Posts Tagged ‘social insects’

humilewhite There’s been a debate simmering among Argentine Ant researchers about the difference between the ant’s ecology in its native South America and in the introduced populations.  The heart of the disagreement is this:  is the introduced Argentine ant dominant because its biology changed during introduction, or because the ecologies of the native and introduced ranges are different?

Like most scientific debates, some aspects are factual in nature while others are semantic.  Sometimes the semantic and the factual become confused in a way that makes it difficult to tease the arguments apart without careful parsing of words, and I think this debate is one of those cases with much needless confusion.

The classic story, raised by Neil Tsutsui et al, is that Argentine Ants passed through a genetic bottleneck at introduction (a natural consequence of founding a new population from a few transported individuals) and the resulting homogenous population lacked the genetic diversity needed to recognize nestmates from non-nestmates.  (more…)

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Camponotus discolor male, queen, and worker

Camponotus discolor male, queen, and worker

Here’s an image I should have taken years ago.  It’s a stylized shot of the different castes in an ant colony, perfect for a textbook illustration of the morphological distinctions among males, gynes, and workers.  Better late than never, I suppose.

photo details: Canon MP-E 65mm 1-5x macro lens on a Canon EOS 20D
ISO 100, 1/250 sec, f/13, flash diffused through tracing paper

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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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wilson1 My copy arrived from Amazon the day before yesterday.  I’ve not given it anything more than a couple cursory thumb-throughs, but I’m immediately left with the impression of schizophrenia.

The bits on social organization, behavior, communication, and levels of selection- mostly Bert Hoelldobler’s sections- seem an engaging and modern review, while the chapters dealing with ant history and evolution- Wilson’s area- are…  How do I say this diplomatically?  Rubbish.

The past ten years have brought immeasurable advances in our knowledge of ant evolution, both in breadth and detail.  Inexplicably, Wilson fails to recognize it.  Really.  He cites some recent paleontology but next to none of the large and growing body of genetic work.  He reproduces the phylogeny of Moreau et al (2006), but the accompanying text reveals that he does not understand its meaning, nor that it can and is being used to connect the vast body of previously disparate natural history tidbits that Wilson himself relates throughout the book.   At best, Wilson’s section is charming but irrelevant, at worst it will serve to further confuse a field that is already finding clarity independent of Wilson.   We could use a comprehensive reference detailing the great evolutionary story of the ants, but at first glance this isn’t it.

Oh, and the production value is high.  It’s a weighty, glossy, attractive book. Lots of illustrations.  The sort of thing that on a coffee table is sure to impress, even if you don’t plan on opening it.

I’ll post more detailed comments as I give it a more proper reading.

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Atta texana queen and worker

Ant queens are those individuals in a nest that lay the eggs.  They’re pretty important, of course, as without reproduction the colony dwindles and disappears.

Understandably, ant-keepers have an interest in making sure their pet colonies have queens.  Conversely, pest control folks trying to get rid of ant colonies need to be sure that they’ve eliminated queens.  Whether your interest is live ants or dead ants, I’ll give some pointers in this post for recognizing queens. (more…)

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Juergen Heinze has a must-read piece in the latest edition of Myrmecological News about how ant colonies are not often simple families as we like to think of them:

Abstract: The social systems of ants are far more variable than has traditionally been believed. In addition to variation in queen number and queen mating frequency, recent research has documented such bizarre phenomena as the parthenogenetic production of females from unfertilized eggs or genetic caste determination. All these affect the genetic structure of ant societies, and it appears that in a large percentage of species colonies do not consist of a single, singly mated mother and her sterile worker offspring. Though it has long been known that kin selection for reproductive altruism can work well without a relatedness value between workers of 0.75, the recent upsurge of discussions about the role of relatedness in kin selection theory may have confused both myrmecologists and non-specialists. The aim of this review is to give an overview of the large range of ant reproductive systems and to correct some misconceptions about the role of the magic value 0.75 in kin selection theory.

Source: Heinze, J. The Demise of the Standard Ant. Myrmecological News 11: 9-20.

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