Adaptive sex-specific life history plasticity to temperature and photoperiod in a damselfly

We investigated four predictions about how temperature, photoperiod and sex affect the life history plasticity and foraging activity of a damselfly. (i) As predicted, increased temperatures increased foraging activity and growth rates, but in contrast with the prediction, late photoperiod (high time stress) did not affect foraging activity and growth rate. (ii) Unexpectedly, the increase in growth rate at increasing temperatures was not larger under high time stress. (iii) As predicted, age and size at emergence decreased at higher temperatures and at the late photoperiod. Temperature-induced life history shifts were direct or the result of behavioural growth mediation depending on the temperature range. Photoperiod-induced life history shifts were direct. (iv) As predicted, males emerged before females but at a smaller size. The degree of sexual size dimorphism was influenced by the joint effects of temperature and photoperiod. We could only detect genetic variation in size plasticity to photoperiod. The match between the sex-specific life history responses to temperature and photoperiod and predictions by relevant optimality models suggests adaptive life history plasticity to these variables.     

Growth temperature and phenotypic plasticity in two Drosophila sibling species: probable adaptive changes in flight capacities

In the sibling species Drosophila melanogaster and D. simulans, growth and development at constant temperatures, from 12 to 30 °C, resulted in extensive variations of adult size and flight parameters with significant differences between species. Changes in body weight, thorax length and wing length were nonlinear, with maximum values of each trait at lower temperatures for D. simulans than for its sibling species. By contrast, the wing/thorax ratio and the wing loading varied monotonically with growth temperature. These traits were negatively correlated, the wing/thorax ratio decreasing with growth temperature while the wing loading increased. Wing/thorax ratio, which is easier to measure, thus appears as a convenient predictor of wing loading. During tethered flight at the same ambient temperature, the wingbeat frequency changed linearly as a function of the wing moment of inertia. More interestingly, the beat rate was strongly correlated with the increase of wing loading at growth temperature above 13 °C. The likely adaptive significance of these morphometrical changes for flight efficiency is discussed.     

Growth and ion accumulation of two rapid-cycling Brassica species differing in salt tolerance

The response of two rapid-cycling Brassica species differing in tolerance to seawater salinity was studied over a period of 24 days. In response to 8 dS m⁻¹ salinity, the two Brassica species showed clear differences in the changes in relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR). The RGR of B. napus was slightly reduced by salinity, wheareas the RGR of B. carinata was largely reduced in the early stages of salinization. LAR of B. napus was affected by salinity in the later stages of growth and significantly correlated with the reduction in RGR. On the other hand, the NAR of B. carinata was decreased by salinity, corresponding to the decrease of the RGR of B. carinata. The NAR of B. napus was not significantly affected by salinity according to analysis of covariance. The shoot concentrations of Na, Mg and Cl increased while the concentrations of K and Ca decreased sharply during the first 5 days of salinization; subsequently, all ion concentrations remained relatively constant. The concentrations of Na, K, Ca, Mg and Cl in the root were similarly affected by salinity. There were no significant differences of ion concentrations between species that could be related to the differences in salt tolerance. Thus, the differences in salt tolerance between species can not be related to differences in specific-ion effects, but may be related to some factor that reduces the NAR of B. carinata during the early stages of growth.     

Cortical contributions to olfaction: plasticity and perception

In most sensory systems, the sensory cortex is the place where sensation approaches perception. As described in this review, olfaction is no different. The olfactory system includes both primary and higher order cortical regions. These cortical structures perform computations that take highly analytical afferent input and synthesize it into configural odor objects. Cortical plasticity plays an important role in this synthesis and may underlie olfactory perceptual learning. Olfactory cortex is also involved in odor memory and association of odors with multimodal input and contexts. Finally, the olfactory cortex serves as an important sensory gate, modulating information throughput based on recent experience and behavioral state.     

The feeding behaviour of some common lotic insect species in two streams of differing detrital content

The trophic relationships of the benthic invertebrates at two places of differing detrital content in an oligotrophic stream system were examined during a 12 month period.
The sites are described and their detrital contents and other abiotic features compared.
The faunal list at each site is fairly similar but certain species are more common at or restricted to one or other site. The reasons for this are briefly discussed.
The predators and omnivores are in two groups: the first feed only on certain prey and are thus limited by the distribution of their prey. The others consume a wide range of prey and have wider distributions.
The predator species are non-selective in their choice of prey which are devoured in an intensity which cannot however be related to their density in the benthos.
In poorer trophic conditions predators adapt by consuming a greater quantity of algae and detritus; cannibalism and interpredator-predation occur. The prey species are more intensely consumed under poor trophic conditions.
The ecology of two species of predatory Plecoptera is examined and the results indicate that competition probably occurs between them.     

