Abstract
Determining how ant colonies optimize foraging while mitigating pathogen and predator risks provides insight into how the ants have achieved ecological success. Ants must respond to changing resource conditions, but exploration comes at a cost of higher potential exposure to threats. Fungal infected cadavers surround the main foraging trails of the carpenter ant Camponotus rufipes, offering a system to study how foragers behave given the persistent occurrence of disease threats. Studies on social insect foraging behavior typically require many hours of human labor due to the high density of individuals. To overcome this, we developed deep learning based computer vision algorithms to track foraging ants, frame-by-frame, from video footage shot under the natural conditions of a tropical forest floor at night. We found that most foragers walk in straight lines overlapping the same areas as other ants, but there is a subset of foragers with greater exploration. Consistency in walking behavior may protect most ants from infection, while foragers that explore unique portions of the trail may be more likely to encounter fungal spores implying a trade-off between resource discovery and risk avoidance.
Highlights
Resource acquisition drives animals into new territories, while threat avoidance limits where animals move
We studied the trails of seven C. rufipes colonies in their rainforest habitat to determine how individual ant trajectories vary in their consistency and coverage of trail space to investigate whether all foragers are at equal risk of encountering a fungal spore
The model picked up other insects or species of ants on the trail or failed to detect a C. rufipes ant as it went across the trail 2.14% of the time
Summary
Resource acquisition drives animals into new territories, while threat avoidance limits where animals move. A potential system is the carpenter ant Camponotus rufipes in southeastern Brazil, which forms trunk trails lasting for multiple months[14,15] Colonies of this ant were recorded as having a chronic infection by the fungal parasite Ophiocordyceps camponoti-rufipides across 20 months[16,17]. This fungus manipulates foragers to leave the nest www.nature.com/scientificreports/. We hypothesize that some individual trajectories will show evidence of searching behavior, but the majority of ants will walk directly across the trail and cover similar areas limiting the exposure of most ants to threats
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