Evolution of a colour pattern: history,development, and selection

Patterns of melanin pigmentation in birds are extremely varied. Nevertheless it is easy to think of many patterns that are never observed, and others that frequently recur in diverse and distantly related species. Using as our model the avian genus Phylloscopus we ask how the restricted range of observed patterns might be attributable to a restricted range of variants produced by developmental perturbations. The patterns we consider consist of unmelanized patches on the wings, crown and rump on otherwise pigmented upperparts. We use reaction-diffusion models to show that gross features of the pattern can be simply predicted from considerations of embryo shape. We suggest that birds are expected to have more patterned heads, because the head region is relatively larger than other regions in the developing embryo. A comparative analysis across many species of birds and a phylogenetic analysis within the genus Phylloscopus show that the component elements of the pattern have repeatedly been lost and gained during evolution. A shift in a threshold reading could explain the appearance and disappearance of the unmelanized patches, perhaps through changes in the sensitivity of melanocytes to epidermal signals. Such threshold shifts would make the transition between patterned and unpatterned forms particularly easy once the patterns have been exposed to selection in some distant ancestor. This partitioning of the roles of selection and development implies that many features of the patterns reflect developmental mechanisms in both immediate and more distant ancestors.     

Developmental genetics of leaf morphogenesis in dicotyledonous plants

A full understanding of the leaf is essential for a full understanding of plant morphology. However, leaf morphogenesis is still poorly understood, in particular in dicotyledonous plants, because of the complex nature of the development of leaves. Mutational analysis seems to be the most suitable strategy for investigations of such processes, and should allow us to dissect the developmental pathways into genetically programmed unit processes. The techniques of developmental genetics have been applied to the study of leaf morphogenesis in model plants, such asArabidopsis thaliana, and several key processes in leaf morphogenesis have been identified. The fundamental processes in leaf morphogenesis include the identification of leaf organs, determination of leaf primordia (occurrence of marginal meristem), and the polar or non-polar elongation of leaf cells. This review will focus on the genes that are essential for these processes and have been identified in mutational analyses. Mutational analyses of the photomorphogenesis is also briefly summarized from the perspective of the plasticity of leaf morphogenesis.     

PEP car☐ykinase containing species in the Brachiaria group of the subfamily panicoideae

In the Gramineae, a survey of species among the Brachiaria group of the subfamily Panicoideae, tribe Paniceae revealed that they are PEP car?ykinase containing species. This group includes the genera Brachiaria, Eriochloa and Urochloa. With the exception of the genus Panicum, these are the only genera within the Panicoideae found to contain PEP car?ykinase species. It is suggested that the PEP car?ykinase species of the genus Panicum, P. fasciculatum, P. maximum, P. molle and P. texanum, might be best placed in the Brachiaria group.     

Photosynthesis in localised regions of oat leaves infected with crown rust (Puccinia coronata): quantitative imaging of chlorophyll fluorescence

Localised changes in photosynthesis in oat leaves infected with the biotrophic rust fungus Puccinia coronata Corda were examined at different stages of disease development by quantitative imaging of chlorophyll fluorescence. Following inoculation of oat leaves with crown rust the rate of whole-leaf gas exchange declined. However, crown rust formed discrete areas of infection which expanded as the disease progressed and these localised regions of infection gave rise to heterogeneous changes in photosynthesis. To quantify these changes, images of chlorophyll fluorescence were taken 5, 8 and 11 d after inoculation and used to calculate images representing two parameters; Φ_II, a measure of PSII photochemical efficiency and ΔFm/Fm′, a measure of non-photochemical energy dissipation (qN). Five days after inoculation, disease symptoms appeared as yellow flecks which were correlated with the extent of the fungal mycelium within the leaf. At this stage, Δ_II was slightly reduced in the infected regions but, in uninfected regions of the leaf, values of Φ_II were similar to those of healthy leaves. In contrast, qN (ΔFm/Fm′) was greatly reduced throughout the infected leaf in comparison to healthy leaves. We suggest that the low value of qN in an infected leaf reflects a high demand for ATP within these leaves. At sporulation, 8 d after inoculation, Φ_II was reduced throughout the infected leaf although the reduction was most marked in areas invaded by fungal mycelium. In the infected leaf the pattern of non-photochemical quenching was complex; qN was low within invaded regions, perhaps reflecting high metabolic activity, but was now much higher in uninfected regions of the infected leaf, in comparison to healthy leaves. Eleven days after inoculation “green islands” formed in regions of the leaf associated with the fungal mycelium. At this stage, photosynthesis was severely inhibited over the entire leaf; however, heterogeneity was still apparent. In the region not invaded by the fungal mycelium, Φ_II and qN were very low and these regions of the leaf were highly fluorescent, indicating that the photosynthetic apparatus was severely damaged. In the greenisland tissue, Φ_II was low but detectable, indicating that some photosynthetic processes were still occurring. Moreover, qN was high and fluorescence low, indicating that the cells in this region were not dead and were capable of significant quenching of chlorophyll fluorescence.     

