ALBERT

Beschreibung: Persistent adaptive challenges are often met with the evolution of novel physiological traits. Although there are specific examples of single genes providing new physiological functions, studies on the origin of complex organ functions are lacking. One such derived set of complex functions is found in the Lepidopteran bursa copulatrix, an organ within the female reproductive tract that digests nutrients from the male ejaculate or spermatophore. Here, we characterized bursa physiology and the evolutionary mechanisms by which it was equipped with digestive and absorptive functionality. By studying the transcriptome of the bursa and eight other tissues, we revealed a suite of highly expressed and secreted gene products providing the bursa with a combination of stomach-like traits for mechanical and enzymatic digestion of the male spermatophore. By subsequently placing these bursa genes in an evolutionary framework, we found that the vast majority of their novel digestive functions were co-opted by borrowing genes that continue to be expressed in nonreproductive tissues. However, a number of bursa-specific genes have also arisen, some of which represent unique gene families restricted to Lepidoptera and may provide novel bursa-specific functions. This pattern of promiscuous gene borrowing and relatively infrequent evolution of tissue-specific duplicates stands in contrast to studies of the evolution of novelty via single gene co-option. Our results suggest that the evolution of complex organ-level phenotypes may often be enabled (and subsequently constrained) by changes in tissue specificity that allow expression of existing genes in novel contexts, such as reproduction. The extent to which the selective pressures encountered in these novel roles require resolution via duplication and sub/neofunctionalization is likely to be determined by the need for specialized reproductive functionality. Thus, complex physiological phenotypes such as that found in the bursa offer important opportunities for understanding the relative role of pleiotropy and specialization in adaptive evolution.

Beschreibung: Local skin-friction reductions have been measured using an array of flush-mounted hot-film probes in a microbubble-modified, zero-pressure-gradient, turbulent boundary layer. The results of earlier integrated skin-friction measurements, that showed the reduction to be a function of plate orientation, gas-flow rate and free-stream velocity, have been confirmed both qualitatively and quantitatively. With the measurement plate oriented so that buoyancy keeps the bubbles in boundary layer, it is shown that skin friction is reduced monotonically for all air-flow rates at each of three free-stream velocities between 4 and 17 m/s. For the opposite plate orientation it is possible for increasing gas injection to lead to smaller local skin-friction reduction at the lowest speeds. Drag reduction appears to persist for as much as 60–70 boundary-layer thicknesses downstream of the injection region. It is further shown, using a probe flush-mounted just upstream of the injection section, that there is no apparent upstream interference due to the gas injection. Spectral measurements indicate that microbubbles can cause a reduction of high-frequency shear-stress fluctuations. This suggests a destruction of some of the turbulence in the near-wall region. © 1985, Cambridge University Press. All rights reserved.

Beschreibung: The behaviour of shear-generated interfacial waves in a cocurrent gas-liquid flow in a small rectangular channel is studied eXperimentally at conditions close to neutral stability. It is found that the linearly most unstable mode, which typically has a frequency of 8–10 Hz and a wavelength 1–4 cm, grows initially - followed immediately by the first overtone. Measurements of the bicoherence spectrum indicate that the overtone and fundamental are coherent in phase, which suggests that energy is transferred from the fundamental to the linearly stable first overtone. This energy transfer mechanism can stabilize the system, as evidenced by data, which shows that the first mode can saturate with a wave slope small as as 0.005. Theory based on weakly nonlinear mode-interaction equations suggests that this steady state should be stable at conditions close to neutral stability where only overtone modes are present. However, under more severe conditions, where the amplitude of the fundamental mode becomes sufficiently large, a subharmonic mode may be eXcited. The generation of the subharmonic, when it is linearly stable with respect to the flat film base state, can be interpreted as a linear instability of the steady state containing the fundamental and overtones. Modes that are sidebands (with wavenumbers = k±8k) to the main peak may also occur. These can participate in interactions with low-frequency modes (i.e. 8k) and thereby transfer energy to frequencies much below the fundamental. It is eXpected that all of these interactions play important roles in determining the wave spectrum of conditions far away from neutral stability. © 1992, Cambridge University Press. All rights reserved.

Beschreibung: The rate of snow accumulation has been measured at the U.S.S.R. station situated at the Pole of Relative Inaccessibility (eastern Antarctic plateau). Five independent methods were used. The results, expressed in g cm−2 year−1, are as follows: (1)Accumulation-stake measurements show an accumulation of 3·1±0·5 in 1965. A maximum value of 3·6 for the 6–year interval 1959–65 is derived from snow-thickness measurements.(2)Firn stratigraphy was found difficult to interpret in terms of annual layers. An upper limit of 12 g cm−2 year−1 is suggested.(3)18O/16O ratios were measured along the upper 235 cm. Assuming that each maximum in the isotope profile corresponds to a summer season, the accumulation would be 8·6±0·9.(4)Gross β radioactivity as a function of depth was measured on three firn sections. The 1955 radioactive fall-out horizon is clearly marked, enabling the derivation of an average accumulation of 3·0±0·3.(5)The average accumulation over the last 80 years, derived from the 210Pb distribution with depth, is 3·1±0·3.A multi-annual average accumulation rate of (3·0±0·3) is thus firmly established, as well as the validity of both the 210Pb method and the 1955 radioactive fall-out horizon method. Stratigraphie studies lead to uncertain results. Oxygen isotope variations give accumulation values which are too high by a factor of two at least.Accumulation values of the same order of magnitude (2·8±0·2) were derived from radioactive fall-out measurements at the U.S. “Plateau” station.

Beschreibung: The rate of snow accumulation has been measured at the U.S.S.R. station situated at the Pole of Relative Inaccessibility (eastern Antarctic plateau). Five independent methods were used. The results, expressed in g cm−2year−1, are as follows:(1)Accumulation-stake measurements show an accumulation of 3·1±0·5 in 1965. A maximum value of 3·6 for the 6–year interval 1959–65 is derived from snow-thickness measurements.(2)Firn stratigraphy was found difficult to interpret in terms of annual layers. An upper limit of 12 g cm−2year−1is suggested.(3)18O/16O ratios were measured along the upper 235 cm. Assuming that each maximum in the isotope profile corresponds to a summer season, the accumulation would be 8·6±0·9.(4)Grossβradioactivity as a function of depth was measured on three firn sections. The 1955 radioactive fall-out horizon is clearly marked, enabling the derivation of an average accumulation of 3·0±0·3.(5)The average accumulation over the last 80 years, derived from the210Pb distribution with depth, is 3·1±0·3.A multi-annual average accumulation rate of (3·0±0·3) is thus firmly established, as well as the validity of both the210Pb method and the 1955 radioactive fall-out horizon method. Stratigraphie studies lead to uncertain results. Oxygen isotope variations give accumulation values which are too high by a factor of two at least.Accumulation values of the same order of magnitude (2·8±0·2) were derived from radioactive fall-out measurements at the U.S. “Plateau” station.