Most amphibians with biphasic life cycles have aquatic eggs and larvae and terrestrial 11 adults that must migrate between terrestrial habitats and aquatic breeding sites. Migration usually 12 occurs at night, which reduces desiccation risk and contributes to predator avoidance. However, 13 some amphibians also migrate during day, and it has been proposed that this evolved as a result 14 of poisonous skin secretions and aposematic coloration that release individuals from visually 15 oriented diurnal predators. Based on this hypothesis and recent observations of 24 hour breeding 16 activity in the poisonous toad Melanophryniscus cambaraensis, we predicted that migration in 17 this species would occur equally during day and night intervals. Contrary to our prediction, we 18 found that migratory activity is strongly diurnal and that this does not owe to environmental 19 variables. We suggest that this is best explained by phylogeny, not contemporary pressures. 20 Diurnality is primitive for M. cambaraensis and evolved in the common ancestor of 21 Agastorophrynia, prior to the chemical defences found in toads (Bufonidae) and poison frogs 22 (Dendrobatidae). This suggests that chemical defences in these groups may have evolved as a result of the diurnal activity that brought them into contact 23 with visually oriented diurnal 24 predators, and not the other way around.
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