The contribution of phenotypic plasticity to adaptation in Lacerta vivipara

Correlation between intraspecific phenotypic variability and variation of environmental conditions could reflect adaptation. Different phenotypes may result from differential expression of a genotype in different environments (phenotypic plasticity) or from expression of different genotypes (genetic diversity). Populations of Lacerta vivipara exhibit larger adult body length, lower age at maturity, higher fecundity, and smaller neonatal size in humid habitats compared to dry habitats. We conducted reciprocal transplants of juvenile L. vivipara to test for the genetic or plastic origin of this variation. We captured gravid females from four populations that differed in the relative humidity of their habitats, and during the last 2 to 4 weeks of gestation, we manipulated heat and water availability under laboratory conditions. Juveniles were released into the different populations and families were divided to compare growth rate and survival of half-sibs in two environments. Growth rate and survival were assessed using capture-recapture techniques. Growth rate was plastic in response to postnatal conditions and did not differ between populations of origin. Survival differed between populations of origin, partially because of differences in neonatal body length. The response of juvenile body length and body condition to selection in the different habitats was affected by the population of origin. This result cannot be simply interpreted in terms of adaptation; however, phenotypic plasticity of fecundity or juvenile size most probably resulted in adaptive reproductive strategies. Adaptation to the habitat by means of genetic specialization was not detected. Further investigation is needed to discriminate between genetic and long-term maternal effects.     

Seasonal patterns of acid fluctuations and resource storage in the arborescent cactus Opuntia excelsa in relation to light availability and size

Summary We investigated relationships between light availability, diel acid fluctuation, and resource storage in the arborescent cactus Opuntia excelsa growing in western Mexico. We compared canopy and understory individuals from a deciduous forest as well as open-grown plants of the same approximate size as those in the understory. During the wet season light availability and daily fluctuations in titratable acidity (an index of carbon uptake) were lower in the understory than in unshaded habitats. In the dry season all plants had reduced levels of acid fluctuation, with the smallest individuals, regardless of habitat, showing the greatest reduction. These data suggest that light availability in the forest understory constrains carbon assimilation during the wet season, but that a factor associated with plant size, possibly water status, limits carbon gain during the dry season. Plants in all habitats remained physiologically active for at least five months into the dry season. We suggest that this was possible due to the maintenance of constant concentrations of water and nitrogen in the photosynthetically active chlorenchyma. Parenchyma in terminal cladodes showed a different seasonal pattern of resource storage; water content and nitrogen concentration were reduced from the wet to the dry season in the parenchyma. Using the parenchyma to supply photosynthetic tissues during times of reduced resource availability allows O. excelsa to assimilate carbon during times of the year when most other trees in the forest are leafless.     

Gray-brown Mouse Lemurs (<Emphasis Type="Italic">Microcebus griseorufus</Emphasis>) as an Example of Distributional Constraints through Increasing Desertification

Climate change will impose new constraints on the distribution of species through desertification. Small-scale endemists common in biodiversity hotspots such as Madagascar are especially threatened. Among them are the gray-brown mouse lemurs (Microcebus griseorufus), which occupy the driest habitats in Madagascar of all Microcebus spp. We studied impacts of aridity on this species to identify critical factors for distributional limits. Accordingly, we compared populations of 2 adjacent habitats that differ in their humidity levels. We found that the more humid habitat provided more high-quality food and maintained a higher population density of Microcebus griseorufus, with individuals in better condition compared to the drier habitat. At the end of the wet, but not in the dry season, Microcebus griseorufus adjusted its home range size to local food plant density, which indicates that individuals optimize food intake in the wet season to prepare for the dry season. We found a negative exponential relationship between food plant density and home range size, which suggests an upper limit for the size of home ranges. According to this relationship, individuals from the drier habitat could not compensate for reduced food availability by enlarging their home range beyond this threshold. Thus, in case of declining food availability during the wet season due to a generally drier climate, individuals will not be able to extend their home ranges to include more food resources, and hence to accumulate enough fat reserves for the dry season. In consequence, they will have to migrate toward more mesic refugia. Migration, however, requires habitat connectivity, which is scarce in Madagascar’s largely anthropogenic and heavily fragmented landscape. Our data suggest that upper limits in home range sizes can limit a species’ ability to adapt to increasing aridity.     

