Résumé: Respirometry is a robust method for measurement of oxygen uptake as a proxy for metabolic rate in fishes, and how species with bimodal respiration might meet their demands from water v. air has interested researchers for over a century. The challenges of measuring oxygen uptake from both water and air, preferably simultaneously, have been addressed in a variety of ways, which are briefly reviewed. These methods are not well-suited for the long-term measurements necessary to be certain of obtaining undisturbed patterns of respiratory partitioning, for example, to estimate traits such as standard metabolic rate. Such measurements require automated intermittent-closed respirometry that, for bimodal fishes, has only recently been developed. This paper describes two approaches in enough detail to be replicated by the interested researcher. These methods are for static respirometry. Measuring oxygen uptake by bimodal fishes during exercise poses specific challenges, which are described to aid the reader in designing experiments. The respiratory physiology and behaviour of air-breathing fishes is very complex and can easily be influenced by experimental conditions, and some general considerations are listed to facilitate the design of experiments. Air breathing is believed to have evolved in response to aquatic hypoxia and, probably, associated hypercapnia. The review ends by considering what realistic hypercapnia is, how hypercapnic tropical waters can become and how this might influence bimodal animals' gas exchange.

Résumé: Aim Two frameworks (BASVIL and PODCAR), based on two different functional representations (ordination and dendrogram), have been proposed for partitioning overall functional beta diversity into two analogous components: turnover and nestedness-resultant dissimilarity, or replacement and difference of functional richness, respectively. We compared the two frameworks by testing the influence of functional representations and partitioning methods on the measurement of overall functional beta diversity and its components. Innovation We computed beta-diversity indices from the two frameworks on a set of communities simulated according to five scenarios of assembly: random, richness gradient, pure nestedness, pure turnover and mixed turnover/loss scenarios. To disentangle the effects of the partitioning approach and those of the functional representation on measurement of functional beta diversity, we also computed PODCAR indices in multidimensional space. Main conclusions BASVIL and PODCAR frameworks led to different results for overall functional beta diversity and their analogous partitioning components. Most of the difference between the two frameworks was due to the functional representation used. The goodness-of-fit measure (mean squared deviation, mSD) to assess the quality of functional spaces showed that the one computed on the basis of the dendrogram used in PODCAR remained lower than that of the functional ordination considered in BASVIL. In addition, only functional turnover derived from the BASVIL framework is independent of difference in functional richness. Finally, BASVIL measured functional variations derived from nested phenomena while PODCAR did not allow separation of this variation derived from richness difference. However, the sensitivity of BASVIL to functionally extreme species may make it difficult to know whether variations of the nestedness-resultant dissimilarity components are due to a turnover with few extreme species or a loss in functional richness. Particular attention with regard to the properties of the two frameworks is required before drawing conclusions regarding processes that structure communities.

Résumé: The African sharptooth catfish Clarias gariepinus has bimodal respiration, it has a suprabranchial air-breathing organ alongside substantial gills. We used automated bimodal respirometry to reveal that undisturbed juvenile catfish (N=29) breathed air continuously in normoxia, with a marked diurnal cycle. Air breathing and routine metabolic rate (RMR) increased in darkness when, in the wild, this nocturnal predator forages. Aquatic hypoxia (20% air saturation) greatly increased overall reliance on air breathing. We investigated whether two measures of risk taking to breathe air, namely absolute rates of aerial O-2 uptake ((M) over dotO(2), air) and the percentage of RMR obtained from air (% (M) over dotO(2), air), were influenced by individual standard metabolic rate (SMR) and boldness. In particular, whether any influence varied with resource availability (normoxia versus hypoxia) or relative fear of predation (day versus night). Individual SMR, derived from respirometry, had an overall positive influence on (M) over dotO(2), air across all contexts but a positive influence on % (M) over dotO(2), air only in hypoxia. Thus, a pervasive effect of SMR on air breathing became most acute in hypoxia, when individuals with higher O-2 demand took proportionally more risks. Boldness was estimated as time required to resume air breathing after a fearful stimulus in daylight normoxia (T-res). Although T-res had no overall influence on (M) over dotO(2), air or % (M) over dotO(2), air, there was a negative relationship between Tres and % (M) over dotO(2), air in daylight, in normoxia and hypoxia. There were two Tres response groups, 'bold' phenotypes with Tres below 75 min (N= 13) which, in daylight, breathed proportionally more air than 'shy' phenotypes with Tres above 115 min (N= 16). Therefore, individual boldness influenced air breathing when fear of predation was high. Thus, individual energy demand and personality did not have parallel influences on the emergent tendency to take risks to obtain a resource; their influences varied in strength with context.