Fire Salamander Larvae Research Articles

Effects of diet quality on morphology and intraspecific competition ability during development: the case of fire salamander larvae

The environmental conditions of the habitats in which organisms live may induce a variety of plastic adaptive responses for numerous developmental, behavioural and morphological traits. One of the most relevant environmental features is the amount of available food occurring in a certain habitat. In this study, we wanted to assess whether, during development of vertebrates, diet quality may induce plastic responses at both behavioural and morphological levels. We tested whether diet may affect the rate of aggressive interactions between fire salamander larvae (Salamandra salamandra) and changes of head morphology during development. We collected 15 newborn larvae from five different localities, and we randomly assigned them to three diets (small nourishing prey, big scant prey, mixed prey). For each larva we recorded the number of snap attempts to a target larva 4 days after salamander collection, and after the 50 days of feeding treatment. We recorded and analysed head shape development using a geometric morphometrics approach. Analyses showed a significant relationship between diet and aggressiveness: larvae fed with small nourishing prey were significantly more aggressive. Diet had a significant effect in determining the quantity of head morphology changes during larval development, but did not affect the characteristics of the morphology; this means that all the larvae showed a similar shape modification, but those treated with the more nourishing prey showed a more pronounced change. These results indicate that diet features may induce both behavioural and morphological plastic responses. High-quality diets may be linked to competition for trophic resources, increasing development rates and determining higher competitive ability.

Long-term consequences of early nutritional conditions on the behaviour and growth of fire salamanders

Early developmental conditions can have a strong influence on the life history. Fire salamanders represent an interesting system due to their biphasic life cycle consisting of an aquatic larval stage and a subsequent terrestrial stage. The environment experienced as larvae affects growth, age at metamorphosis and behaviour. In particular, diet restrictions can cause developmental stress. However, the impact of such developmental stress on the growth and behaviour in a long-lived amphibian are not yet well studied. We manipulated the early diet of sibling pairs of fire salamander larvae. One sibling was raised under food-restriction and the other was raised under conditions of abundant food. We report long-term effects on growth and exploratory behaviour; exploratory behaviour was tested in two sessions, first as young juveniles and later as sub-adults. We found that food-restricted conditions during early development affected exploratory behaviour. Early deficits in body mass and body size were compensated later in life, by approximately 18 months of age. When morphological differences were compensated, the initial differences in exploratory behaviour also disappeared. Thus, compensation not only led to an alignment of body parameters but was also accompanied by an adjustment in exploratory behaviour. No cost of compensation was detected, but future research will need to verify whether the potential costs of compensation are negligible in slow-growing salamanders or whether they are shifted to later life stages. Our study provides novel insights into the life history of fire salamanders and reveals that early larval conditions have effects on individuals long after metamorphosis.

Ecological transcriptomics – a non‐lethal sampling approach for endangered fire salamanders

Summary The analysis of transcriptomes is well‐established and increasingly affordable in studies at the interface of ecology and evolution. Expression analysis of thousands of genes in parallel reveals functions and pathways involved in relevant phenotypic differentiation. The application of such methods typically involves the sacrifice of the analysed organisms, which is potentially subject to ethical and legal constraints. As an alternative to lethal sampling, transcriptome analyses can be performed using small biopsies of dispensable tissues. It has to be verified, however, to what extent such results are representative of the whole organism. Here, we use a custom microarray to compare transcriptomes of tail‐clip samples with those of the remaining whole body of fire salamander larvae (Salamandra salamandra). The microarray was calibrated using target RNA to validate the performance of each probe. We varied water temperature to test whether the thermal response in gene expression can be characterized in both types of sample. A large fraction (51%) of the differentially expressed genes showed parallel changes for both tail clips and whole bodies in response to temperature. While sets of differentially expressed were not identical, they largely belonged to the same functional categories. The gene functions thus revealed a common thermal response of larvae irrespective of the sampled tissue. This included an overexpression of mitochondrial transcripts, an expected thermal acclimatization response of ectotherms. Hence, ecological transcriptomics based on small biopsies represent an alternative to the analysis of lethally sampled tissues in situations where the sacrifice of individuals is not an option.

