The mechanism of action of adrenaline in the induction of sexual reproduction (encystation) in Opalina sudafricana parasitic in Bufo regularis

El Mofty M. M. and Sadek I. A. 1973. The mechanism of action of adrenaline in the induction of sexual reproduction (encystation) in Opalina sudafricana parasitic in Bufo regularis. International Journal for Parasitology3: 425–431. Adrenaline injections induced encystation in the opalinids of normal, hypophysectomized, and gonadectomized toads in the pre-breeding and post-breeding seasons. In normal and gonadectomized male and female toads, adrenaline injections may stimulate the release of ACTH of the anterior pituitary which in turn induces the secretion of androgenic steroids from the interrenal tissue. It is speculated that the breakdown products of these androgenic steroids cause the encystation of the parasites. In hypophysectomized male and female hosts, the injected adrenaline may stimulate the interstitial tissue of the testes and ovaries to secrete androgens, the breakdown products of which induce encystation of the opalinids. Adrenaline or ACTH gave negative results in vitro. Urine of male or female toad injected with adrenaline, ACTH, or testosterone propionate induced encystation in Opalina sudafricana m vitro.     

The effect of fresh toad bile on the induction of encystation in Opalina sudafricana parasitic in Bufo regularis

Opalina sudafricana reacted by encystation to small doses (0.04 ml) of fresh toad bile injected subcutaneously into its host Bufo regularis. It is speculated that androgens present in the injected bile of male toads, and oestrogens found in injected bile of female hosts reach the parasites in the recta of the treated animals and induce them to encyst. High doses of bile killed the parasites and their hosts. Small doses of bile (0·04 ml) added to in vitro cultures induced encystation in the opalinids. High doses killed the opalinids in vitro. There is also the possibility that bufodeoxycholic acid found in the toad bile may play a role in inducing the parasites to divide and encyst.     

Induction of sexual reproduction in Opalina sudafricana by injecting its host Bufo regularis with gibberellic acid

Induction of sexual reproduction in Opalina sudafricana by injecting its host Bufo regularis with gibberellic acid. International Journal for Parasitology4, 203–206. Opalina sudafricana parasitic in the rectum of Bufo regularis was induced to reproduce sexually when its host was injected subcutaneously with 0·3 mg of gibberellin-A₃. This plant growth substance had no effect on the induction of encystation in the parasites in vitro. Urine of toads injected with gibberellin-A₃ induced sexual reproduction (encystation) in the opalinids in vitro. It is speculated that the plant hormone must either be broken down into an active substance by the toad or cause the toad to excrete its own gonadal hormones (or other hormones) into the urine. This active substance or the excreted hormones may induce division in the parasites resulting in the formation of small forms which encyst.     

夜光藻有性繁殖研究进展

夜光藻是全球最主要的赤潮生物之一,也是我国近海常见的浮游甲藻。根据营养方式分为异养的红色夜光藻和混合营养的绿色夜光藻,前者广泛分布于温带和亚热带近岸水域,后者仅分布于热带西太平洋、阿拉伯海、阿曼湾和红海。夜光藻的生活史包括无性繁殖和有性繁殖过程。少部分营养细胞自发转变为配子母细胞,启动了有性繁殖。每个配子母细胞可形成大量配子,具有横沟、纵沟和2根鞭毛,形态与裸甲藻接近。配子两两融合形成合子,合子不经过休眠孢囊阶段直接发育成新的营养细胞。目前,对配子母细胞形成的调控机制、合子发育的影响因素的认识还存在分歧。研究发现,营养细胞经过一定次数的二分裂后都会转变为配子母细胞,而配子的存在能够中止此过程,使营养细胞继续进行二分裂。因此,有性繁殖可能通过产生新个体对种群增长做出贡献,还可能通过释放配子维持无性繁殖,进而促进种群增长。配子在相模湾水域全年都有分布,其丰度峰值与营养细胞丰度峰值同步或提前出现,配子的大量出现可能是赤潮形成的必要条件。对有性繁殖的研究佐证了夜光藻在甲藻的系统进化中处于较为古老的地位。此外,还简单介绍了研究夜光藻有性繁殖的主要方法,回顾了国内的夜光藻研究,并对相关研究进行了展望。     

