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Changing Sexes
Name: Michael
Status: Student
Grade: Other
Location: NV
Country: United States
Date: Summer 2009
Question:
What do you call the ability of an animal, say a Frog, to BE
either sex? Is that asexuality? We know there are many factors that
determine why a Frog might be male or female but what do you call the
ability to be either sex?? This happens only in fish and frogs and maybe
snakes?
Replies:
Hi Michael,
Gender in frogs is fixed - a frog cannot change its gender during its life. Once a
male always a male.
Some fish on the other hand can and do change gender. Australia's Barramundi is not
only very good eating, but it is also hermaphrodite. (From Greek - Hermes and
Aphrodite - a male and a female god) It carries both male and female genitalia,
but different parts work at different parts of its life. All small barramundi are
males, and they get to chase and impregnate as mane females as they can. Later they
become female, and become the subject of all that male attention. Poetic justice I
say.
All snails and earthworms are also true hermaphrodites - when they mate BOTH snails
become pregnant!
In many reptiles gender is not fixed by genetics, but is determined during early
development. Crocodiles, alligators, turtles and some other reptiles are all
gender determined by temperature during incubation.
In crocodiles, an all-male brood typically results from nest temperatures in the
range of 32 to 33 degrees Celsius ( roughly 89 - 91F). When the incubation temperature
moves outside this range either above or below, the result is female crocodiles --
an overabundance of them.
Among turtles, the ideal temperature between 28 and 29C produces an even mix of males
and females. Too high a temperature leads to more females again. Cooler temperatures
favour the males.
In New Zealand the Tuatara - a so-called 'living fossil' - produces more males as the
temperature of the brood chamber increases. Recent studies show that only one degree
celsius is enough to shift the balance.
There is now a concern that global warming may lead to too many female crocodiles and
turtles, and no males to fertilize their eggs. Scientists in New Zealand are already
finding too many male tuatara.
If this were to happen for an extended period, we would see the extinction of many
reptile species.
For more information the following article goes into more detail.
http://www.scientificamerican.com/article.cfm?id=experts-temperature-sex-determination-
reptiles
Nigel Skelton
Tennant Creek High School
AUSTRALIA
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