Don't let the nutrients fly away!

Pitcher plants are beautiful but disturbing. Their vase-shaped pitchers are so elegant to look at, yet violate our notion of plants as passive and peaceful, because they are death traps for unwary insects and other small animals that fall in and drown in the pitcher fluid. Pitcher plants (genus Nepenthes) are one of the few carnivorous plants, who also include the Venus Fly Trap and the Bladderwort, that invert the food chain by gaining some of their nutrients from animals.

Nepenthes bicalcarata (by David Sucianto, via Wikimedia Commons)

Why would a photosynthetic organism need to trap animals? After all, they still have green leaves and chlorophyll, like any other plant. But other nutrients, especially nitrogen, are important to plant growth as well. Pitcher plants can grow in nutrient poor soil because they can supplement their intake of nitrogen and other nutrients by trapping and digesting animals, which are especially nitrogen-rich.

Not all animals will die in pitchers, however. Some insects, including the larvae of several dipteran (fly) species, can live in the pitchers and feed on the organic matter found there. The pitcher species Nepenthes bicalcarata also plays host to an ant species, Camponotus schmitzi, that is found only with N. bicalcarata. The ants are somehow able to walk on the slippery inner surface of the pitcher, and predate upon the fly larvae and other organic material, and also feeds on nectar from the plant.

It would seem at first that this is a lousy deal for the plant. The flies and ants are stealing its food right from its mouth! A new research paper published in PLoS ONE shows how the ants and pitcher plants actually derive mutual benefit.

By looking at the nitrogen isotope ratios in the plant tissue, and using isotope labeling experiments, the researchers showed that nitrogen is being transferred from the ants to the nutrients. They also observed how the ants predate upon the fly larvae that live and mature inside the pitchers. Left to their own devices, these larvae would consume the pitcher's nutrient supply, and then literally fly away with the stolen nutrients when they metamorphose into adults. For this they are (harshly) called kleptoparasites, or "thief-parasites". By capturing and eating the flies while they are still larvae or pupae, the ants put a stop to this thievery. The plant itself then recovers these nutrients in the form of the ant colony's waste products.

The ants are hence not only improving the pitcher's prey-capture efficiency, by keeping the slippery pitcher walls clean, but also prevent the nutrients from escaping with the insects. A fascinating story of symbiosis, that reveals just how dynamic and interconnected all these nutritional and behavioral relationships are in Nature.

Cockroach vs. human arms race

German cockroach (via Wikimedia Commons)

The cockroach is a creature that universally elicits feelings of disgust, but anyone who has tried to catch or kill them would also concede a grudging admiration for their toughness. They thrive on the refuse of our human civilization, and it has been said that if the human race somehow managed to wipe itself out through nuclear war, it would be cockroaches that flourish in the ruins.

Much human ingenuity has also gone into designing new and improved ways to kill cockroaches. Sugar laced with poison is commonly used to bait and exterminate these pests. The large-scale deployment of such traps, however, also constitutes a huge inadvertent experiment on the effectiveness of natural selection. Some populations of the German cockroach, Blatella germanica, have become immune to such traps because they are no longer attracted by the glucose sugar used as bait.

Recent research by a team from North Carolina State University (article abstract) has uncovered the physiological basis for this glucose aversion. The sense of taste is mediated by gustatory sensory neurons (GRNs); different substances activate different neurons and trigger different behavioral responses. In normal, wild-type cockroaches, glucose stimulates sugar-GRNs. The researchers found that this is also the case in the glucose-averse cockroaches, but that glucose also additionally stimulates bitter-GRNs, which are usually simulated by substances such as caffeine to which cockroaches are averse. The activation of bitter-GRNs suppresses the usual response of sugar-GRNs and causes the glucose-averse behavior.

This is a nice and neat story that illustrates how quickly natural selection can act, especially considering how numerous the cockroaches must actually be. Whereas evolutionary arms races between most organisms are limited by the rate at which natural selection can act, our human battles against the organisms that we consider pests and weeds are accelerated greatly by the pace of technological change and innovation. This episode shows, however, that natural selection can sometimes keep up and catch us when we are not wary.

How periodic cicadas evolved their timing

Every few years, the periodic cicadas come into the news, when they simultaneously complete their life cycles and emerge from the ground as winged adults. They swarm over large parts of the eastern United States and attract both curiosity and alarm from residents and the media. After a few weeks, their mating and egg-laying over, they disappear just as quickly as they appeared. Of course, they are not completely gone: their juveniles live underground, having perhaps the longest maturation of any insect, to emerge as adults after a period of 13 or 17 years.

13-year cicada from Brood XIX. Via Wikimedia Commons.

Why 13 or 17 years? These prime-numbered periods have puzzled more mathematically-minded biologists for ages, with one suggestion being that a prime-numbered life cycle would minimize the number of predator life cycles that could synchronize with it (because a prime number has no factors but itself). But how did this situation evolve?

