Variation in growth form in relation to spectral light quality (red/far-red ratio) in Plantago lanceolata L. in sun and shade populations

Plants from a sun and shade population were grown in two environments differing in the ratio of red to far-red light (R/FR ratio). A low R/FR ratio, simulating vegetation shade, promoted the formation of long, upright-growing leaves and allocation towards shoot growth, whereas a high R/FR ratio had the opposite effects. The increase in plant height under the low R/FR ratio was accompanied by a reduction in the number of leaves. Population differences in growth form resembled the differences between plants grown in different light environments: plants from the shade population had rosettes with long erect leaves, whereas plants from the sun population formed prostrate rosettes with short leaves. Plants from the shade population were more responsive to the R/FR ratio than plants from the sun population: the increases in leaf length, plant height, and leaf area ratio under a low R/FR ratio were larger in the shade population. However, differences in plasticity were small compared to the population difference in growth form itself. We argue that plants do not respond optimally to shading and that developmental constraints might have limited the evolution of an optimal response. Received: 8 December 1996 / Accepted: 31 March 1997     

Predation induced changes in behavior and growth rate in three populations of the intertidal snail, Littorina sitkana (Philippi)

We investigated the sublethal effects of a predatory crab, Cancer productus (Randall), on the behavior and growth of its snail prey, Littorina sitkana, by setting up controlled rearing and prey-size selection experiments. L. sitkana were collected from three sites on San Juan Island, WA, USA. These sites varied in snail size, abundance, and vertical distribution, and in the abundance of the crab predator C. productus. Snails from all three populations were raised for 34 days under the following treatments: no-crab control, a non-feeding C. productus encased in mesh box, and an encased C. productus feeding on L. sitkana. The non-feeding crab treatment did not affect snail foraging behavior or growth rate in comparison with the no-crab control. In contrast, the presence of a feeding crab elicited escape behavior in the snails, halted grazing, and consequently reduced growth rates. A population difference in escape behavior was observed: upward migration in snails from rocky shores and hiding in crevices in snails from a mud flat. It thus appears that chemicals leaching from crushed conspecific snails, rather than the presence of the crab predator, act as the “alarm substance” to which L. sitkana react. The magnitude of the growth depression in the presence of feeding crabs was 85%, with no difference among the three populations. Once the feeding crab stimulus was removed, snails in all populations resumed normal growth, suggesting that this response to feeding predators is reversible with changing environmental conditions. Laboratory experiments were set up to determine if all size classes of L. sitkana are equally susceptible to C. productus predation. C. productus consistently selected the largest of three size classes of L. sitkana. These results suggest that slow growth rate and small size in L. sitkana may actually be an adaptation for coexisting with high C. productus abundance, rather than simply a cost of escape behavior.     

Predation induced changes in behavior and growth rate in three populations of the intertidal snail, Littorina sitkana (Philippi)

We investigated the sublethal effects of a predatory crab, Cancer productus (Randall), on the behavior and growth of its snail prey, Littorina sitkana, by setting up controlled rearing and prey-size selection experiments. L. sitkana were collected from three sites on San Juan Island, WA, USA. These sites varied in snail size, abundance, and vertical distribution, and in the abundance of the crab predator C. productus. Snails from all three populations were raised for 34 days under the following treatments: no-crab control, a non-feeding C. productus encased in mesh box, and an encased C. productus feeding on L. sitkana. The non-feeding crab treatment did not affect snail foraging behavior or growth rate in comparison with the no-crab control. In contrast, the presence of a feeding crab elicited escape behavior in the snails, halted grazing, and consequently reduced growth rates. A population difference in escape behavior was observed: upward migration in snails from rocky shores and hiding in crevices in snails from a mud flat. It thus appears that chemicals leaching from crushed conspecific snails, rather than the presence of the crab predator, act as the “alarm substance” to which L. sitkana react. The magnitude of the growth depression in the presence of feeding crabs was 85%, with no difference among the three populations. Once the feeding crab stimulus was removed, snails in all populations resumed normal growth, suggesting that this response to feeding predators is reversible with changing environmental conditions. Laboratory experiments were set up to determine if all size classes of L. sitkana are equally susceptible to C. productus predation. C. productus consistently selected the largest of three size classes of L. sitkana. These results suggest that slow growth rate and small size in L. sitkana may actually be an adaptation for coexisting with high C. productus abundance, rather than simply a cost of escape behavior.     

