The reproductive history of the unisexual, ladies-only salamander species is full of evolutionary surprises.
In a new study, a team of researchers at The Ohio State University traced the animals’ genetic history back 3.4 million years and found some head-scratching details — primarily that they seem to have gone for millions of years without any DNA contributions from male salamanders and still have managed to persist.
For some time, it has been assumed that they steal other species’ sperm, “which the males of sexual species deposit on leaves and twigs and the like. When this happens, it stimulates egg production and the borrowed species’ genetic information is sometimes incorporated into the genome of the unisexual salamanders, a process called kleptogenesis.” It was assumed that the lack of genetic diversity that cloning entails would lead to extinction. However,
“This research shows that millions of years went by where they weren’t taking DNA from other species, and then there were short bursts where they did it more frequently,” said Rob Denton, who led the project as an Ohio State graduate student and is currently a postdoctoral researcher at the University of Connecticut.
“Surprisingly, it doesn’t look like they’re suffering any ill genetic effects. It’s a mysterious scenario that an animal can avoid sexual reproduction for millions of years and not suffer the consequences of that.”
“Most asexual lineages blink out after 100,000 years. We think these have been around for 5 million years,” he said.
A puzzling detail that emerged in the study is that the sampling of DNA from other species appears to have increased in frequency in recent times, he said.
“The reasons for this are sort of tantalizing, and make you wonder: Did this happen because of some sort of environmental change or specific interactions with other species? We don’t know those answers but now we have some provocative questions,” Denton said.
He also noted that the evolutionary history of the unisexual salamander is far different from the history of other unisexual species, such as Amazon mollies.
“The mollies live fast and die hard, in less than a year, but these salamanders live slow and for long periods of time, into their 20s and 30s. And they reproduce every few years,” Denton said.
“These salamanders are just sort of plodding through evolutionary time doing strange and surprising things.” Paper. (paywall)(paywall) – Robert D. Denton, Ariadna E. Morales, H. Lisle Gibbs. Genome-specific histories of divergence and introgression between an allopolyploid unisexual salamander lineage and two ancestral sexual species. Evolution, 2018; DOI: 10.1111/evo.13528 More.
[lectern slowly crumbles in background…]
One question: Has anyone identified a specific problem that the salamanders needed to solve that could only be solved through sexual reproduction? The reason for asking is that, to the extent that evolution is a history of life, we may find many more anomalies — things that, as it happens, work but can’t be generalized or made into a law.
Human history is full of such episodes. That raises the question, can one derive laws from history?
See also: Rapid evolution of asexual species … toward extinction
All rotifers are female (we think) – but the underlying explanation has been challenged
New book challenges sexual selection theory in evolution
Can sex explain evolution?