Seedling stage strategies as a means of habitat specialization in herbaceous plants

The regeneration niche has been little investigated in studies of community assembly and plant distribution. We examined adaptive associations between seedling traits and habitat specialization. Two habitat contrasts were investigated across several evolutionary lineages of angiosperms: species specialized to forest vs. open habitats and to dry vs. wet habitats. We also tested whether effects of shade and drought vary independently or, alternatively, if shade may amplify effects on drought-stressed plants. Seedling response in terms of growth rate, height, slenderness, specific leaf area (SLA) and degree of elongation (longest internode; petiole or leaf-sheath depending on species' morphology) to light and watering treatments was assessed. We used a factorial design involving three light regimes and two watering frequencies. The open-shaded habitat contrast and the dry-wet habitat contrast were investigated using six and five pairs of congeneric species, respectively. The congeneric species pair design controlled for confounding effects of evolutionary history prior to divergence in habitat specialization. Seedling growth rate generally decreased with shade and reduced watering frequency. Plant height was generally largest at intermediate light. Specialization to shaded habitats was associated with a more conservative growth strategy, i.e. showing a more modest growth response to increasing light. Species from all habitats showed the highest relative elongation at intermediate light, except for the moist-habitat species, for which elongation increased with shade. Contrary to our expectations, species from dry habitats grew bigger than species from moist habitats in all treatments. SLA responded to the light treatment, but not to watering regime. The contrasting light and moisture conditions across habitats appear to not have selected for differences in SLA. We conclude that seedling phase strategies of resource allocation in temperate herbs contribute to their habitat specialization. Habitat-specific seedling strategies and trade-offs in response to resource availability and environmental conditions may be important to adaptive specialization.     

Ontogenetic and evolutionary effects of predation and competition on nine-spined stickleback (Pungitius pungitius) body size

1.?Individual- and population-level variation in body size and growth often correlates with many fitness traits. Predation and food availability are expected to affect body size and growth as important agents of both natural selection and phenotypic plasticity. How differences in predation and food availability affect body size/growth during ontogeny in populations adapted to different predation and competition regimes is rarely studied. 2.?Nine-spined stickleback (Pungitius pungitius) populations originating from habitats with varying levels of predation and competition are known to be locally adapted to their respective habitats in terms of body size and growth. Here, we studied how different levels of perceived predation risk and competition during ontogeny affect the reaction norms of body size and growth in (i) marine and pond populations adapted to different levels of predation and competition and (ii) different sexes. We reared nine-spined stickleback in a factorial experiment under two levels of perceived predation risk (present/absent) and competition (high/low food supply). 3.?We found divergence in the reaction norms at two levels: (i) predation-adapted marine stickleback had stronger reactions to predatory cues than intraspecific competition-adapted pond stickleback, the latter being more sensitive to available food than the marine fish and (ii) females reacting more strongly to the treatments than males. 4.?The repeated, habitat-dependent nature of the differences suggests that natural selection is the agent behind the observed patterns. Our results suggest that genetic adaptation to certain environmental factors also involves an increase in the range of expressible phenotypic plasticity. We found support for this phenomenon at two levels: (i) across populations driven by habitat type and (ii) within populations driven by sex.     

Plastic bet-hedging in an amphicarpic annual: an integrated strategy under variable conditions

Amphicarpy is a form of diversified bet-hedging expressed mostly in annual plants, where two types of offspring are produced with two distinct ecological roles: long-range aerial dispersers and highly competitive subterranean, sedentary fruit. Emex spinosa is a semi-arid, amphicarpic annual, inhabiting habitats with different levels of environmental variation. We tested the hypothesis that, in E. spinosa, bet-hedging may be “fine-tuned” by plasticity in the phenotype ratio (aerial/subterranean fruit mass) as a function of environmental conditions. We conducted a greenhouse experiment, manipulating nutrient availability and intraspecific density, to determine the pattern of ratio shifts. In order to determine whether the integrated strategy is an adaptation to variable habitats, a similar common garden experiment was conducted, comparing two natural populations differing in environmental variability. The offspring ratio shifted in response to both nutrient availability and plant density. In pots containing single plants the ratio increased steeply with nutrient availability, while in pots containing eight plants a more moderate increase occurred. These shifts were the result of plasticity in allocation to both achene types, as well as ontogenetic effects on aerial achene production. The degree of response increased with the heterogeneity of the habitat of origin. We found evidence for an adaptive integrated strategy, with bet-hedging “fine-tuned” by phenotypic plasticity. Strenuous conditions tended to shift the offspring ratio towards securing subterranean reproductive success, while favorable conditions resulted in a shift towards dispersible achenes. The authors Asaf Sadeh and Hagai Guterman contributed equally to this study.     

