PRESENCE OF SPOROPHYLLS IN FLOATING KELP RAFTS OF MACROCYSTIS SPP. (PHAEOPHYCEAE) ALONG THE CHILEAN PACIFIC COAST1

Some species of macroalgae continue to live for extended periods of time after detachment and may even maintain reproductive structures, yet very little is known about this process. Here, we describe the presence of sporophylls (with sporogenous tissues) on floating kelp rafts of Macrocystis spp. along the coast of Chile. Surveys were conducted at nine sites (18–50° S) during austral summer 2002, and floating kelp rafts were seen and collected at seven of these nine sites (between 22 and 50° S). Fifteen (26.8%) of the 56 samples had sporophylls, indicating maintenance of sporophylls after detachment. Some of the kelp sporophytes with reproductive blades showed signs of having been afloat for long periods (indicated by the large size of attached stalked barnacles). Additionally, experiments showed that floating kelps released viable zoospores. To understand the reproductive dynamics of floating kelps, we compared these results with information from attached populations of Macrocystis spp. at nearby coastal sites. In general, attached kelp had higher proportions of sporophylls than floating rafts, suggesting that detachment may negatively affect reproductive status. Nevertheless, floating kelps remained functionally reproductive, suggesting that zoospores may be dispersed via floating rafts. Published reports on other macroalgae indicate that some species (Lessoniaceae, Fucaceae, and Sargassaceae) are fertile and probably release zoospores or zygotes while floating or drifting in ocean currents. Because dispersal distances achieved by spores of most macroalgae are relatively short, release of spores from floating algae may be an alternative mechanism of long‐distance dispersal.     

Meiospores produced in sori of nonsporophyllous laminae of Macrocystis pyrifera (Laminariales,Phaeophyceae) may enhance reproductive output

Different lamina of Macrocystis pyrifera sporophytes (i.e., sporophylls, pneumatocyst‐bearing blades, and apical scimitars) in a wave‐sheltered site were found to be fertile. We quantified their sorus surface area, reproductive output (number of spores released) and the viability of released spores (germination rate). Sorus area was greatest on the sporophylls, with sporangia developing on >57% of the total area and smallest on the pneumatocyst‐bearing blades with 21% of the total area bearing sporangia. The apical scimitar released the greatest number of meiospores (cells · mL^?1 · cm^?2) and the sporophylls the least. Meiospores produced from all types of fertile laminae were equally viable. This reproductive plasticity may enhance reproductive output, and contribute to short and long‐distance spore dispersal and the cryptic gametophyte propagule bank for the next generation of sporophytes.     

Comparing and contrasting development and reproductive strategies in the pupal hyperparasitoids Lysibia nana and Gelis agilis (Hymenoptera: Ichneumonidae)

In most animals, the optimal phenotype is determined by trade-offs in life-history traits. Here, I compare development and reproductive strategies in two species of solitary secondary hyperparasitoids, Lysibia nana and Gelis agilis, attacking pre-pupae of their primary parasitoid host, Cotesia glomerata. Parasitoid larvae of both species exploit a given amount of host resources with similar efficiency. However, adults exhibit quite different reproductive strategies. Both species are synovigenic, and female wasps emerge with no mature eggs. However, G. agilis must first host-feed to produce eggs, while L. nana does not host-feed but mobilizes internal resources carried over from larval feeding to initiate oogenesis. Further, G. agilis is wingless, produces large eggs, has a long life-span, and generates only small numbers of progeny per day, whereas these traits are reversed in L. nana. Given unlimited hosts, the fecundity curve in L. nana was “front-loaded,” whereas in G. agilis it was depressed and extended over much of adult life. In L. nana (but not G. agilis), wasps provided with honey but no hosts lived significantly longer than wasps provided with both honey and hosts. Differences in the fecundity curves of the two hyperparasitoids are probably based on differing costs of reproduction between them, with the wingless G. agilis much more constrained in finding hosts than the winged L. nana. Importantly, L. nana is known to be a specialist hyperparasitoid of gregarious Cotesia species that pupate in exposed locations on the food plant, whereas Gelis sp. attack and develop in divergent hosts such as parasitoid cocoons, moth pupae and spider egg sacs. Consequently, there is a strong match between brood size in C. glomerata and egg production in L. nana, but a mismatch between these parameters in G. agilis.     