Intercohort size structure dynamics of fire salamander larvae in ephemeral habitats: a mesocosm experiment.

The size structure of a larval population facilitates interaction asymmetries that, in turn, influence the dynamics of size-structure. In species that exhibit conspicuous aggressive interactions, the competitive effects of the smaller individuals may be overlooked. We manipulated initial size differences between two larval cohorts and young-cohort density of Salamandra infraimmaculata in mesocosms to determine: (1) whether young individuals function primarily as prey or as competitors of older and larger individuals; (2) the resulting dynamics of size variation; and (3) recruitment to the postmetamorph population. Intercohort size differences generally remained constant over time at low young-cohort densities, but reduced over time at high densities due to retardation of the old-cohort growth rate. This suggests a competitive advantage to the young cohort that outweighs the interference advantage of older cohorts previously documented in this species. The increase in mortality from desiccation due to high young-cohort density was an order of magnitude greater in the old cohort than in the young-cohort, further indicating size-dependent vulnerability to competition. However, the conditions least favorable to most of the old-cohort larvae (large size difference and high young-cohort density) promoted cannibalism. Among cannibals, mortality and time to metamorphosis decreased and sizes at metamorphosis increased substantially. Thus, a balance between the competitive advantage to young cohorts, and the interference and cannibalism advantage to old cohorts shapes larval size-structure dynamics. Larval densities and individual expression of cannibalism can shift this balance in opposite directions and alter relative recruitment rates from different cohorts.

The effects of top-down and bottom-up controls on macroinvertebrate assemblages in headwater streams

Headwater stream macroinvertebrates play an important role in processing allochthonous leaf litter, which suggests that bottom-up forces control macroinvertebrates. However, because larvae of stream-breeding salamanders are predators of macroinvertebrates and are abundant consumers in these ecosystems, macroinvertebrates in fishless headwater streams might also be controlled by top-down forces through predation by salamander larvae. The aim of this study was to test if and to what degree taxa richness, abundance, and biomass of macroinvertebrates are affected by bottom-up and top-down forces. We selected headwater streams with high abundances of fire salamander larvae (1.2–2.6 individuals per 1 m of shore length) and manipulated bottom-up and top-down forces on macroinvertebrates by leaf litter addition and by the exclusion of salamander larvae. The amphipod Gammarus fossarum Koch, 1836 was the dominant taxon and responded positively to litter addition. Linear models showed that neither predator exclusion nor leaf litter addition affected richness. However, variation in biomass and density were both explained by the individual and joint effects of bottom-up and top-down forces. These findings suggest that macroinvertebrates in these streams are strongly dependent on the organic matter input and salamander larvae, and headwater streams interact strongly with their adjacent terrestrial areas.

Thermoregulatory strategies in an aquatic ectotherm from thermally-constrained habitats: An evaluation of current approaches

Many ectotherms employ diverse behavioral adjustments to effectively buffer the spatio-temporal variation in environmental temperatures, whereas others remain passive to thermal heterogeneity. Thermoregulatory studies are frequently performed on species living in thermally benign habitats, which complicate understanding of the thermoregulation–thermoconformity continuum. The need for new empirical data from ectotherms exposed to thermally challenging conditions requires the evaluation of available methods for quantifying thermoregulatory strategies. We evaluated the applicability of various thermoregulatory indices using fire salamander larvae, Salamandra salamandra, in two aquatic habitats, a forest pool and well, as examples of disparate thermally-constrained environments. Water temperatures in the well were lower and less variable than in the pool. Thermal conditions prevented larvae from reaching their preferred body temperature range in both water bodies. In contrast to their thermoregulatory abilities examined in a laboratory thermal gradient, field body temperatures only matched the mean and range of operative temperatures, showing thermal passivity of larvae in both habitats. Despite apparent thermoconformity, thermoregulatory indices indicated various strategies from active thermoregulation, to thermoconformity, and even thermal evasion, which revealed their limited applicability under thermally-constrained conditions. Salamander larvae abandoned behavioral thermoregulation despite varying opportunities to increase their body temperature above average water temperatures. Thermoconformity represents a favored strategy in these ectotherms living in more thermally-constrained environments than those examined in previous thermoregulatory studies. To understand thermal ecology and its impact on population dynamics, the quantification of thermoregulatory strategies of ectotherms in thermally-constrained habitats requires the careful choice of an appropriate method to avoid misleading results.

