Is black plumage an adaptation to high elevations in a cosmopolitan bird genus?

Black plumage is expected to absorb and retain more heat and provide better protection against UV radiation compared with lighter plumages. Black plumage is common in species of the genera Turdus and Platycichla that inhabit highlands across different regions of the world. Considering this geographical recurrent pattern we tested the hypothesis that black plumage in these two genera has evolved as a co‐adaptive response to inhabiting highlands, reconstructing ancestral character states for plumage and altitudinal distribution using maximum‐likelihood methods, and a Pagel's multistate discrete method. For these analyses, we used a phylogeny based on mitochondrial and nuclear DNA regions that included 60 of the 66 recognized species in the genera Turdus and Platycichla. We found that black‐plumage coloration evolved independently on eight occasions within these two genera, and species with black plumage occur more often at highlands. Our results support the hypothesis that black‐plumage is adaptative in highlands; but, studies in other bird groups with black‐plumage inhabiting at the same elevations will provide evidence for this adaptive hypothesis or if the evolution of black‐plumage in other groups is explained by other evolutionary forces.     

Is long-lived foliage in Picea mariana an adaptation to nutrient-poor conditions?

Summary This study evaluated the contribution of different ages of foliage to the nutrient and carbon balance of black spruce (Picea mariana (Mill.) B.S.P.) from a nutrient-poor peatland in Alberta. Seasonal patterns of foliar nitrogen and phosphorus concentration and content were examined in six needle cohorts up to 10 years old. Trees were treated to simulate excess nutrient deficiency (removal of all one-year-old foliage), nutrient excess (fertilized with 250, 50, 100 kg ha^–1 NPK split application in June and July), or left as controls. Gas exchange (net assimilation-Na, stomatal conductance-g_s, mesophyll conductance-g_m, water-use efficiency-WUE, dark respiration-RS) was measured on six different needle cohorts in several control trees in 1989 and 1990. Nitrogen and phosphorus concentration decreased with needle age. Foliar nutrient concentration fell from April to June and then was stable until September except for the fertilized trees where it increased. There was no evidence of greater than normal retranslocation of nutrients from older needles for defoliated trees or greater than normal nutrient loading in older needles of fertilized trees. NA, g_s, g_m, WUE, and RS were similar for all needles up to six or eight years old, these older needles having NA of 65% of current needles and similar RS. The results do not support to conclusion that older needles of black spruce are retained as an adaptation to nutrient stress. It does not appear that older needles serve as a nutrient storage site in conditions of excess nutrient availability or a greater than normal nutrient source during times of excess nutrient deficiency. It appears that the maintenance of long-livedfoliage in black spruce does not provide for greater flexibility in tree nutrient allocation. Their contribution to the carbon balance of the tree seems to be sufficient to explain their retention.     

Is non‐loglinear allometry a statistical artifact?

The allometric equation, y = ax^b, is commonly fitted to data indirectly by transforming predictor (x) and response (y) variables to logarithms, fitting a straight line to the transformations, and then back‐transforming (exponentiating) the resulting equation to the original arithmetic scale. Sometimes, however, transformation fails to linearize the observations, thereby giving rise to what has come to be known as non‐loglinear allometry. A smooth curve for observations displayed on a log–log plot is usually interpreted to mean that the scaling exponent in the allometric equation is a continuously changing function of body size, whereas a breakpoint between two (or more) linear segments on a log–log plot is typically taken to mean that the exponent changes abruptly, coincident with some important milestone in development. I applied simple graphical and statistical procedures in re‐analyses of three well‐known examples of non‐loglinear allometry, and showed in every instance that the relationship between predictor and response can be described in the original scale by simple functions with constant values for the exponent b. In no instance does the allometric exponent change during the course of development. Transformation of data to logarithms created new distributions that actually obscured the relationships between predictor and response variables in these investigations, and led to erroneous perceptions of growth. Such confounding effects of transformation are not limited to non‐loglinear allometry but are common to all applications of the allometric method. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Does ozone increase ABA levels by non‐enzymatic synthesis causing stomata to close?

