Cues from Introduced Fish Alter Shelter Use and Feeding Behaviour in Adult Alpine Newts

Amphibians are particularly affected by alien fish introductions and are declining worldwide. However, the behavioural mechanisms behind the observed cases of coexistence and exclusion patterns between adult amphibians and fish are poorly understood. In the present study, we aimed at testing the hypothesis that adult newts display different feeding and space use behaviour in the presence of fish cues (i.e. access less food resources and use more shelters than when fish cues are absent). To achieve this we measured behavioural patterns in 100 adult Alpine newts (Mesotriton alpestris) in a replicated laboratory design (20 tanks × 7 replicates across time). Half of trials involved individuals in indirect (visual and olfactory) contact with goldfish (Carassius auratus), a non‐predatory species for adult newts. In the presence of fish, significantly more newts hid under shelters than in their absence, but this difference decreased over time. A lower number of newts fed in comparison with controls. These results show that newts responded to fish presence even in the absence of direct contact, but the differences were small. Newts decreased vital activities such as exploration of open areas and feeding. They also adjusted shelter use over time, suggesting a process of habituation or a risk assessment in the absence of direct risk. These results reveal that exploring behavioural patterns can aid in understanding the causes of exclusion and coexistence patterns between fish and amphibians.     

Competitive and predatory interactions between invasive mosquitofish and native larval newts

Invasive fish have a high disruptive potential in aquatic ecosystems, in which amphibians may be highly impacted due to intense competition and/or predation on their eggs and larvae. Most studies have focused on the effect of large invasive fishes such as salmonids, whereas the effect of smaller fish on amphibians has been seldom investigated. We experimentally studied effects of the invasive Eastern mosquitofish (Gambusia holbrooki) on pygmy newts (Triturus pygmaeus), a species endemic to the Iberian Peninsula. We set up outdoor mesocosms in Doñana National Park with native aquatic flora and invertebrate fauna, and containing larval newts at two experimental densities. Density of larval newts was also crossed with presence or absence of mosquitofish, either free-swimming or caged, in order to distinguish consumptive and non-consumptive effects. Increased density of coexisting larval newts did not reduce their survival, but reduced their growth and development. Newt survival and size at metamorphosis were dramatically reduced in the presence of free-swimming mosquitofish, whether at low or high fish densities. Caged mosquitofish, however, had no effect on larval newts. In laboratory trials, mosquitofish preyed more efficiently on insect larvae than did larval pygmy newts, highlighting the high competitive potential of mosquitofish. This was confirmed by the depletion of zooplankton that free fish caused in the experimental outdoor mesocosms. Our study suggests that invasive mosquitofish exert a high negative impact on coexisting newt populations. Such effects can be explained by a combination of direct predation, injuries caused by predation attempts, and intense competitive exploitation of common food resources.     

Response of seaward-migrating European eel (Anguilla anguilla) to manipulated flow fields

Anthropogenic structures (e.g. weirs and dams) fragment river networks and restrict the movement of migratory fish. Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures. This study aimed to assess the effect of flow constriction and associated flow patterns on eel behaviour during downstream migration. In a field experiment, we tracked the movements of 40 tagged adult European eels (Anguilla anguilla) through the forebay of a redundant hydropower intake under two manipulated hydrodynamic treatments. Interrogation of fish trajectories in relation to measured and modelled water velocities provided new insights into behaviour, fundamental for developing passage technologies for this endangered species. Eels rarely followed direct routes through the site. Initially, fish aligned with streamlines near the channel banks and approached the intake semi-passively. A switch to more energetically costly avoidance behaviours occurred on encountering constricted flow, prior to physical contact with structures. Under high water velocity gradients, fish then tended to escape rapidly back upstream, whereas exploratory ‘search’ behaviour was common when acceleration was low. This study highlights the importance of hydrodynamics in informing eel behaviour. This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening.     