树干附生尖叶拟船叶藓性比和有性生殖的比例

通过对贵州梵净山树干附生尖叶拟船叶藓的野外调查和室内研究,结果表明,在44个被调查样方共计1320株植株中,尖叶拟船叶藓单株的性比为8♀∶1♂(N=1320),其中25.0%的单株没有进行性表达;其种群的性比为5♀∶1♀♂(雌性种群:混合种群,N=44),没有发现雄性种群;其单株的有性生殖的比例为10.5%,种群的有性生殖比例为9.3%。结果表明尖叶拟船叶藓种群具有明显的雌性偏向,其种群的自然更新更多的是依赖各种营养繁殖。     

Patterns of sexual reproduction in diatoms

Sexual reproduction takes many forms within the diatoms. The variation has been classified by several authors, but in most cases the distinctions between their main categories have depended on the number of gametes produced per gametangium (and thus on how many zygotes per pair of copulating cells), and upon whether fusion is oogamous, anisogamous or isogamous. These classifications are not themselves an adequate basis for taxonomic comparison, which should be based on individual characteristics of the sexual process. Diatoms seem to be primitively oogamous. In araphid pennate diatoms and some raphid diatoms the gametes and gametangia are morphologically alike but physiologically distinct; one gametangium produces active gametes and the other passive ones. This may be the primitive condition in pennate diatoms, providing a link to the oogamy of centrics via the morphological anisogamy of Rhabdonema Kütz.     

Frequent fires do not affect sexual expression and reproduction in Vachellia caven

In environments with high fire frequency the impoverishment of abiotic resources may favour male sexual expression in plants as it is less costly than female expression. Also, fire can modify pollinator communities and thus affect plant reproduction. Here we evaluate the effect of frequent fires on sexual expression, pollination and reproductive success of Vachellia caven (Leguminosae), an andromonoecious tree that is highly dependent on animal pollination and is abundant in burned sites. We expect that increased fire frequency will favour maleness but it will decrease reproductive success due to abiotic resource depletion in repeated burned sites. To test this, we selected focal plants in three unburned sites and three frequently burned sites and measured their sexual expression, basal diameter, pollination and fruit set. The proportion of male inflorescences per plant was not affected by fire and it was negatively related with the diameter of the plant. The proportion of pollinated flowers was not affected by fire, and fruit set increased with maleness only in frequently burned sites. These results indicate that V. caven is adapted to regimes of high fire frequency: not only was there similar fruit set in both burned and unburned sites, but more male plants had higher fruit set in burned sites. Despite the soil impoverishment triggered by repeated fires, V. caven is able to maintain its sexual and reproductive functions, allowing it to persist and maintain viable populations in fire‐prone environments. Abstract in Spanish is available with online material.     

Density-dependent sexual reproduction in natural populations of the rotifer asplanchna girodi

The monogonont rotifer Asplanchna girodi was continuously present in daily and bi-daily plankton samples of Golf Course Pond during the spring of 1977. Two cycles of sexual reproduction occurred during this period. By isolation and culture of females it was possible to determine the reproductive type of collected individuals. Data thus obtained suggest that environmental cues associated with population density are responsible for the production of sexual females.     

Aplanogamous sexual reproduction in Carteria eugametos (Volvocales,Chlorophyta)

Morphological details of sexual reproduction in Carteria eugametos (Volvocales, Chlorophyta) were studied under controlled laboratory conditions. Protoplasts of the two pairing, flagellate cells were released from cell walls to become isogametes. Such gametes were nonmotile and soon fused to form a completely immobile zygote. The zygote then secreted a cell wall to enter the dormant period. After dark treatment, the zygote produced four, eight or 16 quadriflagellate germ cells, and a transparent vesicle enclosing all the germ cells was released from the zygote wall. This type of zygote germination and aplanogamy in C. eugametos is unique and may be related to its peculiar phylogenetic position within the Volvocales (Chlamydomonadales).     

高温刺激对蟾蜍免疫活性和能量消耗的影响

全球气候变化是导致全世界两栖动物种群衰退和灭绝的重要因素之一。为了解无尾两栖类在气候异常导致的极端高温下的生理反应特征和相关适应机制,以雄性中华大蟾蜍(Bufo bufo gargarizan)为对象,研究该物种在高温刺激(环境温度由22 ℃迅速升至32 ℃)0、6、12、24、48 h后的非特异性免疫活性和能量消耗的变化情况。研究结果:与对照组(22 ℃)比较,高温刺激可显著抑制外周血细胞吞噬活性;而脾脏巨噬细胞呼吸爆发在高温刺激下呈现出先增强后减弱的趋势。高温刺激导致血糖含量在第24和48 h显著低于对照组,而对肝糖原含量无显著影响。处理组精巢ATP含量逐渐升高,并于24和48 h显著高于对照组;处理组Na⁺-K⁺-ATPase活性随时间呈现出先下降后上升稳定的趋势,但与对照组相比均无显著性差异,;处理组Ca²⁺-Mg²⁺-ATPase活性在不同时期与对照组相比均无显著性差异。研究结果说明,高温刺激可显著抑制中华大蟾蜍的非特异性免疫功能,并导致血糖的大量消耗;当面对高温胁迫时,雄性大蟾蜍可能会投入更多的能量来维持性腺的正常发育。     

