Inhibition of protein synthesis elicits early grey crescent formation in the axolotl oocyte

Summary In the axolotl (Ambystoma mexicanum Shaw), it was recently shown that cycloheximide (CH) could induce early grey crescent formation (EGC) in non-activated oocytes, maturing in vitro (Grinfeld and Beetschen 1982). Since it was not proved that EGC was a consequence of protein synthesis inhibition rather than a side-effect of the drug, experiments were performed using microinjections of a quite different inhibitor, diphtheria toxin (DT). This toxin also appeared to elicit EGC. Incorporation of (³H) leucine into oocyte proteins in the presence of increasing DT concentrations (10^–11 to 10^–6 M) was then investigated. The frequency of EGC closely parallels the level of protein synthesis inhibition, which is higher in symmetrized oocytes. The lowest CH concentration which can still elicit EGC also exerts a fairly strong inhibition of (³H) leucine incorporation into proteins. It is concluded that protein synthesis inhibition in the late maturing oocyte actually creates specific conditions which allow cytoplasmic rearrangements to occur, leading to grey crescent formation. These results support the interpretation that (a) proteinic inhibitor (s) of symmetrization could be synthesized in the normal maturing oocyte.     

Involvement of the cytoskeleton in early grey crescent formation in axolotl oocytes

Summary Maturing axolotl oocytes which are treated with protein synthesis inhibitors or which are heat-shocked can be induced to reorganize their cytoplasm and to form an early grey crescent. The maturing axolotl oocyte has been used as a model system to study the role of the cytoskeleton in dorsoventral polarization as visualized by grey crescent formation. Results presented here provide evidence for the involvement of microtubules in the formation of the early grey crescent. Whereas inhibitors of microtubule polymerization and antibodies against tubulin both elicit early grey crescent formation, the effect of taxol shows that microtubule polymerization is required at a late stage in this event. The nucleus furnishes important factors required for early grey crescent formation and might play a role in microtubule polymerization.     

Key fish species, northern fur seals, Callorhinus ursinus, and fisheries interactions involving walleye pollock, Theragra chalcogramma, in the eastern Bering Sea

The recent decline of the northern fur seal population breeding on the Pribilof Islands has not yet been explained. This study estimates the amounts and sizes of walleye pollock (the fur seal's main prey) removed by predatory fish, fur seals and commercial fisheries in the main fur seal feeding area in the eastern Bering Sea during summer 1985. Fur seals relied primarily on age-1 pollock during 1985, while predatory fish consumed pollock mainly of ages 0-1. The fishery took pollock older than age-3. This indicated no direct effect of fishery removal on fur seal prey abundance, at least during the study period. In the short term, the 1985 pollock fishery may have indirectly affected fur seal prey abundance in a positive manner by removing adult pollock that compete with fur seals for age-1 pollock.     

Using population viability analysis to examine the potential long-term impact of fisheries bycatch on protected species

Fisheries bycatch is recognised as the dominant anthropogenic threat facing many protected species globally. Estimates of total bycatch are often associated with wide confidence intervals as a result of limited coverage by on-board observers. This makes it difficult for managers to assess risk and design effective management plans. Here, we present a case study of grey seal (Halichoerus grypus) bycatch in static net fisheries across Irish waters, where potentially unsustainable bycatch levels have been reported with typically wide confidence intervals. We used Population Viability Analysis (PVA) to explore potential bycatch scenarios at a national level in order to inform future monitoring and management efforts; including (i) a baseline scenario where the probability of seals becoming bycaught was independent of age and sex; (ii) probability was biased towards juvenile, male, or female seals; (iii) there was net immigration of seals from outside of the national population; and (iv) colony-specific bycatch rates were applied to assess the relative vulnerability of the major grey seal breeding colonies to bycatch mortality. Results demonstrated that (i) higher levels of bycatch reduced population growth, with bycatch of 800 seals per year reducing the national population by 99% over 100 years; (ii) population viability was most sensitive to bycatch mortality of female seals, and more robust to juvenile or male mortality; (iii) recruitment of 500 seals per year prevented population decline despite a worst-case bycatch scenario of 800 seals bycaught per year; (iv) colonies in the south and southwest were the first to show signs of decline under increasing bycatch pressure. PVA provides a clear justification for improved monitoring of seal bycatch to obtain more precise bycatch estimates, and highlights the need for future studies to identify appropriate grey seal management units.     

The dynamics of male harem dominance in southern elephant seals (Mirounga leonina) at the South Shetland Islands

Breeding chronology, harem structure and changes in male harem dominance were studied at Stranger Point, Isla 25 de Mayo/King George Island, principally by extensive field census work during the 2003 breeding season. Males were individually identified and their size estimated by using a photogrammetric method. Peak female haul out for the population occurred on 31 October, when a total of 276 females were observed along 7 km of coastline, distributed in ten harems with a median size of 16 females. Overall sex ratio and harem sex ratio for the breeding population were 1:6.7 and 1:10.6, respectively. A total of 33 males were identified associated with harems. Male size conferred an advantage in terms of dominance hierarchy, since dominant males (4.91±0.15 m) were significantly longer than subordinate males (4.63±0.19 m). Harems were dominated by an average of 4.5 (range 2–7) different males during the breeding season. Elephant seals at Stranger Point breed in very low density aggregations. The main breeding events in this population occurred later than at other breeding sites, which agrees with previous observations in the area. Male movement among harems suggests that differences in mating success among males could be achieved through their different behaviours.     

USING CARBON AND NITROGEN ISOTOPE VALUES TO INVESTIGATE MATERNAL STRATEGIES IN NORTHEAST PACIFIC OTARIIDS

We examine the utility of stable carbon and nitrogen isotope variations to characterize the length of the nursing/lactation period and age at weaning for two northern Pacific otariid species, the northern fur seal (Callorhinus ursinus) and California sea lion (Zalophus californianus). We used two sampling strategies to measure ontogenetic trends in isotope value, and compared our results to observational data on the reproductive strategies used by these otariids. For Zalophus, we found evidence for ¹⁵N enrichment and ¹³C‐depletion in bone collagen representing the first and second year of growth, which is consistent with the ～12–14‐mo weaning age in this population after a suitable turnover rate for bone collagen is considered. Analysis of individual tooth annuli from a different suite of Zalophus specimens suggests that half of the individuals were weaned at ～12 mo of age, and half were dependent on milk for a portion of their second year. For Callorhinus, bone collagen for age classes that contain pre‐weaned individuals were ¹⁵N‐enriched, but values were significantly lower in specimens between 6 and 20 mo of age. These ¹⁵N‐enriched values, presumably acquired during nursing between 0 and 4 mo of age in Callorhinus, were not present in specimens older than 12 mo of age. Thus complete bone collagen turnover in young‐of‐the‐year occurs in 8–10 mo. ¹⁵N enrichment is evident in the first annulus of female Callorhinus individuals, but is not detectable in males. Analyses of Callorhinus tooth annuli show no ontogenetic trends in δ¹³C values. Our study indicates that nitrogen, and in some cases carbon, isotopes can be used to assess reproductive strategies in marine mammals. When coupled with accurate age estimates based on bone growth regressions, this isotopic technique can be applied to historical or fossil otariids to gain insight into the flexibility of maternal strategies within and across species.     

一类灰色项时间序列模型及其应用

利用灰色系统理论与时间序列分析,提出了带灰色项的时间序列模型,对这类模型进行了分析,给出了建模与预报方法,并将其应用于我国农业产值问题的预报与研究之中,模型的正确性得到了检验．