A type of salamander has been found to mate with males from three different species, and then use their genes in equal parts to produce offspring, which all happen to be females.
While you may have been told at school that species are defined by their ability to mate with other organisms and create fertile offspring, there are plenty of examples that tend to bend this rule and the Ambystoma salamanders in parts of North America are a prime example of this. Populations of these salamanders form a bit of a biological oddity, in which some form all female hybrids.
This is where things get a little complicated. Typically found living in the regions surrounding the Great Lakes in North America, the hybrids mate with multiple males from up to five different species, and then things get even weirder. Some of the hybrids will eject the sperm from their eggs, requiring it only to initiate development of the embryo. But other hybrids will take some of the male's DNA, and incorporate it into their offspring, while still only producing females.
This latest study looking into these hybrid salamanders has focused on one of the latter types, which mates with, and takes some genes from while discarding others, three different species of salamander, principally the blue spotted (Ambystoma laterale), small-mouthed (Ambystoma texanum), and tiger salamander (Ambystoma tigrinum). This behavior has been termed “kleptogenesis”, literally meaning to steal genes.
Researchers decided to see exactly which bits of DNA were being taken and used from which species when these hybrid females mated, and found to their surprise that the female hybrids were seemingly using equal parts of genetic material from each male. They think that this balancing of the genome may in some way increase their chances of success, and therefore going on to have other offspring.
“We’re hypothesizing the successful individuals have balanced gene expression,” explained Maurine Neiman, co-author of the paper published in Genome Biology and Evolution. “This balance might have been a prerequisite for the emergence and continued success of this particular hybrid lineage.”
The researchers liken this balancing of the genes to having a sports team made up of equally competent players. If you had an unbalanced sports team and your top player gets injured and can’t play then the team will inevitably lose. The researchers theorize if the salamanders have an unbalanced genome and something happens to the main section of DNA, the amphibians fitness is compromised. By taking an equal number of genes from each species, they are spreading their losses.
How the hybrid salamanders manage to pick the genes from each species is still unknown. In fact, it’s not even certain that the females can control this process. The researchers hope to investigate this next.