Reactive oxygen species (ROS) are widely recognized as important regulators of stomatal aperture and plant gas exchange. The pathways through which stomata perceive ROS share many common linkages with the well characterized signalling pathway for the hormone abscisic acid (ABA), a major driver of stomatal closure. Given reports that ABA receptor mutants have no stomatal response to ozone‐triggered ROS production, as well as evidence that all steps in the ABA biosynthetic pathway can be non‐enzymatically converted by ROS, here we investigated the possibility that ozone closes stomata by directly converting ABA precursors to ABA. In plants where stomata were responsive to ozone, we found that foliar ABA levels rapidly increased upon exposure to ozone. Recovery of gas exchange post‐exposure occurred only when ABA levels declined. Our data suggest that stomatal closure in response to ozone exposure occurs as a result of direct oxidation of ABA precursors leading to ABA production, but the importance of this ROS interaction remains uncertain under normal photosynthetic conditions.     

Is increased maternal basking an adaptation or a pre-adaptation to viviparity in lizards?

Pregnant females modify their thermoregulatory behaviour in many species of viviparous (live-bearing) reptiles, typically maintaining higher and more stable body temperatures at this time. Such modifications often have been interpreted as adaptations to viviparity, functioning to accelerate embryonic development and/or modify phenotypic traits of hatchlings. An alternative possibility is that similar maternal thermophily may be widespread also in oviparous species and if so, would be a pre-adaptation (rather than an adaptation) to viviparity. Because eggs are retained in utero for a significant proportion of development even in oviparous reptiles, maternal thermophily might confer similar advantages in oviparous as in viviparous taxa. Experimental trials on montane oviparous scincid lizards (Bassiana duperreyi) support the pre-adaptation hypothesis. First, captive females (both reproductive and non-reproductive) selected higher temperatures than males. Second, experimentally imposing thermal regimes on pregnant females significantly affected their oviposition dates and the phenotypic traits (body shape, running speed) of their hatchlings. Thus, as for many other behavioural correlates of pregnancy in viviparous reptiles, maternal thermophily likely may have already been present in the ancestral oviparous taxa that gave rise to present-day viviparous forms.     

Fear in the dark? Community‐level effects of non‐lethal predators change with light regime

The total effect of predators on prey is a combination of direct consumption, and non‐consumptive effects (NCEs), such as predator‐induced changes to prey morphology, behaviour and life history. Past research into NCEs has tended to focus on pair‐wise interactions between predators and prey, while in natural ecosystems, species exist in complex communities with several trophic levels made up of multiple autotrophic and heterotropic species. To address how predator NCEs alter the photosynthetic and heterotrophic components of communities, we exposed microbial microcosms to one of three predator treatments: live predators (full predator effect), freeze‐killed predators (NCEs only) or no predators (control), and incubated them under either 12 h:12 h light:dark conditions or continual darkness. Under 12 h:12 h light:dark conditions, NCEs‐only communities never differed from predator‐free communities, but differed from live predator communities. Under conditions of continual darkness, the structure of NCEs‐only communities differed from predator‐free controls, but not from live predator communities, suggesting NCEs can be strong enough to structure communities. Predation threat may cause certain prey to induce defences, such as reductions in movement, which make them less competitive in a community setting. This reduction in competitive ability could lead to these species being driven to extinction through interspecific competition, resulting in similar communities to those in which live predators are present. Heterotrophic species whose rates of resource acquisition depend on movement rates may be affected to a greater extent than autotrophs by predator‐induced reductions in movement, accounting for our observed differences in predator NCEs in ‘dark’ and ‘light’ communities. Our results suggest that the community‐level consequences of fear are greater in the dark. Synthesis Predators affect prey through consumptive and non‐consumptive effects (NCEs) such as alterations to prey behaviour, morphology, and life history. However, predators and prey do not exist in isolated pairs, but in complex communities where they interact with many other species. Using a long term study (>10 predator generations), we show that predator NCEs alone can alter community structure under conditions of darkness, but not in a 12h:12h light:dark cycle. Our results demonstrate for the first time that although the community‐level consequences of predator NCEs may be dramatic, they depend upon the abiotic conditions of the ecosystem.     

Do UV‐A radiation and blue light during growth prime leaves to cope with acute high light in photoreceptor mutants of Arabidopsis thaliana?

