12. Group Composition (WIN-Programm)

it seems that a lower density monolayer should have a faster wound healing res-
ponse. Then why do epithelial cells reach and maintain a much higher density at
homeostasis?
To investigate the effect of cell density on wound healing, we performed
wound trauma experiments on monolayers cultures at different densities, and tra-
cked the cells at the wound edge over time (Fig. Id, Fig. le). We found out that
at homeostatic density, clear outgrowths are characterized by leader cells at the
tips (Fig. Id —e, orange tracks) and follower cells in the wake (Fig. Id —e, green
tracks). These monolayers migrated much further into the wound as compared to
monolayers at lower density (Fig. Id, Fig. le). Velocity correlation length analysis
interestingly revealed an increase in the motion coordination in the monolayers
at homeostatic density compared to the low density case (Fig. 1b, Fig. 1c). For the
case of homeostatic density, this coordination spanned about ten cells, suggesting
that each cell senses and Coordinates its motion with approximately ten neighbors
(Fig. 1c). However, at a density lower than the homeostatic density, we found that
the velocity coordination length is much lower (about 5 cells). These results sug-
gest that, while the homeostatic density maintained by epithelial cells may not be
optimal for individual mobility, it enhances the collective mobility during wound
healing by enabling close communication and coordination among the individual
cells.
Whereas cells use stochastic differences to differentiate roles within the group,
honey bees allocate tasks based on a System of age polyethism, where workers com-
plete different tasks as they age. Broadly, young bees care for brood in the nest Cen-
ter, middle-age bees perform nest maintenance and food processing throughout
the nest, and old bees guard the nest and collect forage outside the nest. Although
previous work has revealed these general behavioral trends as bees age, individual
bees diffcr in when and how they make these transitions.
To address the question of how individuals vary in their life-trajectories, we
introduced 16 cohorts of individually-marked newborn bees into an observation
hive, and used the BeesBook tracking System to monitor individuals over their
entire lifetime (Fig. 2a). Bees within a single cohort (200—400 bees per cohort) are
from the same queen, born on the same day; this enables a comparison both within
the age-matched cohorts, and between cohorts. On a given day, younger bees ten-
ded to spend more time on honey and brood areas, and older bees on pollen and
dance areas (Fig. 2b). The points, representing the average of individual bees on
that day, show that there is considerable Variation in nest usage, even within a single
age-cohort. We are currently analyzing this variability to ask how a bee’s life history
and nestmate interactions relate to the observed variability in behavior.
Similar to the rapid collective response following wound trauma, a honeybee
colony must respond to changes in the environment. Temperatures above 40 °C
are dangerous for brood development, and higher temperatures can destroy the

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