A new paper published in PNAS (open access) from a group of Japanese scientists looks at the phylogeny and population genetics of the known species of periodic cicadas. The periodic cicadas fall within the genus Magicicada, within which are species partly defined by the length of their period. M. tredecim for example is a 13-year species, while M. septendecim is a 17-year species. Within each species there are also multiple "broods", representing different cohorts have the same emergence and mating cycles. One brood may encompass multiple species. Siva blogged here about one such brood in 2004, the ominously-named Brood X, which had an unusually large emergence (the "X" is actually just a roman numeral). The different species fall within three species groups, each with both 13- and 17-year species.

Contrary to expectations, the old species, defined by morphology and period, do not correspond to the evolutionary history as uncovered by molecular phylogeny and haplotyping. The three big species groups are still supported, representing two evolutionary splits at about 3.9 and 2.5 million years ago (Mya). The splits within the species groups, however, are relatively recent, mostly less than 0.5 Mya. Furthermore, the splits correspond more to geographical regions than to life cycle period. The split between 13- and 17-year periods have also evolved multiple times. To quote from the paper:

Our results are broadly consistent with the previous idea that an ancestor of all Magicicada diverged into three species allopatrically, and later, the three became sympatric and each species independently diverged into 13- and 17-y cicadas. Surprisingly, however, the divergence of 13- and 17-y cicadas was asynchronous among the species groups and occurred repeatedly even within a species group. This finding is all of the more interesting given that each species group shows similar eastern, middle, and western phylogeographic divisions similar to post-Pleistocene patterns observed in other North American taxa, suggesting that the three Magicicacda groups shared multiple refugia during the last glacial maximum.

This is a nice surprise, and as the authors point out, the repeated switching between 13- and 17-year forms suggests that there is a single genetic "switch" involved, because it is unlikely that a complex mechanism could be repeatedly gained and lost in such a manner.

Scientific turnover and the fate of old theory

The Arts and Sciences are often seen as non-overlapping complements, as naturally opposed as North and South, or the two sexes male and female. It's therefore surprising to find someone who can make a significant career in both, not just as an amateur but as a paid professional.

Vladimir Nabokov is best known as the author of the novel Lolita, but before becoming famous for his writing in English, he was a professional lepidopterist, an expert on a group of butterflies known as the Blues. An earlier blog post here highlighted some recent research on "his" group of butterflies.

His two careers were also the subject of an essay by Stephen Jay Gould. Gould used Nabokov's example to examine our attitudes to "genius". If Nabokov was a genius in literature, does it follow that his scientific work was also illuminated by the same genius? Was his scientific writing especially fluent or literary, as some literary critics claim? Gould found that, in the opinion of other professional lepidopterists, Nabokov's scientific work was competent and painstaking, but not especially pathbreaking or profound. Nor was his scientific writing unusually poetic or stylistically striking, in the way that his novels were.

In fact, Gould goes as far as to characterize Nabokov as being somewhat of a "stick in the mud." At the time when he was engaged in his butterfly work full-time at the Museum of Comparative Zoology at Harvard, from 1942 to 1948, a revolution was underway in taxonomy. Where previously the morphological characters, such as wing coloration or genital anatomy (a serious preoccupation of much of entomology!) were the means by which new species were defined, the budding science of cytology (the study of cells) had introduced chromosomes as yet another important character. "Cryptic" species with identical morphology were now being defined on the basis of their differing karyotypes (the number and appearance of the chromosomes). Nabokov rejected the use of chromosomes for defining new species, perhaps as a matter of practicality: pinned butterfly specimens in museums only preserve the morphology, so it would be impossible to distinguish karyotype variants in the museum cabinet.

His autobiography, however, seems to belie this depiction of Nabokov as a rigid conservative. Nabokov spoke about "great upheavals... taking place in the development of systematics." The year that Nabokov started working in the Museum was also the year that Ernst Mayr, by then also an emigre to the United States, published his Systematics and the Origin of Species, the book which established the biological species concept, that species (at least for sexual macroorganisms like birds and insects) are defined by their potential for breeding to produce viable offspring. The new emerging school of taxonomy represented by Mayr were strong champions of geographic variation. Species were not immutable, platonic ideals. The variation represented by geographic "races" or subspecies was just as important as the original "type" of a species. Conceptually, this so-called Neo-Darwinian revolution was when darwinism finally became orthodoxy in taxonomy, the field that had inspired it, nearly a century after the publication of the Origin of Species.

