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Some dark chocolates contain heavy metals. Should you be concerned?

News Feed
Wednesday, July 31, 2024

An eight-year study conducted by researchers at George Washington University and ConsumerLab, a company that tests and evaluates health foods and supplements, found certain dark chocolates and cocoa products contain amounts of lead and cadmium that are above California’s strict regulations on the heavy metals.“The amount of lead that was found, in general, was not alarming,” said Leigh Frame, the co-lead author of the study and the executive director of the office of integrative medicine and health at George Washington University. “But most people probably don’t have a great handle on what their heavy metal exposure is.”The study’s findings are not a reason to stop eating dark chocolate, Frame said. Some studies suggest flavonoids found in dark chocolate may lower the risk of heart disease and high blood pressure.But these small exposures to heavy metals, plus other exposures in an individual’s diet, could amount to higher blood lead levels over time. “And that is something that we all need to be aware of,” Frame said.“I would not want someone to be afraid of chocolate. That would be the worst thing that could come out of the study to me,” she said. “Frankly, it’s a small contributor to our diet.”The factsConsumerLabs selected cocoa products to test largely using a ranked survey completed by thousands of respondents on the company’s website every year, the researchers write in the study.ConsumerLabs purchased the products and paid for them to be tested at two independent labs, Frame said. Researchers at George Washington University analyzed the results, without knowing the names and brands of the products that were tested.Forty-three percent of the 72 cocoa-containing products had amounts of lead that exceed California’s maximum allowable dose level for the heavy metal, which is 0.5 micrograms per day. Thirty-five percent of the products had amounts of cadmium that exceed California’s rules.Seventy of the 72 products tested contained amounts of lead lower than the Food and Drug Administration’s benchmark of 2.2 micrograms per day for children. The benchmark is set nearly 10 times lower than the amount of lead from food required to meet the marker the Centers for Disease Control and Prevention uses to identify high blood lead levels.Some samples had “much higher” levels of lead and other heavy metals detected; there was “a bit of variability” in dark chocolate and other cocoa products, Frame said. One sample tested had 3.13 micrograms of lead per serving, the highest detected in the study.The researchers say the heavy metals detected “may not pose any appreciable risk for the average person when consumed as a single-serving.”Jacob Hands, the co-lead author of the study and a medical student at George Washington University School of Medicine and Health Sciences, said the researchers chose California’s regulation for the analysis because it is a conservative estimate. Frame also said the state’s regulation is what is generally used in other studies.The study was published in the journal Frontiers in Nutrition on Wednesday.Hands is a contract researcher for Consumer Labs.BackgroundThe George Washington University study follows the findings of a 2022 investigation by Consumer Reports that detected cadmium and lead in all of the 28 dark chocolate bars tested, as well as follow-up testing of 48 cocoa-containing products in 2023.In response to questions about the GWU study, an FDA spokesperson said, “while the presence of cadmium and lead in chocolate has been the subject of considerable media attention, experts from around the world have found that chocolate is a minor source of exposure to these contaminants internationally.”Chocolate, or cocoa, has been historically used as a medicine to treat fatigue and improve digestion. And studies suggest flavonoids found in cocoa can lower the risk of heart disease, high blood pressure and diabetes. But the type of chocolate matters; darker chocolate often contains higher amounts of cocoa and more flavonoids.Chronic exposure to lead and cadmium is associated with kidney dysfunction and other health problems. Infants, young children and pregnant people can be particularly vulnerable because prolonged lead exposure in early development