Microhabitat and plant structure of Batrachospermum (Batrachospermales, Rhodophyta) populations in four streams of São Paulo State, southeastern Brazil

Microhabitat and plant structure of seven Batrachospermum populations (four of Batrachospermum delicatulum (=Sirodotia delicatula), one of Batrachospermum macrosporum and two of the ‘Chantransia’ stage), including the influence of physical variables (current velocity, depth, irradiance and substratum), were investigated in four streams of São Paulo State, southeastern Brazil. The populations of B. delicatulum and the ‘Chantransia’ stage occurred under very diverse microhabitat conditions, which probably contributes to their wide spatial and seasonal distribution in Brazilian streams. Results suggest branch reconfiguration as a probable mechanism of adaptation to current velocity based on the occurrence of: (i) B. macrosporum (a large mucilaginous form with presumably little ability for branch reconfiguration) under lower current velocity than B. delicatulum; (ii) only dense plants in populations with high current velocities (> 60 cm s^?1), whereas 53–77% of dense plants were seen in populations exposed to lower currents (< 40 cm s^?1); (iii) positive correlations of plant length with internode length in populations under low current velocities and negative correlation in a population with high velocity (132 cm s^?1); and (iv) negative correlations of current velocity with plant diameter and internode length in a population under high flow. This study, involving mainly dioecious populations, revealed that B. delicatulum displayed higher fertilization rates than B. macrosporum. A complementary explanation for a dioecious species to increase fertilization success was proposed consisting of outcrossing among intermingled male and female adjacent plants within an algal spot.     

Reproductive ecology of the freshwater red alga Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in three tropical streams

Batrachospermum delicatulum specimens from three stream segments were analyzed from a tropical region in south‐ eastern Brazil (20°18′– 20°49′S, 49°13′– 49°46′W). Physical and chemical parameters and the spatial placement of thalli were investigated along with the reproductive characteristics of the gametophytic phase. Sequence data of the cox 2‐ 3 spacer region was also utilized to evaluate genetic variation in individuals within and among stream segments. Gametophyte occurred under relatively diverse environmental conditions, whereas thalli abundance was weakly or not correlated to environmental variables within the stream segments. All specimens examined were dioecious. The ratio of male/female plants was relatively low (0.5 to 1.3) and male plants tended to occur as clumps (two or three plants together). High reproductive success was observed, as indicated by the occurrence of 100% fertilized (carposporophytic) female plants. This is similar to previous reports for this and other dioecious species, which is remarkable considering the relatively low proportion of male/female plants. Results support the two hypotheses to explain the high reproductive success in dioecious species. The occurrence of male plants in clumps was evidence for a strict spatial relationship (i.e. male plants located in upstream position of female plants in order to release spermatia, which would be carried by eddies through female plants). In contrast, the occurrence of male and female plants adjacent to each other allowed outcrossing among neighboring plants with intermingled male and female branches, which seemed more applicable to some situations (low turbulence habitats). The cox 2‐ 3 spacer region from the 18 individuals sequenced was 376 bp and the DNA sequence was identical with no base pair substitutions. Likewise, a previous study of another Batrachospermum species showed that the same haplotypes were present in all stream segments from the same drainage basin, even though the stream segments were a considerable distance apart. Short distance dispersal either by small birds or waterway connectivity might explain these findings.     

Biomass Allocation in the Dioecious Tropical Palm Chamaedorea tepejilote and Its Life History Consequences

