Morphological Defenses Research Articles

Biological control of take-all in wheat by endophytic Bacillus subtilis E1R-j and potential mode of action

The bacterial strain E1R-j, isolated as an endophyte from wheat roots, exhibited high antifungal activity to Gaeumannomyces graminis var. tritici ( Ggt). Strain E1R-j was identified as Bacillus subtilis based on morphological, physiological and biochemical methods as well as on 16S rDNA analysis. This strain inhibited mycelium growth in vitro of numerous plant pathogenic fungi, especially of Ggt, Coniothyrium diplodiella, Phomopsis sp . and Sclerotinia sclerotiorum. In greenhouse experiments, soil drenches with cell densities of 10 6, 10 9 and 10 12 CFU ml −1 E1R-j reduced significantly take-all disease, caused by Ggt, in wheat seedling by 62.6%, 68.6% and 70.7%, respectively, compared to the inoculated control, 4 weeks after sowing. Growth parameters such as lengths and fresh weights of roots and shoots of Ggt-inoculated control plants were significantly lower compared to Ggt-inoculated and E1R-j treated plants. Field experiments in the season 2006/2007, heights of wheat plants in the Ggt inoculated plots were significantly reduced compared to the non inoculated treatments. Yield parameters such as kernels per head and thousand kernel weight (TKW) in inoculated control plants were lower compared to the other treatments. In the experimental year 2007/2008, independent treatments with the bacterial strain E1R-j and the fungicide Triadimefon reduced take-all disease in wheat roots by 55.3% and 61.9%, compared to the inoculated control plants. In this season plant height in inoculated control was significantly lower and also the yield parameters seeds per head and especially TKW were drastically reduced compared to the other treatments. E1R-j treatment alleviated the detrimental effects of take-all on grain yield parameters to a similar extent as Triadimefon application. SEM studies revealed that in the presence of E1R-j, hyphae of Ggt showed leakage, appeared ruptured, swollen and shriveled. Following root drench, strain E1R-j was able to colonize endophytically roots and leaves of wheat seedlings. While the population of the bacterial strain in wheat roots steadily increased from the second to the fourth leaf stage, in the leaf tissue the population of the strain rapidly declined. TEM studies also showed that cells of E1R-j were present in roots of wheat seedlings and effectively retarded infection and colonization of Ggt in root tissue; suppression of Ggt by E1R-j was accompanied by disintegration of hyphal cytoplasm. In addition, in the presence of E1R-j cells in Ggt-infected root tissue morphological defense reactions were triggered such as formation of wall appositions and papillae. The results presented indicate that the endophytic strain E1R-j of B. subtilis meets demands required for biocontrol of take-all.

Non-lethal presence of predators modifies morphology and movement rates in Euplotes

Many species are able to modify aspects of their behaviour and morphology in the presence of predators. The aim of this study was to investigate the relationship between the expression of morphological and behavioural defences according to the framework proposed by DeWitt et al (1999). Experiments were carried out using hypotrich ciliates of the genus Euplotes as prey and turbellarians of the genus Stenostomum as predators. The smaller species Euplotes octocarinatus showed a greater proportional increase in width, a reduction in foraging movement rates and an increase in maximum movement rates following exposure to predator cues. The larger Euplotes aediculatus induced lesser changes in width, similar reductions in movement during foraging and no change in maximum speed following predator exposure. These results provide evidence of a cospecialised relationship between morphological and behavioural defences. Despite substantial differences in the absence of predators, movement rates and lateral body width were similar in both species following predator exposure. The observed changes may be considered adaptive, gape limited flatworm predators are unable to ingest large Euplotes and a reduction in movement rates during foraging reduces predator encounter rates, while an increase in maximal movement rates increases chances of predator evasion.

