Light pollution disrupts circadian rhythms and ecosystems worldwide—but for plants, dependent on light for photosynthesis, its effects could be profound. Now scientists writing in Frontiers in Plant Science have found that exposure to high levels of artificial light at night makes tree leaves grow tougher and harder for insects to eat, threatening urban food chains.

“We noticed that, compared to natural ecosystems, tree leaves in most urban ecosystems generally show little sign of insect damage. We were curious as to why,” said corresponding author Dr. Shuang Zhang of the Chinese Academy of Sciences. “Here we show that in two of the most common tree species in Beijing, artificial light at night led to increased leaf toughness and decreased levels of leaf herbivory.”

Shedding some light

Artificial light has increased levels of night-time brightness by almost 10%: most of the world’s population experiences light pollution every night. Because plant properties affect their interactions with other plants and animals, any changes to plants caused by artificial light could have a significant impact on the ecosystem.

“Leaves that are free of insect damage may bring comfort to people, but not insects,” said Zhang. “Herbivory is a natural ecological process that maintains the biodiversity of insects.”

The scientists suspected that plants experiencing high levels of artificial light would focus on defense rather than growth, producing tougher leaves with more chemical defense compounds. To test this, they selected two common species of street tree: Japanese pagoda and green ash trees. Although these trees are similar in many ways, Japanese pagoda trees have smaller, softer leaves which herbivores prefer.

The scientists identified 30 sampling sites spaced by roughly 100 meters on main roads which are usually illuminated all night. To determine the level of exposure to artificial lighting, they measured illuminance at each site. Almost 5,500 leaves were collected and evaluated for insect herbivory and traits that could be affected by artificial light, like size, toughness, water content, and levels of nutrients and chemical defenses.

Larger leaves would indicate resources allocated to growth, while toughness and higher levels of chemical defenses like tannins would indicate resources allocated to defense. Meanwhile, higher levels of water and nutrients indicate higher-quality nutrition to tempt herbivores.

Hard to swallow

For both species of tree, higher levels of artificial light meant tougher leaves. The tougher the leaf, the less evidence of insect herbivory. The more intense the light, the more frequently scientists encountered leaves that showed no signs at all of herbivory.

“The underlying mechanism for this pattern is not yet fully understood,” said Zhang. “It is possible that trees exposed to artificial light at night may extend their photosynthesis duration. Additionally, these leaves might allocate a greater proportion of resources to structural compounds, such as fibers, which could lead to an increase in leaf toughness.”

Japanese pagoda trees exposed to more artificial light had lower levels of nutrients like phosphorus: where Japanese pagoda leaves had more nutrients, more herbivory occurred. But green ash leaves were more strongly influenced by higher light levels: they had higher levels of nitrogen, smaller leaves, and lower chemical defenses.

This could be because green ash trees are less preferred by herbivores, so they can afford to allocate resources to growth. Meanwhile, Japanese pagoda trees put more resources into defense, lowering their nutrient content.

Insects going hungry

“Decreased herbivory can lead to trophic cascading effects in ecology,” said Zhang. “Lower levels of herbivory imply lower abundances of herbivorous insects, which could in turn result in lower abundances of predatory insects, insect-eating birds, and so on. The decline of insects is a global pattern observed over recent decades. We should pay more attention to this trend.”

Although leaf toughness is a mechanical defense against predation, it is possible that other factors contribute to decreased herbivory: for instance, more light could make insects more visible to their predators. Further research will be needed to fully understand the effects of artificial light.

“Our study was conducted in only one city and involved just two tree species,” cautioned Zhang.

“This limitation hinders our ability to generalize the conclusions to broader spatial and taxonomic scales. Research on how urbanization affects insects and insect-related ecological processes is still in its infancy.”

British dormice have declined by a shocking 70% between 2000 and 2022, according to the latest report by the national dormouse monitoring program. But my research indicates that this decline might not be that catastrophic.

Dormice are small mammals that spend the late spring and summer mostly in the tree canopy, then hibernating at ground level when the weather gets cold. In order to know how best to protect them, we need more accurate statistics about their whereabouts, habits and survival rates.

For more than a decade, I have studied the effectiveness of dormouse monitoring. My recently published research questions the effectiveness of the standard survey technique that checks artificial nest boxes or tubes placed at 1.4m from the ground to see if dormice are using them.

Accurate determination of whether dormice are present on a site has ecological, legal and practical significance, so reliable and accurate survey methods are important.

Dormice are of particular interest not just to scientists from a biodiversity perspective, but also commercially, for example, to property developers as they are highly protected.

When any activity is considered on a site with potentially suitable habitat, dormouse surveys are required to establish whether they are present to avoid the risk of killing, injuring or disturbing them or damaging their breeding sites and resting places. There are several cases in the last few years where prosecution has resulted in heavy fines of up to £100,000.

If dormice are present, then the nature or timing of building work may need to be modified to comply with legislation. A license from government authorities such as Natural England or Natural Resources Wales is required for any activity that may affect dormice—that includes ecological surveys for woodland management and property development.

Together with my team of ecology researchers and students, I placed artificial nest boxes at different heights on trees and on isolated posts on two woodland sites in Kent. The boxes on posts could only be reached by dormice coming to the ground and traveling across the woodland floor.

We checked the boxes regularly over several seasons and found that boxes in all three positions were used. If boxes had only been placed in the standard position 1.4 m above ground, following current survey guidelines, significantly fewer dormice would have been detected. Dormice also regularly used the isolated boxes supporting the findings of others that dormice don’t only live in trees as previously thought.

Interestingly, there was a decline in use of the boxes over the years of the project, something we had observed during previous long-term dormouse monitoring projects.

