Lizards develop new chemical language to attract mates in predator-free environments

Researchers decoded the love signals of lizards "spoken" through chemical signals.

Photo Credit: Colin Donihue
  • Scientists discovered that lizards developed novel chemical communication signals when relocated to tiny island groups with no predators.
  • Male lizards began to rapidly produce a new chemical love elixir, not unlike cologne, to call on potential mates.
  • With new technology we're increasingly able to detect and identify the chemicals that make up much of the language of non-human nature.


Most of our understanding of animal communication has come through observations of auditory and visual symbol, such as the guttural caws of a raven or the shifting color scheme on the skin of the chameleon. But the real Rosetta Stone for translating the language of nonhuman nature might be through chemical signals.

As scientists develop and utilize new technology that can detect on and decode these chemical dialects, we are just beginning to better understand what certain creatures are really saying to each other. Most recently, researchers discovered that lizards developed novel chemical communication signals when relocated to tiny island groups with no predators around. Specifically, male lizards began to rapidly produce a new chemical "come-hither" elixir to call on potential mates.

Discovery of lizard love language dialects

Agios Artemios was one of the islets that a lizard group was relocated to.

Photo Credit: Colin Donihue

Researchers from Washington University in St. Louis relocated 12 female and eight male Aegean wall lizards from a single source lizard population in Greece to five tiny islands with no predators. Under these happy conditions, the lizard population proliferated and competed aggressively—evidenced by bite scars—for resources. Researchers tagged each individual lizard so that they could be identified and checked up on over the course of four years.

As the scientists made visits back to the lizard populations to note how they and their offspring were doing, they made a exciting discovery. On each of the islands, the male lizards had made new chemical cocktails different from the chemical secretions of the lizards in the original source population. The changes had happened rapidly, becoming evident to the scientists after just four generations.

Could this be evidence that male lizards spruce themselves up with new, au naturale "cologne" when in new ecological settings? The researchers think so, pointing out that having no predators around likely made all the difference.

"Signals to attract mates are often conspicuous to predators," said Simon Baeckens, a postdoctoral fellow at the University of Antwerp in Belgium and co-author of the new paper, in a university news release. "As such, sexual signals present a compromise between attractiveness and avoidance of detection. However, on these islets, there is no constraint on the evolution of highly conspicuous and attractive signals."

In other words, with no snakes or other predators to clue in on their prey's potent chemical secretions, the male lizards could let loose on their love signals without worry.

"In the experimental islands, we found that the 'signal richness' of the lizard secretions is the highest—meaning that the number of different compounds that we could detect in the secretion is the highest," Baeckens added.

Though the researchers are still working to decode the signals, they note that previous research suggests that this more elaborate signal may advertise high "male quality" and possibly immune function to both lure females and tell other males to scram.

"Lizards deposit their chemical messages encoded in secretions from specialized glands located on their inner thighs," reported Talia Ogliore for Washington University. "The secretions are a waxy cocktail of lipid compounds that contains detailed information about the individual lizard that produced them."

Lizards are able to collect those chemical messages from their environment by rapidly flickering out their slim, nimble tongues. They process those cues via a sensory organ in the roof of their mouths.

Chemical dialects

Most chemical signals between animals fall out of the parameter of human perception, and are therefore more complex to examine. So when studying animal communicative signals, studies have typically prioritized sound and sight.

But chemical "language" is the oldest and most widely used communication mode in nonhuman nature. Life spanning from bacteria to plants to beavers all communicate through this medium. So research like this new paper on lizard love signals represents a valuable opportunity for deciphering ways that animals communicate and perceive the world around them.

"What we've discovered is that within species there is important variation in chemical signals depending on your context: Who's trying to eat you, who wants to mate with you and who you're trying to compete with," said Colin Donihue, a postdoctoral fellow in biology in Arts & Sciences at Washington University in St. Louis and lead author of the new study.

Donihue also pointed out that nonhuman species have spent more than a billion years developing complex chemical languages. Only relatively recently have humans been able to decipher those methods of communication.

"With new technology though we're increasingly able to detect and identify these chemical compounds and this is leading to exciting new possibilities for understanding how species interact and evolve," Donihue told Big Think. "As these chemical assays become more common, cheaper, and easier to conduct, I think we're going to find that there are chemical communicators in the plant and animal world that are every bit as exotic and impressive as the bright feathers or intricate birdsongs that are currently the subject of so much research."

This is likely just the beginning for gaining understanding as to what nonhuman beings, like lizards, are saying to one another right under our noses.

This research was published on April 21 in the Journal of Animal Ecology.

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The surprise reason sleep-deprivation kills lies in the gut

New research establishes an unexpected connection.

Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

Image source: Vaccaro et al, 2020/Harvard Medical School
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We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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