Growth and phenotypic plasticity of two tropical tree species under low light availability

两种热带树种在弱光条件下的生长和表型可塑性 根据耐荫性筛选热带雨林树种,对于在次生林富集区域中更有效地管理具有经济意义的本土树种非常重要。本研究旨在确定全株的光补偿点,比较弱光条件下Cariniana legalis和Gallesia integrifolia 幼苗生长和碳分配有关的表型可塑性。实验所用幼苗在5种光合有效辐射条件下(0.02、1.1、2.3、4.5 和5.9 mol photons m⁻² day⁻¹)培养77天,设置3个重复,并分析了生长和碳分配变量指标。结果显示,在 1.1 mol photons m⁻² day⁻¹ 条件下,C. legalis 的生长速率高于G. integrifolia,而在5.9 mol photons m⁻² day⁻¹ 条件下,C. legalis的生长速率低于G. integrifolia。不同物种间的光补偿点差异显著。根据耐阴分类标准对这两种热带树种进行分类,我们的研究结果表明,C. legalis相对较低的光补偿点和表型可塑性与生长速率有关,比G. integrifolia具有更强的耐荫性。从实际的角度来看,我们证明了两种树种之间生长和光合有效辐射变化的不同关系可以成为在森林丰富工程中比较和选择种植树种的可行工具     

Thermal reaction norms in two Coenagrion damselfly species: contrasting embryonic and larval life-history traits

1. We studied the temperature‐dependence of important life‐history traits both at the embryonic (egg hatching success, embryonic development time and hatchling size) and the larval stage (larval growth rate, larval survival and larval size after 100 days) using full‐sib families of two congeneric damselflies, Coenagrion hastulatum and Coenagrion puella, that differ in latitudinal distribution. Larvae were reared in the laboratory from the egg stage at four temperatures (12, 17, 22 and 27 °C). 2. The observed patterns of thermal plasticity in embryonic traits showed that the northern species was more successful than the southern species at lower temperatures, in line with the pattern of temperature adaptation in thermal reaction norms. 3. At the larval stage, we found no consistent pattern of latitudinal compensation. The thermal family reaction norms indicate, however, the potential for latitudinal compensation to evolve. We observed an ontogenetic shift in thermal optima for larval growth rate, with a higher optimal temperature for growth rate during the first 2 weeks of the larval stage. 4. This is the first indication of the existence of latitudinal compensation at the interspecific level in an invertebrate; it is stage‐specific, being present only in the embryonic stage. We argue that compensation in the embryonic stage may be much more likely than in the larvae and stress the importance of including more then one life‐history stage when drawing conclusions about the adaptiveness of patterns in thermal reaction norms.     

Immune response to nylon filaments in two damselfly species that differ in their resistance to ectoparasitic mites

1. Insects commonly resist parasites using melanotic encapsulation. Many studies measuring immune response use the amount of melanin deposited on an artificial object that has been inserted into the animal as a proxy of the amount of resistance that the host is capable of mounting to natural parasites. 2. The relevance of this methodology to immune response in natural insect populations needs further study. Here, we examined two temperate damselfly species to elucidate the relationships among damselfly size, natural resistance to mites, and the immune response mounted by the same damselflies against nylon filaments. 3. The damselfly species that had high rates of melanotic encapsulation of mites in nature deposited more melanin on the nylon inserts than the species with low rates of natural resistance. 4. In females of this species, those that had resisted mites naturally melanised the nylon filament more aggressively than those that did not resist mites. 5. Our results show some support for the use of nylon filaments to assess natural patterns of immune response in these damselflies, but also suggest that caution should be used in interpreting the responses.     

Phenotypic plasticity and biogeographic variation in physiology of habitat‐forming seaweed: response to temperature and nitrate