Inspection behaviour and inter-individual cooperation in juvenile qingbo: the effects of prior predator exposure and food deprivation

The predation pressure and food availability to which individuals are exposed during their life histories shape inspection behaviour in animals. In this study, we aimed to test whether such behaviours varied with prior experience (predation, starvation or both treatments) or measurement condition (with or without the presence of a predator; here, the snakehead fish, Channa argus) in the fish species Spinibarbus sinensis, known as qingbo. Unexpectedly, prior predator experience showed no significant effect on inspection behaviour as demonstrated by either the frequency or the duration of each activity outside shelter or on cooperation as demonstrated by the inter-individual distance or synchronization of speed. This may have been due to the different adjustments in behaviour among individuals (more shelter use vs. more inspection), the predator treatment used in the present study (exposure to caged predator rather than direct predation) and/or a species-specific strategy in the qingbo. The starved fish displayed shorter inspection latency, increased inspection behaviour and greater cooperation when measured without the predator; however, when measured in the presence of the predator, the starved fish showed increased inspection frequency but shorter inspection duration, possibly due to the compromise between energy needs and predation risk. Similar to those of the predation group, the fish from the double-treated group showed no difference in inspection behaviour compared to the control group under the predator-absent condition, while the high-frequency, short-duration inspection behaviours remained the same as in the starved group. These findings suggested that the adjustment of inspection behaviour and related cooperation are rather complicated according to either predator experience or food deprivation, partially due to the inter-individual differences in behavioural adjustment and/or different environmental conditions.     

Poor Nutritional Conditions During the Early Larval Stage Reduce Risk‐Taking Activities of Fire Salamander Larvae (Salamandra salamandra)

Environmental conditions experienced early in life have been shown to significantly affect growth trajectories at later stages in many vertebrate species. Amphibians typically have a biphasic life history, with an aquatic larval phase during early development and a subsequent terrestrial adult phase after completed metamorphosis. Thus, the early conditions have an especially strong impact on the future survival and fitness of amphibians. We studied whether early nutritional conditions affect the behavioural reaction of fire salamander larvae (Salamandra salamandra) before completion of metamorphosis. Fire salamander larvae reared under rich nutritional conditions were heavier and larger, displayed better body condition overall throughout the first three month of life and metamorphosed earlier compared with larvae raised under poor nutritional conditions. Specifically, we tested whether larvae reared under these different conditions differed with respect to their risk‐taking behaviour and activity. We found no differences in the activity of larvae with respect to their experienced early food conditions. However, larvae reared under poor nutritional conditions hid significantly more often in a risk‐taking test than larvae reared under rich food conditions. This increase in shelter‐seeking behaviour might be an adaptation to reduce the risk of larval drift or an adaptation to compensate for physiological deficits in part by appropriate behavioural reactions. Our results indicate that environmental conditions, such as food availability, may lead to different behavioural strategies.     

Behavioural Correlations May Cause Partial Support for the Risk Allocation Hypothesis in Damselfly Larvae

Prey animals are often confronted with situations that differ in predation risk. According to the risk allocation hypothesis, prey animals should adaptively allocate antipredator behaviour in accordance with the magnitude and frequency of those risk situations. According to the first prediction prey animals should increase foraging in the safe situations and decrease foraging in the dangerous situations as these situations become relatively more dangerous. The second prediction is that with increased time spent in the dangerous situations, progressively more foraging effort is shown in both the dangerous and safe situations, especially in the safer ones. Prey animals may, however, show maladaptive behaviour due to behavioural correlations across risk situations. Here we test for the first time both predictions generated by the risk allocation hypothesis while considering behavioural correlations. We reared larvae of the damselfly Ischnura elegans, from the egg stage, under five rearing risk conditions: (i) in isolation, (ii) in the presence of conspecific larvae, (iii) in the presence of one fish, (iv) in the presence of two fish, and (v) in the presence of two fish for 50% of the time. For each rearing risk condition, we scored their behaviour in the absence and in the presence of fish. In accordance with the first prediction, in the absence of a predator, larvae reared under increasing risk conditions increased their level of foraging. In accordance with the second prediction, in the absence of a predator, larvae that were more frequently exposed to fish during rearing, increased foraging. However, opposite to the predictions from the risk allocation hypothesis, foraging increased both with increasing rearing risk, and with increased predator exposure frequency. The observed positive behavioural correlation of foraging activity across test situations with and without fish, may generate the combination of adaptive patterns in the absence of fish and the maladaptive patterns in the presence of fish. Former studies of the risk allocation hypothesis also found, at best, mixed support, and we hypothesize that behavioural correlations across risk situations, if present, will likely cause partial deviations from model predictions.     

