No sex needed in all-female lizard species

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Already half a decade ago scientists found that some species of lizard do not need males to reproduce. However it has remained unclear how they can do this since asexual reproduction goes together with almost no genetic variation and higher disease vulnerability. A new study published online in Nature on the 21st of February reveals how.

Asexual all-female lizard

The asexual, all-female species (center) is shown flanked by two sexual species which hybridize to form the middle species. Photo by Alistair J. Cullum.

The all-lady lizard species are not alone in the vertebrate world of asexual reproducing species – some 70 species multiply in this way. However, these little lizards do not have a choice. Sexual reproduction has the advantages of rapid generation of genetic diversity, allowing adaptation to changing environments. Since these lizards can’t exchange genetic material, they have a major disadvantage in a changing environment.

Asexual lizard pseudocopulation

Two Desert Grassland Whiptail lizards engaged in pseudocopulation. Photo by Tino Mauricio.

The new research by Peter Baumann and his team reveals that these lizards maintain genetic richness by starting the reproductive process with twice the number of chromosomes than sexual lizard species. The researchers found that these species could maintain diversity and form a gamete by pairing their sister chromosomes (the two chromatids from one chromosome), while in sexual species homologous chromosomes from each parent are paired.

These celibate species have arisen through the hybridization of two or even three different sexual species. Although the precise mechanism is not known, it gives the individual asexual species a great amount of genetic diversity to begin with.

Asexual whiptail lizardsAn interesting aspect to reproduction in these asexual lizards is that mating behavior still occurs even though the populations are all female. One female plays the role of a male and mounts the female that is about to lay eggs. This behaviour is due to hormonal cycles. Since lizards who act out the courtship ritual produce mroe offspring, it can be said that they still require sexual behaviour for maximum reproductive success.

Though asexual reproduction sounds not really exciting, it has great benefits. Reproducing without the need of a male greatly increases the chances of populating a new environment. Living in the dry and sometimes harsh climate of the southwestern United States and northern Mexico, this unique way of reproducing may be the most optimal.

A further understanding of the small but diverse group of animals that reproduce without males is needed, and may shed light on the overwhelming success of sexuality.

Lutes, A. A., Neaves, W. B., Baumann, D. P., Wiegraebe, W., Baumann, P. (2010) Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards. Nature 2010/02/21/online