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See detailMorph switching in a dimorphic population of Triturus alpestris (Amphibia, Caudata)
Denoël, Mathieu ULg; Lena, Jean-Paul; Joly, Pierre

in Evolutionary Ecology (2007), 21(3), 325-335

The usual life cycle of Alpine newts comprises an aquatic larval stage and a terrestrial juvenile and adult stage. However, some populations differ from this pattern in exhibiting facultative ... [more ▼]

The usual life cycle of Alpine newts comprises an aquatic larval stage and a terrestrial juvenile and adult stage. However, some populations differ from this pattern in exhibiting facultative paedomorphosis where some individuals reach sexual maturity while retaining larval traits such as gills and gill slits. While paedomorphic newts can, in some circumstances, initiate metamorphosis, once a newt has commenced metamorphosis, the state is irreversible. Because the frequency of this switching from one morph to the other has never been quantified in the wild, we attempted to estimate switching rate and survival by carrying out a 3-year monitoring survey of a population inhabiting an alpine lake. While morph switching did occur in this population, it involved a relatively low proportion of the paedomorphs (approx. 12%), suggesting that metamorphosis is not favoured in the study population. The hypothesis of paedomorphic advantage was not supported since neither survival nor body condition differed between morphs. The ontogenetic pathway of wild Alpine newts is thus characterised by two forks in the developmental pathway. The first occurs during the larval stage (metamorphosis vs. paedomorphosis), and the second occurs in paedomorphic adults (switching for metamorphosis vs. continuation of the paedomorphic lifestyle). Such a two-level decision process may allow individuals to cope with environmental uncertainty. [less ▲]

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See detailMetamorphosis rate of paedomorphs in a natural newt population
Denoël, Mathieu ULg; Lena, J. P.; Joly, Pierre

Poster (2007)

Facultative paedomorphis is a developmental process in which larvae opt for metamorphosis before maturity or reach sexual maturity while retaining larval traits (e.g., gills). Although metamorphosis is ... [more ▼]

Facultative paedomorphis is a developmental process in which larvae opt for metamorphosis before maturity or reach sexual maturity while retaining larval traits (e.g., gills). Although metamorphosis is not reversible, the paedomorphic state is not a dead end as branchiate adults are able to metamorphose. However, the extent of this process has never been quantified in the wild. Our aim was then to estimate switching rate by carrying out a 3-year monitoring survey of a population of Alpine newts (Triturus alpestris) inhabiting an alpine lake. The data were analysed using a multi-state capture-recapture model. While morph switching did occur in this population, it involved only 12% of the paedomorphs each year (i.e., 17% of recaptured individuals), suggesting that metamorphosis was not favoured in this population during the study period. This rate is lower than in laboratory experiments during which newts from the same population were placed in water drying conditions, but as shown previously paedomorphs can avoid metamorphosis in migrating to permanent water bodies when their pond dries out. These results are in agreement with other studies showing an advantage of a dimorphism in heterogeneous habitats. The ontogenetic pathway of wild Alpine newts is thus characterised by two forks in the developmental pathway. The first occurs during the larval stage, and the second occurs in paedomorphic adults. Such a two-level decision process may allow individuals to cope with environmental uncertainty. This may be particularly adaptive as aquatic conditions can deteriorate over time as shown by yearly changes in body condition of newts [less ▲]

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See detailEvolutionary ecology of facultative paedomorphosis in newts and salamanders
Denoël, Mathieu ULg; Joly, Pierre; Whiteman, Howard H.

in Biological Reviews (2005), 80(4), 663-671

Facultative paedomorphosis is an environmentally induced polymorphism that results in the coexistence of mature, gilled, and fully aquatic paedomorphic adults and transformed, terrestrial, metamorphic ... [more ▼]

