Morphological Defenses Research Articles

Natural mortality, growth parameters, and environmental temperature in fishes revisited

Pauly (1980. J. Cons. Int. Explor. Mer, 39: 175–192) showed that natural mortality rates in fish could be predicted from body growth parameters and environmental temperature but found no evidence for ecological or taxonomic influences. Using an updated database and techniques that avoid some of the earlier analytical problems, we confirm Pauly's conclusion that mortality is correlated with growth and temperature. A path model supports the role of ecological effects on mortality. A phylogenetic effect is also apparent: perciform fishes occupy warmer environments than other species, but in the predator-rich reef habitat they suffer much lower mortality rates. Species that are cryptic or hide in burrows or have morphological defences against predators show the lowest mortality rates.

Flexible inducible morphological defense in anuran larvae

Flexible inducible morphological defense in anuran larvae

Optimizing Time and Resource Allocation Trade‐Offs for Investment into Morphological and Behavioral Defense

Prey organisms are confronted with time and resource allocation trade-offs. Time allocation trade-offs partition time, for example, between foraging effort to acquire resources and behavioral defense. Resource allocation trade-offs partition the acquired resources between multiple traits, such as growth or morphological defense. We develop a mathematical model for prey organisms that comprise time and resource allocation trade-offs for multiple defense traits. Fitness is determined by growth and survival during ontogeny. We determine optimal defense strategies for environments that differ in their resource abundance, predation risk, and defense effectiveness. We compare the results with results of simplified models where single defense traits are optimized. Our results indicate that selection acts in favor of integrated traits. The selective advantage of expressing multiple defense traits is most pronounced at intermediate environmental conditions. Optimizing single traits generally leads to a more pronounced response of the defense traits, which implies that studying single traits leads to an overestimation of their response to predation. Behavioral defense and morphological defense compensate for and augment each other depending on predator densities and the effectiveness of the defense mechanisms. In the presence of time constraints, the model shows peak investment into morphological and behavioral defense at intermediate resource levels.

A trophic cascade with Chaoborus: population dynamics of ex-ephippial generations of Daphnia

Changes in population dynamics and competitive outcome between Daphnia pulex and D. rosea in response to severe predation by Chaoborus larvae were investigated in a field experiment. In a nearly fishless lake with unusually high densities of Chaoborus flavicans and C. obscuripes, the two coexisting Daphnia species developed morphological defense structures to a different degree. An enclosure-exclosure setup was applied to investigate the population dynamics of both species in presence and absence of the predators. The field study followed the population growth of freshly hatched juveniles of D. pulex and D. rosea as they naturally emerged from ephippia in the lake's sediment during spring. Both Daphnia species have a large body size and, in enclosures with Chaoborus only, developed neckteeth and elongated tail spines as inducible defenses. Nevertheless, Chaoborus accounted for high mortality rates in ephippial neonates and strongly reduced the chance of individuals to reach maturity, especially in D. rosea, the dominant species in enclosures without Chaoborus. It is concluded that, in the first generation, when otherwise large and morphologically defended Daphnia are synchronized by ephippial origin to a population of only juveniles, a trophic cascade with Chaoborus may become highly effective.

Spines and behaviour as defences against fish predators in an invasive freshwater amphipod

Selective predation may be an important proximate cause of the success or failure of invader species. Gammarus roeseli is an invasive amphipod, for which the causes of establishment in rivers where the native species, Gammarus pulex, predominates remain unstudied. Freshwater amphipods are important prey for numerous fish predators, but empirical evidence of lower predation rates on exotic prey is scarce. In laboratory experiments, we compared the susceptibility of G. pulex and G. roeseli to fish predation, determined the mechanisms influencing prey selection, and studied the interaction between behavioural and morphological defences. Fish predators (brown trout, Salmo trutta fario) preyed selectively on G. pulex, but not because of differences in attack or capture probability. The presence of spines in G. roeseli appeared to contribute to its underpredation. Differential prey selection in this case might therefore have resulted from the trout's reaction to an adverse stimulus. We found no significant difference in antipredator behaviour between G. pulex and G. roeseli. General behavioural differences were nevertheless found between species, with G. roeseli spending more time under shelters than G. pulex. However, microcosm experiments suggested that this difference was not important for differential predation. Antipredator behaviour may nevertheless be important for G. roeseli against other predators less sensitive to spines.