Abstract The patterns of resource allocation are described for a dioecious tropical palm, Chamaedorea tepejilote. Resource allocation was measured by harvesting fifteen plants of C. tepejilote. The relative allocation of biomass in the stem increased with the size of the plant; that in the leaves decreased and that in the other structures remained roughly constant. Female plants showed a greater total reproductive effort, though male plants produced more inflorescences during the flowering season. Both male and female plants allocated more resources to prop root than to hypogeal roots. The annual productivity of reproductive and vegetative parts of C. tepejilote was estimated using allometric relationships for different plant structures and from demographic data obtained from the field. Annually, female plants allocated significantly more resources to leaves than male plants. Yearly productivity of inflorescences was higher for male plants, while female plants had greater total reproductive productivity (inflorescences and fruits). Correlation analysis showed an increase in reproductive effort with plant size, and an inverse relationship between fecundity and probability of survival, fecundity and residual reproductive value, and reproductive effort and life expectancy; these relationships suggested a cost in reproduction. Additionally, mature plants with different growth rates exhibited differences in fecundity: tall plants (>2.5m height) that grew more than 40 cm in height in four years had lower values of fecundity in comparison to plants of slower growth. These data were discussed in the context of the implications in the life history of a dioecious tropical plant.     

小五台山天然青杨林雌雄群体的生长差异

通过对小五台山天然青杨种群的野外调查,并使用胸径与株高的异速生长模型来分析其雌雄群体间的生长差异,以探究雌雄异株植物青杨在性成熟条件和形态特征中是否存在性间差异。结果表明:(1)在青杨生长过程中,胸径随年龄呈指数型增长,而株高随年龄呈对数型增长;(2)雌雄植株的性成熟条件不同。雌株进入性成熟阶段的最低年龄和胸径都小于雄株;(3)青杨高径生长过程存在性别差异。雌株的异速生长指数显著大于雄株(P=0.024)。表明天然青杨种群中雌株一般性成熟较早,成熟后营养生长偏重于胸径增粗;而雄株性成熟较晚,营养生长偏重于植株增高。相对于雄株,雌株具有较高的树干机械强度。     

REGENERATION AND SEXUAL DIFFERENTIATION OF GRIFFITHSIA JAPONICA (CERAMIACEAE,RHODOPHYTA) THROUGH SOMATIC CELL FUSION1

Hybrid cells were obtained from somatic cell fusion among male, female, and tetrasporangial plants in Griffithsia japonica Okamura by a wound-healing process. Isolated fusion cells regenerated new mature plants with mixed reproductive structures. The plants regenerated from hybrid cells between male and female plants developed into 1) spermatangiate, 2) carpogonial, 3) bisexual with spermatangia and carpogonial branches, 4) mixed-phase with spermatangia and tetrasporangia, or 5) bisexual/mixed-phase plants with spermatangia, carpogonial branches, and tetrasporangia. About 70% of the plants regenerated from hybrid cells between male and female plants produced tetrasporangia that were always formed with spermatangia on a single cell. Some of those tetrasporangia released tetraspores, six of which gave rise to mature plants. The plants regenerated from hybrid cells between male and tetrasporangial plants developed into spermatangiate, tetrasporangiate, or mixed-phase plants with spermatangia and tetrasporangia. The plants regenerated from hybrid cells between female and tetrasporangial plants developed into carpogonial, tetrasporangiate, or mixed-phase plants with carpogonial branches and tetrasporangia. All types of reproductive structures we re functional.     

ONTOGENY OF SEXUAL CONCEPTACLES IN A SPECIES OF BOSSIELLA (CORALLINACEAE)1

The first evidence of conceptacle formation in male and female plants of Bossiella californica ssp. Schmittii is the secretion of a cap below the epithallium. Subsequent development involves the disintegration of the upper enucleate parts of cortical cells below the center of the cap concomitant with the growth of tissue surrounding these cells. Protoplasts in the lower parts of these cortical cells recover and become initials of reproductive cells. Differentiation of each initial in female plants results in a supporting cells bearing 1 or 2, 2-celled carpogonial filaments, and in male plants results in a basal cell bearing 2 or 3 spermatangial mother cells which bud off spermatangia. Following fertilization, supporting cells fuse and form a broad, thin fusion cell from the upper surface of which gonimoblast (carposporangial) filaments arise.     