Facultative paedomorphosis is an environmentally induced polymorphism that results in the coexistence of mature, gilled, and fully aquatic paedomorphic adults and transformed, terrestrial, metamorphic adults in the same population. This polymorphism has been of interest to scientists for decades because it occurs in a large number of caudate amphibian taxa as well as in a large diversity of habitats. Numerous experimental and observational studies have been conducted to explain the proximate and ultimate factors affecting these heterochronic variants in natural populations. The production of each alternative phenotype is based on a genotype x environment interaction and research suggests that differences in the environment can produce paedomorphs through several ontogenetic pathways. No single advantage accounts for the maintenance of this polymorphism. Rather, the interplay of different costs and benefits explains the success of the polyphenism across variable environments. Facultative paedomorphosis allows individuals to cope with habitat variation, to take advantage of environmental heterogeneity in the presence of open inches, and to increase their fitness. This process is expected to constitute a first step towards speciation events, and is also an example of biodiversity at the intraspecific level. The facultative paedomorphosis system is thus ripe for future studies encompassing ecology, evolution, behaviour, endocrinology, physiology, and conservation biology. Few other systems have been broad enough to provide varied research opportunities on topics as diverse as phenotypic plasticity, speciation, mating behaviour, and hormonal regulation of morphology. Further research on facultative paedomorphosis will provide needed insight into these and other important questions facing biologists. [less ▲]

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See detailTrophic specialisations in alternative heterochronic morphs
Denoël, Mathieu ULg; Schabetsberger, Robert; Joly, Pierre

in Naturwissenschaften (Die) (2004), 91(2), 81-84

Polymorphisms are suspected of reducing competition among conspecifics in heterogeneous environments by allowing differential resource use. However the adaptive significance of alternative morphs has been ... [more ▼]

Polymorphisms are suspected of reducing competition among conspecifics in heterogeneous environments by allowing differential resource use. However the adaptive significance of alternative morphs has been poorly documented. The aim of this study is to determine food partitioning of two heterochronic morphs of the Alpine newt, Triturus alpestris, in mountain lakes. The morphs differ in the functional morphology of their feeding apparatus. Only paedomorphs are able to expel water during prey suction behind the mouth through gill slits. We observed a substantial trophic differentiation between morphs in all lakes. Paedomorphs preyed mainly on plankton, whereas metamorphs foraged on terrestrial invertebrates that fell upon the water surface. This resource partitioning may facilitate the coexistence of the alternative morphs in lakes devoid of vertebrate competitors. Food diversity may thus favour the evolutionary maintenance of facultative polymorphism in natural populations. [less ▲]

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See detailShort- and long-term advantages of an alternative ontogenetic pathway
Denoël, Mathieu ULg; Hervant, F.; Schabetsberger, R. et al

in Biological Journal of the Linnean Society (2002), 77(1), 105-112

We documented hypotheses on the evolution of developmental heterochronies by estimating short- and long-term advantages of alternative morphs. In this respect, we compared food energy intakes and body ... [more ▼]

We documented hypotheses on the evolution of developmental heterochronies by estimating short- and long-term advantages of alternative morphs. In this respect, we compared food energy intakes and body condition between paedomorphic and metamorphic Alpine newts (Triturus alpestris, Caudata, Amphibia) in four populations. Because we found a strong correlation between fat reserves and body condition, we used this last parameter as an indicator of long-term gains. In all studied sites, paedomorphic females showed higher body condition than metamorphic ones. Paedomorphic males were also at advantage in two populations. Paedomorphs exhibited higher energy intakes than metamorphs in two populations and similar gains in two others. Our results support unifying theories that predict the occurrence of facultative paedomorphosis in varied habitats as paedomorphs exhibited better energy balance than metamorphs. This work shows the need for considering integrative parameters such as body condition in the comparative study of performances when studying developmental heterochronies. (C) 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77, 105-112. [less ▲]

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See detailFeeding specialization in heterochronic newts (Triturus alpestris, Amphibia, Caudata)
Denoël, Mathieu ULg; Schabetsberger, Robert; Joly, Pierre

Poster (2002)

Polymorphisms are suspected to reduce competition among conspecifics in heterogeneous environments by allowing differential resource use. However, the adaptive significance of alternative morphs has been ... [more ▼]

