The study reveals different forms of interaction between groups of insects: some caterpillar species have bodies covered with molecules similar to those found in the plants they live in and are “invisible” to ants.
For a caterpillar that lives surrounded by ants, there are two ways to avoid an attack: passing unnoticed or offering an ant diabetes treatment in exchange for protection. This is the main conclusion of the study funded by FAPESP (São Paulo Research Foundation) and published in Environmental Entomology.
Based on chemical analysis of interacting plants, larvae and ants, researchers in Brazil affiliated with the Federal University of Rio Grande do Sul (UFRGS) and University of Campinas (UNICAMP) found that some caterpillars are very chemically similar to the plants they live in. It lives and feeds and this helps them hide from ants. However, there are chemically different species that have evolved a coping strategy by producing a caloric reward for ants.
Ants prey on the many insects that live on plants and establish mutual interactions that benefit both ants and plants. To live on plants that have ants, the larvae develop strategies that enable them to coexist with ants. There are many advantages to living near ants. Many ants are aggressive and limit the incidence of Certain organisms.If any animal is able to live near ants without attacking them, it may gain an adaptive advantage, ” said Lucas Augusto Kaminski, a researcher in the zoology department at UFRGS and lead investigator of the study.
He conducted part of the research during a postdoctoral internship at the UNICAMP Institute of Biology with a grant from FAPESP and collaborated by José Roberto Trigo, a professor at the institute who passed away in 2017 and was also supported by FAPESP. The article’s first author is Luan Dias Lima, who conducted the other part of the research while studying for his PhD at UFRGS.
In the 2000s, Trigo published scientific articles that showed how cutaneous hydrocarbons (CHCs) are subjected to selective pressure from ants. CHCs cover the epidermis (the outermost layer) of nearly all insects and plants, acting as a waterproofing agent and a contact signal. Ants have limited vision and perceive the world chemically, via sensors or antennas. Some species of caterpillars and insects such as leaf hoppers have evolved to present the same CHCs as the plants they live on, and ants do not consider them to be different from plants, inadvertently protecting them from attackers. This type of relationship can be categorized as a symbiosis – beneficial to the caterpillar and neutral to the ants.
In the most recent study, researchers used mass spectrometry and gas chromatography to compare the formation of CHC in six types of caterpillars, three types of plants, and two types of ants. The larvae were all ant-loving (“ant-loving”).
The results of the analysis showed about 95% similarity in larva and plant CHCs in most cases, and no similarity with ants CHCs. The conclusion should have been that chemical camouflage was involved. This was just as the researchers expected. However, in some cases, the resemblance was much lower, between 34% and 55%, so the larvae involved must be fully “visible” to the ants.
“It seems that this information did not lead to anything,” Kaminski said. Researchers now have insight: What if the apparent emergence of these species is an evolutionary feature? Then they noticed another difference.
Some caterpillars are known to have organs dedicated to interacting with ants, such as the structures that produce substrate vibrations and the tiny filaments (filaments) used in chemical communication. Other major organs include the glands that produce a sugary liquid as a caloric reward for ants.
In camouflaged species, production of this ‘nectar’ was minimal or the glands were inactive. In eminent species, these organs were well developed and produced a large amount of fluid.
“If the caterpillar stays in hiding, it doesn’t need to give anything to the ants, but if it does produce a reward it should be clear. What is involved here is the evolution of the caterpillar’s contact with the ant,” Barbosa said.
According to the authors, these characteristics may lead to species with nectar-producing glands more and more chemically similar. This phenomenon is known as mimicry and is common among insects.
The similarity of toxic or rewarding species, for example, may be an adaptive advantage. Researchers now suggest that some kind of reward-based mimicry may also take place chemically.
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