P2 Value Research Articles

Sperm Precedence in Eysarcoris lewisi DISTANT(Heteroptera:Pentatomidae)in Relation to Duration between Oviposition and the Last Copulation

The last male sperm precedence (P2) in a pentatomid stink bug, Eysarcoris lewisi DISTANT, was studied using females mated with both normal and sterilized males. The mean P2 value in the first egg masses was about 40%. The mean P2 value increased as deposition of egg masses progressed, and showed almost complete last male sperm precedence in the forth egg masses. Among first egg masses, there was a significant positive correlation between P2 values and duration from termination of the last copulation to beginning of oviposition. these facts indicate that the duration between copulation and oviposition is important in determining P2 values. Females began oviposition an average of 55±37 (mean±S.D.) h after copulation. The function of prolonged copulation in this species is discussed.

?Longevity? of sperm within the female of the melon fly,Dacus cucurbitae (Diptera: Tephritidae), and its relevance to sperm competition

Sperm competition is the competition between sperm from the ejaculates of different males over fertilization of a limited number of ova (Parker, 1970). The probability of paternity of a second male after the female has been mated previously to a first male are often referred as the P2 value (Boorman and Parker, 1976) and has been measured in a wide range of animals (e.g., volume edited by Smith, 1984). The P2 value may vary depending on the mechanism of sperm transfer and on the structure of the male and female reproductive organs (Walker, 1980). There exists a considerable amount of data to show that the paternity of two males is determined in relation to mating order, and the last male advantage is often reported in many insect species (reviewed by Parker, 1970; Gwynne, 1984; Tsubaki, 1988). The mechanisms for this phenomenon are not yet clear except in some restricted cases. There is good evidence for mechanical displacement (removal or repositioning) of sperm of earlier males in many odonates (Waage 1979, 1984; Siva-Jothy, 1988: Siva-Jothy and Tsubaki. 1989) and at least one cricket (Ono et al.. 1989). On the other hand, some studies suggest that the amount of ejaculate is more important than mating order (Dickinson, 1986; Simmons, 1987; Tsubaki and Sokei. 1988). Although sperm viability and

Backfat composition in pigs: Differences between fat thickness groups and sexes

The chemical composition of subcutaneous fat (backfat) from the last rib and shoulder regions was studied in 300 pig carcasses, mean weight 58 kg, falling into 3 fat-thickness groups averaging 8, 12 and 16 mm P2 (65 mm from mid dorsal line at last rib). The carcasses were obtained in 10 abattoirs, in each of which 5 producer groups of 6 pigs were identified: 1 entire male and 1 female for each of the fat-thickness groups. Concentrations of the gross constituents water, lipid and collagen were greatly affected by the thickness of backfat, water and collagen declining and lipid increasing through the fat thickness range. Fatty acids were less affected, although linoleic acid (C18:2) decreased from 14.9% of fatty acids at 8 mm P2 to 10.6% at 16 mm. The concentration of C18:2 measured at the last rib and shoulder positions was highly correlated with subjective and objective measures of tissue firmness at both sites. In each fat thickness group, backfat from entire males contained higher concentrations of water, collagen and C18:2 than that from females. Relationships between concentrations and P2 were curvilinear, changing most at low P2 levels, and were best explained by linear regressions of log components on log P2. Regression lines were parallel in the two sexes and were such that concentrations in entire males were similar to those in females with a 15% lower P2 value. Average values for polyunsaturated fatty acids were higher than standard figures normally quoted, the ratio of polyunsaturated to saturated fatty acids in the leanest group (0.41) being close to the recommended value for the U.K. diet as a whole.

The fidelity of response by 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene in time-resolved fluorescence anisotropy measurements on lipid vesicles. Effects of unsaturation, headgroup and cholesterol on orientational order and reorientational dynamics.

Time-resolved fluorescence anisotropy measurements on 1-[4-(tri-methylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) molecules in lipid vesicles of palmitoyloleoylphosphatidylcholine (POPC), PC extracted from egg yolk (EggPC), dioleoyl-PC (DOPC), dilinoleoyl-PC (DLPC), phosphatidylglycerol extracted from egg yolk (EggPG), dioleoyl-PG (DOPG), sulfoquinovosyldiacylglycerol (SQDG) and digalactosyl-DG (DGDG) with and without cholesterol are presented. The observed intensity decay curves are analyzed simultaneously in terms of the Brownian rotational diffusion model. The analysis thus yields the isotropic fluorescence decay, the initial anisotropy r (0), the order parameters mean value of P2 and mean value of P4 as well as the diffusion coefficient of the long molecular axis. It is shown that increasing unsaturation in the acyl chains of the PC lipids results in an increase in the rotational diffusion rates of the probes and a decrease in the order parameter mean value of P2. However, the value of mean value of P4 remains unchanged. The corresponding orientational distribution function of the probes is bimodal, with fractions lying preferentially parallel and perpendicular to the local vesicle surface. Surprisingly, the fraction of probe molecules lying with their long axes parallel to the bilayer surface increases with increasing unsaturation with a concomitant narrowing in the width of the distribution of the fraction lying perpendicular to it. As expected, cholesterol is found to increase the order parameters in all the systems and to suppress the tendency of the molecules to lie parallel to the bilayer surface. Furthermore, the rotational diffusion coefficients of the probes is found to increase in all the systems except for DLPC. Interestingly, the effects of unsaturation on the reorientational dynamics of TMA-DPH molecules in the vesicle systems are opposite to those found in the corresponding planar multibilayers (Deinum et al. 1988), whereas the same cholesterol effect is observed for the two systems. Nevertheless, the TMA-DPH molecules exhibit higher diffusion coefficients in the vesicle than in the planar multibilayer systems. In addition, a unimodal distribution of the probe molecules is found in the multibilayer systems. The differences between the two systems are ascribed to the differences in the radius of curvature and the hydration of the bilayers. Lastly we rationalize the bimodal distribution of the TMA-DPH molecules in the vesicles in terms of their observed partition between the lipid and aqueous phases.

Occurrence of Maximum and Minimum in the Principal Magnetic Susceptibility versus Temperature Curves

IN an examination of the temperature variation of principal magnetic susceptibilities of paramagnetic salts of the iron group of elements from room temperature down to about 80° K, it has been found in certain cases that the square of the effective magnetic moment (p2) value comes down so rapidly with the decrease of temperature that the corresponding susceptibility actually shows a maximum in the susceptibility versus temperature curve1. The condition for the occurrence of such a maximum can be easily investigated.