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See detailSeasonal variation of morph ratio in facultatively paedomorphic populations of the palmate newt Triturus helveticus
Denoël, Mathieu ULg

in Acta Oecologica: International Journal of Ecology (2006), 29(2), 165-170

Facultative paedomorphosis is a polyphenism in which individuals may express one of two alternative ontogenetic pathways (metamorphosis vs. paedomorphosis) depending on environmental cues. Previous ... [more ▼]

Facultative paedomorphosis is a polyphenism in which individuals may express one of two alternative ontogenetic pathways (metamorphosis vs. paedomorphosis) depending on environmental cues. Previous laboratory experiments showed that drying can cause morph ratio change, suggesting that the maintenance of facultative paedomorphosis is highly dependent on environmental determinants. The aim of this study was to examine seasonal variation in morph ratios in eight ponds from Larzac (southern France) naturally inhabited by palmate newts and to relate it to pond drying. in some ponds, the relative proportion of paedomorphs (i.e. individuals retaining gills at the adult stage) increased after the breeding period, but it remained stable or decreased in other ponds. This seasonal variation in the abundance of the two morphs most probably reflects (1) the emigration of metamorphs leaving the pond to occupy terrestrial habitats and (2) metamorphosis of paedomorphic adults in response to drying of the ponds. This study shows that facultative paedomorphosis in palmate newts is a dynamic process that allows rapid change (i.e. within a single year) in morph ratio to fit environmental variation (i.e. risk of drying) within the aquatic habitats. Long-term studies are needed to model the evolution of the dimorphism according to environmental change. (c) 2005 Elsevier SAS. All rights reserved. [less ▲]

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See detailEditorial Report 2005
Denoël, Mathieu ULg

in Amphibia-Reptilia (2006), 27(3), 479

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See detailEffects of long-term population fluctuations of a top predator on invertebrate communities in subalpine ponds in Colorado
Wissinger, S.; Whiteman, H.; Denoël, Mathieu ULg et al

Conference (2006)

Experimental and comparative data from subalpine ponds with and without tiger salamanders (Ambystoma tigrinum nebulosum) suggest that this species is a keystone predator on benthic and planktonic prey ... [more ▼]

Experimental and comparative data from subalpine ponds with and without tiger salamanders (Ambystoma tigrinum nebulosum) suggest that this species is a keystone predator on benthic and planktonic prey communities. At our study site in central Colorado, the population size of salamanders has fluctuated cyclically over the past 20 years from fewer than 100 to over 5000 individuals. Here we present long-term benthic data that reveal taxon- and habitat-specific correlations with fluctuations in salamander populations. In temporary habitats, benthic biomass changed little during fluctuations in salamander abundance. In permanent ponds, we observed order-of-magnitude changes in benthic biomass that were negatively correlated with salamander abundance. Among the large-bodied and potentially most vulnerable taxa (odonates, caddisflies, beetles, water bugs), several species exhibited negatively coupled cycles, but others fluctuated little or out of phase with changes in salamander abundance. The absence of major shifts in benthic community composition in permanent ponds is probably a result of conflicting predation pressures exerted by different year classes of salamanders. Data on ontogenetic shifts in salamander diet help explain why cyclic fluctuations in the abundance of this predator had only minor impacts on benthic community composition despite having major effects on invertebrate biomass. [less ▲]

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See detailMechanisms of cohort suppression and population fluctuation in tiger salamanders
Whiteman, Howard; Wissinger, Scott; Denoël, Mathieu ULg

Conference (2006)

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians equires that we ... [more ▼]