Effects of Tail Clipping on Larval Performance and Tail Regeneration Rates in the Near Eastern Fire Salamander, Salamandra infraimmaculata.

Tail-tip clipping is a common technique for collecting tissue samples from amphibian larvae and adults. Surprisingly, studies of this invasive sampling procedure or of natural tail clipping – i.e., bites inflicted by predators including conspecifics - on the performance and fitness of aquatic larval stages of urodeles are scarce. We conducted two studies in which we assessed the effects of posterior tail clipping (~30 percent of tail) on Near Eastern fire salamander (Salamandra infraimmaculata) larvae. In a laboratory study, we checked regeneration rates of posterior tail-tip clipping at different ages. Regeneration rates were hump-shaped, peaking at the age of ~30 days and then decreasing. This variation in tail regeneration rates suggests tradeoffs in resource allocation between regeneration and somatic growth during early and advanced development. In an outdoor artificial pond experiment, under constant larval densities, we assessed how tail clipping of newborn larvae affects survival to, time to, and size at metamorphosis. Repeated measures ANOVA on mean larval survival per pond revealed no effect of tail clipping. Tail clipping had correspondingly no effect on larval growth and development expressed in size (mass and snout-vent length) at, and time to, metamorphosis. We conclude that despite the given variation in tail regeneration rates throughout larval ontogeny, clipping of 30% percent of the posterior tail area seems to have no adverse effects on larval fitness and survival. We suggest that future use of this imperative tool for the study of amphibian should take into account larval developmental stage during the time of application and not just the relative size of the clipped tail sample.

Environmental factors determining growth of salamander larvae: A field study

Abstract Larval growth and survival of organisms are strongly influenced by abiotic and biotic factors, as demonstrated by experimental studies performed under controlled laboratory or semi-natural conditions. Even if they have many advantages, experiments cannot cover the full complexity of natural conditions and field studies are needed for a better understanding of how environmental variation determines growth and development rate. Fire salamander Salamandra salamandra females give birth to larvae in a variety of habitats, both epigean and subterranean. In caves, salamander larvae successfully grow and metamorphose, but their growth is more than three times longer than in epigean streams and factors determining these differences require investigation. We performed a field study to understand the factors related to the growth of fire salamander larvae in different environmental conditions, evaluating the relationship between environmental features and larval growth and differences between caves and epigean spring habitats. Both caves and epigean larvae successfully grew. Capture-mark-recapture allowed to individually track individuals along their whole development, and measure their performance. Growth rate was significantly affected by environmental variables: larvae grew faster in environments with abundant invertebrates and few conspecifics. Taking into account the effect of environmental variables, larval growth was significantly lower in caves. Food availability plays a different effect in the two environments. Larval growth was positively related to the availability of invertebrates in epigean sites only. The development rate of hypogeous populations of salamanders is slower because of multiple parameters, but biotic factors play a much stronger role than the abiotic ones.

Influence of water velocity and predation risk on fire salamander (Salamandra infraimmaculata) larval drift among temporary pools in ephemeral streams

In ephemeral streams, floods can temporarily connect isolated pools and provide otherwise spatially restricted organisms with the option to stay in or leave a pool. A field survey of the middle-eastern fire salamander (Salamandra infraimmaculata) larvae demonstrated that 18% disappeared from pools during high-discharge events, and ∼2% were found subsequently in downstream pools. We conducted indoor experiments to test whether larvae alter drift rate in response to different velocities and perceived risk of predation. We manipulated flow velocities within the range of natural ephemeral streams during floods. Anesthetized larvae (passive drifters) drifted out of a central pool faster than conscious larvae at low velocities but not at high velocities, suggesting that conscious larvae actively resisted hydraulic pressures. Drift of small larvae out of a pool in the presence of a caged, larger cannibalistic conspecific was faster than in the absence of a predator, indicating that the larvae perceived and attempted to avoid the predator. Our findings confirm that larval drift that occurs from normally isolated temporary pools in ephemeral streams, is in part behaviorally controlled, and can be mediated by predation risk. We suggest that larval drift can serve as a dispersal pathway for amphibians and may be of particular importance at local spatial scales when the terrestrial habitat surrounding breeding sites is fragmented and movement of terrestrial stages is restricted.

