by Ben Turner
The Cape honeybee worker
has been shown to clone itself millions of times.
has cloned itself
over the past
When hives of the African lowland honeybee (Apis
mellifera scutellata) collapse, they do so because of an
invisible inner threat:
the growing, immortal
clone army of a rival bee subspecies.
That army is possible
because the female workers of the rival subspecies - the South
African Cape honeybee (Apis
mellifera capensis) - can create perfect copies of
themselves, with one individual found to have done so millions of
times in the past three decades.
perpetual-cloning ability, the Cape honeybees sneak into the
hives of their lowland honeybee rivals and churn out copy after copy
(no need for a queen).
Even worse, these clones
are freeloaders, refusing to do any work.
Now, a new study has revealed the genetic foundations of the strange
and formidable adaptation. Unlike most animals, and even their own
queen, the female workers do not reshuffle the DNA of the eggs they
This enables the workers
to consistently recreate a perfect copy of themselves - a clone -
each time they reproduce.
According to the
researchers, the sidestepping of this DNA-reshuffling process is
unlike anything they've ever seen.
It's also incredibly
dysfunctional," lead author Benjamin Oldroyd, a professor of
behavioral genetics at the University of Sydney, told Live
Science, referring to the fact that reshuffling is normally
required to hold chromosomes together during the egg-making
"Yet, somehow they've
managed to do it [still lay eggs]. It's insane; I've not heard
of anything like this before, anywhere."
Honeybee workers and
other social insects have the ability to reproduce via a form of
asexual reproduction called
thelytokous parthenogenesis, in
which females produce female offspring from unfertilized eggs.
Each time she creates
offspring, the single-parent worker bee will replicate the
chromosomes she received from her parents (a queen and a male drone)
Next, she takes the
genetic material from all four chromosomes, reshuffles it and
creates four chromosomes with that mixed-up DNA through a process
guarantees that, even with just one parent, future offspring will be
However, as only two chromosomes out of the four are picked and no
new genetic material is introduced by a sexual partner, this leads
to an average loss of one-third of genetic diversity every time the
shuffling is performed, or every generation,
Benjamin Oldroyd said.
After just a few
generations of parthenogenetic reproduction, the accumulated
loss of genetic material leads to levels of genetic diversity that
are low enough to be lethal.
Most social insects, therefore, rely on a queen that
reproduces sexually on their behalf.
In return, the
genetically diverse workers maintain the health of the colony and
protect the brood of their closely related siblings and cousins.
"It's like in a human
society, we have this tension between what's good for the
individual and what's good for society, and we come up with all
of these social norms that allow us to function," Oldroyd said.
societies, one of the things that evolved to suppress selfish
behavior is [that] the workers generally can't lay eggs."
This is mostly true of
the Cape honeybee, which on the whole abides by the
usual rules of social insect reproduction, according to Oldroyd.
But Cape honeybee workers
have a genetic mutation that enables them to lay eggs
parthenogenetically with all of the genetic material from the four
chromosomes (so they don't throw out any of those chromosomes
With that ability, they
can prevent the immediate loss of genetic diversity caused by the
This allows them to clone
themselves whenever they like for decades, even if cloning in the
much longer term leads to a population that, on the whole, has no
This cloning superpower places colonies on a much finer balancing
point between individualism and sociality. And if they tip over,
they may be at risk of extinction, according to the researchers.
To understand how the clones can create millions of copies of
themselves and yet remain functional, Oldroyd and his team compared
the genomes of Cape honeybee workers with those of their
queen and her offspring.
After forcing the Cape queen to reproduce asexually by fitting her
with surgical tape that prevented her from mating, the team examined
certain DNA sequences of both the Cape queen and the 25 larvae she
Then, they did the same
for four Cape honeybee workers and their 63 larvae.
The team discovered that the asexually reproduced offspring of the
queen had levels of recombination (DNA mixing) 100 times greater
than the genetically identical cloned offspring of the workers - a
finding that suggests the Cape worker bees have evolved a mutation
that prevents recombination.
Without the risk of a
one-third loss of genetic material caused by the asexual reshuffling
process, the workers are free to continually create perfect copies
The workers' ability to clone at will places their colonies in a
much more precarious position, especially once the queen leaves or
dies and the old social order collapses.
Instead of expending
energy to get the colony back on its feet, workers will dedicate
themselves to selfish schemes - such as finding ways to place their
clones into positions of power.
"If you take the
queen away, for instance, instead of raising a new queen like
other bee species might, these bees will just start laying eggs
themselves," Oldroyd said.
"There are also
cells, called queen cells, where the queen lays the eggs
containing future queens.
possible for a worker to fly in from another colony, or one of
the existing workers in that colony to come and replace that
queen egg with one of their clone eggs.
That way, they can be
genetically reincarnated as a queen."
But one lineage of Cape
bee workers has taken this socially parasitic behavior even further,
to the point where,
they no longer need a
queen, and they solely exist by taking over the hives of the
African lowland honeybee...
Members belonging to a
single branch of rogue clone Cape bee workers sneak into
African lowland honeybee hives, which are commonly used for
agricultural purposes, and lay as many eggs as they can, which the
African lowland bees mistake for their own and rear.
The parasitic clone Cape bee larvae are in on this ruse, even
sending signals to their unfortunate hosts to feed them as much as
This cuckoo-like behavior
allows them to grow their bodies and their ovaries almost to the
size of a queen's.
"The Cape bee clones
don't do any work inside those hives because they've become
reproductive," Oldroyd said.
"They just strut
around with this attitude like,
going to work for me.'
It very quickly leads
to the collapse of the hive.
As individuals, these
clones are quite dysfunctional, so you'd expect them to peter
But they're a lot
like the cells in a tumor in this regard - it doesn't matter if
every clone is healthy, so long as enough of them are around to
exploit the host."
The Cape bee workers
that take part in this parasitic behavior are the genetically
identical descendants of a single worker that lived in 1990,
according to Oldroyd.
This single lineage of
clones is responsible for the collapse of 10% of African lowland
honeybee colonies every year.
Now that the researchers have a handle on how the workers can
accomplish their bizarre cloning trick, they want to figure out how
queens can switch on the gene that enables recombination and how the
workers can switch it off.
They also want to
investigate the African lowland hives parasitized by Cape bee
workers, to figure out what triggers the hive collapse.
The researchers published their findings (Adaptive,
caste-specific changes to recombination rates in a thelytokous
honeybee population) June 9 in the journal Proceedings
of the Royal Society B.