Parthenogenetic vs. sexual reproduction in oribatid mite communities

The dominance of sex in Metazoa is enigmatic. Sexual species allocate resources to the production of males, while potentially facing negative effects such as the loss of well‐adapted genotypes due to recombination, and exposure to diseases and predators during mating. Two major hypotheses have been put forward to explain the advantages of parthenogenetic versus sexual reproduction in animals, that is, the Red Queen hypothesis and the Tangled Bank/Structured Resource Theory of Sex. The Red Queen hypothesis assumes that antagonistic predator—prey/ parasite–host interactions favor sex. The Structured Resource Theory of Sex predicts sexual reproduction to be favored if resources are in short supply and aggregated in space. In soil, a remarkable number of invertebrates reproduce by parthenogenesis, and this pattern is most pronounced in oribatid mites (Oribatida, Acari). Oribatid mites are abundant in virtually any soil across very different habitats, and include many sexual and parthenogenetic (thelytokous) species. Thereby, they represent an ideal model group to investigate the role of sexual versus parthenogenetic reproduction across different ecosystems and habitats. Here, we compiled data on oribatid mite communities from different ecosystems and habitats across biomes, including tropical rainforests, temperate forests, grasslands, arable fields, salt marshes, bogs, caves, and deadwood. Based on the compiled dataset, we analyzed if the percentage of parthenogenetic species and the percentage of individuals of parthenogenetic species are related to total oribatid mite density, species number, and other potential driving factors of the reproductive mode including altitude and latitude. We then interpret the results in support of either the Red Queen hypothesis or the Structured Resource Theory of Sex. Overall, the data showed that low density of oribatid mites due to harsh environmental conditions is associated with high frequency of parthenogenesis supporting predictions of the Structured Resource Theory of Sex rather than the Red Queen hypothesis.     

Resource allocation to sexual and vegetative reproduction in a forest herbSyneilesis palmata (Compositae)

The balance between sexual and vegetative reproduction inSyneilesis palmata was examined in relation to environmental conditions and the amount of reproductive resources, which is defined here as the total quantity of dry matter invested in both modes of reproduction. The allocation balance was measured for individual plants of two populations, with different densities in an open habitat, for 2 years, and those of two other populations, under different light intensities in a plantation forest (forest floor and edge), for 3 years. Relative allocation to sexual reproduction decreased with increasing reproductive resources in all populations except for the forest edge, which showed a constant allocation balance. The high density population showed lower relative allocation to sexual reproduction than the low density population, irrespective of the amount of reproductive resources. However the between-year comparison of the high density population suggested that under extremely high density, plants with a small amount of reproductive resources enhanced sexual reproduction, while plants with a large amount of reproductive resources reproduced vegetatively. On the forest floor, plants with small amounts of reproductive resources had higher relative allocation to sexual reproduction than the forest edge population, while plants with large amounts of reproductive resources had a somewhat lower one. The adaptive significance of such allocation patterns are discussed, based on qualitative data on the characteristics of both types of offspring.     

Cycle of gonadal development in Eunicella singularis (Cnidaria: Octocorallia): trends in sexual reproduction in gorgonians

Abstract. Eunicella singularis is a gorgonian species whose members are abundant in hard-bottom sublittoral communities of the Mediterranean Sea. The reproductive biology in this species has been examined to better understand the ability in this species to recover from recent mass mortality events. Eunicella singularis is a stable, gonochoric, iteroparous species that reproduces annually and exhibits a seasonal pattern of gametogenesis characterized by a single annual maturation of the gametes. The sex ratio did not significantly differ from 1:1. Oogenesis lasted 13–17 months, beginning between February and June, and ending with the release of 0.7 planula larvae per polyp between late May and July of the following year. The diameter of mature oocytes ranged 450–860 μm. Spermatogenesis was much shorter than oogenesis and occurred over 5–6 months. Gonadal production of both sexes increased in spring and culminated with the spawning of male colonies in late May–June. Fertilization of oocytes and development of the planula larvae occurred within the polyps of female colonies. Planula release was observed in June and July. The patterns emerging from this and previous studies on sexual reproduction of Mediterranean gorgonians suggest that investment in gonad development appears to be related to resource availability.     

