Fierce competition can poison the breeding pool for some males.
Newts of the genus Taricha have a potent neurotoxin known as TTX flowing through their veins and seeping out of their skin.
Though it’s been assumed that the high concentrations of TTX observed in some newt populations have evolved as a sort of armor against predatory garter snakes, mismatches between snake resistance and newt toxicity suggest that TTX serves other functions.
Newts are known to return to precisely the same breeding site year after year, which is a useful way to ensure that they breed in a safe spot while reducing the time spent in search of a breeding site. However, years of intensive study of California newts has revealed that rather than remaining faithful to their previous breeding site, some newts move into new breeding pools from one year to the next.
A group of researchers, led by Gary Bucciarelli from UCLA, wondered if newts might actually assess the TTX levels of themselves and others to help guide their decisions about where to breed.
Based on prior observations that larvae flee and seek refuge when potentially cannibalistic adult newts release the toxin, the researchers proposed that TTX might also warn adults about potential competitors.
Competition is fierce on the breeding grounds for male newts, who outnumber females 10:1. Bucciarelli describes how male newts will form a large aggregation around a female. “We call this a mating ball and it looks exactly like it sounds. All the males are attempting to out manoeuvre one another and wrestle the female away from the other males. This can go on for days,” he told The Science Explorer.
When they measured the concentrations of TTX secreted by recaptured newts over a period of 5 years, the researchers found that males that had lower TTX levels than their competitors tended to abandon their breeding site and seek out a new one the following year. Their findings were published in the journal Proceedings of the Royal Society B.
Leaving the comforts of a previous breeding site is a big gamble for a newt. “One could imagine that a male that abandons a breeding pool with a lot of competition may have an opportunity to find a mate under better circumstances,” says Bucciarelli, noting that it is also possible that the male will find no mate, the females in the new pool will not like him, or that eggs will be produced but ultimately, won’t succeed.
The researchers were surprised by how strongly the TTX levels of competitors influenced the newts’ decision of where to breed the following year. But even more astonishing was the degree to which the toxin levels of individuals were found to fluctuate over short time scales, as these levels were previously thought to remain relatively stable.
Bucciarelli plans to further explore how these chemical defenses change through time and how widespread the response to TTX level is, completely undeterred by the extreme toxicity of the substance that he studies.
“The tissue sample that I take, which is approximately 2mm in diameter, can have enough toxin in it to poison me to death, as well as several other people too!” he says. “So, it is high risk, but newts are worth it.”
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