Author Archives: Ajay Narendra

A Year in an Ant’s life

There is a new article by Stephane Caut and colleagues from Spain on the funnel ant, Aphaenogaster senilis. They studied resource use by these ants over an entire year and attempt to attribute the variation to colony life cycle and resource availability.

Ref: Caut S, Barroso A, Cerdá X, Amor F & Boulay RR. 2013. A Year in an Ant’s life: Opportunism and Seasonal Variation in the Foraging Ecology of Aphaenogaster senilis. Ecoscience 20: 19-27.

Abstract: Ants are important consumers in most terrestrial ecosystems. They show a great diversity of diets and foraging strategies. Here, we analyzed how circannual variation in resource use by the Mediterranean species Aphaenogaster senilis is related to colony life cycle and resource availability. In southwestern Spain, this species is active almost year-round, but foraging intensity decreases 10-fold between March and November, following larval production. In the summer, ants refrain from foraging at midday to avoid high temperatures. We hypothesized that diet and foraging plasticity could also explain the ecological success of this species. There are several techniques for assessing the diet of ants. Combining isotope analyses with conventional methods can provide better taxonomic resolution of resource utilization. Using a combination of classic and isotopic analyses, we found that 1) the proportion of plant and animal-derived items collected by foragers did not vary significantly from March to November, and 2) isotope analyses indicated a decrease in the trophic level of A. senilis between June and September, suggesting a difference between collected material and items assimilated. Interestingly, most animal prey were collected by individual ants, and many were retrieved alive. Therefore, A. senilis is not only a scavenger, but also a non-negligible predator, particularly of aphids. The abundance of the most common animal-derived items in the diet was proportional to their abundance in the study area. We conclude that A. senilis is an opportunistic species that is able to feed on a variety of resources, which may be key to its ecological success.

Backtracking behaviour in lost ants

Wystrachetal_2013A new article by Antoine Wystrach and his colleagues from Macquarie University have a publication on the charming Australian desert ant Melophorus bagoti. It is a nice story about lost ants exhibiting a strategy called ‘backtracking’. And it is always nice to see a ant navigation story featured on the cover.

Reference: Wystrach A, Schwarz S, Baniel A, Cheng K. 2013. Backtracking behaviour in lost ants: an additional strategy in their navigational toolkit. Proc R Soc B 280: 20131677

Abstract: Ants use multiple sources of information to navigate, but do not integrate all this information into a unified representation of the world. Rather, the available information appears to serve three distinct main navigational systems: path integration, systematic search and the use of learnt information—mainly via vision. Here, we report on an additional behaviour that suggests a supplemental system in the ant’s navigational toolkit: ‘backtracking’. Homing ants, having almost reached their nest but, suddenly displaced to unfamiliar areas, did not show the characteristic undirected headings of systematic searches. Instead, these ants backtracked in the compass direction opposite to the path that they had just travelled. The ecological function of this behaviour is clear as we show it increases the chances of returning to familiar terrain. Importantly, the mechanistic implications of this behaviour stress an extra level of cognitive complexity in ant navigation. Our results imply: (i) the presence of a type of ‘memory of the current trip’ allowing lost ants to take into account the familiar view recently experienced, and (ii) direct sharing of information across different navigational systems. We propose a revised architecture of the ant’s navigational toolkit illustrating how the different systems may interact to produce adaptive behaviours.

Molecular basis of learning in honeybees

A new article addressing the molecular basis of learning in honeybees.


The natural history of adult worker honey bees (Apis mellifera) provides an opportunity to study the molecular basis of learning in an ecological context. Foragers must learn to navigate between the hive and floral locations that may be up to miles away. Young pre-foragers prepare for this task by performing orientation flights near the hive, during which they begin to learn navigational cues such as the appearance of the hive, the position of landmarks, and the movement of the sun. Despite well-described spatial learning and navigation behavior, there is currently limited information on the neural basis of insect spatial learning. We found that Egr, an insect homolog of Egr-1, is rapidly and transiently upregulated in the mushroom bodies in response to orientation. This result is the first example of an Egr-1 homolog acting as a learning-related immediate-early gene in an insect and also demonstrates that honey bee orientation uses a molecular mechanism that is known to be involved in many other forms of learning. This transcriptional response occurred both in na+»ve bees and in foragers induced to re-orient. Further experiments suggest that visual environmental novelty, rather than exercise or memorization of specific visual cues, acts as the stimulus for Egr upregulation. Our results implicate the mushroom bodies in spatial learning and emphasize the deep conservation of Egr-related pathways in experience-dependent plasticity.