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians equires that we understand these mechanisms, and be able to distinguish between anthropogenically induced declines and natural population fluctuations. We have followed a marked population of the Arizona tiger salamander, Ambystoma tigrinum nebulosum, for over 16 years during which time the population has completed two “boom and bust” cycles, generated by a dominant cohort that appears to suppress larval recruitment until it senesces. We tested two hypotheses for this suppression, cannibalism and resource depression, using a series of meso- and microcosm experiments. We found significant lethal and sublethal (behavior, diet, growth rates) effects of cannibalism by large larvae and paedomorphic adults on hatchling and 1st-year larvae, suggesting that both cannibalism and the threat of cannibalism are important in cohort suppression. Resource depression experiments revealed that paedomorphic adults did not affect larval survival, diet, or growth, despite reduced prey densities, because paedomorphs mainly reduced large bodied prey, whereas hatchlings fed primarily on smaller benthic and zooplanktonic invertebrates. Future experiments will determine how hatchlings are impacted by boom cohorts that are more similar in size and diet. Our results lend insight into the mechanisms underlying fluctuations in this population, and suggest that a better understanding of natural population fluctuations will aid amphibian conservation efforts. [less ▲]

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See detailEffects of long-term population fluctuations in a top predator on invertebrate community composition in Alpine ponds
Wissinger, Scott; Whiteman, Howard; Denoël, Mathieu ULg

Conference (2006)

At our remote study site in central Colorado, the population size of tiger salamanders (Ambystoma tigrinum nebulosum) has fluctuated cyclically over the past 20 years from fewer than 100 to over 5000 ... [more ▼]

At our remote study site in central Colorado, the population size of tiger salamanders (Ambystoma tigrinum nebulosum) has fluctuated cyclically over the past 20 years from fewer than 100 to over 5000 individuals. Comparative data between ponds with and without salamanders, and experimental studies suggest that this species is a keystone predator on benthic and planktonic prey communities. Here we present long-term community data that reveal taxon- and habitat-specific correlations in the population size of benthic and planktonic prey with fluctuations in salamander populations. Changes in the abundance of planktonic, but not benthic invertebrates in temporary habitats were correlated with fluctuations in the abundance of salamanders. In permanent ponds, we observed order-of-magnitude changes in benthic biomass that are negatively correlated with salamander abundance. Among the large-bodied and potentially most vulnerable benthic invertebrates (odonates, caddisflies, beetles, water bugs), several species exhibited negatively coupled cycles, but others fluctuated little or out of phase with changes in salamander abundance. The absence of major shifts in benthic community composition in permanent ponds is probably a result of conflicting predation pressures exerted by different year classes of salamanders. Salamander gut samples suggest that ontogenetic shifts in diet might explain why cyclic fluctuations in the abundance of this predator had only minor impacts on benthic community composition despite having major effects on invertebrate biomass. [less ▲]

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See detailMechanisms of larval cohort suppression and population fluctuation in tiger salamanders.
Whiteman, Howard; Wissinger, Scott; Denoël, Mathieu ULg

Conference (2006)

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians requires that we ... [more ▼]

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians requires that we understand these mechanisms, and be able to distinguish between anthropogenically induced declines and natural population fluctuations. We have followed a population of the Arizona tiger salamander, Ambystoma tigrinum nebulosum, over 16 years and through two cycles of population fluctuation, which is typified by the production of “boom” cohorts followed by suppression of larval recruitment by paedomorphic adults in this cohort. We tested two hypotheses for this suppression, cannibalism and resource depression, using a series of meso- and microcosm experiments. We found significant direct (mortality) and indirect (behavior, diet, growth rates) effects of cannibalism by larger larvae and paedomorphic adults on hatchling and 1st-year larvae, suggesting that both cannibalism and the threat of cannibalism play a large role in suppression of larval cohorts. In contrast, paedomorphic adults showed no substantial effects on larval survival, diet, or growth via resource depression, in part because paedomorphic adults reduced availability of large benthic invertebrates, while hatchlings fed primarily on smaller benthos and zooplankton. However, current experiments suggest that hatchlings can be impacted by cohorts of larvae that are more similar in size and diet. Our results lend insight into the mechanisms underlying fluctuations in this population, and suggest that a better understanding of natural population fluctuations will aid amphibian conservation efforts. [less ▲]

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See detailAmphibia-Reptilia: Editorial report 2003-2005
Denoël, Mathieu ULg

Conference (2005, October 01)

