Michael Ragland wrote:
> Published online before print January 21, 2003, 10.1073/pnas.0234412100
> Proc Natl Acad Sci U S A. 2003 February 4; 100 (3): 10781083
> DOI: 10.1073/pnas.0234412100
> 
> Evolution
> Genetic diversity, asymmetrical aggression, and recognition in a
> widespread invasive species
> 
> Neil D. Tsutsui,* Andrew V. Suarez, and Richard K. Grosberg*
> *Center for Population Biology, Division of Biological Sciences,
> University of California, One Shields Avenue, Davis, CA 95616; and
> Department of Environmental Science, Policy and Management, Division of
> Insect Biology, University of California, 201 Wellman Hall, No. 3112,
> Berkeley, CA 94720-3112 
> Edited by May R. Berenbaum, University of Illinois, Urbana, IL, and
> approved December 4, 2002, (received for review July 24, 2002)
>  To whom correspondence should be addressed. E-mail:
> ndtsutsui{at}ucdavis.edu.
> 
> 
>  Abstract  The evolution and persistence of cooperative social
> units depends on the ability to distinguish group members from
> nonmembers. The precision of discrimination, in turn, relies on
> variation in the labels that individuals use to recognize group members.
> However, this same variation can be selected against if individuals that
> are rejected as nonmembers incur a high cost. Here we provide evidence
> that selection against individuals from genetically diverse groups has
> contributed to the formation of the unicolonial colony structure that
> characterizes introduced populations of the invasive Argentine ant
> (Linepithema humile). Studies in both the laboratory and the field
> showed that individuals from less genetically diverse colonies attack
> individuals from more diverse colonies and that attackers survived
> agonistic encounters more than six times as often as recipients of
> aggression. This selection, in concert with reductions in genetic
> diversity after a founder event, likely creates a barrier to the
> establishment of new, genetically diverse introductions from the native
> range and may reduce genetic diversity within established populations in
> the introduced range.
> 
I went to a seminar by a Danish guy (not one of these authors) a few 
years ago, and was amused by the way that he spent an hour talking about 
this system, which, yes, is basically group selection, but never 
mentioned the term.

The good news (for those living with these species) is that the data 
from the Argentinian populations suggest that eventually a "cheater" 
phenotype will evolve, which will be recognised as a member of the 
group, but will not help the super-colony.  This will reduce the fitness 
of the colony, which should reduce it's invasiveness.  All in all, lots 
more fun and games for those working on the species.

Bob

-- 
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5)
FIN-00014 University of Helsinki
Finland
Telephone: +358-9-191 23743
Mobile: +358 50 599 0540
Fax:  +358-9-191 22 779
WWW:  http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: http://www.jnr-eeb.org
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