Predator impacts on stream benthic prey

The impact that predators have on benthic, macroinvertebrate prey density in streams is unclear. While some studies show a strong effect of predators on prey density, others show little or no effect. Two factors appear to influence the detection of predator impact on prey density in streams. First, many field studies have small sample sizes and thus might be unable to detect treatment effects. Second, streams contain two broad classes of predators, invertebrates and vertebrates, which might have different impacts on prey density for a variety of reasons, including availability of refuge for prey and prey emigration responses to the two types of predators. In addition, predatory vertebrates have more complex prey communities than predatory invertebrates; this complexity might reduce the impact that predatory vertebrates have on prey because of indirect effects. I conducted a meta-analysis on the results of field studies that manipulate predator density in enclosures to determine (1) if predators have a significant impact on benthic prey density in streams, (2) if the impacts that predatory invertebrates and vertebrates have differ, and (3) if predatory vertebrates have different impacts on predatory prey versus herbivorous prey. The results of the meta-analysis suggest that on average predators have a significant negative effect on prey density, predatory invertebrates have a significantly stronger impact than predatory vertebrates, and predatory vertebrates do not differ in their impact on predatory versus herbivorous invertebrate prey. Three methodological variables (mesh size of enclosures, size of enclosures, and experimental duration) were examined to determine if cross correlations exist that may explain the differences in impact between predatory invertebrates and vertebrates. No correlation exists between mesh size and predator impact. Over all predators, no correlation exists between experimental duration and predator impact; however, within predatory invertebrates a correlation does exist between these variables. Also, a correlation was found between enclosure size and predator impact. This correlation potentially explains the difference in impact between predatory invertebrates and predatory vertebrates. Results of the meta-analysis suggest two important areas for future research: (1) manipulate both types of predators within the same system, and (2) examine their impacts on the same spatial scale.     

Variation in petiole and internode length affects plant performance in <Emphasis Type="Italic">Trifolium repens</Emphasis> under opposing selection regimes

We studied the effects of genotypic and plastic variation in vertical and horizontal spacer lengths on plant performance in a stoloniferous herb subjected to opposing selection regimes. We hypothesized that longer vertical structures are beneficial if plants are subjected to competition, but they should negatively affect plant performance if plants are exposed to aboveground disturbance. To test these hypotheses we subjected 34 genotypes of Trifolium repens to competition and disturbance treatments. Competition was imposed by a grass canopy consisting of Lolium perenne, and disturbance was simulated by regularly clipping the target plants and all the surrounding vegetation at 1 cm above soil level. Conform to our hypothesis, genotypes with longer vertical structures (petioles) produced fewer ramets than genotypes with shorter petioles in the disturbance treatment. However, genotypes with longer petioles did not perform better under competition than genotypes with shorter petioles. Genotypes with highly plastic vertical structures tended to produce more shoot mass under competition, and they produced fewer ramets if subjected to disturbance. Unexpectedly, horizontal structures (stolon internodes) expanded in response to competition which, furthermore, was associated with enhanced plant performance. However, producing longer internodes is inherently associated with costs in terms of increased resource allocation to the longer structures, but not to benefits in terms of increased resource capture. Positive correlations among the length and plasticity of vertical and horizontal structures may explain the apparent positive effect of producing longer internodes on plant performance. Our data thus support the notion that trait correlations may weaken selective forces acting on a focal trait in a specific environment if opposing selection pressures act on genetically correlated traits.     