Southeastern Australian waters are warming at nearly four times the global average rate (~0.7°C · century^?1) driven by strengthening incursions of the warm oligotrophic East Australian Current. The growth rate hypothesis (GRH) predicts that nutrient depletion will impact more severely on seaweeds at high latitudes with compressed growth seasons. This study investigates the effects of temperature and nutrients on the ecophysiology of the habitat‐forming seaweed Phyllospora comosa in a laboratory experiment using temperature (12°C, 17°C, 22°C) and nutrient (0.5, 1.0, 3.0 μM NO₃^?) scenarios representative of observed variation among geographic regions. Changes in growth, photosynthetic characteristics (via chlorophyll fluorescence), pigment content, tissue chemistry (δ¹³C, % C, % N, C:N) and nucleic acid characteristics (absolute RNA and DNA, RNA:DNA ratios) were determined in seaweeds derived from cool, high‐latitude and warm, low‐latitude portions of the species’ range. Performance of P. comosa was unaffected by nitrate availability but was strongly temperature‐dependent, with photosynthetic efficiency, growth, and survival significantly impaired at 22°C. While some physiological processes (photosynthesis, nucleic acid, and accessory pigment synthesis) responded rapidly to temperature, others (C/N dynamics, carbon concentrating processes) were largely invariant and biogeographic variation in these characteristics may only occur through genetic adaptation. No link was detected between nutrient availability, RNA synthesis and growth, and the GRH was not supported in this species. While P. comosa at high latitudes may be less susceptible to oligotrophy than predicted by the GRH, warming water temperatures will have deleterious effects on this species across its range unless rapid adaptation is possible.     

Sexual comparisons in immune ability, survival and parasite intensity in two damselfly species

Recent evolutionary studies have suggested that females have a more robust immune system than males. Using two damselfly species (Hetaerina americana and Argia tezpi), we tested if females produced higher immune responses (as phenoloxidase and hydrolytic enzymes), had a higher survival (using a nylon implant inserted in the abdomen and measuring survival after 24h) and fewer parasites (gregarines and water mites) than males. We also tested whether immune differences should emerge in different body areas (thorax vs. abdomen) within each sex with the prediction that only females will differ with the abdomen having a higher immune response than their thorax since the former area, for ecological and physiological reasons, may be a target zone for increased immune investment. Animals were adults of approximately the same age. In both species, females were more immunocompetent than males, but only in H. americana females were immune responses greater in the abdomen than in the thorax. However, there were no differences in survival and parasite intensity or the probability of being parasitised between the sexes in either of the two species. Thus, this study lends partial support to the principle that females are better at defending than males despite the null difference in parasitism and survival.     

Integrating life history and physiology to understand latitudinal size variation in a damselfly

Our understanding of latitudinal life history patterns may benefit by jointly considering age and mass at maturity and growth rate. Additional insight may be gained by exploring potential constraints through pushing growth rates to their maximum and scoring physiological cost‐related variables. Therefore, we reared animals of a univoltine Spanish and Belgian population and of a semivoltine Swedish population of the damselfly Enallagma cyathigerum (spanning a latitude gradient of ca 2350 km) in a common environment from the eggs until adult emergence and exposed them to a transient starvation period to induce compensatory growth. Besides age and mass at maturity and growth rate we also scored investment in energy storage (i.e. triglycerides) and immune function (i.e. total activity of phenoloxidase). At emergence, body mass was greater in Spain and Sweden and lower in Belgium, suggesting a genetic component for the U‐shaped latitudinal pattern that was found also in a previous study based on field‐collected adults. The mass difference between univoltine populations can be explained by the shorter development time in the Belgian population, and this despite a higher growth rate, a pattern consistent with undercompensating countergradient variation. In line with the assumed shorter growth seasons, Belgian and Swedish animals showed higher routine growth rates and compensatory growth after transient starvation. Despite a strong link with metabolic rates (as measured by oxygen consumption) populations with higher routine growth rates had no lower fat content and had higher immune function (i.e. immune function decreased from Sweden to Spain), which was unexpected. Rapid compensatory growth did, however, result in a lowered immune function. This may contribute to the absence of perfect compensating countergradient variation in the Belgian population and the lowest routine growth rates in the Spanish population. Our results underscore the importance of integrating key life historical with physiological traits for understanding latitudinal population differentiation.     

Behavioural effects of temperature on ectothermic animals: unifying thermal physiology and behavioural plasticity

Temperature imposes significant constraints on ectothermic animals, and these organisms have evolved numerous adaptations to respond to these constraints. While the impacts of temperature on the physiology of ectotherms have been extensively studied, there are currently no frameworks available that outline the multiple and often simultaneous pathways by which temperature can affect behaviour. Drawing from the literature on insects, we propose a unified framework that should apply to all ectothermic animals, generalizing temperature's behavioural effects into: (1) kinetic effects, resulting from temperature's bottom‐up constraining influence on metabolism and neurophysiology over a range of timescales (from short to long term), and (2) integrated effects, where the top‐down integration of thermal information intentionally initiates or modifies a behaviour (behavioural thermoregulation, thermal orientation, thermosensory behavioural adjustments). We discuss the difficulty in distinguishing adaptive behavioural changes from constraints when observing animals' behavioural responses to temperature. We then propose two complementary approaches to distinguish adaptations from constraints, and categorize behaviours according to our framework: (i) ‘kinetic null modelling’ of temperature's effects on behaviour; and (ii) behavioural ecology experiments using temperature‐insensitive mutants. Our framework should help to guide future research on the complex relationship between temperature and behaviour in ectothermic animals.     

