Reproductive ecology of three ocypodid crabs II. Incubation sites and egg mortality

Mortality of eggs during incubation was estimated for three ocypodid crabs,Scopimera globosa, Ilyoplax pusillus andMacrophthalmus japonicus, and the influence of incubation sites was discussed. These crabs all lived in isolated burrows and fed on sediments during day time low tide.S. globosa andI. pusillus inhabited the upper intertidal sandflats, whereasM. japonicus inhabited the lower intertidal mudflats. Females of bothS. globosa andI. pusillus remained in their plugged burrows without feeding throughout incubation and the mortality of eggs was low despite large broods relative to body size. On the other hand, females ofM. japonicus fed actively on surface mud during incubation and the mortality of eggs was high despiite small broods relative to body size. InS. globosa andI. pusillus, the ovaries of ovigerous females were small until egg-hatching, whereas inM. japonicus, the ovaries grew rapidly during incubation and females were able to produce consecutive broods. I conclude that incubation of eggs in burrows may be advantageous in species which inhabit the upper interidal sandflats, even though the crabs cannot forage during incubation, since otherwise their eggs would be exposed to strong heat stress and desication during the summer. Furthermore, such species may produce few large broods because of less frequent interruption of feeding than that associated with production of many small broods.     

The relationship among egg size,density and food level on larval development in the wood frog (Rana sylvatica)

Summary Although inter- and intraspecific variation in egg size among amphibians has been well documented, the relationship between egg size and fitness remains unclear. Recent attempts to correlate egg size intraspecifically with larval developmental patterns have been equivocal. In this study the development of larvae derived from large eggs and small eggs, from a single population in Maryland were compared under a range of food levels and larval population densities. Both food level and density had significant effects on the length of the larval period and size at metamorphosis. However, the response among larvae derived from different egg sizes was not additive. At low densities and high food levels, larvae from small eggs had longer larval periods and a larger size at metamorphosis than larvae derived from large eggs. In contrast, at high densities larvae from small eggs had longer developmental periods but were smaller at metamorphosis than larvae from large eggs. In addition, larvae from small eggs were more sensitive to density irrespective of food level. These results suggest that optimal egg size is correlated with environmental factors, which may explain the maintenance of both geographic and within population variation in egg size commonly observed in amphibians.     

Comparative egg morphology of six Meccus species and Triatoma recurva (Stål, 1868) Hemiptera: Reduviidae

We investigated the morphology and morphometry of eggs from the colonies of the Entomology Laboratory at ENCB‐IPN belonging to six species of the genus Meccus and Triatoma recurva, using both light and scanning electron microscopy. Egg ornamentation is an important parameter to consider in the differentiation of species. Samples were observed under a scanning electron microscope. Measurements of fifty eggs per species included length, width, and opercular diameter, which were used for the morphometric analysis. The results showed that the seven species display a polygonal ornamentation dominated by hexagons; the operculum shows also a polygonal ornamental characteristic in each species. Morphometry provided valuable information for discriminating between closely related species of the genus Meccus and Triatoma recurva, a species akin to this group, thereby facilitating the complete discrimination of these species.     

Effect of pulsed exposure to heavy metals (copper and cadmium) on some population variables of <Emphasis Type="Italic">Brachionus calyciflorus</Emphasis> Pallas (Rotifera: Brachionidae: Monogononta)

Heavy metals are widely recognized as potential toxic agents to zooplankton, yet experiments are usually performed with a continuous exposure to the metal being analyzed. Here we describe experiments that examined the influence of pulsed exposure of the heavy metals copper and cadmium to a parthenogenetic population of the planktonic rotifer Brachionus calyciflorus. Our protocol called for exposure durations of 3, 6, 12, and 24 h to either copper (as CuSO₄) at concentrations of 0.0375, 0.075, 0.15 mg l⁻¹ or cadmium (as CdCl₂) at concentration of 0.025, 0.05, 0.1 mg l⁻¹. Control animals were treated in similar ways but did not receive exposure to heavy metals. Four end points were used to evaluate the outcome of exposure: population growth (r), body size, egg ratio, and egg hatching percent. Increase in heavy metal concentration and exposure time had an adverse influence on the population growth of B. calyciflorus. However, while the response of B. calyciflorus was similar for both heavy metals, the magnitude of the impact of cadmium was more severe. Population growth varied depending on which heavy metal was tested, as well as its concentration and the duration of exposure (r = 0.11–0.28 day⁻¹). There was a significant reduction in lorica size of B. calyciflorus subjected to different exposure times and concentrations of both Cd and Cu. Egg ratios were inversely related to population density in controls and in treatments involving Cu, but not for Cd. While nearly 100% of eggs hatched in the control treatments, egg hatching in experimental treatments containing Cu, were reduced (range = 16–41%) depending on the exposure time and the concentration. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

