Normally male animals are larger and stronger, but in salamanders the females have a secret weapon: they are much more poisonous than the males.

In animals, poison usually serves as a defense mechanism, but in the rough salamander it may also play a role in the search for a suitable partner, it appears. from research in salamanders in California.

Long tail
The rough salamander, officially Find granulosa is called, consists of more than half of the tail and grows to a total length of 12 to 22 centimeters. It has rough, grainy skin, hence the name rough salamander. The familiar spots and patterns are missing: the animal is brown above and yellow below. When threatened, it curls up, revealing its yellow belly. This warning is not unwarranted. Many salamanders are poisonous, but the rough salamander takes the cake. It is even deadly to humans. Only the common garter snake is immune to the powerful neurotoxin tetrodotoxin, which is also found in other highly venomous animals such as the pufferfish and the great blue-ringed octopus. Rough salamanders live along the coast from southeastern Alaska to California.

Toxic females
Until now, little was known about how salamanders produce venom and what its precise purpose is. The first step to solving this puzzle is to see if males and females have the same amount of the substance in them. In animals that reproduce through sex, external differences, such as color, body size or teeth, are often very important to stay alive and reproduce effectively. If one sex produces more poison than the other, that says a lot about its usefulness.

“We have long thought that venom levels in salamanders do not change during their lives and that males and females have approximately the same amount of venom in their skin. But that turns out not to be the case. We discovered that female salamanders carry much more venom than males,” said researcher Gary Bucciarelli of the University of California Davis. “We have seen that there are large fluctuations in the venom concentrations of females. That could have all kinds of reasons. For example, it can help in the search for a suitable partner.”

Not too close to the skin
The researchers already knew that rough salamanders were sexually dimorphic in other areas, such as tail height, size and weight. The tetrodotoxin oozes from the salamander’s skin, so the team was able to easily take samples from more than 850 salamanders at 38 different sites in California. They noted the sex, mass, size and tail height of each salamander, and whether the females were pregnant. Each salamander examined was marked so that they were not tested twice. The salamander skin was analyzed for venom strength. Ultimately, it was very clear that venom production differed in males and females and that there was therefore a sexually dimorphic trait.

Deadly snack
The females produce much more poison. The venom content of females also fluctuated more than was the case among the group of males. The heavier the salamander, the more toxins it contains. “For predators, these higher concentrations mean a greater danger,” says Bucciarelli. He confirms that female salamanders are more dangerous than males. “Rough newts should only be handled by professionals as they can contain up to 54,000 micrograms of tetrodotoxin per animal. When an unfortunate animal ingests this potent toxin, it can lead to hospitalization or death. A dose of 42 micrograms per kilo of body weight is already potentially fatal.”

The question remains why females produce more venom. A possible explanation is that they are more vulnerable during the reproduction period. The abundance of poison may also make it possible for the females to transfer poison-producing bacteria to their eggs, so that the offspring receives protection from day one through the nerve poison.

Complex roles
The differences between the sexes and the fluctuating poison levels make it clear that we are not just dealing with a defense mechanism, but that there is a more complex role for the tetrodotoxin. For example, it seems that the toxin acts as a guide in the search for a suitable partner. “The breeding patterns of the rough salamander are highly dependent on precipitation patterns,” says Bucciarelli. “Due to the extreme drought in California, the collection of samples has not been very balanced, but we still have the feeling that the pattern is holding up very well. Our next plan is to investigate what the drought and forest fires are doing to the rough salamanders and their venom concentrations. We are very curious to see how the males and females behave in the midst of these types of natural disasters.”

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