Study reveals environmental impact on sexual vs. asexual reproduction

A recent study done at the University of Toronto, completed by professor Aneil Agrawal and post-doctoral student Lutz Becks of the ecology and evolutionary biology department, states that the environment helps to determine whether a species reproduces sexually or asexually.

The study, which took about 17 weeks to complete, determined that species that lived in spatially heterogeneous environments, with a variety of other plants and animals, were more likely to reproduce sexually, rather than asexually. In other words, various genotypes are favoured in different environments, when one part of an environment differs from another. Considering the diversity of life and organisms, sexual reproduction remains widespread and this “evolutionary force” remains a powerful and important one to study in biology.

Understanding why organisms choose to reproduce sexually as opposed to asexually is one of the “outstanding mysteries” in evolutionary biology, states Agrawal. The experiment shows that the organisms produced from sexual reproduction were more proficient at survival in a variety of environments and had different characteristics and stronger genes, in contrast to their asexually-reproduced counterparts. While organisms that reproduced sexually were able to adapt through various environments, organisms that were reproduced asexually were competent in only one environment.

Rotifers (small aquatic organisms) were studied in the experiment. As these organisms have the ability to reproduce both sexually and asexually, they were released in either homogeneous or heterogeneous environments. The trend for sexual reproduction, in contrast to asexual reproduction, was higher in heterogeneous environments and was lower in homogenous environments, over a period of more than 70 generations.

Experiments that use a hypothesized element to test its effect on the evolution of sex are not very widespread; however, there are several theories that attempt to answer the question. While environmental heterogeneity is not the only reason that sexual reproduction is more common than asexual reproduction, it is an important advance in understanding that the environment does play a key role. In order to better understand sexual reproduction’s dominance over asexual reproduction in nature, more controlled experiments would need to be conducted by studying various other elements.

The study, which was used as the basis for the paper “Higher rates of sex evolve in spatially heterogeneous environments”, was published on October 13 in Nature. The study was funded by the Natural Sciences and Engineering Research Council of Canada, as well as with a fellowship that was awarded to Becks by the Volkswagen Foundation in Germany.

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