Herps
that don’t need
Him.
Parthenogenic reptiles.
education from conservation
Uni Sex biologist
Kit Prendergast.
Parthenogenetic offspring are essentially
clones. Four species of butterfly lizard
(Leiolepis spp.) are known to use this form
of reproduction. Image by vod67.
M
ost vertebrate species reproduce sexually,
requiring both male and female. However, there are also
instances of bona fide virgin births. Parthenogenesis, in
which females can reproduce without the genetic input of
a male, is a comparatively common strategy among
reptiles (it is completely absent in mammals), and has
been recorded in eight families of lizards and three
families of snakes. Some taxons are obligatorily
parthenogenetic; the entire species consisting of females.
Others are facultatively parthenogenetic; when males are
in short supply, females have the potential to reproduce
asexually.
Genetic technologies have provided a breakthrough, as
parthenogenesis is now able to be confirmed through
comparative examination of the DNA of mother and
offspring. If the offspring has a DNA sequence that does
not match its mother, this is clear proof that it was
produced through sexual means. Unlike humans, some
reptiles are able to store viable sperm for months or even
years. Hence, a female of unknown history that has been
isolated for some time may appear to be reproducing
parthenogenetically, whereas in reality she is utilising
stored sperm. For example, a female Eastern Diamond-
backed Rattlesnake (Crotalus adamanteus) once gave
birth to nineteen baby snakes through sexual reproduction
by storing sperm for more than five years! Furthermore,
observations of an apparently all-female population could
arise due to sampling biases, such as recording offspring
influenced by temperature-dependent sex determination,
or collecting data at a time of year when only females are
active, or in a habitat partitioned by gender. Having said
that, genetic sequencing studies have shown that
parthenogenic species and facultative parthenogenesis
may not be such a rare anomaly as was once thought.
In order to become parthenogenetic from a sexually-
reproducing ancestor, two constraints must be overcome:
1) egg development must be able to be initiated independ-
ently of sperm; and 2) meiosis - the production of gametes
- has to be modified so that the eggs produced retain the
same number of sets of chromosomes as the parent.
Normally, gametogenesis results in halving the number of
chromosomes from two sets (diploid) to one set (haploid),