Predator induced life-history shifts in a freshwater cladoceran

Summary Life-history theory predicts that maturity and resource allocation patterns are highly sensitive to selective predation. Under reduced adult survival, selection will favour genotypes capable of reproducing earlier, at a smaller size and with a higher reproductive effort. When exposed to water that previously held fish, (size selective predators which prefer larger Daphnia), individuals of Daphnia hyalina reproduced earlier, at a smaller size and had a higher reproductive investment. Hence the prey was able to switch its life history pattern in order to become less susceptible to predation by a specific predator. The cue that evokes the prey response is a chemical released by the predator.     

Effects of microhabitat,time of day,and weather on predation of gypsy moth larvae

Summary Wire cages with different-sized meshes were placed on trunks and around leaves at different heights in oak trees and in forest litter. Gypsy moth, Lymantria dispar, instars II–V tethered with threads were placed in each cage (instars II–III only in leaf cages) as well as outside the cages. Predation of larvae decreased from near ground to mid-crown in trees and was highest in litter and very low on leaves. Predation in litter was not strongly related to cage type, suggesting that small, invertebrate predators were active there, but IV–V instars on trunks were mainly killed by relatively large predators, probably forest mice and shrews. Influences of the time of day and weather on predation were evaluated by observing tethered V–VI instars in litter and on tree trunks hourly. Ants, particularly carpenter ants (Camponotus ferrugineus) and Formica sp., and probably vertebrates, were conspicuous predators in the litter. Ants were most active at lower relative humidities, while other predators were apparently not influenced by humidity. No daily activity rhythms of predation were noted. Invertebrates appear to be important predators of larvae only in the litter whereas vertebrates, such as forest mice and shrews, also readily attack larvae on tree trunks.     

Regulation and modulation of electric waveforms in gymnotiform electric fish

Weakly electric gymnotiform fish specialize in the regulation and modulation of the action potentials that make up their multi-purpose electric signals. To produce communication signals, gymnotiform fish modulate the waveforms of their electric organ discharges (EODs) over timescales spanning ten orders of magnitude within the animal’s life cycle: developmental, reproductive, circadian, and behavioral. Rapid changes lasting milliseconds to seconds are the result of direct neural control of action potential firing in the electric organ. Intermediate-term changes taking minutes to hours result from the action of melanocortin peptides, the pituitary hormones that induce skin darkening and cortisol release in many vertebrates. Long-term changes in the EOD waveform taking days to weeks result from the action of sex steroids on the electrocytes in the electric organ as well as changes in the neural control structures in the brain. These long-term changes in the electric organ seem to be associated with changes in the expression of voltage-gated ion channels in two gene families. Electric organs express multiple voltage-gated sodium channel genes, at least one of which seems to be regulated by androgens. Electric organs also express multiple subunits of the shaker (Kv1) family of voltage-gated potassium channels. Expression of the Kv1 subtype has been found to vary with the duration of the waveform in the electric signal. Our increasing understanding of the mechanisms underlying precise control of electric communication signals may yield significant insights into the diversity of natural mechanisms available for modifying the performance of ion channels in excitable membranes. These mechanisms may lead to better understanding of normal function in a wide range of physiological systems and future application in treatment of disease states involving pathology of excitable membranes.     

