Age, distribution and abundance of viable resting eggs of Acartia pacifica (Copepoda: Calanoida) in Xiamen Bay, China

The distribution and abundance of viable resting eggs of copepod Acartia pacifica in Xiamen Bay, China, were determined in the laboratory by the presence of nauplii hatched from the sediments. Sediment cores to a depth of 30 cm, sliced at 1.0 cm intervals, showed that most viable resting eggs of A. pacifica occurred near the sediment surface (0-5 cm), and the number of viable eggs sharply decreased with depth of the sediment, although resting eggs remained viable as deep as 23 cm. ²¹⁰Pb analyses of the sediments indicated that the maximum age of viable eggs of A. pacifica was 20.5 years and the mean egg age was 4.3 years. The egg mortality of A. pacifica in the sediment was 0.1408 year⁻¹, or 85.92% annual egg survival, calculated by regressing ln(egg density) on the age of the sediment. The horizontal distribution of viable resting eggs ranged from 2.27×10³ to 3.85×10⁵ m⁻², with a mean value of 9.49×10⁴ m⁻². Regressions between viable eggs of A. pacifica and all fine-fraction particle size classes (at 2 μm intervals) were not significant. The accumulation of viable resting eggs that can persist for an extended period of time provided evidence for the existence of an egg bank of A. pacifica in the seabed of Xiamen Bay.     

Reproductive isolation among geographically and temporally isolated marine Brachionus strains

Using a polyclonal antibody against the mate recognition pheromone (MRP) of Brachionus rotundiformis Koshiki strain, we investigated the behavioral reproductive isolation and the similarity of MRP among geographically and temporally isolated B. rotundiformis strains. Males of the Koshiki strain did not discriminate in mating attempts among females of the Koshiki strain and those of conspecific allopatric strains from Hamana, Fiji, Thailand and Spain. Likewise, Koshiki males attempted mating with statistically indistinguishable frequency with Koshiki females and B. plicatilis strains. However, copulation was not consummated between Koshiki males and B. plicatilis females. The amount of anti-MRP binding to three allopatric B. rotundiformis strains was similar to that of the Koshiki strain, but binding to Hamana and the B. plicatilis strain was significantly lower. Four temporally separated B. rotundiformis populations were hatched from resting eggs collected from 0, 5, 10 and 15 cm depth in the sediment of Kai-ike pond in Koshiki island, Japan. Sediment age was determined using the ²¹⁰Pb method, allowing us to estimate that resting eggs from 15 cm depth were produced 65 years ago. Results of mating assays and anti-MRP binding showed that no behavioral reproductive isolation exists among the four temporally isolated Koshiki strains. B. rotundiformis appears to be reproductively isolated from B. plicatilis, but heterospecific matings are still attempted between B. plicatilis and B. rotundiformis, suggesting that the MRP remains sufficiently similar to elicit circling behavior.     

Spine development in Brachionus quadridentatus from an Australian billabong: genetic variation and induction by Asplanchna

Fertilized resting eggs of Australian Brachionus quadridentatus hatched 2–3 days after hydration into females with or, more frequently, without posterior lateral spines. These females then produced clones with short-spined or long-spined phenotypes. Asplanchna girodi induced females from two short-spined clones and one long-spined clone to produce daughters with significantly longer posterior lateral spines. In all clones, there were significant differences in spine development among offspring of mothers within Asplanchna and control treatments. The range of phenotypes reported in one short-spined clone is observed in the billabong and includes much of the variation described for the species, with mehleni (long-spined) phenotypes occurring with Asplanchna. In B. quadridentatus, the ecological significance of long-spined, basic phenotypes, and of the spine-development response to Asplanchna, is unclear. In laboratory cultures, females of all clones were attached to the substratum or water surface, and were safe from Asplanchna; in nature, females are epiphytic and probably rarely susceptible to Asplanchna. Most (96%) resting eggs produced in cultures and kept under culture conditions hatched after a 7-day latent period. This raises questions regarding natural conditions which might prevent hatching and allow accumulation of resting eggs in a sediment egg bank. Hatching of resting eggs in nature may be enhanced in sediments which dry and then become flooded after rains.     

