https://phys.org/news/2018-07-unisexual-salamander-evolution-strange.html

First, a bit about the unisexual Ambystoma salamander: They're female, and they reproduce mainly through cloning and the occasional theft of another salamander 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.

Scientists who study these amphibians and their relatives, which are also called mole salamanders, have theorized that the theft of sperm is part of what has kept the unisexuals around so long. If all they ever did was clone themselves, biologists reason, they'd be vulnerable to all kinds of problems that unfold when you don't mix up the DNA pool and would disappear from the earth fairly quickly.