入侵植物藿香蓟表型可塑性对种间竞争的响应

本文以恶性入侵植物藿香蓟（Ageratum conyzoides L.）与其伴生种紫苏（Perilla frutescens (L.) Britt.）为研究对象,分析不同种间竞争距离下藿香蓟功能性状的表型可塑性。结果显示：（1）较高的藿香蓟初始高度可显著减小其后续的相对株高生长（回归系数β = −0.137）,相对株高生长与其初始高度呈显著负相关,藿香蓟的株高生长速度显著高于紫苏;（2）竞争等级对藿香蓟收获时的地上生物量、比茎长和花蕾强度有显著影响（P < 0.05）,在竞争距离为5 cm时,藿香蓟比茎长和花蕾强度显著高于其他组别;（3）竞争的不对称性仅影响藿香蓟的比茎长,初始高度高于藿香蓟的紫苏株数越多,藿香蓟的比茎长就越长（β = 3.374）;（4）除高生长,藿香蓟其余7个性状均表现出较高的表型可塑性,变异系数CV值在0.17～0.55。藿香蓟综合表型可塑性在不同竞争距离下存在显著差异,在紫苏-藿香蓟距离为2.5 cm时,藿香蓟表型可塑性指数低,竞争距离为10或20 cm时,可塑性指数显著提高。综合来看,面对紫苏的近距离竞争（2.5 cm）,藿香蓟的生长和繁殖普遍受到抑制,表现为较低的表型可塑性。但随着竞争距离增加,藿香蓟能快速适应种间竞争,表型可塑性较高。在5 cm的竞争距离下,藿香蓟避阴反应强烈,可通过比茎长的增加在光资源获取上获得优势。     

Models of coral growth: spontaneous branching,compactification and the Laplacian growth assumption

In stony corals it is often observed that specimens collected from a sheltered growth site have more open and more thinly branched growth forms than specimens of the same species from more exposed growth sites, where stronger water currents are found. This observation was explained using an abiotic computational model inspired by coral growth, in which the growth velocity depended locally on the absorption of a resource dispersed by advection and diffusion (Kaandorp and Sloot, J. Theor. Biol 209 (2001) 257). In that model a morphological range was found; as the Péclet-number (indicating the relative importance of advective and diffusive nutrient transport) was increased, more compact and spherical growth forms were found. Two unsatisfactory items have remained in this model, which we address in the present paper. First, an explicit curvature rule was responsible for branching. In this work we show that the curvature rule is not needed: the model exhibits spontaneous branching, provided that the resource field is computed with enough precision. Second, previously no explanation was given for the morphological range found in the simulations. Here we show that such an explanation is given by the conditions under which spontaneous branching occurs in our model, in which the compactness of the growth forms depends on the ratio of the rates of growth and nutrient transport. We did not find an effect of flow. This suggests that the computational evidence that hydrodynamics influences the compactness of corals in laminar flows may not be conclusive. The applicability of the Laplacian growth paradigm to understand coral growth is discussed.     

Characteristics of African wild dog natal dens selected under different interspecific predation pressures

To successfully reproduce, many carnivorous mammals need access to suitable den sites. Den site selection is often based on fitness related criteria like escape from predators, food availability and shelter from extreme weather conditions. African wild dogs are cooperative breeders that use a den to give birth to their offspring. They often co-exist with lions and spotted hyenas, both of which are known to kill African wild dog pups. Little is known about den site selection by African wild dogs. In this study, we compared vegetation characteristics and distribution of roads and waterholes around den sites and random sites, in areas with high and low lion and spotted hyena densities. In both areas, African wild dogs selected den sites in closed woodland with little visibility, which is likely to reduce detection by predators, increase the likelihood of escape when detected, and might provide shelter from extreme weather conditions. In the high predator density area, African wild dogs seemed to spatially avoid predators by selecting den sites in this type of habitat relatively further away from waterholes and roads. African wild dogs have high energetic costs of gestation. Therefore, even when predation risk is relatively low, they are likely to try to maximise their fitness by choosing a den site in habitat that will provide optimal protection for their offspring, leaving little additional options to respond to a higher predation pressure.     