has been associated with a higher risk of learning disabilities or lower IQ levels.Young children in the United States are eating and drinking far less lead than they did decades ago — from 43 micrograms per day in 1980, to around 1 microgram per day in 2016 — according to the FDA.However, lead contamination in food products remains a concern. In the fall, the FDA warned of “extremely high” levels of lead detected in three brand names of cinnamon applesauce puree pouches. And the agency continues to send public health alerts recommending that consumers stop using and dispose of certain ground cinnamon products contaminated with lead.Frame said the good news is kids generally don’t like eating dark chocolate. The darker the chocolate, the more the cocoa powder and the potential for higher amounts of lead, cadmium or other metals.“I don’t think we need to worry as much about kids,” Frame said.And cocoa powders — such as mixes used for hot chocolate — are often more akin to milk chocolate with less raw cocoa than dark chocolate, she said.What the industry saysChristopher Gindlesperger, the senior vice president of public affairs and communications for the National Confectioners Association, the trade organization for the candy industry in the United States, said chocolate and cocoa are safe to eat, and food safety and product quality “remain our highest priorities.”“Consumers understand that chocolate and candy are occasional treats and not center-of-the-plate foods,” Gindlesperger wrote in an email.Why are heavy metals in dark chocolate?Cadmium in the soil can transfer into a cacoa tree growing there, leading to a “natural contamination,” said Tewodros Godebo, an assistant professor of environmental health sciences at Tulane University School of Public Health and Tropical Medicine.Lead, though, appears to be introduced during the production of cocoa products, not from the soil, but potentially during drying, processing or packaging, Godebo said.What other experts are sayingKatarzyna Kordas, an associate professor of epidemiology and environmental health at University of Buffalo, said in an email that the study’s findings demonstrate “not all chocolate or cocoa products are created equal.” Some contain more metal than others.The amount of a metal someone is exposed to is a function of how much of the contaminant is in the food, how much the person consumes and whether they’re eating on an empty or full stomach, Kordas said. “We tend to absorb proportionally more metals on an empty stomach,” she said.But the amount of lead or cadmium detected in the study is often below stringent reference values and that suggests “the level of concern may be low,” Kordas said.Godebo said California’s regulations on heavy metals are “very conservative,” making it difficult to translate what the amounts of cadmium or lead mean for the general population. People are exposed to metals every day, and other types of foods, vegetables and fruits can be more significant sources of heavy metals, he said.“Of course, we want a negligible amount of exposure,” Godebo said. “But, literally, it’s impossible.”In a study published in June, Godebo and other researchers at Tulane University tested 155 dark and milk chocolates for lead and other heavy metals and concluded eating one ounce of dark chocolate a day “poses no health concerns for adults.” The researchers also determined four of the chocolate bars tested had cadmium levels that could pose a risk to young children.“What we’ve found is that it’s quite safe to consume dark and milk chocolates,” Godebo said in a statement in June about the study.Should I eat dark chocolate?Frame said she continues to eat chocolate.People can eat a diverse diet of different foods to reduce any potential exposure to lead, or other heavy metals, from a part of their diet, Frame said.Anyone concerned about their exposure to lead, cadmium or other metals should ask their physician for a blood test, Frame said. “Then you’ll have a ground truth,” to determine whether relatively small exposures in your diet could be adding up to higher blood lead levels.“I think it’s pretty clear, actually, that having one ounce of chocolate a day is not detrimental,” Frame said. But people can be cognizant of how much they’re having and how often, she said.Frame said she eats chocolate every other day.“It makes it feel more like a treat,” she said.

