Chaoborus Kairomone Research Articles

Evaluation of alternative hypotheses to explain temperature-induced life history shifts in Daphnia

Negative correlations between environmental temperature and body size are widespread in planktonic organisms, and ectotherms generally, but remain poorly understood. Here we evaluate experimentally two alternative hypotheses suggested to explain life history shifts induced by raised temperature using parthenogenetic clones from two Daphnia species. Explanation 1 proposes that the life history shifts could be adaptive if increased temperature is used as an indirect cue to indicate increased risk from size-selective predators. Explanation 2 proposes that at larger body size energy becomes more limiting as temperature increases because of a less favourable assimilation: metabolism balance. In a factorial laboratory experiment we examine the effects of three rearing temperatures on the growth and reproductive traits of Daphnia raised in water with fish kairomone, Chaoborus kairomone, or in uncontaminated water. None of the three predictions of explanation 1 were met by the data. In both D. pulex and D. curvirostris, and some other published studies, data suggested that at larger body sizes the sum of growth and reproduction was lower at high temperature, supporting our prediction from explanation 2. However, we propose a novel third explanation based on new evidence of temperature-dependence in both reproductive effort and cost in D. pulex.

Predator‐induced phenotypic plasticity in the exotic cladoceran Daphnia lumholtzi

Summary1. The exotic cladoceran Daphnia lumholtzi has recently invaded freshwater systems throughout the United States. Daphnia lumholtzi possesses extravagant head spines that are longer than those found on any other North American Daphnia. These spines are effective at reducing predation from many of the predators that are native to newly invaded habitats; however, they are plastic both in nature and in laboratory cultures. The purpose of this experiment was to better understand what environmental cues induce and maintain these effective predator‐deterrent spines. We conducted life‐table experiments on individual D. lumholtzi grown in water conditioned with an invertebrate insect predator, Chaoborus punctipennis, and water conditioned with a vertebrate fish predator, Lepomis macrochirus.2. Daphnia lumholtzi exhibited morphological plasticity in response to kairomones released by both predators. However, direct exposure to predator kairomones during postembryonic development did not induce long spines in D. lumholtzi. In contrast, neonates produced from individuals exposed to Lepomis kairomones had significantly longer head and tail spines than neonates produced from control and Chaoborus individuals. These results suggest that there may be a maternal, or pre‐embryonic, effect of kairomone exposure on spine development in D. lumholtzi.3. Independent of these morphological shifts, D. lumholtzi also exhibited plasticity in life history characteristics in response to predator kairomones. For example, D. lumholtzi exhibited delayed reproduction in response to Chaoborus kairomones, and significantly more individuals produced resting eggs, or ephippia, in the presence of Lepomis kairomones.

The supposed lack of trade-off among Daphnia galeata life history traits is explained by increased adult mortality in Chaoborus conditioned treatments

In recent years, some studies addressing the modification of phenotypically plastic traits of Daphnia in the presence of chemical cues (kairomones) from invertebrate predators have reported a lack of trade-off among resource allocation of traditional life history traits (growth and reproduction) (Spitze, 1991; Black, 1993; Weber & Declerck, 1997). In this study, we term this finding the `Chaoborus paradox'. The Chaoborus paradox contrasts with the generally accepted theory that facultative changes in life history traits are associated with costs or a modification in resource allocation. In order to unravel the Chaoborus paradox, we have tested four groups of traits that may explain resource allocation. These were (1) the trade-off between present and future reproduction, (2) reduced growth of morphological features (body length, helmet length, spine length, carapace width) prior to maturity (pre-maturity) or (3) during the first adult instar (at maturity), and (4) an increase in feeding and assimilation rates to fuel the amount of resources available to the organism. As experimental animal we used Daphnia galeata (Cladocera) and to simulate invertebrate predation we used the Chaoborus (phantom midge larvae) kairomone. A clear trade-off existed between present and future reproduction. Survival was less in the presence of Chaoborus kairomone and therefore more resources could be channelled into growth and reproduction early in life at the cost of dying younger when compared to control animals. The other groups of traits (reduced growth of morphological features and an increase the amount of resources) offer partial solutions to the Chaoborus paradox for single clones only and not for the whole population.

Genetic differentiation in life history between Daphnia galeata populations: an adaptation to local predation regimes?

