Acid glycosidases from hen oviduct and egg albumen

Activities of seven acid glycosidases: β-N-acetylhexosaminidase (β-HEX), α- and β-galactosidase (α- and β-GAL), α- and β-mannosidase (α- and β-MAN), α-glucosidase and α-fucosidase in magnum region of hen (Gallus gallus domesticus) oviduct, and four acid glycosidases: β-HEX, β-GAL, α- and β-MAN in egg albumen, were investigated. β-HEX from magnum and egg albumen hydrolysed 4-methylumbelliferyl-β-N-acetylhexosamine-6-sulphate (4-MeUmbGlcNAc-6-SO₄) like mammalian β-HEX form A. Multiple forms of magnum and egg albumen β-HEX, β-GAL, α- and β-MAN were separated by strong anion exchange chromatography and chromatofocusing method. Chromatofocusing of the magnum resulted in the appearance of multiple forms for β-HEX with pI of 6.18, 5.43, 5.55, 5.34, 5.27 and 5.16, for β-GAL with pI of 4.98, 4.84, 4.77, 4.64 and 4.68–4.63, for α-MAN with pI of ≥ 7.4, 6.75, 6.62 and 6.26, and for β-MAN two forms with pI of 6.37 and 5.77. Chromatofocusing of egg albumen yields multiple forms for β-HEX with pI of 6.24, 6.08, 5.55 and 5.35, for β-GAL two forms with pI of 5.10 and 4.86–4.80 for α-MAN multiple forms with pI of ≥ 7.4, 6.80, 6.60 and 6.30, and for β-MAN forms with pI of 6.30 and 5.77. In conclusion, this study was the first to show β-HEX activity against 4-MeUmbGlcNAc-6-SO₄ in the magnum and albumen of bird eggs, corresponding to β-HEX A activity in mammals. Main multiple forms of β-HEX, β-GAL, α- and β-MAN occurring in the magnum were revealed in the egg albumen. Comparison with a cock of the same breed showed that hen egg magnum and albumen has the same multiple forms of the enzymes that are found in the epididymides and seminal plasma of the cock.     

Phonotaxis of the female parasitoid Emblemasoma auditrix (Diptera, Sarcophagidae) in relation to number of larvae and age

The dipteran parasitoid Emblemasoma auditrix locates its host acoustically. Analysis showed that phonotactic female flies usually carry fully developed larvae within their uteri. The mean number of larvae per female at the beginning of the season was 37.9 (range from 10 to 50). The number of larvae decreased rapidly with increasing singing activity of the host cicada (Okanagana rimosa). In high-density host populations the parasitoid is likely to become egg-limited. A possible selective phonotactic responsiveness depending on the number of larvae or the age of the female was tested with song models. Phonotaxis depended on both the temporal structure and the frequency content, but in the field no correlation was found between the number of larvae and the preferences for the acoustic signal. Experiments in the laboratory showed that flies without host contact broadened their phonotactic stimulus range with age.     

Effects of elevated egg corticosterone levels on behavior, growth, and immunity of yellow-legged gull (Larus michahellis) chicks

Eggs of vertebrates contain steroid hormones of maternal origin that may influence offspring performance. Recently, it has been shown that glucocorticoids, which are the main hormones mediating the stress response in vertebrates, are transmitted from the mother to the egg in birds. In addition, mothers with experimentally elevated corticosterone levels lay eggs with larger concentrations of the hormone, which produce slow growing offspring with high activity of the hypothalamo-adrenal axis under acute stress. However, the effects and function of transfer of maternal corticosterone to the eggs are largely unknown. In the present study, we injected corticosterone in freshly laid eggs of yellow-legged gulls (Larus michahellis), thus increasing the concentration of the hormone within its natural range of variation, and analyzed the effect of manipulation on behavioral, morphological, and immune traits of the offspring in the wild. Eggs injected with corticosterone had similar hatching success to controls, but hatched later. Mass loss during incubation was greater for corticosterone-treated eggs, except for the last laid ones. Corticosterone injection reduced rate and loudness of late embryonic vocalizations and the intensity of chick begging display. Tonic immobility response, reflecting innate fearfulness, was unaffected by hormone treatment. Elevated egg corticosterone concentrations depressed T-cell-mediated immunity but had no detectable effects on humoral immune response to a novel antigen, viability at day 10, or growth. Present results suggest that egg corticosterone can affect the behavior and immunity of offspring in birds and disclose a mechanism mediating early maternal effects whereby stress experienced by females may negatively translate to offspring phenotypic quality.     

Negative effects of elevated testosterone on female fecundity in zebra finches

Although factors influencing androgen deposition in the avian egg and its effects on nestling fitness are recently receiving considerable attention, little is known about the potential costs of high testosterone levels in the females. Our study aimed at determining the effect of injections of testosterone (T) in female zebra finches (Taeniopygia guttata), on clutch size, egg mass, yolk mass, and yolk androgen content. Females were given a single bolus injection of T in a range of doses after laying the first egg. Results show that administration of T negatively affected clutch size; the strength of this effect increased with increasing doses of T. Females injected with the highest testosterone dose showed suppressed oviposition of the third and the fourth eggs. Interestingly, testosterone administration made females produce eggs with relatively large yolks, suggesting that T may mediate the trade-off between number and size of eggs. Testosterone injection resulted in elevated levels of androgen in the eggs, in contrast to control clutches, which showed a decreasing pattern of androgen concentration along the laying sequence. We conclude that high androgen investment in eggs may be limited by physiological requirements of the ovulatory process.     