Simulated herbivory induces extrafloral nectary production in Prunus avium

1. Induced chemical responses to herbivory have been widely documented, however less attention has been given to the induced morphological defences, particularly those that mediate protection mutualisms. One of the most widely studied mutualisms is the ant-plant protection mutualism, in which ants and other predatory arthropods defend plants against herbivores in exchange for food or housing. 2. Chemical and morphological traits that mediate this protection mutualism attract beneficial partners to plants. Thus induction of traits can lead to greater protection by mutualists when herbivores are present. In this study we examined whether extrafloral nectaries (EFNs) are induced in response to simulated herbivory in Prunus avium. 3. In a greenhouse experiment, continuous damage to seedlings was simulated in two treatments intended to mimic different types of herbivores: (i) 50% of the area of each leaf was removed using a paper hole punch (e.g. insect herbivore simulation), and (ii) 50% of the area of each leaf was removed using scissors (e.g. browsing mammal simulation). Seedlings in the control group were not damaged. 4. Post-treatment, damaged plants produced significantly more EFNs per leaf on pre-existing leaves, as well as those that emerged following the onset of damage, than plants in the control group. Regardless of treatment, leaves emerging earlier supported fewer EFNs than leaves emerging later in the experiment. 5. Allocation to defence by seedlings, which have limited resources available, suggests the protection mutualism could be important to plant fitness in the field. Further study of patterns of EFN induction in P. avium seedlings is needed to better understand the significance of this induced response.

Evaluating inducible morphological defences in the common freshwater ciliate, Coleps hirtus

Experiments examined whether the ciliate, Coleps hirtus, changed its morphology in the presence of zooplankton known to prey on ciliates. While caudal spine length was not affected, Coleps were longer and thinner in the presence of Cyclops than in their absence.

Habitat segregation mediates predation by the benthic fish Cottus gobio on the exotic amphipod species Gammarus roeseli

Predation is often considered as one of the most important biotic factor determining the success of exotic species. The freshwater amphipod Gammarus roeseli has widely colonized Western Europe, where it is frequently found in sympatry with the native species (Gammarus pulex). Previous laboratory experiments revealed that G. roeseli may have an advantage over G. pulex through differential predation by native fish (brown trout). Morphological anti-predator defences (spines) were found responsible for lower rates of predation on the invasive G. roeseli. Here, using both field surveys and laboratory experiments, we tested if a differential of predation exists with other fish predators naturally encountered by gammarids. The main predators present in our field site were nocturnal benthic feeders (mainly bullheads, Cottus gobio). Fish diet analysis showed that, compared to its global availability in the river, G. roeseli was less consumed than G. pulex. In the field, however, G. roeseli was found mainly in the aquatic vegetation whereas G. pulex was found in all habitat types. Laboratory experiments in microcosms revealed that G. roeseli was less prone to predation by C. gobio only when vegetation was present. Depending on the type of predator, the differential of predation could therefore be mediated by antipredator behaviour, and a better usage of refuges, rather than by morphological defences.

ANTIPREDATOR DEFENSES ALONG A LATITUDINAL GRADIENT IN RANA TEMPORARIA

Antipredator defenses are expected to decrease toward higher latitudes because predation rates are predicted to decrease with latitude. However, latitudinal variation in predator avoidance and defense mechanisms has seldom been studied. We studied tadpole antipredator defenses in seven Rana temporaria populations collected along a 1500-km latitudinal gradient across Sweden, along which previous studies have found increasing tadpole growth and development rates. In a laboratory common garden experiment, we measured behavioral and morphological defenses by raising tadpoles in the presence and absence of a predator (Aeshna dragonfly larva) in two temperature treatments. We also estimated tadpole survival in the presence of free-ranging predators and compared predator densities between R. temporaria breeding ponds situated at low and high latitudes. Activity and foraging were generally positively correlated with latitude in the common garden experiment. While all populations responded to predator presence by decreasing activity and foraging, high-latitude populations maintained higher activity levels in the presence of the predator. All populations exhibited defensive morphology in body and tail shape. However, whereas tail depth tended to increase with latitude in the presence of predator, it did not change with latitude in the absence of the predator. Predator presence generally increased larval period and decreased growth rate. In the southern populations, predator presence tended to have a negative effect on metamorphic size, whereas in the northern populations predators had little or a positive effect on size. Latitude of origin had a strong effect on survival in the presence of a free-ranging predator, with high-latitude tadpoles experiencing higher mortality than those from the low latitudes. In the wild, predator densities were significantly lower in high-latitude than in mid-latitude breeding ponds. Although the higher activity level in the northern populations seems to confer a significant survival disadvantage under predation risk, it is probably needed to maintain the high growth and development rates. However, the occurrence of R. temporaria at high latitudes may be facilitated by the lower predator densities in the north.