When the same is not the same: phenotypic variation reveals different plant ecological strategies within species occurring in distinct Neotropical savanna habitats

Variations in abiotic characteristics such as soil water availability and fertility impose different selective pressures on plant populations. This may produce intraspecific variability in functional traits, even at a fine spatial scale. We investigated whether functional traits related to water-use efficiency, resource-retention strategy, soil nutrient acquisition, and fire tolerance differ in species that occur in two different habitats of Brazilian Cerrado: rocky savannas and savanna woodlands. Rocky savannas occur over sandstone, quartzite outcrops and have shallow nutrient-poor and low-moisture rocky soils, while savanna woodlands occur over well-drained and deep soils with frequent fire regimes. We measured nine functional traits of 40 tree species that occur in both habitats. Rocky savanna individuals exhibited a greater water-use efficiency strategy. The resource-retention strategy in rocky savanna individuals was corroborated by lower adult maximum height. However, despite the lower nutrient availability in rocky savanna soils, we only detected lower leaf phosphorus content in individuals from this habitat. Furthermore, individuals from both habitats had equally thick bark, suggesting that the fire-defense strategy is related to a stable, rather than plastic trait. Overall, our results highlight the central role of contrasting soil water availability patterns in driving phenotypic plasticity within species. We conclude that savanna species are responding to water and nutrient availabilities, via plasticity in traits related to the resource-retention strategy, and preparing for future fires, via uniformly thick bark. Wide plant distribution in contrasting habitats is possible for species that can shift ecological strategies to survive in nutrient- and water-limited habitats such as rocky savannas.     

Water use efficiency of twenty-five co-existing Patagonian species growing under different soil water availability

The variation of plant water use efficiency (WUE) with water availability has two interacting components: a plastic response, evident when individuals of the same genotype are compared (e.g. wet versus dry years), and an interspecific response, evident when different species living in habitats with different water availability are compared. We analysed the WUE of 25 Patagonian species that belong to four life forms (grasses, shrubs, annual herbs and perennial herbs) in relation to the climatic conditions of 2 years and the mean historic water availability experienced by each species. To estimate water availability, we calculated the effective soil water potential (EWP) of each species, based on available information about soil water dynamics, phenology and root system structure. To estimate WUE, we used isotopic discrimination of leaf C (Δ¹³C) and mean annual water vapour difference between leaves and atmosphere (Δe) measured in situ. For the plastic response, for every species and life form, WUE increased from the dry to the wet year. We hypothesize that photosynthesis was less nutrient limited in the wet than in the dry year, facilitating higher net photosynthesis rates per unit of stomatal conductance in the wet year. For the interspecific response, WUE was lower in species native to drier habitats than in species native to wetter habitats. This response was mostly accounted for by a decrease in Δe with EWP. Annual herbs, which avoid drought in time (they have the earliest growth cycle), and shrubs, which avoid drought in space (they have the deepest roots), showed the highest EWP and WUE. We conclude that the conventional wisdom which states that the highest WUE occurs within a species during the driest years, and among species in the driest habitats, does not always hold true, and that co-existing life forms drastically differ in water availability and water economy.     