新疆石河子棉蚜越冬卵的发育规律

棉蚜雌性蚜交配个体平均产卵量为 6 3± 1 1粒 ;未交配个体也产卵 ,卵亦变色 ,但卵量极少。越冬卵经 5 %NaOH浸泡 2 4h后卵壳透明 ,镜下观察可见受精卵胚胎发育到体躯分节期开始越冬。冬后胚胎发育仅处在颗粒团状的饱满卵应为无效卵 ,不会孵化 ;颜色发亮的卵处理后胚胎外貌清晰可见 ,此种卵当天即可破壳。棉蚜卵为滞育卵 ,春季降水对孵化有促进作用 ;室外棉蚜卵的饱满率和饱满卵的孵化率较低。该地区秋冬气候特点可能是石河子地区棉蚜卵低温条件下安全越冬的重要因素     

The interplay between colonization history and gene flow in passively dispersing zooplankton: microsatellite analysis of rotifer resting egg banks

Zooplanktonic organisms that disperse passively as diapausing eggs often exhibit surprisingly strong population subdivision given their high colonization ability. Here we attempt to disentangle the impacts of colonization history and gene flow on these organisms by studying the population genetic structure of the rotifer Brachionus plicatilis. The resting egg banks of B. plicatilis in fourteen salt lake populations in the Iberian Peninsula were examined using seven microsatellite loci. A remarkably high degree of geographical structuring was found (F_st=0.43), with a significant pattern of isolation by distance. Microsatellite loci were in genetic equilibrium, ruling out inbreeding as an important force in population structuring. Comparisons are drawn with previously published phylogeographical data. Surprisingly, introgression of nuclear genes was detected in neighbouring populations with divergent mtDNA haplotypes. These results stress the long lasting impact of colonization history and the modulating effect of gene flow at local scales in these organisms.     

Sensitivity of North American sturgeons and paddlefish to fishing mortality

Sturgeons and paddlefish exhibit unusual combinations of morphology, habits, and life history characteristics, which make them highly vulnerable to impacts from human activities, particularly fisheries. Five North American sturgeons (shortnose, Gulf, pallid, Alabama, and green sturgeon) are listed as endangered or threatened by management authorities. Managers have instituted fishery closures for the three other species of North American sturgeons (Atlantic, white, and shovelnose) and paddlefish because of low stock abundance at some point in this century. Reproductive potential in four species I examined (Atlantic, white, and shortnose sturgeon, and paddlefish) is more sensitive to fishing mortality than it is for three other intensively-fished coastal species in North America: striped bass, winter flounder, and bluefish. The sturgeons and paddlefish are generally longer-lived than the three other coastal species, and also have an older age at full maturity, lower maximum fecundity values, and older ages at which 50% of the lifetime egg production is realized with no fishing mortality.     

First report on egg deposition and egg morphology of the endangered endemic Romanian perch

The surface of the whitish translucent egg of Romanichthys valsanicola is sculptured in an irregular honeycomb–like pattern. The micropyle consists only of a type I micropylar channel.     

Development of human and mouse strain of Hymenolepis nana in mice

Ferretti G., Gabriele F. and Palmas C. 1981. Development of human and mouse strain of Hymenolepis nana in mice. International Journal for Parasitology11: 425–430. An Hymenolepis nana strain isolated from human faeces was transferred in the mouse. At first, the q ratio (the number of parasites to the number of eggs used) was very low. After 10 passages adaptation was complete: when mice of different age and strain (CD₁ and BDF₁) were infected with eggs of the above strain and eggs of 2 different murine strains, no differences emerged in the q ratio or in the parasite mean dry weight. Survival also appeared the same in the 3 parasite strains, however, human and murine strains live for a shorter time in BDF₁ than in CD₁ mice. Discussion bears on the hypothesis that the difficulties that emerge during the first passages may be connected to the adult and not to the larval phase.     

A comparison of in vitro and in vivo estimates of the viability of Taenia pisiformis eggs aged under controlled conditions, and their ability to immunise against a challenge infection

Storing the eggs of T. pisiformis for periods of 0 to 9 days at a temperature of 36–38°C and relative humidity of 87–93 % revealed at least 4 stages in the ageing process. Firstly, a stage in which eggs hatched and activated in vitro and were also fully infective for rabbits. Secondly, a stage in which eggs hatched and activated in vitro but underwent only partial development in rabbits. Thirdly, a stage in which eggs hatched and activated in vitro, and presumably therefore in vivo, but no evidence of infection could be found when they were fed to rabbits. Fourthly, a stage in which eggs either did not hatch, or if they did hatch, the oncosphere was rapidly digested. In vitro techniques for assessing viability of T. pisiformis eggs were not a reliable guide to their infectivity for rabbits. ‘Senescent’ eggs, that is eggs which produced evidence of early infection in rabbits but did not complete their development to cysticerci, failed to produce immunity to challenge infection with T. pisiformis eggs.     

The strontium content of roe collected from spawning brown trout Salmo trutta L. reflects recent otolith microchemistry

The relationship between the strontium content of the outer layers of otoliths (an indication of recent marine, estuarine or riverine habitat use) and the strontium content of roe in ripe female brown trout Salmo trutta was examined in fish collected from the Pomahaka River and the lower reaches of the Clutha River, South Island, New Zealand. A close relationship was found between the strontium content of roe and the outer layers of otoliths. This finding suggests that spawned eggs collected from redds could potentially be used to track the extent of upstream spawning migrations by anadromous brown trout.