Isolation and Absolute Configuration Determination of Aliphatic Sulfates as the Daphnia Kairomones Inducing Morphological Defense of a Phytoplankton.

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Fern Laminar Scales Protect Against Photoinhibition from Excess Light

The laminar scales of the fern Elaphoglossum paleaceum were studied to determine if they act as a morphological mechanism to protect leaves from excess light. We hypothesized that if scales serve this purpose, then individual plants growing in high light would have greater laminar scale density than those in low light. For our first experiment, plants from high light roadsides were collected and subjected to artificial scale removal and then exposed to super-saturating pulse of light for 30 min. We found that leaves with their scales removed exhibited significantly greater photoinhibition than leaves with scales intact. Leaves with intact scales recovered fully after twelve hours whereas those with scales removed remained photoinhibited. Scale density on the adaxial side of leaves was positively correlated with light intensity. The data from this study indicate that fern laminar scales help reduce photoinhibition and potentially function as a morphological defense against photodamage.

Variability in grazer-mediated defensive responses of green and red macroalgae on the south coast of South Africa

Variabilities in the responses of several South African red and green macroalgae to direct grazing and the responses of one green alga to cues from grazers were tested. We used two feeding experiments: (1) testing the induced responses of three red and one green algae to direct grazing by mesograzers and (2) a multi-treatment experiment, in which the direct and indirect effects of one macrograzer species on the green alga Codium platylobium were assessed. Consumption rates were assessed in feeding assays with intact algal pieces and with agar pellets containing non-polar extracts of the test algae. Defensive responses were induced for intact pieces of Galaxaura diessingiana, but were not induced in pellets, suggesting either morphological defence or chemical defence using polar compounds other than polyphenols. In contrast, exposure to grazing stimulated consumption of Gracilaria capensis and Hypnea spicifera by another grazing species. In the multi-treatment experiment, waterborne cues from both grazing and non-grazing snails induced defensive algal traits in C. platylobium. We suggest that inducible defences among macroalgae are not restricted to brown algae, but that both the responses of algae to grazers and of grazers to the defences of macroalgae are intrinsically variable and complex.

Flexible architecture of inducible morphological plasticity

1. Predator-induced morphological defences are produced in response to an emergent predator regime. In natural systems, prey organisms usually experience temporal shifting of the composition of the predator assemblage and of the intensity of predation risk from each predator species. Although, a repetitive morphological change in response to a sequential shift of the predator regime such as alteration of the predator species or diminution of the predation risk may be adaptive, such flexible inducible morphological defences are not ubiquitous. 2. We experimentally addressed whether a flexible inducible morphological defence is accomplished in response to serial changes in the predation regime, using a model prey species which adopt different defensive morphological phenotypes in response to different predator species. Rana pirica (Matsui) tadpoles increased body depth and tail depth against the predatory larval salamander Hynobius retardatus (Dunn); on the other hand, they only increased tail depth against the predatory larval dragonfly Aeshna nigroflava (Martin). 3. Rana pirica tadpoles with the predator-specific phenotypes were subjected to removal or exchange of the predator species. After removal of the predator species, tadpoles with each predator-specific phenotype changed their phenotype to the nondefensive basic one, suggesting that both predator-specific phenotypes are costly to maintain. After an exchange of the predator species, tadpoles with each predator-specific phenotype reciprocally, flexibly shifted their phenotype to the now more suitable predator-specific one only by modifying their body part. The partial modification can effectively reduce time and energy expenditures involved in repetitive morphological changes, and therefore suggest that the costs of the flexible morphological changes are reduced.

Isolation and Absolute Configuration Determination of Aliphatic Sulfates as the Daphnia Kairomones Inducing Morphological Defense of a Phytoplankton-Part 2

4,8-Dimethylnonyl sulfate (1) and 3-methyl-4E-decenyl sulfate (2) were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). The absolute configuration at C4 of 1 was determined by Ohrui's method applied to alcohol 3. The absolute stereochemistry at C3 of 2 was determined by (1)H-NMR analysis of the (R)-1NMA ester of alcohol 11.

