Parthenogenesis in Varanus ornatus, the Ornate Nile Monitor

Parthenogenesis in Varanus ornatus, the Ornate Nile Monitor.
Parthenogenesis in varanids has been reported in two other species of monitor,
the Komodo dragon, Varanus komodiensis (Watts et al) and the Argus monitor,
Varanus panoptes (Lenk et al). All reported cases had occurred in captivity. That
is also the case with our report. As far as we are aware, this is the first reported
case of parthenogenesis in Varanus ornatus. The female Varanus ornatus in
question is on display in Reptile Village Zoo, Kilkenny, Ireland.
Varanus ornatus occur in tropical forest of Central and West Africa. Our female
was obtained as a wild caught hatchling in 1998; the exact country of origin is
unknown, but most likely Ghana. She had a snout vent length of 110mm.
This female was fed on a diet of insects (crickets, locust), snails and fish,
progressing to mice and rats, quail eggs, chicks and crab meat as she grew. She
was housed alone all her life except for 3 occasions, when we tried to co-habit
her with another female Varanus ornatus. This female was also obtained as a
hatchling around a year after the first, in 1999. All attempts to co-habit the
animals ended unsuccessfully, with fighting breaking out within seconds of them
being placed into an unfamiliar, larger enclosure. They were separated each time
they fought, and were only left in the enclosure for a maximum of 5 minutes each
time.
Both females in our possession are proven females by the fact that they have
both produced unfertile eggs for us on two different occasions each. The only
other monitors either has seen or been with are each other. When eggs were
laid, it was immediately assumed that they were not viable and so were
discarded. Our females are named “Nasty” and “Nice”. Both animals are very
aggressive with “Nice” being slightly less aggressive than “Nasty”. “Nice” is the
female who has reproduced through parthenogenesis.
Fig. 1 - Female Varanus ornatus - “Nice”.
Fig 2 – Close-up of head of female “Nice”.
On the 4th June 2008, the monitor in question, “Nice”, was given a general health
check and was weighed and measured. She was 4.48kg in weight and 520mm in
SVL and 1310mm in TL. At this point she did not visually appear to be gravid.
On the 16th of July 2008, she laid 21 eggs in the corner of her enclosure.
Oviposition took approximately 30 minutes with the female meticulously covering
all of her eggs with the bedding in her enclosure. Once she had finished covering
her eggs, we began to uncover them and take them from the enclosure. The
female was quite defensive of her nest, but was very tired form the strain of egg
laying.
Normally at this point, we would have discarded the eggs. On this occasion, both
because we had a large incubator set up for various other species bred here at
the zoo, and because of the incidence of parthenogenesis in varanids, we
decided to incubate the eggs.
The eggs were placed in containers of vermiculite and incubated at 27 degrees
Celsius. The eggs were checked every other day. Within a week, some of the
eggs started to decompose. Any eggs which had collapsed and started to grow
mould were removed from the incubator and discarded.
On the 6th of November 2008, 113 days after oviposition, only 7 eggs remained
with only 4 of those looking good. It was decided at this point to remove all the
eggs from the incubator and discard them. Starting with the decomposing eggs,
each one was removed and cut open to check the contents. On slicing open one
of the better quality eggs, I discovered a half developed embryo inside.
Fig 3 – Half developed embryo, cut from egg.
It was clearly identifiable as a saurian. Colours had begun to form with clear
bands marked on the tail. All limbs and digits were fully formed with claws. It had
a total length of 130mm and an SVL of 53mm. The remaining 3 good eggs were
immediately placed back in the incubator.
Fig 4 – Half developed embryo, dorsal view.
Fig 5 – Half developed embryo, ventral view.
The remaining 3 eggs remained in the incubator for another 88 days. They were
checked on a daily basis. During this time another egg started to decompose and
was removed, opened and shown to be unviable and discarded.
On the 2nd of February 2009, 201 days after oviposition, the final 2 eggs started
to decompose. One egg had started to grow mould on it and after dissection was
shown to be unviable. The final remaining egg, while starting to smell a little, still
appeared solid. The decision was made to cut open the egg. On dissection I
discovered a dead, fully formed monitor. It had been dead for a day or so and
necrosis just started. The egg sac had been fully absorbed, so it would appear
that the animal had starved to death in the egg, being unable to hatch.
Fig 6 – Fully formed monitor. Note depleted egg sac.
The animal was fully formed, apart from only developing 3 digits on the front left
foot. There may have been further internal abnormalities. It has a total length of
227mm and an SVL of 93mm. The animal was sexed as a male by both probing
and candling. This would be consistent with other cases of parthenogenesis in
varanids.
Fig 7 – Dorsal view.
Fig 8 – Ventral view.
It would seem that facultative parthenogenesis is more common in varanids than
we realise; isolation from other members of the species, for long periods of time,
possibly being the trigger. While this might help fragmented animals in the wild in
the short term, it could cause genetic problems over longer periods.
At present the 2 specimens are preserved here in Reptile Village Zoo for future
DNA work.
Our female laid another clutch on the 2nd of August 2009, again without being
introduced to a male. She started to eat the eggs as soon as she laid them. We
managed to rescue 11 to incubate them. She ate 3 that we know of, and may
have laid and ate more earlier on that morning. The 11 eggs started to
decompose within a week. None of which turned out to be viable.
References;
Lenk P, Eidenmueller B, Staudter H, Wicher R, Wind M.
A pathenogenetic Varanus.
Amphibia-Reptilia. 2005;26:507–514.
Watts P.C, Buley K.R, Sanderson S, Boardman W, Ciofi C, Gibson R.
Parthenogenesis in Komodo dragons.
Nature. 2006;444:1021–1022.
Brenneman RA, Barber RC, Huebinger RM, et al.
Characterization of ten microsatellite marker loci in the Komodo Monitor
(Varanus komodoensis)
CONSERVATION GENETICS Volume: 8 Issue: 4 Pages: 1017-1020. AUG
2007
Fitch AJ, Goodman AE, Donnellan SC.
Isolation and characterisation of microsatellite markers for the Australian monitor
lizard, Varanus acanthurus (Squamata : Varanidae) and their utility in other
selected varanid species
MOLECULAR ECOLOGY NOTES Volume: 5 Issue: 3 Pages: 521-523 SEP
2005
Ciofi C, Bruford MW
Isolation and characterization of microsatellite loci in the Komodo dragon
Varanus komodoensis
MOLECULAR ECOLOGY Volume: 7 Issue: 1 Pages: 134-136 Published:
JAN 1998