We studied how plants acclimated to growing conditions that included combinations of blue light (BL) and ultraviolet (UV)‐A radiation, and whether their growing environment affected their photosynthetic capacity during and after a brief period of acute high light (as might happen during an under‐canopy sunfleck). Arabidopsis thaliana Landsberg erecta wild‐type were compared with mutants lacking functional blue light and UV photoreceptors: phototropin 1, cryptochromes (CRY1 and CRY2) and UV RESISTANT LOCUS 8 (uvr8). This was achieved using light‐emitting‐diode (LED) lamps in a controlled environment to create treatments with or without BL, in a split‐plot design with or without UV‐A radiation. We compared the accumulation of phenolic compounds under growth conditions and after exposure to 30 min of high light at the end of the experiment (46 days), and likewise measured the operational efficiency of photosystem II (?PSII, a proxy for photosynthetic performance) and dark‐adapted maximum quantum yield (F_v/F_m to assess PSII damage). Our results indicate that cryptochromes are the main photoreceptors regulating phenolic compound accumulation in response to BL and UV‐A radiation, and a lack of functional cryptochromes impairs photosynthetic performance under high light. Our findings also reveal a role for UVR8 in accumulating flavonoids in response to a low UV‐A dose. Interestingly, phototropin 1 partially mediated constitutive accumulation of phenolic compounds in the absence of BL. Low‐irradiance BL and UV‐A did not improve ?PSII and F_v/F_m upon our acute high‐light treatment; however, CRYs played an important role in ameliorating high‐light stress.     

Is non‐host pollen suitable for generalist bumblebees?

Current evidence suggests that pollen is both chemically and structurally protected. Despite increasing interest in studying bee–flower networks, the constraints for bee development related to pollen nutritional content, toxicity and digestibility as well as their role in the shaping of bee–flower interactions have been poorly studied. In this study we combined bioassays of the generalist bee Bombus terrestris on pollen of Cirsium, Trifolium, Salix, and Cistus genera with an assessment of nutritional content, toxicity, and digestibility of pollen. Microcolonies showed significant differences in their development, non‐host pollen of Cirsium being the most unfavorable. This pollen was characterized by the presence of quite rare δ7‐sterols and a low digestibility. Cirsium consumption seemed increase syrup collection, which is probably related to a detoxification mixing behavior. These results strongly suggest that pollen traits may act as drivers of plant selection by bees and partly explain why Asteraceae pollen is rare in bee generalist diet.     

Physiological and ecological responses to drought and heat stresses in Osmanthus fragrans ‘Boyejingui’

为了探讨植物对干旱、高温及协同胁迫的响应, 该研究以木犀(Osmanthus fragrans) ‘波叶金桂’为材料, 采用盆栽质量控水法模拟干旱胁迫(对照、轻度、中度和重度)和高温胁迫, 利用动态顶空气体循环吸附法和热脱附-气相色谱-质谱(TDS-GC-MS)联用技术对其挥发性有机化合物(VOCs)进行测定; 同时测定其非结构性碳(NSC)含量及次生代谢酶活性。结果表明: 干旱胁迫对‘波叶金桂’叶片NSC组分含量影响不显著; 可溶性糖和淀粉含量在高温胁迫下显著降低, 在协同胁迫后持续性下降, 重度协同胁迫下, 葡萄糖、果糖、蔗糖和淀粉分别比对照降低47.7%、46.4%、34.4%和38.2%。干旱胁迫和协同胁迫下3-羟基-3-甲基戊二酸单酰辅酶A还原酶(HMGR)、1-脱氧木酮糖-5-磷酸还原酶(DXR)活性表现出先上升后下降, 而脂氧合酶(LOX)活性表现出持续性上升趋势; 高温胁迫后, HMGR、DXR和LOX活性显著高于对照。干旱胁迫下萜烯类VOCs释放量表现出先上升后下降趋势, 中度干旱胁迫和高温胁迫下分别比对照高37.9%和32.3%; 协同胁迫下萜烯类释放量逐渐降低, 干旱、高温和协同胁迫诱导醛类释放量明显增加。上述结果表明: 干旱胁迫条件下, ‘波叶金桂’通过NSC进行自我渗透调节, 同时合成大量萜烯类化合物来提高抗旱性; ‘波叶金桂’调控萜烯类化合物合成以及绿叶挥发物(GLVs)的释放抵御高温胁迫; 协同胁迫下萜烯类化合物的合成途径受阻, ‘波叶金桂’提高GLVs合成与释放量抵御协同胁迫; 中度和重度协同胁迫导致‘波叶金桂’细胞膜严重受损, 自我调节能力降低。     