Nabokov was aware of this theoretical revolution - how could he have ignored it? This was a tremendous change from the lepidoptery of his youth, which could well be said to be truly "butterfly collecting". As he observed:

"Since the middle of the [19th] century, Continental lepidopterology had been, on the whole, a simple and stable affair, smoothly run by the Germans. Its high priest, Dr. Staudinger, was also the head of the largest firm of insect dealers. Even now, half a century after his death, German lepidopterists have not quite managed to shake off the hypnotic spell occasioned by his authority. He was still alive when his school began to lose ground as a scientific force in the world. While he and his followers stuck to specific and generic names sanctioned by long usage and were content to classify butterflies by characters visible to the naked eye, English-speaking authors were introducing nomenclaturial changes as a result of a strict application of the law of priority and taxonomic changes based on the microscopic study of organs. The Germans did their best to ignore the new trends and continued to cherish the philately-like side of entomology. Their solicitude for the "average collector who should not be made to dissect" is comparable to the way nervous publishers of popular novels pamper the "average reader"--who should not be made to think. 

"There was another more general change, which coincided with my ardent adolescent interest in butterflies and moths. The Victorian and Staudingerian kind of species, hermetic and homogeneous, with sundry (alpine, polar, insular, etc.) "varieties" affixed to it from the outside, as it were, like incidental appendages, was replaced by a new multiform and fluid kind of species, organically consisting of geographical races or subspecies. The evolutionary aspects of the case were thus brought out more clearly, by means of more flexible methods of classification, and further links between butterflies and the central problems of nature were provided by biological investigations."  

(Speak, Memory: An Autobiography Revisited, pp.122-123)

So it wasn't that Nabokov was a conservative who didn't like change. He had already spanned the era between "hobbyist" and scientific entomology. He was already witness to a revolution (in science, and also in his homeland of Russia). There's a quip I've heard attributed to the physicist Max Planck, that science doesn't progress because people come to accept new theories on the strength of their evidence; it progresses because old scientists who believe the old theories die out. It's certainly an exaggeration, but we are equally certainly products of our education. Every generation in science has its own revolution of understanding, and maybe it's unfair to expect someone to accommodate a second one, just as he or she was getting comfortable with the first!

Imitation, flattery, and body-plans

If imitation is the highest form of flattery, then ants might be among the most celebrated creatures of the insect world. A delightful essay in Current Biology describes some of the more uncanny cases of ant-mimicry among arthropods, among them the treehopper Cyphonia clavata.

Ant-mimicking treehopper Cyphonia clavata. Via Flickr.

The 'ant' that's apparently riding on the back of the treehopper is actually an extension of its headshield. The green coloration of the rest of its body blends in with its leafy background, so on first glance you only see the black 'ant'. The mimic is seated in reverse: if you look carefully at the 'abdomen' of the 'ant', you'll see the green eye of the treehopper staring right back at you. This makes sense because in their defensive posture, ants move backwards.

Creatures that mimic ants are called myrmecomorphs ('ant-shaped', from Greek). There are certainly a lot of ants out there to be imitated (Antweb has high-resolution scans of ant specimens from around the world). One statement in this essay got me thinking:

"... there are about 2,000 species that mimic ants. Not surprisingly, these are nearly all insects or spiders, as a certain degree of body plan resemblance to ants is probably a prerequisite to becoming a myrmecomorph. ... ant mimicry must have evolved many times independently."

Treehoppers are true bugs (Hemiptera) in the family Membracidae. They are known for their headshields, also called helmets, which are responsible for the great diversity of form in this family. Some of them look like they may have inspired the fascinators worn by some of the women at the recent Royal wedding.

Diversity of treehopper headshield forms - Cyphonia clavata is at bottom right. Via Nature

Developmental biologists have now found that the helmet is actually a body plan innovation (original paper abstract), something that's incredibly rare in evolution. New structures are typically formed by modifying or reducing existing parts of anatomy, but innovations such as new appendages or new body segments are much rarer.

Insects typically have a pair of legs on each of the three thoracic segments (T1 to T3), and wings on the 2nd and 3rd (T2 and T3). The helmet arises from the 1st thoracic segment (T1), and anatomical observations have suggested in the past that they might be homologues of wings. By looking at gene expression in a developing treehopper, biologists found that wing-specific transcription factors (which control the expression of other genes), especially Nubbin, are expressed in the developing helmet, which indicates that it's developmentally homologous to wing appendages. They suggest that the Hox genes responsible for suppressing wing formation in T1 have been suppressed in treehoppers, allowing the evolution of the helmet. Because they aren't needed for flight, they aren't faced with the same physical constraints and so have been able to develop into a wild variety of shapes and sizes.

So coming back to the statement about body plan resemblances quoted above, perhaps the idea is more beguiling than it actually should be. An ant mimic for sure will have to be bilaterally symmetrical, of the right ant size, but beyond that I don't think the prerequisites for mimicry can be quantified. For conceptual proof of this, watch this famous octopus species mimic in turn a brittlestar, lionfish, and sea snake.

