Promiscuity Means More Offspring for Female Salamanders

A study of the mating habits of female fire salamanders is the first to prove under natural conditions the benefit of multiple paternities.

For years, scientists assumed that females were monogamous and that males increased their reproductive success by mating with a variety of partners. Through new studies like this one, however, researchers are beginning to construct a world in which polyandry, or when females mate with a variety of males, is the rule and monogamy the exception.

The team, from Bielefeld University and the Technische Universität Braunschweig, captured pregnant salamanders while they were on their way to deposit their eggs and transferred them to their lab where the salamanders then laid their larvae. Each day, the scientists collected the larvae and returned both mothers and offspring to the forest.

Before sending them on their way, however, the researchers took a small tissue sample they used to run tests in order to determine how many males each female had mated with. Because female salamanders are able to store sperm from a variety of males in an internal organ, the researchers also ran tests to determine whether the sperm of different males had been mixed.

During courtship, male fire salamanders deposit their sperm on the ground in a packet the female then gathers, later deciding which one she wants to keep. Based on the analyses, the researchers determined that the females mated with as many as four different males, with the mixing of sperm from a variety of mates leading to more eggs being fertilized and, ultimately, more larvae.

"Accordingly," the press release outlining the study explains, "polyandry and sperm competition seems to be an important mechanism to increase reproductive success and therefore fitness of a female in this terrestrial vertebrate species."

The study was published in the journal Molecular Ecology.