The evolution of activity breaks in the nest cycle of annual eusocial bees: a model of delayed exponential growth.
BACKGROUND
Social insects show considerable variability not only in social organisation but also in the temporal pattern of nest cycles. In annual eusocial sweat bees, nest cycles typically consist of a sequence of distinct phases of activity (queen or workers collect food, construct, and provision brood cells) and inactivity (nest is closed). Since the flight season is limited to the time of the year with sufficiently high temperatures and resource availability, every break reduces the potential for foraging and, thus, the productivity of a colony. This apparent waste of time has not gained much attention.


RESULTS
We present a model that explains the evolution of activity breaks by assuming differential mortality during active and inactive phases and a limited rate of development of larvae, both reasonable assumptions. The model predicts a systematic temporal structure of breaks at certain times in the season which increase the fitness of a colony. The predicted pattern of these breaks is in excellent accordance with field data on the nest cycle of the halictid Lasioglossum malachurum.


CONCLUSIONS
Activity breaks are a counter-intuitive outcome of varying mortality rates that maximise the reproductive output of primitively eusocial nests.
Mitesser
Oliver
O
Forschungsstation Fabrikschleichach, Universität Würzburg, Glashüttenstr, 5, D-96181 Rauhenebrach, Germany. mitesser@biozentrum.uni-wuerzburg.de
Weissel
Norbert
N
Strohm
Erhard
E
Poethke
Hans-Joachim
HJ
D000818:Animals; D001516:Bees / Q000502:physiology*; D005075:Biological Evolution; D008954:Models, Biological; D009425:Nesting Behavior; D012919:Social Behavior