Thermal tolerance of common North American ants (Hymenoptera: Formicidae)

Ants are nearly ubiquitous in terrestrial environments, occupying diverse habitats and ecological niches.  We examined the critical thermal maxima of several colonies of common North American ant species.  We were specifically interested in 1) inter-colony variation in thermal tolerance, 2) intra-colony variation in thermal tolerance, 3) interspecies variation in thermal tolerance, and 4) the relationship between mass and thermal tolerance.  Ants were collected from multiple locations centered around Lubbock County, Texas and Pulaski County, Arkansas between 2011 and 2013.  Prior to thermal trials, ants were housed in plastic contrainers with ad libidum food.  Five ants per colony were then moved to clear plastic vials and submerged in a hot water bath with an initial temperature of 28 C.  The temperature of the bath was increased approximately 1 C / min until the point at which the ants lost the ability to right themselves.  Critical thermal maxima differed significantly among species and habitat types.  There was a significant, but weak, relationship between mass and thermal tolerance.  The range of thermal tolerances were broader among colonies than within.  This research illustrates the importance of examining relevant units in studies of ant thermal tolerance and sheds new light on the thermal physiology of ants.  Given the important roles of ants in environmental functioning and the potential for warmer temperatures, the physiological ecology of ants is highly relevant and important.