Some Ambystoma salamander populations are all female, and they reproduce by cloning themselves, though they do mix it up by stealing sperm they find on leaves and twigs left behind by males of other species. Like salamanders who reproduce sexually, these females are also excellent at regenerating various body parts. However, according to new findings published in the Journal of Zoology last week, these all-female salamanders regrow their tails faster.
Lineages of unisexual salamanders have survived for millions of years. Without incorporating stolen DNA into their genome, their genes stay relatively static. Having a limited gene pool typically means that harmful mutations get passed on. Yet these salamanders thrive. Previous work suggested that unisexual salamanders might regenerate their body parts at faster rates.
To investigate, a team of Ohio State University researchers led by Robert Denton compared a unisexual population of mole salamanders (Ambystoma talpoideum) with a closely related heterosexual species called small-mouthed salamanders (Ambystoma texanum). The team collected their egg masses from wetlands in Crawford County, Ohio, and they reared 10 unisexual salamanders and 30 small-mouth salamanders. When the amphibians were between 10 and 12 months old, the team snipped off 40 percent of the tail and watched them regenerate.
Members of the all-female population grew their tails back 36 percent faster than their heterosexual relatives.
Both groups of salamanders regenerated their tails at about the same rate for the first three weeks. But while unisexual salamanders had brand-new tails in an average of 7.6 weeks, the small-mouthed salamanders took another month or so. Additionally, since unisexual salamanders are bigger, they have more tail to grow back. After taking size and weight differences into account, the team estimated that all-female salamanders regenerated their tail tissue 1.5 times the rate of small-mouthed salamanders.
The higher tissue regeneration rates likely have something to do with the fact that these unisexual salamanders are polyploids: They have more than two sets of chromosomes. Most animals (including humans) are diploids with one set from mom and another from dad. But these salamanders are triploids with combinations of two or more distinct genomes from sexually reproducing species. An increased number of genomes may provide a regenerative advantage. "Is it because they have more genomes or because they reproduce differently?" Denton said in a statement. "We don’t know, and it’s difficult to disentangle with these animals."