SAD Ants (Seasonality Affected Decsion-making)

Should I, could I, would I? We make decisions at every moment, every day, every week, every month, and every season. These decisions are influenced by the environment and social interactions. Many animals exhibit social behaviors, such as feeding aggregations and communal nest sites. Ants can be considered the world’s most successful social insects. They are eusocial; share a common nest site, cooperate in caring for the young, sterile individuals work for the benefit of the few reproductive, and offspring contribute to the colony labor while parents are still present. These insects maximize their fitness by increasing accuracy when choosing among a set of options.

Temnothorax unifasciatus

Figure 1. Temnothorax albipennis ants build nests in rock crevices.

Temnothorax albipennis (Fig. 1) ant colonies engage in sophisticated chemical cues to reach consensus decisions. Stroeymeyt et al. (2014) showed that nest preference of these colonies is influenced by a season-specific pheromone that might aid in tuning decision-making according to seasonal constraints. Essentially, nest choice is determined by the season of the year and the presence of a substance. “Temnothrax ants inhabit fragile natural cavities—such as rotting twigs, hollow acorns, and rock crevices—so colonies frequently have to emigrate to a new nest if the conditions are no longer favorable.” Since several species of Temnothorax have been found to occupy different nest sites depending on the season, the researchers decided to investigate decision-making mechanisms during summer, autumn, and winter. Nest preference was found to be significantly different in the summer versus the winter (Fig. 2).  In the winter familiar nests were attractive and nest choice was influenced by positional cues. In the summer colonies considered the familiar nest unsuitable and nest choice was determined by presence of a scent mark.

Figure 2. Nest preference after 24 hours. Nests differed in position (FP: familiar position, occupied by familiar nest during exploration; UP: unfamiliar position) and in origin (dotted: previously explored; white: previously unexplored). Full squares with horizontal lines, rectangles and whiskers, respectively, represent the median, interquartile range and full range of colony items observed in each nest.

Would the same seasonality occur with the introduction of naïve nest-mates? Since ants are known to have certain chemical signals that can influence the behavior of other ants, these chemicals could contain private or social information. Results showed that when informed workers laid nest-marking chemicals inside familiar nests it triggered aversion towards those nests in naïve sister colonies, even when naïve colonies had never come in contact with those nests. This allows for one to conclude that these nest-marking chemicals act as pheromones to provide social information about the nest quality and influence nest choice.

Pheromones allow the ants to modify their decision for nest choice. Interestingly, the overall finding of Stroeymeyt et al. (2014) was that ants do not have to necessarily aim to maximize their accuracy when searching for a new home. Perhaps other variables such as decision time, value of chosen option in terms of energy cost, food proximity, or just survivability are prioritized.

Stroeymeyt, N. et al. (2014) Seasonality in communication and collective decision-making in ants. Proc. R. Soc. B 281: 20133108

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