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Many
of us associate plankton with the ocean, because we learn
that baleen whales filter-feed on these great masses of organic material. But did you know that we have plankton right here
in our own Mojave Desert? |
| Rotifers,
the tiny animals that along with other small creatures and
plant matter, make up plankton,
can live just about anywhere you find standing water! Read
on to find out how rotifers survive in the desert when their
water dries up! |
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- Rotifers
are the smallest animals ON EARTH: it doesn't get
much cooler than that!
- They
are multicellular organisms of
about 1,000 cells but are only about the size of
an amoeba!
- They
have complete digestive systems.
- Most
rotifers are female.
- Rotifers
can reproduce either sexually, asexually, or both!
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- When
their pools dry up, they can survive as little metabolically
depressed spheres
called quiescent embryos.
- When
it rains, they can rehydrate and develop into adults!
- The
cycle often repeats over and over with each pond forming
rain storm!
- You
can find rotifers in the raingutters of your house, temporary
pools, desert washes and other small temperary bodies
of water! Don't bother looking in water that houses fish,
baby fish LOVE to eat rotifers making them hard to find
if they are there at all!
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- Male
rotifers do not eat!
- There
can be thousands of rotifers in a pond the size
of a bathtub!
- They can
survive years with no water in a quiescent embryo phase!
- Zooplankton are
the most ABUNDANT aquatic animals
on Earth!!!
- Just
like bacteria,
rotifers were discovered by van
Leeuwenhoek about
200 years ago!!!
- The
word rotifer is derived from a latin word meaning "wheel".
van
Leeuwenhoek named
them for the wheel-like structures around their
mouths.
- They have
hardened jaws called "trophi", but please do
not confuse their "teeth" with your soccer trophy.
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Size: They
are only about 2mm (1/12 inch) in length, making them just
barely visible without a microscope. They are about the
size of the single-celled amoeba, yet rotifers have nearly
1000 cells and even have organs and jaws!
Color: Though
rotifers can be various colors, they are usually fairly
clear in appearance with their insides visible! |
They have
a full digestive system, complete with grinding jaws called
trophi. They also have a "corona" (corona
means crown in Latin) which is a round ciliated structure
surrounding their mouth. Rotifers can use the cilia,
or long finger or hair-like structures, to move food into
their mouths and manipulate the water around them in order
to move! |
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They
prefer small bathtub-sized pools with little turbulence
and no fish to eat them. Rotifers have also been known to
live in freshwater lakes, larger ponds, puddles, brackish water,
salt water, damp soil, damp moss, and even in rain gutters!!!
Rotifers can
be free swimming or sessile.
They can even live in water that is temporary! In fact,
that is one of the reasons they do so well in the desert!
They can hangout in the dry mud for years in a quiescent embryo stage
and then, when it rains again, rehydrate and develop into
adults!
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Rotifers
eat algae, single celled organisms,
debris, bacteria and
other
zooplankton.
Some species have even been known to be cannibalistic!
They can feed in a variety of ways. Different species have different
feeding methods. The three categories of rotifer feeders are: filterers,
graspers, and capturers. Filterers feed by taking in relatively
large volumes of water using their trophi to filter out the food
particles. Graspers will hold on to their food with their corona
and chew it with their trophi. The last group, the capturers, will
trap their food using their corona and then chew it up. The capturers
appear most aggressive when observed while eating. Rotifers tend
to be primarily omnivorous,
so they eat both plant and animal material. Make sure you check
out "WheelBase",
a totally cool website full of awesome rotifer mouthparts! |
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Rotifers
can reproduce in a variety of ways. One class of rotifer, the
Bdelloidea, is thought to reproduce only by asexual methods!
Males have never been identified for this class! Some
rotifers, like the seisonids, reproduce sexually and the males
are fully developed. Another class, Monogononta, can reproduce via
cyclical parthenogenesis as
is explained below. |
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| Females
reproduce asexually (as
seen in the right of the above diagram) most of the time, but in
times of environmental
stress such as the water getting scarce, they will
produce daughters that can produce eggs by meiosis (as
seen on the left above). Meiosis is
a process of cell division that produces haploid eggs.
These haploid eggs are capable of sexual reproduction. If not fertilized,
these haploid eggs
develop into males (blue above). Like the eggs, the males are haploid,
they have half the amount of genes as females. Males do not eat,
they only drift about and produce sperm. This haploid sperm
can
fertilize other haploid eggs.
Once fertilized,
the eggs can be stable "resting
eggs" or
what we sometimes call quiescent embryos.
Many years can pass and the resting embryos remain
stable even without water. Once there is water available, they can
hatch and develop into parthenogenetic females,
continuing in the cycle to the right above. |
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Rotifers
are studied mostly by ecologists and
limnologists (people that study ponds, lakes, and other inland
waters).
They
can be collected
with a plankton net,
the yellow and grey cannister with the mesh funnel attached
you can see to the right. They are often brought
back to the laboratory to be looked at under a microscope.
The descriptive characteristics of the water in which they
live are often measured using instruments like the black
ones you see in this picture. Temperature, salinity,
pH and conductivity are
key features scientists often investigate when researching aquatic organisms. |
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1.
What are the smallest animals on Earth? Rotifers, of COURSE!
2.
What do rotifers eat? Anything that fits in their mouths! Typically,
algae, debris, other zooplankton, bacteria, and single
3.
What do rotifers do if their pond dries up? They die, unless
they happen to be quiescent embryos or resting eggs and then
they hang out until it rains again!
4.
What is your favorite thing about rotifers? |
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Dr.
Peter Starkweather received his PhD from Dartmouth College in
1976. Since that time, his research has largely centered around
zooplankton ecology and evolution. Feeding behavior, behavioral
and population dynamics, along with energetics and biogeography
are all topics of interest and research in the Starkweather Lab.
Tune
in to Episode Three of Desert Survivors to learn more about rotifers,
zooplankton and ecological research! |
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| Desert
USA - for informatin on over 60 desert organisms! |
| WheelBase -
Check out their awesome pics of trophi and corona! |
| CHAOS
Demonstrators - Has some fun experiments
to try with rotifers! |
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