Growth rate and physiology of Yersinia enterocolitica; influence of temperature and presence of the virulence plasmid

The effect of temperature on the growth rate, protein pattern and fatty acid composition of Yersinia enterocolitica strain W22703 pYV⁺, its plasmidless isogenic derivative W22703 pYV^- and four recent field isolates was examined.
The growth rate was clearly influenced by presence or absence of the virulence plasmid: pYV^- strains grew consistently faster than pYV⁺ strains. This difference in growth rate was high at 30–35°C, moderate at 1–10°C and 25°C, but hardly significant at 15–20°C.
Increasing the growth temperature above 25°C resulted in the induction of the 220 kDa virulence plasmid-encoded Yop1 protein. In the 1–20°C range no obvious temperature- or plasmid-related differences in protein patterns could be detected.
The fatty acid composition showed a clear temperature-dependent change: with all strains the degree of saturation was low at 1°C and gradually increased with raising temperatures. All strains had similar fatty acid patterns, except one of the field isolates which showed aberrant C16 : 1 and cyclic fatty acid contents in the 5–25°C and 15°C ranges respectively. With strain W22703, the presence or absence of the virulence plasmid did not significantly alter the fatty acid pattern.     

Growth temperature and genetic variability of wing dimensions in Drosophila: opposite trends in two sibling species

Thirteen linear wing dimensions were measured in 10 isofemale lines of Drosophila melanogaster and D. simulans grown at seven constant temperatures from 12 to 31 degrees C. Within-line (environmental) variability, estimated by the within-line coefficient of variation (CVw), exhibited similar variation patterns in the two species, that is higher values at extreme (low or high) temperatures. The magnitude of variation was, however, greater in D. simulans, which appears to be more responsive to thermal change. A clear hyperbolic relationship between trait mean value and CVw was also observed in both species, arising from measurement errors which are relatively more pronounced on shorter traits. Genetic variability was analysed by considering both the genetic CV (CVg, evolvability) and isofemale line heritability (intraclass correlation). Both parameters provided independent information, as shown by a lack of correlation between them. Moreover, CVg was negatively correlated with trait mean value, while heritability showed a positive correlation. With respect to thermal environment, both parameters exhibited similar reaction patterns which contrasted the two species. Genetic variability in D. melanogaster followed a convex reaction norm, with higher values at extreme (high or low) temperatures, and this observation agrees with previous independent investigations. Surprisingly, D. simulans revealed an opposite pattern, with a maximum genetic variability in the middle of the range. Such data point to the danger of drawing general conclusions from the analysis of a single species.     

Chemical composition of 24 wild species differing in relative growth rate

The chemical composition of 24 plant species which showed a three-fold range in potential growth rate was investigated. The carbon content of whole plants was lower for fast-growing species than for slow-growing ones. Fast-growing species accumulated more organic N-compounds, organic acids and minerals, whereas slow-growing species accumulated more (hemi)cellulose, insoluble sugars and lignin. No correlations with relative growth rate were found for soluble phenolics, soluble sugars and lipids. The costs to construct 1 g of plant biomass were rather similar for fast- and slow-growing species, both when expressed as C needed for C-skeletons, as glucose to provide ATP and NAD(P)H, and as total glucose costs. Therefore, we conclude that, despite the differences in chemical composition between fast- and slow-growing species, variation in the costs of synthesis of whole plant biomass cannot explain interspecific variation in relative growth rate of herbaceous species.     

Phenotypic plasticity of body size in Drosophila: effects of a daily periodicity of growth temperature in two sibling species

Abstract. Variation of wing and thorax length under thermoperiodic growth conditions was analysed in four strains of two sibling species, Drosophila melanogaster and D. simulans , from two European localities. Results were compared to those obtained with constant temperatures ranging from 12 to 31 °C.
Under constant temperatures the data basically confirmed previous results: concave reaction norms for wing and thorax length; a monotonically decreasing norm for wing : thorax ratio; and an increasing norm for sex dimorphism (female : male ratio). Phenotypic variability was maximum at extreme temperatures and minimum at middle ones. Slight differences were observed according to the geographical origin: the difference between strains from Bordeaux (France) and Cordoba (Spain) was maximum at low temperatures but disappeared at about 28 °C.
According to the temperatures chosen, alternating thermal regimens had either no effect or produced a significant size reduction, probably reflecting a periodic stress. The magnitude of this effect was proportional to the amplitude of the thermoperiod but not to the quality (cold or heat) of the stress. In a similar way, the wing : thorax ratio was either not modified or reduced significantly, indicating that wing length was relatively more affected than thorax length by alternating thermal regimens. Sex dimorphism also showed either no change or a significant increase, indicating that males were relatively more reactive than females to alternating conditions. Finally, regimens of broad amplitudes increased the phenotypic variability, again an indication of stressful effects. All these observations should be taken into account when analysing phenotypic variability in nature and trying to understand natural selection in wild-living populations.     

