March of the supersoldiers

Ancestral Developmental Potential Facilitates Parallel Evolution in Ants,” a study out of McGill University published Jan. 6 in Science, shines light on a different class of ant: the supersoldier. The study was able to manipulate normal ant development to produce this rare ant type, characterized by an oversized head. Although the study was focused only on ants, researchers suggest that turning on this “hidden trait” may give us further insight into the process of evolution.

The ant is an insect of the family Formicidae. Deemed “social insects,” because of their ability to interact and work together to feed each other and survive as a unit, ants are categorized into three castes within any given colony: the queen, her males and the workers. Within the caste of workers, some ant genera, such as Pheidole, have two subcastes of workers: the minor worker and the soldier. Compared to the minor worker soldiers are much larger, and within the ant colony have the important tasks of protecting the nest and processing the food.

The genera Pheidole is the most species rich ant genus, consisting of more than 1,100 ant species. The genus contains eight types of species which produce those ants dubbed “supersoldiers.” Although they engage in the same activity as normal soldiers, their main function is more specific — they use their large heads to block the entrance of the nest during an enemy-ant raid.

The study was able to produce supersoldiers by mutating larvae. This was done by inducing the larvae with juvenile hormone or “methoprene.” Eggs produced by the queen ant often develop into different castes as a result of differences in the environment, the temperature and/or the nutrients in which they develop, however, the juvenile hormone is the key that allows the transformation into the supersoldier. Most remarkable is that the study was able to induce the ant larvae into becoming supersoldier ants in species such as P. hyatti and P. spadonia, which normally do not produce supersoldiers.

Having induced supersoldiers in different species, the study was able to demonstrate that the trait to produce supersoldiers has not disappeared, but has remained hidden in the ant’s genome. Specifically, the trait has remained in all Pheidole related species that derived from a common ancestor. As the study states, the phenotypic (observable) expression of supersoldiers was subsequently lost [in P.hyatti and other non-supersoldier species], but the ancestral potential to produce them was retained.”

This comes on the heels of a related study, where a research team from Sussex University and the University of Sao Paolo discovered the first known soldier bee. Characterized by a small head and larger legs, the soldiers provide defence and forewarning against attack, similar to supersoldier ants.

In an interview with the BBC, Ehab Abouheif of McGill University, who led the supersoldier ant study, said he believes that the information garnered from the respective studies could change the way evolution, as a whole, is viewed by scientists. With the re-evolution and induction of the supersoldier subcaste, the study was able to show that although the trait is shut off in the majority of ant species, the activation of the developmental pathway to becoming a supersoldier may be as simple as a flick of a switch.

One of the long held beliefs about evolution is that many ancestral traits, such as humans with ape-like hair, are lost through the generations and therefore cannot reappear in subsequent generations. These new findings beg the questions: are there other species out there — perhaps us — with ancestral traits similarly hidden in our genes? Can these traits be unlocked, as in the case of the supersoldier?