Growth performance ofAlaria esculenta off helgoland

Alaria esculenta (L.) Grev. sporophytes, raised in culture and originating from the North of Iceland were immersed in the sea near Helgoland (North Sea) for the period from February to August. Notable growth of the thalli was found between February and May, when the water temperature was similar to that of their original habitat in Iceland. Less conspicuous growth but development of sporophylls took place between May and July. The temperature rose to 16.8° C during the first half of July and remained on the same level during August, when the plants deteriorated. The present experiments yield additional evidence that the regional distribution ofA. esculenta is temperature controlled.     

Structural characteristics and biological activity of Fucoidans from the brown algae Alaria sp. and Saccharina japonica of different reproductive status

Structural characteristics and the antitumor activity of fucoidans isolated from vegetative and reproductive tissue of the brown algae Alaria sp. and Saccharina japonica were studied. The reproductive status of the brown algae affected the yield of fucoidans and their structural characteristics. The fucoidan yield was 5.7% (w/w on the basis of the dried algae weight) for fertile and 3.8% for sterile Alaria sp. and 1.42 and 0.71% for fertile and sterile S. japonica, respectively. The fucoidans from fertile Alaria sp. and S. japonica had a slightly higher degree of sulfation and a somewhat more homogeneous monosaccharide composition, with predominate amounts of fucose and galactose, than those isolated from sterile algae tissue. The fucoidans from both the sterile and fertile brown algae tissue tested possessed selective cytotoxicity towards human breast cancer (T-47D) and melanoma (RPMI-7951) cell lines, but not to normal mouse epidermal cells (JB6 Cl41), and effectively inhibited the proliferation and colony formation of the breast cancer and melanoma cell lines. The fucoidans from reproductive tissue of brown algae possessed higher antitumor activity than those from vegetative plants.     

PHYSIOLOGICAL INVESTIGATIONS ON ALARIA ESCULENTA (LAMINARIALES,PHAEOPHYCEAE). II. ROLE OF TRANSLOCATION IN BLADE GROWTH1,2

Laboratory studies on blade growth in Alaria esculenta (L.) Grev. showed 3 periods of rapid blade elongation during the year: October–November, February–April and late June. The first two periods are characteristic of many Laminariales; the unique June peak may reflect local nutrient conditions. While the distal blade functions as a source, supplying organic matter to the blade meristem, the stipe can be a source during periods of rapid growth or a sink during late summer when blade growth is slow. Maximum enhancement of elongation rate of blade meristems was observed in 40–50 cm blades; longer blades showed no further increase in growth rate. This blade length-growth promotion relationship may be independent of seasonal variations in meristematic activity. ¹⁴C tracer experiments suggested that separate growth promotion effects by distal blade, sporophylls and stipe were not additive in the intact thallus. The preferential source of assimilate for blade meristem growth was the distal blade. Secondary sources: sporophylls, which were activated following excision of the primary source; and stipe, which began to translocate assimilate when both sources were removed. The role of secondary sources in nature is discussed. Profiles of radioactivity in alcohol-soluble organic matter in blades are evaluated in relation to tracer profiles in higher plants and mechanisms of translocation.     

AUXIN,AN ENDOGENOUS REGULATOR OF GROWTH IN ALGAE?1,2

The effects of 5 pairs of synthetic auxins and chemically related, but biologically inactive, derivatives (e.g., 2,4- and 3,5-dichlorophenoxyacetic acid, respectively) on blade growth of the brown alga, Alaria esculenta (L.) Grev.(Laminariales) were studied. The significant result was the inability to divide the growth responses into auxin and non-auxin groups. At high concentrations (10^?3 M) 9 test substances inhibited blade growth; lower concentrations (<10^?3 M) were either slightly inhibitory or showed no effect. The data suggest that a higher plant auxin-specific recognition mechanism is lacking in this alga. As this mechanism is central to higher plant concepts of growth control by auxin, the role of auxin as an endogenous regulator of growth in Alaria, and perhaps other algae as well, seems unlikely. This interpretation is consistent with recent negative biochemical data from auxin binding studies using subcellular preparations from algae.     