Egg-size variation in the bluethroat (Luscinia s. svecica): constraints and adaptation

We examined inter- and intra-clutch egg-size variation in the bluethroat (Luscinia s. svecica), an open-nesting passerine breeding in the sub-alpine region in southern Norway. By removing first clutches shortly after egg-laying, we induced laying of a repeat clutch. Females significantly reduced the number of eggs from the first to the second nesting attempt, but increased mean egg size. Females in good condition laid significantly larger eggs than those in poor condition. Consistent with predictions of the brood survival hypothesis, assuming an adaptive investment in last eggs to ensure survival of all eggs in the clutch, we found that the size of the last eggs in first clutches was generally larger than the mean egg size of the clutch, and that the relative size of the last egg increased with clutch size. However, a large last egg reflected a general increase in egg size throughout the laying sequence rather than a specific investment in the last egg only. Egg size was not significantly influenced by sex or paternity (within-pair versus extra-pair) of the embryo. In repeat clutches the last egg was not consistently larger than the mean for the clutch. We conclude that female bluethroats face resource limitations during egg formation early in the season, and that the patterns of increase in egg size with laying order for first clutches, and from first to repeat clutches, can largely be explained by proximate constraints on egg formation.     

Phenoloxidase-like activities and the function of virus-like particles in ovaries of the parthenogenetic parasitoid Venturia canescens

The ichneumonid endoparasitoid Venturia canescens successfully develops inside the hemocoel of another insect by using maternal protein secretions, including nucleic acid-free virus-like particles (VLPs), to manipulate host physiology. These VLPs consist of four major proteins, which are produced mainly in the calyx tissue and transferred into the host insect together with the egg. One of the protein-coding genes (vlp1), with similarities to phospholipid-hydroperoxide glutathione peroxidases (PHGPx), exists in allelic forms producing two protein variants with different protein properties. Here, we summarise observations indicating that oocytes and eggs are the source of reactive electrons, which potentially damage the lining and membranes of calyx tissues. We discuss the possible role of VLP1 in counteracting the damaging effects of oxidised phospholipids on membranes surrounding VLPs in the calyx lumen.     

Complementary roles for dynein and kinesins in the Xenopus egg cortical rotation

Aligned vegetal subcortical microtubules in fertilized Xenopus eggs mediate the "cortical rotation", a translocation of the vegetal cortex and of dorsalizing factors toward the egg equator. Kinesin-related protein (KRP) function is essential for the cortical rotation, and dynein has been implicated indirectly; however, the role of neither microtubule motor protein family is understood. We examined the consequence of inhibiting dynein--dynactin-based transport by microinjection of excess dynamitin beneath the vegetal egg surface. Dynamitin introduced before the cortical rotation prevented formation of the subcortical array, blocking microtubule incorporation from deeper regions. In contrast, dynamitin injected after the microtubule array was fully established did not block cortical translocation, unlike inhibitory-KRP antibodies. During an early phase of cortical rotation, when microtubules showed a distinctive wavy organization, dynamitin disrupted microtubule alignment and perturbed cortical movement. These findings indicate that dynein is required for formation and early maintenance of the vegetal microtubule array, while KRPs are largely responsible for displacing the cortex once the microtubule tracks are established. Consistent with this model for the cortical rotation, photobleach analysis revealed both microtubules that translocated with the vegetal cytoplasm relative to the cortex, and ones that moved with the cortex relative to the cytoplasm.     

Profiling the morphological distribution of O-linked oligosaccharides

The morphological distribution of oligosaccharides is determined in the egg jelly surrounding Xenopus laevis eggs. This biological system is used to illustrate a method for readily identifying and quantifying oligosaccharides in specific tissues. The extracellular matrix surrounding X. laevis eggs consists of a vitelline envelope and a jelly coat. The jelly coat contains three morphologically distinct layers designated J1, J2, and J3 from the innermost to the outermost and is composed of 9-11 distinct glycoproteins. Each jelly layer is known to have specific functions in the fertilization of the egg. We developed a rapid method to separate and identify the oligosaccharides from X. laevis egg jelly layers. Identification was based on the retention times in high-performance liquid chromatography (porous graphitized carbon column), exact masses, and tandem mass spectrometry. Over 40 neutral and 30 sulfated oligosaccharides were observed in the three jelly layers. Neutral oligosaccharide structures from different jelly layers were both unique and overlapping, while sulfated oligosaccharides were detected only in layers J1 and J2. Neutral oligosaccharides unique to jelly layer J3 and the combined layers J1+J2 had similar core structures and similar residues. However, differences between these two sets of unique oligosaccharides were also observed and were primarily due to the branching carbohydrate moieties rather than the core structures.     

Effects of Karenia brevis diet on RNA:DNA ratios and egg production of Acartia tonsa

Karenia brevis is a harmful alga associated with deleterious effects on zooplankton, but the exact cause (e.g. toxin, nutritional inadequacy or starvation) of these adverse effects is not clear. RNA:DNA ratios, fecundity and fecal pellet production of Acartia tonsa were measured on mono-algal and mixed-algal culture diets of K. brevis and Peridinium foliaceum to examine the usefulness of RNA:DNA ratios as an indicator of nutrition and to determine if adverse effects of K. brevis are due to the presence of toxins, poor nutritional quality or starvation. RNA:DNA ratios and egg production values were significantly higher for 100% P. foliaceum diet compared to 100% K. brevis diet. Significant differences in egg production, but not RNA:DNA ratios, were found between the various mixed diets, suggesting egg production is a more sensitive indicator of nutritional quality than RNA:DNA ratios. Changes in RNA:DNA ratios, fecundity and fecal pellet production of copepods fed two different toxic K. brevis strains were nearly identical, indicating that the presence of brevetoxins has little affect on A. tonsa. The similarity in RNA:DNA ratios, egg production, percent hatching and fecal production between the 100% K. brevis diet and starved copepods suggests that A. tonsa does not consume K. brevis when offered as its sole food source.