Researchers discovered lead and cadmium in tested cocoa products, but the levels are not alarming, they said.

An eight-year study conducted by researchers at George Washington University and ConsumerLab, a company that tests and evaluates health foods and supplements, found certain dark chocolates and cocoa products contain amounts of lead and cadmium that are above California’s strict regulations on the heavy metals.

“The amount of lead that was found, in general, was not alarming,” said Leigh Frame, the co-lead author of the study and the executive director of the office of integrative medicine and health at George Washington University. “But most people probably don’t have a great handle on what their heavy metal exposure is.”

The study’s findings are not a reason to stop eating dark chocolate, Frame said. Some studies suggest flavonoids found in dark chocolate may lower the risk of heart disease and high blood pressure.

But these small exposures to heavy metals, plus other exposures in an individual’s diet, could amount to higher blood lead levels over time. “And that is something that we all need to be aware of,” Frame said.

“I would not want someone to be afraid of chocolate. That would be the worst thing that could come out of the study to me,” she said. “Frankly, it’s a small contributor to our diet.”

The facts

  • ConsumerLabs selected cocoa products to test largely using a ranked survey completed by thousands of respondents on the company’s website every year, the researchers write in the study.
  • ConsumerLabs purchased the products and paid for them to be tested at two independent labs, Frame said. Researchers at George Washington University analyzed the results, without knowing the names and brands of the products that were tested.
  • Forty-three percent of the 72 cocoa-containing products had amounts of lead that exceed California’s maximum allowable dose level for the heavy metal, which is 0.5 micrograms per day. Thirty-five percent of the products had amounts of cadmium that exceed California’s rules.
  • Seventy of the 72 products tested contained amounts of lead lower than the Food and Drug Administration’s benchmark of 2.2 micrograms per day for children. The benchmark is set nearly 10 times lower than the amount of lead from food required to meet the marker the Centers for Disease Control and Prevention uses to identify high blood lead levels.
  • Some samples had “much higher” levels of lead and other heavy metals detected; there was “a bit of variability” in dark chocolate and other cocoa products, Frame said. One sample tested had 3.13 micrograms of lead per serving, the highest detected in the study.
  • The researchers say the heavy metals detected “may not pose any appreciable risk for the average person when consumed as a single-serving.”
  • Jacob Hands, the co-lead author of the study and a medical student at George Washington University School of Medicine and Health Sciences, said the researchers chose California’s regulation for the analysis because it is a conservative estimate. Frame also said the state’s regulation is what is generally used in other studies.

The study was published in the journal Frontiers in Nutrition on Wednesday.

Hands is a contract researcher for Consumer Labs.

Background

The George Washington University study follows the findings of a 2022 investigation by Consumer Reports that detected cadmium and lead in all of the 28 dark chocolate bars tested, as well as follow-up testing of 48 cocoa-containing products in 2023.

In response to questions about the GWU study, an FDA spokesperson said, “while the presence of cadmium and lead in chocolate has been the subject of considerable media attention, experts from around the world have found that chocolate is a minor source of exposure to these contaminants internationally.”

Chocolate, or cocoa, has been historically used as a medicine to treat fatigue and improve digestion. And studies suggest flavonoids found in cocoa can lower the risk of heart disease, high blood pressure and diabetes. But the type of chocolate matters; darker chocolate often contains higher amounts of cocoa and more flavonoids.

Chronic exposure to lead and cadmium is associated with kidney dysfunction and other health problems. Infants, young children and pregnant people can be particularly vulnerable because prolonged lead exposure in early development has been associated with a higher risk of learning disabilities or lower IQ levels.

Young children in the United States are eating and drinking far less lead than they did decades ago — from 43 micrograms per day in 1980, to around 1 microgram per day in 2016 — according to the FDA.

However, lead contamination in food products remains a concern. In the fall, the FDA warned of “extremely high” levels of lead detected in three brand names of cinnamon applesauce puree pouches. And the agency continues to send public health alerts recommending that consumers stop using and dispose of certain ground cinnamon products contaminated with lead.

Frame said the good news is kids generally don’t like eating dark chocolate. The darker the chocolate, the more the cocoa powder and the potential for higher amounts of lead, cadmium or other metals.

“I don’t think we need to worry as much about kids,” Frame said.

And cocoa powders — such as mixes used for hot chocolate — are often more akin to milk chocolate with less raw cocoa than dark chocolate, she said.

What the industry says

Christopher Gindlesperger, the senior vice president of public affairs and communications for the National Confectioners Association, the trade organization for the candy industry in the United States, said chocolate and cocoa are safe to eat, and food safety and product quality “remain our highest priorities.”

“Consumers understand that chocolate and candy are occasional treats and not center-of-the-plate foods,” Gindlesperger wrote in an email.

Why are heavy metals in dark chocolate?

Cadmium in the soil can transfer into a cacoa tree growing there, leading to a “natural contamination,” said Tewodros Godebo, an assistant professor of environmental health sciences at Tulane University School of Public Health and Tropical Medicine.

