Hexbyte Glen Cove Partners in crime: Agricultural pest relies on bacteria to overcome plant defenses thumbnail

Hexbyte Glen Cove Partners in crime: Agricultural pest relies on bacteria to overcome plant defenses

Hexbyte Glen Cove

A recent study shows that insect larvae may rely on microscopic partners to help them eat plant leaves. Credit: Egor Kamelev from Pexels

Although insect larvae may seem harmless to humans, they can be extremely dangerous to the plant species that many of them feed on, and some of those plant species are important as agricultural crops. Although plants cannot simply flee from danger like animals typically would, many have nonetheless evolved ingenious strategies to defend themselves from herbivores. Herbivorous insect larvae will commonly use their mouths to smear various digestive proteins onto plants that they want to eat, and when plants detect chemicals commonly found in these oral secretions, they can respond to the injury by producing defensive molecules, including proteins and specialized metabolites of their own that inactivate the insect’s digestive proteins and thus prevent the insect from obtaining nutrients from the plant.

Of course, the existence of such chemical defense mechanisms in is a problem that herbivorous insects must counter. One way that insects have evolved to overcome these problems is by forming partnerships with . For example, the digestive oral secretions of the Colorado potato beetle (Leptinotarsa decemlineata) include bacteria that can suppress the defense mechanisms of the tomato plants that the beetle commonly feeds on. The beetle and the bacteria have thus achieved “symbiosis,” which is a term that biologists use to describe a mutually beneficial partnership: The beetle provides the bacteria with a comfortable environment inside its mouth and other secretory organs, and the bacteria help the beetle consume nutrients from tomato plants.

To Prof. Gen-ichiro Arimura of Tokyo University of Science, this is a fascinating result: “Although it is well known that symbiotic microorganisms in animals (especially bacteria in the intestines of herbivores such as pandas and cows) affect biological activities such as digestion and reproduction, the fact that they affect the prey (i.e., the plants) is not so well known.” In other words, the fact that the insect’s bacterial partners work to alter biochemical processes within the living plant before it is eaten is a matter of considerable interest to scientists.

Levels of damage to A. thaliana leaves after exposure to S. litura larvae raised under conditions that did or did not sterilize their oral secretions. The asterisk indicates a statistically significant difference between the damage levels under the different conditions. Credit: Professor Gen-ichiro Arimura, Tokyo University of Science

Prof. Arimura and his research team, in collaboration with Okayama University, wondered whether such partnerships with bacteria may apply in the case of the insect Spodoptera litura, the larvae of which are major pests that commonly damage crops in Asia. In an article recently published in the journal New Phytologist, Prof. Arimura’s research team experimented with applying the oral secretions of S. litura larvae to mechanically damaged leaves of the thale cress plant (Arabidopsis thaliana). When the researchers sterilized the oral secretions to kill or remove any bacteria that might be present in them, they found that applying these secretions to the plant leaves stimulated the expression of defense-related genes and the production of oxylipins that play important roles in defending A. thaliana cells from digestion. However, when the researchers applied oral secretions that had not been sterilized, the bacteria present within the oral secretions acted to prevent the expression of defense-related genes and the production of oxylipins. In contrast, the bacteria stimulated the production of salicylic acid and abscisic acid, two chemicals that act to suppress the production of oxylipins.

These findings are compelling evidence that bacteria in the oral secretions of S. litura assist the larvae in overcoming plant defense mechanisms, and the researchers wanted to identify the bacteria responsible. Tests of the larvae’s oral secretions revealed the presence of a bacterium called Staphylococcus epidermidis, and further experiments confirmed the S. epidermidis acted to suppress plant defense mechanisms.

These results provide important insights into how S. litura counteracts the defense mechanisms of the plants that it feeds on, and Prof. Arimura hopes that knowing more about the relationship between the larvae and the bacteria will help crop scientists develop techniques to protect important crop species from S. litura. Such techniques may help farmers reduce their use of environmentally harmful pesticides, and Prof. Arimura expresses optimism that his research will thus “contribute to the creation of a safe and secure food supply and a rich environment.”

