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Subject:
From:
Peter Borst <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Fri, 16 Aug 2002 08:33:15 -0400
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The "Proposal for the Sequencing of a New Target Genome: White Paper
for a Honey Bee Genome Project" contains the following statements:

>The bee community has met three times to mobilize for a HBGP (#1
>organized by Robinson in Bellagio, Italy; #2 organized by Menzel in
>Berlin; #3 held as part of a USDA Comparative Insect Genomics
>workshop). At all three meetings a HBGP was recognized as a high
>priority; at #3 the honey bee emerged as one of the top two insect
>prospects for genome sequencing

>honey bees live in societies that rival our own in
>complexity,internal cohesion,and success in dealing with the myriad
>challenges posed by social life, including those related to
>communication, aging, social dysfunction and infectious disease.

I do not wish to advance a particular point of view, but a large
number of people have already weighed in heavily in favor of full
speed ahead. What is particularly interesting is the rationale behind
this endeavor. The effort to obtain funding and priority has
compelled the proponents to make some bold claims for the potential
benefits. One is an understanding of "social genes". But do these
even exist? Maybe not. Read on:

Excerpts from

The Evolutionary Dynamics of Social Organization in Insect Societies
By Joachim Erber & Rob Page

Insect societies have intrigued natural historians and biologists
since Aristotle. Scholars have puzzled over the self-sacrificing
altruism expressed by sterile colony members-the workers-as well as
the complex division of labor and the capability of mass-action
responses to the environment. For example, a colony of 20 to 30
thousand honey bees, at one moment in time, may have several thousand
individuals engaged in foraging behavior; and thousands of others
engaged in nest construction, feeding young larvae, or processing
honey; while others guard the entrance or thermoregulate the nest.
However, when an intruder challenges the entrance of the nest,
hundreds or even thousands of worker honeybees may respond
immediately by stinging the intruder and, in doing so, sacrifice
their lives.

Social insects presented Darwin with major difficulties for his
theory of evolution by natural selection. How can you explain the
evolution of self-sacrificing worker castes when evolution is a
result of the survival and reproduction of individuals? Even more
perplexing is the question of how the sterile workers evolved their
own traits, different from their reproductive mothers (the queens)
when they don't reproduce.

The social behavior of insects is a result of complex interactions at
different levels of biological organization. Genes give rise to
proteins and peptides that build the nervous and muscular systems,
regulate their own synthesis, interact with each other, and affect
the behavior of individuals. Social behavior of an insect colony
emerges from the complex interactions of individuals.

Division of labor self-organizes within groups of cohabiting
individuals. This has been demonstrated in two empirical studies.
Sakagami and Maeta (1987) forced females of the solitary carpenter
bee, Ceratina flavipes, to share the same nests. Normally, these bees
excavate their own nests by burrowing into the centers of pithy plant
stems. ... When pairs of females were forced to share the same nest,
a division of labor occurred in every case. One bee became the
principal egg layer and guard, while the other did most of the
foraging. Hence a task and reproductive division of labor emerged
between these normally solitary individuals. This occurred in the
absence of an evolutionary history of nest sharing.

Jennifer Fewell demonstrated a similar phenomenon with the desert
harvester ant, Pogonomyrmex barbatus. Like most species of ants,
young queens excavate a nest in the ground. ... In every case, one
female did significantly more of the nest excavating. Queens were
tested for the amount of time they spent digging before they were
paired. In every case, the queen in the pair that did more digging on
her own, also did more digging when paired.

These simple relationships, stimulus-response and the correlation of
behavior and the stimulus intensity, represent mechanisms that
transform individual behavior into a social organization. The result,
division of labor, is an inescapable property of group living because
of the behavioral properties of solitary individuals. The
evolutionary transition from solitary life history to social life
does not require any new genes or new features of the neural system,
or new forms of behavior. Insects that live solitary lives already
have all of the necessary behavioral components for organized social
living.

There is no "social genome" directing the organization of colonies.
The genes responsible for social organization reside in individuals
just as they did in their solitary ancestors. In many social insect
species the individuals that demonstrate a division of labor are
sterile, the workers. The genes affected by selection must change
properties of the neural system that affect the interactions of
neurons and the behavior of workers. Changes in division of labor
emerge from changes in the interactions of the behavior of the colony
members and their environment.

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