Sexual Interference and Sexual Defense in the Smooth Newt,Triturus vulgaris (Amphibia,Urodela, Salamandridae)

• 1 When a male smooth newt encounters a ♀ who is already engaged in courtship, he may mimic her behaviour during the spermatophore deposition and transfer stages of the courtship. He thereby usurps the courting ♂ and may inseminate the ♀ himself. Such sexual interference depresses the short-term, and perhaps long-term, mating success of the courting ♂.
• 2 In the presence of a potential rival, the courting ♂ alters certain aspects of his sexual behaviour. He displays more intensely to the ♀ and attempts to draw her away from the rival by increasing the duration of his display. He may also “check” that it is the ♀, and not the rival, who will elicit the deposition of a spermatophore from him. These changes in the behaviour of the courting ♂ are interpreted as defense against sexual interference.
• 3 Female smooth newts may be multiply inseminated as a consequence of sexual interference; this may result in sperm competition. However, ♀♀ seem to find competitive interactions between ♂ ♂ “aversive”.
• 4 Sexual interference by ♀-mimicry and associated defensive behaviour patterns are common in the urodele amphibians. Interference can be thought of as a “side-payment” conditional mating strategy.

     

Amphibian skin may select for rare environmental microbes

Host-microbe symbioses rely on the successful transmission or acquisition of symbionts in each new generation. Amphibians host a diverse cutaneous microbiota, and many of these symbionts appear to be mutualistic and may limit infection by the chytrid fungus, Batrachochytrium dendrobatidis, which has caused global amphibian population declines and extinctions in recent decades. Using bar-coded 454 pyrosequencing of the 16S rRNA gene, we addressed the question of symbiont transmission by examining variation in amphibian skin microbiota across species and sites and in direct relation to environmental microbes. Although acquisition of environmental microbes occurs in some host-symbiont systems, this has not been extensively examined in free-living vertebrate-microbe symbioses. Juvenile bullfrogs (Rana catesbeiana), adult red-spotted newts (Notophthalmus viridescens), pond water and pond substrate were sampled at a single pond to examine host-specificity and potential environmental transmission of microbiota. To assess population level variation in skin microbiota, adult newts from two additional sites were also sampled. Cohabiting bullfrogs and newts had distinct microbial communities, as did newts across the three sites. The microbial communities of amphibians and the environment were distinct; there was very little overlap in the amphibians'' core microbes and the most abundant environmental microbes, and the relative abundances of OTUs that were shared by amphibians and the environment were inversely related. These results suggest that, in a host species-specific manner, amphibian skin may select for microbes that are generally in low abundance in the environment.     

Morphological integration and ontogenetic niche shift: a study of crested newt limbs

This study deals with the ontogenetic and evolutionary aspects of integration patterns in the limbs of crested newt species, which, like most amphibians, have a biphasic life history with two morphologically distinct stages (larval vs. juvenile and adult) that occupy different environments (aquatic vs. terrestrial). We analyzed the structure and pattern of correlation between limb skeletal elements at three ontogenetic stages (larval, juvenile, and adult) of four closely related species that differ in their preferences of aquatic habitats (more terrestrial and more aquatic). We found dynamic changes in the pattern of morphological integration between successive ontogenetic stages, as well as changes over the course of crested newt phylogeny. Generally, equivalent ontogenetic stages of different species of crested newts show higher concordance in the correlation pattern than successive ontogenetic stages within species. Among species, two opposing correlation patterns were observed: in more terrestrial species, homologous limb elements are less correlated and within-limb elements are more correlated; in aquatic species, the reverse pattern occurs. These results indicate that the function seems to be the covariance-generating factor, which has shaped the patterns of morphological integration of crested newt limbs.     

