelyn Hutchinson and the Invention of Modern Ecology. Yale University Press, New Haven, Conn.– may treat this important episode: Hutchinson was MacArthur’s thesis advisor, but I have not read it.
This hasn’t been officially announced yet, but I learned about it last week and it’s not really a secret given that Nature is already advertising for editors (here and here) for a new journal whose description is in the second ad:
Nature Ecology and Evolution — the latest member of the Nature family — will be published from January 2017, and we are now looking for editors to complete its launch team. The journal will publish the most significant research across the breadth of whole-organism and environmental biology, and will bring together all of the sub-disciplines of ecology and evolution, including palaeontology, molecular evolution and conservation biology.
We are now recruiting scientists from ecology- and evolution-related disciplines to become Associate or Senior Editors. This is a rare and exciting opportunity to help shape and launch a new academic journal. Candidates must have a PhD in a relevant discipline, and preferably postdoctoral experience, with a strong research record.
This will be a must-read journal for those of us in the field, and it’s also an opportunity for those interested in editing a good journal to apply for jobs now.
Here’s a scientifically based cartoon from SMBC about the relationship between ecology and immortality in Heaven. (One might call it “ecological theology.”) Sadly, the r versus k distinction has lost momentum over the years, as they are two ends of a continuum, and there are alternative as well as mixed reproductive strategies for single species. More important, there is a huge biological problem with one of the artist’s assumptions. Can you spot it?h/t: Gregg
As the capstone to Snake Week, let’s take a closer look at how the squirrel-like mammal being eaten by Tetrapodophis in Julius Csotonyi’s striking reconstruction died. In my earlier post, I took note of the fact that the describers of the newly discovered four-legged fossil snake had inferred from its skeleton that it was a constrictor (and thus the earliest known constricting snake, implying that constriction is an ancestral characteristic of snakes), and included Csotonyi’s lovely reconstruction showing the four-legged Tetrapodophis doing in and beginning to swallow a squirrel-like mammal. Here’s a reprise of the picture.
A multituberculate (?) being eaten by Tetrapodophis. Reconstruction by Julius Csotonyi.
The snake killed the ‘squirrel’, so we know who killed it, but what killed the ‘squirrel’? In police procedural talk, we’ve got the murderer, but we want to know the cause of death for the coroner’s report. Coincidentally, a new paper in the Journal of Experimental Biology, appearing at almost the same time as the description of Tetrapodophis, asks exactly that question, and shows via straight-forward and well-done experiments, what, in fact, is the ‘squirrel’s’ cause of death.
It was long thought that constricted prey died of suffocation, but it had also been suggested that the prey died of cardiac arrest due to drop in blood pressure. This had been suggested, in part, by the rapidity with which prey died, seemingly more rapidly than they would suffocate. What Scott Boback and colleagues have shown, using anesthetized rats fed to boa constrictors, with a set of catheters and probes in them to record their heart rates and blood pressures, is that there is a sharp and sudden drop in peripheral arterial pressure, an increase in central venous pressure, and a slowing of the heart rate. They conclude:
[S]nake constriction induces rapid prey death due to circulatory arrest.
I’m not sure if their experiments quite exclude asphyxia as a contributing cause, but it certainly shows the importance of the circulatory crisis caused by constriction.
Some of the media coverage has overstated the novelty of this result. For example, National Geographic headlined “Why We Were Totally Wrong About How Boa Constrictors Kill”, while Science, somewhat less over the top, headlined “Surprise: Snakes don’t kill by suffocation“. However, as Boback et al. note, circulatory collapse was first suggested over 80 years ago, and has been a viable idea for quite a while. Harry Greene, our foremost student of snake natural history, taking an ecumenical approach to the cause of death, wrote in his fine Snakes, in 1997, that constriction acted by “interfering with breathing and blood circulation so that the victim is immobilized within a minute or so”, while in a later, standard, herpetology text, Laurie Vitt and Janalee Caldwell (2009) wrote, “The tightening continues, and ultimately, circulatory failure causes death.” So Boback and colleagues have done a fine and needed study, but don’t believe the (media) hype!
In writing this post, I wondered what to call the prey in Csotonyi’s reconstruction. It could not be a rat, as in Boback’s study, as there were no rats, or rodents of any kind, in the Cretaceous. On the other hand, it does look like a squirrel (a rodent as well, again not possible for the Cretaceous), so I settled on ‘squirrel’, with scare quotes. A likely mammal for Tetrapodophis to have eaten is some sort of multituberculate, an extinct type of mammal found in the Cretaceous, and convergent on rodents in their dentition (gnawing incisors with a diastema before the molariforms). And, some of them showed arboreal adaptations, as do tree squirrels, but even more so, having prehensile tails. In the reconstruction below, accompanying a paper by Farish Jenkins and David Krause, the multiberculate Ptilodusis shown to be quite squirrel-like, except for its opossum-like prehensile tail.
Cover illustration from Science by L.L. Sadler accompanying Jenkins and Krause (1983).
Boback, S.M., K.J. McCann, K.A. Wood, P.M. McNeal, E.L. Blankenship and C. F. Zwemee. 2015. Snake constriction rapidly induces circulatory arrest in rats. Journal of Experimental Biology 218:2279-2288. abstract
Greene, H.W. 1997. Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley.
