UTA study: Asexual reproduction causes dangerous genetic mutations

A team led by biologists at The University of Texas at Arlington has published a study that supports the theory that species that reproduce asexually have more harmful genetic mutations than those that use sexual reproduction.

Jose Maldonado, a UTA doctoral student in biology, is the lead author of the new paper, entitled “Parthenogenesis doubles the level of amino acid substitution in whiptail mitochondria.” It was published in May in Evolution, the flagship journal of evolutionary biology.

Co-authors include TJ Firneno, a postdoctoral research fellow at the University of Denver who received his Ph.D. from UTA in 2020; Alexander Hall, product application specialist at Thermo Fisher Scientific who received his Ph.D. from UTA in 2016; and Matt Fujita, UTA professor of biology, who is Maldonado’s faculty advisor and previously served in the same role for Firneno and Hall.

Parthenogenesis is a natural form of asexual reproduction in which the growth and development of an embryo occurs without fertilization by a sperm. It is generally believed that sexual reproduction causes fewer harmful genetic mutations than asexual reproduction.

In their new study, Maldonado and his co-authors tested this theory by studying Aspidoscelis, a genus of whip-tailed lizards. Due to their high abundance and distribution throughout the southwestern United States and northern Mexico, these reptiles are excellent model systems for studying the basic cellular mechanisms of parthenogenesis and the genomic consequences of asexuality.

The team used whole mitochondrial genome data from asexual and sexual whiptail lizards to investigate their prediction that parthenogenetic lineages accumulate mutations more rapidly than sexual lineages.

“Our study shows that when whiptail lizards transition from sexual to asexual reproduction, it is followed by the accumulation of harmful mutations in the mitochondrial genome,” Maldonado said. “If asexuals accumulate more harmful mutations than their sexual counterparts, as our findings show, this could explain why asexual reproduction is rare in nature and why sex is the dominant form of reproduction in the natural world.”

The team sampled several populations of asexual and sexual whiptail species across the southwestern United States and received additional tissue samples from collections at the Burke Museum of Natural History and Culture in Seattle and the American Museum of Natural History in New York City.

Their research shows that the transition to asexuality leads to relaxed natural selection in parthenogenetic lizards and the accumulation of nonsynonymous mutations, which alter gene protein sequences and are often targets of natural selection. This supports previous theoretical predictions that “loss of sex should lead to the accumulation of irreversible deleterious mutations due to reduced purification selection efficiency, and sex facilitates elimination of harmful mutations,” they wrote.

“The main finding from our study is that asexual vertebrates, or at least these lizards, accumulate amino acid substitutions, which are potentially harmful to organisms, at much higher rates than sexual species,” Firneno said. “This is important because there’s a paradox that it’s much more expensive to reproduce sexually, but it’s a diffuse form of reproduction.”

– Written by Greg Pederson, College of Sciences

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