不同气味对虎皮鹦鹉取食行为影响

研究发现许多鸟类具有发育良好的嗅觉系统,但气味是否影响鸟类取食行为的研究报道较少。本研究开展了长尾林鸮（Strix uralensis）、金雕（Aquila chrysaetos）、家犬和家猫的粪便气味以及香水和香烟的气味对虎皮鹦鹉（Melopsittacus undulates）取食行为影响的比较研究。研究发现,虎皮鹦鹉在香水气味下的取食意图显著低于长尾林鸮粪便气味和无气味对照;在金雕粪便、猫粪便、香水及香烟气味下的取食频次显著低于无气味对照,同时香水及香烟气味下的取食频次显著低于长尾林鸮粪便气味,说明虎皮鹦鹉可能通过气味识别潜在的风险,进而调整取食行为。     

Patterns of Phenotypic Divergence in Wing Covariance Structure of Calopterygid Damselflies

Comparing species differences in covariance patterns of traits subject to divergent selection pressures can increase our understanding to the mechanisms of phenotypic divergence. Different species of calopterygid damselflies have diverged in the melanized wing patch of males. This trait serves multiple ecological functions and has behavioral consequences in terms of sexual selection, interspecific interactions, reproductive isolation. We compared the phenotypic variance-covariance matrices (P) of wing traits among nine populations of four European species of calopterygid damselflies. We found modest divergence in covariance structure among populations of the same species, but strong divergence between species. Interestingly, the orientation of the first eigenvector of P (P _max ) differed more between closely related species than between distantly related species, although this pattern was absent when overall covariance structures were compared. We also found that distantly related species but geographically closer had converged towards a similar covariance structure. Finally, divergence in covariance structure was correlated with divergence in wing patch length, but not with other wing traits. This last finding suggests that divergent selection on wing patch length might have affected the stability of P. These results indicate that P might not only reflect ancestral developmental pathways but might also be influenced by current ecology.     

Host selection by the pine processionary moth enhances larval performance: An experiment

The development of a phytophagous insect depends on the nutritional characteristics of plants on which it feeds. Offspring from different females, however, may vary in their ability to develop in different host species and therefore females should place their eggs on host plants that result in the highest performance for the insect offspring. Causes underlying the predicted relationships between host selection and offspring performance may be: (1) a genetic association between larval ability to exploit particular hosts and the female insect's host preference; and (2) phenotypic plasticity of larvae that may be due to (a) maternal effects (e.g. differential investment in eggs) or (b) diet. In this work, we analyse the performance (i.e. hatching success and larval size and mortality) of the pine processionary (Thaumetopoea pityocampa) caterpillar developing in Aleppo (Pinus halepensis) or maritime (Pinus pinaster) pines. Larvae of this moth species do not move from the individual pine selected by the mother for oviposition. By means of cross-fostering experiments of eggs batches and silk nests of larvae between these two pine species, we explored whether phenotypic plasticity of offspring traits or genetic correlations between mother and offspring traits account for variation in developmental characteristics of caterpillars. Our results showed that females preferentially selected Aleppo pine for oviposition. Moreover, the offspring had the highest probability of survival and reached a larger body size in this pine species independently of whether or not batches were experimentally cross-fostered. Notably, the interaction between identity of donor and receiver pine species of larvae nests explained a significant proportion of variance of larval size and mortality, suggesting a role of diet-induced phenotypic plasticity of the hatchlings. These results suggest that both female selection of the more appropriate pine species and phenotypic plasticity of larva explain the performance of pine processionary caterpillars.     

Environmental effects on adult growth patterns in the male sailfin molly,Poecilia latipinna (Poeciliidae)

Synopsis Widespread male body size variation in P. latipinna appears to be attributable to genetic variation in the size at maturation. The contribution of adult growth needs to be assessed because adult growth rates may vary with size at maturation and local environment. In our laboratory study we examined adult growth patterns as a function of size at maturation and juvenile experience (favorable or unfavorable conditions). In our field study we assessed adult growth as a function of initial size and environmental condition (using males in enclosures in contrasting habitats). Adult growth rates in the laboratory were an order of magnitude higher than rates observed in field enclosures. Growth rates varied with male size, increasing with increasing male size in the laboratory study but decreasing with increasing male size in the field study. The laboratory results alone would have cast considerable doubt on the ability to interpret size distributions of field-collected males, but the field results indicate that adult growth is sufficiently low that it can be ignored as a source of body size variation within and among populations.