Lead, though, appears to be introduced during the production of cocoa products, not from the soil, but potentially during drying, processing or packaging, Godebo said.

What other experts are saying

Katarzyna Kordas, an associate professor of epidemiology and environmental health at University of Buffalo, said in an email that the study’s findings demonstrate “not all chocolate or cocoa products are created equal.” Some contain more metal than others.

The amount of a metal someone is exposed to is a function of how much of the contaminant is in the food, how much the person consumes and whether they’re eating on an empty or full stomach, Kordas said. “We tend to absorb proportionally more metals on an empty stomach,” she said.

But the amount of lead or cadmium detected in the study is often below stringent reference values and that suggests “the level of concern may be low,” Kordas said.

Godebo said California’s regulations on heavy metals are “very conservative,” making it difficult to translate what the amounts of cadmium or lead mean for the general population. People are exposed to metals every day, and other types of foods, vegetables and fruits can be more significant sources of heavy metals, he said.

“Of course, we want a negligible amount of exposure,” Godebo said. “But, literally, it’s impossible.”

In a study published in June, Godebo and other researchers at Tulane University tested 155 dark and milk chocolates for lead and other heavy metals and concluded eating one ounce of dark chocolate a day “poses no health concerns for adults.” The researchers also determined four of the chocolate bars tested had cadmium levels that could pose a risk to young children.

“What we’ve found is that it’s quite safe to consume dark and milk chocolates,” Godebo said in a statement in June about the study.

Should I eat dark chocolate?

Frame said she continues to eat chocolate.

People can eat a diverse diet of different foods to reduce any potential exposure to lead, or other heavy metals, from a part of their diet, Frame said.

Anyone concerned about their exposure to lead, cadmium or other metals should ask their physician for a blood test, Frame said. “Then you’ll have a ground truth,” to determine whether relatively small exposures in your diet could be adding up to higher blood lead levels.

“I think it’s pretty clear, actually, that having one ounce of chocolate a day is not detrimental,” Frame said. But people can be cognizant of how much they’re having and how often, she said.

Frame said she eats chocolate every other day.

“It makes it feel more like a treat,” she said.

Read the full story here.
Photos courtesy of

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How Microplastics Get into Our Food

Kitchen items—sponges, blenders, kettles—are abundant sources of microplastics that we all consume