Vigour of a dioecious shrub and attack by a galling herbivore

1. The pattern of attack by the leaf‐galling insect Neopelma baccharidis (Homoptera: Psyllidae) was studied in three populations of the dioecious shrub Baccharis dracunculifolia (Asteraceae) in south‐eastern Brazil. The plant vigour hypothesis, which predicts higher rates of attack and increased herbivore performance on the longest plant shoots, was tested. This work also provides further information for the study of differential herbivory in dioecious plants. 2. In total, 9200 shoots were collected randomly from 46 male and 47 female plants belonging to the three populations. Shoot length, number of leaves per shoot, rate of galling, and survival of psyllids did not differ between male and female plants. Another population on the Campus of the Federal University of Minas Gerais was used only to determine the pattern of shoot growth. 3. The hypothesis of sex‐mediated herbivory was not corroborated in this study. 4. The frequency of galling increased with increasing shoot length, as predicted by the plant vigour hypothesis. Nevertheless, the number of oviposition sites (leaf buds) increased with shoot length. 5. The performance of the galling herbivore was not related to shoot length in the plant populations studied. 6. In conclusion, Neopelma baccharidis did not select shoots based on length only.     

SEXUAL DIFFERENTIATION OF GRIFFITHSIA (CERAMIALES, RHODOPHYTA): NUCLEAR PLOIDY LEVEL OF MIXED-PHASE PLANTS IN G. JAPONICA1

Mixed-phase plants of Griffithsia japonica Okamura spontaneously occurred in a laboratory culture. Four female plants produced tetrasporangia and spermatangia in addition to their normal female reproductive structures (bisexual/mixed-phase plants), and four male plants produced tetrasporangia as well as spermatangia (male/mixed-phase plants). To determine the nuclear ploidy level of these mixed-phase plants, relative nuclear sizes of male, female, tetrasporangial, and mixed-phase plants were measured using a microscopic image analysis system. Haploid gametophytes could be distinguished from diploid tetrasporophytes by relative nuclear sizes, with the later having nuclei twice the size of the former. Relative nuclear sizes of the mixed-phase plants were similar to those of the haploid plants. Thus, the mixed-phase plants were determined to be haploid. Haploid mixed-phase plants of G. japonica have a potential to produce male, female and tetrasporangial reproductive structures. Sex determination models are discussed to explain "haploid" mixed-phase phenomena in red algae .     

Sex ratio, reproductive investment and flowering phenology in dioecious Rhamnus alaternus (Rhamnaceae)

Guitián, J. 1995. Sex ratio, reproductive investment and flowering phenology in dioecious Rhamnus alaternus (Rhamnaceae). - Nord. J. Bot. 15: 139–143. Copenhagen. ISSN 0107–055X.
During 1992 and 1993 I investigated the reproductive biology of the dioecious Mediterranean shrub Rhamnus alaternus in a population in the northwest Iberian Peninsula. Reproductive investment was estimated as the mean total dry weight of reproductive organs per branch tip. I also estimated number of flowers produced per plant and population sex ratio, and investigated the spatial distribution of the sexes and flowering phenology. The sex ratio was 1:1, and the spatial distribution of the sexes was random. Male plants produced 2.6 times more flowers than female plants, but the overall reproductive investment by females was 5- to 9-fold higher. In both years of study, male plants commenced flowering first. The male and female flowering peaks coincided closely (in late March) in both years. The results of this study suggest that male and female R. alaternus differ most notably in the amount of resources allocated to reproduction.     

Mating tactics in the sub-Antarctic deep-sea squid <Emphasis Type="Italic">Onykia ingens</Emphasis> (Cephalopoda: Onychoteuthidae)