Highlights of the Week

Some interesting news and articles from around the web for this week:

Cicadas are emerging en masse in the Midwestern United States after yet another 13-year cycle.
Cicadas are insects which are known for their loud and distinctive sounds produced by a mechanism called 'tymbalization' in their abdomens. Several species in the genus Magicicada in the US are called 'periodical cicadas' because they transition into the adult phase of their life cycle in a synchronized manner in cycles of 13 or 17 years. This summer the time has come for the emergence for the so-called brood XIX. These emergences happen in such numbers that early European settlers thought that the cicadas were the pestilential "locusts" of the Bible, and their carcasses litter forests in a deep crunchy layer. Find out more about cicadas at this website from the University of Michigan.

Mathematics and biology have a deep and subtle relationship. 
Viruses, for example, have self-assembling coats made up of protein subunits, which tile together in specific geometric forms. Disrupt these geometries, and one might be able to render a virus harmless.... Other fields of mathematics, such as chaos theory, can help in modeling natural phenomena such as plankton dynamics in the ocean. (I wish this essay was illustrated, though.)

How do flatworms regenerate their missing body parts?
The planarians (flatworms) are favorite classroom examples for regeneration because of their freakish ability to regenerate a complete worm when cut into multiple pieces. New research shows that cells in the worms called neoblasts, which can be thought of as analogous to stem cells in other animals, are pluripotent, meaning that they can develop into any cell type in the body. Researchers have also found some of the factors that determine whether a newly divided cell in a regenerating animal will develop into part of the head or the tail.

Fire ants link up into waterproof rafts

Many insects, such as the aptly-named water-striders, are able to exploit surface tension and literally walk on water. However, the majority are only moderately hydrophobic, and because they are denser than water, have to struggle all the harder to remain afloat the larger they are.

Fire ants live in places which are frequently inundated by water. Individual ants placed in water can float, but not very well. How then do they cope with flooding? It turns out that they assemble themselves into ant 'rafts', cooperating to improve their buoyancy and waterproofing.

Insect cuticle itself is already water-repellent to some extent, but alone it is not enough to explain how a clump of ants, gripping onto each other mandible-to-leg, is more buoyant per unit mass than an individual ant. The answer lies in their ability to trap a layer of air (called a 'plastron') around their bodies. By clumping together, they increase the size of these plastrons, and can entrap larger air bubbles within the clump. These lower the effective density of the ant mass, and also allow them to breathe (insects breathe through pores in their cuticle) even when submerged.

Quotable quotes from the paper:

"Ants were scooped with spoons into 100-mL beakers rimmed with talc powder and weighed to count their numbers. Using the natural adhesion of the ants, a few swirls of the beaker was sufficient to roll the ants into balls."
"Not surprisingly, ant spheres that are placed on solid surfaces quickly disintegrate as the ants flee in all directions."
"By harnessing two live ants with an elastic band, we found that the maximum tensile force between them is F = 620 ± 100 dyn (N = 11), or more than 400 times body weight."

Reference:
Mlot, Tovey, & Hu. "Fire ants self-assemble into waterproof rafts to survive floods." Proceedings of the National Academy of Sciences, USA (10 May 2011) vol. 108 no. 19 pp. 7669-7673.

Highlights of the Week: Catching up on Blogging

It's been a while since I've written anything new, and the explanation is straightforward: classes just started up again and have hit me like a freight train. Two weeks in, I've just had a chance to catch my breath.

But I've still been keeping an eye out for interesting articles and news on the Web, and here's my selection of cool stuff from the past week (okay, two weeks...):



Green Porno film star and director talks about her work. Isabella Rossellini's short film series, Green Porno and its follow-up Seduce Me ("A potential sponsor called to say they liked the films but that they couldn't support anything that had the word "porno" in it") are short (1-2 mins), award-winning gems about the peculiar sex lives of different animals. She stars in all of them as the animals, dressing up in fantastic paper costumes (see above).

Vladimir Nabokov's biogeographic theory on the origin of the Polyommatus blues butterflies has been confirmed by lepidopterists using molecular techniques. Aside from being a successful author in both his native Russian and his adopted English (in which he wrote his most famous book, Lolita), he was a great butterfly enthusiast and was for a time curator of Lepidoptera in Harvard's Museum of Comparative Zoology.

Woodpecker skulls inspire the design of more effective shock absorbers. Fun fact: woodpecker skulls decelerate by up to 1200 g each time it hammers (more than 20 times a second!), whereas humans would be concussed by an acceleration/deceleration between 80-100 g.

World Wildlife Foundation launches a new document format, similar to Adobe's PDF format, but which doesn't allow the document to be printed, to raise awareness about excessive paper use. As expected, the file extension is .wwf. Good idea, or gimmick?

The Galapagos Islands, biodiversity hotspot and inspiration for Darwin's theory of evolution, have been taken off UNESCO's list of endangered World Heritage Sites. Doesn't mean that they're out of danger, though. Ironically, the effects of tourism are the greatest threats to the islands today, as the booming tourist industry encourages development and immigration to the archipelago.

Photo gallery of the world's 10 most threatened rainforests, including Sundaland, the Philippines, and India-Burma.

