Detection of wolf spider courtship signals against complex chromatic backgrounds by intended and unintended receivers

Abstract

We used video digitization and playback of courting male Schizocosa ocreata wolf spiders to examine responses of intended receivers and eavesdroppers viewing manipulated spider color displayed against background treatments of complex litter with different chromatic contrast. Intended receivers (female S. ocreata) were more likely to detect males with higher background intensity contrast, while a different pattern for receptivity suggests chromatic contrast matters more for mate recognition. Social eavesdroppers (conspecific males) were similar but had a significant interaction of spider color x background, suggesting possible differences in color perception between sexes. Interceptive eavesdroppers (predators) differed across taxa in some respects but were similar in others. Vertebrates (toads) were quicker to orient than invertebrates (spider predators). Toads took longer to respond to control spiders on complex color backgrounds but were quicker with the same spider against complex greyscale backgrounds. Color differences among prey stimuli appear to be less important than contrast for both toads and wolf spiders with dichromatic vision. However, color of the prey spider stimulus matters more for jumping spiders with trichromatic vision, as they respond more quickly to natural color and RGB average color than gray monochrome stimuli. Analyses of chromatic and luminance intensity contrast values for spiders and backgrounds suggest that for both intended female receivers and eavesdroppers, intensity and chromatic contrast influence detection and mate recognition in complex and subtle ways. These results support the hypothesis that receivers with different visual sensory capacities vary in response to color and contrast of courting male spiders against complex backgrounds.