Animals that Sequester Toxins from their Diet

Animals that sequester toxins from their diet

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You’re probably aware that many animals are toxic or poisonous but did you know that not all toxic animals naturally produce these dangerous chemicals? In fact, there are some creatures that sequester toxins from the foods they eat which they can then put to good use for things like hunting or self-defense.

What is Toxin Sequestration?

What is toxin sequestration?
Poison Dart Frogs, like the Dyeing Poison Frog (Dendrobates tinctorius), Sequester Toxins from their Diet

The term toxic sequestration is used to describe a process whereby animals will accumulate toxins from the foods they eat and then store them in their bodies for later use. These toxins are often stored within the animal’s tissues and it’s been shown that even though a toxin may only be produced by one organism, it can become abundant within an ecosystem where other animals are feeding on it.

One of the primary reasons that toxic sequestration exists is for protection. Some animals may have limited self-defense tactics but by storing toxins from their diet, they’re able to repel predators. This is often demonstrated in the form of a bad taste. When predators attempt to eat these toxic sequesters, they’re met with a bitter taste that they eventually learn to avoid.

However, some animals will also use this to their advantage when hunting by mimicking the toxins produced by their own prey. This allows them to enter an environment where prey is abundant without being detected before going in for the kill. Many animals use chemicals as a form of communication. When these are sequestered by another animal, it allows them to influence their interactions with these species.

In some cases, the toxins are not used for either self-defense or predation but the animal may gain antimicrobial benefits and other advantages.

The toxins can come from a variety of food sources including the consumption of venomous or toxic prey. The animal then accumulates these toxins and stores them in its own body. You may wonder how the animal is not harmed by storing these toxins but they’re specially adapted with things like toxin sponges that absorb any excess and prevent the animal from coming to any harm.

As well as eating venomous animals, these creatures may also obtain toxins from the plants they eat and will often seek out these food sources to ensure sufficient accumulation of their chosen toxin. Plants often produce a wide range of chemicals like tannins, glycosides, and alkaloids, all of which are brilliant forms of natural defense. Even decaying plant matter found on the forest floor can contain toxins which can then be sequestered by maggots and other larvae.

Of course, how much of a toxin the animal requires differs between species but this is a phenomenon we see in everything from insects to amphibians and reptiles to birds. Each animal is perfectly adapted to its own needs so some may be much more toxic than others.

In a marine environment, animals may feed on aquatic plants and algae to obtain toxins but it’s also very common for them to sequester toxins from the microorganisms included in their diet. Look at the jellyfish or sea anemones, these creatures have stinging cells which can be sequestered by the fish and sea slugs that feed on them.

Evolutionary Significance of Toxin Sequestration

Evolutionary significance of toxin sequestration
Ladybugs Release Reflex Blood when Threatened, Containing Toxic Alkaloids Sequestered from their Aphid Diet

Animals must be able to adapt to their environment to survive and we see adaptations in many different forms. Toxin sequestration is a prime example of how certain animals have adapted to gain a competitive advantage over other species in their environments. This ensures that they’re able to survive and reproduce with as little risk as possible. Moreover, if a species has traits that allow it to survive, these are passed down through the generations and potentially made stronger, therefore giving even greater rise to the survival of that species.

When it comes down to genetics, we see younger generations inheriting traits such as the ability to obtain and store toxins as well as the ways in which they use them. The more these toxins are used, the more the animal will adapt.

However, since these animals rely on other species for their toxins, it’s interesting to see how they have co-evolved alongside their target species. This occurs over time, and we see certain adaptations developing between predator and prey species. What’s more, the presence of certain toxins in any given environment will have an influence over which adaptations occur, resulting in traits that are designed to enhance survival.

This leads us to look at the influence of the evolutionary arms race seen between predator and prey species. Over time, predators may develop resistance to certain toxins and this forces the further evolution of their prey to become more potent.

One of the main reasons that toxin sequestration even exists is to deter predators which naturally increases an animal’s chance of survival. By sequestering these toxins, the animal becomes less desirable to predators and, in some cases, may even be harmful. Couple this with things like bright colors and patterns and a predator is far more likely to pass on this meal.

