are monarch caterpillars poisonous to birds

Monarch butterflies and their close relatives thrive on poisonous milkweed, thanks to genetic mutations that block the effects of the plant’s toxins while allowing the poisons to accumulate in the caterpillar or adult insects as deterrents to hungry predators.

Turns out some of those insect-eating predators evolved similar mutations in order to feast on monarchs.

In a study appearing this week in the journal Current Biology, researchers at the University of California, Berkeley, and UC Riverside report monarch-like genetic mutations in the genomes of four organisms that are known to eat monarchs: the black-headed grosbeak, a migratory bird that snacks on the butterflies at their overwintering home in Mexico; the eastern deer mouse, a close relative of the Mexican black-eared deer mouse that feeds on butterflies that fall to the ground; a tiny wasp that parasitizes monarch eggs; and a nematode that parasitizes insect larvae that feed on milkweed.

All four organisms have evolved mutations in one or more copies of a gene for the sodium-potassium pump — the same mutations, in fact, as milkweed butterflies, and ones that the researchers and their collaborators showed two years ago were critical to the monarch’s ability to eat milkweed without succumbing to its toxins.

The toxins are cardiac glycosides that interfere with this pump, which helps enable heartbeats and nerve firing. It’s so important in humans that we use a third of all the energy we generate from food to power the pump. It’s not surprising, then, that when the toxins throw a wrench in the pump, the heart and other organs stop, too. Even horses and humans can die of cardiac arrest if they consume enough of the milkweed toxins, which are still used as an arrow poison by hunter-gatherer groups in Africa and South America. Until recently, small amounts of related chemicals from foxglove were widely used to treat congestive heart failure.

“The toxins move up the food chain from plants — what biologists call the first trophic level — to insect herbivores, the second, and then to predators and parasitoids — a third trophic level,” said evolutionary biologist Noah Whiteman, UC Berkeley professor of integrative biology and of molecular and cell biology. “In response, the predators and parasitoids have evolved resistance to the toxins at the same sites that we discovered were changing in the monarch, and sometimes to the same amino acids. This might be the first time that the same resistance mutations have been found in the third and second trophic levels that evolved in response to the latter feeding on toxic plants.”

“It’s remarkable that convergent evolution occurred at the molecular level in all these animals,” said co-author Simon “Niels” Groen, assistant professor of evolutionary systems biology in UC Riverside’s nematology department and a former UC Berkeley postdoctoral fellow. “Plant toxins caused evolutionary changes across at least three levels of the food chain.”

Birds do it, wasps do it. Even nematodes do it.

Since the 1980s, scientists have been aware that certain insects, such as beetles, aphids, and monarch butterflies, have evolved to consume milkweed plants and store toxins in their bodies, even after changing into different species, in order to ward off predators. Geneticists have spent the last ten years identifying the precise genetic mutations that made this possible. These mutations were all in the sodium pump and allowed the pump to function in spite of the toxins. According to Whiteman’s theory, the animals that consume butterflies must have also developed resistance mutations. But were they the same?.

A female black-headed grosbeak (right) and a black-backed oriole (top) are seen in this January 1980 photo devouring monarch butterflies in Mexico. When combined, these two species have the potential to devour a million butterflies every season. (Photo by Lincoln Brower, copyright Linda Fink).

Following the publication of the black-headed grosbeak genome last year, Whiteman and Groen quickly searched for and discovered sodium pump mutations that were almost exactly the same as those that had evolved in the monarch Later, the team broadened their investigation by examining previously sequenced genomes of additional animals that consume monarchs, and they discovered comparable mutations.

The Mexican black-headed grosbeak, or Pheucticus melanocephalus, is a summer resident of California that is well-known for devouring monarch butterflies in the Michoacán state mountains where they overwinter. In a single winter, hundreds of thousands to one million monarchs were eaten by the black-headed grosbeak and another bird, the black-backed oriole (Icterus abeillei), according to one study.

But based on their actions, it was clear that the two birds’ resistance to the toxins found in milkweed that the butterfly had stored in its body was not equal. The oriole would de-wing the butterfly and then gut the abdomen, eating only the insides, whereas the grosbeak would rip off the wings and devour the abdomen whole. Both the wings and the exterior, or cuticle, are more concentrated in cardiac glycoside toxins. Orioles also discarded monarchs with higher levels of cardiac glycosides.

When a black-headed grosbeak removes the wings from a monarch butterfly, it usually only consumes the abdomen. (Photo courtesy of Mark Chappell, UC Riverside).

According to a recent study, the grosbeak’s ability to withstand the toxins in monarchs is due to single-nucleotide mutations that it has developed in its sodium pump genes in two of the three same locations where monarchs have evolved mutations that help make them the most resistant organism to the cardiac glycosides found in milkweed. The two most widely expressed copies of the sodium pump gene are missing these mutations in none of the other 150 or so sparrow-related “passerine” birds whose genomes are known. The oriole’s genome has yet to be sequenced.

It “solves this mystery from forty years ago where the biology was pretty well worked out, but we just couldn’t see how grosbeaks are doing this by going down to the lowest possible level of organization, the genome,” according to Whiteman. Amazingly, it appears that they are developing resistance by employing the same mechanisms in the same locations in the genetic code as the bugs, beetles, and aphids that consume milkweeds, as well as the monarch butterfly. ”.

Because sago palms thrive in arid desert regions, our sprinkler systems and roof runoff are not assisting them in surviving.

Contrary to popular belief, too much water in the soil prevents sagos from absorbing manganese, which is vital to their health. The result is the browning, frizzy leaves on the fronds.

Many of the small gingers like Kaempferias would do well. Holly ferns provide a distinct texture to the landscape and are tolerant of low light levels.

Unfortunately, the mild toxins found in butterflies and caterpillars of the monarch butterfly do not repel many creatures in the wild. While frogs, snakes, and anoles (those green or brown lizards) won’t hesitate to eat a monarch, birds will They are immune to the toxin. There’s really only one thing you can do to keep predators away from the caterpillars.

We have sago palms at the front of our condos, thanks to our builder. Last year, I managed to control scale insects, but this year, all of the fronds are turning brown. What causes this, and how do I save the palms?.

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