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Posts Tagged ‘biology’

Here’s an image for the textbooks:

gracilis2Ants, like butterflies, pass through egg, larva, and pupa phases on their way to adulthood. While in Florida earlier in this summer I found a nest of the twig ant Pseudomyrmex gracilis with brood present in all stages, providing the material to make these images.

The key was placing the developing ants on a glass slide.  This provided distance between them and the cardboard background, so that the backdrop is blurred while the insects remain in sharp focus.  These images are not what I’d call fine art, but I’m happy with them as solid illustrations of ant biology.

gracilis3

photo details (both photos): Canon mp-e 65mm 1-5x macro lens on a Canon EOS 50D
ISO 100, f/11, 1/160 sec, twin flash diffused through tracing paper

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One of the most vociferous debates in taxonomy is over a catchy-sounding concept called DNA barcoding.  Since nearly all organisms carry a version of the COI gene in the mitochondrion, the idea is that the DNA sequence of the gene can serve as a standard identification marker.  A barcode, of sorts.  Of course, the practice only works if species have unique COI sequences.  Which they do, much of the time, and the barcoders consequently have been successful in garnering research money and churning out publications.

So what’s the problem? (more…)

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wilson1Who is supposed to read The Superorganism?

I can’t really tell.  While I’m enjoying Holldobler & Wilson’s latest tome, I am perplexed at the book’s target audience.  The text switches between broadly anthropomorphic prose clearly aimed for a general audience and obtuse jargon digestible only by the experienced biologist.

I get the feeling that the authors- at least one of them, anyway- desired a technical book more along the lines of Bourke & Franks, while the marketing department at Harvard University Press wished to trade on the authors’ name recognition with a glossy coffee-table production.  The tug-of-war behind the scenes must have been impressive, and the effect is surreal.  It’s a bit like hanging your automobile’s operating manual in a gilded frame over the mantle.  The result is not unpleasant, mind you, but I can’t help to think the authors missed an opportunity to produce either a comprehensive professional review or an engaging popular work instead of compromising in the middle.

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cephalotes24

A trail of Atta leafcutting ants in Gamboa, Panama.

From the recent literature:

The Journal of Experimental Biology has a lab study by Dussutour et al documenting how leafcutter ants avoid traffic jams under crowded trail conditions.  Apparently, unladen ants increase a narrow trail’s efficiency by following the leaf-carrying ants instead of trying to pass their slower sisters. See also commentary by JEB and Wired.

source: Dussutour, A., Beshers, S., Deneubourg, J. L., Fourcassie, V. 2009. Priority rules govern the organization of traffic on foraging trails under crowding conditions in the leaf-cutting ant Atta colombica. J Exp Biol 2009 212: 499-505.

In the journal PLoS One, Youngsteadt et al document that the seeds of the neotropical ant plant Peperomia macrostachya are dispersed by just a single species of Camponotus in spite of a high ant diversity at the study site.

source: Youngsteadt E, Baca JA, Osborne J, Schal C, 2009. Species-Specific Seed Dispersal in an Obligate Ant-Plant Mutualism. PLoS ONE 4(2): e4335. doi:10.1371/journal.pone.0004335

A smattering of ant taxonomic papers in the online journal Zootaxa includes work on Lordomyrma by Bob Taylor, Pheidole by Jack Longino, and the Egyptian Solenopsis by Mostafa Sharaf et al.

source: Zootaxa Hymenoptera

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Aphaenogaster cockerelli, Arizona

Aphaenogaster cockerelli, Arizona

Here’s a new study in Current Biology from Adrian Smith, Bert Hoelldobler, and Juergen Liebig:

Abstract: Cheaters are a threat to every society and therefore societies have established rules to punish these individuals in order to stabilize their social system [1–3]. Recent models and observations suggest that enforcement of reproductive altruism (policing) in hymenopteran insect societies is a major force in maintaining high levels of cooperation [4–6]. In order to be able to enforce altruism, reproductive cheaters need to be reliably identified. Strong correlational evidence indicates that cuticular hydrocarbons are the means of identifying cheaters [7–14], but direct proof is still missing. In the ant Aphaenogaster cockerelli, we mimicked reproductive cheaters by applying a synthetic compound typical of fertile individuals on nonreproductive workers. This treatment induced nestmate aggression in colonies where a queen was present. As expected, it failed to do so in colonies without a queen where workers had begun to reproduce. This provides the first direct evidence that cuticular hydrocarbons are the informational basis of policing behaviors, serving a major function in the regulation of reproduction in social insects. We suggest that even though cheaters would gain from suppressing these profiles, they are prevented from doing so through the mechanisms of hydrocarbon biosynthesis and its relation to reproductive physiology. Cheaters are identified through information that is inherently reliable.

In less technical language, fertile ants smell different than infertile ants, and when researchers painted the fertility odor on non-reproducing workers, in colonies that already had active queens, the hapless ant was attacked by her sisters.  So colonies have a way to maintain social order that does not rest entirely on the altruism of individuals to forgo reproduction.  They, like us, have police.

Of course, we already knew that ants, bees, and wasps engage in this sort of policing.  What is novel in the Smith et al study is an experimental test of how the worker police recognize the cheaters.  As in much of ant communication, the cue is chemical.

source: Smith, A. A., Hoelldobler, B., Liebig, J. 2009. Cuticular Hydrocarbons Reliably Identify Cheaters and Allow Enforcement of Altruism in a Social Insect. Current Biology 19: 78-81. doi: 10.1016/j.cub.2008.11.059.

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cephalotes47

Another year passes.  The economy is in the toilet.  Violence spreads in the middle east.  In these trying times, one question must weigh on the minds of concerned citizens: “What’s happening in world of ant science?”

Of course.  Here are the myrmecological highlights of 2008: (more…)

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Neivamyrmex nigrescens, Arizona

Neivamyrmex nigrescens, Arizona

Army ants have a decidedly tropical reputation.  The term conjures spectacular images of swarms sweeping across remote Amazonian villages, devouring chickens, cows, and small children unlucky enough to find themselves in the path of the ants.  Of course, the habits of real army ants are not nearly so sensational, but they are at least as interesting.

(more…)

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fingerLast week the Howard Hughes Medical Institute announced that they will be funding Danny Reinberg, Shelley Berger, and Juergen Liebig to sequence three ant genomes.  Their interest is research on aging, hoping that solving the puzzle of why genetically identical ant nestmates can either live for a year as a worker or twenty as a queen will unlock some clues to aging in our own species.   I think that’s a stretch, but whatever.  We myrmecologists will be able to probe the ant genomes for plenty of other worthwhile reasons.

Three species were chosen to represent varying levels of caste differentiation.  Harpegnathos saltator (pictured) is a ponerine from India with gynes that are scarcely different from workers.  Camponotus floridanus is an American formicine with more strongly differentiated gynes and a polymorphic worker caste.  And an as-yet-undetermined species of Pheidole will represent an ant with multiple discrete worker castes.  Genomic information compared among the castes of these species will allow us to pinpoint genes and regulatory pathways that determine both the morphological and the behavioral differences among the castes.  Cool stuff.

Here’s a prediction.  Since the worker caste appears to have evolved only once, at the origin of the ants, the developmental pathways that determine whether a female becomes a gyne or a worker will be shown to be fundamentally the same across all species.  In contrast, differentiation within the worker caste evolved multiple times, so those mechanisms among species will show differences.  Specifically, the genes expressed to make a major Camponotus should not necessarily be the same as those needed to make a soldier Pheidole.  With these genomes in hand it will be considerably easier to see if this is indeed the case.

I should note that three additional ant genomes (Solenopsis invicta, Linepithema humile, and one of the leafcutter ants) are in the works by other research groups.   So we myrmecologists will get six genomes to play with in the next few years, and as full genome-sequencing drops to less than $10,000 we’ll likely see several more as well.  Exciting times!

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