Thigmomorphogenesis: Field and laboratory studies of Abies fraseri in response to wind or mechanical perturbation

Field- and greenhouse-grown Abies fraseri (Pursh) Poir. (Fraser fir) were analyzed for wind- or mechanically-induced flexure changes. These changes included inhibition of stem and needle elongation, reinforcement of branch bases around the stem, and increased radial growth in the direction of the mechanical perturbation (MP). Mature trees exposed to high wind conditions were severely flag-formed. These modified tree crowns had a lower drag than crowns of non-flag formed trees in wind-tunnel tests. In both field-grown and greenhouse-grown A. fraseri , MP induced a decrease in flexibility and increased elasticity of the stems. The increased radial growth of the stems overrode the increase in elasticity, resulting in the overall decrease in flexibility. The increase in radial growth caused by wind or mechanical flexure was due to greater cell divisions of the vascular cambium, resulting in increased numbers of tracheids. The decrease in stem elongation in these trees was due, at least in part, to a decrease in tracheid length. The potential biological and mechanical significance of these induced growth changes in trees are addressed. The data support the thigmomorphogenetic theory, which states that plants respond to wind and other mechanical perturbations in a way that is favorable to the plant for continued survival in windy environments.     

New views of humpback whale flow dynamics and oral morphology during prey engulfment

The rise of inexpensive, user‐friendly cameras and editing software promises to revolutionize data collection with minimal disturbance to marine mammals. Video sequences recorded by aerial drones and GoPro cameras provided close‐up views and unique perspectives of humpback whales engulfing juvenile salmon at or just below the water surface in Southeast Alaska and Prince William Sound. Although humpback feeding is famous for its flexibility, several stereotyped events were noted in the 47 lunges we analyzed. Engulfment was rapid (mean 2.07 s), and the entrance through which the tongue inverts into the ventral pouch was seen as water rushes in. Cranial elevation was a major contributor to gape, and pouch contraction sometimes began before full gape closure, with reverberating waves indicating rebounding flow of water within the expanded pouch. Expulsion of filtered water began with a small splash at the anterior of the mouth, followed by sustained excurrent flow in the mouth's central or posterior regions. Apart from a splash of rebounding water, water within the mouth was surprisingly turbulence‐free during engulfment, but submersion of the whale's head created visible surface whirlpools and vortices which may aggregate prey for subsequent engulfment.     

不同基因型砧木嫁接黄瓜结瓜盛期光合特性的比较

采用CIRAS-Ⅱ型便携式光合作用系统,对黑籽南瓜和新培育的白籽南瓜A22种不同基因型砧木嫁接黄瓜结瓜盛期的光合特性进行比较。结果表明：在结瓜盛期,2种砧木嫁接黄瓜不同叶位的叶片净光合速率均有一定差异,其中A2嫁接黄瓜中部和下部叶片的净光舍速率显著高于黑籽南瓜嫁接的黄瓜。A2与黑籽南瓜相比其嫁接黄瓜利用光能范围较广且光饱和时净光合速率、RuBP最大再生速率和表观量子效率分别高出黑籽南瓜嫁接的黄瓜23．2％、12．6％和8．2％。2种砧木嫁接的黄瓜CO2饱和点与羧化效率均相近,CO2补偿点A2低于黑籽南瓜嫁接的黄瓜。A2嫁接黄瓜叶片叶绿素a、b及叶绿素总量均明显高于黑籽南瓜嫁接的黄瓜,可溶性蛋白含量与黑籽南瓜嫁接的黄瓜差异不显著。A2嫁接黄瓜的雌花节率和平均单株产量分别高出黑籽南瓜嫁接的黄瓜25．2％和29．4％,A2嫁接黄瓜果实可溶性糖、可溶性蛋白和VC含量分别高出黑籽南瓜嫁接的黄瓜6.3％、15,2％和15．4％。     