Polymorphisms are suspected to reduce competition among conspecifics in heterogeneous environments by allowing differential resource use. However, the adaptive significance of alternative morphs has been poorly documented. The aim of this study was to test this hypothesis by comparing diets of syntopic heterochronic morphs (paedomorphs and metamorphs) in the Alpine newt, Triturus alpestris in three European alpine lakes. Feeding performance was also tested in the laboratory. The two morphs differ in the functional morphology of their feeding apparatus. Only paedomorphs are able to expel water behind the mouth during prey suction through gill slits. We observed a substantial trophic differentiation between morphs consistently in all lakes. Paedomorphs primarily preyed on plankton whereas metamorphs foraged on terrestrial invertebrates that fell to the water surface. Laboratory observations were consistent with field patterns. In paedomorphs, prey capture success rate was better than in metamorphs when foraging on aquatic crustaceans, but was less successful when foraging on terrestrial invertebrates caught at the water surface. By reducing competition, resource partitioning contributes to the coexistence of the alternative morphs in lakes devoid of vertebrate competitors and predators. Food diversity is thus an important factor favoring the evolutionary maintenance of facultative paedomorphosis in natural populations. [less ▲]

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See detailSize-related predation reduces intramorph competition in paedomorphic Alpine newts
Denoël, Mathieu ULg; Joly, Pierre

in Canadian Journal of Zoology (2001), 79(6), 943-948

Evolutionary theory assumes that facultative paedomorphosis in newts and salamanders is adaptive in allowing either a younger age at maturity or resource partitioning between the heterochronic morphs. In ... [more ▼]

Evolutionary theory assumes that facultative paedomorphosis in newts and salamanders is adaptive in allowing either a younger age at maturity or resource partitioning between the heterochronic morphs. In newt populations that only take the metamorphic ontogenetic pathway, juveniles are terrestrial and avoid food competition with larvae and breeding adults. In contrast, in populations where paedomorphosis occurs, branchiate newts of all sizes coexist in the aquatic habitats, posing the question of whether intramorph competition exists and its relationship with the evolution of paedomorphosis. We studied size-related predation in such a size-structured community of branchiate Alpine newts (Triturus alpestris) inhabiting a deep alpine lake. Although gape limitation may explain such size-related predation, individuals also exhibited selectivity according to prey size. Amongst small prey that were within the capture range of all newt size classes, smaller newts preyed on smaller items than did larger ones. We assume that such decisions favour the coexistence of different-sized individuals. It is suspected that such size-selective predation on items which are avoided by water-living metamorphs allows the maintenance of facultative paedomorphosis, in favouring resource partitioning between morphs. [less ▲]

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See detailAdaptive significance of facultative paedomorphosis in Triturus alpestris (Amphibia, Caudata): resource partitioning in an alpine lake
Denoël, Mathieu ULg; Joly, Pierre

in Freshwater Biology (2001), 46(10), 1387-1396

1. Facultative paedomorphosis is a polymorphism that has important evolutionary implications in promoting morphological differentiation and variation in habitat use. It occurs in several urodele species ... [more ▼]

1. Facultative paedomorphosis is a polymorphism that has important evolutionary implications in promoting morphological differentiation and variation in habitat use. It occurs in several urodele species throughout the world. Several hypotheses based on life-history theory have been proposed to explain the wide range of habitats in which facultative paedomorphosis occurs, suggesting multifactorial causes. 2. In harsh habitats, such as mountain lakes, paedomorphosis might promote niche partitioning between morphs. This hypothesis was tested by comparing micro-habitat use and diet of two coexisting morphs in an alpine lake. 3. Paedomorphs occupied all microhabitats in the lake while metamorphs occurred only along the shoreline or at the water surface. Paedomorphic newts were frequent in deep water, where they foraged mainly on plankton. Plankton was poorly exploited by metamorphic newts, which fed mainly on terrestrial insects. Difference between morphs in microhabitat use, and consequently in the diet, were consistent in both sexes and in juveniles. 4. In adults, the mass and energy value of stomach contents did not differ between morphs, suggesting a similar food availability in the habitats occupied. 5. This study indicates habitat partitioning between morphs involving dietary differences. Specific benefits and costs of each ontogenetic pathway may allow their coexistence in this deep and fishless lake. Paedomorphosis benefits individual newts by making new food resources available and presumably reducing competition at the shore of the lake. However, the proximate causes of such an ontogenetic switch remain unclear. [less ▲]

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See detailNeoteny and progenesis as two heterochronic processes involved in paedomorphosis in Triturus alpestris (Amphibia: Caudata)
Denoël, Mathieu ULg; Joly, Pierre

in Proceedings of the Royal Society B : Biological Sciences (2000), 267(1451), 1481-1485

