A seemingly ordinary freshwater snail from New Zealand is surprising scientists with its extra chromosomes, offering a rare glimpse into how species evolve. Researchers at the University of Iowa have discovered that this snail recently duplicated its entire genetic blueprint—a phenomenon called polyploidy— shedding light on how major evolutionary leaps might occur in animals.
This unusual find was published in the journal Genome Biology and Evolution. What makes this snail so special? Unlike most animals, including humans, which possess two complete sets of chromosomes (diploids), this species has multiple copies of its genetic material.
The team chose to study this particular snail because it can reproduce both sexually and asexually. This dual reproductive strategy is often linked to polyploidy, as asexual reproduction makes it easier for females to pass on extra chromosomes when cloning offspring. For a long time, biologists have been puzzled about whether these extra chromosomes help or hinder species over time.
To unravel this mystery, the researchers painstakingly pieced together the snail’s genome by analyzing roughly 20,000 genes from 30 individuals within the same lineage. Imagine completing a complex puzzle where all the pieces are almost identical—that’s the challenge they faced! Their reconstruction revealed that this snail species underwent whole-genome duplication somewhere between 1 and 2 million years ago.
“Typically, having more than two genome copies is considered an anomaly,” explains Kyle McElroy, co-author of the study. Now a postdoctoral researcher at Iowa State University, he completed his doctorate at the University of Iowa in 2019. “But it appears that when this rule is broken, organisms often try to correct it over time.” The exact reason why having two copies of the genome seems to be the dominant norm remains unclear.
Interestingly, this snail isn’t fully back to a diploid state yet. It’s still in transition, with some genes retaining multiple copies while others have returned to two. This intermediate stage is exceptionally rare in animals and provides scientists with a unique window into an evolutionary turning point.
This discovery sparks new questions about the triggers for whole-genome duplication and its role in creating new traits. “Events like this could mark evolutionary milestones by providing the raw genetic material for groundbreaking innovations,” suggests Maurine Neiman, senior author of the study and professor in the University of Iowa’s Department of Biology.
The snail’s unusual genetic makeup reveals an ongoing process of evolution unfolding right before our eyes, underscoring the complexity and dynamism of life’s journey on Earth.