PHYSIOLOGICAL INVESTIGATIONS ON ALARIA ESCULENTA (L.) GREV. (LAMINARIALES). I. ELONGATION OF THE BLADE1,2,3

A seasonal rhythm in blade elongation rate was observed in Alaria esculenta. Maximum (3.0–3.6 cm/week) and minimum (0.5–1.0 cm/week) rates were recorded in June and September, respectively. Translocation of growth-promoting metabolites occurs within the main blade and between the sporophylls and blade. Bidirectional flow of growth-promoting metabolities within the stipe was demonstrated. Seasonal effects of nutrients (NO₃- and PO₄^3-) and photoperiod on blade elongation were shown in long-term laboratory experiments. Control of seasonal blade growth by exogenous and endogenous factors is discussed.     

Fine-tuned spatiotemporal dynamics of sporophylls in movement-assisted dichogamy: A study on Clerodendrum infortunatum

Hermaphroditism is cost-effective because a common investment in reward and attractive structures yields benefits through both male and female reproductive success. However, the advantage is accompanied by an increased risk of self-pollen deposition, which is generally disadvantageous. Hermaphroditic plants reduce self-pollen deposition by separating sporophylls (a term applied to the stamens and carpels) either spatially (herkogamy) or temporally (dichogamy). In movement-assisted dichogamy, both sporophylls show coordinated motion in opposite directions. However, the effectiveness of this movement in reducing self-pollen deposition may be compromised at the point when the sporophylls cross each other and are close enough to interfere, resulting in a transition phase problem. The solution to this problem lies in the details of the spatiotemporal dynamics of the sporophylls in relation to their reproductive maturity. We studied these details across the floral lifetime of a protandrous shrub, Clerodendrum infortunatum (Lamiaceae), in rainforest fragments of the Western Ghats, India. We took photos of flowers at regular time intervals and measured sporophyll angles from the images. We also carried out a field experiment to determine stigma receptivity. We found that the stigma lobes remained narrowly opened at transition, and the stigma surfaces remained non-receptive. Our findings suggest that the effectiveness of dichogamy is maximized through two properties of the transition phase: physical resistance to self-pollen deposition by narrow stigma lobe opening and chemical non-receptivity of the stigma during this phase. This study emphasizes the importance of accessory adaptations in movement-assisted dichogamy to tackle the transition phase problem.     

Pollen limitation,fruit abortion,and autonomous selfing in three populations of the perennial herb Ruellia nudiflora

Multiple factors determine plant reproductive success and their influence may vary spatially. This study addresses several factors influencing female reproductive success in three populations of Ruellia nudiflora, specifically we: (i) determine if fruit set is pollen‐limited and if pollinator visitation rates are related to this condition; (ii) estimate fruit set via autonomous self‐pollination (AS) and relate it to the magnitude of herkogamy; and (iii) evaluate if fruit abortion is a post‐pollination mechanism that determines the magnitude of pollen limitation. At each site we marked 35 plants, grouped as: unmanipulated control (C) plants subjected to open pollination, plants manually cross‐pollinated (MP), and plants excluded from pollinators and only able to self‐pollinate autonomously (AS). Fruit set was greater for MP relative to C plants providing evidence for pollen limitation, while a tendency was observed for lower fruit abortion of MP relative to C plants suggesting that fruit set is influenced not only by pollen delivery per se, but also by subsequent abortion. In addition, although pollinator visits varied significantly among populations, the magnitude of pollen limitation did not, suggesting that pollinator activity was not relevant in determining pollen limitation. Finally, fruit set tended to decrease with the degree of herkogamy for AS plants, but this result was inconclusive. These findings have contributed to identify which factors influence reproductive success in populations of R. nudiflora, with potentially relevant implications for population genetic structure and mating system evolution of this species.     