Behavioural activity levels and expression of stress proteins under predation risk in two damselfly species

Abstract 1. It has become apparent that predators may strongly decrease prey fitness without direct contact with the prey, as they induce the development of defence systems that limit the availability of energy for growth and reproduction. Recent studies suggest that stress proteins may help prey organisms deal with this stress. The pattern is not general, however, and little is known about species differences in physiological traits in coping with predator stress, and covariation of physiological with other antipredator traits. 2. To explore these issues, we quantified levels of constitutive and fish‐induced stress proteins (Hsp60 and Hsp70) and anti‐predator behaviours in larvae of two damselfly species that differ in lifestyle. Both stress proteins were fixed at higher levels in Erythromma najas, which has a slow lifestyle, than in Lestes sponsa, which has a fast lifestyle. Similarly, anti‐predator behaviours were fixed at safer levels in E. najas than in L. sponsa. 3. These results suggest that stress proteins may be part of anti‐predator syndromes of damselfly larvae, and there may be trait co‐specialisation between stress proteins and behavioural anti‐predator traits. Studies formally testing these hypotheses in more species may prove rewarding in advancing our understanding of the functional integration of physiological anti‐predator traits in relation to the prey’s lifestyle.     

Seasonal time constraints shape life history,physiology and behaviour independently,and decouple a behavioural syndrome in a damselfly

The integration of traits into ‘syndromes' has been suggested as a useful framework to advance insights in trait responses to environmental stressors. Yet, how stressors shape the consistency (‘repeatability') of traits and their covariation at the individual level remains debated. We studied how seasonal time constraints shape trait repeatability and integration of life-history, behavioural and physiological traits along a fast–slow continuum, using the ‘pace-of-life syndrome' as a framework. We manipulated the photoperiod during the larval development of the damselfly Ischnura elegans, generating a time-relaxed early, a control, and a time-constrained late group. The photoperiod treatment did not seem to affect the voltinism of the larvae. As predicted, late-period larvae accelerated development and growth, yet this acceleration was no longer detectable for growth and metabolic rate during the final instar, possibly due to costs of the initial life-history acceleration. This warrants caution when inferring a species' pace-of-life based on a specific developmental stage. The late-period larvae were as predicted more active (only during the later stages of the final instar) and bolder than the control larvae, but not different from the early-period larvae. Most studies on time constraints only compared late and control animals, thereby potentially wrongly concluding adaptive responses to time constraints. Activity, boldness and body mass were repeatable, while growth and metabolic rates were not. Notably, repeatabilities did not change under time constraints. There was no support for an overall trait integration in a pace-of-life syndrome, yet activity and boldness covaried positively as expected. Importantly, this ‘behavioural syndrome' was decoupled in the late-period larvae, which might be adaptive to enhance energy acquisition to fuel the accelerated development rate. Our results suggest that besides the predicted plastic acceleration of life-history, plastic changes in behavioural trait integration may also be an important but overlooked adaptive aspect of responding to time constraints.     

Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate

Summary Which factors cause fast-growing plant species to achieve a higher relative growth rate than slow-growing ones? To answer this question 24 wild species were grown from seed in a growth chamber under conditions of optimal nutrient supply and a growth analysis was carried out. Mean relative growth rate, corrected for possible ontogenetic drift, ranged from 113 to 356 mg g^–1 day^–1. Net assimilation rate, the increase in plant dry weight per unit leaf area and unit time, varied two-fold between species but no correlation with relative growth rate was found. The correlation between leaf area ratio, the ratio between total leaf area and total plant weight, and relative growth rate was very high. This positive correlation was mainly due to the specific leaf area, the ratio between leaf area and leaf weight, and to a lesser extent caused by the leaf weight ratio, the fraction of plant biomass allocated to the leaves. Differences in relative growth rate under conditions of optimum nutrient supply were correlated with the soil fertility in the natural habitat of these species. It is postulated that natural selection in a nutrient-rich environment has favoured species with a high specific leaf area and a high leaf weight ratio, and consequently a high leaf area ratio, whereas selection in nutrient-poor habitats has led to species with an inherently low specific leaf area and a higher fraction of root mass, and thus a low leaf area ratio.