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See detailFeeding habits in a dimorphic metapopulation of the tiger salamander Ambystoma tigrinum nebulosum
Denoël, Mathieu ULg; Wissinger, Scott; Whiteman, Howard

Conference (2003)

Facultative paedomorphosis in salamanders refers to the presence of two ontogenetic pathways in natural populations – paedomorphosis, in which individuals retain gills at the adult stage, and ... [more ▼]

Facultative paedomorphosis in salamanders refers to the presence of two ontogenetic pathways in natural populations – paedomorphosis, in which individuals retain gills at the adult stage, and metamorphosis, in which larvae metamorphose. The Mexican Cut Nature Preserve (Colorado, USA) is composed of numerous ponds which are inhabited by paedomorphic and metamorphic tiger salamanders. While paedomorphs usually stay in the same aquatic habitat all their life, metamorphs may leave water and colonize other ponds. The aim of this study was to determine the feeding habits of the two morphs from this metapopulation. To this end, adults were caught by dip-netting, stomach-flushed, measured and marked. Paedomorphs were only found in permanent waters. Metamorphs were present in all habitats, but particularly in the temporary ponds. Diet differed between ponds – reflecting their invertebrate composition – with a preponderance of either microcrustaceans, fairy shrimp or insect larvae. In ponds inhabited by the two morphs, paedomorphs consumed more prey items. Because dry mass and energy content varied between invertebrates, feeding on some of them, such as fairy shrimp in the temporary ponds where they are abundant, gave high energy intake to the predators. Because such resources are only available to the dispersive morph, metamorphs are at the advantage in being able to avoid competition with paedomorphs in permanent ponds and in using transient resources from the productive temporary waters. [less ▲]

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See detailSexual interactions in triadic encounters involving paedomorphic and metamorphic Alpine newts Triturus alpestris
Denoël, Mathieu ULg

Poster (2003)

Sexual selection theories suppose that morphologically-contrasting alternative morphs may exhibit different mating tactics. Facultative paedomorphosis in newts is a suitable process to explore this ... [more ▼]

Sexual selection theories suppose that morphologically-contrasting alternative morphs may exhibit different mating tactics. Facultative paedomorphosis in newts is a suitable process to explore this question because it implies the coexistence of two morphs differing by the presence of gills and epigamic traits. The aim of this study was to find out whether paedomorphs (i.e. adult retaining larval traits) and metamorphs use similar behavioural patterns to attract mates in the presence of a rival and whether there are differences in sexual activity and success between alternative morphs. Sexual interactions in triadic encounters were staged and analysed in a standardised experimental design. The two kinds of males did not differ in terms of sexual activity, spermatophore deposition or female responsiveness. Both rival paedomorphic and metamorphic males exhibited sexual interference, but in most encounters, intruders just disturbed the courting pair. Sperm transfer success was lower in triadic encounters than in dyadic encounters. These results illustrate that inter-morph breeding also occurs in the presence of competitors, but that the success rate of the newts is considerably decreased in such competitive situations. Moreover, newts do not use alternative reproductive tactics depending of their status (i.e. paedomorph or metamorph). [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 detailLe monde fascinant des salamandres et des tritons
Denoël, Mathieu ULg

Scientific conference (2002)

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See detailPaedomorphosis in the Alpine newt (Triturus alpestris): decoupling behavioural and morphological change
Denoël, Mathieu ULg

in Behavioral Ecology and Sociobiology (2002), 52(5), 394-399

Paedomorphosis is a heterochronic pattern leading to morphological change, i.e. retention of larval characters in the adult phenotype. The aim of this study was to find out whether behaviour and ... [more ▼]

Paedomorphosis is a heterochronic pattern leading to morphological change, i.e. retention of larval characters in the adult phenotype. The aim of this study was to find out whether behaviour and morphology are decoupled in heterochronic phenotypes. To this end, I compared qualitative and quantitative aspects of courtship behaviour in syntopic metamorphic and paedomorphic Alpine newts, Triturus alpestris. Morphologically, the two morphs differ considerably (e.g. by the presence of gills only in paedomorphs), but their patterns of sexual behaviours are exhibited at similar frequencies and males use the same alternative reproductive tactics to attract unresponsive females. These results show that morphology and behaviour follow different ontogenetic pathways and are thus decoupled. Decoupling of the two traits offers the possibility of morphological evolution without alteration of sexual patterns. [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 detailBiogeography and ecology of paedomorphosis in Triturus alpestris (Amphibia, Caudata)
Denoël, Mathieu ULg; Duguet, R.; Džukić, Georg et al

in Journal of Biogeography (2001), 28(10), 1271-1280

Aim Paedomorphosis is an evolutionary change in which larval structures are retained in adult animals. In newts and salamanders, this heterochronic process is widely represented and concerns the retention ... [more ▼]

Aim Paedomorphosis is an evolutionary change in which larval structures are retained in adult animals. In newts and salamanders, this heterochronic process is widely represented and concerns the retention of gill slits. We want to find out whether ecological and geographical determinants may be associated with paedomorphosis in the Alpine newt Triturus alpestris. Location Europe. Methods Determination of the main characteristics of all known aquatic sites containing paedomorphic Alpine newt individuals. Results Although metamorphs are common in Europe, paedomorphs are only found at the southern margin of the geographical range of the species: mainly in Italy and in the Balkans. They were recorded in eighty-seven aquatic sites. No single trend was outlined for the analysed ecological parameters of the aquatic and terrestrial habitats (e.g. altitude, maximum water depth, drying and presence of forest). Main conclusions Contrary to the first models of paedomorphosis, the main traits of aquatic and terrestrial habitat do not explain the occurrence of paedomorphs in natural populations. Although they were found in favourable aquatic habitats surrounded by hostile terrestrial landscapes, they also exist in temporary waters located at proximity of appropriate terrestrial environments. These results support models predicting paedomorphosis in varied environments, but require complementary investigations on the costs and benefits of the alternative ontogenetic pathways. On the other hand, the southern limitation of the heterochronic phenomenon suggests a genetic basis for paedomorphosis in the studied species. [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 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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