Species of the water flea Daphnia exhibit constitutive as well as phenotypically inducible anti-predator defence strategies, involving life history, morphological and behavioural traits. We explored the hypothesis of genetic differentiation in anti-predator defence strategies using Daphnia clones originating from two different water bodies: Tjeukemeer (the Netherlands) and Fish Pond (Belgium). Both water bodies are inhabited by zooplanktivorous fish. In contrast to Tjeukemeer, Fish Pond is also inhabited by larvae of the phantom midge Chaoborus. The life history responses of the two sets of clones to kairomones from fish (Perca), to kairomones from Chaoborus, and to a mixture of both were compared. Clones from Tjeukemeer and Fish Pond showed strong responses to the presence of fish kairomone, with reductions in adult and neonate body length, in age at first reproduction and in the total number of neonates produced during the first three adult instars. Responses to Chaoborus kairomone were much less pronounced, although there was a tendency towards an increase in the number of neonates in the first brood. Significant inter-population genetic differences were found for all the investigated traits. However, there was no indication for genetic adaptation of the Fish Pond clones to negative size-selective predation by Chaoborus. Compared to Tjeukemeer clones, Fish Pond clones had a lower size at first reproduction, produced smaller neonates and produced a higher number of neonates in their first brood. This suggests adaptation to positive rather than to negative size selective predation. Genetic differences between populations were observed mainly for constitutive life history traits, rather than for phenotypic shifts in response to the presence of predator kairomones.

THE ROLE OF YOLK PROTEIN DYNAMICS AND PREDATOR KAIROMONES FOR THE LIFE HISTORY OFDAPHNIA MAGNA

Resource allocation for reproduction of daphniids is strongly determined by the production of yolk protein. It is the main process channeling material into the reproductive pool of the animals. My investigations of yolk protein dynamics provided evidence that Daphnia are able to exhibit flexible brood reduction behavior and that individuals do not use all of the produced yolk protein for reproduction. The animals show parental optimism, meaning that they start to produce more material for offspring than they actually release. Yolk protein dynamics were influenced by predator-released kairomones. Fish kairomones influenced the beginning of yolk production resulting in a shorter time until first reproduction. In addition, daphniids exposed to fish kairomones used more of the produced yolk protein for reproduction than did control animals. The fish kairomone did not influence the rate of yolk production. In contrast, Chaoborus kairomones influenced the rate of yolk production, but did not change either the beginning of yolk production or the proportion of yolk that was used for egg production. The yolk protein dynamics of daphniids and their ability to exhibit flexible brood reduction behavior can help to explain kairomone-induced life history modifications of daphniids in numerous life history experiments.

Interactions Between Predator Kairomone and Food Level Complicate the Ecological Interpretation of Daphnia Laboratory Results

The effect of food concentration on the phenotypic response of life history traits to two predator kairomones was investigated in Daphnia. For the experiment, one clone of Daphnia galeata was used as the prey organism and solutions containing infochemicals (kairomones) of Chaoborus (phantommidge) and Perca (perch) simulated the presence of potential predators. The combined effect of food level and predator kairomone on phenotypic plasticity of Daphnia life history is complex. At low food levels, the responses in life history traits to kairomones are enhanced. For example, in the Perca treatment, this leads to a younger age at first reproduction. The presence of Chaoborus kairomone decreases survival so that death often occurs before reproduction is reached. This results in a strong decrease in the intrinsic rate of population increase and might contribut to the pronounced summer decline of some Daphnia populations during periods of food shortage.

Predator-induced life history shifts in Daphnia: a synthesis of studies using meta-analysis

"Predator-induced life history shifts in Daphnia: a synthesis of studies using meta-analysis." Internationale Vereinigung für theoretische und angewandte Limnologie: Verhandlungen, 27(5), p. 3233

Morphological defenses induced in situ by the invertebrate predator Chaoborus: comparison of responses between Daphnia pulex and D. rosea.