Photoperiodic long-day control of sporophyll and hair formation in the brown alga Undaria pinnatifida

Two photoperiodic responses, the development of sporophylls and hairs, havebeen quantified in sporophytes of the brown alga Undaria pinnatifida. In a finalexperiment, the algae were cultivated in outdoor, 2000-L seawater tanks in agreenhouse for up to 12 weeks, and daylength was regulated by automatic blindsmounted on top of the tanks. Vegetative young sporophytes were treated undershort-day (SD; 8 h light per day) or long-day conditions (LD; 16 h light perday), at 12 h light per day or in a night-break regime (NB; 8 h light per day,7.5 h dark, 1 h light, 7.5 h dark). The earliest sporophyll development wasobserved 6, 7 or 9 weeks under LD, NB or SD conditions, respectively. After 12 weeksthe sporophylls were significantly longer and wider under LD or NB conditions than inthe SD regime, and only half of the experimental algae had formed sporophyllsunder SD conditions, but all algae under LD or NB conditions. In a foregoing 7-weekculture experiment performed in 300-lL indoor tanks, enhanced sporophyll formationhad also been observed under LD and not under SD conditions (NB omitted). In bothexperiments, blade elongation rates remained high until the end of theexperiments in SD, but declined during sporophyll initiation in LD, NB or at 12 hlight per day. Another difference caused by photoperiod was observed in regard to thedevelopment of surface hair spots which occurred in both experiments on the bladesin LD, NB or at 12 h light per day with identical densities, but were completelylacking under SD conditions. It is concluded that U. pinnatifida is afacultatative long-day plant in regard to reproduction forming vigorously sporophyllsin long days, and an obligate long-day plant in regard to hair formation.     

Comparative Study of Polysaccharides from Reproductive and Sterile Tissues of Five Brown Seaweeds

Sterile and reproductive tissues of five brown algae (Sargassum pallidum, Silvetia babingtonii, Fucus evanescens, Saccharina japonica, and Alaria ochotensis) from Russian Far East seas were compared for the content and monosaccharide composition of fucoidans as well as the content of laminarans and alginic acids. It was proved that reproduction has an apparent effect on fucoidan content and its monosaccharide composition. Fucoidan content in fertile tissues was shown to be 1.3–1.5 times as high as in sterile ones. Based on the present and previously reported data, we believe that fucoidan accumulation during the development of reproductive structure is a general trend for brown seaweeds. Reproduction also caused changes in the monosaccharide composition. As a result, fertile plants synthesized fucoidan with less heterogeneous monosaccharide composition in comparison with sterile ones. Structural changes of this polysaccharide are species-specific and perhaps depend on the type of the synthesized polysaccharide. The fertile plants of S. babingtonii yielded the highest fucoidan content [25% dry weight (dw)] among the tested species, whereas the maximum alginic acid content was found for the sterile tissues of S. japonica—up to 43% dw. There was no general trend in alginic acid content variation during sporulation. The alginic acid content was much higher in the sterile tissues of S. japonica in comparison with the fertile ones. On the contrary, the fertile tissues of A. ochotensis contained more alginic acid than the sterile ones.     

Relationship between interspecific pollen transfer and pistil length in sympatric congeners,Clerodendrum trichotomum and C. izuinsulare

Interspecific pollen transfer (IPT) often leads to reproductive interference. Although character displacement of reproductive traits in plants is often considered a consequence of reproductive interference, few studies have tested whether intraspecific variation in floral morphology changes the intensity of reproductive interference among pollinator-sharing plants. We investigated whether intraspecific variation in pistil length changes the proportion of IPT (interspecific pollen transfer) in sympatric populations of Clerodendrum trichotomum and C. izuinsulare on the two islands. On Toshima Island, C. izuinsulare flowers with shorter pistils were significantly less likely to receive C. trichotomum pollen, and there was a slight tendency for longer pistiles of C. trichotomum flowers to receive less C. izuinsulare pollen, suggesting that IPT has caused character displacement in pistil length in these congeneric plants. In contrast, we did not detect any relationship between pistil length and the proportion of IPT for the two species on Niijima Island. The discrepancy between the islands may reflect differences in pollinator assemblages.     

