DIEL EFFECTS ON CHEMICALLY-MEDIATED ANTIPREDATOR RESPONSES IN THE WOLF SPIDER Pardosa milvina (ARANEAE: LYCOSIDAE)
The wolf spider Pardosa milvina shows effective anti-predator behavior (reduced activity) in the presence of chemical cues (silk and excreta) from the larger co-occurring wolf spider Hogna helluo. Anti-predator behavior is costly consequently Pardosa may mediate their activity based on the level of predation risk. We measured diel effects on Pardosa activity level and Hogna predation efficiency with and without the presence of Hogna silk and excreta. We placed individual Pardosa on a peat moss substrate previously occupied by Hogna for 24 h or control substrates and recorded movement during a 20-minute period. Four treatment groups were used (N=20/treatment): 1) Hogna chemical cues during the day, 2) Hogna cues at night, 3) no cues during the day, and 4) no cues at night. We then measured Hogna predation latency on Pardosa in each treatment. There were significant effects of time of day, chemical cue presence, and interaction between the two factors on Pardosa movement. Pardosa showed a significant reduction in activity at night compared to the day. Pardosa also showed the greatest reduction in movement when exposed to Hogna cues at night and most movement in the absence of cues during the day. Preliminary analysis shows a change in Hogna predation success based on Pardosa activity levels and the presence of Hogna cues. Hogna is capable of locating and killing Pardosa in the absence of light, but since they showed a significant reduction in orientation and lunge responses to the presence of visual cues from Pardosa, we believe that Hogna may shift to vibratory and tactile cues while predating upon Pardosa at night.