Lutz, C. C., Robinson, G. E. 2013. Activity-dependent gene expression in honey bee mushroom bodies in response to orientation flight. Journal of Experimental Biology 216, 2031-2038.

Lab life: Don’t bristle at blunders

From Nature

In a July 1991 Nature paper1, astronomers Andrew Lyne, Matthew Bailes and S. L. Shemar made an electrifying announcement: the discovery of the first planet outside our Solar System. To everyone’s surprise, it was not orbiting a Sun-like star but a pulsar — the dense, spinning neutron-star offspring of a supernova explosion. The putative planet gave itself away by altering the period of radio-frequency flashes given off by the pulsar.

Unfortunately, Lyne and Bailes had to retract this result a few months later after uncovering an error, which they reported2 in Nature in January 1992. The astronomers courageously announced that they had not corrected adequately for Earth’s motion around the Sun. Lyne’s revelation of the blunder at a meeting of the American Astronomical Society that month won him a standing ovation. But the story had a happier ending.

Immediately after Lyne’s presentation, astronomer Aleksander Wolszczan announced that he and his colleague Dale Frail had discovered two planets orbiting another pulsar using the same technique. These turned out to indeed be the first discoveries of extrasolar planets. Wolszczan told me that Lyne’s original paper had acted as a “confidence booster”, convincing him that the signals in his data were real. By the time Lyne withdrew his result, Wolszczan had performed enough tests to be certain.

Blunders are an essential part of the scientific process. Research is not a linear march to the truth but a zigzag path, involving trial and error. Mistakes are not the exclusive province of sloppy or inexperienced scientists. Even the brightest luminaries — including Charles Darwin and Albert Einstein — made serious blunders.

Truly innovative ideas require a willingness to embrace risks, and acceptance of the fact that errors can be portals to progress. Although this is well known in some private companies engaged in research and development, academics today are slow in recognizing the necessity of blunders.

Chemist Linus Pauling knew it. His former postdoc, Jack Dunitz, recalls being told: “Mistakes do no harm in science because there are lots of smart people out there who will immediately spot a mistake and correct it. You can only make a fool of yourself and that does no harm, except to your pride. If it happens to be a good idea, however, and you don’t publish it, science may suffer a loss.”

Knotty problem

Preposterous ideas can lead to important insights. In 1867, the eminent physicist William Thomson (Lord Kelvin) proposed3 that atoms were not point-like but ‘knotted vortex tubes of the ether’. Ether was the supposed fluid that pervaded space, providing a medium for electricity and magnetism.

Inspired by work on vortices in fluids by the nineteenth-century German physicist Hermann von Helmholtz, Kelvin identified three characteristics of knotted vortex tubes that made them attractive models for atoms.

First, vortices in fluids were astonishingly stable — mirroring to Kelvin the “unalterable distinguishing qualities” of atoms — and each knot could be classed according to its geometrical properties. Second, the variety of chemical elements could reflect the “endless variety” of knots. Finally, just as smoke rings vibrate, the oscillations of ether vortex tubes might produce atomic spectral lines.

To explain the periodic table, Kelvin needed to classify knots according to their forms, discarding any that could be manipulated from one to another. In Kelvin’s theory, the circular ‘unknot’ represented the hydrogen atom; the triple-looped ‘trefoil’, carbon.

Kelvin’s theory of vortex atoms is obviously wrong. The ether does not even exist. But these failures did not deter everyone. Whereas physicists lost interest for a while, knots began to intrigue mathematicians, becoming an active area of study for decades.

In the 1980s, knot theory reconnected with physics. Mathematician Vaughan Jones discovered an algebraic expression that is unique for every knot. Physicist Edward Witten linked it to quantum field theory, the branch of physics that describes fields and the subatomic world. In classical physics, the path of a particle travelling from point A to point B is determined by Newton’s laws of motion. In the quantum regime, one has to consider all the possible paths connecting A to B, including winding and knotted ways.