Fossilized leaf-mimic lacewings

Lacewings, or Neuroptera, are a order of insects with very distinctively patterned wings, as their names (both in English and Latin) suggest. Among insects in general, many species, especially the well-known leaf katydids, are mimics of flowering-plant leaves. Such leaf mimicry presumably is a form of camouflage that functions in either defence or in aid of predation.

Paleontologists working in China have discovered a rare set of lacewing fossils (open access article) from Middle Jurassic rocks at a site in Inner Mongolia which are leaf mimics - a useful adaptation given their large size. However, their age means that they pre-date the Cretaceous radiation of flowering plants. The relationship between flowering plants (angiosperms) and insects has been characterized as a synergistic adaptive radiation - both groups flourished in diversity on similar timescales, an observation explained by pointing to the frequent close relationships and associations between insects and angiosperms. Therefore, leaf mimicry has long been thought to be a post-angiosperm phenomenon, and virtually all known leaf-mimics pretend to be angiosperm leaves. These lacewings, however, appear to mimic cycads or bennettiales, both of which are non-flowering seed plants (gymnosperms) that dominated the pre-angiosperm plant world. Both fossil and extant cycads have distinctive pinnate leaves, which the lacewings resemble. These are very different in form from the typical angiosperm leaf.

On the whole this is a very neat story - close insect-plant associations or coevolution appeared long before the rise of the angiosperms. The change in plant communities from gymnosperm-dominated to angiosperm-dominated, however, would have diminished the effectiveness of these cycad mimics, and might explain their disappearance. Perhaps some later fossil discoveries, likely coming from China, the new hot-bed for paleontology, might shed more light on the affair....

Down with Kin Selection?

Oecophylla weaver ants in Gombe. Photo by Axel Rouvin via Wikimedia Commons.

The concepts of kin selection and inclusive fitness are centerpieces of modern evolutionary biology. Almost every biologist has some familiarity with at least the outline of the issue, and they are staples in textbooks and in the classroom. Briefly, these ideas were introduced in the mid-20th century to explain the apparent paradox of how altruism and cooperation might evolve in a biological system. If natural selection favors the spread and fixation of genes that cause an individual to have more offspring, how can we explain the evolution of traits which involve one individual aiding another at some cost to itself?

Cooperation might seem to be intuitively beneficial, but consider a population of animals which all sacrifice a bit of their potential individual fitness in order to cooperate for some greater good, e.g. defending the nest from predators. They will get good returns on their investment if they all cooperated honestly. However, such a group is prone to invasion by so-called 'cheaters', which take but do not give back. A group of cooperators without defences against cheating will rapidly be overtaken by cheaters, and hence any cooperative endeavour is doomed to crumble.

It was to resolve theoretical problems like these that the idea of inclusive fitness was introduced. Individual fitness is simply the number of offspring that one produces. Inclusive fitness, on the other hand, counts not just one's own offspring, but the offspring of relatives, multiplied by the factor of relatedness. The process by which it functions is kin selection - if one helps one's relatives and contributes to their individual fitness, then one is contributing to one's inclusive fitness. A gene for cooperation could hence spread and be resistant to cheating, because it is more likely to be present in relatives of an individual that already bears that gene, than in unrelated individuals. The essence of the idea is found in a prescient quip by the geneticist JBS Haldane, who said that he "would [lay down his life] to save two brothers or eight cousins" (Wikiquote) - because the relatedness (more rigorously, the probability that a gene is identical by descent) of siblings is 1/2 and that of cousins is 1/8.

A new look at the math (the derivations are in the supplementary material, but the main paper is unfortunately hidden behind a paywall) behind inclusive fitness theory is now claiming that it is no better than standard natural selection theory in explaining one of the key problems of biology, the evolution of eusociality (edit 28/8/2010: Harvard Gazette press release). The group, comprising mathematical biologists Martin Nowak and Corina Tarnita, and the father of sociobiology EO Wilson, explain that inclusive fitness is merely a different way of 'doing the accounting' which is somewhat more complicated than it needs to be. That is, it is too specific, relying on certain assumptions (additive fitness effects, pairwise interactions only, weak selection) which are fulfilled in only a few exceptional cases. It is not an adequately general theory, in the mathematical sense of the word. They also challenge the validity of Hamilton's rule, the simple-looking equation that states that a gene for a cooperative behavior will spread if:

Relatedness > cost/benefit

Population biologists trying to test Hamilton's rule in actual organisms have found it difficult to measure these quantities. The authors of this paper, using a more explicit derivation, found that cooperation does spread when something is greater than the cost to benefit ratio, but this 'something' (as they put it) is not relatedness. In place of inclusive fitness theory, they propose that the more general game-theoretic theory of natural selection, used in conjunction with precise models of population structure, is adequate to explain the evolution of cooperation, without invoking kin selection.

