of years before the first modern humans evolved, ants were practicing
many of the social innovations we consider to be our own: division of
labor, agriculture, and even slavery.
Indeed, these traits have been taken to their extreme in many ant
species, such as the case of slavemaker ants, which have become so
specialized for raiding food from the colonies of other ants that they
can no longer feed themselves or raise their younger siblings.
Recent work on ants suggests that we may need to add genetic
engineering to the list of innovations ants have evolved to employ. In
two species of harvester ants, populations have been discovered in
which queens mate with males of another species to produce genetically
novel hybrid workers.
In a new study, Dr. Sara Helms Cahan and colleagues demonstrate that
both of the species involved have effectively given up the ability to
produce pure-species workers in favor of the hybrids, thereby becoming
completely dependent on one another for survival.
Female ants are generally found in two forms: reproductive queens and
sterile workers. The role, or caste, of an individual is determined for
life at a certain stage in her development.
In virtually all ant species, it is the environment in which a female
is raised, rather than a genetic predisposition, that determines which
caste she will adopt.
However, in two harvester ant populations in southern New Mexico,
queens and workers from the same colonies are genetically very
different; in both species at the site, only t
he queens are genetically
derived from a pure species-specific lineage, whereas all the workers
are hybrids that possess a combination of genes from the two species in
a single individual.
It is not currently known whether the ants benefit from having hybrids
do the work, but, as is evident from the researchers' own attempts at
selective breeding and genetic engineering, combining genomes is an
easy way to produce novel characteristics that may be highly
advantageous for growth, environmental tolerance, or disease
Regardless of the specific advantages, however, it is clear that these
ants have committed themselves to the hybrid workforce strategy.
When the researchers prevented queens from mating with males of the
other species, very few succeeded in making any workers at all, a
handicap that would lead to certain population failure in the field.
The new findings suggest that specialization involving reliance on
interspecific hybrid workers has left these species unable to survive
independently of one another.
Sara Helms Cahan, Glennis E. Julian, Steven W. Rissing, Tanja
Schwander, Joel D. Parker, and Laurent Keller: "Loss of Phenotypic
Plasticity Generates Genotype-Caste Association in Harvester Ants"
Published in Current Biology, Volume 14, Number 24, December 14, 2004,
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