September
10, 2018, Universitaet Mainz
One of
the great puzzles of evolutionary biology is what induced certain living
creatures to abandon solitary existence in favor of living in collaborative
societies, as seen in the case of ants and other social, colony-forming
insects. A major characteristic of so-called eusocial species is the division
of labor between queens that lay eggs and workers that take care of the brood
and perform other tasks. But what is it that determines that a queen should lay
eggs and that workers shouldn't reproduce? And how did this distinction come
about during the course of evolution? Evolutionary biologist Dr. Romain
Libbrecht has been considering these problems over the past years and in
cooperation with researchers at Rockefeller University in New York City has
found a completely unexpected answer: one single gene called insulin-like
peptide 2 (ILP2), which is probably activated by better nutrition, stimulates
the ovaries and triggers reproduction.
"It
may seem almost inconceivable that just one single gene should make all the
difference," Libbrecht pointed out. The researchers drew their conclusion
from a comparison of 5,581 genes in seven ant
species in four different subfamilies that differ from
each other with regard to numerous characteristics. But in one thing are they
all alike: there is always a greater expression of ILP2 in the brain of
reproductive insects. Queens thus
have higher levels than workers. A further finding indicates that this peptide
is found only in the brain, where it is produced in a small cluster of just 12
to 15 cells.
Division
of reproduction and brood care as the basis of social colony formation
It is
postulated that the origins of social behavior in insects are to be found in
wasp-like ancestors that alternated between reproduction and brood care phases.
A female wasp would lay an egg and take care of the larva until it pupated.
However, these two phases were separated and their associated duties assigned
to different individuals, namely queens and workers, during the evolution of
eusociality.
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