What then, of the crown jewel of kin selection, the explanation of eusociality in hymenopterans? Hymenopterans are the insects which include bees, wasps, and ants. They have an unusual genetic system called haplodiploidy: females lay either fertilized (diploid) or unfertilized (haploid) eggs. The former hatch into females, and the latter into males. The ants are perhaps the most successful and best known eusocial animals. Kin selection theory explains the cooperation between female, sterile worker ants (who might easily defect and start laying eggs of their own) in terms of their relatedness - sisters are more closely related to each other (relatedness of 3/4) than daughters are to mothers (1/2), and so cooperation among sisters can spread. Not all eusocial animals have haplodiploid sex determination - termites, for example, do not. As more eusocial animals have been found, it turns out that the number of haplodiploid lineages is in the minority. An alternative explanation has to be found for eusociality, because the kin-selection based explanation as given above was now most probably an exception to the rule.

Naked mole rats are eusocial mammals. Photo via Wikimedia Commons.

Ed Wilson has proposed for some time now that eusociality is to be explained by theories other than the traditional haplodiploid hypothesis (in Quarterly Rev. Biol., Bioscience (pdf), PNAS) . Briefly summarizing, his model, which is adopted and refined in this paper, involves the formation of groups subject to selection, the predisposition to group-formation by certain 'preadaptations' (they cite the example of solitary bees being behaviorally programmed to complete tasks in sequence - hence they naturally divide labor when forced to cohabit), and selection acting at multiple levels. Hence organismal traits and population structure are sufficient, without having to invoke the concept of inclusive fitness.

This analysis is quite satisfying because it represents the convergence of two different approaches to population biology: that rooted in mathematical theory and that rooted in natural history. The strong claims that it makes will certainly trigger robust debate. However it turns out, it will be interesting to see how the study of eusociality will respond. As the authors note (quite provocatively, given the highly charged reception to the original publication of Sociobiology in the 1970s), "[w]e have not addressed the evolution of human social behavior here, but parallels with the scenarios of animal eusocial evolution exist, and they are, we believe, well worth examining."

Zombie ants in news, and musings on science reporting...

Markings on fossil leaves appear to be the 'death grip' of ants infected by the so-called zombie fungus, Ophiocordyceps. The fungus causes the infected ants to move to a position on nearby vegetation and die immobilized there, such that the sprouting fruiting body of the fungus will more efficiently spread its spores over yet more ants. This grip leaves distinctive markings on the leaves, which were recognized by a group led by David Hughes (disclosure: I have met David and heard him talk about his work).

Having this fossil evidence allows us to be able to give a minimum age for the history of this fungal life-style. Despite advances in the study of molecular evolution, fossil evidence is still the most direct way to pin a date on events in the history of life. Earlier hopes that the rate of changes in nucleotide or amino-acid sequences could provide an objective 'molecular clock' (first proposed in the 1960s by Emile Zuckerkandl and Linus Pauling - yes, that Linus Pauling) turned out to be premature, because rates of molecular evolution are not generally uniform across species and even in single lineages over time, and therefore need to be calibrated, typically against the fossil record.

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On the topic of science reporting: The Guardian newspaper article linked above is better than most newspaper science reporting, however, it still illustrates a few sticky points that nag at me when I read about science in the news.

Chief among these is the lack of citations. That is disconcerting, especially to someone in an academic setting where proper attribution is always emphasized. Science reporters are quite uneven in how they cite things: some simply omit any mention of where the research they describe is going to be published (or has been published), some state the journal name and leave it at that, and only in a few cases is a full citation (or in this article: a link to a PubMed record) given. Here, however, note that the PubMed link is to an earlier paper on a related topic, but not about the issue being directly reported. The article says that the scientific report is published in Biology Letters, but a quick search in the journal's website turned up no hits. Hence I can only conclude that it's yet to be published, and the reporter was privy to a prepublication preview.

Unfortunately, this affects blogging, too. I'm happy to highlight interesting papers and newspaper reports on biology, but without having seen the original paper, if new research is being presented, it is hard to assess the quality and reliability of the work, and whether it really is worth being blogged about. Worse yet, the reporter may have distorted the actual conclusions, or misrepresented the facts, ... the list goes on.

So the next time you see a newspaper article reporting new research, do keep an eye out - drop a comment here if you see something noteworthy that shows how caution is necessary.

Entomophagy for the Environment?

The Guardian reports on a new Food and Agriculture Organization (FAO) report that suggests insect-eating as a way to mitigate the human demand for meat, especially in countries where insects are already consumed as part of local cuisines: "the FAO's priority will be to boost the eating of insects where this is already accepted but has been in decline due to western cultural influence."

It's easy to dismiss the idea as cranky or silly, but there is a valid point in there - people in industrialized nations already eat shrimp, which are quite similar. And it's not all about fried locust, either. Insects could be useful as feed for more conventional livestock, or turned into some kind of homogeneous patty, the better to disguise their origins.

