University of São Paulo: Sorceress ants help scientists understand the influence of the environment on the color of species

MEven without known predators, reinforcing a dangerous color pattern, until then, explained the variation in the colors of the wasp species known as witch ants across the Americas. By analyzing the presence of melanin in their exoskeletons and crossing with the climatic data of each species, the entomologist Vinicius Marques Lopez showed that morphological characteristics, such as the color of the animals, can be under the influence of climatic factors, depending on humidity, vegetation and exposure to ultraviolet radiation. The data meet the consensus of the scientific community and open up new alternatives for understanding how animal life is presented in different regions.

The article entitled Color lightness of velvet ants ( Hymenoptera: Mutillidae ) follows an environmental gradient describes the study by Lopez, a doctoral candidate in Entomology at the USP campus of Ribeirão Preto, and was published in August of this year in the Journal of Thermal Biology . The work was supervised by Rhainer Guillermo-Ferreira, a professor at the Federal University of Triângulo Mineiro (UFTM) and at the Postgraduate Program in Entomology at USP, had the collaboration of other researchers from national and international institutions and had the support of the Improvement Coordination of Higher Education Personnel (Capes).

Neither ants nor witches
One of the ways to get to know these insects is the way they are called in Brazil, and the most common is “witch ant”. The researcher explains that, despite being commonly confused with ants, the more than five thousand species of the Mutillidae family are, in fact, wasps. This confusion happens due to the fact that females do not have wings, and this also explains the etymology of the group’s name, which comes from “mutilated”.

Due to the different and eye-catching colors, the group is popularly called “witch woman” also because of the strangeness and mystery that the animal carries for indigenous groups. Also due to their colors, they are called “little leopards” in some regions of the country. Another name that gives away their characteristics is “velvet ant”: these wasps have small cuticles that cover their bodies and give them a velvety appearance. The nickname “alone ant” reflects the behavior of this insect. “They are solitary wasps, usually found alone, different from other wasps and ants that are always accompanied by others of the species”, he explains.

This group of ants, or rather wasps are found worldwide, mostly along the North, Central and South America. In the United States, the insect is known as cow-killer , or “kill-cow” in free English translation. The name caught on because of the animal’s painful bite – although the sting is not capable of killing a cow, it is among the most dangerous.

In addition to the bite, the group has a series of defense strategies, such as making sounds when contracting the abdomen and a rigid exoskeleton that is proof against biting and crushing attempts. Lopez explains that, evolutionarily, these mechanisms are adaptations against predation on other animals – and that includes their strong colors – however, it is not known who the predators of Mutillidae are .

Does the weather or predators color wasps?
To avoid predators in nature, animals can seek to imitate dangerous species through adaptive strategies called mimicry. According to the scientist, there are two main types of mimicry that explain the color variation of these wasps across the globe: the Batesian and the Müllerian. The first one concerns cases in which the model animal presents characteristics that are undesirable to predators and is imitated by another that is not so lucky, such as the real, poisonous coral, which has its stripes imitated by the false coral, which does not present any danger. to prey.

In Müllerian mimicry, both the mimic and the model have aspects that should be avoided by predators. Unlike the Batesian, who can “get the wrong idea” and teach the predator that those colors or shapes indicate risk, when he feeds on a false coral and nothing bad happens, for example, the Müllerian seeks to reinforce a pattern.

Studies on these insects explained the wide variation in the color of wasps across the American continent by Mullerian mimicry. But why mimicry if there are no predators? Seeking another explanation for the colors in Mutillidae , the researchers hypothesized, in the area of ​​ecogeography, that colors, as well as other morphological characteristics of animals, can vary according to environmental gradients.

One of the hypotheses is photoprotection, which says that animals will be darker in places with more ultraviolet radiation, because melanin, the pigment that gives color to our hair, skin and eyes and also to the exoskeleton of these insects, acts as a protector against DNA degradation, explains Lopez. Another says that animals will be darker in more humid environments and the third is called thermal melanism, in which animals tend to be darker in colder environments, with less sun. “Since they are ectothermic, they need external heat sources to maintain their temperature and start their activities, so being dark speeds up heat absorption,” he says.

“I’m explaining to you to confuse you”
To analyze the wasp color variation according to the environmental gradient, the researcher photographed parts of the family’s species, belonging to the USP Museum of Zoology (MZ), and used a computer program that crosses the color data with geographic information origin of the collection of each species. In addition, the phylogenetic relationships between species were taken into account, through a family tree, which corrects the bias of kinship between individuals.

Data show that darker species tend to live in environments with more vegetation, higher relative humidity and higher ultraviolet radiation. “Our results corroborate the hypothesis of photoprotection and go against thermal melanism: in environments with high ultraviolet radiation, species are darker and there was no significant relationship between color and temperature”, he says.

“The results obtained provide evidence that the climate and the environment can act as ecological filters and selective frameworks that drive the evolution of the color of the sorcerer ants”, he adds. According to him, the findings revive a hypothesis by Henry Walter Bates (1825-1892), discoverer of the Batesian and naturalist mimicry of Charles Darwin’s time, in which he suggests that mimetic coloring and against predation may be under the influence of climatic factors and not only from predators.