Cave-epigean behavioral variation of the whip spider Phrynus longipes (Arachnida: Amblypygi) evidenced by activity, vigilance, and aggression

Caves are peculiar ecosystems; they are most often small, isolated habitats that lack the energy that sunlight provides. Cave-adapted species, isolated from epigean (i.e., surface) selection pressures, have been discovered with aphotic adaptations like blindness, depigmentation, and enhanced extra-optic sensory systems. This evolutionary process, however, only occurs in a fraction of cave ecosystems. Many cave species, especially those in tropical latitudes, occur with epigean conspecifics with ongoing gene flow and epigean migration. This includes populations of the amblypygid Phrynus longipes (Pocock 1894), which occur in both epigean and cave environments. I hypothesized that cave and epigean populations exhibit behavioral variation to meet the selection pressures of their respective environments. I conducted open-arena and interaction behavioral assays to test for behavioral variation between populations. Assays revealed that cave and epigean amblypygids exhibited environment-specific behavioral variation. Cave animals were more vigilant and engaged in hunting behaviors, but were less active in general, relative to epigean conspecifics. Comparative modeling indicated that aggressive behaviors during agonistic interactions were the best predictors of environment. Indeed, epigean interactions escalated to physical aggression sooner and included longer weaponry displays than did the interactions of cave conspecifics. Trial design allowed for measurements of territorial behavior, which showed that residency effects were more profound in epigean interactions than in those of cave conspecifics. The high density of amblypygids in the cave population may have resulted in more tolerant, less aggressive behaviors relative to epigean conspecifics. Thus, these findings fit the ecological and demographic conditions of each environment.