Current theories on the evolution of paedomorphosis suppose that several ontogenetic pathways have appeared according to different selective pressures. The aim of this study was to find out whether two ... [more ▼]

Current theories on the evolution of paedomorphosis suppose that several ontogenetic pathways have appeared according to different selective pressures. The aim of this study was to find out whether two distinct processes can lead to paedomorphosis in the Alpine newt, Triturus alpestris. In this respect, we compared age structures of paedomorphic and metamorphic individuals in two newt populations where the two forms lived syntopically. Whereas paedomorphosis resulted in a slower rate of somatic development in one population, it resulted in an acceleration of sexual maturation in the other population. These processes correspond to neoteny and progenesis, respectively. These results suggest that phenotypic plasticity can result from contrasted ontogenetic pathways between two populations of the same species. They give support to models that consider gonadic development as the target of selection under different environmental pressures. [less ▲]

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See detailPédomorphose, occupation de l’espace, régime alimentaire et performances prédatrices
Denoël, Mathieu ULg; Joly, Pierre; Poncin, Pascal ULg

Conference (2000)

Chez certaines espèces, les trajectoires du développement dépendent d’une interaction genotype-environnement qui détermine l’apparition de polyphenismes. Parmi ceux-ci, la pédomorphose concerne le ... [more ▼]

Chez certaines espèces, les trajectoires du développement dépendent d’une interaction genotype-environnement qui détermine l’apparition de polyphenismes. Parmi ceux-ci, la pédomorphose concerne le maintien de caractères larvaires chez un descendant adulte, un phénomène relativement répandu chez les amphibiens urodèles. Plusieurs hypothèses basées sur des observations et des expérimentations ont été proposées afin d’expliquer l’existence de tels exemples de plasticité phénotypique montrant ainsi que les pédomorphes pouvaient être sélectionnés en faveur de conditions aquatiques avantageuses. L’objectif de notre d’étude était de déterminer si adopter un trait d’histoire de vie alternatif (pédomorphose vs metamorphose) peut constituer un avantage en terme du partage des ressources. Nous avons ainsi analysé l’occupation de l’espace et le régime alimentaire d’une population de triton alpestre (Triturus alpestris) ainsi que les performances prédatrices en laboratoire. Nos résultats montrent que, plus qu’un avantage d’une forme sur une autre, il y aurait un avantage d’une stratégie avec deux tactiques : la pédomorphose et la métamorphose. En effet cette stratégie permet aux tritons de profiter de l’ensemble des ressources présentes dans leur habitat. Un triton pédomorphe paraît ainsi avantagé sur le fond et dans la colonne d’eau où il peut capturer à haut succès des proies hors de la compétition avec les métamorphes, tandis que ces derniers occupent des habitats où sont accessibles des proies exogènes (par exemples des diptères imagos) pour lesquelles ils sont compétitivement supérieurs. [less ▲]

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See detailEffect of drying on paedomorphosis in Triturus alpestris
Denoël, Mathieu ULg; Joly, Pierre; Poncin, Pascal ULg

Conference (2000)

Paedomorphosis consists in the retention of larval characters in adult individuals. It has been observed in several species of newts and salamanders. Optimality models were proposed to explain why it ... [more ▼]

Paedomorphosis consists in the retention of larval characters in adult individuals. It has been observed in several species of newts and salamanders. Optimality models were proposed to explain why it occurs in a large range of aquatic habitats. These models predict that paedomorphs can be advantaged in two situations as contrasted as favourable habitats (paedomorph advantage) or harsh habitats where the newts can benefit of delaying metamorphosis provided that competition with metamorphosed individuals is relaxed (best-of-a-bad-lot hypothesis). This last tactic implies that the habitats are stable enough to ensure the survival of individuals that can not leave the pond. In this respect, our aim was to describe behaviour of paedomorphic Alpine newts (Triturus alpestris) dealing with lake drying. We studied a population from an Alpine lake that splits into two parts during summer, one of them drying then totally. We analyzed age structures by means of skeletochronology and capture-marking-recapture. Paedomorphs and metamorphs showed similar age structures with sexual maturity occurring at 4-5 years, suggesting that most paedomorphs did not metamorphose. CMR data revealed that a great proportion of the paedomorphs marked in the drying part of the lake did not metamorphose and survived to drying. We also carried out laboratory experiments using two-compartiments aquaria to simulate lake drying. These experiments proved that paedomorphic newts could cross terrestrial habitats to reach a pond. Thus paedomorphic newts can migrate on land while keeping their larval attributes rather than metamorphosing when their pond is drying up. Such a tactic appears adaptive because polymorphism in such a deep lake reduces competition between individuals (pers. obs.). [less ▲]