Subsequent work linked knots, quantum field theory and string theory, which by describing particles as vibrations of strings, harks back to Kelvin’s idea. Today, knots are used in chemistry and biology to analyse the actions of enzymes on DNA molecules. In a process known as site-specific recombination, enzymes align segments of the genetic sequence, cut the two strands of DNA open and recombine the four ends in various ways, which can be described using knot theory.

Extraordinary claims

Blunders are sometimes hard to correct. Modern experiments can be so intricate and require such big investments in time and funds that replicating them becomes prohibitive. When a result is widely assumed to be wrong, few scientists are motivated to repeat the work.

But there can be rewards for doing so. The sensational claim4 in Science by geomicrobiologist Felisa Wolfe-Simon and her colleagues to have discovered a bacterium that substitutes arsenic for phosphorus to sustain its growth brought a wave of criticism.

A few critics checked the experiment, including microbiologist Rosemary Redfield at the University of British Columbia in Vancouver, Canada, who blogged the process (see The effort proved fruitful, showing that the bacterium goes to great lengths to dodge arsenic. Redfield and her colleagues detected no arsenic in the bacterium’s DNA to much lower limits than in the original paper. Molecular biologist Dan Tawfik and his team at the Weizmann Institute of Science in Rehovot, Israel, identified the mechanism by which some of the proteins of this and related bacteria bind to phosphate and not to arsenate.

Although one lesson is obvious — extraordinary claims require extraordinary evidence — the original paper still had some scientific value. It stimulated discussion and inspired curiosity about different possibilities for life.

In the nineteenth century, Scottish author Samuel Smiles wrote: “We often discover what will do, by finding out what will not do; and probably he who never made a mistake never made a discovery.” His statement should not be taken as advocacy for slapdash science but as an encouragement to think originally and take calculated risks.

Can research failure be accommodated in today’s fast-paced, funding-starved, impact-driven atmosphere? I believe it must. We should make space for risky scientific proposals in grant and evaluation processes.

Until a decade ago, the committees that allocated observing time on the Hubble Space Telescope were encouraged to give up to 10% of the time to proposals with a low probability of success but potentially high return. A similar philosophy could be adopted more widely.

One problem is that committees tend not to approve risky programmes. Efforts to reach consensus converge to a mean. Such obstacles can be overcome if decisions are left to one person. In the case of Hubble, a pool of ‘director’s discretionary time’ on the telescope is available, for which anyone can apply. From it came the Hubble Deep Field, one of the most detailed images of the Universe ever made.

Today, telescopes including Hubble are turned towards addressing the profound outcome of another ‘blunder’. Einstein regretted his attempt to model a static cosmos using a repulsive-gravity force (see ‘Did Einstein ever say “biggest blunder”?’). But since it was revealed by supernovae observations in 1998 that our Universe is accelerating, understanding the nature of that repulsive force is one of the biggest challenges that physics faces today.


Cue competition: role of polarisation pattern in free flying songbirds

An interesting article tackling the role of pattern of polarised skylight in the departure direction of songbirds during twilight.

Schmaljohann et al., 2013. Response of a free-flying songbird to an experimental shift of the light polarization pattern around sunset. Journal of Experimental Biology 216, 1381-1387.


The magnetic field, the sun, the stars and the polarization pattern of visible light during twilight are important cues for orientation in nocturnally migrating songbirds. As these cues change with time and location on Earth, the polarization pattern was put forward as a likely key reference system calibrating the other compass systems. Whether this applies generally to migratory birds is, however, controversially discussed. We used an experimental approach in free-flying birds to study the role of polarization for their departure direction in autumn. Experimental birds experienced a 90 deg shift of the band of maximum polarization during sunset, whereas control birds experienced the polarization pattern as under natural conditions. Full view of the sunset cues near the horizon was provided during the cue conflict exposure. Here we show that both the experimental and the control birds being released after nautical twilight departed consistently towards south-southeast. Radiotelemetry allowed tracking of the first 15 km of the birds’ outward journey, thus the intrinsic migration direction as chosen by the birds was measured. We found no recalibration of the magnetic compass after pre-exposure to a cue conflict between the natural magnetic field and the artificially shifted polarization pattern at sunset. The lacking difference in the departure direction of both groups may suggest that birds did not recalibrate any of the compass systems during the experiment. As free-flying migrants can use all available orientation cues after release, it remains unknown whether our birds might have used the magnetic and/or star compass to determine their departure direction.