The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Coral reef fishes represent one of the most spectacularly diverse assemblages of vertebrates on the planet, but our understanding of their mode of diversification remains limited. Here we test whether the diversity of the damselfishes (Pomacentridae), one of the most species-rich families of reef-associated fishes, was produced by a single or multiple adaptive radiation(s) during their evolutionary history. Tests of the tempo of lineage diversification using a time-calibrated phylogeny including 208 species revealed that crown pomacentrid diversification has not slowed through time as expected under a scenario of a single adaptive radiation resulting from an early burst of diversification. Evolutionary modeling of trophic traits similarly rejected the hypothesis of early among-lineage partitioning of ecologically important phenotypic diversity. Instead, damselfishes are shown to have experienced iterative convergent radiations wherein subclades radiate across similar trophic strategies (i.e., pela...

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Iterative ecological radiation and convergence during the evolutionary history of damselfishes (Pomacentridae).

Adaptive radiation is the process by which a single ancestral species diversifies into many descendants adapted to exploit a wide range of habitats. The appearance of ecological opportunities, or the colonisation or adaptation to novel ecological resources, has been documented to promote adaptive radiation in many classic examples. Mutualistic interactions allow species to access resources untapped by competitors, but evidence shows that the effect of mutualism on species diversification can greatly vary among mutualistic systems. Here, we test whether the development of obligate mutualism with sea anemones allowed the clownfishes to radiate adaptively across the Indian and western Pacific oceans reef habitats. We show that clownfishes morphological characters are linked with ecological niches associated with the sea anemones. This pattern is consistent with the ecological speciation hypothesis. Furthermore, the clownfishes show an increase in the rate of species diversification as well as rate of morphological evolution compared to their closest relatives without anemone mutualistic associations. The effect of mutualism on species diversification has only been studied in a limited number of groups. We present a case of adaptive radiation where mutualistic interaction is the likely key innovation, providing new insights into the mechanisms involved in the buildup of biodiversity. Due to a lack of barriers to dispersal, ecological speciation is rare in marine environments. Particular life-history characteristics of clownfishes likely reinforced reproductive isolation between populations, allowing rapid species diversification.

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Mutualism with sea anemones triggered the adaptive radiation of clownfishes

Fishes have evolved multiple mechanisms for sound production, many of which utilize sonic muscles that vibrate the swimbladder or the rubbing of bony elements. Sonic muscles are among the fastest muscles in vertebrates and typically drive the swimbladder to produce one sound cycle per contraction. These muscles may be extrinsic , typically extending from the head to the swimbladder, or intrinsic , likely a more-derived condition, in which muscles attach exclusively to the bladder wall. Recently discovered in Ophidiiform fishes, slow muscles stretch the swimbladder and associated tendons, allowing sound production by rebound (cock and release). In glaucosomatids , fast muscles produce a weak sound followed by a louder one, again produced by rebound, which may reflect an intermediate in the evolution of slow to superfast sonic muscles. Historically, the swimbladder has been modeled as an underwater resonant bubble . We provide evidence for an alternative hypothesis, namely that bladder sounds are driven as a forced rather than a resonant response, thus accounting for broad tuning, rapid damping, and directionality of fish sounds. Cases of sounds that damp slowly, an indication of resonance, are associated with tendons or bones that continue to vibrate and hence drive multiple cycles of swimbladder sound. Stridulation sounds, best studied in catfishes and damselfishes, are produced, respectively, as a series of quick jerks causing rubbing of a ribbed process against a rough surface or rapid jaw closing mediated by a specialized tendon. A cladogram of sonic fishes suggests that fish sound production has arisen independently multiple times.

Mechanisms of Fish Sound Production

animal movements and the acquisition and allocation of resources provide mechanisms for individual behavioural traits to propagate through population, community and ecosystem levels of biological organization. Recent developments in analytical geochemistry have provided ecologists with new opportunities to examine movements and trophic dynamics and their subsequent influence on the structure and functioning of animal communities. we refer to this approach as ecogeochemistry—the application of geochemical techniques to fundamental questions in population and community ecology. we used metaanalyses of published data to construct δ2H, δ13c, δ15N, δ18O and Δ14c isoscapes throughout the world’s oceans. These maps reveal substantial spatial variability in stable isotope values on regional and oceanbasin scales. we summarize distributions of dissolved metals commonly assayed in the calcified tissues of marine animals. Finally, we review stable isotope analysis (SIa) of amino acids and fatty acids. These analyses overcome many of the problems that prevent bulk SIa from providing sufficient geographic or trophic resolution in marine applications. we expect that ecologists will increasingly use ecogeochemistry approaches to estimate animal movements and trace nutrient pathways in ocean food webs. These studies will, in turn, help provide the scientific underpinning for ecosystembased management strategies in marine environments.

Ocean ecogeochemistry: a review

The damselfishes, with more than 340 species, constitute one of the most important families that live in the coral reef environment. Most of our knowledge of reef-fish ecology is based on this family, but their trophic ecology is poorly understood. The aim of the present study was to determine the trophic niches of 13 sympatric species of damselfishes by combining stable isotope (δ15N and δ13C) and stomach content analyses. Isotopic signatures reveal three main groups according to their foraging strategies: pelagic feeders (Abudefduf sexfasciatus, A. sparoides, A. vaigiensis, Chromis ternatensis, C. dimidiata, Dascyllus trimaculatus and Pomacentrus caeruleus), benthic feeders (Chrysiptera unimaculata, Plectroglyphidodon lacrymatus and Amphiprion akallopisos) and an intermediate group (D. aruanus, P. baenschi and P. trilineatus). Stomach contents reveal that planktonic copepods and filamentous algae mainly represent the diets of pelagic feeders and benthic feeders, respectively. The intermediate position of the third group resulted from a partitioning of small planktonic prey, small vagile invertebrates and filamentous algae. In this last feeding group, the presence of a wide range of δ13C values in P. trilineatus suggests a larger trophic niche width, related to diet-switching over time. Some general considerations about the feeding habits of damselfishes reveal that their choice of habitat on the reef and their behavior appear to be good predictors of diet in this group. Benthic (algae and/or small invertebrates) feeders appear to be solitary and defend a small territory on the bottom; zooplankton feeders remain in groups just above the reef, in the water column.

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Trophic niches of thirteen damselfishes (Pomacentridae) at the Grand Récif of Toliara, Madagascar

Mochokidae are able to produce pectoral spine stridulation sounds. During sound production, high speed videos were used to study the pectoral fin movements to identify the mechanisms involved. A call consisted of a series of pulses and occurred during a spine sweep, which was in fact made up of a series of jerky movements. The morphology of the pectoral spines and associated muscles was also observed in different species. The contractions of adductor profundus and superficial adductor allows adduction and abduction movements (sweep) of the spine, respectively. Simultaneously, the contraction of the arrector ventralis or the arrector 3 of the pectoral spine allows the pulling and pressing the ridges of the dorsal process, against the rough lateral face of the spinal fossa. This results in the rubbing of the ridges of the dorsal process, producing sounds. In Synodontis the analogy for sound production would be a brake shoe pressing against a wheel.

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Grégory Fabri

Papers

Trophic niches of thirteen damselfishes (Pomacentridae) at the Grand Récif of Toliara, Madagascar

Functional study of the pectoral spine stridulation mechanism in different mochokid catfishes