When the Temperature is Hot, Australian Bearded Dragons They are Not!


This title is a misconception devised to convey the idea of sexual determination of Australian Bearded Dragons (ABD).  ABD have male sex chromosomes, but look, behave, and reproduce like females depending upon temperature. Fundamentally, biology courses redundantly emphasize chromosome selection regarding the sexual determination of organisms. Throughout high school and much of college, genetic literature has instilled within me, the notion that biological sex is a 50/50 probability. In addition, the inheritance of two X chromosomes usually produce female offspring, while XY chromosomal inheritance yields male offspring.

As a recent student of courses such as animal communication and genetics, I have learned that nature often create exceptions; contrary to broad genetics literature taught in introductory level academia, various species of organisms can produce males by inheriting two X chromosomes, whereas the inheritance of XY chromosomes yield females. Relatively, humans can have congenital abnormalities that produce offspring with both sexual genitalia, termed as “hermaphroditism.”

While there are many scenarios we encounter in science, nature throws another curveball called “sex-reversal,” which conveys the idea that factors can induce alternating sex change within embryos. Temperature is the factor that induces sex change within ABD embryos. Holleley et. al found that incubation of ABD embryos containing two Z chromosomes (male) can alter the sex to become female. This means that ABD sex is determined by chromosome complement and environmental temperature. Z and W chromosomes in Reptiles replace the conventional X and Y chromosomes of basic genetic literature, with ZZ producing males and ZW yielding females.

Among 131 adult ABD, chemical analysis of controlled breeding experiments found eleven individuals with male chromosomes that are actually female. Then, breeding of sex-reversed females with normal males shows that sex determination is a result of incubation temperature.

In addition to the aforementioned paragraph, sex-reversed mothers laid nearly twice as many eggs per year than normal females, thus resulting to sex imbalance, and over feminized populations.

One future concern regarding sex determination of ABD is rapid climate change. The implications of increased climate temperatures may prevent ABD from producing offspring which in the long run, could lead to extinction. Sex-reversed females have increased each year during the study (2003-2011) from 6.7 percent to 22.2 percent. Is this trend indicative of global warming? Maybe one day the correlation between each concept will be understood, but for now we wait for ABD to approach the “last man on earth” saying.

by Sheream Reed


Holleley, C., O’meally, D., Sarre, S., Graves, J., Ezaz, T., Matsubara, K., Georges, A. (2015). Sex reversal triggers the rapid transition from genetic to temperature-dependent sex. Nature, 523, 79-82. doi:10.1038/nature14574

Image: http://www.scoopnest.com/user/BI_Science/617014987446423552


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