Wlf 314 Essay # 2: Parthenogenesis in reptiles
Reptiles are the only vertebrates known to exhibit parthenogenesis. Data collected on the
offspring of two female Komodo dragons (Varanus komodoensis) from different institutions shows that
parthenogenesis can be a common occurrence in Komodo dragons. The female Komodo dragons had
both been isolated from males. Parthenogenesis is a concern for endangered reptiles, such as the
Komodo dragon, because it produces offspring which are genetically identical to the mother. This can
have implications on genetic diversity, and is of special concern when considering populations which are
already small. Major interests on this subject have to do with how parthenogenesis evolved. What kinds
of selective pressures would result in the evolution of parthenogenesis and how does this asexual
reproduction affect the fitness of an individual. Also when and how often parthenogenesis occurs and
how it affects the genetic variation in a natural population ore of particular interest, especially for
threatened or endangered species.
Parthenogenesis is known to occur in about 70 species of vertebrates. The discovery of the
commonality of parthenogenesis in reptiles has implications for captive breeding programs. The
accuracy of reptile stud books is now in question given that parthenogenesis could have occurred
instead of sexual reproduction. The previously mentioned Komodo dragons were found to exhibit
facultative parthenogenesis, that is, in the presence of a fertile male, the females will reproduce
sexually, and parthenogenesis will only occur in the absence of a male. The facultative nature of
parthenogenesis in Komodo dragons was demonstrated by Sungai, a female Komodo dragon living at
the London Zoo, UK. Sungai produced an entire clutch which was determined to be parthenogenetically
produced by analysis of the DNA of the clutch members and the mother. Although the clutch members
were not all exact copies of one another, they were all homozygous at the tested loci (Watts 2006). The
very low probability of sexual reproduction producing this degree of homozygosity determined, by
exclusion of sexual reproduction, that Sungai produced this clutch by parthenogenesis.
How parthenogenesis could be selected for is a perplexing question. The authors of this article
argue that the reason for the evolution of parthenogenesis in Komodo dragons is related to the fact that
the only viable offspring that come from parthenogenesis are male, which means sexual reproduction
can immediately resume. I think parthenogenesis must have evolved in different lineages multiple times.
There is a species of lizard that is an entirely female population, hence the parthenogenesis that they
exhibit leads only to female offspring, so the mechanisms and selective pressures for their
parthenogenesis must differ from those of a Komodo dragon. The reasons for having an entirely
asexually reproducing female population seem obscure. Perhaps parthenogenesis in this species of
female lizards started out with a mechanism similar to parthenogenesis in Komodo dragons, but a
modified version of it which only produced exact clones of the mother became fixed in the population
through some random chance event leading to an entirely female population. The reasons for asexual
reproduction are somewhat obvious; in the absence of a mate reproduction can still occur, and the
Komodo dragons seem to have evolved a quick path back to sexual reproduction. Parthenogenesis
seems like it is a good adaptation to increase individual fitness, which, after all, is said to be the main
goal of life. Obviously the Komodo dragons have realized the importance of genetic variation to
individual fitness.