Are compound leaves an adaptation to seasonal drought or to rapid growth? Evidence from the Amazon rain forest

Aim To assess the hypotheses that compound leaves of trees in the Amazon forest are an adaptation to drought and/or rapid growth. Location Amazon rain forest, South America. Methods Genera from 137 permanent forest plots spread across Amazonia were classified into those with compound leaves and those with simple leaves. Metrics of compound leaf prevalence were then calculated for each plot and regression models that accounted for spatial autocorrelation were used to identify associations between climate variables and compound leaf structure. We also tested for associations between compound leaf structure and a variety of ecological variables related to life history and growth strategies, including wood density, annual increase in diameter and maximum height. Results One plant family, Fabaceae, accounts for 53% of compound‐leaved individuals in the dataset, and has a geographical distribution strongly centred on north‐east Amazonia. On exclusion of Fabaceae from the analysis we found no significant support for the seasonal drought hypothesis. However, we found evidence supporting the rapid growth hypothesis, with possession of compound leaves being associated with faster diameter growth rates and lower wood densities. Main conclusion This study provides evidence that possession of compound leaves constitutes one of a suite of traits and life‐history strategies that promote rapid growth in rain forest trees. Our findings highlight the importance of carefully considering the geographical distribution of dominant taxa and spatial clustering of data points when inferring ecological causation from environment–trait associations.     

Is local adaptation in Mimulus guttatus caused by trade‐offs at individual loci?

Local adaptation is considered to be the result of fitness trade‐offs for particular phenotypes across different habitats. However, it is unclear whether such phenotypic trade‐offs exist at the level of individual genetic loci. Local adaptation could arise from trade‐offs of alternative alleles at individual loci or by complementary sets of loci with different fitness effects of alleles in one habitat but selective neutrality in the alternative habitat. To evaluate the genome‐wide basis of local adaptation, we performed a field‐based quantitative trait locus (QTL) mapping experiment on recombinant inbred lines (RILs) created from coastal perennial and inland annual races of the yellow monkeyflower (Mimulus guttatus) grown reciprocally in native parental habitats. Overall, we detected 19 QTLs affecting one or more of 16 traits measured in two environments, most of small effect. We identified 15 additional QTL effects at two previously identified candidate QTLs [DIV ERGENCE (DIV)]. Significant QTL by environment interactions were detected at the DIV loci, which was largely attributable to genotypic differences at a single field site. We found no detectable evidence for trade‐offs for any one component of fitness, although DIV2 showed a trade‐off involving different fitness traits between sites, suggesting that local adaptation is largely controlled by non‐overlapping loci. This is surprising for an outcrosser, implying that reduced gene flow prevents the evolution of individuals adapted to multiple environments. We also determined that native genotypes were not uniformly adaptive, possibly reflecting fixed mutational load in one of the populations.     

Use of non‐limiting substrates to increase size; a generic strategy to simultaneously optimize uptake and minimize predation in pelagic osmotrophs?

Coexistence of two organisms competing for the same nutrient is possible if one is an ‘uptake’, and the other a ‘predation defence’ specialist. In pelagic food webs this principle has been linked to cell size. Small osmotroph cells, with their high surface : volume ratio, have been argued to be uptake specialists, while larger osmotrophs avoiding the intense grazing pressure from small protozoan predators might represent ‘predation defence’ specialists. This may seem like an obligatory trade‐off situation that necessitates a choice of either being small or being large, and thus being potentially dominant in oligotrophic or in eutrophic environments, respectively. However, in a more precise form, the theory for nutrient diffusion states that it is the ‘surface : cell requirement of limiting element’ ratio, rather than the ‘surface : volume’ ratio, that is important. The distinction is crucial, since it opens up the possibility of there being life strategies that use a non‐limiting element to increase size. Hypothesized to maximize uptake and predator defence simultaneously, such strategies should be particularly successful. We suggest that this strategy is exploited by osmotrophs with different size and physiology, such as heterotrophic bacteria, unicellular cyanobacteria and diatoms. Since the strategy implies a shift in organism stoichiometry, the biogeochemical implications are strong, illustrating the tight relationships between physical micro‐scale processes, organism life strategies, biodiversity, food web structure, and biogeochemistry.     

