A project undertaken at The Australian National University, and supervised by Prof. Craig Moritz.
Reproduction among animals is virtually synonymous with sex. The alternative – asexual or clonal reproduction – is incredibly rare, with fewer than 0.1% of vertebrate species able to reproduce without a genetic contribution from both sexes. This phenomenon has perplexed evolutionary biologists for decades, particularly as clonal reproduction has one significant advantage over sexual reproduction – no males are required!
If a species consists entirely of female clones, each and every individual can bear offspring and populations can grow rapidly without the limitation of needing to find a mate. Why then are asexual animals exceedingly rare?
Faced with this paradox, evolutionary biologists have proposed disadvantages of asexual reproduction. Firstly, as these organisms are clones, they may lack the required genetic diversity to adapt to changes in the environment. Additionally, harmful genetic mutations may accumulate in clonal lines over the course of many generations, leading to their eventual extinction.
A number of recent studies have explored the genetic consequences of asexual reproduction and found mixed evidence in support of these hypotheses. However, a full genome-scale analysis is lacking, as is a comparison of genomic diversity in asexual organisms and closely related sexually reproducing species. In this project, we seek to fill this gap by characterising genomic diversity in an asexual system and comparing the genomes of closely related asexual and sexual forms.
The Australian gecko, Heteronotia binoei, is a well-known asexual vertebrate. It consists of at least ten sexually reproducing forms distributed across the continent, and all-female clones that dominate populations in the central and western deserts. Previous genetic studies showed that these clones arose from crosses between two different sexual forms in Western Australia before expanding their ranges, with some spreading 1000’s of kilometers, as far as the central deserts. These hybridisation events are also predicted to have occurred multiple times, generating several clonal lineages.
As a result, these clones are expected to be quite diverse – far from the single static genome that comes to mind when we think of clones. Is this genomic diversity key to their long-term survival? How does it compare to the diversity of sexual forms? Where exactly does it come from and how is it generated? These questions are the driving force behind our research and in answering them we seek to improve understanding of this system and reproductive modes more broadly.
In this research project we will: (1) investigate genome evolution and function in asexual forms of H. binoei by exploring variation in genome structure and the way that genes are expressed (i.e., turned on or off) and (2) compare levels of genomic diversity in sexual and asexual forms. We aim to shed new light on how the transition from sexual to asexual reproduction shapes genomic diversity. In turn, this can help us understand the consequences of abandoning sex and why so few species are able to adopt a clonal existence. It can also improve our understanding of why and when genetic diversity is crucial – a basic question in evolution, with relevance to resilience of crops and livestock, and even threatened species.