茄子直播

The evening primrose shows sexual reproduction carries a lower risk of harmful mutations than asexual reproduction (photo by Professor Marc Johnson)

Sex and the single evening primrose

Sex or no sex? That depends on how you feel about harmful mutations, says new research from the University of Toronto.

Using various species of the evening primrose (Oenothera) as his model, Jesse Hollister, a former 茄子直播 post-doctoral fellow, and his colleagues have demonstrated strong support for a theory that biologists have long promoted: species that reproduce sexually, rather than asexually, are healthier over time, because they don鈥檛 accumulate harmful mutations.

鈥淭hese findings allow us to understand why an enormous diversity of species around the world go through the laborious process of sexual reproduction,鈥 said Hollister, who completed the research while working at 茄子直播 Mississauga鈥檚 department of biology and the department of ecology and evolutionary biology on the downtown campus.

The research, published online recently by the journal , was authored by Hollister, along with his supervisors, Professor Marc Johnson and Professor Stephen Wright. Hollister is now an assistant professor at Stony Brook University in New York.

For decades, evolutionary biologists found sexual reproduction to be a paradox. Mathematically, asexual reproduction seemed to make more sense. Each organism 鈥 not just half the population 鈥 could produce offspring, and all its genes were passed on, rather than the 50 per cent from each parent in offspring from sexual unions.

One key issue they didn鈥檛 take into account, said Hollister, was the accumulation of harmful mutations over time. New mutations occur naturally in every species from one generation to the next. When species reproduce sexually, their genes are separated, shuffled and recombined in various ways, so each offspring doesn鈥檛 receive all of their parents鈥 mutations in addition to the naturally occurring ones. In asexual reproduction, however, the species copies the existing genome as a whole, effectively cloning itself. Therefore, they pass on all the mutations that naturally accumulate from generation to generation.

鈥淎sexual reproduction leads to a buildup of deleterious mutations over time; it鈥檚 called Muller鈥檚 Ratchet,鈥 Hollister said. 鈥淭he species鈥 average fitness is reduced and they are less able to compete in the ecological arena than sexual species, so they have an increased probability of extinction.鈥

The evening primrose was the ideal system for studying the evolutionary importance of sex, Hollister noted, because about 30 per cent of the species in the genus have evolved to reproduce asexually, each at a different time. With the assistance of the 1,000 plant transcriptome project, led by Gane Ka-Shu Wong at the University of Alberta, and sequencing aid from the BGI-Shenzen in China, the 茄子直播 researchers were able to examine 30 pairs of species. One species in the pair reproduced sexually; the other, asexually. Some of the asexually reproducing species were younger than others in evolutionary terms, allowing the researchers to see the effects of asexual reproduction over time.

鈥淲hat we found was exactly what we predicted based on theory,鈥 said Hollister. 鈥淭he power of our study is that we examined many independent transitions to asexuality over different time scales and were able to take a snapshot in the present of the genetic variation in species pairs.鈥

Johnson, a professor in the department of biology at UTM, said this research has shed new light on the paradox of sex.

鈥淭his is the first solid genetic support for the theory that a significant cost to being asexual is an accumulation of deleterious mutations,鈥 Johnson said. 鈥淭his study has allowed us to unlock part of the mystery of why sex is so common: it鈥檚 good for your health, at least if you are a plant.鈥

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