The presence of plankton predators may induce altered morphology in their potential prey. To date, the mechanism of induction and adaptive value of such defensive responses have been examined in the laboratory. This study investigated the morphological defense structures induced by the invertebrate predator Chaoborus in two coexisting Daphnia species, D. pulex and D. rosea, in the field. In Piscivore Lake (Gräfenhain, Germany), continuous and intense biomanipulation had led to near elimination of planktivorous fish and greatly increased abundances of Chaoborus (up to >10 larvae l-1). Here, the density of Chaoborus was manipulated within the lake by an enclosure/exclosure setup and resulting morphological responses of Daphnia spp. were investigated in situ. Three replicate enclosures (4.6 m3) contained no Chaoborus (predator exclusion bags), whereas Chaoborus entered three others at ambient densities (predator enclosures). In both species of Daphnia, formation of neckteeth and elongation of the tail spine were recorded in the predator enclosures, but not in the predator exclusion treatments. Additionally, D. rosea responded to predator inclusion with an increase of the size at first reproduction. Despite the induced defense structures, the presence of Chaoborus caused increased mortality of both Daphnia species. In addition, Chaoborus affected the coexistence of the two populations of Daphnia by causing higher relative mortality in D. rosea. Neckteeth formation was always more pronounced in D. pulex than in D. rosea of the same size. Neckteeth were induced specifically in vulnerably sized juvenile instars of D. pulex, but were not found in all vulnerable instars of D. rosea. In D. rosea, neckteeth were few or absent in the ephippial hatchlings, and neckteeth formation ceased before juveniles reached a body size outside the range that larger larval stages of Chaoborus could ingest. This study provides the first experimental demonstration in the field of the inducibility of morphological defense structures in Daphnia at ambient densities of Chaoborus larvae, and quantifies these in situ responses. This expands on earlier observations of a correlation between predator density in the field and the expression of neckteeth in Daphnia. The term "maximum size for neckteeth formation" (MSNF) is defined as the limit in body size above which no production of neckteeth was evident. This limit was used to distinguish the size classes of Daphnia that show a sensitive response to Chaoborus kairomone. This new term may be used for further comparisons among species and among different types of predator-induced responses as well as for the evaluation of the adaptive value of defense structures.

Components of additive variance in life‐history traits of Daphnia hyalina: seasonal differences in the response to predator signals

We attempted to separate the additive variance of life‐history parameters (size at first reproduction (SFR), proportion of total production allocated to reproduction) of Daphnia hyalina in a mesotrophic lake during different seasons into genetic components and phenotypic plasticity. Every month we randomly isolated juveniles of 20 clones from the lake and measured their life‐history parameters immediately after isolation, i.e., under the influence of all modifying factors in the lake. The measurements were repeated after the clones had been kept in the laboratory for at least six generations without predator signals (controls) and with the addition of fish and Chaoborus kairomones. SFR increased monotonously from July to December in fresh field isolates. Laboratory controls showed always much larger SFR, but approached field value in December. Most of the size difference was due to maternal effects. Reproductive allocation showed a different pattern than SFR with a minimum in September both in field samples and laboratory controls. Fish kairomone reduced SFR in July and August when fish predation is high, but not later in the year. On the contrary, Chaoborus kairomone increased SFR in September and October when Chaoborus larvae are abundant in the lake, but not in summer. This indicates a seasonal shift in the clonal composition of D. hyalina populations towards clones adapted to the specific predation pressure. Reproductive allocation changed in response to fish kairomone in July and August, but not in response to Chaoborus kairomone. In this mesotrophic lake, fish have a stronger direct and indirect impact on Daphnia life history than Chaoborus larvae.

Predator-induced life history shifts inDaphnia: a synthesis of studies using meta-analysis

Daphnia respond to kairomones from a variety of predators by altering their morphology, behavior, and life history. I use the statistical technique of meta-analysis to quantitatively evaluate the results of 27 independent studies that examine various life history responses of Daphnia to kairomones released from three common predators: Chaoborus, Notonecta, and planktivorous fish. Daphnia exhibit a fundamentally different set of life history responses to Chaoborus (delayed reproduction, decreased size of first clutch, slight tendency toward increased size at maturity) than they do to Notonecta and fish (earlier reproduction, increased clutch size, smaller size at maturity). These opposite responses appear to be related to different patterns of prey selection exhibited by the predators. Food level does not affect the life history responses of Daphnia to Chaoborus kairomones; however, the length of exposure to these kairomones does influence the degree of delay in reproduction. In addition, changes in size at maturity in response to predator kairomones are positively correlated with changes in both age at maturity and size of the first clutch. While the life history shifts exhibited by Daphnia in the presence of Notonecta and fish appear to be clearly adaptive, the fitness consequences of Chaoborus-induced responses are unclear.