Costs, benefits and the evolution of inducible defences: a case study with Daphnia pulex

Phenotypic plasticity is one major source of variation in natural populations. Inducible defences, which can be considered threshold traits, are a form of plasticity that generates ecological and evolutionary consequences. A simple cost-benefit model underpins the maintenance and evolution of these threshold, inducible traits. In this model, a rank-order switch in expected fitness, defined by costs and benefits of induction between defended and undefended morphs, predicts the risk level at which individuals should induce defences. Here, taking predator-induced morphological defences in Daphnia pulex as a threshold trait, we provide the first comprehensive investigation into the costs and benefits of a threshold trait, and how they combine to reflect fitness and predict the switchpoint at which induction should occur. We develop reaction norms that show genetic variation in switchpoints. Further experiments show that induction can confer a survival benefit and a cost in terms of lifetime reproductive success. Together, these two traits combine to estimate expected fitness and can predict the switchpoint between an undefended and a defended strategy. The predictions match the reaction norm data for clones that experience these costs and benefits, and correspond well to independent field data on induction. However, predictions do not, and cannot, match for clones that do not gain a benefit from induction. This study confirms that a simple theory, based on life history costs and benefits, is a sufficient framework for understanding the ecology and evolution of inducible, threshold traits.

Specificity of inducible seaweed anti-herbivory defences depends on identity of macroalgae and herbivores

Meso-herbivores can strongly affect biomass accrual and macrophytobenthic commu- nity structure. To counter grazing effects, constitutive and induced anti-herbivory responses evolved in seaweeds. Feeding-assayed induction experiments were conducted in the laboratory to investigate whether 14 d grazing periods by either the periwinkle Littorina brevicula or the abalone Haliotis dis- cus induced anti-herbivory defences in the green alga Ulva pertusa and the brown alga Laminaria japonica. Where appropriate, assays were repeated with artificial food containing lipophilic algal extracts, using dichloromethane (DCM) as a solvent, to test whether or not snails induced chemical defences. While exposure to periwinkles reduced palatability of fresh L. japonica pieces for naive conspecific grazers, no such effect was displayed by abalone-exposed L. japonica pieces. Patterns of grazer specificity in the palatability of fresh algae were not confirmed when using artificial food con- taining algal DCM extracts. This suggests that L. japonica either induced morphological defences or periwinkle-deterrent substances originated from the non-lipophilic fraction of defensive chemicals. Grazer-specific induced responses were not apparent in U. pertusa assays. This study revealed that the induction of chemical anti-herbivory responses depends not only on the type of grazer but also on the type of alga on which the grazer feeds.

Isolation of New Aliphatic Sulfates and Sulfamate as the Daphnia Kairomones Inducing Morphological Change of a Phytoplankton Scenedesmus gutwinskii

New aliphatic sulfates and sulfamates were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). Their structures were determined by spectroscopic and synthetic studies.

Does defoliation induce chemical and morphological defenses in the leaves of silver birch seedlings under changing climate?

We examined the effects of defoliation con-currently with elevated temperature and CO2 on some chemical and morphological characteristics in the leaves of silver birch seedlings (Betula pendula). We also analyzed the consequent changes in the palatability of leaves for adult blue alder leaf beetles (Agelastica alni). Under the different climatic treatments, the seedlings were subjected to three fertilizer treatments (0 kg, 130 kg and 270 kg N ha−1) and defoliation treatments (0%, 25% and 50% of the total leaf area). In each climatic treatment, fertilization increased the nitrogen content in the leaves, but decreased total concentrations of soluble phenolics, detected by high-performance liquid chromatography (HPLC), and insoluble condensed tannins. Defoliation, both independently and in combination with elevated temperature and CO2, decreased the concentrations of the phenolics. Compared to the intact controls, the leaves of the defoliated seedlings were smaller and tougher. Under elevated temperature, the beetles consumed a smaller amount of the leaves of plants subjected to the high fertilization, while under ambient climatic conditions, fertilization increased the feeding. The total leaf consumption was higher under the ambient climatic conditions than under elevated temperature, elevated CO2 or the combination of elevated temperature and CO2.