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See detailCourtship behavior in the Alpine newt Triturus alpestris at two different densities of males
Denoël, Mathieu ULg; Hector, Marie-Pierre; Poncin, Pascal ULg

in Herpetologica (2005), 61(4), 373-379

The aim of this laboratory experiment was to examine courtship behavior and reproductive success under two different perceived male densities ill the Alpine newt (Triturus alpestris). Male behavioral ... [more ▼]

The aim of this laboratory experiment was to examine courtship behavior and reproductive success under two different perceived male densities ill the Alpine newt (Triturus alpestris). Male behavioral patterns were similar at unbiased and male-biased operational sex ratios (OSR). Although the exhibition of hiring behaviors is risky in the presence of other males, no difference in the frequencies of displays was found at the two male, densities. Similarly, the responsiveness of females towards males and the Success rate of the encounters (i.e. spermatophore transfer) were not explained by file OSR. Our results show that courting Alphine newts do not change their courtship patterns when other males are present and do not interact directly. However they are not necessarily opposed to those of previous experiments showing sexual interference awl ,female aversion in male-biased OSR with possibility of interactions. These observations suggest that the evolution of courtship behavior may not be driven by the risk of sexual interference with other males prior to potential physical contact and that the benefits of breeding regardless of OSR can overcome the risk of Competition at male-biased OSR. [less ▲]

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See detailHabitat partitioning in facultatively paedomorphic populations of palmate newts Triturus helveticus
Denoël, Mathieu ULg

in AMBIO : A Journal of the Human Environment (2005), 34(6), 476-477

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See detailPersistence and dispersion of an introduced population of Alpine Newt (Triturus alpestris) in the limestone plateau of Larzac (Southern France)
Denoël, Mathieu ULg

in Revue d'Ecologie (La Terre et la Vie) (2005), 60(2), 139-148

Persistence and dispersion of an introduced population of Alpine Newt (Triturus alpestris) in the limestone plateau of Larzoc (southern France). - The study of introduced populations is interesting to ... [more ▼]

Persistence and dispersion of an introduced population of Alpine Newt (Triturus alpestris) in the limestone plateau of Larzoc (southern France). - The study of introduced populations is interesting to better understand the geographic distribution and adaptability of species in different environments. The recent finding of an Alpine Newt population (Triturus alpestris) in the limestone plateau of Larzac (Department of Herault, France) provides the opportunity to examine the success of this species in the French supra-Mediterranean environment, Indeed, this species is absent from southern France although present in a large part of France and in northern Spain. The introduction site and all water bodies within a 2.5 km radius were surveyed between spring and autumn 2003. Because of the introduction date and the life expectancy of newts, all observed individuals are descendants of the introduced animals. They persist and breed in the study site despite the coexistence with Palmate Newts (Tri-turus helveticus). Body condition decreases in summer in these two species, but was lower in Alpine Newt males than in Palmate Newt males in autumn. Alpine Newts were found in only one of the other nine ponds, indicating a 1.5 km dispersion. Few Alpine Newts were present at this site, but reproduction was effective. These results show that the Alpine Newt can survive in southern France despite the presence of other newt species, but that the dispersion speed and rate towards other ponds are low. [less ▲]

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See detailEffects of widespread fish introductions on paedomorphic newts in Europe
Denoël, Mathieu ULg; Džukić, Georg; Kalezic, Milos L.

in Conservation Biology (2005), 19(1), 162-170

As a result of factors such as global warming, habitat destruction, and species introduction, amphibians are declining worldwide. No one, however, has analyzed the status of polymorphic amphibian species ... [more ▼]

