Study: Monarch Caterpillars Get Angry When They’re Hungry
Humans aren't the only animals that get "hangry" when deprived of a meal.
"The less food that is present, the higher their level of aggression," study coauthor Elizabeth Brown of Florida Atlantic University told New Scientist.
The idea for the study was born when the wife of fellow Florida Atlantic University researcher Alex Keene saw two monarch caterpillars fighting over a milkweed plant in the couple's garden, The New York Times reported.
"I decided to investigate monarch caterpillars because I was intrigued by their combative behavior, which I observed first-hand in my own garden," Keene explained in a Florida Atlantic University press release. "They are large and easily recognizable compared to many other insects. These are charismatic animals that everyone loves, and there's a growing appreciation for their potential to tell us about how the brain controls behavior."
The researchers gave the caterpillars three different amounts of food, New Scientist reported. The less milkweed the caterpillars received, the more aggressive they became. The caterpillars who were larger and closer to metamorphosis were the most aggressive, probably because they required more energy, Brown said.
Caterpillar aggression looked like a "combination of boxing and 'bumper' cars," the press release detailed, with caterpillars head butting or knocking other caterpillars away from the food.
"I went to grad school with a guy who played rugby in college," Keene told The New York Times. "A flying head butt is a fair assessment."
The attacked caterpillar would then shuffle away from the food, defeated. This is a big problem for the losing caterpillar, since monarch caterpillars essentially eat non-stop from hatching to forming a cocoon.
The researchers hope to build on this study to learn more about the genetic drivers of aggressive behavior.
"There's a lot we could learn about more complex animals from this ecologically relevant insect model," Keene told New Scientist.
The research could also have conservation implications. Monarch caterpillars mainly dine on milkweed: They can strip an entire plant in two weeks and, when they are at their largest, consume a leaf in less than five minutes, the press release noted. But this dependence on milkweed has made the species vulnerable. The number of monarch butterflies has decreased in the U.S. over the last 20 years, according to the U.S. Fish and Wildlife Service, and one factor is the use of pesticides that harm milkweed.
"It's interesting to think about how this would potentially impact the survival of these caterpillars, when they're crowded onto plants," University of Michigan monarch biologist D. André Green, who was not part of the study, told The New York Times. "The amount of milkweed is decreasing. This may become a bigger issue."
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The speed and scale of the response to COVID-19 by governments, businesses and individuals seems to provide hope that we can react to the climate change crisis in a similarly decisive manner - but history tells us that humans do not react to slow-moving and distant threats.
A Game of Jenga<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>
Cutting Off Circulation<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>
The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
Is it Time to Declare a Climate Emergency?<p>At what stage, and at what rise in global temperatures, will these tipping points be reached? No one is entirely sure. It may take centuries, millennia or it could be imminent.</p><p>But as COVID-19 taught us, we need to prepare for the expected. We were aware of the risk of a pandemic. We also knew that we were not sufficiently prepared. But we didn't act in a meaningful manner. Thankfully, we have been able to fast-track the production of vaccines to combat COVID-19. But there is no vaccine for climate change once we have passed these tipping points.</p><p><a href="https://www.weforum.org/reports/the-global-risks-report-2021" target="_blank">We need to act now on our climate</a>. Act like these tipping points are imminent. And stop thinking of climate change as a slow-moving, long-term threat that enables us to kick the problem down the road and let future generations deal with it. We must take immediate action to reduce global warming and fulfill our commitments to the <a href="https://www.ipcc.ch/sr15/" target="_blank" rel="noopener noreferrer">Paris Agreement</a>, and build resilience with these tipping points in mind.</p><p>We need to plan now to mitigate greenhouse gas emissions, but we also need to plan for the impacts, such as the ability to feed everyone on the planet, develop plans to manage flood risk, as well as manage the social and geopolitical impacts of human migrations that will be a consequence of fight or flight decisions.</p><p>Breaching these tipping points would be cataclysmic and potentially far more devastating than COVID-19. Some may not enjoy hearing these messages, or consider them to be in the realm of science fiction. But if it injects a sense of urgency to make us respond to climate change like we have done to the pandemic, then we must talk more about what has happened before and will happen again.</p><p>Otherwise we will continue playing Jenga with our planet. And ultimately, there will only be one loser – us.</p>
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