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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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See detailOptimality of feeding on land versus in water in juvenile Alpine newts (Triturus alpestris veluchiensis)
Denoël, Mathieu ULg

Poster (2005)

Most newts experience both terrestrial and aquatic environments during their adult life. A large number of studies explored the feeding habits in the aquatic habitat while very few focused on the ... [more ▼]

Most newts experience both terrestrial and aquatic environments during their adult life. A large number of studies explored the feeding habits in the aquatic habitat while very few focused on the terrestrial component and none compared the two systems within a single population. The aim of this study was to find out which foraging tactic is the most successful in terms of energy intake. To this end, I analysed the feeding habits of metamorphosed juveniles in the Alpine newt inhabiting a Greek alpine lake and its surrounding lands. The diet reflected the range of prey available in the two habitats, but invertebrates, which fell on the water surface, were also ingested by aquatic newts. These two lifestyles had different energy outcomes because the highest number of terrestrial invertebrates taken in the terrestrial habitat than in the aquatic one provided higher energy gains to terrestrial juveniles. However, different mortality rates between habitats (highest probability of freezing risk on high-elevated lands than in deep waters) and an expected lower energy intake on land when air temperature is low could explain the persistence of the aquatic foraging tactic in the population. [less ▲]

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See detailAre cannibalistic morphs of the tiger salamander obligatory cannibals?
Denoël, Mathieu ULg; Whiteman, Howard; Wissinger, Scott

Conference (2005)

Tiger salamanders exhibit alternative trophic morphologies, with cannibals developing a larger head and longer teeth than typical larvae. Resource partitioning is known between morphs, with cannibal ... [more ▼]

Tiger salamanders exhibit alternative trophic morphologies, with cannibals developing a larger head and longer teeth than typical larvae. Resource partitioning is known between morphs, with cannibal morphs usually foraging on conspecifics and rarely on small organisms. Our aim was to determine whether the cannibal and typical morphs shift their diets across time and particularly whether conspecifics are necessarily the main prey of cannibals and plankton the primary prey of typicals. We found that only the cannibal morph foraged on conspecifics, but not all the time. Cannibalism typically occurred only early after the ontogenetic divergence between morphs. Cannibals shifted their diet later in the summer to plankton, and this ontogenetic shift led to dietary overlap with the typical morph. In contrast to other studies, our findings suggest that the cannibal morphology actually allows the consumption of a larger variety of prey, rather than specialization on specific resources (i.e., conspecifics). The outcomes of the cannibalistic ontogenetic pathway include a higher biomass intake from food and a larger size than typicals. From a foraging perspective, the cannibalism pathway is clearly advantageous over the typical morphology. However, the increased diet breadth of cannibal morphs found in this study suggests that the maintenance of the polyphenism is more complex than has previously been suggested. [less ▲]

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See detailCourtship behaviour at low and high water temperatures in the Alpine newt
Denoël, Mathieu ULg; Mathieu, Maryève; Poncin, Pascal ULg

Poster (2005)

Environmental factors are known to have a major effect on behavioral patterns of organisms. Among these factors, temperature particularly affects ectotherms. However, although many studies focused on ... [more ▼]

Environmental factors are known to have a major effect on behavioral patterns of organisms. Among these factors, temperature particularly affects ectotherms. However, although many studies focused on acoustic communication, the effect of environmental temperature on visual courtship displays and sexual performance has been little explored. The aim of this work was to determine the effect of temperature on the sexual behaviour of the Alpine newt Triturus alpestris in controlled laboratory conditions. Temperature had a major effect on the two sexes: at low temperatures, the frequencies of several displays, including sperm deposition, is lowered. This variation is in fact caused by the female responsiveness, which is temperature-dependent. However, some other behaviours, such as the fanning movement of the male’s tail (i.e., the main courtship display) are directly dependent on temperature: at lower temperatures, the tail beats at a lower rate but for a longer time. The similar reproductive success at the two temperatures indicates that breeding in cold water is not necessarily costly. It 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. [less ▲]

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See detailFeeding performance in heterochronic alpine newts is consistent with trophic niche and maintenance of polymorphism
Denoël, Mathieu ULg

in Ethology (2004), 110(2), 127-136

The feeding performances of two heterochronic morphs of the Alpine newt Triturus alpestris were investigated in laboratory experiments. Although both morphs are able to feed in the aquatic habitat, the ... [more ▼]

The feeding performances of two heterochronic morphs of the Alpine newt Triturus alpestris were investigated in laboratory experiments. Although both morphs are able to feed in the aquatic habitat, the hydrodynamics of prey capture differ between morphs. In paedomorphs water sucked with prey is expelled behind the mouth through gill bars. In metamorphs, water is expelled by the mouth as gill slits are closed. Feeding performance was better in paedomorphs than in metamorphs when foraging on aquatic crustaceans, but paedomorphs were less successful when foraging on terrestrial invertebrates caught at the water surface. These differences in prey capture success related to prey type allow the two morphs to use specific resources in their aquatic habitat. These results are consistent with previous studies that showed diet differentiation between morphs in natural populations. Such resource partitioning is a factor favouring the maintenance of facultative paedomorphosis in natural populations. [less ▲]

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See detailTerrestrial versus aquatic foraging in juvenile Alpine newts (Triturus alpestris)
Denoël, Mathieu ULg

in Ecoscience (2004), 11(4), 404-409

Many species of newts and salamanders forage in both terrestrial and aquatic environments during their life. However, the relative benefits of the two foraging patterns remain unknown because all previous ... [more ▼]

Many species of newts and salamanders forage in both terrestrial and aquatic environments during their life. However, the relative benefits of the two foraging patterns remain unknown because all previous studies have focused on only one habitat. The aim of this study was to find out which foraging tactic is the most successful in terms of energy intake. To this end, I analyzed trophic habits in metamorphosed juveniles in the Alpine newt, Triturus alpestris veluchiensis, inhabiting an alpine lake (Drakolimni) and the surrounding lands (Tymphi Mountains, northern Greece). The diet of the newts reflected the range of prey available in the two habitats, but aquatic newts also foraged on invertebrates that fell on the water surface. The two lifestyles have different energy outcomes. Terrestrial invertebrates provided high energy gains mainly to terrestrial juveniles because of the low number of this prey type in the lake. However, terrestrial juveniles are expected to suffer higher mortality (freezing on land is more probable than in deep waters) and a lower energy intake when air temperature is low, i.e., the main pattern in high-elevation sites, except during mid-summer. Persistence of the aquatic foraging tactics in the population may depend on a trade-off between costs and benefits. [less ▲]

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