Multimodal learning in ants, species differences in Ectatomma

Associative learning has been proposed to be an important evolutionary advancement; however few studies have compared associative learning across species. The ants Ectatomma ruidum and Ectatomma tuberculatum are well known and widespread ants in the neotropics with overlapping ranges, however they occupy different niches. We used these ants to compare learning in an effort to link memory consolidation to the ecology of an organism and to examine how different brain neuropils may influence learning. We found E. ruidum learned significantly better and remembered longer than E. tuberculatum, however neither ants were trainable when only a single sensory modality (olfactory) was used. E. ruidum only learned when we combined an olfactory cue with a tactile stimulus. This multimodal learning pattern suggested for these ants, perhaps given their complex environments, that olfactory cues must be coupled to tactile stimuli to elicit memory consolidation. When given this multimodal system, some E. ruidum exhibited single triail learning. Ectatomma tuberculatum on the other hand did not show increased learning with this multimodal approach, which may be due to this ant’s reliance on visual cues. Indeed, E. tuberculatum have significantly larger optic lobes than E. ruidum. We discuss the implication of this learning paradigm in relationship to these ants ecology and their brains.