The present review examines the developments in the elucidation of the mechanisms of amphibian respiration and olfaction. Research in these two areas has largely proceeded along independent lines, despite the fact that ventilation of the nasobuccopharyngeal cavity is a basic element in both functions. The English naturalist Robert Townson demonstrated, in the 1790s, that amphibians, contrary to general belief, ventilated the lungs by a pressure-pump mechanism. Frogs and other amphibians respire by alternatively dilating and contracting the buccopharyngeal cavity. During dilatation, with the mouth and glottis closed, air is sucked in through the open nostrils to fill the cavity. During contraction of the throat, with nostrils closed and glottis open, the air in the buccopharyngeal cavity is pressed into the lungs. During expiration, the glottis and nostrils open and air is expelled from the lungs ‘by their own contraction from a state of distention’. Herholdt (1801), a Danish army surgeon, independently described the buccal pressure-pump mechanism in frogs, his experiments being confirmed by the commissioners of the Société Philomatique in Paris. Haro (1842) reintroduced a suction mechanism for amphibian respiration, which Panizza (1845) refuted: excision of the tympanic membranes prevented lung inflation, the air in the buccopharyngeal cavity leaving through the tympanum holes. Closure of the holes with the fingers restored lung inflation. The importance of cutaneous respiration in frogs and other amphibians was discovered by Spallanzani (1803), who found that frogs might survive excision of the lungs and that the amounts of exhaled carbon dioxide were small compared with those eliminated through the skin. Edwards (1824) confirmed and extended Spallanzani's findings, and Regnault & Reiset (1849) attempted to establish the relative importance of skin and lungs as respiratory organs in frogs. The problem was solved by Krogh (1904a) who measured respiration through the skin and lungs separately and simultaneously. Krogh (1904a) confirmed that carbon dioxide was chiefly eliminated through the skin, correlated with its high diffusion rate in water and tissue, whereas the pattern of oxygen uptake varied seasonally, the pulmonary uptake being lower than the cutaneous during autumn and winter, but substantially higher during the breeding period. Dolk & Postma (1927) confirmed this respiratory pattern. More recently, Hutchison and coworkers have examined the relative role of pulmonary and cutaneous gas exchange in a large number of amphibians, equipped with head masks for the separate measurement of the lung respiration in normally ventilating animals (Vinegar & Hutchison, 1965; Guimond & Hutchison, 1968; Hutchison, Whitford & Kohl, 1968; Whitford & Hutchison, 1963, 1965, 1966). As early as 1758, Rösel von Rosenhof suggested that the lungs of frogs in water functioned as hydrostatic organs that permitted the animal to float at the surface or rest on the bottom of the pond. The suggestion was inspired by observations made in the second half of the seventeenth century by members of the Royal Academy of Sciences in Paris. The French anatomists demonstrated that a tortoise, presumably the European freshwater turtle Emys orbicularis, could regulate its buoyancy by changing the volume of the lungs, to descend passively or ascend in the water. The hydrostatic function of the lungs has been repeatedly rediscovered, by Emery (1869) in the frog, by Marcacci (1895) in frogs, toads and salamanders, by Whipple (1906b) in a newt, by Willem (1920, 1931) in frogs and Xenopus laevis, by Speer (1942) in several anurans and urodeles, and finally by de Jongh (1972) in Xenopus laevis. In the second half of the nineteenth century a number of important papers appeared which confirmed and extended Townson's (1794) and Panizza's (1845) analysis of the normal respiratory movements in frogs. Lung ventilation cycles, interspaced by oscillatory movements of the throat, might periodically be replaced by a sequence predominated by inspirations, resulting in lung inflation, followed by exhalations that restored normal lung volume. Babák (1912a) established that inflations were reactions to the experimental manipulations, and that in resting, undisturbed frogs, lung ventilations normally occurred singly, interspaced by series of approximately 10–50 buccal oscillations. Extensive comparative studies early in the century showed that the respiratory mechanisms and patterns were basically similar in all anurans and urodeles investigated. The modern era of investigations in amphibian respiration began with the work of de Jongh & Gans (1969). They recorded pressures in the buccal cavity, lungs and visceral cavity and electrical activity of some 15 muscles possibly associated with respiration in the bullfrog Rana catesbeiana. The respiration recorded in the frogs was predominated by cycles of lung inflation and deflation, consistent with substantially but not excessively disturbed frogs. Studies by other investigators on various anuran species showed respiratory patterns that varied strongly with respect to the frequency and degree of lung inflations, presumably reflecting degrees to which the experimental conditions affected the breathing.