When Amy Lusher moved in with her partner, one of the first things she did was get rid of all the plastic kitchenware in their household and replace it with items made of glass, wood and stainless steel. As a senior researcher in microplastics at the Norwegian Institute for Water Research, Lusher was acutely aware of how all the chopping, whisking, scraping and heating we do when preparing meals may release tiny particles of plastic into the food we eat. “It’s coming from our cooking. It’s coming from our packaging. It’s in most of our bottles,” she says.By now scientists like Lusher have found microplastics coming off dishwashing sponges, blenders, kettles—you name it. According to one 2024 study, plastic cookware may contribute thousands of microplastic particles each year to homemade food. Old plastic kitchenware was the worst culprit, and the researchers also concluded that microplastic shedding may be exacerbated by heating cookware or using hard or sharp utensils on it.Researchers have been trying for years to determine how many microplastic particles humans ingest when consuming everything from seafood to beer to honey. According to one estimate, every American consumes between 39,000 and 52,000 microplastic particles every year.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Microplastics are tiny—smaller than five millimeters in size. Some are directly manufactured by humans, such as beads in exfoliating scrubs or glitter. Others result from environmental degradation of larger objects, such as plastic bottles or toys. “Microplastics are released in quantities far beyond human imagination,” says Lei Qin, a food scientist at Dalian Polytechnic University in China. By one estimate, 10 to 40 million metric tons of microplastics are released into the environment per year—about two to six times the weight of the Great Pyramid of Giza.They then accumulate inside our body. Studies have found microplastics in human brains (roughly the amount in a heaping teaspoon of table salt), as well as in our stomach, lungs and bones. Researchers have linked microplastics with a higher risk of stroke, inflammatory bowel disease and dementia. “We are at an early stage, but there is growing evidence that exposure to microplastics is linked to inflammation, coronary artery disease and neurodegenerative impairment,” says John Boland, a chemist at Trinity College Dublin. And although scientists have been looking for a while now at how much microplastic we may be ingesting with seafood or tap water, “it’s only really been in the last few years that we’ve started looking at exposure through things that we touch, things that we handle, especially in the kitchen,” Lusher says.To explore what is it exactly that happens with plastics in the kitchen, Lusher and her colleagues from the U.K. and Norway prepared jelly. They used either old or new plastic cookware to heat water, stir the jelly mixture, store it, chill it and cut it into pieces. The result: jelly prepared with new plastic cookware had about nine microplastic particles per sample on average, and jelly made with the old plastic cookware had 16. In other words, when jelly was made with worn-out items, it had 78 percent more microplastics than when it was prepared with new ones. "[Old cookware items] tend to release more plastic, probably because they’ve already become brittle,” Lusher says.Other research also lends evidence that wear and tear generates high levels of microplastic particles. Take cutting boards: in one study, when plastic boards were used to cut meat, up to 196 microplastic particles were incorporated into each ounce of meat, while none were found in meat that had been prepared on a bamboo board. Slicing ingredients and pushing a knife along the board to move them may also be worse than simply pressing with a knife to chop them, another study showed. “It’s the friction, the metal against the plastic,” Lusher says.Friction is also the mechanism by which blenders with plastic jars can release large amounts of microplastics. When scientists in Australia used a blender to crush ice blocks, the way you might when making, say, a frozen margarita, they found that billions of plastic particles were released in just 30 seconds of blending. “If the ice block has a sharp edge, like some hard food, it can peel off lots of plastic,” says Cheng Fang, a chemist at the University of Newcastle, Australia, and the study’s senior author.Scrubbing dishes with a sponge can also release hundreds of tiny plastic particles in just 30 seconds. The good news is that rinsing the dishes well afterward removes most of the residue. The bad news: the sponge microplastics go down the drain and accumulate in the environment, so they may end up in our food anyway.Opening and closing plastic bottles—which also creates friction—can also generate microplastic residues. “You’re shearing off plastic pieces all the time,” Boland says. In fact, according to one study, most microplastics in bottled water originate from twisting the cap. Each time you open and close a plastic bottle, the study found, you produce about 500 microplastic particles.Heating plastic kitchenware is a source of particles as well. Warming it up, like you may do in a microwave, Boland says, “dramatically accelerates the release of microplastics.” In a 2025 study, disposable plastic cups that were filled with scalding 95-degree-Celsius water released 50 percent more microplastics than cups filled with cooler, 50-degree-C water. Plastic kettles, too, could be a problem. The simple act of boiling water in a new kettle will leave you with between six million and eight million microplastic particles per cup, Boland and his colleagues found. Fewer and fewer particles are released with each successive use, however. In their study, after 40 boils in the kettle, only 11 percent of the initial microplastic load leached into the water.While it might be tempting to compare the numbers of microplastics released from various sources side by side, Lusher warns that it would be like comparing “apples to pears.” That’s because, she says, different labs use different methodologies: some count only larger microplastics, and others include nanoplastics (particles smaller than 0.001 mm). Some control for lab microplastic pollution, and others don’t. “If the handling of the data is totally different between each study, then there’s absolutely no point comparing it,” she says.Lusher says that this absence of methodological standards makes it hard to clearly identify the worst microplastic offenders in our kitchens. It still makes sense to “try to reduce the amount of plastic that we are exposed to,” simply because “we still don’t know what the long-term effects will be on health.”There are a few things you can do as well to lower the microplastic load produced in your kitchen. First of all, replace any plastic cutting boards with wooden ones if possible, and if you have a plastic kettle, consider swapping it for a stainless-steel product. (Make sure the lid is not plastic.) Substitute plastic storage containers with glass ones. If you do buy a new plastic kettle, boil and pour out the water in it a couple of times before preparing your first hot drink. And if you use plastic cutting boards, try to make sure they are relatively new.From a broader perspective, we could develop plastics that don’t shed easily into food. “If there are no alternatives, what can you do to the plastic to make it safer?” Boland says. Potentially, for example, manufacturers could create kettles with an inner lining that would prevent microplastic leakage during boiling. (Boland’s experiments suggest that it could be possible.) While such safer products may be technically feasible, he says, substantive change likely won’t happen without regulations that push the industry to make better plastics. “We need the regulators to drive industry to do the right thing,” he says.