Large pollen at high temperature: an adaptation to increased competition on the stigma?

Pollen availability is a major constraint of plant reproductive success. Because pollen size trades-off with the quantity of produced grains, the link between climate characteristics and the determination of pollen size is of fundamental importance. To minimize the rate of water loss due to desiccation, a plant should produce larger grains that also have a lower surface-to-volume ratio. We used a comparative analysis to examine the hypothesis predicting increase in pollen size as a response to desiccation intensity. To test the hypothesis, we correlated the data on pollen size with the climate characteristics, temperature and desiccation intensity of the flowering period, for 232 plant species of 11 taxonomic groups. The analysis showed a positive relationship between the pollen size and temperature, but not with the desiccation intensity. We discuss the potential mechanisms by which increased temperature is an indicator of high competition among pollen grains on the stigma, which in turn is expected to promote large pollen. Our work provides insight into the temperature dependence of pollen production in plants and reveals a link between environmental temperature and the intensity of limitation of plant reproductive success by pollen availability. The result is relevant in the context of global climate change. We also discuss why environmental temperature has to be controlled in studies dealing with pollen production, particularly in investigations of size-number trade-off.     

Does sex matter? Gender‐specific responses to forest fragmentation in Neotropical bats

Understanding the consequences of habitat modification on wildlife communities is central to the development of conservation strategies. However, albeit male and female individuals of numerous species are known to exhibit differences in habitat use, sex‐specific responses to habitat modification remain little explored. Here, we used a landscape‐scale fragmentation experiment to assess, separately for males and females, the effects of fragmentation on the abundance of Carollia perspicillata and Rhinophylla pumilio, two widespread Neotropical frugivorous bats. We predicted that sex‐specific responses would arise from higher energetic requirements from pregnancy and lactation in females. Analyses were conducted independently for each season, and we further investigated the joint responses to local and landscape‐scale metrics of habitat quality, composition, and configuration. Although males and females responded similarly to a fragmentation gradient composed by continuous forest, fragment interiors, edges, and matrix habitats, we found marked differences between sexes in habitat use for at least one of the seasons. Whereas the sex ratio varied little in continuous forest and fragment interiors, females were found to be more abundant than males in edge and matrix habitats. This difference was more prominent in the dry season, the reproductive season of both species. For both species, abundance responses to local‐ and landscape‐scale predictors differed between sexes and again, differences were more pronounced in the dry season. The results suggest considerable sex‐mediated responses to forest disruption and degradation in tropical bats and complement our understanding of the impacts of fragmentation on tropical forest vertebrate communities.     

Does Bt rice pose risks to non‐target arthropods? Results of a meta‐analysis in China

Transgenic Bt rice expressing the insecticidal proteins derived from Bacillus thuringiensis Berliner (Bt) has been developed since 1989. Their ecological risks towards non‐target organisms have been investigated; however, these studies were conducted individually, yielding uncertainty regarding potential agroecological risks associated with large‐scale deployment of Bt rice lines. Here, we developed a meta‐analysis of the existing literature to synthesize current knowledge of the impacts of Bt rice on functional arthropod guilds, including herbivores, predators, parasitoids and detritivores in laboratory and field studies. Laboratory results indicate Bt rice did not influence survival rate and developmental duration of herbivores, although exposure to Bt rice led to reduced egg laying, which correctly predicted their reduced abundance in Bt rice agroecosystems. Similarly, consuming prey exposed to Bt protein did not influence survival, development or fecundity of predators, indicating constant abundances of predators in Bt rice fields. Compared to control agroecosystems, parasitoid populations decreased slightly in Bt rice cropping systems, while detritivores increased. We draw two inferences. One, laboratory studies of Bt rice showing effects on ecological functional groups are mainly either consistent with or more conservative than results of field studies, and two, Bt rice will pose negligible risks to the non‐target functional guilds in future large‐scale Bt rice agroecosystems in China.