The influence of temperature on diving behaviour in the alpine newt, Triturus alpestris

An aquatic lifestyle poses serious restriction to air-breathing animals in terms of time and energy spent during a dive cycle. The diving frequency increases with water temperature, therefore an ectotherm's time budget greatly depends on the thermal characteristics of the aquatic environment. Available data suggests that time costs caused by temperature-dependent dive frequency can be partially compensated for by adjusting the swimming speed and diving angle during dive cycle. We tested this prediction by examining the influence of temperature on the diving behaviour of the alpine newt, Triturus alpestris. The ascending speed and angle showed disparate patterns of temperature dependency, with a minor influence on travel duration. Surprisingly, at higher temperatures, the diving newts saved most of their time by restricting swimming activity in the water column during their return to the bottom and not by adjusting their ascending duration. Hence, aquatic newts have the capacity to reduce temperature-dependent time costs of aerial breathing primarily by behavioural modifications during the descending phase of the dive cycle.     

Aggressive behaviour and dominance relationships of the dark chub,Zacco temmincki with special reference to their individual recognition

Aggressive behaviour and dominance relationships ofZacco temmincki were observed by introducing fish into an enclosed pond. Chase (-flee), lateral display, parallel swim and butt were the principal behavioural patterns in aggressive encounters between fish, while chase, resulting in lateral display by the chased fish was the most common behavioural sequence. Initially, mutual behavioural patterns such as parallel swim and mutual lateral display were most evident among the total aggressive acts although chase became dominant three days after introduction into the pond. The dominance matrix constructed from chase-flee interactions during all observation periods contained many reverse attacks (336 out of 2,740 chases). These reverse attacks did not concentrate upon a specific period and were not site-dependent. Examination of chase-flee interactions and the subsequent behavioural pattern revealed that a chased fish reacted to the chaser either by attacking in turn, or performing lateral display etc. roughly in relation to the dominance rank of the chaser. This result implies that fish recognized each other to a great extent during aggressive encounters. It seems likely that such individual recognition was initiated during the early period when mutual behaviour was most frequent, and that some attacks against the dominance order were caused as a result of revolts rather than mistakes.     

Context-Dependent Plastic Response during Egg-Laying in a Widespread Newt Species

Previous research on predator-induced phenotypic plasticity mostly focused on responses in morphology, developmental time and/or behaviour during early life stages, but the potential significance of anticipatory parental responses has been investigated less often. In this study I examined behavioural and maternal responses of gravid female smooth newts, Lissotriton vulgaris, in the presence of chemical cues originating from invertebrate predators, Acilius sulcatus water beetles and Aeshna cyanea dragonfly larvae. More specifically, I tested the extent of oviposition preference, plasticity in egg-wrapping behaviour and plasticity in egg size when females had the possibility to lay eggs at oviposition sites with and without predator cues during overnight trials. I found that individuals did not avoid laying eggs in the environment with predator cues; however, individuals that deposited eggs into both environments adjusted the size of the laid eggs to the perceived environment. Females deposited larger eggs earlier in the season but egg size decreased with time in the absence of predator cues, whereas individuals laid eggs of average size throughout the investigated reproductive period when such cues were present. Also, egg size was found to be positively related to hatching success. Individuals did not adjust their wrapping behaviour to the presence of predator cues, but females differed in the extent of egg-wrapping between ponds. Females’ body mass and tail depth were also different between ponds, whereas their body size was positively associated with egg size. According to these results, female smooth newts have the potential to exhibit activational plasticity and invest differently into eggs depending on temporal and environmental factors. Such an anticipatory response may contribute to the success of this caudate species under a wide range of predator regimes at its natural breeding habitats.     

Etude de l'influence des facteurs visuels sur les comportements sexuels et agressifs de Mollienesia (Poecilia) velifera (Pisces,Poeciliidae)

