Genetic diversity in tempo determines foraging range in ants

The foraging behavior of a colony arises from the activity of individual workers.  In this paper we explore the phenotypic differences among the workers of the western harvester ant, Pogonomyrmex occidentalis in order to understand the temporal pattern of foraging in colonies.  We know that the genetic diversity of colonies influences the temporal pattern of foraging: with greater genetic diversity colonies begin foraging earlier and forage for greater duration.  

We test two mechanisms to account for this pattern.  The Temperature Hypothesis predicts that early foragers will be more active at lower temperatures than late foragers and will be the first workers to initiate foraging.  Late foragers will be more active at high temperatures.  The Tempo Hypothesis predicts that early foragers will be the first to forage because they have the higher overall tempo of activity at all temperatures.  

We measure the movement activity of samples of early and late foragers from 32 colonies over a range of temperatures from 9-37̊C.  We find that early workers are more active at all temperatures than late workers, supporting the Tempo Hypothesis.  Early and late foragers tend to belong to different patrilines, suggesting that there is a genetic basis for the difference in the tempo of behavior.  We also find that colonies that have greater number of patrilines, due to greater mating frequency by the queen, have a greater range temporal range of foraging.  

Methods
The data were collected from the movement activity of early and late foragers from naturally occurring colonies of Pogonomyrmex occidentalis.  Early workers were the first workers to begin foraging in the morning while late workers were the last to forage in the morning.  The movement activity was measured from video image differencing over a range of temperatures.  We report the movement for ten minute periods for individual workers at each temperature from  9-37̊C.  We also report the patriline identity for each worker within each colony.