Th
Weird!
We have become familiar with several organisms that reproduce asexually bacteria, hydra, and
other seemingly simple organisms. But did you know that some animals can reproduce asexually, as well?
And did you know that some organisms switch between sexual and asexual reproduction based on their
circumstances? Nature has given
eird but true reproduction examples to learn about!
Me, Myself and I
Parthenogenesis is a process of reproduction that occurs
fertilization an egg develops without ever having been
fertilized by a sperm. For example, turkeys almost always reproduce
sexually. A male turkey fertilizes the egg of a female turkey, and a
baby turkey (called a poult) develops. It has half the chromosomes of
the mother and half the chromosomes of the father. This is what
usually happens, but rarely
rarely - a female turkey will produce
fertile eggs in the total absence of a male. The eggs often result in
sickly poults, and nearly always are male turkeys.
Leonie the Zebra Shark
Parthenogenesis also can occur in sharks. Ordinarily,
sharks reproduce sexually. However, some aquariums around the
world have reported rare instances in which a female shark who
has never been in a tank with a male shark has been able to
have babies. In an aquarium in Australia, a lonely zebra shark
named Leonie had three shark pups that were identical to
herself. There are more examples of this type of asexual
reproduction in the hammerhead shark and the blacktip shark.
In these cases, the sharks had reached sexual maturity in
captivity in the absence of males, and the offspring were also
shown to be genetically identical to the mothers.
Komodo dragons are known to rarely reproduce using parthenogenesis, as
well. In 2008, the Sedgwick County Zoo in Wichita, Kansas, announced that their
female Komodo dragon, Gaia, had hatched two babies both identical to herself.
the zoo has no male Komodo dragons! Interestingly, both
babies were males.
Snake Eggs
Turkey Pouts
Gaia the Komodo Dragon
Scientists are finding that snakes may use parthenogenesis to
reproduce more often than previously thought. In captivity, there are
several examples of pit-vipers and other snakes having babies that are
genetically identical to their mother. However, a recent study of wild snakes
found that 1 of 22 copperhead snake mothers had given birth
parthenogenetically, as had 1 of 37 cottonmouth snakes collected. This
surprised even scientists
©Flying Colors Science
Hi, Mom!
Every case of parthenogenesis results in babies that are genetically identical to the parent.
more vulnerable - a disease or environmental change that kills one could kill .
the case of the whiptail lizard of the southwest United States.
What is so different about them? There are NO males - the
is female! These female lizards reproduce using asexual
parthenogenesis just like the animals above, but before the eggs
form,
These chromosomes recombine in different ways, so baby whiptail
lizards do not necessarily have the same chromosomes as their
Whiptail Lizard
mother.
.
What About My Dog?
Mammals, including humans,
asexual parthenogenesis. This is because in mammals,
chromosomes from both an egg and sperm are needed for an embryo to develop normally. Only one
parthenogenetic mammal has ever lived a mouse created by Japanese scientists in 2004. This was only
made possible through very advanced scientific genetic modification and could never happen naturally.
Switch It Up
Some species alternate between sexual and asexual reproduction strategies, an ability known as
heterogamy. For example, the freshwater crustacean
reproduces by parthenogenesis (asexual)
in the spring to rapidly populate ponds. But when the intensity of competition and predators increases, it
switches to sexual reproduction. Many protists and fungi alternate between sexual
and asexual reproduction, as well. For example, the slime mold
undergoes binary fission (asexual) when conditions are good. However, when
conditions turn unfavorable, the cells cluster together and switch to sexual
reproduction, which leads to the production of spores. The hyphae of the common
mold (
) are capable of producing both asexual as well as sexual spores.
Many algae similarly switch between sexual and asexual reproduction.
A number of invertebrate animals (and some less advanced vertebrates) are
also known to alternate between sexual and asexual reproduction. Heterogamy
happens in a few types of insects, such as the aphid, whose life cycle is quite
complicated. In the summer, wingless females reproduce by parthenogenesis. They
that the mother and all her many offspring live on becomes too crowded. When this
occurs, some offspring randomly develop into adults with wings, and the mother
produces some male babies. These winged aphids fly to new plants, and mate to
create eggs through sexual reproduction.
Aphid
One Last Weird But True
is a microscopic fungi that lives in a symbiotic relationship with the roots of
many plants. A 2004 article in the journal Nature reported that the modern
fungi, which reproduces asexually, is identical to fossil records dating back to the Ordovician period, 460
million years ago.
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Name____________________________
1. Can some animals reproduce by asexual reproduction? Is this rare?
2. What is parthenogenesis?
3. Give two examples of parthenogenesis.
4. How could the scientists studying Leonie be sure that she had NO contact with male sharks?
5. What is it called when some species alternate between sexual and asexual strategies to reproduce?
6. Give two examples of heterogamy.
7. Why would heterogamy be advantages (beneficial) to the organisms that can do it?
8.
The text says that
start
reproducing sexually
. How would sexual
reproduction help the species survive in this type of environment?
9. Explain how asexual reproduction is responsible for the
million years.
not changing for 460
10. Could you ever expect a mammal such as a rabbit, dog, or giraffe to reproduce asexually?
Why or why not?
11. Whiptail lizards reproduce asexually, but yet do have genetic diversity in their offspring. How is this
possible?
12. Why are Gaia the Komodo Dragon and Leonie the Zebra Shark special mothers?
13.
©Flying Colors Science