One of the most striking features of cave fishes is their pronounced ocular regression. They are, however, perfectly adapted since they multiply and display the behaviour patterns which are biologically important in their surroundings. It is therefore of interest to study the relative role of visual factors in the corresponding behaviour patterns in related epigean species.Other authors have previously demonstrated the dominant role of chemical stimuli in the releasing of sexual behaviour patterns in M. sphenops, of which some forms are cavernicolous. In M. velifera and M. latipinna, on the contrary, visual factors seem more important. The releasers of the aggressive behaviour patterns of these three species seem to be predominantly visual. In the present study, the importance of visual factors has been verified experimentally in M. velifera by comparing the observed behavioural differences in experimentally blinded individuals and normal controls.The results of the pre-experimental phase show that there is no difference between these two groups before blinding, neither in the frequency of the patterns, nor in their numerical values.The results of the first experimental phase confirm the importance of visual releasers in the sexual behaviour patterns of M. velifera. Thus, sexual approaches, mouth—abdomen contacts and copulation attempts are totally absent in blinded pairs. Sexual motivation however is still present since the gonopodal flexions are equally frequent in both groups. On the other hand, it seems that aggressive behaviour patterns are maintained in blinded individuals but only when the partners are very close to each other or when an actual contact has taken place.The comparison of pairs in which only one of the partners is blinded (second experimental phase), as well as results of the first phase, suggest that experimental blinding does not cause hormonal changes liable to influence the observed patterns. In addition to this, the role of the ♀ in courtship has been specified. When a ♀ individual is intact and receptive, it will initiate courtship when it is placed in the company of an inactive blinded partner.     

Effect of salmonid introduction and other environmental characteristics on amphibian distribution and abundance in mountain lakes of northern Spain

Amphibians are currently experiencing a severe worldwide decline. Several factors, such as habitat alteration, climate change, emerging diseases or the introduction of exotic species, have been signalled as being responsible for the reduction of amphibian populations. Among these, the introduction of fish predators has been repeatedly indicated as a factor affecting the distribution of many species. The present study was developed to examine the effect of fish presence and other environmental factors on the distribution and abundance of amphibian species in mountain lakes of the Cantabrian Range in northern Spain. We found no effect of salmonid presence on the distribution and abundance of two widespread anuran species Bufo bufo and Alytes obstetricans , whereas Rana temporaria showed a non-significant tendency to be absent from salmonid-occupied lakes. However, the presence of introduced salmonids was the main negative factor explaining the distribution of the newt species Triturus helveticus , Triturus alpestris and Triturus marmoratus . The effect on these species is likely to be due to increased larval mortality, as adult and egg predation by fish, or oviposition avoidance by female newts has rarely been recorded. Fish removal and the creation of alternative breeding habitats for amphibians are proposed as conservation measures to recover amphibian populations in the vicinity of fish-stocked lakes.     

Size-dependent male mating behaviour and sexual harassment in a population of Atlantic mollies (Poecilia mexicana) from a sulphur creek

The Atlantic molly Poecilia mexicana inhabits a variety of habitats. In previous studies, small males from clear-water populations showed considerably more sexual behaviours than large males. Males from a sulphur creek, the El Azufre, or from a sulphur cave (cave molly) showed comparatively low sexual activity, and typical size-dependent mating behaviour was either absent or large males showed even more sexual behaviour than smaller ones. Sexually deprived cave molly males increased their sexual activity, but small males still did not show more sexual behaviour than large ones, suggesting that the genetic basis for typical size-dependent mating behaviour has been lost. Likely, the extreme abiotic conditions (hypoxia and toxic hydrogen sulphide) have selected against energetically costly behaviours. In this paper, we examined how El Azufre males would respond to sexual deprivation. We found these males to also increase their sexual activity after sexual deprivation but, unlike cave mollies, small males now showed more sexual behaviour than large ones, suggesting that the genetic basis for this behaviour is not lost in this population. Differences between populations may be due to the less harsh characteristics of El Azufre (e.g. less H₂S), resulting in weaker selection against energy-consuming behaviours. Furthermore, we tested for potential costs of male sexual harassment for females in terms of reduced feeding efficiency in the presence of a male, as was shown for P. mexicana from a clear-water population, but was not found in cave mollies or the El Azufre fish. Test females were either starved for 1 week to increase hunger levels or male sexual deprivation and female starvation were combined; however, we found no evidence for male sexual harassment even after these treatments. Our results parallel previous findings in the cave molly and suggest that El Azufre males have lost specific behavioural traits that cause sexual harassment.     

