Intersex inflorescences of Rumex acetosa demonstrate that sex determination is unique to each flower

* A triploid intersex individual of the normally dioecious species Rumex acetosa showed extreme variability in gynoecium development. Analysis of the development and distribution of these flowers on inflorescences enabled insight to be gained into the mechanism of sex determination. * Floral phenotypes on intersex inflorescences were classified according to gynoecium development. Flower morphology was investigated by scanning electron and light microscopy. Organ identity gene expression in intersex floral primordia was assessed using in situ hybridization. * The distribution of the different floral phenotypes shows that each individual flower is determined separately, and that the phenotype of each flower is not influenced by its position on the inflorescence, or by the phenotype of neighbouring flowers. C-function gene expression persisted in gynoecia that had ceased development. * Gynoecium development in mutant flowers resembled the phenotype of the Arabidopsis mutant ettin and suggests that a hormone gradient may be involved. C-function expression does not appear to control the extent of female development, and indicates that genes which are downstream of the organ-identity genes must control organ suppression.     

Characterization of microsatellite loci in the marine seaweeds,Fucus serratus and F. evanescens (Heterokontophyta; Fucaceae)

Fucus serratus and F. evanescens commonly occur on Northern European shores. Nine microsatellite loci were developed for F. serratus (8–22 alleles, observed heterozygosities = 0.367–0.850) and one for F. evanescens (seven alleles, observed heterozygosity = 0.804). Cross‐amplification was apparent, as five F. serratus loci were polymorphic in F. evanescens and 2–5 were polymorphic in F. vesiculosus, F. distichus, and F. spiralis.     

Hybridization and introgression in a mixed population of the intertidal seaweeds Fucus evanescens and F. serratus

The introduced Fucus evanescens (hermaphroditic) and the native F. serratus (dioecious) have been in secondary contact along the Danish coast of the Kattegat Sea for 60–100 years and dioecious hybrids have been observed at Blushøj for several years. Hybridization in Fucus is unusual because it appears to always involve a hermaphroditic and a dioecious parental pair. We determined the degree and spatial patterns of introgression for 286 individuals using 10 microsatellite loci and cpDNA. Hybrids accounted for nearly 13% of the population, yet parental species were well differentiated (F_ST = 0.633). The presence of F. evanescens chloroplasts in 100% of F₁ hybrids revealed asymmetrical hybridization. Fucus evanescens cpDNA was observed in 50% of introgressed and 5.4% of pure F. serratus, but no F. serratus cpDNA was found in F. evanescens. In contrast, nuclear DNA introgression was symmetrical with an equal amount (≈1.5%) of genes introgressed into each parental species. Survivorship and viability data suggest selection against hybrids in the hybrid zone.     

雌雄异株植物性别鉴定的研究进展

雌雄异株植物为研究植物的性别决定和进化提供了一个模式体系,由于不同性别的植物具有不同的经济价值,所以其性别鉴定的研究不仅具有重要的理论意义,而且具有极为重要的实践价值。从外部形态、生理生化指标、染色体组型、同工酶、特异蛋白质分子、分子标记等方面,对近15年来国内外有关雌雄异株植物性别鉴定研究的进展作了总结,并对各种鉴定方法的优缺点进行了评价,同时对其研究发展趋势作了展望。     

Sry‐negative XX sex reversal in purebred dogs

The gene responsible for testis induction in normal male mammals is the Y‐linked Sry. However, there is increasing evidence that other genes may have testis‐determining properties. In XX sex reversal (XXSR), testis tissue develops in the absence of the Y chromosome. Previous polymerase chain reaction (PCR) assays indicated that autosomal recessive XXSR in the American cocker spaniel is Sry‐negative. In this study, genomic DNA from the breeding colony of American cocker spaniels and from privately owned purebred dogs were tested by PCR using canine primers for the Sry HMG box and by Southern blots probed with the complete canine Sry coding sequence. Sry was not detected by either method in genomic DNA of affected American cocker spaniels or in the majority (20/21) of affected privately owned purebred dogs. These results confirm that the autosomal recessive form of XXSR in the American cocker spaniel is Sry‐negative. In combination with previous studies, this indicates that Sry‐negative XXSR occurs in at least 15 dog breeds. The canine disorder may be genetically heterogeneous, potentially with a different mutation in each breed, and may provide several models for human Sry‐negative XXSR. A comparative approach to sex determination should be informative in defining the genetic and cellular mechanisms that are common to all mammals. Mol. Reprod. Dev. 53:266–273, 1999. © 1999 Wiley‐Liss, Inc.     