Isolation and Absolute Configuration Determination of Aliphatic Sulfates as the Daphnia Kairomones Inducing Morphological Defense of a Phytoplankton

2,6-Dimethylheptyl sulfate (1) and 6-methyloctyl sulfate (3) were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). The absolute stereochemistry at C2 of 1 was determined by (1)H-NMR analysis of the (R)-MTPA ester of alcohol 2. The absolute configuration at C6 of 3 was determined by Ohrui's method applied to alcohol 4.

Population divergence in growth rate and antipredator defences in Rana arvalis

Growth and development rates often differ among populations of the same species, yet the factors maintaining this differentiation are not well understood. We investigated the antipredator defences and their efficiency in two moor frog Rana arvalis populations differing in growth and development rates by raising tadpoles in outdoor containers in the nonlethal presence and absence of three different predators (newt, fish, dragonfly larva), and by estimating tadpole survival in the presence of free-ranging predators in a laboratory experiment. Young tadpoles in both populations reduced activity in the presence of predators and increased hiding behaviour in the presence of newt and fish. Older tadpoles from the slow-growing Gotland population (G) had stronger hiding behaviour and lower activity in all treatments than tadpoles from the fast-growing Uppland population (U). However, both populations showed a plastic behavioural response in terms of reduced activity. The populations differed in induced morphological defences especially in response to fish. G tadpoles responded with relatively long and deep body, short tail and shallow tail muscle, whereas the responses in U tadpoles were often the opposite and closer to the responses induced by the other predators. U tadpoles metamorphosed earlier, but at a similar size to G tadpoles. There was no evidence that growth rate was affected by predator treatments, but tadpoles metamorphosed later and at larger size in the predator treatments. G tadpoles survived better in the presence of free-ranging predators than U tadpoles. These results suggest that in these two populations, low growth rate was linked with low activity and increased hiding, whereas high growth rate was linked with high activity and less hiding. The differences in behaviour may explain the difference in survival between the populations, but other mechanisms (i.e. differences in swimming speed) may also be involved. There appears to be considerable differentiation in antipredator responses between these two R. arvalis populations, as well as with respect to different predators.

Plant trichomes indirectly enhance tritrophic interactions involving a generalist predator, the red imported fire ant

Morphological defense traits of plants such as trichomes potentially compromise biological control in agroecosystems because they may hinder predation by natural enemies. To investigate whether plant trichomes hinder red imported Wre ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), as biological control agents in soybean, Weld and greenhouse experiments were conducted in which we manipulated Wre ant density in plots of three soybean isolines varying in trichome density. Resulting treatment eVects on the abundance of herbivores, other natural enemies, plant herbivory, and yield were assessed. Trichomes did not inhibit Wre ants from foraging on plants in the Weld or in the greenhouse, and Wre ant predation of herbivores in the Weld was actually greater on pubescent plants relative to glabrous plants. Consequently, Wre ants more strongly reduced plant damage by herbivores on pubescent plants. This eVect, however, did not translate into greater yield from pubescent plants at high Wre ant densities. Intraguild predation by Wre ants, in contrast, was weak, inconsistent, and did not vary with trichome density. Rather than hindering Wre ant predation, therefore, soybean trichomes instead increased Wre ant predation of herbivores resulting in enhanced tritrophic eVects of Wre ants on pubescent plants. This eVect was likely the result of a functional response by Wre ants to the greater abundance of caterpillar prey on pubescent plants. Given the ubiquity of lepidopteran herbivores and the functional response to prey shown by many generalist arthropod predators, a positive indirect eVect of trichomes on predation by natural enemies might be more far more common than is currently appreciated.

Foraging of a Small Planktivore (Pseudorasbora parva: Cyprinidae) and its Behavioral Flexibility in an Artificial Stream