Fire salamander (Salamandra salamandra) in Larzac plateau: low occurrence, pond-breeding and cohabitation of larvae with paedomorphic palmate newts (Lissotriton helveticus)

th November; revised on 2014, 18 th January; accepted on 2014, 31 st January Abstract. Alternative reproductive strategies are widespread in caudate amphibians. Among them, fire salamanders (Salamandra salamandra) usually rely on streams to give birth to aquatic larvae but also use ponds, whereas palmate newt larvae (Lissotriton helveticus ) typically metamorphose into terrestrial juveniles, but can also reproduce in retain- ing their gills, a process known as paedomorphosis. Here we report repeated observations of an unusual case of coex- istence of these two alternative traits in the same pond (Larzac, France). The prevalence of fire salamanders in South- ern Larzac was very low (pond occupancy: 0.36%). The observed abundance of fire salamander larvae and paedo- morphic newts was also low in the studied pond. On one hand, the rarity of this coexistence pattern may suggest that habitat characteristics may not be optimal or that competition or predation processes might be operating. However, these hypotheses remain to be tested. On the other hand, as this is the only known case of breeding in Southern Lar - zac, it could be considered to be at a high risk of extirpation.

Influence of fire salamander larvae on among-pool distribution of mosquito egg rafts: oviposition habitat selection or egg raft predation?

Many amphibian populations are in decline worldwide. Surprisingly, few studies have examined how such declines may benefit mosquitoes. Amphibian larvae may compete with and prey upon mosquito larvae, and may alter oviposition habitat selection (OHS) of mosquito adults. However, often overlooked, observed among-pool egg distributions attributed to OHS may additionally or alternatively be explained by egg predation. Temporary pools of mountainous areas of the Mediterranean serve as larval habitat for both the mosquito, Culiseta longiareolata, and the salamander, Salamandra infraimmaculata. We found Culiseta larvae and egg rafts to be highly vulnerable to predation by pre-metamorphosing Salamandra larvae, but not to metamorphosing ones. In outdoor mesocosm experiments, oviposition avoidance by Culiseta females in response to caged Salamandra was not demonstrated regardless of salamander developmental stage. Egg raft abundance was significantly reduced in free-roaming, pre-metamorphosing Salamandra but not by metamorphosing ones. Thus, Salamandra larvae may have little deterrence on Culiseta oviposition. Instead, fewer egg rafts are attributed largely to egg predation. This study highlights the importance of egg raft predation in addition to OHS when interpreting the influence of predators on prey egg distributions. It also highlights that a cost of declining amphibian populations is their reduced impacts on mosquito populations.

Skin swabbing of amphibian larvae yields sufficient DNA for efficient sequencing and reliable microsatellite genotyping

Skin swabbing, a minimally invasive DNA sampling method recently developed on adult amphibians, was tested on larvae of fire salamanders (Salamandra salamandra). The quality and quantity of the sampled DNA was evaluated by (i) measuring DNA concentration in DNA extracts, (ii) sequencing part of the mtDNA cytochrome b gene (692 bp) and (iii) genotyping eight polymorphic nuclear microsatellite loci. The multiple-tubes approach was used for calculating allelic dropout (ADO) and false allele (FA) rates to evaluate the reliability of the genotypes. DNA extracts from tissue samples of road-killed individuals were included in the study as positive controls. Our results showed that skin swabs of fire salamander larvae can provide DNA in sufficient quantity and quality, as sequencing was successful and no allelic dropouts or false alleles were detected. This method, tested for the first time on amphibian larvae, has proven to be an efficient and reliable alternative to the controversial tail fin clipping procedure.

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.