Anthropogenic chemicals (insecticides) disturb natural organic chemical communication in the plankton community

The present paper reviews the results of several experiments dealing with the effects of insecticides on natural organic chemical communication in the plankton community. Some species of the cladoceran Daphnia develop protuberant structures (neckteeth, high helmets, long tailspines), an anti-predator strategy, when exposed to a chemical (kairomone) released from predators, such as larvae of the midge Chaoborus. The same morphological changes in Daphnia are induced by exposure to high concentrations of carbamate and organophosphorus insecticides, when animals are in the final embryo to the first instar stage. Lower (sublethal) concentrations of insecticides also can affect morphology of the Daphnia, if the animals are exposed to both insecticides and the Chaoborus kairomone simultaneously. The Chaoborus kairomone reduces clutch size and increases maturation time of Daphnia and thus reduces Daphnia's population growth rate. Low concentrations of insecticide cause a more marked reduction in the population growth rate when Daphnia were exposed simultaneously to the Chaoborus kairomone, and synergism in the effects of the two kinds of chemicals has been detected. Because kairomones are a messenger in the chemical communication between planktonic predators and preys, it could be said that anthropogenic chemicals (insecticides) disturb natural organic chemical communication in the plankton community. This is similar to the effect of environmental endocrine disrupters (EEDs) which are anthropogenic chemicals that disturb chemical communication between tissues or organs in the bodies of animals.

Variation in the neonate size of Daphnia pulex: the effects of predator exposure and clonal origin

Daphnia pulex clones originating from twelve small pond habitats were exposed to chemical cues from a size-selective predator, larvae of the phantom midge Chaoborus. Exposure delayed the onset of reproduction and increased the size at first reproduction. On the other hand, the neonates produced by these larger mothers were slightly smaller than the neonates produced by the smaller control mothers. In cladocerans, neonate size is usually positively correlated to the size of the mother. Thus exposure to Chaoborus kairomone apparently had direct effects on neonate size counterbalancing the maternal effects. Daphnia clones collected from Chaoborus-free and Chaoborus-rich environments exhibited different responses. In first adult instar, the clones from Chaoborus inhabited environments increased their offspring size under Chaoborus exposure whereas clones from Chaoborus-free environments did not. This may reflect clonal adaptation to the predation prehistory of their original habitat since larger neonates more quickly reach a size protected from the predator.

Predator‐Induced Morphological Defenses: Costs, Life History Shifts, and Maternal Effects in Daphnia Pulex

This study was designed to measure and separate the physiological costs of inducible defenses from life history trade—offs and maternal effects in the waterflea Daphnia pulex. Juveniles of D. pulex produce morphological changes ("neckteeth") and undergo life history shifts as defenses against predatory Chaoborus (phantom midge) larvae. These traits are induced by a chemical cue (kairomone) released by the predator. I performed life history experiments with and without Chaoborus kairomones at different food levels to quantify the induced changes and their potential physiological costs. The Daphnia clone used in this study also increased its body depth in response to the predator substance. Life history shifted toward a larger body size (both length and depth) and higher fecundity, which was balanced by an increased time to reach maturity and by increased adult instar durations. Reproductive effort was higher in the typical morph in the first adult instar, indicating resource allocation shifts towards growth in the protected morph. However, even in the absence of predation the chemically induced protected morph tended to show an increased intrinsic rate of population growth (r). The longer time to reach maturity was not a direct physiological cost of neckteeth production, but a trade—off for larger body size. The life history shifts are independent of neckteeth formation. Developmental mechanisms leading to life history changes occurred after neckteeth were induced and could thus be uncoupled from neckteeth formation and its direct costs. In this study no direct costs were found. Carbon incorporation rates for the two morphs, at high and low food, were not different. As a maternal effect, the large females of the induced morph produced larger neonates which, in turn, matured at a larger size. Morphological changes, life history shifts, and maternal effects acted in concert to form defenses against Chaoborus. This study shows that the often assumed high physiological costs resulting from the formation or maintenance of the defenses are not necessary to explain the evolution of inducible defenses. As morphological changes increase the visibility of Daphnia pulex, a fitness disadvantage can be caused by a changing predator regime (e.g., fish). The results of this study suggest that environments with changing predator selectivities favor the evolution of inducible defenses.

Combined effect of the insecticide carbaryl and the Chaoborus kairomone on helmet development in Daphnia ambigua

The cladoceran Daphnia ambigua was exposed to both the insecticide carbaryl and the kairomone released from the predator Chaoborus simultaneously, and its morphological changes were analyzed. Daphnia developed helmets in response to the kairomone, but not in response to carbaryl at low (sublethal) concentrations (1–3 µg 1−1). However, the carbaryl enhanced the development of high helmets and prolonged the maintenance period of the helmets over instars in the presence of the kairomone. These results suggest that sublethal concentrations of the insecticide alter predator-prey interactions by inducing helmet formation in Daphnia, which may reduce vulnerability of the Daphnia to predation.