Social
insects could offer clues to understanding genetic conflict
…………………………………………………………………
BY JADE BOYD
Rice News Staff
Two Rice University
biologists believe social insects like ants and bees could
provide clues to why some animals — including humans
— have developed a curious quality in which the genes
of their parents vie in direct competition, waging a kind
of biochemical war.
Social insects are best known as exceptions to the general
rule that relations between individuals are competitive.
They have evolved social organizations that are so harmonious
that the colony itself is often considered a single individual,
or “superorganism,” for purposes of biological
study. In an article in the April 12 issue of Science, David
Queller and Joan Strassmann propose that social insects
may also provide extraordinary exceptions to another general
rule: that relations within individuals are completely harmonious.
The suggestion grows out of theories that aim to explain
possible genetic conflicts between the genes that individuals
receive from their mothers and fathers. For mom’s and
dad’s genes to battle it out requires both means and
motive. Until recently, the means were thought to be absent
because genes could not tell which parent they came from.
However, this “veil of ignorance” is sometimes
lifted through a process called “imprinting,”
in which mothers and fathers label some of their genes before
passing them on to their young.
The “motive” comes, as always in evolution, from
how genes best reproduce themselves. In the classic mammalian
case of imprinting, paternally derived genes strive to create
a large placenta that favors the developing child —
who carries the father’s genes — over the health
of the mother — who doesn’t share the paternal
genes. Maternally derived genes favor a smaller placenta
that would protect the mother’s health and her ability
to produce future offspring who will carry on her genetic
line.
In most other
respects, however, maternal and paternal genes should be
in agreement. Queller and Strassmann, both professors of
ecology and evolutionary biology, believe that certain social
insects — ants, bees and wasps — are an exception
because they have a peculiar genetic system called haploidiploidy,
in which all the males result from unfertilized eggs. This
results in unusual genetic patterns where different groups
of siblings and cousins share more genetic links on their
father’s side than their mother’s, or vice versa.
For example, haploidiploid sisters always share paternal
genes, but they have only a 50 percent chance of sharing
maternal genes.
This pattern of asymmetrical relatedness provides the motive
for conflict between maternal and paternal genes. The many
kinds of social interactions in social insects provide the
opportunity. Evolutionary theory predicts individuals with
a deeply divided self: maternal and paternal genes should
battle over sex ratios, kin recognition, who should be the
queen and who should lay eggs.
“We don’t yet know if bees, ants or wasps have
imprinted genes, let alone what the imprinted genes do,
but this presents biologists with an unusual opportunity,”
said Queller. “Evolutionary theories are sometimes
accused of simply explaining what we already know rather
than predicting the unknown. Here is a rare chance where
evolutionary theory makes a complex set of predictions,
completely unpolluted by what we already know.”
Finding imprinting in social insects might also provide
clues to how imprinting affects higher-order species such
as mammals. In humans, imprinting is known to underlie several
genetic diseases, and also is thought to be a possible barrier
to cloning.
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