Secondary invasion of <Emphasis Type="Italic">Acer negundo</Emphasis>: the role of phenotypic responses versus local adaptation

During plant species invasions, the role of adaptive processes is particularly of interest in later stages of range expansion when populations start invading habitats that initially have not been disposed to invasions. The dioecious tree Acer negundo, primarily invasive in Europe in wet habitats along riversides and in floodplains, has increased its abundance in dry habitats of industrial wasteland and ruderal sites during the last decades in Eastern Germany. We chose 21 invasive populations from wet and from dry habitats in the region of Halle, Saxony-Anhalt, Germany, to test whether Acer negundo exhibits a shift in life-history strategy during expansion into more stressful habitats. We analyzed variables of habitat quality (pH, soil moisture, exchangeable cations, total C and N content) and determined density, sex ratio and regeneration of the populations. In addition, we conducted germination experiments and greenhouse studies with seedlings in four different soil moisture environments. Local adaptation was studied in a reciprocal transplant experiment. We found habitat type differentiation with lower nutrient and water supply at the dry sites than at the moist sites and significant differences in the number of seedlings in the field. In accordance, seeds from moist habitats responded significantly faster to germination treatments. In the transplant experiment, leaf life span was significantly larger for populations originating from dry habitat types than from moist habitats. This observed shift in life history strategy during secondary invasion of A. negundo from traits of establishment and rapid growth towards traits connected with persistence might be counteracted by high gene flow among populations of the different habitat types. However, prolonged leaf life span at dry sites contributed remarkably to the invasion of less favourable habitats, and, thus, is a first indication of ongoing adaptation.     

Changes in sexual selection resulting from novel habitat use in the sand goby

Resource availability may determine local breeding systems and may also vary locally between different habitats, affecting the way individuals distribute themselves between these habitats. For nest-breeding fishes, nest site availability is a crucial resource that has been found to affect local sexual selection regimes and thus breeding systems. In this study, we compared the availability and size distribution of nest sites and their consequences for habitat preference, fish distributions and the breeding system in sand gobies ( Pomatoschistus minutus ) breeding in two different habitats. The usual breeding sites of sand gobies are shallow sandy beaches, but here we report their breeding in a novel environment, on rocky bottoms. We found obvious differences between the two habitats. The density of occupied nests was nearly 50 times higher in rock habitat than on sand bottoms. However, competition for nest sites was stronger on sand; nearly all natural nest sites found were in use and empty nest sites were occupied at a much higher rate on sand than in rock habitat. In addition to the numerical differences, nests were larger and contained more eggs in rock habitat than in sand habitat. Moreover, we found significant habitat-specific differences in fish size distribution. The intensity of intrasexual competition as a result of the degree of nest site availability explains the observed patterns within the habitats, but not between them. These habitat-related differences are better explained by the larger average size of nests on rocky bottoms. The effect of nest size on habitat preference was confirmed experimentally by laboratory experiments. When nest size did not differ between the habitats, gobies originating in the two environments showed an equal preference for the sand habitat.     

VARIATION AMONG POPULATIONS OF XANTHIUM STRUMARIUM (COMPOSITAE) FROM NATURAL AND RUDERAL HABITATS

We assessed the mechanisms underlying the ability of cocklebur to spread from its natural riverside habitats and establish weedy populations in urban waste areas. We collected fruits from plants growing in natural and urban ruderal habitats and planted 2 maternal families from each of 9 habitat populations in 3 experimental gardens. The gardens were all in full sunlight but differed in the availability of water and nutrient resources. Plant performance in the gardens was measured by numbers and size of fruits produced. Traits known to be associated with cocklebur reproductive success were also measured: times to emergence and anthesis, photosynthetic capacity, mean stomatal conductance, relative growth rate, and biomass allocation to leaves and stems. Although there were significant differences among populations in the tradeoff between rate of growth in height and timing of anthesis, these population differences were not associated with habitat. Apart from a tendency to produce larger fruits in ruderal populations, there were no detectable differences in the characteristics of plants from natural vs. ruderal habitats. Plants from both habitats did have substantial and significant plastic responses to growth environment. In the three experimental gardens, fruit numbers increased with resource availability but fruit size did not differ significantly. As resource availability increased, plants from both habitats sustained growth longer and became more branchy. Canonical discriminant analysis of all the somatic and reproductive traits together supported the idea that natural and ruderal populations do differ in their overall plastic response to resource availability. The subtly different plastic responses of plants from the two habitats do not arise by substantial adjustments in a few dominant traits, but instead by relatively minor adjustments in a host of functionally interrelated phenological, morphological, and physiological traits. It is these small but coordinated differences in the plastic responses of many traits that appear to differentiate cocklebur from natural vs. weedy urban habitats.     

