Formica polyctena

Formica polyctena is a species of European red wood ant in the genus Formica and large family Formicidae. It is found in many European countries. It is a eusocial species, that has a distinct caste system of sterile workers and a very small reproductive caste. The ants have a genetic based cue that allow them to identify which other ants are members of their nest and which are foreign individuals. When facing these types of foreign invaders the F. polyctena has a system to activate an alarm. It can release pheromones which can trigger an alarm response in other nearby ants. It is found in Austria, Belgium, Bulgaria, Czech Republic, Finland, France, Germany, Hungary, Italy, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Poland, Romania, Russia, Serbia and Montenegro, Slovakia, Spain, Sweden, Switzerland, and Ukraine. Formica polyctena like many ant, wasp and bee species, displays a eusocial system. Eusocial insects are characterized by cooperative care of young among members of a colony, distinct caste systems where some individuals breed and most individuals are sterile helpers, and overlapping generations so mother, adult offspring and immature offspring are all living at the same time. In a eusocial colony, an individual is assigned a specialized caste before they become reproductively mature, which makes them behaviorally distinct from other castes. Red wood ants exhibit all of these characteristics, with queens and males that make up the reproductive caste and sterile female workers that aid in brood care and colony maintenance. Workers in ant colonies are typically sterile females that do not reproduce. F. polyctena is consistent with this model, with almost completely sterile workers that do not lay eggs. This is in contrast to other Formica species that have workers that actually do reproduce, disrupting the eusocial system. F. polyctena’s high proportion of worker sterility indicates a strict obligate polygynous colony structure that most likely allows for a stable unicoloniality, or the cooperation of several nests. In other words, workers do not have the ability to disrupt the strict social segregation of reproduction by reproducing themselves. Thus they uphold a multi-queen, multi-nest cooperation that may not be advantageous to their genes since they act altruistically toward non-kin. In F. polyctena colonies, there appears to be a separate group of designated foraging workers. The number of foragers correlates with the size of the colony. Foragers also tend to be older workers. However, if foragers are lost or die, other workers from the nest can replace them, indicating some flexibility in designated roles within the colony. These replacement workers have a shorter life expectancy as foragers, indicating that there could be some physiological development as the workers age that allows them to be effective foragers. In order to prevent costly conflict between fellow nestmates or involuntarily altruistic behavior toward ants from a foreign nest, individual ants need to distinguish between their fellow nestmates and foreigners. It has been demonstrated that Formica polyctena uses genetically-based cues as a nestmate recognition mechanism. Since F. polyctena, like all ant species, lives in colonies with high genetic relatedness, this type of mechanism would be successful in distinguishing between colonies. Beye, Neumann and Moritz conducted a study where pairs of ants from different nest were introduced to each other to see if they fought, tolerated or avoided one another. Pairs of ants from the same nests were introduced as well to act as a control. Genetic similarity between these ants was measured as well. A strong positive correlation existed between antagonistic behavior and genetic dissimilarity. Thus, F. polyctena ants mostly likely recognize their fellow workers through some genetically produced signal. Nest populations in close physical proximity to one another didn’t necessarily demonstrate either extremely aggressive or passive behavior toward each other, indicating that nest proximity does not influence recognition. Additionally, nest distance did not correlate with genetic similarity. Essentially, F. polyctena has adapted some form of genetically-based cue that allows nestmates to distinguish between each other and foreign individuals. Beye, Neumann and Moritz believe that these genetic cues act to keep nest colonies separate in homogenous environments that offer no other nestmate recognition strategies. Alarm behavior can be triggered in Formica polyctena by the release of pheromones. When ants come across a specific pheromone, they approach the source with jaws wide open, as if confronting a threat. Specifically in F. polyctena, these chemical alarm signals elicit a response not only within the nest, but along foraging paths. In particular, the formic acid sprayed by ants when attacked can trigger a predator alarm response in nearby ants, gathering reinforcements to attack the predator. In this way, formic acid doubles as a chemical weapon against predators and an alarm signal in F. polyctena. Due to the close living situation of individuals in a F. polyctena colony, diseases can spread rapidly, causing significant damage to the colony’s population. Therefore, F. polyctena has evolved responses to combat the spread of disease. When an individual ant develops an immune response to some disease, the other workers can sense this. The workers decrease mouth-to-mouth exchanges of liquid, and prevent the infected individual from moving around. The healthy workers also increase antennal contact and grooming of the infected ant. This is believed to either remove pathogens from the ant that could cause such an immune response, or act as a “social vaccination.” Aubert and Richard proposed this social vaccination model, where they argue that if fellow nestmates groom an infected ant, they will be exposed to small amounts of the pathogens or molecules that could trigger an immune response within the healthy individuals. In essence, the healthy individuals develop a resistance to the pathogens carried by the infected individual before the pathogens can spread and infect them.