More information:
Yukiyo Yamasaki et al, Phytohormone‐dependent plant defense signaling orchestrated by oral bacteria of the herbivore Spodoptera litura, New Phytologist (2021). DOI: 10.1111/nph.17444

Partners in crime: Agricultural pest relies on bacteria to overcome plant defenses (2021, May 27)
retrieved 28 May 2021
from https://phys.org/news/2021-05-partners-crime-agricultural-pest-bacteria.html

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Hexbyte Glen Cove Study: Humpback whales aren't learning their songs from one another thumbnail

Hexbyte Glen Cove Study: Humpback whales aren’t learning their songs from one another

Hexbyte Glen Cove

Credit: CC0 Public Domain

Humpback and bowhead whales are the only mammals other than humans thought to progressively change the songs they sing through a process of cultural learning.

But maybe the humpbacks are no longer part of that trio. Humpbacks might be singing songs that are not as ‘cultured’ as once assumed.

A new study by a University at Buffalo researcher is directly contradicting the widely accepted cultural transmission hypothesis suggesting that learn their songs from other whales.

“It seems like that is not correct,” says Eduardo Mercado, a professor of psychology in UB’s College of Arts and Sciences. “Our findings indicate that neither cultural transmission nor contributes significantly to how change their songs over time.

“I think the results are provocative and will probably make other whale researchers livid or dismissive, but at least the discussion won’t be boring!”

The study, published Tuesday (Feb. 9) in the Journal of Comparative Psychology, analyzed songs from groups of humpbacks that were not in acoustic contact with each other, yet still produced acoustically comparable songs.

“The idea that humpback whales are a distinguished part of the animal kingdom because of their ability to culturally learn songs is apparently not true,” says Mercado. “But to me, what the whales are doing is actually more impressive.

“Cultural transmission implies that what’s heard is copied. That means it doesn’t matter what is heard or what is copied. But what we found is very specific and precise, without a trace of arbitrary vocalization. The songs change over time in a fashion that’s even more precise than what humans do when language develops.”

The talented club DJ serves as an appropriate metaphor for changing whale .

“DJs can’t just randomly go from one song to the next,” says Mercado. “They have to think about beat matching, tempo and mood in order to maintain a continuous flow.

“I think that might be true of the whales. When they make changes, they do so in relation to what preceded it. They’re basically beat matching when they change songs—and we found similarities in populations that had no social contact or genetic links.”

Mercado says existing research claims that humpback populations isolated from one another do not change their songs in the same way. Each population is original, taking their songs in original directions.

“These things are not true,” says Mercado. “I compare songs over 40 years and compare populations that have never been in contact with one another, and they’re doing basically the same thing.”

Despite large and sometimes rapid changes, whales often end up singing similar songs, according to Mercado. The cultural transmission hypothesis is attractive in part because it’s hard to imagine what mechanism might instigate the song variation.

But previous research has relied heavily on subjectively defined categories. Songs sounding like a human snore would be placed in a “snore” category. Any subsequent analysis would depend on how well the categories captured the intricacies of the song.

“I didn’t categorize things at all and used purely acoustic measurements,” says Mercado, who specifically chose published records of data to avoid any suggestion of cherry picking the data. “This paper is based on direct measurements of sound features without any categorization or subjective labeling.”

Mercado says the results of the current study question the role of vocal imitation and cultural transmission in whale song, but they do not resolve why the songs are changing.

“These results tell me that whales are sophisticated in ways that researchers and observers hadn’t previously considered,” says Mercado. “What we’re hearing is a level of acoustic sophistication which is beyond the ability of humans.

“That’s something that deserves both appreciation and further study. I’d like to examine why whale song changes and explore the benefit of that change.”

More information:
Eduardo Mercado et al, Similarities in composition and transformations of songs by humpback whales (Megaptera novaeangliae) over time and space., Journal of Comparative Psychology (2021). DOI: 10.1037/com0000268

Study: Humpback whales aren’t learning their songs from one another (2021, February 12)
retrieved 14 February 2021

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