Multiple reproductive strategies of a spring ephemeral plant,Fritillaria maximowiczii,enable its adaptation to harsh environments

Spring ephemeral plants that experience harsh environments have developed specific reproductive characteristics. These characteristics are of great importance to the survival and reproduction of these species, particularly for rare and endangered plants. Fritillaria is a genus consisting of spring ephemeral plants with significant medicinal and ornamental value whose wild resources are highly threatened and whose reproductive characteristics and adaptative evolutionary mechanisms are still not well understood. Fritillaria maximowiczii is positioned at the most basal clade on the Fritillaria phylogenetic tree, whose reproductive characteristics remain obscure. In this study, we report the flowering dynamics, pollination biology and breeding system of F. maximowiczii. The flowering process of F. maximowiczii can be divided into seven stages. Based on the pollen/ovule ratio, the outcrossing index and a field pollination experiment on a natural population, F. maximowiczii showed high levels of outcrossing and self-compatibility. Three types of pollinators were observed: two kinds of bumblebees, and spiders. Diverse herkogamy and dichogamy may have considerably improved its reproductive success rate. Furthermore, a special reproductive mode not previously reported in wild populations of Fritillaria, apomixis, was strongly suspected based on a high fruit setting rate (36.84%). Our study suggests F. maximowiczii has developed multiple reproductive strategies to adapt to harsh environments and ensure population reproduction, and the diverse reproductive mechanisms may be related to its primitive phylogenetic position in the genus. This study not only broadens our understanding of mechanisms of ecological adaptation in spring ephemeral plants but also provides key data for the conservation of Fritillaria.     

Reproduction strategies of Macrocystis pyrifera (Phaeophyta) in Southern Chile: The importance of population dynamics

Macrocystis pyrifera is an ecologically dominant species along the temperate Northern and Southern Pacific Coast of America, showing some similarities and differences at population and community level. In general, this kelp is reported to be reproductive all year round. Annual populations present in wave-protected areas of southern Chile suggest that the reproductive strategies of this population can be different. In this study we explore the reproductive strategies of annual M. pyrifera present in wave-protected areas and perennial populations encountered in exposed areas of southern Chile (41^∘S). Our results show that M. pyrifera present in wave-exposed locations has a reproductive strategy that is similar to populations in the northern hemisphere. These populations reproduce all year round and their strategy is to produce high numbers of sporophylls and ensure that most of them (over 90%) become sporogenous. On the other hand, the protected populations with an annual life cycle, produce more spores per area of sorus. In a few months, they are able to produce sufficient propagules to recolonize areas before the adult plants disappear in autumn.     

TRANSLOCATION OF 14C IN MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1,2

Translocation patterns in the giant kelp, Macrocystis integrifolia Bory, were investigated in situ using ¹⁴C tracer; sources and sinks were identified. Export was first detected after 4 h of labeling; experiments were routinely 24 h continuous ¹⁴C application. Mature blades exported ¹⁴C to young blades on the same frond and on younger fronds, as well as to sporophylls and frond initials at the bases of the fronds. Blades <0.3 m from the apex imported and did not export; this distance did not change seasonally. In spring export from blades 0.3–1.25 m from the apex was exclusively upwards; older blades also exported downwards. In fall downward export began 0.5 m from the apex, and blades >2 m from the apex exported exclusively downwards. Carbon imported by frond initials, young fronds, and sporophylls in fall may partly be stored for growth in early spring. No translocation was seen in very young plants until one blade (secondary frond initial) bad been freed from the apical blade; this blade exported to the apical blade for a time, but imported when it began to develop into a frond. The second and third formed blades on the primary fronds (sporophylls also exported when <0.3 m from the apex, and later stopped. Frond initials and sporophylls on later-formed fronds did not export at all. The translocation pattern in M. integrifolia differs from that previously reported in M. pyrifera in seasonal change and in distances from the apex at which the changes take place.     

