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Author Topic: Can anyone solve why cicadas spend 17 years underground?  (Read 469 times)

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Offline gaden

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Seventeen years is a long time to hang out underground. Why do they come out all at once?


Why Do Brood V Cicadas Spend 17 Years Underground?
https://www.mentalfloss.com/article/80262/why-do-brood-v-cicadas-spend-17-years-underground

Quote
Biologist Stephen Jay Gould explained it like this:

“They are large enough to exceed the life cycle of any predator, but they are also prime numbers (divisible by no integer smaller than themselves). Many potential predators have 2–5 year life cycles. Such cycles are not set by the availability of periodical cicadas (for they peak too often in years of nonemergence), but cicadas might eagerly be harvested when the cycles coincide. Consider a predator with a cycle of five years; if cicadas emerged every 15 years, each bloom would be hit by the predator. By cycling at a large prime number, cicadas minimize the number of coincidences (every 5X17, or 85 years, in this case).”

Staying out of sync with predators’ life cycles keeps the cicadas from becoming a reliable source of food.

The long cycles might also be the result of North America’s prehistoric climate. Periodical cicadas evolved during a time when glaciers advanced and retreated over what is now the eastern U.S. Temperatures would have been unpredictably warm or cool and often too low for the insects to fly or mate. When researchers calculated the chances of survival for cicadas with different life cycles in this kind of climate, they found that the longer the insects stayed underground, the lower the chance they’d emerge during a too-cool summer. Over time, the scientists suggest, insects with shorter cycles died out, while those who by chance took longer to develop survived and reproduced.

There are other explanations for the broods’ impressive synchronization and overwhelming numbers. Some scientists suggest that high population densities are necessary to produce the deafening choruses that males use to attract mates. Another idea is that there’s safety in numbers. Cicadas don’t have much in the way of defenses, but when billions emerge at the same time, there are simply too many for predators to eat them all. Even after birds and other animals have had their fill, there are plenty of cicadas left to mate, lay eggs, and start the 17-year process yet again.

Offline CoconutXO

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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #1 on: May 20, 2020, 04:21:54 PM »
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There are approximately 3,000 cicada species, seven of which represent periodical cicadas. Three periodical species — Magicicada septendecim, Magicicada septendecula and Magicicada cassini — have 17-year life cycles, while four species — Magicicada tredecim, Magicicada neotredecim, Magicicada tredecassini and Magicicada tredecula — follow a 13-year life cycle.

Cicadas hatch from eggs as nymphs and don't go through the larva stage.






Offline gaden

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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #2 on: May 20, 2020, 05:35:19 PM »
I have my theories on why cicadas have 17 years hibernation.  It's because they wait 17 years before the female cicada becomes legal at 18.

Offline CoconutXO

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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #3 on: May 21, 2020, 05:10:19 PM »
Periodical cicadas make use of the molecular clock in their long life cycle.

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The year of cicada emergence is cued by what I and others believe to be an internal molecular clock,” she said. “The clock is most likely calibrated by environmental cues that signify the passage of a year, such as the trees leafing out, changing the composition of the xylem fluid on which they feed.

The molecular clock keeps track of the passage of years. The accumulation of 13 or 17 years triggers the emergence of fifth instar nymphs. The day of emergence is triggered by accumulated ground temperature. This was demonstrated by James Heath in a study published in 1968.

“My colleagues and I hypothesize a molecular clock in periodic cicadas that somehow keeps track of the years,” he said. “That is what we’re looking for now. We suspect it is tied to yearly cycles of the trees they are feeding upon.”

In 2007 in Cincinnati, it was warm in January but there was a hard freeze in February, and then a normal spring, which caused maple trees to produce two leaf sets that year. Hundreds of cicadas feeding on those trees emerged a year early, after the trees produced 17 leaf sets in 16 years.

During years when they are set to emerge, the time of year is determined by soil temperature.“Emergence is temperature driven,” said Dr. Kritsky. “During the last emergence in our area, I planted temperature probes in the ground all over campus to track the emergence. The cicadas emerged over a period of two weeks after the soil temperature reached 65 °F (18 °C).”

https://entomologytoday.org/2016/03/22/how-do-cicadas-know-when-to-emerge-from-the-ground/














Offline Olive Juice

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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #4 on: May 21, 2020, 08:49:35 PM »
I think it's good strategies to emerge en masse to reproduce at will, with less likelihood to be eaten by predators, and thus ensuing greater survivability of the species.

Offline CoconutXO

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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #5 on: May 22, 2020, 12:08:04 AM »
The strategy of emerging only in odd years to increase the species' survivability is sound. Predators that feed on the en-masse cicadas in one year wouldn't be able to do it again the next year and their populations would have to shrink back to normal size, thus maintaining the status quo of ecological balance.

A 16 year species of cicada, for example, would theoretically had to experience the population decimation from some predatory wasp species that emerge from the 2, 4, 8, and 16 year cycle, but with the 17 year dormancy, there would be much less takers.

Birds and squirrels reproduce annually, and thus their populations would experience an automatic trimming in the time between the emergence. Wasps and beetles are the probable insects that drive the periodical cicadas' evolution since they also have similar reproductive cycles.

































































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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #6 on: May 22, 2020, 06:32:45 AM »
The sound of millions of cicadas in Vietnam:




Offline gaden

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Re: Can anyone solve why cicadas spend 17 years underground?
« Reply #7 on: May 22, 2020, 10:24:49 AM »
Why do cicadas sing sad songs?


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