Evaporative water loss simulation improves models’ prediction of habitat suitability for a high-elevation forest skink

Accurate evaluation of habitat availability for wildlife is relevant for ecological applications. Researchers have frequently used models to simulate habitats thermally suitable for reptiles, but these results have limited application for species highly selective for habitat humidity. Here, we use the biophysical Niche Mapper™ model to investigate impacts of vegetation cover on the habitat quality of a high-elevation forest skink, Sphenomorphus taiwanensis, and to predict changes in habitat suitability in a future warmer climate (3 °C increase in air temperature). We assess habitat suitability with different densities of canopy cover in our study areas using two ecologically relevant estimates for lizards: maximum activity time and evaporative water loss (EWL) during the activity season. We measured preferred body temperature and EWL of this species for model parameterization, and behavioral response to EWL to supplement habitat quality assessment. The results indicated that this species is sensitive to EWL and reduces its activity when dehydrated. The model predicted that denser canopy levels increase microclimate cooling and humidity, and that most canopy levels are thermally suitable for this species, as the lizard can thermoregulate to manage adverse temperatures. Nevertheless, increasing canopy density could significantly decrease EWL during activity. In the warmer climate scenario, simulated maximum activity time and EWL changed little because of thermoregulation behavior. Our results suggest that habitat preference of this species is a consequence of water and energy requirements, and we note that combining EWL and maximum activity time data can enhance model accuracy of lizards’ habitat quality in a warmer climate.     

昆明地区滇蛙与昭觉林蛙同域分布种群的生境利用比较

现有两栖类生境研究报道多局限于定性描述,缺乏定量数据和统计分析支撑。以蛙的发现点为圆心,作半径1m的样圆,测量12个生态因子。调查共记录滇蛙(Ranapleuraden)133只和昭觉林蛙(Ranachaochiaoensis)62只。采用两独立样本t-检验和非参数Mann-WhitneyU-检验比较两种蛙对同一生境的利用,结果表明,在干燥草地生境仅最高植物高度差异显著;湿润草地生境至水源距离和水百分比差异极显著,水草百分比和湿泥百分比差异显著;水体生境各种生态因子的差异均不显著。主成分分析结果显示,在不同生境中滇蛙和昭觉林蛙所选择的因子往往相同或者顺序颠倒,但这些因子的值几乎均是反向分离的,即小生境不相同。两种蛙的生境利用各有偏好。滇蛙日间活动主要在水体,而昭觉林蛙则在湿润草地和干燥草地。两种蛙对泥地生境利用都少。不同体长的滇蛙对水体生境利用度均较高。昭觉林蛙随着体长增加,对隐蔽条件好的湿润草地和干燥草地生境利用度增加,对水体的利用度减少。     

Interclonal differences, plasticity and trade-offs of life history traits of Cyperus esculentus in relation to water availability

Cyperus esculentus is an exotic clonal (or pseudoannual) weed in Japan, and its range is steadily increasing. To investigate its interclonal variation and phenotypic plasticity in response to water availability, five clones of C. esculentus , collected from different sites in Japan, were grown singly in pots placed outdoors under dry and wet conditions. All the traits examined showed considerable variation among the five clones. However, two clones from Tochigi were similar to each other; thus, they might have originated from the same founder population. The clone from Ibaraki was quite different from the others. Therefore, it is suggested that the Japanese populations of C. esculentus might have resulted from multiple introductions of genotypes from geographically separated and, hence, genetically differentiated, source populations. All the clones also showed considerable plasticity in response to water availability. Clones with a larger ramet number had a greater plasticity, whereas tuber size was invariant across water treatments. Highly plastic traits had generally low interclonal variation in plasticity. All the clones had high productivity and produced more ramets and tubers under wet conditions than under dry conditions. Moreover, water availability could partially regulate the mode of its reproduction; wet conditions favored tuber production (vegetative propagation) while dry conditions favored sexual reproduction. A number of trade-offs occurred between the traits of clonal growth, storage and sexual reproduction, indicating that allocation among the competing functions/organs is mutually exclusive in plants. The results obtained here suggest that C. esculentus is more likely to invade wet habitats than dry habitats.     