PLASTIC RELATIONSHIPS BETWEEN REPRODUCTIVE AND VEGETATIVE MASS IN SOLIDAGO ALTISSIMA

To test several predictions of a model of linear, size-dependent reproductive output in plants, we analyzed the relationship between shoot vegetative (v) and reproductive (r) mass in five experiments on Solidago altissima from an invading population in Switzerland. There was large environmentally-induced and genetic variation in r and v. A large amount of variation in r could be explained by variation in v, using the simple linear model. There was a minimum size for sexual reproduction, and above this size, shoots devoted a relatively constant proportion (about one third) of their biomass to reproductive structures. We detected significant genetic variation for both the minimum size and the slope of the r-v relationship, but there was no evidence for an hypothesized trade-off between minimum size and slope. There was significant genotype-environment interaction for the slope of the r-v relationship. There were also developmental effects on the r-v relationship: plants grown from seeds behaved differently than those of the same genotype grown from rhizomes.     

亚轮生奇异蕨(Adoketophyton subverticillatum)在贵州都匀泥盆系蟒山群的发现及其意义

Adoketophyton subverticillatum (Li et Cai) Li et Edwards (亚轮生奇异蕨)是云南早泥盆世坡松冲植物群中颇具代表性的、研究较为详细的一种植物, 目前对其整体形态特征和解剖结构都有较深入的认识。本文通过系列针修法, 将采自贵州都匀包阳剖面蟒山群下段的一块植物化石新材料归入A. subverticillatum。基于目前对 Adoketophyton时空分布的认识, 认为该属可作为早泥盆世植物群的代表分子, 并据此推断蟒山群下段的时代应为早泥盆世。Adoketophyton subverticillatum在都匀的发现, 表明贵州都匀蟒山群中的植物与云南坡松冲植物群在属、种一级上存在扩散与交流现象。Adoketophyton以及其他相关植物的研究表明, 在高大气CO₂浓度的早泥盆世, 叶性结构如孢子叶、苞片、枝叶复合体等已广泛分布于华南板块。     

Senescence in growth and reproductive allocation in a bunchgrass

• Senescence is a puzzling phenomenon. Few convincing studies of senescence in perennial herbaceous plants exist. While ramets are known to senesce, whether senescence of bunchgrasses actually occurs is not clear.
• In this study, we grew a set of plants of Elymus excelsus, a bunchgrass, to examine plant size, sexual reproduction and bud formation in individual plants in relation to their gradual ageing, in order to determine whether E. excelsus experiences senescence. We collected data in two consecutive years (2009 and 2010) from field samples of plants from 1 to 5 years old. Using regression models, we performed age‐related analyses of growth and reproduction parameters.
• Our results showed that individual plant size (diameter, individual biomass), total biomass of ramets, number and biomass of reproductive ramets, percentage of ramets that were reproductive, reproductive allocation, over‐wintering buds and juvenile ramets all declined with age. However, vegetative growth (number and biomass of vegetative ramets) did not decrease with age.
• Those plants that survived, dwindled in size as they aged. However, no plants shifted their resource allocation between growth and reproduction as they aged, so the shift in allocation did not account for the fall in size.

     

Sex-specific reproductive trade-offs in the gregarious fucoid macroalga Ascophyllum nodosum

The existence of sex-specific reproductive trade-offs is well established in plants. They usually occur because females invest more resources into reproduction than males, and have to compensate by sacrificing growth or defence. Investigations into by-sex differences in resource allocation by seaweeds are comparatively scarce. A small number of authors report differences between the sexes in some red algae, but known by-sex differences in brown algae are largely confined to the reproductive structures. In this study, sex-specific reproductive trade-offs are investigated in the common temperate brown alga Ascophyllum nodosum from three distinct populations. Quantified investments into growth, defence, and reproduction of a large number of individuals (n = 720) selected across a full annual cycle are presented in parallel with feeding trials using a common gastropod herbivore and a comprehensive assessment of the biotic and abiotic stressors impacting on A. nodosum at three sites. These reveal that sex-specific reproductive trade-offs occur in two of the three populations, as females invest more into reproduction than males and are subsequently less chemically defended for the months post gamete release. Feeding trials confirm that this leaves females more vulnerable to grazing pressure during these months, although mortality and competitive ability appear unaffected in the field. Possible causes of the trade-offs made by females are discussed, and new avenues of investigation are identified which could reveal interesting parallels between seaweeds and higher plants.