Animals that Acquire Toxins from their Diet

Many creatures within the animal kingdom rely on toxins for a variety of reasons. With reptiles, amphibians, marine life, and even birds getting in on the action, toxin sequestration is probably far more common than you’d ever imagined.

1. Hooded Pitohui (Pitohui dichrous)

There are only a small handful of toxic birds and the hooded pitohui is one of these rare examples. For many years, it was believed that only reptiles, amphibians, and insects could be toxic but the discovery of birds like the hooded pitohui challenged this theory.

Found in Indonesia and Papua New Guinea, the hooded pitohui is found in dense rainforests and its populations are typically localized to specific forests.

These birds can store batrachotoxin in both their skin and feathers. This is a neurotoxin which is actually the same toxin found in the poison dart frog which this bird uses as a way of repelling predators and making itself unpalatable. Just like the poison dart frog, the hooded pitohui also boasts bright coloration which may also serve as a warning. It is also thought that the presence of these toxins in the skin and feathers is a way to deter parasites. 

It is generally believed that while the toxins of the hooded pitohui can be harmful to some of its predators, they’re unlikely to cause any damage to humans. That said, during the 90s, when this bird’s toxicity was discovered (thought to be an evolutionary adaptation in response to the dynamics of its ecosystem), scientists noticed that handling the skins of these birds caused irritation to their hands.

While more research is needed into the source of the hooded pitohui’s toxins, it is agreed that the same chemical is found in the choresine beetle which this bird is known to prey on.

2. Poison Dart Frogs (Dendrobatidae family)

I couldn’t possibly write a list of animals that use toxin sequestration without talking about the poison dart frog. This is perhaps one of the most well-known types of animals to engage in this process as a way of defending themselves against predators. But before we get into the nitty-gritty, it’s also worth noting that poison dart frogs also have bright coloration as an aposematic warning to predators that they’re not to be messed with. 

If the predator does take that warning and attempts to eat the frog, then it’s in for a nasty surprise since these small amphibians have skin glands that hold onto alkaloids like batrachotoxin, histrionicotoxin, and pumiliotoxins that affect the nervous system of any predator that dares to eat them.

They obtain these toxins through their diet of mites, ants, and termites and this is something that has co-evolved over time. Plus, the dietary preference of these frogs appears to be determined by the alkaloid levels of the prey.

Found in South and Central American tropical rainforests, poison dart frogs should not be touched by humans in the wild. However, they can surprisingly be kept as pets but this is because the owner can control their diet, ensuring that they are unable to sequester toxins from what they’re eating. That said, there are some indigenous communities within the range of the poison dart frog that harvest the toxins and use them on their arrow tips when hunting.

3. African Crested Rat (Lophiomys imhausi)

Don McCulley / Wikimedia Commons / CC0

Most animals that sequester toxins from their diet are insects, marine creatures, or amphibians. But there’s one species of mammal that’s also jumped on this toxic bandwagon; the African crested rat.

Found in eastern Africa in both montane and bamboo forests, these maned rodents have several ways of defending themselves against predators. For starters, their ornate fur and coloration serve as a preliminary warning to anything that wants to eat them. But if potential predators don’t pay attention to this warning, they’ll be faced with a concoction that can affect their sodium-potassium pump within their cells. 

The toxin responsible for this is known as ouabain, a type of cardiac glycoside, which the rat obtains by chewing bark from specific trees, such as the poison arrow tree. Once it has chewed the bark, the rat then covers its fur with the material; they even have specialized hairs that allow the chewed-up bark to adhere. Something that’s very unique to this rodent species, and certainly this is the only mammal known to sequester toxins in this way. 

Unlike many of the animals on this list, the toxin-covered fur of the African crested rat could pose some risk to humans. However, there’s still a lot to learn about this although it’s still strongly advised not to handle any wild specimens you come across.

