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See detailSexual compatibility between two heterochronic morphs in the Alpine newt, Triturus alpestris
Denoël, Mathieu ULg; Poncin, Pascal ULg; Ruwet, Jean-Claude

in Animal Behaviour (2001), 62(3), 559-566

Paedomorphosis, in which individuals retain ancestral characteristics in the adult stage, is widespread in newts and salamanders and is suspected to play an important role in evolution. In some species ... [more ▼]

Paedomorphosis, in which individuals retain ancestral characteristics in the adult stage, is widespread in newts and salamanders and is suspected to play an important role in evolution. In some species, paedomorphosis is facultative with some individuals forgoing metamorphosis. Optimality models have been proposed to explain the maintenance of this polymorphism, but require the integration of reproductive patterns into the models. We investigated the frequencies of inbreeding and outbreeding in two syntopic heterochronic morphs of the Alpine newt. The two morphs are sexually compatible: encounters between and within morphs were equally successful in terms of spermatophore transfer. Behavioural observations were in agreement with the sexual compatibility observed. Nevertheless, paedomorphic males displayed to females less frequently than metamorphic males. The two morphs differ largely on the basis of sexual secondary characteristics, but the majority of these traits did not affect mating success. Because of the large flow of genes between the two heterochronic morphs and because of the absence of spatial and temporal isolation, these results do not support sympatric speciation models, but are in favour of the maintenance of polymorphism in natural populations. (C) 2001 The Association for the Study of Animal Behaviour. [less ▲]

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See detailAlternative mating tactics in the alpine newt Triturus alpestris alpestris
Denoël, Mathieu ULg; Poncin, Pascal ULg; Ruwet, Jean-Claude

in Journal of Herpetology (2001), 35(1), 62-67

Sexual behaviors in dyadic encounters in the alpine newt, Triturus alpestris alpestris, is described to test whether male behavior is influenced by external cues, that is, female responsiveness. Depending ... [more ▼]

Sexual behaviors in dyadic encounters in the alpine newt, Triturus alpestris alpestris, is described to test whether male behavior is influenced by external cues, that is, female responsiveness. Depending on this factor, a male exhibits one of the two following tactics during the sperm transfer phase. The male either waits for a positive response from the female before initiating sperm transfer ("waiting" tactic), or creeps and deposits a spermatophore in front of a nonresponsive female ("luring" tactic). The sperm transfer success rates of these tactics are 31% and 6%, respectively,and encounter success rates, 64% and 8%, respectively. The success of the second tactic is linked to behaviors that lure the female, notably quiver and distal lure. The same individual can exhibit both tactics, and neither body size nor condition appears to influence the tactic a male exhibits. These tactics can be interpreted as the result of a conditional strategy, that is, a strategy that allows an individual to incorporate information about its ability to obtain fitness through alternative tactics and then express the tactic that maximizes its fitness. More particularly, these tactics are examples of a side-payment strategy, that is, a strategy that allows individuals to achieve small gains by capitalizing on passing opportunities. [less ▲]

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See detailThe effect of food on growth and metamorphosis of paedomorphs in Triturus alpestris apuanus
Denoël, Mathieu ULg; Poncin, Pascal ULg

in Archiv für Hydrobiologie (2001), 152(4), 661-670

The effect of food level on growth and metamorphosis of paedomorphs was examined in an experimental replicated design in Triturus alpestris apuanus. Paedomorphosis concerns the retention of larval ... [more ▼]

The effect of food level on growth and metamorphosis of paedomorphs was examined in an experimental replicated design in Triturus alpestris apuanus. Paedomorphosis concerns the retention of larval characteristics in adult individuals. Newts that forgo metamorphosis and then retain gill and gill slits in the adult stage maintain an aquatic life but keep potential for undergoing metamorphosis. Paedomorphs metamorphosed later in treatments with food as a non-limiting factor than in stressful treatments where food was limited. Timing of metamorphosis did not differ between males and females. Food level greatly affected growth rates. These results confirm and extend optimality models that predict paedomorphosis under advantageous aquatic conditions (paedomorph advantage hypothesis) and metamorphosis in stressful aquatic habitats. [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 detailTritons et salamandres du bord de l'eau
Denoël, Mathieu ULg

Article for general public (2001)

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See detailThe effect of food on ontogenetic pathway switching in paedomorphic Alpine newts
Denoël, Mathieu ULg; Poncin, Pascal ULg

Poster (2001)

Paedomorphosis concerns the retention of larval characteristics in adult individuals. Newts that forgo metamorphosis and then retain gill and gill slits in the adult stage maintain an aquatic life but ... [more ▼]