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See detailFacultative paedomorphosis in the Alpine newt, Triturus a. alpestris: feeding habits and habitat use in an Alpine lake
Denoël, Mathieu ULg; Joly, Pierre; Poncin, Pascal ULg

in Miaud, C.; Guyetant, G. (Eds.) Current Studies in Herpetology (1999)

Feeding habits and micro-habitat use were compared between metamorphs and paedomorphs in a population of the Alpine newt, Triturus a. alpestris in the French Alps. This population occupies a deep Alpine ... [more ▼]

Feeding habits and micro-habitat use were compared between metamorphs and paedomorphs in a population of the Alpine newt, Triturus a. alpestris in the French Alps. This population occupies a deep Alpine lake. The paedomorphs largely outnumbered the metamorphs. Whereas paedomorph diet was mainly composed of plankton, that of metamorphs was especially composed of larval and adult insects. The spatial use of the habitat also differed between the two forms: the paedomorphs occupied all the micro-habitats (shore, bottom, water column and surface) while the metamorphs were only found along the shore and at the water surface. In such a deep lake paedomorphosis may have persisted because of a different use of both feeding resources and micro-habitat [less ▲]

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See detailFirst evidence of progenesis in Triturus (Amphibia)
Denoël, Mathieu ULg; Joly, Pierre

Poster (1998)

Paedomorphosis is defined as the retention of subadult morphology in reproductive adults. Two main processes can produce this heterochronic pattern : neoteny and progenesis, but progenesis has not been ... [more ▼]

Paedomorphosis is defined as the retention of subadult morphology in reproductive adults. Two main processes can produce this heterochronic pattern : neoteny and progenesis, but progenesis has not been yet demonstrated in newts. Distinction between them can be obtained from the determination of age at first reproduction using the squelettochronological method. In this study, we sampled more than 300 Triturus alpestris in two populations : one in a French Alpine lake and the other in an Italian pond. Results show that paedomorphs from the Italian pond are mature earlier and at a smaller size than metamorphs (Progenesis) whereas paedomorphic and metamorphic newts from the French population do not differ in size and age (Neoteny). Adaptative significance of Paedomorphosis is discussed in relation to the stability of the aquatic habitat [less ▲]

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See detailPédomorphose facultative chez Triturus alpestris : comparaison des structures d'âge des tritons métamorphes et pédomorphes
Denoël, Mathieu ULg; Joly, Pierre

Conference (1998)

La pédomorphose est définie comme la rétention de caractères subadultes ancestraux chez le descendant adulte. Ce processus hétérochronique est relativement répandu au sein des urodèles. Ainsi, les adultes ... [more ▼]