The polychaete Cirriformia punctata is chemically defended against generalist coral reef predators

The Caribbean cirratulid polychaete, Cirriformia punctata (Grube, 1856), is bright orange and burrows just below the surface of fine carbonate sand with only its filamentous tentacles and gills exposed to potential predators. In addition to its conspicuous coloration, C. punctata lacks obvious structural and morphological defenses. We hypothesized that C. punctata protects itself from predation using secondary metabolites as a chemical defense. Feeding bioassays were performed using whole worms to determine palatability against two generalist coral reef predators: the bluehead wrasse, Thalassoma bifasciatum, and the brown anemone, Aiptasia sp. Additionally, assays were conducted with hermit crabs of the genus Paguristes, but with limited success. In all assays, C. punctata was unpalatable to consumers. The tentacles and body of the worm were separately assayed using T. bifasciatum to determine whether the defensive mechanism was differentially allocated to body regions that are differently exposed to potential predators. Both the tentacles and body of C. punctata were unpalatable to T. bifasciatum, indicating no specific allocation of defenses. Crude organic extracts of whole C. punctata were unpalatable to T. bifasciatum, confirming that the worm defense is chemical rather than morphological. Chemical defenses of Cirriformia spp. appear to be generally effective against taxonomically diverse potential consumers.

Formation of morphological defences in response to YOY perch and invertebrate predation in two Daphnia species coexisting in a mesotrophic lake

This study examined the formation of morphological defences by two coexisting Daphnia species, the large-sized D. pulicaria (2 mm) and the small-sized D. mendotae (1.4 mm), in response to the presence of young-of-the-year (YOY) yellow perch (Perca flavescens) and invertebrate predators (Chaoborus, Leptodora) during summer in a mesotrophic lake. We hypothesized that due to differential size-selective predation risk by YOY fish and invertebrates, the large-sized and the small-sized Daphnia species would show different morphological responses to predation threats. We followed changes in two morphological traits (relative length of the tail spine in D. pulicaria and of the helmet in D. mendotae) among different periods during summer according to YOY fish and invertebrate predation. We defined four YOY fish predation periods based on the presence of YOY perch in the pelagic zone of the lake and the relative abundance of Daphnia preys in their gut contents, and two invertebrate predation periods based on exclusive or mutual occurrence of the invertebrate predators. The large-sized (D. pulicaria) and the small-sized (D. mendotae) species showed different morphological responses to YOY fish and invertebrate predators, respectively. The tail spine ratio of the juveniles and adults of D. pulicaria did not change in response to YOY fish predation or to invertebrate predation. A gradual increase in the helmet ratio was observed in the small-sized D. mendotae over the summer period. This change was related to the co-occurrence of the invertebrate predators (Chaoborus and Leptodora) and to YOY fish predation. The warmer temperature cannot be accounted for helmet elongation since it was constant across depths, and not related with the co-occurrence of D. mendotae and YOY perch.

Linking antipredator behaviour, ingestion, gut evacuation and costs of predator-induced responses in tadpoles

Many prey organisms reduce their activity to reduce predation risk. A common argument is that a reduction in activity is one of the highest costs of defence. I exposed predator-induced and predator-naive morphs to a short-term predator environment and recorded behavioural, life-historical, physiological, and morphological responses. In contrast to expectation, reduced activity was not one of the highest costs of responding to predators. Predator-exposed tadpoles ingested the same amount of food with less feeding effort and evacuated food from their guts at a higher rate. Despite these advantages, predator-exposed tadpoles still paid costs in responding to predators, in decreased development rate. They did not have reduced survival or reduced growth. Costs in responding to predators are probably caused by physiological factors, such as reduced conversion rates, increased metabolic rates or by allocation to morphological defences, such as increased tail depth. My results show that feeding activity is not linked to the amount of food ingested and that physiological mechanisms, such as gut evacuation, decouple feeding activity and ingestion from growth, development and survival. There was no adaptive response in gut morphology. My study improves the understanding of the underlying internal and physiological mechanisms mediating the trade-off between activity and costs of predator-induced defences.

Models of ontogenetic allometry in cladoceran morphology studies

Ontogenetic variation of morphological traits in cladocerans is usually analysed by a simple allometry function. We found that common cyclomorphic and inducible traits in Bosmina and Daphnia sometimes deviate from simple allometry, however. Consequently, simple allometric analysis may at times be inadequate since important aspects of the ontogenetic development may not be revealed. We suggest that other allometric models should be used more extensively in ontogenetic studies of cladocerans morphology. Especially, complex allometric functions may help analyse the effects of size-selective predation on morphological defence traits when predators prefer prey of intermediate size.