Paedomorphosis concerns the retention of larval characteristics in adult individuals. Newts that forgo metamorphosis and then retain gill and gill slits in the adult stage maintain an aquatic life but keep potential for undergoing metamorphosis. They are thus good biological models to test evolutionary hypotheses predicting ontogenetic pathway switching in unfavourable and stressful environments. They are also interesting targets to understand their maintenance in a large range of habitats. Our aim was then to examine the effect of food level on growth and metamorphosis of paedomorphic Alpine newts Triturus alpestris apuanus (Amphibia, Salamandridae) in an experimental replicated design. Paedomorphs metamorphosed later in treatments with food as a non-limiting factor than in stressful treatments where food was limited. Timing of metamorphosis did not differ between males and females. Food level greatly affected growth rates. These results confirm and extend optimality models that predict paedomorphosis under advantageous aquatic conditions (paedomorph advantage hypothesis) and metamorphosis in stressful aquatic habitats. [less ▲]

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See detailSexual compatibility between two heterochronic morphs in the Alpine newt
Denoël, Mathieu ULg; Poncin, Pascal ULg

Poster (2001)

Numerous populations of newts and salamanders are dimorphic: while some larvae become mature and thus paedomorphic, others metamorphose and become adult later. The two morphs largely differ in morphology ... [more ▼]

Numerous populations of newts and salamanders are dimorphic: while some larvae become mature and thus paedomorphic, others metamorphose and become adult later. The two morphs largely differ in morphology. According to sexual selection theories, we could expect some female choice towards the alternative morphs. Although paedomorphosis can be adaptive in allowing resource partitioning and an earlier age at maturity, it is worth to determine the strength of sexual isolation between morphs. Indeed, whereas sexual compatibility may promote maintenance of polymorphism by mixing genes, sexual isolation could be the first step to sympatric speciation. We staged more than 200 encounters involving the four possible crosses within and between the heterochronic morphs of the Alpine newt, Triturus alpestris (Amphibia, Caudata). We took into account both quantitative and qualitative aspects of behaviours, with particular emphasis on the success of sperm transfer. We also determined secondary sexual characters. The success of heterotypic and homotypic encounters was similar, involving then sexual compatibility between the two heterochronic morphs. Paedomorphs and metamorphs displayed identical behavioural patterns at similar frequencies. Females did not appear to be selective against males on the basis of their epigamic characters. Our results do not support hypotheses predicting sympatric speciation from polymorphic species. On the other hand, they are in favour of the models predicting maintenance of polymorphism [less ▲]

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See detailAvantages sélectifs d'un phénotype hétérochronique. Eco-éthologie des populations pédomorphiques du Triton alpestre, Triturus alpestris (Amphibia, Caudata)
Denoël, Mathieu ULg

Doctoral thesis (2001)

Facultative paedomorphosis is a polyphenism that has important evolutionary implications in promoting morphological differentiation and habitat use variation, and has occurred in several urodele species ... [more ▼]

