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  • Julia Riley

Social Tree Skinks can store sperm

In a recent study published in the Journal of Heredity, myself and colleagues found that female Tree Skinks (Egernia striolata) can reproduce even when they have not encountered a male for more than a year by storing sperm! This is the first evidence of this type of reproductive behaviour among social lizards.

Tree Skinks are typically monogamous and live in family groups. For a completely different study, we separated females from males. We were very surprised when some of those females gave birth more than a year later and all the offspring were fathered by a male that was not the female’s social partner in the wild.

This discovery of female sperm storage suggests Tree Skinks may use this phenomenon as a kind of genetic ‘bet-hedging’ - reducing the risk of inbreeding and enhancing offspring survival by electing to mate with more genetically diverse males than their main partner. But, mating outside the pair poses risks too. There is the possibility of being caught in the act and/or the offspring being rejected by their social partner. But being able to store sperm from extra-pair matings over the long-term likely provides reproductive advantages for females. Documenting female sperm storage in a new lizard species sheds light on the unappreciated control that females have over reproduction and maximising their own fitness.

Overall, our study highlights how even well-planned studies sometimes take an unexpected turn and lead to exciting new discoveries! We also now know that female Tree Skinks, already famous for family-living, are likely one-step ahead of their male partners.

A female Tree Skink hanging out with her two offspring.

This post was revised from a media release from Macquarie University by Lucy Mowat. In addition, a great blog has been written about this article by Alexis Oetterer for the American Genetic Association. You can check it out here.

Check out the paper here and this is its citation:

Riley JL, Stow A, Bolton PE, Dennison S, Byrne R, Whiting MJ (2021) Sperm storage in a family-living lizard. Journal of Heredity,


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