Ferraro, D.P., Topa, P.E. and Hermida, G.N. 2011. Lumbar glands in the frog genera Pleurodema and Somuncuria (Anura: Leiuperidae): histological and histochemical perspectives. —Acta Zoologica (Stockholm) 00: 1–14. Abstract The skin in the lumbar region of nine species of Pleurodema and in the monotypic genus Somuncuria (Anura: Leiuperidae) bears macroglands [lumbar gland (LG)]. Lumbar glands of Pleurodema bibroni, P. borellii, P. brachyops, P. bufoninum, P. cinereum, P. cordobae, P. kriegi, and P. thaul, as well as Somuncuria somuncurensis, were examined using histological and histochemical methods. The epidermis and the dermis of LGs are described. Also, skin of LGs presents characteristic features as the interruption of the Eberth–Katschenko layer and the presence of a differentiated type of gland only observed in macrogland and not previously described for Pleurodema or Somuncuria; this is termed lumbar serous gland. These glands are filled with a granular product, which occasionally is immersed in a matrix. Differences in the secretory products of mucous and serous glands are described, as well as inter‐ and intraspecific variability of gland structure. The mode of toxin expulsion from macroglands and the homology between lumbar and inguinal glands among anuran families are discussed.
Anurans show a wide variety of anti-predator mechanisms, and the species of the Neotropical clade Leiuperinae display several of them. Most species of Edalorhina, Physalaemus and Pleurodema show eyespots, hidden bright colours, macroglands in a inguinal/lumbar position, defensive behaviours and/or chemical defence. We conducted a histological analysis of dorsal and lumbar skin and revised the colour patterns, defensive behaviours and glandular secretions to study the diversity and evolution of anti-predator mechanisms associated with macroglands. We describe 17 characters and optimize these in a phylogenetic hypothesis of Leiuperinae. In the most recent common ancestor of Edalorhina + Engystomops + Physalaemus + Pleurodema, a particular type of serous gland (the main component 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 with aposematism (hidden bright colours and eyespots) evolved independently in several species. Our results provide phylogenetic evidence for the startle-first hypothesis, which suggests that behavioural displays arise as sudden movements in camouflaged individuals to avoid predatory attacks, before the origin of bright coloration.
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