Comparative dynamics of small mammal populations in treefall gaps and surrounding understorey within Amazonian rainforest

Variation in food resource availability can have profound effects on habitat selection and dynamics of populations. Previous studies reported higher food resource availability and fruit removal in treefall gaps than in the understorey. Therefore, gaps have been considered "keystone habitat" for Neotropical frugivore birds. Here we test if this prediction would also hold for terrestrial small mammals. In the Amazon, we quantified food resource availability in eleven treefall gaps and paired understorey habitats and used feeding experiments to test if two common terrestrial rodents ( Oryzomys megacephalus and Proechimys spp.) would perceive differences between habitats. We live-trapped small mammals in eleven gaps and understorey sites for two years, and compared abundance, fitness components (survival and per capita recruitment) and dispersal of these two rodent species across gaps and understorey and seasons (rainy and dry). Our data indicated no differences in resource availability and consumption rate between habitats. Treefall gaps may represent a sink habitat for Oryzomys where individuals had lower fitness, apparently because of habitat-specific ant predation on early life stages, than in the understorey, the source habitat. Conversely, gaps may be source habitat for Proechimys where individuals had higher fitness, than in the understorey, the sink habitat. Our results suggest the presence of source-sink dynamics in a tropical gap-understorey landscape, where two rodent species perceive habitats differently. This may be a mechanism for their coexistence in a heterogeneous and species-diverse system.     

Evaluating the role of contracting and expanding rainforest in initiating cycles of speciation across the Isthmus of Panama

Climatic and geological changes across time are presumed to have shaped the rich biodiversity of tropical regions. However, the impact climatic drying and subsequent tropical rainforest contraction had on speciation has been controversial because of inconsistent palaeoecological and genetic data. Despite the strong interest in examining the role of climatic change on speciation in the Neotropics there has been few comparative studies, particularly, those that include non-rainforest taxa. We used bird species that inhabit humid or dry habitats that dispersed across the Panamanian Isthmus to characterize temporal and spatial patterns of speciation across this barrier. Here, we show that these two assemblages of birds exhibit temporally different speciation time patterns that supports multiple cycles of speciation. Evidence for these cycles is further corroborated by the finding that both assemblages consist of 'young' and 'old' species, despite dry habitat species pairs being geographically more distant than pairs of humid habitat species. The matrix of humid and dry habitats in the tropics not only allows for the maintenance of high species richness, but additionally this study suggests that these environments may have promoted speciation. We conclude that differentially expanding and contracting distributions of dry and humid habitats was probably an important contributor to speciation in the tropics.     

Between- and within-population differences in Phragmites australis

Phragmites australis (common reed) is a dominant clonal species in the interface between land and water in many European wetlands. Along the land-water gradient, strong consistently different selective forces might operate to give rise to genetic substructuring. I have investigated the occurrence of genetic substructuring in European P. australis populations. The present paper examines whether seedlings, from seeds collected at both ends of the land-water gradient, showed differences in response to nutrient supply. Under controlled conditions, the relative growth rate (RGR) in the exponential growth phase, and growth characters of 10-week old seedlings were assessed. Among populations, no differences in response to nutrient supply were found. Although total dry weight was not related to the geographic origin of the populations, northern/western compared to southern/eastern European populations (1) formed more but shorter shoots, (2) formed thinner but longer rhizomes, and (3) invested more dry matter in leaves at the expense of stems. It was concluded that these trait differences are likely to originate from differences in the length of the growing season in the native habitat. Within populations, ’water-side’ seedlings had a higher RGR under sub-optimal while for ’land-side’ seedlings this was under optimal nutrient conditions. Ten-week-old ’water-side’ seedlings had a higher total dry weight than ’land-side’ ones, irrespective of nutrient loading. Differences in growth could not clearly be related to differences in single biomass allocation and morphological traits. A discriminant analysis on these traits, however, revealed that ’water-side’ seedlings showed higher plasticity in discriminant scores than ’land-side’ seedlings in response to nutrient supply. Discriminant scores also pointed towards a subtle trade-off between height versus expansion growth of seedlings, from the water to landward side. In the Romanian population, this could be related to morphological differences between ploidy levels. Overall, it was concluded that within populations, selection on growth form rather than on adaptations to the nutrient status of the habitat might have taken place. Received: 20 August 1998 / Accepted: 29 July 1999     

