D3328: Movement activity differs with reproductive status in workers of the ant Harpegnathos saltator

In the ponerine ant, Harpegnathos saltator, workers are capable of sexual reproduction, and when a colony’s queen dies some workers assume her role and become gamergates- workers with queen-like physiology. Though morphologically identical, behaviorally gamergates appear “inactive”, “slow”, and display “minimal movement”, while non-reproductive workers appear relatively “fast” and “active”. While these movement activity differences have been reported anecdotally, to our knowledge they have never been investigated experimentally. Here, we quantify and statistically compare two measures of movement activity (1. displacement, the straight-line distance between observed locations from one day to the next, and 2. the relative frequency of ‘in transit’ observations) for H. saltator gamergates and non-reproductive workers over a period of weeks to test these reported differences. Our findings corroborate the anecdotal reports of movement activity differences between H. saltator gamergates and non-reproductive workers. Gamergates had an average daily displacement 2.2 times less than that of workers and were 18.5 times less likely to be observed in transit. Though outside the scope of this study, lower movement activity by gamergates may reflect resource reallocation to meet the physiological demands of egg production, or perhaps a mechanism to reduce oxidative stress. Our findings suggest lower movement activity should be considered part the reproductive syndrome of this ant species.