La pédomorphose est définie comme la rétention de caractères subadultes ancestraux chez le descendant adulte. Ce processus hétérochronique est relativement répandu au sein des urodèles. Ainsi, les adultes reproducteurs, dénommés "pédomorphes", conservent les fentes branchiales larvaires. Chez le Triton alpestre, sujet de notre étude, la pédomorphose est facultative en ce sens que les deux traits d'histoire de vie - la métamorphose et la pédomorphose - existent. Certaines populations ne présentent que des individus métamorphes, tandis que d'autres présentent un mélange des deux formes. La pédomorphose était souvent associée à des milieux stables et froids d'altitude. Mais différentes populations ont aussi été découvertes dans des milieux instables de basse altitude. La présence d'animaux pédomorphes dans ce type de milieu ne paraissait dès lors pas adaptative. L'objectif de cette étude a été d'étudier les structures d'âge de deux populations où cohabitent tritons pédomorphes et métamorphes : une population peuplant un lac profond (le lac de la Cabane) situé à 1950 mètres d'altitude dans les Alpes-de-Haute-Provence (France) et une autre habitant une petite mare située à une altitude de 600 mètres à Parana, en Toscane (Italie). L'âge des animaux a été déterminé par squelettochronologie sur phalange et humérus. Au total, nous avons pu déterminer l'âge de 116 adultes de la population française et 128 de la population italienne. Nos résultats montrent une différence de trait d'histoire de vie nette entre les populations de haute et de basse altitude. Ainsi, au lac de la Cabane les structures d'âge des animaux métamorphes et pédomorphes sont identiques, tant en ce qui concerne les mâles que les femelles. La taille des animaux est elle aussi identique. Par contre, à Parana, les pédomorphes atteignent leur maturité sexuelle très jeunes : à un an chez les mâles et à un ou deux ans chez les femelles. Les métamorphes ne deviennent, par contre, matures que plus tardivement : les mâles, à 2-3 ans, et les femelles à 4-5 ans. La pédomorphose ne dure que peu de temps car les pédomorphes peuvent se métamorphoser. Les pédomorphes de cette population sont plus petits que les métamorphes. Chez le Triton alpestre, des cas de populations pédomorphiques ne sont constatés que dans les péninsules italiennes et balkaniques, laissant ainsi supposer une base génétique. Ayant montré que le succès des pédomorphes et leur trait d'histoire de vie, en l'occurrence leur structure d'âge, diffèrent entre les populations, nous pouvons considérer la pédomorphose comme une stratégie alternative influencée par différents facteurs environnementaux. Seules les populations ayant un potentiel génétique pour la pédomorphose peuvent répondre aux pressions de l'environnement, lesquelles, selon leurs caractéristiques, peuvent mener à des patrons de pédomorphose de différents types. En cas de catastrophe ou de colonisation de nouveaux milieux, la pédomorphose par progenèse permet une augmentation rapide de la population. Par contre dans des systèmes d'altitude, où une maturité précoce est peut-être impossible, l'avantage d'une stratégie pédomorphe peut être recherché, par exemple, au niveau des niches alimentaires ou spatiales, ce qui constitue un autre volet de notre étude. [less ▲]

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See detailFacultative paedomorphosis in the Alpine newt, Triturus a. alpestris: feeding and spatial advantages of paedomorphs in an Alpine lake
Denoël, Mathieu ULg; Joly, Pierre; Poncin, Pascal ULg et al

Poster (1998)

Paedomorphosis in newts and salamanders is defined as the retention of larval morphology in reproductive adults. In Triturus, Paedomorphosis is facultative because some larvae transform while other retain ... [more ▼]

Paedomorphosis in newts and salamanders is defined as the retention of larval morphology in reproductive adults. In Triturus, Paedomorphosis is facultative because some larvae transform while other retain larval characteristics such as gill slits and mature as Paedomorph. This heterochronic process is thought to be an important micro- and macroevolutionary mechanism. In a population of a French alpine lake (le lac de la Cabane), Alpine newt Paedomorphs (Triturus a. alpestris) are abundant and coexist with a Metamorph minority. The coexistence of both morphs and the dominance of one on the other beg a few questions such as what ecological factors favour the paedomorph strategy. In this study, we analysed the feeding and spatial distribution of the Paedomorphs and Metamorphs of the Lac de la Cabane in June, July, August and October 1998. Newts were caught in the main four microhabitats of the lake : the shore, the bottom (3-7 meters deep), the water column and the surface, at dawn, during the day and in the evening. In this way, we caught 1481 newts to record their spatial position. We flushed the stomachs of 822 of these newts (the total prey number identified is more than 60 thousand). The feeding strategies of Metamorphs and Paedomorphs are very different : while Paedomorphs prey principally on plankton (Daphnia, Chydorus, ...), Metamorphs prey on a lot of exogenous invertebrates (flyes, aphids, ...). This characteristic is observed for males, females and juveniles. Cladocerans are also eaten by Metamorphs, but in much smaller quantity. The Paedomorph newts live in all the microhabitats of the lake while Metamorphs are hardly ever found on the deep bottom and in the water column. The spatial niche of Metamorphs is thus smaller than that of Pedomorphs. The data presented here suggest that the success of both morphs can be strongly influenced by environmental conditions, and that Paedomorphosis may be maintained and favoured by the spatial and feeding advantages of Paedomorphs into a deep lake. [less ▲]

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