Induced sex change in black sea bass

Experiments were conducted to identify factors involved in sex change in the protogynous black sea bass Centropristis striata . Black sea bass maintained in the ratio of 8 females (F):0 males (M) for 9 months reversed sex while those kept at the ratios of 6F:2M or 4F:4M did not. Female black sea bass implanted with 1·0 mg 11-ketotestosterone (11-KT) or 10 mg fadrozole (FAD) changed sex and began spermiating while those implanted with 0·1 mg 11-KT or 1·0 mg FAD underwent incomplete sex reversal. One fish implanted with 1·0 mg FAD initiated sex change but was not spermiating at the end of the study. One fish in the control group, the largest fish in the study, initiated sex change. These results suggest that the presence of males may restrict sex reversal in black sea bass and that high 17β-oestradiol:11-KT is required for maintaining ovarian function.     

Distribution of ceramidephosphoinositol in red seaweeds

An inositol-containing sphingophospholipid ceramidephosphoinositol (CPI) found for the first time in red macrophytic algae proved to be typical of the Rhodophyta. The CPI content varied among the algal species from trace amounts to 15.7% of the total phospholipids and depended on season. Red seaweeds provide a more convenient source of ceramidephosphoinositol than other organisms.     

Sex-ratio evolution in sex changing animals

Sex allocation theory is often able to make clear predictions about when individuals should facultatively adjust their offspring sex ratio (proportion male) in response to local conditions, but not the consequences for the overall population sex ratio. A notable exception to this is in sex changing organisms, where theory predicts that: (1) organisms should have a sex ratio biased toward the "first" sex: (2) the bias should be less extreme in partially sex changing organisms, where a proportion of the "second" sex matures directly from the juvenile stage; and (3) the sex ratio should be more biased in protogynous (female first) than in protandrous (male first) species. We tested these predictions with a comparative study using data from 121 sex changing animal species spanning five phyla, covering fish, arthropods, echinoderms, molluscs, and annelid worms. We found support for the first and third predictions across all species. The second prediction was supported within the protogynous species (mainly fish), but not the protandrous species (mainly invertebrates).     

Natural sex change in the temperate protogynous Ballan wrasse Labrus bergylta

Wild Ballan wrasse Labrus bergylta were sampled monthly over 2 years in western Norway to identify the natural process of sex change in this species. Light microscopy of standard histological‐stained and immunohistochemistry‐treated gonad tissue showed that spermatogonial germ cells tended to proliferate around the periphery of the lamellae before filling into the slowly receding, apoptotic central areas of the lamellae. Sex change occurred following the breeding season. From July to September, fish were most often in an early state of gonadal transition (ET), characterized by degenerating previtellogenic oocytes and pockets of proliferating spermatogonia in the germinative epithelia. The majority of fish with late transitional gonads, that were typically dominated by spermatogenic cells, developing efferent ducts and the beginning of lobule formation, were found between October and November. Sex steroid profiles of fish representing the different sexual phases showed that breeding females had the highest concentrations of 17β oestradiol (E₂) and the lowest concentration of 11 ketotestosterone (11KT). Concentrations of E₂ decreased greatly in ET fish at the beginning of sex change and remained low in all subsequent phases. The opposite trend was demonstrated in 11KT profiles. Initial‐phase female fish had minimal concentrations of 11KT, but these increased during subsequent transitions. Sex change occurred most often in fish 34–41 cm total length (L_T) and the median of fish in the size‐frequency overlap of female and male fish was 36 cm L_T.     

Biogeography of Alaskan seaweeds

A recent survey of seaweed specimens collected in Alaska over the past two centuries, together with the application of molecular techniques to recent collections, has revealed a surprisingly diverse flora given the history of glaciation, large areas of unsuitable habitat, and otherwise harsh environmental conditions. The number of recognized species has increased from 376 in 1977 to about 550 today. Species show a variety of biogeographic patterns: species that occur primarily to the south and have their northern limit in Alaska, species that occur primarily to the west and have their eastern limit in Alaska, species that are primarily Atlantic but extend through the Arctic to Alaska, and a number of endemics. Within these broad distribution patterns are more localized patterns often involving disjunctions. These disjunctions, the occurrence of endemic species, patterns of genotype distributions, and the overall richness of the seaweed flora support the idea that marine refugia must have existed in Alaska during Pleistocene glaciations.     

