The evolution of ants appears to have witnessed a phenomenon in which it was worth trading quality for quantity, a new study suggests. By increasing the number of workers in each anthill, the “investment” in the protective layer that covers the body of each insect became less and less.
It’s as if each ant colony decided to produce many disposable parts instead of a few excellent components. At least in evolutionary terms, the bet seems to have paid off: the insect lineages that followed this unconscious strategy diversified more than those that did not adopt this path.
The conclusions were published on the 19th in the specialized journal Science Advances, as part of work coordinated by Arthur Matte, of the University of Cambridge (United Kingdom), and Evan Economo, of the University of Maryland (United States).
The duo and their colleagues studied the variability in the thickness of the cuticle, the tough outer layer of insect anatomy that protects them from predator attacks and other types of mechanical damage, while serving as a barrier against microbes, temperature variations and moisture loss.
The functions of the cuticle are similar to those of human skin, but it is even more essential to the survival of insects, in addition to requiring a considerable investment of nutrients to be produced by the body. The intriguing detail is that, in ants, the thickness of this layer varies a hundred times (between 1.3 micrometers and 110 micrometers – each micrometer corresponds to a millionth of a meter).
The hypothesis put forward by the researchers is that such variability is probably linked to different types of investment of each species in the production of the cuticle. This type of economic reasoning is quite common in evolutionary studies.
Although living things are not capable of consciously choosing how their development will take place (and even if they understood it, they would not be able to control it), natural selection does it for them. Indeed, it ends up being the difference between strategies that produce many results and those that are less successful. Only the first are perpetuated in the population and, in practice, equivalent to a successful investment.
To test this idea, the researchers used microtomography techniques to map the cuticle of a considerable variety of ant species. They worked with 880 individuals, with workers represented in 440 different species, queens in 136 species and males in 73 species. Additionally, they compared the cuticle of ants to that of their “cousin” insects, such as wasps.
Understanding the differences between queens and workers, on the one hand, and between the sexes, on the other, is important because queens and males spend almost their entire life cycle protected inside the anthill, while workers perform a wide variety of tasks, often outside the nest, that could affect the need for cuticle development.
In fact, the researchers’ analysis confirmed the existence of enormous variations in the workers’ cuticles. In the two species that invest the most and the least in this part of the anatomy, the integument corresponds to 35% and 6.6% of the animals’ body volume, respectively. The question was whether there was an association between evolutionary patterns and this variability, which the researchers sought to analyze by taking into account relatedness between species and factors such as colony size, habitat, diet and the presence of defensive spines in the cuticle.
In theory, habitat differences could influence cuticle thickness, because in some contexts the tendency to lose moisture from the organism is much higher, which would require greater external protection. Defensive spines would also require more investment, while diet could interfere with the availability of nutrients needed to “assemble” the cuticle throughout development.
Climatic conditions of habitat and food are associated with these variations: species from warmer locations, or those that are carnivorous or feed on fungi, tend to have thicker cuticles on average. But the factor most strongly associated with cuticle variations is colony size: the more individuals in the anthill, in general, the thinner the outer layer of the body.
The researchers calculate that this variable explains almost half of the variability between ant species. Most importantly, there is a link between the large-scale production of “second-rate” workers and the diversification of ant species over time.
The team of scientists propose that this process could have facilitated the increase in the social complexity of anthills and the colonization of more resource-poor environments by the animals.
About The Author
