Salamanders just aren’t that into you
A type of mole salamander has found a way to achieve the perfect society – all female. At some point, about 2 million years ago, a hybrid of different mole salamander species started reproducing in a way that only produced females. This is really, really rare. In fact, this ancient family is the oldest known line of all-female vertebrates (animals with spines). They’re basically the amazons of the amphibian world.
These salamanders can be found in North America and they belong to the genus Ambystoma, which includes the famous axolotl. They may look like wet lizards, but they’re actually amphibians, with many spending their lives both in and out of water.
A quick sex-ed lesson:
This unique line of mole salamanders is what you call “unisexual,” meaning they have only one sex, female. They have the advantage that every individual in the species is able to bear offspring. But there’s a reason that unisexual lines aren’t common in animals.
Most unisexual species reproduce through asexual reproduction. This is when an organism’s offspring are exact genetic copies of itself. This is different to sexual reproduction where the genes of the parents of a bisexual species combine in different ways to create offspring with a very different sets of genes. Genes are the biological “code” for what makes us… us. Brown hair, short, skinny, purple feathered or blue tongued – all of that is decided by genetics.
But if we could just copy ourselves, why bother with sex? I hear you ask. Sexual reproduction allows for a species to be more resilient to *bad things.* For example, imagine there’s a crash (this is the correct group term) of feathered rhinos. If a disease came along that only affected purple feathered rhinos, all the green, magenta and orange feathered rhinos would be fine. But if they were all purple-feathered… You get the picture. In terms of evolution, there’s safety in diversity!
It’s always ladies night at the mole salamander bar
So the question is, if this line of all-lady mole salamanders reproduce asexually, why hasn’t some obnoxious disease wiped them out?
It’s because they’ve found a unique way to diversify their offspring. These unisexual salamanders use a technique called kleptogenesis – they’re sperm stealers. They breed with other similar Ambystoma such as the blue spotted salamander or the tiger salamander, taking their pick of the gene pool. This is an advantage as they are able to mate with five different species, increasing the range of habitats they can be in, so long as there is a sperm donor present.
Most of the time the genetics of the male are rejected, and the sperm is only used to initiate the development of the female’s eggs. However, occasionally as much as 25% of the genetics from the sperm donor will be used to form the new offspring. This is how these incredible creatures have managed to have genetic diversity without using standard sexual reproduction.
Doing it better
Not only are these salamanders of interest to scientists for their fascinating reproductive habits, but they have another interesting quirk. Most salamanders can regenerate their tails after they lose them to escape a predator. But scientists have found these unisexual salamanders are able to regenerate their tails 1.5 times faster than normal salamanders. The reason for this is unknown, but this makes them even more interesting to research as unlocking the secret to regeneration is of prime interest.
Clearly, there are benefits to this unique society of salamanders. And perhaps there are more secrets they can tell us as scientists continue their research.