Ultraviolet light influences habitat preferences in a fish under predation risk

Environmental light conditions are of general importance in predator–prey interactions. In aquatic systems, prey individuals experience different levels of predation risk depending on the properties of the visual environment, such as structural complexity or water transparency. To reduce the threat of predation, prey should move to habitats providing better protection against visual predators. We studied the role of UV wavelengths in habitat choice behaviour under predation risk in a fish, the three-spined stickleback (Gasterosteus aculeatus) that uses UV signals in different contexts of intraspecific communication. In a laboratory experiment sticklebacks were exposed to a predatory threat and given the choice between two escape habitats, one providing full-spectrum conditions including UV light (UV+) and one without UV wavelengths (UV−). Fish from two rearing treatments were tested, one group had been raised under natural lighting conditions (UV+), the other group under UV-deficient lighting conditions (UV−). Sticklebacks from the UV+ group preferred the UV− habitat as a refuge which suggests that predator avoidance behaviour is UV-related in this species with UV− conditions presumably being advantageous for prey fish. However, individuals from the UV− treatment group were equally attracted to both presented light habitats. It is possible that these fish could not discriminate between the two light habitats due to physiological limitations caused by their rearing conditions. Further control trials with neutral-density filters revealed that the UV− habitat preference of UV+ fish in the main experiment was rather not influenced by a difference in achromatic brightness between the UV+ and UV− habitat.     

The morphological plastic response to water current velocity varies with age and sexual state in juvenile Atlantic salmon, Salmo salar

1. Salmonids, like many other fish species, exhibit morphological plasticity to variations in water current velocity. However, little is known about how this response varies with age and alternative sexual tactics that usually coexist in the same area. We therefore sampled immature 1- and 2-year-old and sexually mature Salmo salar parr to determine how the morphological response to slow and rapid water currents varies across these groups.
2. Both 1- and 2-year-old immature parr in rapid habitats can be distinguished from individuals in slow habitats using a combination of fin measurements. In contrast, body shape measurements were useful only to distinguish 2-year-old individuals in the different habitat types. We also showed that mature parr are notably robust, irrespective of habitat type. For these individuals, only their body length differed between slow and rapid water currents, being bigger in slow water currents.
3. Our results imply that fins are the first structures to respond to water current velocity, followed by changes in body shape as individuals grow bigger. The robust phenotype observed for mature parr is likely to pose extra limitations on movement due to an increase in drag forces, thus contributing to their smaller size in rapid water currents.     

Do clonal growth form and habitat origin affect resource-induced plasticity in Tibetan alpine herbs?

To investigate how growth form and habitat origin affect phenotypic plasticity to resource supply in the Tibetan alpine herbs, the phalanx-type species Stipa capillacea and the guerilla-type species Carex montis-everestii were sampled from two different habitats (alpine steppe and alpine scrubland) and grown under three levels of light intensity and two levels of nutrient supply. Interspecific differences in light-induced plasticity were detected only in number of ramets, specific leaf area and leaf sheath length. Plasticity in plant biomass, number of ramets and rhizome length in response to light intensity differed between the two habitats. Stipa plants were more plastic than Carex plants in number of ramets and specific leaf area in response to light intensity. Carex plants from the alpine scrubland expressed greater light-induced plasticity in plant biomass and number of ramets than those from the alpine steppe, and Stipa plants showed less interhabitat differences in plasticity, which may be closely related to their contrasting growth forms. Clonal growth form and habitat origin affected nutrient-induced plasticity in none of the measured traits. It may be the guerilla growth form that makes Carex plants more efficiently adapted to highly heterogeneous light conditions in scrubland, and less habitat-dependent plasticity contributes to success of the phalanx-type Stipa plants in alpine habitats. The results are discussed in the context of foraging for heterogeneously distributed essential resources and adaptation to habitat origin.