Food
Health
Science

Amazing iguanas conquered Fiji after a 5,000-mile journey

Iguanas are incredible reptiles that can live without food or water for long periods of time. They rafted 5,000 miles from North America to Fiji and Tonga. The post Amazing iguanas conquered Fiji after a 5,000-mile journey first appeared on EarthSky.

Watch a video about how iguanas floated 1/5 of the way around the world to colonize Fiji. Thumbnail image via Bjørn Christian Tørrissen/ Wikipedia (CC BY-SA 4.0). For many years, scientists have wondered where the iguanas that inhabit the remote and isolated islands of Fiji and Tonga came from. Finally, a team of researchers from the University of California, Berkeley, and the University of San Francisco said on March 17, 2025, they have an answer. These reptiles likely arrived on the islands by rafting from western North America. This means the iguanas traveled 5,000 miles (8,000 km) on natural rafts across the Pacific Ocean. To solve the mystery, the researchers analyzed the DNA of more than 200 iguana specimens from museums around the world. They also discovered that the iguanas arrived on the islands about 34 million years ago, either as soon as the islands formed or shortly afterward. The scientists published their study in the peer-reviewed journal Proceedings of the National Academy of Sciences on March 17, 2025. Simon Scarpetta, the study’s lead author, is a herpetologist and paleontologist, former postdoctoral fellow at UC Berkeley, and current assistant professor in the USF Department of Environmental Sciences. Fiji and Tonga iguanas broke a record Iguanas are fascinating animals: They can change color, detach their tails, have a third eye on top of their heads, know how to swim and can dive for 30 minutes. But traveling 5,000 miles (8,000 km) from the west coast of North America to these distant islands is a big deal. The four species that inhabit the islands of Fiji and Tonga have earned the well-deserved record for the longest known transoceanic dispersal of any non-human terrestrial vertebrate. These iguanas belong to the genus Brachylophus. Although iguanas commonly float on natural rafts made of fallen trees and plants – and transport themselves using this system – making such a long journey seemed impossible. Jimmy McGuire, co-author of the study and professor of integrative biology and herpetology curator at the Museum of Vertebrate Zoology, said: That they reached Fiji directly from North America seems crazy. There are 45 species of Iguanidae that live in the Caribbean and the tropical, subtropical and desert regions of North, Central and South America. Therefore, scientists looked for the origin of the Brachylophus genus in nearer locations. Central and South America seemed more likely options than North America. 2025 EarthSky lunar calendar is available. A unique and beautiful poster-sized calendar with phases of the moon for every night of the year. Get yours today! This is a male Fiji crested iguana. Image via Michael Howard/ Wikipedia (CC BY 2.0). The mysterious origin of Brachylophus iguanas Seeing iguanas floating on rafts in the Caribbean is a common sight. In fact, this is what happened centuries ago, when they embarked on a 600-mile (970-km) journey from Central America to colonize the Galapagos Islands. Scientists hypothesized that, if this had occurred previously, the iguanas could have continued their journey further to reach Fiji and Tonga from the western Pacific. Researchers also proposed the idea that they could have arrived from tropical South America, via Antarctica or Australia. However, there is no genetic or fossil evidence to support these hypotheses. According to McGuire: When you don’t really know where Brachylophus fits at the base of the tree, then where they came from can also be almost anywhere. So it was much easier to imagine that Brachylophus originated from South America, since we already have marine and land iguanas in the Galapagos that almost certainly dispersed to the islands from the mainland. This is a Fiji banded iguana at the Vienna Zoo in Austria. Image via Robert F. Tobler/ Wikipedia (CC BY-SA 4.0). Their origin confirmed! Previous genetic analyses of some iguanid lizard genes were inconclusive about the relationship of Fiji and Tonga iguanas to the rest. A few years ago, during his postdoctoral studies, lead author Simon Scarpetta began a detailed investigation of all Iguania genera with the goal of clarifying the group’s family tree. McGuire explained that: Different relationships