Offspring sex ratios in relation to mutual ornamentation and extra-pair paternity in the Black Swan Cygnus atratus

In sexually dichromatic birds, females may adaptively adjust the sex ratio of their offspring prior to hatching in relation to male ornamentation, for example, by producing more sons when paired to a highly attractive partner. However, to our knowledge no studies have investigated offspring sex ratio modification in species in which both sexes are ornamented, and it is unknown whether such a process would be adaptive. Here we examine variation in offspring sex ratio in the mutually ornamented Black Swan Cygnus atratus . Brood sex ratio was not related to the degree of ornament elaboration in either parent, or to extra-pair paternity. We suggest that parental attractiveness may not be inherited in a sex-linked manner, or may be largely non-heritable. Thus, females may not benefit from biasing the sex ratio of their offspring in relation to parental attractiveness.     

Translocation of 32P between interacting mycelia of a wood-decomposing fungus and ectomycorrhizal fungi in microcosm systems

Interactions between saprotrophic and ectomycorrhizal fungi have been largely ignored, although their mycelia often share the same microsites. The mycelial systems show general similarity to each other and, although the enzymatic potential of the saprotrophic fungi is generally considered to be higher, the importance of organic nutrient sources to ectomycorrhizal fungi is now widely accepted. In the experiments described here, nutritional interactions involving transfer of elements from one mycelium to the other have been monitored dynamically using radioactive tracers and a non-destructive electronic autoradiography system. Microcosms were used in which mycelial systems of the ectomycorrhizal fungi Suillus variegatus and Paxillus involutus , extending from Pinus sylvestris host plants, were confronted with mycelia of the saprotroph Hypholoma fasciculare extending from wood blocks. The fungi showed a clear morphological confrontation response. The mycorrhizal mycelium often formed dense patches over the Hypholoma mycelia. Up to 25% of the ³²P present in the Hypholoma mycelium was captured by the mycorrhizal fungi and translocated to the plant host within 30 d. The transfer of ³²P to the saprotroph from labelled mycorrhizal mycelium was one to two orders of magnitude lower. The significance of this transfer as a 'short cut' in nutrient cycling is discussed.     

Experiments on food preference and chemical sense in Pycnogonida

Food choice experiments were carried out with three species of pycnogonids: Nymphon rubrum, N. gracile , and Endeis spinosa.
Running sea-water that had circulated over different possible food-sources (hydroids, actiniarians, octocorals, synascidians) was offered to the pycnogonids at one side of a basin, pure sea-water or sea-water that had flowed over a different source of food at the other.
The experiments, though few in number, seemed to indicate that:
(1) Pycnogonids are capable of detecting the presence or absence of various coelenterate species.
(2) They are able to discriminate between different food-sources, i.e. the nature of the chemical substances produced by the food determines the degree of attraction.
(3) The preferential sequence for the three pycnogonids tested is: Nymphon rubrum prefers Dynamena over Tubularia and Laomedea ; these are preferred over Actinia and Metridium ; there is no attraction to Alcyonium. Nymphon gracile prefers Laomedea over Dynamena. Endeis spinosa prefers Laomedea over Dynamena ; these are preferred over Actinia ; there is no attraction to Morchellium.
(4) Experimental amputation of appendages indicates a high probability that the chemo-receptors of the pycnogonids are not located on the chelifores, palps, or ovigers. They may be located (a) all over the body, possibly in innervated epidermal bristles; and/or (b) in the distal part of the proboscis, bearing sensory setae; and/or (c) on the walking legs.     

The Water Relations of Pinus sylvestris III. Diurnal and Seasonal Patterns of Water Potential

The water potential (ψ) in twigs from four clones of Scots pine (Pinus sylvestris L.) growing in close proximity to each other was measured in a pressure chamber during five selected periods between May 1972 and March 1973. Diurnal and seasonal patterns of ψ are presented in relation to irradiance, air temperature and vapour pressure deficit (VPD) for one cloudy and one clear day in each experimental period. Significant differences in ψ were found amongst most of the clones. Larger amplitudes and earlier day-time minima in ψ were found during the summer than during the winter. Noon values of ψ of less than ?12 bars were regularly found during the summer months. Plots of ψ against irradiance or VPD during a day, showed marked hysteresis as the result of the simultaneous influence on ψ of several environmental factors. Close linear relations resulted when ψ was plotted against potential evaporation rate (calculated from the Penman-Monteith formula). The slopes of these regression lines, essentially the flow resistance, showed marked seasonal variations. At both high and low evaporation rates, the clone that grew the fastest had the lowest values of ψ, and the clone that grew the slowest had the highest values of ψ, while the other two clones had intermediate values. Differences in solute potential or in stomatal, plant or soil resistance are discussed as possible explanations of the more or less constant differences between the clones during the year of observations.     

Differential Effects of Day and Night Temperature on Development to Flowering in Rice

There are conflicting reports with regard to difference in effectsof day temperature (T_D) and night temperatures (T_N) on plantdevelopment. The objective of this study is to determine whetherthere are different effects ofT_DandT_Non development from sowingto flowering in rice (Oryza sativaL.). Plants of 24 rice cultivars were grown in naturally-lightedgrowth chambers at five diurnally constant (22, 24, 26, 28 and32 °C) and four diurnally fluctuating temperatures (26 /22,30 /22, 22 /26 and 22 /30 °C forT_D/T_Nwith 12hd^-1each) witha constant photoperiod of 12hd^-1. The treatments were selectedto enable the separation of effects ofT_DandT_Non developmentrate (DR). The response of DR to constant temperatures was typically nonlinear.This nonlinearity could not explain the difference in floweringdates between fluctuating temperatures with the same mean dailyvalue but oppositeT_D/T_Ndifferences. Differential effects ofT_DandT_NonDR to flowering were detected in all but one cultivar. In mostcases,T_Dexerted a greater influence thanT_N, in contrast withmany previous reports based on the assumption of a linearitybetween DR and temperature. The data were further analysed bya nonlinear model which separated effects ofT_DandT_N. The estimatedvalue for the optimumT_Nwas generally 25 –29 °C, about2 –4 °C lower than the estimated optimumT_Din mostcultivars. The effects ofT_DandT_Non DR were found to be interactivein some cultivars. These results form a new basis for modellingflowering dates in rice. Oryza sativa; rice; flowering; development; day and night temperature; thermoperiodicity     

The Evolution of Feathers*

Existing hypotheses on the evolution of feathers are reviewed with the assumptions that feather evolved from reptilian scales and that pennaceous feathers evolved before downy feathers. Observations with a scanning electron microscope demonstrate that basic to the structure of pennaceous feathers is the lamelliform structure of barbules, the planes of which are oriented at right angles to the plane of the feather vane. Thus the structure of the vane is more open than generally realized. The airtight vane of flight feathers is assumed a later specialization. Most of the existing hypotheses assume that the feather acts as a relatively solid barrier between the skin of the bird and the exterior and they are therefore not in agreement with the actual structure of feathers. A hypothesis is needed which explains the adaptive value of a pennaceous feather being porous. The hypothesis is put foward that feathers evolved due to selection for a water-repellent integument. For purely physical reasons a porous surface repels water drops more strongly than does a solid surface of the same material. Physicists have pointed out that the structure of feathers conforms closely with the theoretical requirements for water-repellency. Possibly feathers started to evolve on reptiles living at the seashore, where the main advantage of increased water-repellency was to reduce cooling from evaporation of water off a wet integument.