Nocturnal and diurnal predator and prey interactions with crab spider color polymorphs.

Understanding the complex interplay of factors shaping polymorphic changes within individuals represents a longstanding conundrum in biology. Some crab spiders (Thomisidae) are examples of sit-and-wait predators that can change their body coloration. Many factors may influence crab spider color polymorphism with multiple explanations receiving various levels of support. Here we examined the daytime and nighttime activities and predator and prey interactions for two yellow-white polymorphic crab spiders, Thomisus labefactus and Ebrechtella tricuspidatus in the field. We thereupon conducted a manipulative experiment using dummies with color morphs visibly resembling the spiders when placed on background-matched flowers. We measured the spectra reflected from the dummies and their floral backgrounds and used insect visual models to determine if they are likely to be visible to a range of insects by night and day. We found that both color morphs of each species were more active by night than by day. Our visual models revealed that the spider's bodies were unlikely to be cryptic. Together, these results suggest that the crab spiders might exploit flower colorations during the night but not during the day. They also indicated that explanations of why crab spiders utilize certain color polymorphs are context dependent and will vary with time, and whether predators, prey, or both, are present. Significance statement: Crab spiders are an excellent model for investigating a long-standing challenge in evolutionary biology: understanding the causes and consequences of polymorphic coloration in animals. Studies have postulated a range of explanations with some support for each. Broader studies encompassing all interactions between spiders and their predators and prey across the day and night are urgently needed. Here we combined an around-the-clock spider activity survey with field experiments and insect visual models to show that the types of interactions between spider color morphs and their predators and prey differ over the day and night. Our study suggests that outcomes of experiments examining the adaptive drivers of polymorphisms may be dependent upon the context within which the observations were made, and that examining interactions across temporal contexts is required to fully uncover the various drivers of the polymorphisms. [ABSTRACT FROM AUTHOR]