Facultative paedomorphosis is a polyphenism that has important evolutionary implications in promoting morphological differentiation and habitat use variation, and has occurred in several urodele species throughout the world. Several hypotheses based on life-history theory have been proposed to explain the wide range of habitats where facultative paedomorphosis occurs, suggesting multiple causes. In populations experiencing facultative paedomorphosis, some individuals metamorphose and mature (metamorphs), while others attain sexual maturity while still retaining traits of larval somatic morphology (paedomorphs). The paedomorphic process by which the development of somatic and reproductive organs is shifted between related individuals is assumed to significantly contribute to macro-evolutionary processes. Indeed, it implies large phenotypic variations in the absence of deep genetic changes. A way to explain the importance of these developmental heterochronies is to show their adaptive value in the micro-evolutive stage. The aim of this thesis is to determine the advantages gained by an individual that adopts a paedomorphic developmental pathway rather than a metamorphic one. To do this, we studied five factors: habitat use; resource partitioning; age and size structures; sexual compatibility; and the effect of environmental factors. The ecological and ethological characteristics of several mixed populations (composed of both paedomorphic and metamorphic individuals) of the Alpine newt Triturus alpestris (Amphibia, Salamandridae) were investigated from 1997 to 2000. These populations were located in France, Italy and Greece. The habitats occupied by dimorphic populations of the Alpine newt are highly variable. We have found the two morphs in syntopy in deep permanent lakes, and in small shallow and temporary ponds. Aquatic habitats were surrounded by various terrestrial habitats. As a result, it was not possible to correlate any particular environment type with the maintenance of the polymorphism in natural populations. The only common trait of the paedomorphic populations was that they were located at the southern margin of the range of the species (Italy, the Balkan peninsula, and southeastern France). Such a restriction of the distributional range of paedomorphosis suggests that this trait is maintained by genes which are shared only by these populations. Such a restriction may be due to Holocene colonizations from Pleistocene refugia, in which case paedomorphosis may have appeared in these refugia during the last glaciations. Nevertheless, as long as the phylogeny of the group remains uncertain, we cannot reject the possibility of an earlier origin of paedomorphosis. The two morphs primarily differed in space use and feeding habits. These differences were particularly marked in deep alpine aquatic habitats, where the paedomorphs occupy deep waters devoid of competitors, such as fish. In such waters, the paedomorphs were more abundant on the bottom and in the water column, whereas the metamorphs mainly occupied the water surface and shore. The paedomorphs primarily ingested plankton, while the metamorphs mainly foraged on terrestrial prey that had fallen on the water surface. Although these feeding habits depend on newt habitats - plankton being more abundant in the water column, and terrestrial prey at the water surface - the trophic spectrum in each habitat still differed. While the energetic values of the prey eaten by the two morphs strongly differed, by ingesting a large number of planktonic organisms, the paedomorphs attained similar or even larger caloric intake rates than metamorphs. The paedomorphs' superior body condition suggests that they may have higher long-term success than the metamorphs. Differences in body condition may also reflect the terrestrial life habit of the metamorphs, since metamorphosed individuals are able to avoid competition with reproductive adults and larvae by leaving the water. In the paedomorphic populations, several size-structured cohorts of larvae coexist, and competition among these cohorts is lowered by size-selective predation, since small larvae catch smaller prey than larger larvae and paedomorphs. Although this difference in diet was in part due to gape-size limitation, the gilled individuals also size-selected prey among a range of catchable items. Resource partitioning then favoured the coexistence of the two adult morphs, and their gilled descendants, which coexist with them. The two morphs also differed in feeding performance. Whereas the paedomorphs were better predators than metamorphs on water fleas, metamorphs were more adept at capturing large terrestrial invertebrates (flies). These differences in feeding performances were caused by the morphological particularities of the two morphs. Paedomorphs had a fish-like feeding structure with a unidirectional water flow passing through the oral cavity, and then being expelled through gill slits on the posterior side of the head. In contrast, metamorphs had a smaller oral cavity and a bidirectional water flow due to closed gill slits. Although the metamorphic structure produces less suction, it allows for catching bigger prey because of a larger gape-size (biting rather than sucking). Our measures of feeding performances confirmed the data from natural populations, with each of the morphs preferentially eating their predicted prey. The particular use of micro-habitats by the two morphs is also in agreement with optimality models predicting predation in the more profitable patches. In the Alpine newt, paedomorphosis can be produced by two main processes: neoteny and progenesis. In some populations, the two morphs reached sexual maturity at the same age (neoteny); in other populations, sexual maturity was reached earlier by paedomorphs (progenesis). Progenesis was observed in unstable water habitats. Pond drying suppressed the possibility of late maturation, which is characteristic of a neotenic developmental pathway. On the other hand, the precocious sexual maturation of paedomorphs favoured the fast colonization of new habitats, owing to a high intrinsic rate of natural increase. Neoteny was typical of permanent waters with harsh constraints on growth. By forgoing metamorphosis, larvae also avoid the cost of changing of structure (decrease in body weight in our experiments). Progenetic paedomorphosis appears then as a major trait that can be selected due to the advantages of earlier maturation. The two morphs are sexually compatible; thus, metamorphs can "exchange" genes with paedomorphs at each generation. While the two morphs markedly differ in their secondary sexual characteristics, females did not show any preference related to these characteristics. The absence of sexual isolation between the morphs shows that they are not involved in a sympatric speciation process. The maintenance of the polymorphism is more advantageous than the formation of two isolated species. Paedomorphosis occurs in aquatic habitats where total drying can occur, and where the maintenance of facultative paedomorphosis is maintained by metamorphs that have paedomorphic genes but do not (permanently) express them. In such habitats, the sexual isolation of the two morphs would lead to the extinction of paedomorphosis in the event of pond drying or similar catastrophe. Because the environment can modify the ontogenetic pathway, paedomorphosis in the Alpine newt can be considered a polyphenism. Indeed, restricting the amount of water or food available induces paedomorphs to metamorphose. The marking of individual paedomorphs in a natural population proved that metamorphosis also occurs in the field. However, salamander density and progressive drying of aquaria did not have any apparent effect on paedomorph metamorphosis. When the possibility of a short migration across dry land was given, paedomorphs moved towards an available water basin and maintained their larval somatic characters during the migrations. By being able to migrate on land towards permanent water, paedomorphs are able to retain a feeding morphology that favors them in microhabitats where plankton is abundant. Facultative paedomorphosis in the Alpine newt allows populations to cope with environmental variability, and is adaptive in allowing precocious maturation or a larger use of resources in spatially heterogeneous environments. Thus, it is not surprising that paedomorphosis can evolve in such dissimilar environments as lowland temporary ponds and highland deep lakes. In such places, paedomorphosis appears to be the best solution as long as fish predation is relaxed. The introduction of fish throughout Europe is thus a serious problem, and has resulted in the extinction of several large paedomorphic populations. If this trend is not stopped rapidly, paedomorphosis in the Alpine newt - and in other species - will belong to the past. [less ▲]

