in the
underwater forests of northern japan
the residents of this sunken wreck are
waiting for the summer temperatures
to reach 16 degrees celsius
[Music]
that for some is the time for mating
a kind of giant grass called a copper
dye
this is a male
[Music]
and in female terms he’s particularly
handsome
[Music]
he’s a meter long and weighs 15 kilos
[Music]
much larger than the diminutive female
[Music]
and he is ready to breed
[Music]
he attempts to mate with her and with
any of the other dozen or so females
that live in his territory
whenever he gets the chance
but females from around 10 years old
take little notice of his advances
[Music]
[Music]
this is because when any large female
reaches a critical body size
she can begin a dramatic transformation
over just a few months particular
enzymes
inside her body cease to work
and male hormones start to circulate
as time passes her head
expands and her chin gets longer
a she has changed into a he
and with this comes a change in
temperament
the old male who ruled all the females
here
is challenged to a face-off
the more bulbous the head the more
it intimidates an opponent
[Music]
the territory has a new ruler
only the largest females transform
themselves
in this way
but the change enables them to have more
mates
so they will have many more offspring
carrying their genes
[Music]
but a new male can’t afford to be
complacent
inside the body of every cobody female
there is a new mail-in waiting
[Music]
