Python reproductive physiology
by Winslow Murdoch
My recollections having attended Dave Barkers lecture
At the Mid Atlantic show, I had the chance to hear a great lecture (by
Dave Barker) on reproductive biology of pythons. He had great slides of
actual developing (but dead) eggs, ovarian function, and anatomy.
Unfortunately, all the pictures came as a direct cause of death by
natural causes to various desirable pythons, but when you have over a
thousand snakes, s#%* happens! I also learned a few pearls that some of
you might find interesting.
What follows is my recollection of the presentation, though my
terminology is a bit rusty...bear with me
- the reproductive effort for a given cycle is predetermined two years
before a given cycle. as a result, if a female was ill, or stressed two
years ago, and now has a small clutch, this would be totally
explainable, even if the animal had since gained lots of weight and
looked huge, it still might have only a few eggs/babies. Conversely, a
thin/ dehydrated/ stressed animal may have been fat two years ago, and
now drops a huge clutch of eggs/babies. this might stress her out and
lead to her death, but more commonly, she will deposit a large number of
infertile small unfertilized ovum (slugs), and two years later,
regardless of how well she ate, etc., she will have a small clutch.
Perhaps if you extrapolate this, you should give the third year off to
maximize the fecundity, and maternal health of your animals
.
- Sexually mature male pythons produce live active motile sperm in
large quantities year round. This occurs as early as 9 months of age,
and continues throughout their lives. they do go into a cycle when
cooled that induces the testes to increase in mass, but if they are paired with a
receptive cycling female at any time of the year, they should still be
able to sire good offspring. therefore, the females state, and cycling
is the most important factor determining breeding success.
- The paired male copulatory organ only acts as a surface conduit for
the inseminating sperm to swim over to the female. there is no hollow
tube etc. the hemipenes usually bifurcate at the tip. there is a shallow
groove that runs along the length of the hemipene, and also bifurcates
at the tip (the spermatic sulcus). the sperm swim and divide up, and
follow one of the two end grooves, which sit up in the female's cloaca,
and end at each opening of the females paired oviducts. they then swim
up to the oviduct cephalad (head directed) end, and stay there for
insemination. this can occur weeks or even months later, but is more
successful if the mating occurred a few weeks before ovulation.
- the ovaries are like a thin ribbon of tissue that runs along either
side, about
one fifth of the snakes length. the follicles for the next years mating
are predetermined, and start very slow growth two years before that
season. on any given season, predetermined follicles will start
vitellogenesis. stored fat is mobilized from the coelomic fat bodies in
the peritoneal cavity, into the blood stream, and is taken up by the
liver. the liver converts this fat into vitellagin? and albumin
proteins. These are then carried by the blood stream to the follicles.
Follicles start off the size of tiny amber raisins (tapioca), and grow
within the ribbon of tissue.
- If the female was under nourished, dehydrated, ill, or in any way
stressed during vitellogenesis, she will either arrest the process (if
stressed early in the cycling attempt), or will produce most or all
slugs at the time of egg laying. The follicles will never attain the
viable size of a full term viable egg, and will be ovulated too small
and sometimes too early for them to develop further. If healthy, the
ovary has these huge full term egg sized follicles that are like water
melons in panty hose. the ovarian tissue is stretched as thin as paper.
- Ovulation occurs when the ovum tear out of the "panty hose", and
settle free in the peritoneal cavity. the snake then goes
through a "regurgitation like sequence" that starts at the tail, and
works the ovum forward (cephelad) into the paired lateral (side) positioned
oviductal funnel structures that open up facing the tail and funnel the
ovum up toward the snakes "chest". The oviducts then each immediately
take a 180 degree bend, letting the ova drop caudally (towards the tail)
into first the right , then the left oviduct in an alternating fashion, until all the
ovum have been put into their new panty hose like structures. as the
ovum pass into the oviducts, they are met by the stored sperm that then
inseminate/fertilize them. this whole ovulation process takes between
8-24 hours, and has been described as lumping (as there are two sets of
ovum passing each other in opposite directions at the same time). The
female should be left alone while lumping!
- in the oviducts, eosinophil white blood cells surround the ovum, and
scamper all along and around them, depositing a trail of protein and
calcium substances that makes up the shell (like spiders webbing an egg
case). once the shells are fully formed, the proper term for these
developing babies is an egg.