My main bugbear about the article is that it talks about insects in the title but the picture shows scorpions on sticks. To be fair, the text of the article does say "insects and other creepy-crawlies," so it's not entirely wrong.

Picture this - Drosophila germ band formation

Explaining Drosophila development just after the cellularisation process to a student can be tough. I tried to and ended up searching youtube for animations. It's mentally difficult to picture the invagination of the mesoderm and then the migration of blastoderm cells to initiate germ band formation from worded descriptions. I am quoting this segment from the wikipedia on germ band extension "During this process the ventral germ-band extends around the posterior end of the embryo, effectively folding over onto the dorsal side of the egg. Multiple individual cells intercalating mediolateral to the anterior-posterior axis drive the resulting global elongation of the embryo." How does one get a handle on that?

Developmental Biology was one of my favorite subjects in NUS, taught by the enthusiastic and nurturing Prof Lim Tit Meng (now director of the Singapore Science Centre). Those days we had plasticine models to play with to help us figure out gastrulation. If you didn't have good spatial cognitive skills, good luck to you. So I am highlighting this video from the Garland Science channel that immediately solves the problem. Two thumbs up. It gets five popcorns from me.

How Caterpillars Crawl

How do caterpillars crawl? We might imagine them as a gooey tube inching forward in waves, but a research group at Tufts has found that their bodies behave in a more complex way, which they term 'visceral-locomotory pistoning', where the elastic gut of the caterpillar stretches and moves independently of the body wall. In order to peer inside the caterpillar's body, they used X-ray synchotron radiation, but later found a much easier way - using newly-hatched caterpillars, which are small and translucent to visible light. The biomechanics of soft-bodied animals is an inherently challenging subject. Modeling the physics is difficult because there are no rigid elements (skeletons, shells, and the like); it is also a challenge to find suitable reference points to track during motion.

Check out the fascinating video abstract freely available on the Current Biology website.

(Via New York Times)

Delusory Parasitosis

"I knew I’d been crazy during that period, but I didn’t know I’d been crazy with a condition that had a name, and that although it wasn’t common, it was well known in psychiatric literature. Not just psychiatric literature. Delusory parasitosis is where psychiatry meets academic entomology and pest control."

Author Jenny Diski writes about delusory parasitosis, also called Ekbom Syndrome, a psychiatric syndrome where a person imagines that he or she is being invaded by tiny invisible bugs. As she tells it, it's something that the unsuspecting entomologist or pest control specialist will be unnerved to encounter for the first time!

The entomologist whom she cites, Nancy Hinkle, has written a review of Ekbom Syndrome for Annual Review of Entomology (2010, vol 55: 77-94, doi:10.1146/annurev.ento.54.110807.090514).

(Scratching cat photo: Pavel Ševela / Wikimedia Commons)

Flower-petal coccoons

Bees with a sense of style! The solitary bee Osmia (Ozbekosmia) avosetta from Turkey and Iran uses colorful petals from a legume plant to make its nests; each cell has two layers of petals sandwiching a thin layer of mud. Other Osmiine bees also use petals in their nest construction. A particularly beautiful example of animal architecture.

Original paper from the American Museum Novitates (AMNH), and NPR report with pictures.

(Via Sar)

Fungus-Derived Genes Make Aphids Red

Carotenoids are pigments produced by many organisms, among them bacteria, plants, algae, and fungi. They're what gives carrots, red leaves, and some flowers their reddish/orange color. However, no animal has been known to produce them or to have the metabolic pathways required for carotenoid biosynthesis, until now.

In Science, Nancy Moran and Tyler Jarvik report the discovery of carotenoid biosynthesis genes in the genome of the pea aphid, Acyrthosiphon pisum, which has a body color polymorphism (some individuals are red, others are green). It was formerly thought that they got their pigmentation from their diet, or from their bacterial gut symbionts. Suspicions were raised, however, when no trace of a carotenoid pathway could be found in the primary bacterial symbiont of aphids, Buchnera, which is among the best-studied of bacterial symbioses, and in two other symbiont bacteria. Because the genome of the pea aphid was recently released, they searched for, and found, carotenoid synthesis genes, which are most closely related to similar genes in the fungi. This led them to conclude that aphids have gained the carotenoid biosynthesis pathway by lateral gene transfer from fungi.

Lateral gene transfer (also horizontal gene transfer) was long thought to be a rare or exceptional phenomenon, but this adds one more example to a growing list of transfer events which have been uncovered by new genomic methods.

References:
Moran & Jarvik, Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids, Science 328, 624-627 (30 Apr 2010). (DOI: 10.1126/science.1187113)
Takema Fukatsu, Perspectives: A Fungal Past to Insect Color, Science 328, 574-575 (30 Apr 2010).

