Whether an organism reproduces by sexually mating or by cloning itself has dramatic consequences for the genetic profile that is passed on to offspring.

Biologists at the University of Iowa studied a snail species found in freshwater lakes in New Zealand that can reproduce both sexually and asexually (without a male partner). The researchers found that female snails that reproduced asexually had rapid and large-scale structural changes in their genomes compared to their sexual relatives.

“We were seeing a unit of genes about 15,000 bases long increasing from hundreds of copies in sexually reproducing snails to thousands of copies in those that reproduce asexually,” says Kyle McElroy, now an evolutionary biologist at Iowa State University who conducted the research when he was a doctoral student with Maurine Neiman, professor in the Department of Biology at the UI. “Those new copies amount to millions of additional bases in the asexual genomes. This finding was really surprising to us because this is the first-ever discovery of major genomic changes associated with asexual reproduction.”

That change in genome structure in sexual or asexual organisms—and the speed at which that transformation occurs—is important in illuminating the consequences of clonal reproduction and also could yield insights into diseases such as cancer.

“The genes we focused on, ribosomal RNA genes, regularly change copy number in tumors,” McElroy says. “Indeed, genome evolution under asexual reproduction is potentially informative with respect to tumor growth because tumors also grow clonally.”

McElroy is corresponding author on the study, titled, “Asexuality associated with marked genomic expansion of tandemly repeated rRNA and histone genes.” It was published online April 22 in the journal Molecular Biology and Evolution.

Neiman is the study’s senior author. Contributing authors from Iowa include biology professor John Logsdon Jr. and graduate student Joseph Jalinsky.