Larval salamanders and diel drift patterns of aquatic invertebrates in an Austrian stream

Summary 1. Aquatic predators may influence drift periodicity either directly or indirectly (by non-consumptive effects involving chemical cues). We took drift samples (eight successive 3-h sampling intervals over a 24-h period) on five dates (September 2007, March, April, June and August 2008). Samples were taken at three sites (one site with trout throughout the year, two sites without trout but with fire salamander larvae as top predators from April to August, but without vertebrate predators during the rest of the year) in a stream near Vienna, Austria, to examine the effects of predators on drift periodicity. 2. Of 45 331 specimens caught, the most abundant taxa were Ephemeroptera (32.3%; mainly Baetidae), Diptera (21.5%; mainly Chironomidae), Amphipoda (17.4%; all Gammarus fossarum), Plecoptera (5.4%), Coleoptera (3.5%) and Trichoptera (1.2%). For more detailed analyses, we chose Ephemeroptera (Baetidae; n = 13 457) and Amphipoda (G. fossarum; n = 7888), which were numerous on all sampling dates. 3. The number of drifting baetids and amphipods, as well as total drift density, was generally higher at night than by day, although without predators these differences were significant for Gammaridae but not for Baetidae. 4. When broken down to size classes, night–day drift ratios generally were not significantly different from equality in all size classes of baetids when larval fire salamanders and trout were absent. When predators were present, however, baetid drift density was usually higher at night, except in the smallest and largest size classes. In all size classes of G. fossarum, drift density was usually higher at night, whether with or without the top predators. 5. Although we could study predator effects on drift periodicity at three sites on only a single stream, it seems that non-consumptive effects may affect Baetidae. Salamander larvae, most probably via kairomones, induced a shift towards mainly nocturnal drift, which could be interpreted as predator avoidance.

Compensatory Development and Costs of Plasticity: Larval Responses to Desiccated Conspecifics

Understanding constraints on phenotypic plasticity is central to explaining its evolution and the evolution of phenotypes in general, yet there is an ongoing debate on the classification and relationships among types of constraints. Since plasticity is often a developmental process, studies that consider the ontogeny of traits and their developmental mechanisms are beneficial. We manipulated the timing and reliability of cues perceived by fire salamander larvae for the future desiccation of their ephemeral pools to determine whether flexibility in developmental rates is constrained to early ontogeny. We hypothesized that higher rates of development, and particularly compensation for contradictory cues, would incur greater endogenous costs. We found that larvae respond early in ontogeny to dried conspecifics as a cue for future desiccation, but can fully compensate for this response in case more reliable but contradictory cues are later perceived. Patterns of mortality suggested that endogenous costs may depend on instantaneous rates of development, and revealed asymmetrical costs of compensatory development between false positive and false negative early information. Based on the results, we suggest a simple model of costs of development that implies a tradeoff between production costs of plasticity and phenotype-environment mismatch costs, which may potentially underlie the phenomenon of ontogenetic windows constraining plasticity.

Effects of Background Color and Predation Risk on Color Change in Fire Salamander Larvae

The threat-sensitivity hypothesis assumes individuals should demonstrate flexibility in response to perceived predation risk and vary the intensity of anti-predator responses in concert with perceived risk of predation. Substrate color matching is adaptive as it enables organisms to become less conspicuous to both their prey and predators. I hypothesized that newborn fire salamander (Salamandra infraimmaculata) larvae will respond fast through physiological color change to contrasting backgrounds, becoming lighter against a white background and darker against a black background. Additionally, in accordance with the threat-sensitivity hypothesis, I expected a background color x predator interaction—i.e., that predator presence will further enhance the focal larvae color-matching response.To explicitly test these hypotheses I conducted a replicated outdoor mesocosm experiment. I used a two-by-two factorial design: pools of black or white background color crossed with the presence or absence of a larger cannibalistic conspecific. Digital photos of the focal larvae's dorsal view revealed that larval brightness and chroma changed accordingly against the contrasting black and white backgrounds to increase background matching. Although not statistically significant, larvae tended to show a stronger color-change response towards enhanced background matching in the presence of the free predator. Larval survival was strongly reduced in the presence of the larger conspecific, with no apparent effect of background color. This study demonstrates thatSalamandralarvae are capable of environmentally induced physiological color change and highlights the need for further investigation into the interplay between threat intensity, mechanisms of risk assessment, and physiological antipredator responses.

