Effects of Moderate Water Deficit (Stress) on Wheat Seedling Growth and Plastid Pigment Development

Etiolated 6-day-old wheat (Triticum aestivum L. cv. Chris) seedlings were subjected to osmotic stress by an application of polyethylene glycol 12 h prior to the exposure to a continuous 72-h light period. The water potential of the primary leaf of stressed seedlings was between –9 and –14 bars throughout the light period. Stress impaired seedling growth, leaf unfolding, and the increase in leaf area. The imposed osmotic stress reduced total chlorophyll accumulation, particularly after 9 h light, suggesting that this is the approximate time period for the depletion of the protochlorophyll(ide) pool and the pool of an essential protochlorophyll(ide) precursor. The chlorophyll a/b ratio of extracts from stressed and non-stressed plants was the same during the 72-h greening period. Water deficit stress impaired carotenoid accumulation sooner than the impairment of chlorophyll production suggesting either a smaller carotenoid pool size of precursors or that the metabolic pathway of carotenoid synthesis was more sensitive to stress. Shifts from the usual plastid pigment absorbance maxima were not observed in these studies.     

Cryptic sexual dichromatism occurs across multiple types of plumage in the Green-backed Tit Parus monticolus

Several recent studies have found instances of cryptic sexual dichromatism within avian taxa. Although this dichromatism has been found in plumage produced through a variety of proximate mechanisms, little is known about how dichromatism varies across these types of plumage within a single species. We used a reflectance spectrometer to measure colour within the Green-backed Tit Parus monticolus , a species which displays multiple types of pigment and structural colours. We found significant differences in spectral measurements corresponding to hue, chroma, and brightness between male and female carotenoid, melanin, structural white, grey and structural blue plumage. The only plumage that did not appear to show sexual dichromatism was the olive plumage of the back. These findings suggest that the mechanism(s) producing cryptic dichromatism in the Green-backed Tit are non-specific and act across multiple types of plumage, rather than within a single type, such as carotenoid-based or structurally produced.     

The response of stream fish to local and reach‐scale variation in the occurrence of a benthic aquatic macrophyte

1. The aquatic macrophyte Podostemum ceratophyllum has been shown to increase stream productivity, abundance and biomass of benthic invertebrates, and local occurrences of some stream fishes. However, experimental evidence that fishes preferentially associate with Podostemum is lacking, and the value of Podostemum as a predictor of stream fish assemblage composition has not been studied. 2. We conducted two short‐term (2 week), small‐scale (36 m²) experimental manipulations of Podostemum cover in the Conasauga River (Georgia and Tennessee, U.S.), and found higher abundances of benthic insectivorous fishes in patches with augmented (>80%) compared to reduced (7%) Podostemum cover. In an observational study, we quantified associations among percent cover of Podostemum, fish species richness, land cover, shoal length and base‐flow turbidity at 20 randomly selected shoals from a 39‐km reach that spanned a gradient of decreasing forest land cover. 3. Richness of all fish species and of lotic fishes peaked in the centre of the study reach, and richness was weakly correlated with predictor variables. Occupancy models for individual species also indicated that longitudinal position was a strong covariate for 13 of 19 species examined, with little support that Podostemum cover influenced occupancy. 4. Local associations may reflect choices by benthic fishes to utilise Podostemum, whereas downstream decline in fish species richness and Podostemum cover may reflect altered capacity of the system to support native species.