In nature, prey animals are not exposed to a single stressor but rather to a wide array of threats and dangers. Thus, fleeing prey need flexible behaviors that increase fitness and chances of survival. This study sought to understand how a small planktivore, Pseudorasbora parva, modifies its foraging behavior in a complex environment where multiple dangers exist. Fish were reared in a flume consisting of two types of microhabitats; pools representing a profitable site with a higher predation risk, and riffles representing a safer but otherwise unfavorable site due to low foraging success and flow velocity stress. The results showed that P. parva exhibited a high degree of flexibility in behavior reflecting the conflicting conditions of high velocity and predation risk. There was a trade-off between foraging rate and predation risk because prey escaped to the riffle when the pool which was the preferred habitat, was occupied by the predator. Microhabitat selection, feeding behavior, shoaling and swimming distance also reflected its adjustable responses with regard to variation of the risk of predation. The fish, under pressure of predation and high flow velocity, became more slender in body shape that might increase the swimming performance suited to avoidance behavior and minimize the swimming energy expenditure. This phenotypic modification may be a result of trade-off between morphological defense and swimming cost for fish inhabiting streams. These results suggest that small preys are able to demonstrate various compensatory behaviors in response to multiple conflicting conditions.

Factors affecting the expression of inducible defences in Euplotes: genotype, predator density and experience

Summary Inducible defences alter the strength of interaction in food webs. Their effectiveness depends both on the maximum level of induction and the speed at which induction happens. Maximum level and speed of induction should therefore evolve in concert. We examined the effect of genotype, number of predators and previous exposure to predators on speed and maximum level of induction in a morphological defence expressed by eight clones in three species of the ciliate Euplotes. Both speed and maximum level of induction, and the reaction to predator density varied among genotypes. These results show that there is genetic variance for all aspects of this inducible defence and the potential for complex evolutionary change under selection. Higher predator densities led to higher maximum levels of defence and, for one measure of induction speed, more rapid induction. Previous exposure to predators had no detectable effect on either speed or maximum level of induction. Our results demonstrate that Euplotes can precisely and rapidly adjust their morphological defence to the magnitude of predation risk. The speed of induction and the maximum level of defence varied among genotypes and this will lead to variation in defence level and vulnerability under natural conditions. Variation in prey vulnerability is a key factor promoting stability in food webs.

Contrasting life histories of the predatory cladocerans Leptodora kindtii and Bythotrephes longimanus

The predatory cladocerans, Leptodora kindtii (Focke, 1844) and Bythotrephes longimanus (Leydig, 1860), express markedly different life-history traits. Leptodora produce small-bodied neonates that mature at small sizes but continue to grow throughout life. Bythotrephes produce larger neonates in both relative and absolute terms that grow rapidly to a large size at maturity whereupon they curtail somatic growth and divert resources mainly to reproduction. Despite their remarkable differences, the sets of life-history traits of both species appear to be solutions to the same basic selection pressures imposed by visually discriminating gape-limited fishes and foraging constraints imposed by prey size. Leptodora stresses pre-contact (transparency) while Bythotrephes stresses postcontact (caudal spine) modes of morphological defense against fishes. Mounting these disparate modes of defense has consequences for selection on timing and allocation to body growth that may underlie competitive imbalance between the species. Owing to the production of large-bodied neonates that grow rapidly, Bythotrephes quickly attain body sizes that both admit them to a broader prey base in size and taxonomic variety, and allow shorter prey handling times, in comparison to Leptodora. This provides Bythotrephes with a wider and more exploitable prey base from an earlier age and may explain why Leptodora has declined in density following Bythotrephes invasion into some North American lakes. The divergent sets of life-history traits expressed by Leptodora and Bythotrephes parallel two dominant life-history strategies evolved by phytoplanktivorous species of the order Cladocera.

Aliphatic sulfates released from Daphnia induce morphological defense of phytoplankton: isolation and synthesis of kairomones

Six aliphatic sulfates, kairomones released from a crustacean Daphnia pulex induce morphological changes of phytoplankton Scenedesmus gutwinskii at ppb (10 −9 g/mL) concentrations.