The elucidation of the role of the buccopharyngeal ventilation in amphibian olfaction can be traced to the realization in the 1890s that the nasal cavity has a double function in being both the seat of the sense of smell and part of the respiratory passages. The ability of amphibians to smell and to react to air-borne or water-borne chemical cues in the environment thus depends on the oscillatory movements of the buccal floor which ventilate the nasal cavity. Experimental evidence for a sense of smell was, however, lacking, and it was first furnished in urodele feeding early in the present century. Despite the demonstration of the fundamental role of the nasobuccal oscillatory ventilation in olfactory responses to food in newts, the oscillatory throat movements in amphibians continued, however, to be referred to as respiratory. Evidence concerning the role of the buccopharyngeal ventilation in respiration had been circumstantial until Whitford & Hutchison (1963, 1965, 1966) determined the relative importance of cutaneous and pulmonary/buccopharyngeal respiration in lunged and lungless salamanders. In lungless salamanders, the buccopharyngeal mucosa accounted for approximately 25% of the total oxygen consumption, and it was concluded that buccopharyngeal oscillatory ventilation in salamanders is primarily respiratory in function, a possible olfactory function being secondary. During the last decades an extensive literature has accumulated on the role played by olfaction in the life of urodeles, but also in feeding in anurans. Often the descriptions of behaviour elicited by air-borne or water-borne odours also note increased oscillatory movements of the buccal floor, indicating the importance of the ventilation of the nasal cavity. In the elucidation of the functional significance of buccal oscillations in vertebrate evolution, the reptiles are of particular interest because such oscillations are also known in chelonians, crocodiles and some lizards. Olfaction plays a role in the life of chelonians and crocodiles which respire by means of suction mechanisms. The throat movements are thus not concerned with the ventilation of the lungs but presumably with olfaction. It is thus indicated that in lower vertebrates, including the amphibians, the shallow oscillatory movements of the buccal floor primarily serve to establish olfactory contact with the surrounding medium, air or water, whereas a respiratory function is secondary.

Complexity in the networks of interactions among and between the living and abiotic components forming ecosystems confounds the ability of ecologists to predict the economic consequences of perturbations such as species deletions in nature. Such uncertainty hampers prudent decision making about where and when to invest most intensively in species conservation programmes. Demystifying ecosystem responses to biodiversity alterations may be best achieved through the study of the interactions allowing biotic communities to compensate internally for population changes in terms of contributing to ecosystem function, or their intrinsic functional redundancy. Because individual organisms are the biologically discrete working components of ecosystems and because environmental changes are perceived at the scale of the individual, a mechanistic understanding of functional redundancy will hinge upon understanding how individuals' behaviours influence population dynamics in the complex community setting. Here, I use analytical and graphical modelling to construct a conceptual framework for predicting the conditions under which varying degrees of interspecific functional redundancy can be found in dynamic ecosystems. The framework is founded on principles related to food web successional theory, which provides some evolutionary insights for mechanistically linking functional roles of discrete, interacting organisms with the dynamics of ecosystems because energy is the currency both for ecological fitness and for food web commerce. Net productivity is considered the most contextually relevant ecosystem process variable because of its socioeconomic significance and because it ultimately subsumes all biological processes and interactions. Redundancy relative to productivity is suggested to manifest most directly as compensatory niche shifts among adaptive foragers in exploitation ecosystems, facilitating coexistence and enhancing ecosystem recovery after disturbances which alter species' relative abundances, such as extinctions. The framework further explicates how resource scarcity and environmental stochasticity may constitute ‘ecosystem legacies’ influencing the emergence of redundancy by shaping the background conditions for foraging behaviour evolution and, consequently, the prevalence of compensatory interactions. Because it generates experimentally testable predictions for a priori hypothesis testing about when and where varying degrees of functional redundancy are likely to be found in food webs, the framework may be useful for advancing toward the reliable knowledge of biodiversity and ecosystem function relations necessary for prudent prioritization of conservation programmes. The theory presented here introduces explanation of how increasing diversity can have a negative influence on ecosystem sustainability by altering the environment for biotic interactions – and thereby changing functional compensability among biota – under particular conditions.