产卵于温暖且热稳定巢内的蜥蜴具有相对较高但较窄范围的孵化温度

作者用蜡皮蜥(Leiolepis reevesii)为模型动物,检验产卵于温暖且热稳定巢内的蜥蜴应有相对较高但较窄的孵化温度的假设。卵在三个恒定温度(27、30和33℃)、一个波动温度处理下孵化。温度的平均值而非方差影响孵化期,27、30和33℃的平均孵化期分别为101.1、69.6和55.3d。幼体性别不受孵化温度影响。不同处理孵出的幼体仅有稍许形态差异,但运动表现差异显著。27℃孵出幼体在跑道上的表现比其它处理孵出幼体差。卵能在27℃和33℃下孵化,但这两个孵化温度并不适宜。蜡皮蜥适宜的孵化温度范围可能处于最频繁的巢温变化范围(28℃-32℃)内。与其它在低温生境或温暖生境但产卵于浅巢的有鳞类爬行动物相比较,蜡皮蜥有相对较高但较窄适宜的卵孵化温度。因此,作者的数据支持上述假设。     

Structure of the C-terminal domain of the pro-apoptotic protein Hrk and its interaction with model membranes

The protein harakiri (Hrk) is a pro-apoptotic BH3-only protein which belongs to the Bcl-2 family. Hrk appears associated to the mitochondrial outer membrane, apparently by a putative transmembrane domain, where it exerts its function. In this work we have identified a 27mer peptide supposed to be the putative membrane domain of the protein at the C-terminal region, and used infrared and fluorescence spectroscopies to study its secondary structure as well as to characterize its effect on the physical properties of phospholipid model membranes. The results presented here showed that the C-terminal region of Hrk adopts a predominantly α-helical structure whose proportion and destabilization capability varied depending on phospholipid composition. Moreover it was found that the orientation of the α-helical component of this C-terminal Hrk peptide was nearly perpendicular to the plane of the membrane. These results indicate that this domain is able of inserting into membranes, where it adopts a transmembrane α-helical structure as well as it considerably perturbs the physical properties of the membrane.     

Dipolar relaxation in a lipid bilayer detected by a fluorescent probe, 4'-dimethylaminochalcone

The dynamic behavior of polar molecules in egg phosphatidylcholine (PC) bilayers has been studied using a membrane fluorescent probe, 4'-dimethylaminochalcone (DMAC). Time and spectrally resolved fluorescence spectroscopy of DMAC incorporated in PC liposomes, as compared to studies of the probe in organic solvents, shows the existence of two independent populations, associated with different extent and speed of dipolar solvent relaxation. The first DMAC population represents approximately 69% of the fluorescence-emitting molecules, has a short fluorescence decay time (0.32 ns) and undergoes Stokes shift of 80 nm. The remaining 31% fraction of DMAC molecules has a decay time of 0.74 ns and undergoes a high (106 nm) Stokes shift. A fraction of the shift, ca. 24 nm for the first and 46 nm for the second population, is attributed to the fast (<0.1 ns) rotational relaxation of nearby dipolar molecules, which might be water. This two-state model accounts well for the detailed fluorescence properties of DMAC in egg PC, i.e. its broadened steady-state spectrum, its average fluorescence quantum yield and its complex wavelength-dependent fluorescence decays.     

Phospholipid binding properties and functional characterization of a sea urchin phospholipase Cdelta in urchin and mouse eggs

We recently identified a novel phospholipase Cdelta isoform, PLC-deltasu, in sea urchin gametes, whose precise functional role during fertilization and early embryogenesis remains unknown. Here, we characterized the binding of the PLC-deltasu PH domain to different phosphatidylinositol (PI) phospholipids and studied changes in its localization during fertilization. The PLC-deltasu PH domain bound most strongly to PI(3,4)P(2) and PI(3,5)P(2) phospholipids, in contrast to the PLCdelta1 PH domain which bound predominantly to PI(4,5)P(2). A green fluorescent protein tagged PLC-deltasu PH domain localized to the plasma membrane and its localization increased at fertilization and following addition of a Ca(2+) ionophore. However, recombinant PLC-deltasu failed to cause Ca(2+) signals like those seen at fertilization, in mouse and sea urchin eggs. Our findings suggest that PLC-deltasu is unlikely to be directly involved in the process of egg activation but may play a role in mediating extracellular signals transmitted via the PI 3'-kinase pathway.     

Vasodilator effects of peptides derived from egg white proteins

The aim of this work was to investigate the effect of several peptides, identified before and after simulated gastrointestinal digestion of an egg white hydrolysate, on the vascular function, in rat aorta. The sequences IVF, RADHPFL and YAEERYPIL (0.1 mM) induced vasodilatation in intact aortic rings, with the maximum percentage of dilation corresponding to RADHPFL (40.5 ± 7.0%). Two of the end products of the gastrointestinal digestion, RADHP and YPI, also showed vasodilator activity with degrees of relaxation higher than 50%. However, all these peptides failed to induce relaxation in endothelium-denuded aortic rings. The relaxation induced by RADHP was concentration-dependent and it was partially blocked by the nitric oxide synthase inhibitor l-NAME (100 μM) and by the B₁ bradykinin receptor antagonist Des-HOE 140 (30 nM), thus showing that it was mediated by NO production through the activation of B₁ bradykinin receptors. These findings suggest that these peptides could reduce the vascular resistance and could be used as functional food ingredients in the prevention and treatment of hypertension.