Ocean acidification disrupts induced defences in the intertidal gastropod Littorina littorea.

Carbon dioxide-induced ocean acidification is predicted to have major implications for marine life, but the research focus to date has been on direct effects. We demonstrate that acidified seawater can have indirect biological effects by disrupting the capability of organisms to express induced defences, hence, increasing their vulnerability to predation. The intertidal gastropod Littorina littorea produced thicker shells in the presence of predation (crab) cues but this response was disrupted at low seawater pH. This response was accompanied by a marked depression in metabolic rate (hypometabolism) under the joint stress of high predation risk and reduced pH. However, snails in this treatment apparently compensated for a lack of morphological defence, by increasing their avoidance behaviour, which, in turn, could affect their interactions with other organisms. Together, these findings suggest that biological effects from ocean acidification may be complex and extend beyond simple direct effects.

Temporal environmental variation and phenotypic plasticity: a mechanism underlying priority effects

Understanding the role of history in the formation of communities has been a major challenge in community ecology. Here, we explore the role of phenotypic plasticity and its associated trait‐mediated indirect interactions as a mechanism behind priority effects. Using organisms with inducible defenses as a model system, we examine how aquatic communities initially containing different predator environments are affected at the individual and community level by the colonization of a second predator. Snails and tadpoles were established in four different caged‐predator environments (no predator, fish, crayfish or water bugs). These four communities were then crossed with three predator colonization treatments (no colonization, early colonization, or late colonization) using lethal water bugs as the predator. The snails responded to the caged predator environments with predator‐specific behavioral and morphological defenses. In the colonization treatments, snails possessing the wrong phenotype attempted to induce phenotypic changes to defend themselves against the new risk. However, snails initially induced by a different predator environment often suffered high predation rates. Hence, temporal variation in predation risk not only challenged the snail prey to try to track this environmental variation through time by adjusting their defensive phenotypes, but also caused trait‐mediated interactions between snails and the colonizing predator. For tadpoles within these communities, there was little evidence that the morphological responses of snails indirectly effected tadpole predation rates by colonizing water bugs. Unexpectedly, predation rates on tadpoles by colonizing water bugs were generally higher in the three caged‐predator treatments, suggesting that water bugs elevated their foraging activity in response to potentially competing predators. In summary, we demonstrate an important priority effect in which the initial occurrence of one species of predator can facilitate predation by a second predator that colonizes at a later date (i.e. a TMII) suggesting that phenotypic plasticity can be an important driver behind priority effects (i.e. historical exposure to predators).

Change in phenotypic plasticity of a morphological defence in Daphnia galeata (Crustacea: Cladocera) in a selection experiment

Some water fleas Daphnia change their head morphology to reduce predation risk in response to chemical substances (kairomones) released from larvae of the invertebrate predator Chaoborus (Insecta: Diptera). We tested for evidence of the costs associated with elongation of the head spine in Daphnia galeata and the consequences of these costs on the inducibility of head spine elongation in predictable and unpredictable environments. We exposed D. galeata in outdoor experimental ponds to conditions under which predation pressure by Chaoborus larvae and the concentration of kairomones from this predator were controlled for about 70 days. In the laboratory, we then used Daphnia clones collected from the outdoor ponds to investigate the inducibility of head spine formation in response to Chaoborus kairomones. The inducibility of head spine formation increased in D. galeata from the ponds that had contained both predators and kairomones, whereas in water fleas from the ponds containing only kairomones the plasticity (inducibility) of head spine formation decreased compared with that in the control ponds. These results suggest that the production of a defensive head spine, its phenotypic plasticity, or both entail some costs. Contrary to our predictions, exposure to Chaoborus kairomones in the laboratory resulted in head lengths that were not significantly different among any of the clones from the three outdoor treatments. We found no evidence for costs associated with head spine elongation in terms of fecundity, time to maturity, or intrinsic rate of natural population increase. Average within-clone partial correlations calculated for head length and intrinsic rate of natural population increase, corrected for body length, were not significantly negative, indicating no cost of defence. This was probably because food conditions in the laboratory were so good that the costs of defence could not be detected. Furthermore, community-level changes, such as changes in food conditions caused by manipulation of the predation regime in the outdoor ponds, might have worked as selection pressures and confounded the results.