Restriction of sexual reproduction in the moss Racomitrium lanuginosum along an elevational gradient

1. Terrestrial plant populations located at the margins of species’ distributions often display reduced sexual reproduction and an increased reliance on asexual reproduction. One hypothesis to explain this phenomenon is that the decline is associated with environmental effects on the energetic costs to produce reproductive organs.
2. In order to clarify the changing processes of sexual reproduction along an elevational gradient, we investigated the sexual reproductive parameters, such as the number of sporophytes and gametangia, in Racomitrium lanuginosum, a dioicous moss found on Mt. Fuji.
3. Matured sporophytes were present only below 3,000 m, and the number of sporophytes per shoot tended to be lower at higher elevation habitats. The numbers of male inflorescences per shoot and antheridia per inflorescence and shoot significantly decreased with increasing elevation. In contrast, the numbers of female inflorescences per shoot and archegonia per inflorescence and shoot varied little across elevations.
4. Synthesis. Our results suggest that the reasons for this limitation are assumed to be limitations in sporophyte development that result in abortion, and the spatial segregation between males and females. Possible reasons for the abortion of sporophytes are the inhibitory effects of low air temperature, a shortened growth period, and winter environmental conditions at higher elevations. Remarkable differences between male and female on various reproductive parameters found in this study are thought to affect the mode of sexual reproduction under the harsh environment. These differences between males and females may be caused by differences in the costs of production and development of gametangia, sensitivity to environmental stressors, and phenological patterns.

     

The importance of sexual and asexual reproduction in the recent evolution of Allium vineale

In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. In the whole sample, 77 nuclear multilocus genotypes and four chloroplast haplotypes (chlorotypes) were found. Populations exhibited a high degree of subdivision for nuclear and cytoplasmic markers as estimated from hierarchical F-statistics; at the same time, identical chlorotypes could be found in populations separated by large distances. Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring. Nevertheless, within each chlorotype, the distribution of markers from pairs of nuclear loci was incompatible with a purely clonal structure, suggesting that many multilocus genotypes have originated by sexual recombination rather than by mutation within asexual lineages. It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe.     

Loss and gain of sexual reproduction in the same stick insect

The outcome of competition between different reproductive strategies within a single species can be used to infer selective advantage of the winning strategy. Where multiple populations have independently lost or gained sexual reproduction it is possible to investigate whether the advantage is contingent on local conditions. In the New Zealand stick insect Clitarchus hookeri, three populations are distinguished by recent change in reproductive strategy and we determine their likely origins. One parthenogenetic population has established in the United Kingdom and we provide evidence that sexual reproduction has been lost in this population. We identify the sexual population from which the parthenogenetic population was derived, but show that the UK females have a post‐mating barrier to fertilisation. We also demonstrate that two sexual populations have recently arisen in New Zealand within the natural range of the mtDNA lineage that otherwise characterizes parthenogenesis in this species. We infer independent origins of males at these two locations using microsatellite genotypes. In one population, a mixture of local and nonlocal alleles suggested males were the result of invasion. Males in another population were most probably the result of loss of an X chromosome that produced a male phenotype in situ. Two successful switches in reproductive strategy suggest local competitive advantage for outcrossing over parthenogenetic reproduction. Clitarchus hookeri provides remarkable evidence of repeated and rapid changes in reproductive strategy, with competitive outcomes dependent on local conditions.     

浙江丽水中国石龙子的食性、两性异形和雌性繁殖

丽水分布的中国石龙子（Ｅｕｍｅｃｅｓ ｃｈｉｎｅｎｓｉｓ）摄入的食物均为无脊椎动物,分别属于环节、软体和节肢动物,涉及３０余科,成体和幼体的食物生态位宽度分别为７．２６和６．６９,成体的幼体的食物生态们重叠度为０．５９。性成熟雄性个体大于雌体。成雄和幼体的头长和头宽随体长ＳＶＬ的增长速率大于成雌,成雄头长随ＳＶＬ的增长速度显著大于幼体,成雌和幼体的头长随ＳＶＬ的增长速率无显著差异。成雄头部大于成雌