Every year, in late spring and early summer, female turtles will crawl out of the ocean from the moonlight, place eggs on the beach, often returning to beaches born many years ago.
Sometimes, when turtles appear to build nests, researchers like Julianna Martin are patiently looking at the shadows.
For her doctoral study, Martin, a PhD student at Central University in Florida, has been analyzing turtle tears. Yes, the turtle’s tears. So on a few summer nights in 2023 and 2024, she would bet on the beach and wait for the turtles to start laying eggs. At that time, she said, the reptiles entered a kind of “tr”, allowing scientists like her to collect samples including tears.
Martin told me that she would climb up the sand turtle with a foam swab and then wipe her eyes with the foam to absorb the chicken tears they emit. Turtles often shed tears to drive away excess salt. (As far as we know, they are not sad.)
Martin then brought the tears back to her lab for analysis.
This strange job has a purpose. Martin is checking for turtles tears to see if they contain specific bacteria. She said such discoveries could help unleash one of the biggest and most awesome mysteries in biology: how animals use the Earth’s invisible magnetic field to navigate.
The “Holy Grail” of Sensory Biology
After the little turtles hatched, they dug out of the sand and climbed into the ocean, where they embarked on an epic journey that could carry them thousands of miles into the sea. For example, the Loggerhead hatched in Florida swims on the Atlantic Ocean, arrives at islands near the Portuguese coast, and eventually returns to the beaches in Florida to build a nest as an adult.
It is worth noting that turtles usually return to Florida and even the same beach.
“These young turtles can still travel on their own and guide themselves even though they have never appeared in the ocean.” Kenneth Lohmanna biologist at the University of North Carolina at Chapel Hill studied turtle navigation.
Researchers like Lohmann learned that turtles, Many other speciesit seems to use the Earth’s magnetic field navigation. This is the subtle magnetic force produced by the molten metal core surrounding the earth, unlike the force around the magnet. The strength and direction of the field vary on the surface of the earth, making it useful for navigation. In addition, even if other space prompts (such as light) are not, there is a magnetic field.
However, it remains a mystery how animals feel these magnets. Decades of research have failed to improve the mechanisms of so-called magnetoreceptors or any dedicated organ that can sense magnetism. Robert Fitak, a consultant to Martin Already writtenit’s like knowing that animals can respond to vision, but can’t find any eyes.
“This is the last feeling we actually know nothing about,” Sensory Biologist Eric’s Guarantee Already said About magnetic injury. “The solution to the problem I’m going to talk about is the biggest holy grail in sensory biology.”
Scientists have proposed many theories about this method. All of them are total fools.
Popular theories are rooted in quantum mechanics and are very complex. The theory suggests that when certain photosensitive molecules called invisible pigments absorb light, they produce something called radical pairs—two separate molecules each and one unpaired electron. These two unpaired electrons are quantum entangled, which actually means that their spin states are interdependent: they either point in the same direction or opposite directions, and they ping in between.
This theory shows that the Earth’s magnetic field affects the spin state of these free radical pairs, which in turn affects the results of chemical reactions in animals. These chemical reactions (which theoretically explain them like their possible odor or visual effects) encode information about the Earth’s magnetic field. (If you want to dig deeper, I recommend watching This lecture or Read this article)
Another theory shows that animals have a large amount of magnetic substances, such as mineral magnetite, in their bodies. According to this theory, these magnetic positions are affected by the Earth’s magnetic field (like a compass), and animals can feel these effects to find out where they are.
Martin and Fitek’s research is exploring this latter theory, but there is an important turning point. They suspect that turtles and other animals may rely on magnetite to sense Earth’s magnetic field, but may not produce the magnetite itself. Instead, they argued that turtles may have a symbiotic relationship with the bacteria that produce magnetite (actually living compass), thus sensing the magnetic field and somehow conveying the information to the turtle.
This is not an outrageous idea. Magnetic bacteria (technically, magnetic bacteria) are real and are common in aquatic environments around the world. In addition, there evidence Magnetic bacteria help navigation of another microbial organism called protozoa. The question is, can they help turtles navigation, too?
Magnetic bacteria are a thing
Magnetic bacteria are very cool. Caroline Monteil, a microbial ecologist at the French Institute CEA, said the microbial ecologist Monteil said the microbial organisms have basically built-in compass. The needle contains chains of magnetic particles produced by microorganisms, which you can see under a microscope (as shown below). It is worth noting that these needles, like real compass, keep bacteria consistent with the Earth’s magnetic field lines. As bacteria roam, they are in line with the direction of the planet’s magnetic force.
Magnetic sensing is useful for bacteria, said Fitak, an assistant professor at UCF. Magnetic bacteria require specific levels of oxygen to survive, and these levels tend to vary with depth. For example, deeper sediment levels in streams may have less oxygen. In most parts of the world, the direction of the magnetic field is at least perpendicular to the Earth’s surface – meaning, up and down – allowing bacteria to move vertically through their environment to find the best habitat, as if they were on a fixed track.
In at least one case, magnetic bacteria work with other organisms to help them find their own way. one Excellent research A discovery published in 2019, microscopic organisms in the Mediterranean are called organisms because their bodies are covered by magnetic bacteria and therefore able to sense magnetism. When the authors place the north pole of the rod magnet next to the droplets filled with creatures, they swim towards it. The abortion wandered away as they flipped the magnet. (Different magnetic microorganisms are attracted to the North Pole or the South Pole, usually depending on where they live.)
You can actually see this in the video below.
Monteil, the study’s lead author, said it’s unclear how magnetic bacteria actually guide protozoa.
Now, back to the turtle: The theory Fitak and Martin explored is that like protozoa, turtles may also contain magnetic bacteria in their bodies—those living compass, and somehow able to read them. Some microorganisms in the microbiome help digestion. Others provide instructions. perhaps.
One idea, Martin said, is that bacteria can gather near nerves in turtles to provide information about their spatial location. Some of the nerves are close to the tearing pipe, which is ultimately why she crawled on the beach to collect turtle tears. The goal is to figure out whether the tears contain magnetic bacteria, she said. This suggests that these animals may be using bacteria for navigation.
“We’re not sure how magnetic bacteria promote magnetic induction, but this seems like a good starting point,” Martin said.
Although her research is still ongoing, Martin has not found evidence of the magnetic bacteria in the tears of 30 tortoises she has analyzed so far. It was disappointing, she said, but it did not rule out the possibility that these bacteria would exist in the turtles and help them navigate.
“There are many other ideas about how magnetic bacteria can provide information about the Earth’s magnetic field to organisms,” she said. “There are a variety of other locations and other taxa that might better study this theory.”
Other scientists studying animal navigation are skeptical.
Monteil said symbiosis with magnetic bacteria is unlikely to be what makes sea turtles navigate. Part of the problem is that there are no known mechanisms to communicate with the turtle. It is unclear if it is indeed a symbiotic, magnetic bacteria will stand out from this relationship – can turtles provide the conditions required for bacteria to survive? perhaps. Maybe not.
More importantly, Montel says magnetic bacteria are widely present in the environment, so even if Martin does find them in turtle tears, it will not help prove this theory. Just because the presence of magnetic bacteria does not mean they are helping the animal navigate.
But then again, other theories are completely unproven – some of them are strange.
“I don’t think it’s impossible,” Montyre said of sea turtles and other organisms that use magnetic bacteria for navigation. “Nothing is impossible. Life is amazing and has found ways to do things we could not have imagined before.”
“We didn’t know until we knew.”