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See detailEco-éthologie des populations pédomorphiques du Triton alpestre
Denoël, Mathieu ULg

Conference (2001)

La pédomorphose est un processus évolutif impliquant la rétention de caractères larvaires chez l’adulte reproducteur. Chez les salamandres et les tritons, la pédomorphose peut être facultative. Ainsi ... [more ▼]

La pédomorphose est un processus évolutif impliquant la rétention de caractères larvaires chez l’adulte reproducteur. Chez les salamandres et les tritons, la pédomorphose peut être facultative. Ainsi, dans une même population, alors que certaines larves atteignent la maturité tout en conservant leurs attributs larvaires (fentes branchiales, branchies), d’autres se métamorphosent en juvéniles qui atteindront leur maturité en phase terrestre avant de retourner à l’eau. Il s’agit ainsi de ce que certains dénomment une néoténie. La coexistence des deux formes alternatives adultes – les pédomorphes et les métamorphes – offre dès lors la possibilité d’examiner l’aspect adaptatif du polymorphisme et de valider les hypothèses évolutives relatives à la pédomorphose. A cette fin, plusieurs populations pédomorphiques du triton alpestre (Triturus alpestris) de France, d’Italie et de Grèce ont été étudiées entre 1996 et 2000. Un accent particulier a été mis dans la détermination des structures d’âge, du régime alimentaire et de l’occupation de l’espace. Des expériences de laboratoire ont également permis d’analyser la performance de la structure trophique des tritons et de caractériser l’effet de paramètres environnementaux sur la pédomorphose. Ces analyses montrent que les deux formes alternatives ont des structures d’âge similaires dans certaines populations (processus néoténique) alors que les pédomorphes acquièrent leur maturité plus précocement que les métamorphes dans d’autres populations (processus progénétique). La progenèse était observée dans des milieux instables. Le régime alimentaire des deux formes différait nettement dans trois lacs alpins. Les pédomorphes se comportaient comme des planctonophages tandis que les métamorphes ingéraient dans l’eau des proies exogènes au milieu aquatique. L’occupation de l’habitat n’était pas identique. La différence de régime peut être expliquée par une différence de performance de leur structure trophique : les pédomorphes étant plus performants dans la capture du plancton tandis que les métamorphes, eux, le sont dans la capture d’invertébrés terrestres. Les expériences de laboratoire ont aussi montré que l’absence de proies et l’assèchement du milieu induisaient la métamorphose. En conclusion, la pédomorphose facultative offre différents avantages qui ne sont pas nécessairement identiques dans tous les milieux. Elle est adaptative en conférant une maturité précoce dans des milieux imprévisibles et une utilisation optimale des ressources dans des habitats hétérogènes. Un tel processus est également un polyphénisme permettant un changement de tactique (métamorphose) en cas de détérioration de l’habitat. [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 detailLe comportement social des urodèles
Denoël, Mathieu ULg

in Cahiers d'Ethologie (1999), 19

It could be misleading to consider that the social behaviour of newts and salamanders is simple and can be generalized. Indeed, individuals are faced with external and internal conditions which are ... [more ▼]

It could be misleading to consider that the social behaviour of newts and salamanders is simple and can be generalized. Indeed, individuals are faced with external and internal conditions which are extremely variable. In response to these factors, they may respond in a particular way. The behavioural variations, called alternative tactics, allow individuals to improve their fitness, i.e. to ensure the survival of their genes. They can be exhibited in reaction to a large range of factors such as the mere presence or density of competitors, the operational sex-ratio, the behaviour and kinship of the other individuals, the abiotic characteristics of the environment, the experience of the individuals involved. These alternative tactics are favoured in urodeles. Indeed, although the main process of fertilization is internal, they breed by means of a spermatophore deposited in the external environment. Each species of newts and salamanders exhibits specific behavioural patterns as they developed and evolved in particular environments which have exerted selective pressures on the individuals and in this way on the species. As a consequence, the understanding of patterns of behaviour requires that we know the environment in which they appeared. The main occurrence of parental care and territoriality in terrestrial environments may be explained by the features of these habitats in which eggs could not survive without protection, and in which adults may defend areas of particular interest and communicate by means of pheromones. All of these characteristics show that we have to study the behaviour of individuals of different species under several conditions. Without such an analysis, it would be difficult to understand biodiversity. [less ▲]

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See detailSignification adaptative de la néoténie chez le Triton alpestre
Denoël, Mathieu ULg

Scientific conference (1999)

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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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