4. Ladybugs (Coccinellidae family)

I’m sure that most of you will have held a ladybug only to discover that it left a trail of yellowish fluid on your hands. As a child, we’d always scream that the bug had peed on us but in reality, it’s actually blood.

This secretion is known as reflex blood and is a ladybug’s way of deterring predators. It releases this fluid from its leg joints when threatened and it contains toxic alkaloids which are sequestered from their diet of aphids.

These toxins are then stored in their cuticles and hemolymph and released whenever the beetle needs to warn off a potential threat. If a predator doesn’t heed the warning of the ladybug’s bright coloration, it’ll be met with a foul taste from the liquid which gives the ladybug a survival advantage.

Fortunately, this secretion poses no threat to humans and we should be thankful to the humble ladybug (of which there are more than 6000 species) as they’re excellent natural pest controllers, especially in agriculture.

5. Monarch Butterfly (Danaus plexippus)

The monarch butterfly is well known for its annual migration but did you know that these beautiful creatures also carry a toxic secret? You’ll notice that monarchs have bright coloration and striking patterns which is a first line of defense against predation. 

But if those predators choose not to heed that warning then the monarch has another trick up its sleeve; cardiac glycosides. These are toxins that affect the sodium-potassium pump which can have seriously harmful effects on predators. Fortunately, monarchs pose no threat to humans.

What’s concerning, however, is that studies have shown that the high levels of toxins in the monarch’s body do have an impact on their coloration. It’s almost as though they have to sacrifice one for the other.

Monarch butterflies, like the other animals on this list, get their toxins from their food. You may be aware that these insects feed almost exclusively on milkweed as larvae and it’s during this time that they sequester and store the toxins. As adults, they hold onto these toxins despite their diet changing to include nectar from various flower species.

What’s really interesting is to see the co-evolution of the milkweed plant and the monarch butterfly. Over time, monarchs have adapted to using this plant as food and reap the benefits of the toxins that make them unpalatable to predators. But what does the milkweed get from this evolved relationship? Well, the development of the toxins means that herbivores want to keep as far away from milkweed as possible, allowing the plant to thrive without the risk of being eaten.

6. Milkweed Bug (Oncopeltus fasciatus)

There are many species of milkweed bugs and they may come in a variety of sizes and colors. But one thing that they all have in common is that they sequester toxins from their diet of milkweed plants. Just like the monarch butterfly, these bugs store cardenolides in their bodies which make them very unappetizing to predators. Plus, since these toxins interfere with the cells, they can cause harm to anything that tries to eat the bugs.

Just like the monarch, the milkweed bug has co-evolved with the milkweed plant, and not only do they sequester toxins, but they also have bright colors that serve as a warning to anything that might eat them. It’s thought that the concentration of toxins within an individual’s body correlates to the intensity of their coloration. 

Found all over North America, there’s no need to worry if you happen upon a milkweed bug since their toxins pose no threat to humans. Plus, we have to consider that they are an important part of their ecosystem since they’re pollinators of the milkweed plants that they feed on.

7. Blue-Capped Ifrit (Ifrita kowaldi)

The blue-capped ifrit is one of the few toxic birds and is found exclusively in the rainforests of New Guinea.

Interestingly, while there aren’t a huge number of toxic birds in the world, many of them are found in New Guinea, and it’s thought that this is related to their diet. In the forests here, there are many Choresine beetles, and these insectivorous birds feed on them. 

Choresine beetles contain a toxin known as batrachotoxin, which is known to cause irritation to the skin when the birds are handled. For a potential predator, that’s certainly something they’d want to avoid, so being able to sequester toxins from their diet gives the blue-capped ifrit a survival advantage and acts as a form of self-defense. In fact, locals in New Guinea that have tasted the bird say that the toxins cause a burning sensation worse than the hottest chilies!

These birds store the toxins in their skin and release it onto the feathers. While irritation is one side effect, it’s also believed that batrachotoxin may also permanently open nerve channels which can result in paralysis.

8. Tiger Keelback Snake (Rhabdophis tigrinus)

The tiger keelback snake is found across Asia in a range of different habitats. Like many snakes, it can be dangerous to humans if you are bitten and that’s because of the potent cocktail of toxins these snakes carry.

