Abstract
We report the first instance of ontogenetic variation in web-decorating behaviour among conspecific populations of a spider. Small juveniles of Argiope appensa frequently spin discoid decorations in the Philippines, but only rarely do so in the Mariana Islands of Micronesia. Because discoid decorations have a defensive function, we suggest that natural selection against their main predators, araneophagic wasps, diverse in the Philippines but poorly represented in the Marianas, may be driving this difference in decoration frequency. Alternatively, because there can be a trade-off between defense through decorating and prey capture success, the cost of discoid decorations may be higher in the Marianas because of differences in prey-community structure.