Laboratory Studies on the Vulnerability of Young White Sturgeon to Predation

AbstractDespite evidence of annual spawning by white sturgeon Acipenser transmontanus in rivers of the northwestern United States and Canada, in some years and locations little or no recruitment of age‐0 white sturgeon has been observed. We examined the vulnerability of white sturgeon larvae and juveniles to predation to further understand possible causes of mortality. We were particularly interested in the vulnerability of older larvae and juveniles because at about 25 mm total length (TL) white sturgeon develop sharp dorsal and lateral scutes that may act as a morphological defense. In the laboratory, white sturgeon ranging from newly hatched larvae to about 170‐mm TL juveniles were exposed to predatory fishes they might encounter in the natural environment. We found that channel catfish Ictalurus punctatus (mean TL = 464 mm) and northern pikeminnow Ptychocheilus oregonensis (mean TL = 472 mm) ate white sturgeon up to mean sizes of 121 and 134 mm TL, respectively. Conversely, similarly sized walleyes Sander vitreus ingested almost no white sturgeon, although juvenile walleyes (mean TL = 184 mm) ate white sturgeon up to 59 mm TL. The smallest predator we tested, prickly sculpins Cottus asper (mean TL = 126 mm), ate white sturgeon up to a mean TL of 50 mm. Our study demonstrated that predation is a likely cause of mortality of age‐0 white sturgeon and may be contributing to the year‐class failures that have been observed. In addition, the results from this study could be used to reduce the predation risk of artificially propagated white sturgeon released to augment declining populations since fish could be reared to sizes where their vulnerability is low.

Genetic basis of phenotypic plasticity for predator-induced morphological defenses in anuran tadpole, Rana pirica, using cDNA subtraction and microarray analysis

Anuran tadpoles ( Rana pirica) are induced to develop a higher tail and a bulgy body as predator-specific morphological responses when they are exposed to predatory larval salamanders. Subtractive hybridization was performed using induced tadpole body skin and normal tadpoles’ body skin. A total of 196 clones showed higher expression, and 104 clones showed lower expression, when they formed bulgy bodies. In the subtraction, carboxypeptidase B, trypsinogen, elastase I, fibrinogen, elastase II, triacyl-glycerol lipase, and α1-antitrypsin genes showed lower expression. In contrast, RT-like protein, bullous pemphigoid antigen, phosphoserine aminotransferase, uromodulin, tetranectin, chaperonin-like protein, zinc finger protein, osteonectin, aldehyde dehydrogenase, Sec 23A protein, and ribosomal protein showed higher gene expression. Microarray analysis was also performed using this subtracted cDNA (nine replicates). Results of the microarray data essentially corresponded with those of the subtraction data, and the degree of the suppressed genes was much stronger than that of the expressed genes. Carboxypeptidase B showed the strongest suppression, and its inhibition range was from 1/100 to 3/100 compared with that of control body skin. Strong suppression was also observed with trypsinogen, elastase I, fibrinogen, and elastase II as well. These results can be interpreted as increases of fibrinolysis by strong depression of both carboxypeptidase B and other genes simultaneously, resulting in the retention of blood vessels and facilitating the circulation of blood. Expression was observed in phosphoserine aminotransferase, aldehyde dehydrogenase, RT-related protein, chaperonin-like protein, tetranectin, bullous pemphigoid antigen, uromodulin, and Sec 23A protein. They were significantly ( p < 0.05) increased and were at least 1.5 times greater compared with the control. From the appearance, it seems that the bulgy shaped body is highly connecting to the bullous pemphigoid (BP) antigen that causes the skin blistering disorder, and tetranectin and uromodulin may be related to the extracell matrix through myogenesis, protein secretion, and ion transport, respectively. Since the RT-related protein gene derived from retrotransposon (L1) is known to disrupt mammalian transcriptomes, retrotransposon may be involved with phenotypic plasticity for morphological defense by Rana prica against predator threat.

Predation of freshwater jellyfish on Bosmina : the consequences for population dynamics, body size, and morphology

Invertebrate predators may cause strong changes in behaviour, life-history, and morphology of prey species. However, little is known about the influence of jellyfish on such characteristics of their prey. This study analyses the impacts of the freshwater jellyfish Craspedacusta sowerbii on life history and morphological defenses in a population of the cladoceran Bosmina longirostris . Length of mucro and antennule, size-dependent number of eggs, size at maturity, and size of juveniles, adults, and egg-carrying females were investigated during a 23 days experiment using medusae-enriched and control enclosures filled with natural plankton populations. Significant differences in parameters investigated were found not only between treatments, but also within treatments over time. Changes in Bosmina life-history parameters and morphology in controls were probably due to predation by cyclopoid copepods. The significant increase in the size of adults and egg-carrying females as well as the increase in mucro and antennule length in medusae-enriched enclosures are discussed as defense strategies against the freshwater jellyfish.