The nature that surrounds us is full of mysteries and, as a society, we have only discovered a little part of it. One of them is that female dragonflies of the genus Ischnura imitate the blue color, characteristic of males, to avoid mating when they have not reached sexual maturity.
This is one of the answers that Dr. Beatriz Willink Castro, a biologist graduated from the University of Costa Rica (UCR), obtained in her doctoral thesis carried out at the University of Lund, Sweden, under the supervision of Professor Erik Svensson, specialist in the behavior of these dragonflies. This research is made up of three components of biology: what happens in the field at the population level, its behavior and a study on a macroevolutionary scale.
Her comprehensive approach earned her the 2020 Presidential Award from the American Association of Naturalists, given to the best article published in The American Naturalist magazine, ranked 13th among publications on evolutionary biology. Willink is the first Latin American to win this award.
“I’ve always liked that feeling of understanding how something works. My priority as a biologist is to obtain more complete and comprehensive explanations of a phenomenon”, commented Dr. Willink, professor at the School of Biology at UCR.
According to the 32-year-old biologist, since the 1980s there has been a tendency to study communication signals between the sexes. However, this has historically been aimed at investigating the signals of the males to attract females.
“That may be because it is more common for males to signal to females than the other way around. In most animals, males compete with each other to attract females. But, it is not so obvious if there is this competition between females or when they emit signals to the males”, she expressed.
A line of research
In the field of biology, this research is developed as part of the theory of sexual conflict, an area not very explored. Signs among dragonflies The genus Ischnura has about 70 species of damselflies (dragonflies) and they are all related to each other. Damselflies are highly visual insects, as they have highly developed eyes. Additionally, there is a lot of color variation between species, especially in females. In the case of males they are visually distinguished, because they have a blue patch on the abdomen.
In some species, such as the main species in this study, there are three types of genetically determined females, but regardless of this difference, they all have a blue patch when young and sexually immature. However, in two types, as the females become adults, the patch becomes covered with a dark pigment and disappears. In contrast, the third type keeps the patch for its entire life.
These dragonflies are known as female mimetic males, and Willink, along with his colleagues, found that they use this strategy to avoid over-mating. A feminist statement by dragonflies. “One possible reason for this evolution is that juvenile females that have not reached sexual maturity need to identify themselves and indicate to the males that they are not sexually fit,” the researcher commented.
Females would avoid mating because it takes time away, can cause physical harm, and transmit disease. In addition, the males do not benefit either, since they are females that do not have eggs, or if they do, they are not yet viable. After all, individuals benefit by maximizing their reproductive capacity, according to the biologist.
To reach these conclusions, the team studied the field data in order to verify that females with a blue patch do indeed mate less, with a drastic difference from those without this visual characteristic. In addition, they confirmed that these dragonflies are less fertile, as they produce eggs with lower reproductive potential
They also did an experiment, which consisted of making young females look mature by hiding their blue patch and, at the same time, making the mature ones look younger by painting them a blue patch.
“We simply used nail polish of different colors and an experimental design with two females of the same morphotype, together, in each trial, but one had the color that corresponded to her age and the other was manipulated to look younger than she was or older. Thus, we could see if by manipulating this patch of abdominal color we could deceive the males, attracting them or pushing them away”, explained the researcher.
Evolutionary history
For the macroevolutionary part of the research, the biologists carried out a small reconstruction of the evolutionary history of the species of the genus Ischnura, to analyze the kinship relationships and what colors they have.
“We wanted to see what the macroevolutionary pattern was and how this trait evolves in species. We saw that this patch is probably very old in males and was present even from the common ancestor of all current species. In females, when there is the genetic morphotype of imitating males, they almost always have a blue patch and in the few cases that do not have it, it is because the males do not either”, explained Willink.
The scientist assured that the patch has also evolved in females who are not mimetic of males, but only when they are sexually immature. This has occurred in several species that are not particularly related to each other; in other words, that temporary blue signal had to have evolved several times and independently in different branches of the evolutionary tree.
Currently, Dr. Willink collaborates in the research on the cultural evolution in hummingbirds by means of phylogenetic analyzes (kinship between species), along Dr. Marcelo Araya, from the South Headquarters of the UCR.
The next objective of Dr. Beatriz Willink is to do a post-doctorate in developmental biology, in which she intends to understand which genes and developmental mechanisms control the coloration of female damselflies, through molecular analysis, and investigate how it is that that resemblance to the male evolved.
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