Female toxin-producing newts are surprisingly more poisonous than males
Female Taricha newts produce more tetrodotoxin than males, suggesting it could be a signal as well as a defense
Tetrodotoxin, the neurotoxin that makes a blue-ringed octopus deadly, also protects Taricha newts — but we don’t understand how they produce it, or what purposes it serves for them. A first step to answering these questions is understanding whether different levels appear in males and females. In sexually reproducing animals, dimorphic traits such as color or canine tooth size can be key for survival and reproductive fitness. Investigating whether toxin production is a sexually dimorphic trait in newts gets us closer to understanding it.
“It had long been considered that newts’ toxin concentrations do not change in their lifetime and that males and females tend to have the same toxin concentrations. Now, we have shown that female newts actually contain more toxin than male newts,” said Dr Gary Bucciarelli of the University of California Davis, corresponding author of the article in Frontiers in Amphibian and Reptile Science. “We observed significantly greater and more drastically fluctuating toxin concentrations in females, which may have numerous causes, like mate selection.”
A toxic trait
The scientists already knew that Taricha newts were sexually dimorphic in other traits, like tail height, size, and mass. The tetrodotoxin seeps from the newts’ skin, so they took small samples from more than 850 newts across 38 different sites in California. They recorded sex, size, mass, and tail height for all newts, and whether female newts were pregnant. They also marked newts that had been captured and released so they would know which newts had previously been sampled.
They analyzed the skin to quantify the levels of toxin present and compared this between males and females. They also analyzed the relationship between the variables already known to be sexually dimorphic and toxin levels, and how toxin levels changed at sites where it was possible to sample more than once across the breeding season.
The female is deadlier than the male
They found that females carried more toxin than males. The differences in levels produced by females were not significant, compared to those between females and males. Males and females’ levels fluctuated at the same times and in the same direction, but the change in females’ levels of toxin was greater.
“For would-be predators, these higher concentrations pose a serious threat,” said Bucciarelli, confirming that this means female newts are more dangerous than males. “Taricha newts should not be handled unless by knowledgeable personnel, because they can contain up 54 milligrams of tetrodotoxin per individual. Doses up to 42 micrograms per kilo of bodyweight can lead to hospitalization or death.”
Tetrodotoxin also appeared to interact with other sexually dimorphic traits, suggesting that there may be a cost to high toxin levels: heavier newts produced higher levels of the toxin than lighter newts. The median concentration of toxin was always higher in females regardless of size or weight.
The females’ higher levels of toxin, and the similarity of levels between different females, indicates that the mechanisms of toxin production could be different between the sexes. It’s possible that resources needed to produce the toxin are invested differently by females, or females’ skin may be able to carry more toxin. Higher levels of toxin could protect females that are vulnerable while reproducing, or they may make it possible for females to transfer toxin-producing bacteria to eggs, potentially protecting their offspring.
Pick your poison
Although the toxin has previously only been thought of as a defense against snakes, the sex differences and fluctuating levels of toxin suggest it may have a more complex role. For example, the toxin may act as a cue that helps newts decide where they seek mates and which mates they choose.
“Taricha newts’ breeding patterns are highly dependent on precipitation patterns,” said Bucciarelli. “Given the drought conditions of California, we did not always have a balanced design when field sampling. However, we feel the pattern is still very strong.”
“Our next plan is to explore how drought and fire affect newts and their toxin concentrations and how each sex responds to these natural disasters.”
JOURNAL
Frontiers in Amphibian and Reptile Science
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
An amphibian toxin phenotype is sexually dimorphic and shows seasonal concordant change between sexes
ARTICLE PUBLICATION DATE
28-Nov-2023
COI STATEMENT
The authors GB, LK declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision
Yale study gives grandmother gecko a place of honor — and a new name
Peer-Reviewed PublicationNew Haven, Conn. — Yale paleontologists have identified a new fossil lizard, found in the western United States, which they say was an ancestor of modern geckos. And they gave it a name that honors the lead researcher’s grandmother and great aunt.
The discovery of the new species, which they named Helioscopus dickersonae, suggests that gecko ancestors appeared in North America much earlier than previously known.
“This discovery emerged from a larger investigation of two fossil lizard skulls from Dinosaur National Monument in Utah,” said Dalton Meyer, a graduate student in Yale’s Department of Earth and Planetary Sciences and first author of a study in the journal Proceedings of the Royal Society B.
“These skulls had both been previously described as part of a European genus of skink ancestors, but we wanted to investigate that further with 3D data,” Meyer said.
Specifically, Meyer and his colleagues used computed tomography (CT) scans to develop 3D images of the skulls, which both dated back to the late Jurassic period, 163.5 to 145 million years ago. While one of the skulls was indeed an early skink, the researchers found, the other was not.
“It is one of the earliest known gecko relatives in the fossil record,” Meyer said. “This means that the gecko line made it to North America nearly 100 million years before the prior known earliest record.”
Scientifically, the discovery also offers vital information about specialized physical features of the gecko skull and how they developed. For example, unlike modern geckos, Helioscopus dickersonae was not primarily nocturnal. It had a prominent pineal foramen — a hole in the top of its head that many lizard species use to sense sunlight and judge the length of daylight hours.
Helioscopus dickersonae, Meyer said, was likely similar in appearance to banded geckos or leopard geckos, in that it didn’t have the adhesive toe pads that many modern geckos have. Based on more complete fossil skeletons from similar species found in Europe, he speculated that Helioscopus dickersonae may have been a skilled tree climber even without the toe pads.
Yet much remains unknown about how this early gecko fared in North America, other than the fact that it went extinct sometime within 90 million years of its arrival on the continent. Nothing like Helioscopus dickersonae appears in the fossil record in the Cretaceous period, which followed the Jurassic.
In naming the new species, Meyer chose “helioscopus,” which roughly translates into “sun watcher,” and “dickersonae,” which honors his grandmother, Helen Dickerson, his great aunt, Shirley Dickerson, and Mary Cynthia Dickerson (no relation), who was the first curator of herpetology at the American Museum of Natural History in New York City.
“Both my grandmother and great aunt were extremely important people in my life, and my great aunt passed away while I was in the early stages of working on this fossil,” Meyer said. “I was truly honored to have a chance to get to use their family name in this new species, in part as a memorial that will now persist long after I am gone.”
Co-authors of the study are Yale graduate students Chase Brownstein and Kelsey Jenkins. The study’s senior author is Jacques Gauthier, professor of Earth and planetary sciences in Yale’s Faculty of Arts and Sciences and curator-in-charge for reptiles at the Yale Peabody Museum.
JOURNAL
Proceedings of the Royal Society B Biological Sciences
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