However, unlike many snakes that primarily naturally produce their venom, the tiger keelback snake relies more heavily on toxins sequestered from its diet. These are bufadienolides which are typically found in amphibians; a key part of the snake’s diet. That said, it is also possible for these snakes to produce toxins of their own which is what makes them so lethal.

The snake is equipped with nuchal glands at the back of the neck where it stores the toxins taken from its diet of frogs and toads. While these toxins are stored here, the snake may add its own naturally occurring toxins to enhance the potency of the mix. This is an excellent example of how this snake has evolved not only its own methods of self-defense but also through its choice of foods. Even more interesting is that studies have shown their diet is still evolving. Moreover, where snakes that fed on a diet of poisonous amphibians were observed, they tended to show greater antipredatory behaviors than those whose diet did not result in them sequestering toxins.

It does this as a form of self-defense so that it becomes unpalatable to predators. This is something that proves particularly useful to the tiger keelback snake since the location of its teeth at the back of the mouth makes it difficult for it to strike effectively at potential threats.

9. Pipevine Swallowtail Caterpillar (Battus philenor)

Like many toxic animals, the pipevine swallowtail has a primary method of defense in the form of its bright patterns and coloration which serve as a warning to predators. Like the monarch butterfly I discussed earlier, the pipevine swallowtail sequesters its toxins during its stage as a caterpillar but these toxins remain with the individual into its adult life.

These toxins are obtained from pipevine plants and contain aristolochic acids which make the butterfly taste terrible to predators. In some cases the toxin can even prove lethal to predators. The same can be said for humans as these toxins can be harmful if ingested, not that many of us go around eating butterflies but still, it’s a warning worth heeding.

Pipevine swallowtails are found in the southern parts of North America and down into Mexico in Central America. They’re known for their beautiful colors and patterns but studies have shown that their appearance is vastly affected by their diet. The fewer toxic plants this species is able to feed on, the less vibrant its colors will be.

10. Eastern Red-Spotted Newt (Notophthalmus viridescens)

Found across the eastern and central parts of North America, the eastern red-spotted newt is an interesting creature that goes through three life stages. Starting life as aquatic larvae, these creatures are found in freshwater habitats. However, they then enter a terrestrial eft stage when they can be found around shores and in wooded areas. Once they reach their adult stage, they return to the water although they are able to survive on land when necessary.

What’s even more intriguing is that this is one of the rare examples of an amphibian that uses tetrodotoxin as a form of defense. This is the same chemical found in pufferfish and blocks sodium channels which can lead to paralysis and even death if enough of the toxin is delivered. It is for this reason that humans are advised not to handle the eastern red-spotted newt and why consuming it is heavily discouraged.

So where does this toxin come from? Well, the eastern red-spotted newt feeds on a diet of small invertebrates. Some of the mites and ants they consume are what’s responsible for these toxins. Interestingly, while the toxins that are secreted onto the skin are a deterrent for predators, their effectiveness varies depending on what predators are found in the environment of any given individual.

11. Sea Hares (Aplysia spp.)

Despite their name, sea hares are not actually related to their terrestrial namesakes. In fact, they are a type of mollusc and they take their name from the long projections on their heads that slightly resemble the ears of a hare.

Sea hares are found all over the world in a variety of marine habitats and while they do carry toxins, they’re not considered dangerous to humans aside from some minor irritation that may occur by handling them.

But if you’re a sea hare predator then you’d better watch out. When these critters feel threatened, they’ll release toxin-containing ink that acts as a smokescreen to predators and also causes them to lose their senses. Moreover, these toxins, such as secondary metabolites, sit in the sea hare’s skin, making them unpalatable to predators.

It’s the algae in their diet that provides them with their toxic traits and they’re easily able to ‘sniff’ this out using the rhinophores on their heads. Not only do they take toxins from the food they eat but it’s also been observed that the type of seaweed or algae they consume gives them their coloration.

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