Theory concerning the evolution of life history (the schedule of reproduction and survival) focuses on describing the life history which maximises fitness. Although there is an intuitive link between life history and fitness, there are in fact several measures of the ‘black box’ concept of fitness. There has been a debate in the bio-mathematical literature on the predictive difference between the two most commonly used measures; intrinsic rate of increase r and net reproductive ratio R0. Although both measures aim to describe fitness, models using one of the measures may predict the opposite of similar models using the other measure, which is clearly undesirable. Here, I review the evolution of these fitness measures over the last four decades, the predictive differences between these measures and the resulting shift of the fitness concept. I focus in particular on some recent developments, which have solved the dilemma of predictive differences between these fitness measures by explicitly acknowledging the game-theoretical nature of life-history evolution.

The evolution and origin of primate social organisation has attracted the attention of many researchers, and a solitary pattern, believed to be present in most nocturnal prosimians, has been generally considered as the most primitive system. Nocturnal prosimians are in fact mostly seen alone during their nightly activities and therefore termed ‘solitary foragers’, but that does not mean that they are not social. Moreover, designating their social organisation as ‘solitary’, implies that their way of life is uniform in all species. It has, however, emerged over the last decades that all of them exhibit not only some kind of social network but also that those networks differ among species. There is a need to classify these social networks in the same manner as with group-living (gregarious) animals if we wish to link up the different forms of primate social organisation with ecological, morphological or phylogenetic variables. In this review, we establish a basic classification based on spatial relations and sociality in order to describe and cope properly with the social organisation patterns of the different species of nocturnal prosimians and other mammals that do not forage in cohesive groups. In attempting to trace the ancestral pattern of primate social organisation, the Malagasy mouse and dwarf lemurs and the Afro-Asian bushbabies and lorises are of special interest because they are thought to approach the ancestral conditions most closely. These species have generally been believed to exhibit a dispersed harem system as their pattern of social organisation (‘dispersed’ means that individuals forage solitarily but exhibit a social network). Therefore, the ancestral pattern of primate social organisation was inferred to be a dispersed harem. In fact, new field data on cheirogaleids combined with a review of patterns of social organisation in strepsirhines (lemurs, bushbabies and lorises) revealed that they exhibit either dispersed multi-male systems or dispersed monogamy rather than a dispersed harem system. Therefore, the concept of a dispersed harem system as the ancestral condition of primate social organisation can no longer be supported. In combination with data on social organisation patterns in ‘primitive’ placentals and marsupials, and in monotremes, it is in fact most probable that promiscuity is the ancestral pattern for mammalian social organisation. Subsequently, a dispersed multi-male system derived from promiscuity should be regarded as the ancestral condition for primates. We further suggest that the gregarious patterns of social organisation in Aotus and Avahi, and the dispersed form in Tarsius evolved from the gregarious patterns of diurnal primates rather than from the dispersed nocturnal type. It is consequently proposed that, in addition to Aotus and Tarsius, Avahi is also secondarily nocturnal.

Chemical information, carried by genes, is one of several types of information important for the functioning of cells and organisms. While genes govern the two-dimensional flow of information, the cell walls are at the basis of a structural, three-dimensional framework of plant form and growth. Recent data show the walls to be a cellular ‘organelle’ undergoing dynamic changes in response to a plethora of stimuli. In this review, an integrated approach, rooted in the organismal perspective, is taken to consider the role of cell walls in the biology of plants. First, the complexity of molecular and biochemical events leading to the biosynthesis of wall components is described within the framework of its spatial cellular organisation, and the major regulatory check-points are characterised. Second, cell walls form a structural and functional continuum within the whole plant and thus could be defined in relation to the protoplasts that produce them and in relation to the plant itself. Model systems of suspension-cultured cells are used to reveal the existence of a bidirectional exchange of information between the protoplast and its walls. The ‘plasticity’ of plant cell reactions, seen in defence responses or in changes in wall composition, to e.g. stress, plant growth regulators or chemical agents as well as the role of cell walls and/or wall components in somatic embryogenesis are also discussed. Third, being a continuum within the plant body, the walls fulfil vital functions in plant growth and development. The examples characterised include the determination of cellular polarity and the plane of cell division, cytokinesis, and the role of plasmodesmata in cell-to-cell communication and the formation of functional symplastic domains. Fourth, the exocellular control of morphogenetic processes is described and the potential of cell walls as determinants or reservoirs of positional information is indicated. Particular emphasis is put on the (bio)chemical signals coming through or derived from cell walls as well as the mechanical properties of the walls. Based on those data, the ‘plant body’ concept is formulated. The plant is thus treated as a unit filled with intertwining networks: (1) symplastic, (2) the endomembrane system and (3) cytoskeletal, with cell walls providing an architectural scaffolding and communication ports formed within (4) the cytoskeleton-plasma membrane-cell wall continuum.