Evolution of macroglands and defensive mechanisms in Leiuperinae (Anura: Leptodactylidae)

Abstract

Anurans show a wide variety of anti-predator mechanisms, and the species of the Neotropical clade Leiuperinaedisplay several of them. Most species of Edalorhina, Physalaemus and Pleurodema show eyespots, hidden brightcolours, macroglands in a inguinal/lumbar position, defensive behaviours and/or chemical defence. We conducted ahistological analysis of dorsal and lumbar skin and revised the colour patterns, defensive behaviours and glandularsecretions to study the diversity and evolution of anti-predator mechanisms associated with macroglands. Wedescribe 17 characters and optimize these in a phylogenetic hypothesis of Leiuperinae. In the most recent commonancestor of Edalorhina + Engystomops + Physalaemus + Pleurodema, a particular type of serous gland (the maincomponent of macroglands) evolved in the lumbar skin, along with the absence of the Eberth?Katschenko layer.A defensive behaviour observed in leiuperines with macroglands includes four displays (?crouching down? behaviour,rear elevation, body inflation and eye protection), all present in the same ancestor. The two elements associated withaposematism (hidden bright colours and eyespots) evolved independently in several species. Our results providephylogenetic evidence for the startle-first hypothesis, which suggests that behavioural displays arise as suddenmovements in camouflaged individuals to avoid predatory attacks, before the origin of bright coloration.