Abstract
The frequency and form of visual signals can be shaped by selection from predators, prey or both. When a signal simultaneously attracts predators and prey, selection may favour a strategy that minimizes risks while attracting prey. Accordingly, varying the frequency and form of the silken decorations added to their web may be a way that Argiope spiders minimize predation while attracting prey. Nonetheless, the role of extraneous factors renders the influences of top down and bottom up selection on decoration frequency and form variation difficult to discern. Here we used dummy spiders and decorations to simulate four possible strategies that the spider Argiope aemula may choose and measured the prey and predator attraction consequences for each in the field. The strategy of decorating at a high frequency with a variable form attracted the most prey, while that of decorating at a high frequency with a fixed form attracted the most predators. These results suggest that mitigating the cost of attracting predators while maintaining prey attraction drives the use of variation in decoration form by many Argiope spp. when decorating frequently. Our study highlights the importance of considering top-down and bottom up selection pressure when devising evolutionary ecology experiments.
Highlights
Top down and bottom up selection drives variations in frequency and form of a visual signal
The strategy of decorating at a high frequency with a variable form attracted the most prey, while that of decorating at a high frequency with a fixed form attracted the most predators. These results suggest that mitigating the cost of attracting predators while maintaining prey attraction drives the use of variation in decoration form by many Argiope spp. when decorating frequently
Spiders of the genus Argiope are the most ardent decorators; with most of its 701 species decorating their webs with some form of conspicuous silk bands[12,14,16]
Summary
Top down and bottom up selection drives variations in frequency and form of a visual signal. Varying the frequency and form of the silken decorations added to their web may be a way that Argiope spiders minimize predation while attracting prey. One hypothesis suggests that decorations are used as a deceptive signal that lures insects toward the web by mimicking cues the insects use to search for food[12,13,15,16] This same hypothesis postulates that when decorations are used as prey attractants they may lure unwanted bird and wasp predators and parasites[12,16,17,18,19,20]. It might be hypothesized that decoration variability has foraging and predation consequences for the spiders
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