Threatened tadpoles of Bokermannohyla alvarengai (Anura: Hylidae) choose backgrounds that enhance crypsis potential

Abstract

Crypsis results from a complex interaction among prey coloration, background matching, behaviour and predator visual perception. Tadpoles are known to have varied adaptations to escape predation, but the use of crypsis is little explored, although it is likely for certain species. We investigated potential escape mechanisms related to active escape (fleeing) and crypsis improvement in Bokermannohyla alvarengai tadpoles, proposing a new method to measure cryptic potential. We studied the range of distances covered by threatened and fleeing tadpoles and the proportion of tadpoles that seek shelter or remain exposed after fleeing. We hypothesized that tadpoles that remain exposed may use alternative strategies to avoid detection, such as reaching deeper microhabitats or positioning themselves on substrates that confer greater crypsis than the ones they were on before disturbance. A significantly greater proportion of tadpoles remained exposed after disturbance and positioned themselves on backgrounds that offered greater cryptic potential, but did not differ in depth. Tadpoles may respond to a trade-off between sheltering and being cryptic. On the one hand, they may remain close to retreat sites or they may escape to microhabitats that provide appropriate background matching as a means to achieve crypsis. On the other hand, the absence of matching backgrounds in the tadpoles' vicinities may induce them to seek shelter. © 2010 The Linnean Society of London.