As a result of factors such as global warming, habitat destruction, and species introduction, amphibians are declining worldwide. No one, however, has analyzed the status of polymorphic amphibian species at a national or continental scale, although some local reports exist. Our aim was to report on the loss of intraspecific heterochrony as a loss to diversity in determining the consequences of fish stocking on European populations of paedomorphic newts. Paedomorphosis is a polymorphism in which larval traits are retained in the adult stage. We surveyed 39 paedomorphic populations of the alpine ( Triturus alpestris) and palmate ( T. helveticus) newts, all but one of which initially occupied fishless ponds and lakes in France, Italy, Slovenia, Bosnia, Montenegro, and Greece. Exotic fishes were found in 44% of the studied aquatic habitats, with a 100% presence in Montenegro. At all sites paedomorphs disappeared and metamorphs declined. Only fish explained these population changes because alternative factors such as drying were not significant. More catastrophically, fish introductions occurred in habitats known to support the largest populations of newts and even some endemic subspecies. If management and legislative measures are not taken to stop fish stocking, protect paedomorphs as conservation units at national and international levels, and restore natural habitats, all the largest paedomorphic populations may disappear in the near future. Their disappearance would represent a loss of one of the rare, fascinating examples of intraspecific heterochrony. [less ▲]

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See detailEffect of water temperature on the courtship behavior of the Alpine newt Triturus alpestris
Denoël, Mathieu ULg; Mathieu, Maryève; Poncin, Pascal ULg

in Behavioral Ecology and Sociobiology (2005), 58(2), 121-127

Temperature is expected to have an effect on the behavioral patterns of all organisms, especially ectotherms. However, although several studies focused on the effect of temperature on acoustic displays in ... [more ▼]

Temperature is expected to have an effect on the behavioral patterns of all organisms, especially ectotherms. However, although several studies focused on the effect of temperature on acoustic displays in both insects and anurans, almost nothing is known about how environmental temperature may affect ectotherm visual courtship displays and sexual performance. The purpose of this study was to determine the effect of environmental temperature on the sexual behavior of Alpine newts (Triturus alpestris). We subjected T. alpestris to two different temperatures in controlled laboratory conditions. Temperature had a major effect on both male and female behaviors: at low temperature, the frequencies of several displays, including tail-raising during sperm deposition, are lowered. This variation is caused indirectly by temperature because it is due to female responsiveness, which is temperature-dependent. However, the fanning movement of the male's tail during its main courtship display is independent of female behavior: at lower temperatures, the tail beats at a lower rate, but for a longer time. The similar reproductive success (i.e. sperm transfer) at the two temperature ranges indicates that breeding in cold water is not costly but instead allows males and females to mate early in the season. This is particularly adaptive because, in many habitats, the reproductive period is shortened by drying or freezing conditions, which may impair survival of branchiate offspring. This study also demonstrates the necessity of considering environmental parameters when modeling optimality and characteristics of ectotherm behaviors. [less ▲]

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See detailFish introduction is a major cause of paedomorphosis extinction in European newts (Triturus spp.)
Džukić, Georg; Ćirović, Ruža; Denoël, Mathieu ULg et al

in Froglog (2005), 69

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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 detailConsequences of fish introductions on paedomorphic newts (Triturus alpestris and T. helveticus)
Denoël, Mathieu ULg; Dzukic, Georg; Kalezic, Milos

Poster (2005)

Fish stocking is largely recognized as a major thread to amphibian populations. Although it acts at a local level, it is widespread at a world scale. Despite this good knowledge, the effect of fish on ... [more ▼]

Fish stocking is largely recognized as a major thread to amphibian populations. Although it acts at a local level, it is widespread at a world scale. Despite this good knowledge, the effect of fish on alternative phenotypes has only been described in a few local studies. Our aim was to report on the loss of intraspecific heterochrony as a loss to diversity in determining the consequences of fish introductions on paedomorphs (morphs retaining gills at the adult stage) of two European species of newts. We surveyed almost all the main known paedomorphic populations of the Alpine (Triturus alpestris) and palmate (T. helveticus) newts, which all but one initially occupied fishless ponds and lakes in France, Italy, Slovenia, Bosnia, Montenegro, and Greece. Exotic fish were found in almost half of the studied aquatic habitats. Introductions involved several ornamental and large predatory species of fish. At all sites, in which fish were introduced, paedomorphs disappeared and metamorphs declined. The largest known populations of newts, including some endemic subspecies, were concerned. If measures are not taken to stop fish stocking, protect paedomorphs as conservation units, and restore natural habitats, all the largest paedomorphic populations may disappear in the near future. [less ▲]

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