Olfactory learning in two Amblypygi species Paraphrynus laevifrons and Phrynus pseudoparvulus.

A wide diversity of arthropod taxa have demonstrated the capacity for learning, but most of our current understanding comes from only a select subset of this highly diverse clade, with most studies focusing on various insect groups. Amblypygids (Order Amblypygi, Class Arachnida), however, are emerging as a model group for studying sensory integration and the neural substrates associated with learning and memory, especially as it relates to navigation. These nocturnal creatures possess specialized sensory appendages and one of the largest and most complex mushroom bodies - the part of the arthropod brain associated with learning and memory - of any arthropod. Prior field studies on multiple species demonstrate sophisticated homing abilities while laboratory-based behavioral assays in Phrynus marginemaculatus confirm olfactory-based learning associated with a refuge. In this study, we expand these laboratory-based assays to test the olfactory learning ability of two additional amblypygid species - Paraphrynus laevifrons and Phrynus pseudoparvulus - for which field data suggest complex navigation. We trained each species to associate an open refuge with a distinct chemical stimulus, using slightly different species-specific experimental details. We found evidence of olfactory learning in the training trials for both species, with an unexpected pattern of seeming avoidance learning of hexanol. Our test trials did not show significant associations with the trained stimulus, but this may have been in part due to our experimental design. Ultimately, we find some evidence of olfactory learning in additional amblypygid species, but our findings raise additional questions and highlight the need for species-specific study designs.