have been inferred in these various analyses, none with particularly strong support. So there was still this uncertainty about where Brachylophus really fits within the iguanid phylogeny. Simon’s data really nailed this thing. Scarpetta compiled DNA from genomic sequences of more than 4,000 genes and from tissues of more than 200 iguana specimens found in museum collections around the world. When comparing these data, one result stood out clearly: Fiji and Tonga iguanas are closely related to iguanas of the genus Dipsosaurus. The most widespread of this genus is the North American desert iguana, Dipsosaurus dorsalis, adapted to the scorching heat of the deserts of the southwestern United States and northern Mexico. Scarpetta stated that: Iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, so my thought process is, if there had to be any group of vertebrate or any group of lizard that really could make an 8,000 kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one. This is a male Brachylophus bulabula at the Berlin Aquarium in Germany. Image via JSutton93/ Wikipedia (CC BY-SA 4.0). The origin of the islands and their colonization In addition to demonstrating that Brachylophus iguanas did indeed arrive from North America, the scientists also established that they reached Fiji and Tonga around 34 million years ago. They rejected alternative models involving colonization from adjacent lands because they didn’t correspond with this period of time. In fact, biologists had previously proposed that Fijian and Tongan iguanas could have descended from an older, more widespread lineage in the Pacific (now extinct). However, the dates did not match. This exhaustive analysis also explains when the genetic divergence of Brachylophus iguanas from their closest relatives, the North American Dipsosaurus desert iguanas, occurred. The study suggests that Brachylophus iguanas may have even colonized the volcanic islands of Fiji and Tonga as soon as land emerged 34 million years ago or shortly after their formation, thus diverging from Dipsosaurus iguanas. According to Scarpetta: We found that the Fiji iguanas are most closely related to the North American desert iguanas, something that hadn’t been figured out before, and that the lineage of Fiji iguanas split from their sister lineage relatively recently, much closer to 30 million years ago, either post-dating or at about the same time that there was volcanic activity that could have produced land. This is a female Gau iguana. Image via Mark Fraser/ Wikipedia (public domain). How did they get to the islands? Despite being very resilient creatures, it’s still surprising they were able to undertake this adventure. Dispersal over water is the main way newly formed islands are populated with plants and animals. And this is quite impressive. Let’s imagine the situation … A modern-day sailor using the wind to reach Fiji from California would need about a month to get there. Can you imagine how long it would take the iguanas floating on a raft? Fortunately, iguanas are accustomed to going long periods of time without food or water. On the other hand, the rafts they traveled on were likely made of fallen trees and other plants. Fortunately, iguanas are herbivores, and the raft itself would have provided them with food. The dispersal of animals often leads to the evolution of new species and entirely new ecosystems. Other islands besides Fiji and Tonga may have also hosted iguanas, but volcanic islands tend to disappear as easily as they appear. Evidence of other Pacific Island iguanas, if they existed, has likely been lost. So Fiji’s iguanas are an outlier, lying alone in the middle of the Pacific. Unfortunately, all four species from Fiji and Tonga are listed as critically endangered. This is primarily due to habitat loss and exploitation by smugglers who fuel the exotic pet trade. A Fijian crested iguana on at the Taronga Zoo in Australia. Image via Pelagic/ Wikipedia (CC BY-SA 4.0). Bottom line: Iguanas are incredible reptiles that can live without food or water for long periods of time. This allowed them to travel 5,000 miles from North America to Fiji and Tonga and conquer the islands. Via University of California, Berkeley Source: Proceedings of the National Academy of Sciences Colorful iguanas are our lifeform of the weekThe post Amazing iguanas conquered Fiji after a 5,000-mile journey first appeared on EarthSky.

Food
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Extinction

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