DNA分子标记在雌雄异株植物性别鉴定中的应用

雌雄异株植物中不同性别的植株所产生的经济效应和生态效应存在一定的差异,在生产实践中,选取适宜性别的植株进行栽培有助于提高效率,避免不必要的浪费。然而,性别鉴定的常用方法大多是根据表型、代谢产物含量及活性等方面的差异,在成株阶段进行的,鉴定结果的可靠性和准确性都有一定的局限。近几年,DNA分子标记技术应用于雌雄异株植物的性别鉴定研究中,获得了快速准确的鉴定结果。在比较常用性别鉴定方法的基础上,主要就常用DNA分子标记在雌雄异株植物性别鉴定中的研究进展做一概述并对该领域的研究提出展望。     

Constant relative age and size at sex change for sequentially hermaphroditic fish

A general problem in evolutionary biology is that quantitative tests of theory usually require a detailed knowledge of the underlying trade-offs, which can be very hard to measure. Consequently, tests of theory are often constrained to be qualitative and not quantitative. A solution to this problem can arise when life histories are viewed in a dimensionless way. Recently, dimensionless theory has been developed to predict the size and age at which individuals should change sex. This theory predicts that the size at sex change/maximum size (L50/L(max)), and the age at sex change/age at first breeding (tau/alpha) should both be invariant. We found support for these two predictions across 52 species of fish. Fish change sex when they are 80% of their maximum body size, and 2.5 times their age at maturity. This invariant result holds despite a 60 and 25 fold difference across species in maximum size and age at sex change. These results suggest that, despite ignoring many biological complexities, relatively simple evolutionary theory is able to explain quantitatively at what point sex change occurs across fish species. Furthermore, our results suggest some very broad generalities in how male fitness varies with size and age across fish species with different mating systems.     

Ethnobotany of seaweeds: clues to uses of seaweeds

Extensive uses of fresh and dried seaweeds by coastal populations over the world can furnish clues to potential food and other uses of seaweeds, just as the first extraction of a seaweed gelatin now used for bacteriological purposes was discovered by a housewife in search of a pudding. Ethnic uses as food depend heavily on closely related species suitable for making cool, gelatinous dishes or concoctions, or on species suitable for adding to soups or stews. Rarely, single species like cochajugo (Durvillea antarctica) in Chile and rimu (Durvillea antarctica) in New Zealand point to different kinds of food preparation. Oriental cuisine incorporates many different species of seaweeds in a wide variety of ways, whereas commercial western uses depend upon extracts of wall materials to suspend, emulsify or stabilize a broad variety of foods and products.     

The costs of sex due to deleterious intracellular parasites

A major problem in evolutionary theory is to explain the widespread occurrence of sexual recombination. This is particularly difficult in anisogamous species where the familiar ‘two-fold cost of sex’ is encountered. Another cost has recently been identified: that fusion of gametes allows intracellular parasites or deleterious ‘selfish’ genomes to invade a population. These costs of anisogamy and the ability of cytoplasmic agents to invade a sexual population are quantified, allowing the costs and consequences of different modes of reproduction to be compared. It is found that the costs of selfish elements are likely to be very high and, in particular, that isogamous sexual reproduction (the putative ‘primitive’ form) is not cost-free, but incurs a fitness reduction of the order of 90%; thus a large selective disadvantage occurs in the initial evolution of sex which is ignored in standard analysis. Even once anisogamy has evolved, the low levels of ‘paternal leakage’ observed in many extant organisms may allow selfish cytoplasmic elements to spread, resulting in moderate to large decreases in host population fitness. However, much of the cost of selfish elements is avoided in sexual lifecycles with a large number of asexual cellular divisions between sexual reproduction: this greatly impedes the spread of selfish agents and reduces the fitness loss attributable to selfish elements.     

New sequence-tagged site molecular markers for identification of sex in Distichlis spicata

Sex-linked molecular markers have become valuable tools for understanding sex ratio evolution and sex-specific physiology in pre-reproductive plants. To develop new accurate methods for sexing Distichlis spicata juveniles and nonflowering individuals, we converted a random amplified polymorphic DNA-polymerase chain reaction marker that co-segregated with the female phenotype into a set of sequence-tagged site markers. We tested the marker pair on known males and females from populations in Oregon and California. A single band was obtained for all female samples but never for males.     

