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.     

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.     

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.     

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.     

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.     

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.     

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.     

Spatial seed and pollen games: dispersal,sex allocation,and the evolution of dioecy

The evolutionary forces shaping within‐ and across‐species variation in the investment in male and female sex function are still incompletely understood. Despite earlier suggestions that in plants the evolution or cosexuality vs. dioecy, as well as sex allocation among cosexuals, is affected by seed and pollen dispersal, no formal model has explicitly used dispersal distances to address this problem. Here, we present a game‐theory model as well as a simulation study that fills in this gap. Our model predicts that dioecy should evolve if seeds and pollen disperse widely and that sex allocation among cosexuals should be biased towards whichever sex function produces more widely dispersing units. Dispersal limitations stabilize cosexuality by reinforcing competition between spatially clumped dispersal units from the same source, leading to saturating fitness returns that render sexual specialization unprofitable. However, limited pollen dispersal can also increase the risk of selfing, thus potentially selecting for dioecy as an outbreeding mechanism. Finally, we refute a recent claim that cosexuals should always invest equally in both sex functions.     

Nutritional composition of edible Hawaiian seaweeds

Fresh seaweeds, both wild and cultivated,are commonly eaten as food in the HawaiianIslands. Before Western contact, limu (seaweed) was a regular part of thediet, and is thought to have contributedvitamins and essential mineral nutrientsnot found in other staple food items. Twenty-two species of edible Hawaiianmacroalgae (6 Chlorophyta, 4 Phaeophyta, 12Rhodophyta) were analyzed for protein,lipid, carbohydrate, ash, caloric, mineraland vitamin content. Halymeniaformosa and Porphyra vietnamensisranked highest in total protein contentamong the species analyzed. Most speciescontained less than 5% crude lipid,although two Dictyota species hadover 16% crude lipid based on dry weight. Soluble carbohydrates ranged from 4.5 to39.9% dry weight. Ash values ranged from22.4% to 64.2%. Dictyotasandvicensis and Monostromaoxyspermum had caloric content each over3000 cal g^-1 ash-free dry weight. Allspecies contained measurable quantities of11 essential mineral elements. The majorityof Hawaiian seaweeds tested contained-carotene (vitamin A), and Enteromorpha flexuosa contained thehighest amount of vitamin C (3 mg g^-1).     

Resources and possibilities for exploitation of North Adriatic seaweeds

Suggestions for a small-scale exploitation of seaweeds in the northern Adriatic are given along with a survey of the fresh weight biomass and chemical composition of individual species. The intertidal is occupied by Fucus virsoides. In polluted sites, it is replaced by seasonal annuals. Cystoseira species are dominant in the upper subtidal and represent the major part of seaweed resources in this area. In polluted sites they are replaced by Halopteris scoparia and Dictyota dichotoma. Peaks in biomass were found in spring in the upper water layers and in early summer lower in the subtidal. The protein content of most species exhibited maxima in spring. Elevated values were found in plants from polluted and estuarine habitats.     

Seasonal variation in antifungal,antibacterial and acetylcholinesterase activity in seven South African seaweeds

Seven seaweeds were collected from the intertidal zone at Rocky Bay on the east coast of South Africa. The species were Caulerpa racemosa var. laetevirens, Codium capitatum, Halimeda cuneata, Ulva fasciata, Amphiroa bowerbankii, Amphiroa ephedraea and Dictyota humifusa. Six bimonthly collections were made within a few days of the new moon to correspond with spring tide. Methanol extracts were tested for antifungal, antibacterial and acetylcholinesterase (AChE) inhibitory activity. No seasonal variation was observed in antifungal activity, with D. humifusa extracts being the most active. The seaweed extracts inhibited the growth of the Gram-positive bacteria, with Bacillus subtilis being more susceptible than Staphylococcus aureus. Dictyota humifusa was the only seaweed able to inhibit the Gram-negative Escherichia coli. Seasonal variation in antibacterial activity was observed, with the extracts generally having no activity in summer and having antibacterial activity in late winter (July collection) and early spring (September and November collections). Dictyota humifusa was the most effective seaweed species, having antibacterial activity throughout the year. All the extracts tested had AChE inhibitory activity, with no seasonal variation in the levels of activity. Dictyota humifusa extracts were the most effective at inhibiting AChE activity.     

Parental control of sex ratio in Gammarus duebeni,an organism with environmental sex determination

Parental sex ratio control was investigated in Gammarus duebeni, an amphipod with an environmentally mediated sex determining system. The effect on the F2 generation sex ratio of the photoperiodic conditions experienced by a) the P generation during and after copulation, b) the F1 generation before and after sex determination, and c) the F2 generation themselves during the period of sex determination, was tested. The photoperiodic conditions the F2 generation experienced during the period of sex determination had a significant effect on their sex ratio (more males were produced under long-day than under short-day conditions), but the photoperiodic conditions experienced by the F1 generation males and females or the P generation on the F1 male's side had no effect on the F2 sex ratio. However, the photoperiodic conditions the P generation on the F1 female's side experienced significantly affected the F2 sex ratio. When these animals experienced long-day conditions the F2 generation became female biased and when they experienced short-day conditions, male biased. It is proposed that the mechanism of control operates through the F1 generation mothers whilst in an embryonic stage of development in the P generation mother's brood pouch. The photoperiodically mediated effects of the embryonic F1 generation mother and the F2 generation on sex determination are additive. A mechanism by which both F1 generation maternal and F2 generation sex ratio control could operate in the field is proposed.     

The many costs of sex

Explaining the evolution of sex is challenging for biologists. A 'twofold cost' compared with asexual reproduction is often quoted. If a cost of this magnitude exists, the benefits of sex must be large for it to have evolved and be maintained. Focusing on benefits can be misleading, as this sidelines important questions about the cost of sex: what is the source of the twofold cost: males, genome dilution or both? Does the cost deviate from twofold? What other factors make sex costly? How should the costs of sex be empirically measured? The total cost of sex and how it varies in different contexts must be known to determine the benefits needed to account for the origin and maintenance of sex.     

Antiviral compounds in extracts of Korean seaweeds: Evidence for multiple activities

Extracts of 13 Korean seaweeds, previously shown to contain antiviral activity, were investigated in more detail in order to learn the nature of the antiviral compounds and their mechanisms of action. One extract, from Codium fragile, was active against all three test viruses (herpes simplex, HSV; Sindbis, SINV; polio), whereas the others were more selective. Thus four species, Enteromorpha linza, Colpomenia bullosa, Scytosiphon lomentaria, and Undaria pinnatifida, were active against HSV and SINV, but not poliovirus. The other eight were active against either HSV or SINV. In all cases there was evidence for photosensitizers, since the antiviral activities required or were enhanced substantially by light. In general UVA (long wave ultraviolet) was much more effective than visible light in promoting activity, although the extract of Sargassum sagamianum could be activated equally by either. In experiments to determine the site of action of these antiviral extracts, the predominant activity was virucidal (i.e. direct inactivation of virus particles), rather than inhibition of virus replication, although Sargassum sagamianum also could protect cells against subsequent virus infection. These results imply that different antiviral compounds are present among the extracts, and furthermore the activities cannot be explained in terms of common ingredients such as polysaccharides or tannins. We suggest that seaweeds may be a source of potentially useful and interesting antiviral compounds. This revised version was published online in June 2006 with corrections to the Cover Date.