Parasite makes ant mimic fruit

Parasites frequently modify the behavior of their hosts to encourage the infection of new hosts. For example, see this video (taken from the Planet Earth documentary) of the fungus Cordyceps that makes insects climb to the top of grass stems, and then erupts its fruiting body from the host's body, and disperses its spores over more hapless hosts from this elevated position. Yanoviak et al. (Am Nat 2008. Vol. 171, pp. 536–544; DOI: 10.1086/528968) describe a case of parasite-induced mimicry in the ant Cephalotes atratus. A nematode infection causes the gasters (rear portion of the abdomen) to become bright red and swollen, resembling a berry fruit, where normally it is black and inconspicuous. The infected gasters are also full of parasite eggs. Birds that feed on berries would then pop off these packets of parasite propagules, and pass out the eggs in their faeces. Ants congregate around bird faeces, which represent food resources to them, and collect them to feed to their brood, completing the cycle.

Here's the lesson from all this, kids: don't eat dung.

Synchotron Radiation Tomography Illuminates Hidden Bugs

http://news.bbc.co.uk/2/hi/science/nature/7324564.stm

We've all seen pictures of ancient insects trapped in the golden, honey-like transparency of amber. Amber is fossilized tree resin, that when it was formed, trapped and preserved the form of insects and other small animals that it flowed over. But much amber is cloudy, and short of breaking it open, there's not been anyway to look inside to see what fossils might be found within. Now, scientists at the European Synchotron Radiation Facility in Grenoble, France have used high-intensity X-ray radiation to peek inside the amber and through computerized tomography (the same method as CT scans used in medicine) reconstructed 3-D images of fossils found in the amber. This was previously not possible with conventional X-ray sources. What's even neater - they use a method called 3D printing to produce a plastic resin scaled up model of the fossils in the amber, so palaeontologists have something tangible to manipulate and observe, rather than just pictures on a screen. Really amazing!

Indian biopiracy fears stifle research

An entomological collaboration between American and Indian scientists to study the insects of the Western Ghats in India was derailed by the Indian National Biodiversity Authority's refusal to allow the Ashoka Trust for Research in Ecology and the Environment to export insect specimens to institutions in the US for researchers there to examine.

The NBA objected to the large number (200,000) of specimens that were to have been sent for identification, citing biopiracy concerns, while claiming that there is no rule against exporting "a few specimens." They instead recommended that researchers send photographs instead [see: Jayaraman, K. S., 2008. Entomologists stifled by Indian bureaucracy. Nature, 457: 7 (6 Mar 2008; doi:10.1038/452007a)]

One valid concern the authorities have is that Indian taxonomic expertise needs to be built up and by exporting so many specimens, foreign researchers would benefit at the cost of locals. The 'marketing' of biodiversity as a potential economic resource has led many countries with rich biodiversity but comparatively less technical expertise to impose protectionist laws aimed at keeping wealth within their borders. Personally I think this protectionism is misguided, for the following reasons:

1. Taxonomic expertise will always be limited because it is a small field. There will always be the necessity to send specimens to external institutions because no single country will have enough experts to identify everything. Some commentators say that more local students should be sent to study in Western institutions and return to their home countries to work on the local biodiversity - but to what effect if once they return, the lines of communication between them and the outside world are severed? Their work will then become blinkeredly local and have no effect or influence.
   

2. The need to study biodiversity and document it cannot wait for the slow training of new taxonomists and systematists (especially in the face of the field's waning popularity), because of the ongoing destruction of habitats. This leads to the perverse consequence of legitimate scientific research being hampered (because in science, rules must be obeyed) while illegitimate habitat destruction proceeds without obstruction (because illegal clearing and burning is illegal anyway).
   

3. The chances of wholesale biopiracy are slim: taxonomy is not the most economically profitable of scientific endeavours. Common courtesy now also requires that local host institutions from the countries which supply the research materials be provided with a complete set of specimens collected. Presumably in this case too the Indian researchers will have their own set of insects. Bioprospecting success stories seem to be too few to warrant such paranoia - perhaps I might be wrong about this and if so would hope to hear more about them.
   

4. It's simply not cricket - being so possessive betrays a mindset of colonial victimization. Being ungenerous now won't realistically make up for a past history of colonial oppression.

Ultimately, this will only hurt the Indian researchers and Indian science. The bureaucrats seem to have forgotten that animals and plants don't obey human borders. Perhaps they wish to prosecute animals which migrate from the country for treason? I like to draw an analogy with literature. If one is possessive and protectionistic about one's country's literature, what is the result? One would prevent the translation of one's literary works into other languages because other cultures might 'steal ideas' and plot devices. Foreigners who came to learn the country's language and who bought the books would be treated with suspicion. Ultimately the literary scene in the country would die out from inbreeding depression.

We don't hear India (or Bangladesh for that matter) complaining about how Westerners read Tagore and adopt his ideas, if anything they are justifiably proud of his literary influence on the world at large. Why can't the same be said of India's biodiversity?