Jenkins, F.A. and D.W. Krause. 1983. Adaptations for climbing in North American multituberculates (Mammalia). Science 220:712-715. abstract (pdf of JEB commentary)
There’s been a lot of mediaattention the last few days about the prospect of a derelict Russian passenger ship, the Lyubov Orlova, crossing the Atlantic from Canada (where it was last berthed) and crashing into Ireland or Britain, spilling disease-ridden, inbred, cannibal rats on their shores. The ship was being towed to the Dominican Republic when it broke away and floated off last year. The Sun has had perhaps the most dire take on the story, headlining their piece “Ship of Ghouls“.
A scary picture from the Sun.
That the ship, laden with cannibal rats, might fetch up on shore, however, seems very unlikely. As the Guardian reports, both the Irish and British coastguards downplay the possibility. In particular, Irish officials note that they have looked for it, can’t find it, and suspect that it may have sunk.
But there’s another reason that it is highly unlikely, having nothing to do with whether or not the ship is still afloat, and because it reveals an important biological principle, it’s worth a mention here at WEIT: an ecosystem without primary producers cannot be sustained except for very brief periods of time. Unless those rats have been raising crops on the ship, the last one, cannibal or not, died some time ago.
There are very few “laws” in biology in the strong sense with which the term “law” is used in physics. Mendel’s “laws” of heredity, for example, have numerous exceptions and limiting conditions. When I teach genetics, I refer to them not as “laws”, but as Mendel’s “useful generalizations”. But one of the biological principles that does have law-like status is that primary producers must be at the base of every food web, and that energy is lost at every step in the food chain. Perhaps the reason these principles are law-like is because they derive so directly from the laws of thermodynamics: energy must be put in to a system to avoid entropy increase (so we must have producers to capture energy) and no energy transfer is 100% efficient (so there’s less energy available further up the food chain than at the bottom).
These ecological principles are often expressed in terms of a “trophic pyramid“, a visual representation of the fact that primary producers (usually green plants that capture energy by photosynthesis, but also photosynthetic and chemosynthetic bacteria) outnumber herbivores (primary consumers), who outnumber carnivores (secondary consumers), who outnumber top carnivores (tertiary consumers; there are rarely more than four or five levels in a food chain).
Trophic pyramid.
The exact shape of the pyramids depends on the efficiency of energy transfer between levels, and whether the pyramid is based on number of individuals, biomass, or energy flow units. As a rough guideline, efficiency of transfer between levels is often estimated at about 10%; the efficiency of capture of solar radiation is much lower. These important details can be investigated here and here, for example, but they do not alter the fundamental principles.
Viewing ecosystems in this manner owes much to an extremely influential paper, “The trophic-dynamic aspect of ecology“, by the young limnologist Raymond Lindeman, who tragically died of an obscure form of hepatitis a few months before the paper was published. The very interesting story of how the paper was almost not published, first being rejected by Ecology for being too theoretical, but finally accepted, has been told by Bob Cook.
Raymond Lindeman (1915-1942). He could have told you why there are no cannibal rats threatening Ireland and the UK.
So, what does this all mean for the people of Ireland and Britain? You can relax. Although rodents will resort to cannibalism when food supplies run low (though I’ve never seen it in rats myself, which, by the way, are much friendlier and make better pets than mice), an ecosystem based on cannibalism cannot persist, because there is no energy input to the system, and there cannot be a 100% efficient transfer, so the rat-level in the “food chain” will continually decrease in number and biomass. How long a bunch of rats resorting to cannibalism would last depend on details such as the number of rats, their caloric needs, etc., but suffice it to say that no reasonable numbers for those details could get the rats to last nearly a year. The caloric needs of mammals are quite high, and they need to eat a lot. (This may not be a comforting thought, but a ship full of anacondas and reticulated pythons could last a year or more at sea, without even having to eat one another, because of their low caloric needs. They would come ashore hungry, though.) The reason I say “probably”, rather than “definitely”, is because it is conceivable that large stores of food were left behind, and depending on the quantity, these could support a rat population for some time (recall that in most zombie movies the survivors rely on canned goods for survival, although in the last season of the Walking Dead they did begin farming). But since the ship was being towed for salvage, I doubt the kitchens and larders were full.
JAC Warning: This stuff is graphic, so if you are a d*g lover you may not want to watch.
by Greg Mayer
A video of a python disgorging a dog on a street in Bangkok is making the rounds, and has been the subject of an article in the Daily Mail.
The python appears to be a reticulated python (Python reticulatus). The video dramatically illustrates the flexibility and movability of snakes’ jaws. In most reptiles, the lower jaw articulates with the quadrate bone (q in the picture below), a firm part of the upper jaw. In snakes, the quadrate is only loosely attached to the skull, and there are other points of mobility in the skull. In the lower jaw, the anterior tooth bearing bone on each side, the dentary (d in the picture below), does not have a bony suture with its contralateral partner (as you do– feel your chin just below your lower incisors)– but only a soft tissue connection which is quite stretchable, allowing the two sides of the lower jaw to be widely separated.
The dog, of course, is quite dead, having been constricted before being swallowed. Constriction compresses the thoracic cavity, and leads to cessation of blood flow, killing the prey even before suffocation occurs. The saliva coating and compression of the dog’s body help it slide out backwards, instead of having the limbs get “stuck” somewhere in the snake’s alimentary canal.
My guess would be that the snake disgorged the prey because it was being harassed or bothered by people in the street. If it had been in the forest, it would have found a quiet nook in which to digest.