- python embryos are well developed by the
time they are laid. as a result, they have high oxygen demands that
outstrip their mothers blood supply's ability to meet. any delay in egg
deposition (into the life giving oxygen in the nest pile) causes the egg
to die (i.e., egg bound females never have the eggs salvaged that aren't
laid, as they suffocate almost as soon as the last normally delivered
egg has passed). any inadvertent laying of the eggs in the water bowl
will also cause the egg to drown in a matter of a minute or two.
I hope this is informative to some of you, and not too pseudo scientific
or esoteric.
Probing issues were also discussed at the lecture, and I will also
include some of my own observations.. Interestingly, the anatomy of
males and females is not that different. Both have paired, rather large
musk (or scent) glands in the base of the tails. These have a duct that
goes to a papilla opening just to the mid-line of the opening of the
"sac" in females, and inverted hemipene sac in males. The papilla points
in toward the mid-line at an angle, and has an opening the size of a
pin. This would be essentially impossible to perforate while probing,
even if you tried. Males inverted paired hemipene sheaths run varying
lengths (eight to fifteen subcaudal scale equivalents) down inside the
base of the tail, and end in a blind sac. These sacs then have a fragile
connective tissue strand that attaches their ends to the vertebral
column near the tip of the tail. Females have a similar sac-like
structure, but it ends in a much shallower blind cavity that is rarely
more than three to five subcaudal scale equivalents deep. There are also
similar connective tissue strands that end up in the tail tip.
During ecdesis, the inner lining of these hemipene, and analogous female
shallow sacs are shed. The resultant cast is much more obvious in males,
and is actually one way to sex your snake without probing. They can
sometimes be found floating in the water bowl, and have been mistaken
for tapeworm segments by surprised novice herpetoculturalists (like me
every time I see one). At times, this cast fails to shed, and it forms a
plug that fills the hemipenal orifice to the cloaca. This gets mixed
with secretions from the scent glands, and takes on a brownish color. It
can often be seen coming out of the cloaca, from the direction of the
tail. It can be manually pulled out of the hemipenal sac, and has
therefore been given the improper but descriptive term "sperm plug".
Probing requires that any sperm plugs be removed, although their
presence almost guarantees a male, unless it is mistaken for something
else. A clean or sterile probe is lubricated with sterile water, saline,
or surgi-lube water soluble medical lubricant (which has been noted to
be spermicidal, but likely not a clinically significant cause of
infertility). The probe is then inserted under the cloacal vent scale,
and then directed into the cloaca, and down either side of the vent
toward the tail. In males, you expect to have the probe slip into the
sac, and progress unobstructed for at least five, but commonly nine to
fifteen subcaudal scale equivalents. In females, the average distance is
three to five. Probing distances are largely species dependent. One
common mistake is to use too small a probe, with just a little too much
force. The sac is easily punctured in this scenario, and a female can
easily be mis-probed as male. Occasional blood may be found on
withdrawing the probe. This can be from a puncture of the sac, or can
happen without other serious discernible trauma. Punctured sacs
generally heal without a problem, but rarely can lead to cloacitis, and
infections which can be fatal.
Babies can also be popped accurately, especially in the first two weeks
of life. At this young age, they do not have the muscular tone to resist
popping. Older snakes can still sometimes be accurately sexed with this
method but you are only sure if you have a male when the hemipene pops
out. If it’s not an obvious male, you still need to probe it as it could
be a tense, non popping male or a female. The technique requires two
hands. One hand holds the base of the body just above the cloaca, and
the other hand is held such that the thumb pad sits on the ventral
aspect of the tail, just caudal to the vent, with the thumb tip pointed
up toward the vent. Gentle firm pressure is exerted in a rocking motion
up towards the vent (squeezing toothpaste), and the scent gland papillae
will protrude. Just next to these, and often looking like the same
structure, you will either find a protruded hemipene, or the hemipenal
sac orifice, which has a little vascular red rim to the tip. The females
also protrude their scent papillae, but you don’t see the hemipene, or
the red tip to the bulge. Sounds easy, but it’s not, and in delicate
snake neonates like green tree pythons, it has been associate with
severing the vertebrae, and later causing "kinky tail" syndrome.
That’s all for now. Sorry for all the med speak and descriptions, but
this is snake lingo at the non professional level, and if you are into
it, it goes with the territory.
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