This drop off is the basis of the claim that dormice are in serious decline and, while this may well be true as habitat loss and climate change are undoubtedly affecting dormice, it is important to remember the dormice were obviously present before the boxes were installed.

It is possible that boxes were initially explored and used as novel features but that the dormice then returned to their previous nesting sites. A further factor may be the increased presence of parasites, particularly when boxes are also used by birds.

On-the-ground detection

Our results suggest that current survey and monitoring guidelines for dormice need to be reviewed and that dormice might not be declining quite as dramatically as has been suggested. Boxes in the tree canopy would be likely to yield more accurate data, but the cost would make it unlikely to be viable. And the issue of whether the boxes would be used for more than a few seasons remains.

Dormice hibernate in winter at ground level. There would be many advantages of a method based on this—not least that it would be less invasive, reducing the ethical and welfare concerns about regularly disturbing potentially breeding dormice. We’ve been working with the company Paws for Conservation to test the feasibility of using highly trained dogs to detect hibernating dormice, under a specific research license.

Using reward-based training, detection dogs can be trained to locate dormice, while ignoring all other small mammals likely to be encountered nearby. A cold winter that provides ideal hibernation conditions for dormice will give us the chance to test this promising technique under field conditions.

But it’s not just about dormice—we need reliable methods to provide robust data so we can evaluate conservation actions to make sure monitoring techniques are delivering the best possible results for all species.

Science thrives on debate, and conservationists need to be open to opportunities for improvement. We have a responsibility to do the best we can, not just for specific animals but for our wider environment.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The wing dynamics of flying animal species have been the inspiration for numerous flying robotic systems. While birds and bats typically flap their wings using the force produced by their pectoral and wing muscles, the processes underlying the wing movements of many insects remain poorly understood.

Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL, Switzerland) and Konkuk University (South Korea) recently set out to explore how herbivorous insects known as rhinoceros beetles deploy and retract their wings. The insight they gathered, outlined in a paper published in Nature, was then used to develop a new flapping microrobot that can passively deploy and retract its wings, without the need for extensive actuators.

“Insects, including beetles, are theoretically believed to use thoracic muscles to actively deploy and retract their wings at the wing bases, similarly to birds and bats,” Hoang-Vu Phan, the lead author of the paper, told Tech Xplore. “However, methods of recording or monitoring muscular activity still cannot determine which muscles beetles use to deploy and retract their wings nor explain how they do so.”

The hindwings (i.e., back wings) of beetles resemble foldable origami structures, as they can be neatly folded and stowed under the elytra (i.e., a hardened forewing typically found in beetles) while they are resting and then passively deployed when they fly. Many past studies aimed at replicating the dynamics of beetle wings in robots thus utilized origami-like structures, without paying much attention to movements at the base of the hindwings.

“This research is a follow-up of my previous work published in Science in 2020, where we discovered the shock-absorbing function of rhinoceros beetles’ hindwings during in-flight collisions,” Phan explained. “During the experiments, I accidentally captured a full two-phase wing deployment, and wondered why the beetle uses such a complex procedure if driven by active muscles.”

In his previous examinations of rhinoceros beetles, Phan observed that these insects can leverage their elytra and flapping forces to passively deploy their hindwings for flight. Once their flight is over and they land on a surface, they then use the elytra to push the hindwings back onto their body. Both these actions are passive in nature, as they do not entail the use of thoracic muscles that support the flight of birds and bats.

“By implementing this passive mechanism into flapping-wing robots, we demonstrated for the first time that unlike existing flapping robots that keep their wings fixed in a fully extended configuration, our robot can fold the wings along the body when at rest and passively deploy its wings to take off and maintain stable flight,” Phan said.

The researchers leveraged the insight they acquired from their study of rhinoceros beetles to build a flapping microrobot that weighs 18 grams. This microrobot, which is approximately two times larger than an actual beetle, can passively deploy and retract its wings.

“For simplicity, we used elastic tendons installed at the armpits that allow the robot to close its wings passively,” Phan said. “By activating flapping motion, the robot can passively deploy its wings to take off and maintain stable flight. Thereafter, by stopping the flapping after landing, the wings can be rapidly and passively retracted back to the body without the need for any additional actuators.”

The recent work by Phan and his colleagues unveiled that the mechanisms underlying how beetles deploy and retract their hindwings are passive and do not rely on muscle movements. It then introduced a viable strategy to reproduce these mechanisms in microrobots, thus increasing their similarity to insects.

“Our robot with foldable wings can be used for search and rescue missions in confined spaces,” Phan said. “For example, it can enter a collapsed building where humans cannot access. With its tiny scale, the robot can fly into narrow spaces. When flight is not possible, the robot can land or perch on any surface, and then switch to other locomotion modes such as crawling.”

Notably, when the team’s microrobot is crawling, its wings rest along its body, which reduces the risk that they will be damaged while also enhancing the robot’s mobility in narrow spaces. Once it finds a good spot to take flight, the robot can then simply deploy its wings again and switch back into flight mode.

“Our flapping robot could also help biologists to study the biomechanics of insect flight and could be disguised as spy insects to explore the life of real insects in forests, for which conventional rotary-wing drones are not applicable,” Phan said. “In addition, the flapping robot could be used to carry out engineering research or as an engineering toy for kids, as its low-flapping frequency is very safe and human-friendly.”

So far, Phan and his colleagues have assessed their microrobot’s performance in a series of preliminary tests, which yielded promising results. In the future, their design could be further improved and tested in various real-world scenarios, to further validate its potential.

“In future studies, it would be interesting to explore whether other insects, such as tiny flies, use similar passive strategies in the context of limited muscle availability,” Phan added. “We also aim to improve the agile flight of our robot, and to implement ground locomotion capabilities such as perching and crawling, similar to its biological counterparts.”

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