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A gas-exchange structure interacts with the environment and is constantly challenged by contaminants that may elicit defense responses, thus compromising its primary function. It is also exposed to high concentrations of [O.sub.2] that can generate reactive oxygen species (ROS). Revisiting the lung of mammals, an integrative picture emerges, indicating that this bronchi-alveolar structure deals with inflammation in a special way, which minimizes compromising the gas-exchange role. Depending on the challenge, pro-inflammatory or antiinflammatory responses are elicited by conserved molecules, such as surfactant proteins A and D. An even broader picture points to the participation of airway sensors, responsive to inflammatory mediators, in a loop linking the immunological and nervous systems and expanding the role played by respiratory organs in functions other than gas-exchange. A byproduct of exposure to high concentration of [O.sub.2] is the formation of superoxide ([O.sup.*-.sub.2]), hydrogen peroxide ([H.sub.2][O.sub.2]), hydroxyl radical (H[O.sup.*]), and other ROS, which are known to be toxic to different types of cells, including the lung epithelium. A balance between antioxidants and oxidants exists; in pulmonary epithelial cells high intracellular and extracellular levels of antioxidants are found. Antioxidant adaptations related to plant and animal life-styles involve a broad range of overlapping strategies based on well-conserved molecules. Glutathione (GSH) is an abundant and ubiquitous thiol-tripeptide antioxidant, also present in lungs, whose role in providing information on the intracellular redox state of animals and plants is well established. In these organisms, GSH influences gene expression associated with stress, maximizing defense responses. Several enzymatic antioxidants, such as glutathione peroxidase (GPx), glutathione reductase, glutathione S-transferase, and glucose 6-phosphate dehydrogenase participate in the redox system; in animals that are stress-tolerant GPx is a key element against oxidative assaults. Most importantly, alternative roles of ROS as signaling molecules have been found in all plants and animals. For example, alveolar macrophages produce [O.sup.*-.sub.2] that act as second messengers, in addition to having a bactericidal role. The nonradical ROS [H.sub.2][O.sub.2] signals inflammation in mammalian lungs, apoptosis in different animal tissues, and is also involved in stomatal closure, root development, gene expression, and defense responses of plants. Antioxidant adaptations in some water-breathing animals involve the excretion of [H.sub.2][O.sub.2] by diffusion through gas-exchange structures. The fine balance among a multitude of factors and cells makes the difference between damage and protection in animals and plants. Knowledge about the mechanisms and consequences of these molecular interactions is now starting to be integrated.

Several genera of frogs from Madagascar, classified in the family Mantellidae, subfamily Mantellinae, possess structures commonly called ‘femoral glands’ on the ventral side of their shanks. The question arises as to the origin and phylogenetic significance of these glands. A molecular phylogeny based on 3601 nucleotide DNA sequences of three mitochondrial and two nuclear genes of 30 mantellid species provided strong support for monophyly of the included mantellines, all characterized by enlarged femoral gland clusters, as well as for those with gland clusters of coordinated central arrangement of secretion ducts. However, the phylogeny also strongly supported the hypothesis of convergent evolution of structurally similar glands in unrelated frogs ( Indirana, Petropedetes), and several trends of convergent evolution of gland structure within mantellines. We studied the light microscopic structure of the femoral glands in a representative array of 18 mantellid species. Males of all species of the subfamily Mantellinae were characterized by clusters of distinct single glands. Each was structurally similar to an enlarged granular gland and secreted independently, probably through a single duct. By contrast, the largely semi-aquatic frogs in the genus Mantidactylus had a specialized cluster of glands, in which the secretion ducts led into a macroscopically recognizable central depression. In Boophis opisthodon, a mantellid species of the subfamily Boophinae without externally recognizable femoral glands, we observed a large number of enlarged granular glands of various sizes in the ventral skin of the shank. This observation is consistent with the hypothesis that the large and more uniform organs of mantellines are derived granular glands. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 529–539. [ABSTRACT FROM AUTHOR]