Sanio's laws revisited. Size-dependent changes in the xylem architecture of trees

Early observations led Sanio [ Wissen. Bot. , 8 , (1872) 401] to state that xylem conduit diameters and lengths in a coniferous tree increase from the apex down to a height below which they begin to decrease towards the tree base. Sanio's law of vertical tapering has been repeatedly tested with contradictory results and the debate over the scaling of conduit diameters with distance from the apex has not been settled. The debate has recently acquired new vigour, as an accurate knowledge of the vertical changes in wood anatomy has been shown to be crucial to scaling metabolic properties to plant and ecosystem levels. Contrary to Sanio's hypothesis, a well known model (MST, metabolic scaling theory) assumes that xylem conduits monotonically increase in diameter with distance from the apex following a power law. This has been proposed to explain the three-fourth power scaling between size and metabolism seen across plants. Here, we (i) summarized available data on conduit tapering in trees and (ii) propose a new numerical model that could explain the observed patterns. Data from 101 datasets grouped into 48 independent profiles supported the notions that phylogenetic group (angiosperms versus gymnosperms) and tree size strongly affected the vertical tapering of conduit diameter. For both angiosperms and gymnosperms, within-tree tapering also varied with distance from the apex. The model (based on the concept that optimal conduit tapering occurs when the difference between photosynthetic gains and wall construction costs is maximal) successfully predicted all three major empirical patterns. Our results are consistent with Sanio's law only for large trees and reject the MST assumptions that vertical tapering in conduit diameter is universal and independent of rank number.     

Nutritional and functional biology of exudate-feeding ants

Feeding extensively on plant exudates and honeydews, many tropical arboreal ant species exhibit δ¹⁵N values characteristic of herbivores. Consistent with hypothesized herbivory, these taxa behave in feeding assays as though more N-deprived than are strictly carnivorous ants. However, to an as yet uncertain degree, relationships with N-upgrading and/or recycling microsymbionts may lower isotopic ratios, making ants appear to be more herbivorous than they actually are. Nutritional (N) contributions from microsymbionts have been inferred for a variety of ant taxa based on intracellular or extracellular associations between ants and bacteria. However, stronger and more specific inferences are possible when variability in microsymbiont locations within the digestive system is considered in the context of taxonomic variability in ant diets and digestive anatomy. Diets of exudate feeders may vary predictably in ratios of usable carbohydrates (CHOs) to N, depending on the extent to which they tend melezitose-producing Homoptera. Status of the peritrophic membrane, proventricular structure, and number and placement of Malpighian tubules can be interpreted as traits contributing to supply of N and/or CHOs to microsymbionts. In general, a more integrative understanding of ant diets, digestive anatomy, and associated microsymbionts helps to set out specific hypotheses to be tested experimentally and (where possible) in a phylogenetic context.     

Influence of a salinity gradient on the vessel characters of the mangrove species Rhizophora mucronata

BACKGROUND AND AIMS: Although mangroves have been extensively studied, little is known about their ecological wood anatomy. This investigation examined the potential use of vessel density as a proxy for soil water salinity in the mangrove species Rhizophora mucronata (Rhizophoraceae) from Kenya. METHODS: In a time-standardized approach, 50 wood discs from trees growing in six salinity categories were investigated. Vessel densities, and tangential and radial diameters of rainy and dry season wood of one distinct year, at three positions on the stem discs, were measured. A repeated-measures ANOVA with the prevailing salinity was performed. KEY RESULTS: Vessel density showed a significant increase with salinity, supporting its use as a prospective measure of salinity. Interestingly, the negative salinity response of the radial diameter of vessels was less striking, and tangential diameter was constant under the varying environmental conditions. An effect of age or growth rate or the presence of vessel dimorphism could be excluded as the cause of the absence of any ecological trend. CONCLUSIONS: The clear trend in vessel density with salinity, together with the absence of a growth rate and age effect, validates the potential of vessel density as an environmental proxy. However, it can only be used as a relative measure of salinity given that other environmental variables such as inundation frequency have an additional influence on vessel density. With view to a reliable, absolute proxy, future research should focus on finding wood anatomical features correlated exclusively with soil water salinity or inundation frequency. The plasticity in vessel density with differing salinity suggests a role in the establishment of a safe water transport system. To confirm this hypothesis, the role of inter-vessel pits, their relationship to the rather constant vessel diameter and the underlying physiology and cell biology needs to be examined.