The biogeography of seaweeds in Southeast Alaska

Aim This article reviews the history of seaweed collections in Southeast Alaska from the early Russian explorers to contemporary efforts. It summarizes other studies of Southeast Alaskan seaweeds from a biogeographical perspective, and compares the known seaweed flora near three population centres (Ketchikan, Sitka and Juneau) with those of other regions within Alaska, and with nearby regions. Location For this article, Southeast Alaska includes all inside and outside waters of the Alexander Archipelago from Dixon Entrance (54°40′ N, 133°00′ W) to Icy Point (58°23′10″ N, 137°04′20″ W). Methods The literature on seaweeds occurring in Southeast Alaska is reviewed from a biogeographical perspective, and herbarium records for Southeast Alaska from the Alaska Seaweed Database project are used to provide an overview of the biogeography of the area. Records for the population centres of Ketchikan, Sitka and Juneau are compared with records from other areas within Alaska and with nearby regions to determine floristic similarities. Results Southeast Alaska has the most diverse seaweed flora of any region of Alaska. A list of species known to occur in Southeast Alaska is appended (in Supplementary Material) and includes their reported occurrences in three population centres (Juneau, Ketchikan and Sitka). Recognition of at least three distinct biogeographical areas associated with these three centres is supported by a comparison of their floras with those of other regions in the North Pacific. A close relationship of some species with conspecifics in the north‐west Atlantic is also noted. In contrast, ecological, physiological and genetic differentiation of Southeast Alaskan seaweeds from conspecifics in Washington State or even from different areas of Southeast Alaska are documented. A ShoreZone coastal habitat system, which is being implemented to inventory and map the entire shoreline of Southeast Alaska, is defining new biogeographical units called ‘bioareas’ on the basis of the distribution of canopy kelps and lower intertidal algal assemblages. Main conclusions Southeast Alaska has the most diverse seaweed flora of any region of Alaska. This is a reflection of its extensive coastline, with varied past and present environmental conditions. Different parts of Southeast Alaska show similarities to different areas outside Southeast Alaska. Despite this, much remains to be learned about the biogeography of seaweeds in Southeast Alaska, and many questions remain to be answered.     

植物雌雄异株性别决定研究进展

植物中雌雄性别分化是一种进化的性状。雌雄异株在多个开花植物谱系中独立演化, 但各个支系的性染色体状态、性别决定区域与性别决定基因不尽相同。多样的植物性染色体和性别决定系统为研究植物性别相关基因的形成机制、性别决定区域和性染色体进化提供了极好的机会。随着测序技术的进步和分析方法的提高, 近年来越来越多物种性别决定的相关分子机制得到解析, 并将理论成果应用于提升经济效益与城市环境等实际问题中。本文将从目前的研究现状和方法, 性别决定单、双基因模型的建立, 植物性染色体进化过程等方面进行总结, 对未来植物性别决定的研究提出四点建议: (1)研究方向逐步从基因研究扩展到调控途径研究; (2)从单一物种转向相关科属比较研究; (3)改进现有性别决定基因模型或探索新模型和性别模式物种; (4)加强性别鉴定技术在实际生产中的研发工作。同时探讨性别决定理论研究未来在农业生产、园艺绿化种植中幼苗性别鉴别筛选等方面的应用前景。     

Carbohydrates of the seaweeds,Desmarestia ligulata and D. firma

Crystalline mannitol and some oligosaccharides were separated from ethanolic extracts of Desmarestia ligulata and D. firma. Laminaran, ‘fucans’ and alginic acid were also isolated from both species. The laminaran from D. ligulata comprised both M- and G-chains but no M-chains were found in the laminaran from D. firma. In both species the amount of ‘fucan’ was small, particularly in D. firma. Both ‘fucans’ contained glucuronic acid, galactose, xylose and fucose and that from D. ligulata also contained mannose. After sequential extraction of D. ligulata with water, acid and alkali evidence was obtained for the presence of cellulose, a uronan, and protein in the residual material.     

中国沿海海藻的种类与分布

我国沿海海藻现有记录835种。本文根据各海区的物种组成、物种的温度性质、特有属(种)的分布和各海区属的相似性比较,分析各海区海藻区系特点和亲缘关系。讨论了温度、海流和地理环境对海藻分布的影响。     

Sorbitol and sorbitol phosphate in brown seaweeds

Small amounts of D-sorbitol were extracted from 15 species of brown seaweeds representing four orders, independent of seasonal effects. Sorbitol phosphate was also isolated and identified.