Functional equivalency of created and natural wetlands: diet composition of red-spotted newts (Notophthalmus viridescens viridescens)

Evaluating the adequacy of created wetlands to replace functions of lost natural wetlands is important because wetland mitigation is a major tool used to offset wetland losses. However, measurements such as vegetative cover and wildlife presence may not be evidence enough that created wetlands are functioning properly and thus, examining the ecology of wetland biota such as amphibians may be a more useful surrogate for function. Our objectives were to measure the diet composition of adult red-spotted newts (Notophthalmus viridescens viridescens) and compare the selection of prey by newts between created and natural wetlands. Newts were trapped during the spring and summer of 2009 and 2010, and the stomach contents of 149 newts were obtained with gastric lavage. Invertebrate prey availability was obtained within a 5 m radius of each captured newt. Selection of prey by newts was nonrandom, but was only minimally affected by wetland type. Both dietary breadth and prey selection were affected primarily by time of year, likely driven by temporal variation in invertebrate abundance. Our results suggest that the function of providing an adequate prey base for a generalist wetland predator such as the red-spotted newt is being fulfilled for the created wetlands that we examined.     

Expression of sexual ornaments in a polymorphic species: phenotypic variation in response to environmental risk

Secondary sexual traits may evolve under the antagonistic context of sexual and natural selection. In some polymorphic species, these traits are only expressed during the breeding period and are differently expressed in alternative phenotypes. However, it is unknown whether such phenotypes exhibit phenotypic plasticity of seasonal ornamentations in response to environmental pressures such as in the presence of fish (predation risk). This is an important question to understand the evolution of polyphenisms. We used facultative paedomorphosis in newts as a model system because it involves the coexistence of paedomorphs that retain gills in the adult stage with metamorphs that have undergone metamorphosis, but also because newts exhibit seasonal sexual traits. Our aim was therefore to determine the influence of fish on the development of seasonal ornamentation in the two phenotypes of the palmate newt (Lissotriton helveticus). During the entire newt breeding period, we assessed the importance of phenotype and fish presence with an information‐theoretic approach. Our results showed that paedomorphs presented much less developed ornamentation than metamorphs and those ornamentations varied over time. Fish inhibited the development of sexual traits but differently between phenotypes: in contrast to metamorphs, paedomorphs lack the phenotypic plasticity of sexual traits to environmental risk. This study points out that internal and external parameters act in complex ways in the expression of seasonal sexual ornamentations and that similar environmental pressure can induce a contrasted evolution in alternative phenotypes.     

There is no place like home: Larval habitat type and size affect risk-taking behaviour in fire salamander larvae (Salamandra salamandra)

Individual life histories are strongly influenced by early environmental conditions and experiences. They shape morphology as well as behaviour and can promote adaptive divergence and phenotypic plasticity with regard to different habitat types. The fire salamander (Salamandra salamandra) in the Kottenforst forest in Bonn, Germany, exhibits two genetically distinct ecotypes occurring in two larval habitats, either ponds or streams. In this study, we investigated whether both ecotypes differ in risk-taking behaviour, measured as the behavioural response during a shelter-emergence test and a shelter-seeking test, and whether larval habitat type and size impact these behaviours. Our results revealed an influence of size as well as habitat type. Larger larvae of both habitats appear to be more risk-prone, as they spent more time outside the starting shelter in the shelter-emergence test. Irrespective of size, pond larvae sought shelter more often in the shelter-seeking test and are thus considered to be less risk-prone. These results indicate that larvae conform to a given niche by adjusting their behaviour. Future studies are needed to disentangle the role of genetic adaptation or phenotypic plasticity and to investigate long-term consequences of the larval habitat for the adult phenotype. Thereby, efforts should be made to create a concise set of multiple tests assessing behavioural patterns.     

Postprandial thermophily in the Danube crested newt, Triturus dobrogicus

(1) Preferred temperatures were compared between fed and fasted newts with respect to their locomotor activity (LA) in an aquatic thermal gradient (5–32.5°C). (2) Locations and LA of 17 newts in postabsorptive phase were recorded over 24 h. (3) Nine randomly chosen newts were fed (10% of their body mass) and behaviour of all newts was recorded over the next 24 h. (4) Fasted newts preferred similar water temperatures during periods of both LA and inactivity. (5) Newts preferred 2–3°C higher water temperatures after feeding irrespective of the behavioural state.