Differential aggressiveness between fire salamander (Salamandra infraimmaculata) larvae covaries with their genetic similarity

Responding differentially to kin and non-kin is known to be adaptive in many species. One example is the inclusive fitness benefits of reducing aggression toward closer relatives. Little is known, however, about the ability of animals to assess differential degrees of genetic relatedness and to respond accordingly with differential levels of aggression. In the present study, we tested whether aggressiveness between body mass-matched pairs of fire salamander (Salamandra infraimmaculata) larvae covaried with the genetic similarity between them. We quantified aggressiveness at three levels of genetic similarity by selecting pairs within and across pools from recently genotyped populations. We also assessed aggression between pairs of siblings. Aggression and associated injuries decreased as genetic similarity increased across the groups. These findings suggest that cannibalistic salamanders can assess their degree of genetic relatedness to conspecifics and vary their behavioral responses depending on the degree of similarity between them along a genetic relatedness continuum.

Case selection by a limnephilid caddisfly [Potamophylax latipennis (Curtis)] in response to different predators

Some organisms use morphological structures obtained by behavioural processes to lower mortality by predation. We test whether larvae of the limnephilid caddisfly Potamophylax latipennis (Curtis) vary their responses to the presence of different predators (dragonfly naiads, fire salamander larvae or brown trout) by choosing organic or mineral cases. We offered both case types to larvae, and simulated differences in predation risk using water conditioned with chemicals from the different predators. Our results show that Potamophylax larvae detect and discriminate predators using water-borne chemical cues and alter their choice of case type according to the perceived predation risk. Moreover, the distribution of larvae bearing cases of different anti-predator value matches the spatial variation in predation risk in the field.

No Behavioral Control over Mating Frequency in Queen Honey Bees (Apis melliferaL.): Implications for the Evolution of Extreme Polyandry

Ever since the seminal papers of Hamilton (1964), a common focus of sociobiology has been the genetic relationships among individuals of insect societies. At issue are agents that reduce the average relatedness among colony members since they are difficult to interpret in light of the evolution of sociality by kin selection. One such factor is polyandry or female multiple mating. Low levels of polyandry are common among the social Hymenoptera, occurring across a broad range of taxa and social systems (Page and Metcalf 1982; Page 1986; Crozier and Pamilo 1996). In spite of that, high mating frequencies (‚2 mates/ female) are relatively rare among the highly eusocial Hymenoptera, limited to only one or a few genera in each of the ants, bees, and wasps (Boomsma and Ratnieks 1996). These extraordinary levels of polyandry have been of particular interest among students of social insect research since their adaptive significance is still in question and highly debated (Kraus and Page 1998; Sherman et al. 1998). The genus Apis has been studied in depth for both queen reproductive behavior and mating frequency, facts that allow insight into the evolution of extreme polyandry in these species. The reproductive behavior of honey bee queens (Apis mellifera) occurs early in their lifetimes. Virgin queens initiate mating behavior when they are about 1 wk old by briefly exiting the colony and orienting to local landmarks (Ruttner 1956). After such orientation * To whom correspondence should be addressed; e-mail: drtarpy@

Non-consumptive effects of larval Salamandra on crustacean prey: can eggs detect predators?

Predators affect prey populations not only by prey consumption but also in nonconsumptive ways including modifying prey behavior. I tested the effects of fire salamander larvae (Salamandra infraimmaculata) on populations of co-occurring crustacean species in artificial outdoor pools. I also tested whether these effects were due entirely to prey consumption by Salamandra larvae or alternatively to some nonconsumptive effect. The soil (containing crustacean eggs) added to the artificial pools was collected from a dried-out temporary pool that is inhabited by Salamandra during the early part of the hydroperiod. I randomly assigned the pools to one of three treatments: control, free Salamandra, or caged Salamandra. Free salamander larvae could roam the entire pool and prey upon crustaceans. Caged salamander larvae were placed within a cage with having 250-μm mesh windows. They could not prey upon the crustaceans but could, for example, influence them by chemical cues. Densities of the three dominant crustacean species (Arctodiaptomus similis, Ceriodaphnia quadrangula and Cyzicus sp.) were drastically reduced in both salamander treatments compared to the control. Crustacean densities, however, were not significantly different between the two salamander treatments. One plausible explanation is that crustacean eggs can detect the presence of this predator via chemical cues and delay hatching.