Linking Morphological and Behavioural Defences: Prey Fish Detect the Morphology of Conspecifics in the Odour Signature of their Predators

AbstractPredation is a strong selective force acting on both morphology and behaviour of prey animals. While morphological defences (e.g. crypsis, presence of armours or spines or specific body morphologies) and antipredator behaviours (e.g. change in foraging or reproductive effort, or hiding and fleeing behaviours) have been widely studied separately, few studies have considered the interplay between the two. The question raised in our study is whether antipredator behaviours of a prey fish to predator odours could be influenced by the morphology of prey conspecifics in the diet of the predator. We used goldfish (Carassius auratus) as our test species; goldfish exposed to predation risk significantly increase their body depth to length ratio, which gives them a survival advantage against gape‐limited predators. We exposed shallow‐bodied and deep‐bodied goldfish to the odour of pike (Esox lucius) fed either form of goldfish. Deep‐bodied goldfish displayed lower intensity antipredator responses than shallow‐bodied ones, consistent with the hypothesis that individuals with morphological defences should exhibit less behavioural modification than those lacking such defences. Moreover, both shallow‐ and deep‐bodied goldfish displayed their strongest antipredator responses when exposed to the odour of pike fed conspecifics of their own morphology, indicating that goldfish are able to differentiate the morphology of conspecifics through predator diet cues. For a given individual, predator threat increases as the prey become more like the individual eaten, revealing a surprising level of sophistication of chemosensory assessment by prey fish.

FLEXIBLE DEFENSE STRATEGIES: COMPETITION MODIFIES INVESTMENT IN BEHAVIORAL VS. MORPHOLOGICAL DEFENSES

Competition is predicted to affect the expression of inducible defenses, but because costs of behavioral and morphological antipredator defenses differ along resource gradients, its effects on defenses may depend on the traits considered. We tested the predictions from different defense models in tadpoles of the common frog Rana temporaria, which exhibit both types of defenses. In an outdoor experiment, we exposed the tadpoles to nonlethal predators (Aeshna dragonfly larvae) and to a gradient of intraspecific competition. Morphological responses did not follow any of the expected patterns, since investment in defense was not affected by resource level. Instead, tail depth decreased in the absence of predators. Behavioral defenses followed a state-dependent model. Overall, the defense strategy of the tadpoles revealed a shift from morphological and behavioral defenses at low tadpole density to morphological defense only at high density. This difference probably reflects the different efficiency of the defenses. Hiding is an effective means of defense, but it is unsustainable when resources are scarce. Morphological responses become more important with increasing density to compensate for the increase in behavioral risk-taking. Our results indicate that competition can strongly affect reaction norms of inducible defenses and highlight the importance of integrating ecological parameters that affect the cost-benefit balance of phenotypic plasticity.

Predator-induced changes in morphology of a prey fish: the effects of food level and temporal frequency of predation risk

In a series of experiments, we investigated the effects of food availability and risk frequency on the dynamics of predator-induced changes in growth and morphology of prey fish using goldfish (Carassius auratus) as our test species. In experiment 1, we fed goldfish high or low food rations and exposed them to either alarm cues from conspecifics, cues from swordtails or a water control. After 60 days, goldfish in the alarm cue treatment significantly increased their body depth and body weight but had smaller body length than goldfish exposed to swordtails cues or water, likely reducing their vulnerability to gape-limited predators. Importantly, food level had an impact on the amplitude of the morphological changes. In experiment 2, goldfish were exposed to two different frequencies of predation cues or a water control for 50 days. The cues were either continued or discontinued from day 51 to 100, and all cues were resumed from day 101 to 150. We found that goldfish exposed to predation cues increased their depth and weight at a faster rate than did the goldfish exposed to water, and of particular significance was the fact that frequency of risk had an effect on the amplitude of the change. When the cues were interrupted, the increase in growth rate parameters was reduced to the level of the goldfish exposed to water. However, when the cues were resumed, the rate increased to match the growth rate of the goldfish that were continuously exposed to the cues. Finally, we staged encounters between goldfish of differing morphologies and yellow perch (Perca flavescens) and found that deep-bodied goldfish had better survival than the shallow-bodied ones. These experiments illustrate the dynamic nature of inducible morphological defences.