The behavior of polar deep-sea nekton is very poorly known. To obtain insight into mating behavior of the abundant and ecologically important sub-Antarctic deep-sea squid Onykia ingens, our goals were to (1) quantify spermatophore production; (2) determine the preferred location for spermatangia deposition; (3) investigate whether male and female O. ingens mate with multiple mates; and (4) discuss the location of implanted spermatangia in light of mating behavior and egg fertilization. Toward this end, we examined male and female O. ingens specimens from Falkland Island and New Zealand waters. Male O. ingens store up to 198 spermatophores (mean 103 ± 61; n = 12) in their reproductive system, which are produced over a period of considerable somatic growth (200–400 mm ML), and which may have a considerable size range. Males insert their long extendible terminal organ in the mantle cavity of the female, potentially through the funnel, to deposit spermatophores in one or more of four regions on the female’s body. Most implanted spermatangia (52.5 %) were found in the funnel region, but many were also found inside the mantle cavity closer to the oviducts. Males with longer terminal organs therefore may be able to position closer to the oviducts where fertilization chances are higher than for spermatangia located in the funnel region. The number of implanted spermatangia per individual female (4–60, mean 29 ± 20; n = 24), the multiregional spermatangia deposition, and the different outer appearance of spermatangia, suggested that females have multiple mating events. Since males produce more spermatophores (up to 200) than the number of spermatangia in one region (<60), it is likely that males too mate with more than one female. We show how quantitative assessment of reproductive characteristics can provide insight into the reproductive behavior of deep-sea species for which in situ observations are currently lacking.     

Impacts of floral gender and whole-plant gender on floral evolution in Ecballium elaterium (Cucurbitaceae)

Investigation of gender specialization in plants has led to several theories on the evolution of sexual dimorphism: reproductive compensation, based on enhanced reproductive efficiency with gender specialization (flowers should be larger on dioecious plants); Bateman's Principle, based on sex-specific selection (display for pollinator attraction in males and seed set in females); and intersexual floral mimicry, based on mimicry of a reward-providing gender by a non-reward providing gender (reduced dimorphism in dioecious plants due to increased spatial separation of male and female flowers). These theories were evaluated in Ecballium elaterium, which contains two subspecies, elaterium (monoecious) and dioicum (dioecious). Our results show that flowers of the dioecious subspecies are larger and allocate more to reproductive organs than do flowers of the monoecious subspecies. Both subspecies are sexually dimorphic (male flowers larger than female flowers). Variance in flower size among populations is greater in the dioecious subspecies. Finally, there is sufficient genetic variation to enable ongoing response to selection; genetic correlation constraints on independent response of female and male flowers may be stronger in the monoecious subspecies. Our findings provide support for aspects of all three theories, suggesting that the evolution of floral dimorphism is based on a complex interplay of factors.     

A REEXAMINATION OF THE POLLEN-DONATION HYPOTHESIS IN AN EXPERIMENTAL POPULATION OF ASCLEPIAS EXALTATA

The evolution of large floral displays in hermaphroditic flowering plants has been attributed to natural selection acting to enhance male, rather than female, reproductive success. Proponents of the “pollen-donation hypothesis” have assumed that maternal resources, rather than levels of effective pollination, limit fruit set. We investigated the pollen-donation hypothesis in an experimental population of poke milkweed, Asclepias exaltata, where effective pollination did not limit fruit set. Specifically, we examined the effects of flower number per plant, and flower number per umbel on male reproductive success (number of fruits sired) and female reproductive success (number of fruits matured). In 1990, a paternity analysis was performed on fruits collected from 53 plants whose inflorescences were not manipulated. Flower number per plant was significantly correlated with male success, but not with plant gender. Flower number per plant was also significantly correlated with female success, but umbel number and stem number per plant together explained more than half (58%) the variation in female success. The percentage of fruit set was not significantly correlated with flower number per plant. Plants with large floral displays did not disproportionately increase in male reproductive success, relative to female success, as predicted by the pollen-donation hypothesis. In 1991, the effect of flower number per umbel on male and female reproductive success was investigated. Flower number per umbel was manipulated on four umbels per plant by removing flowers to leave 6, 12, or 18 flowers in each umbel. Plants with the largest umbels effectively pollinated twice as many flowers on other plants, but produced only 1.35 times as many fruits as plants with 6 and 12 flowers per umbel. Relative maleness of plants with large umbels was nearly twice that of small and medium umbels. Although these observations are consistent with the pollen-donation hypothesis at the level of umbels, they are problematic, because much of the variation in flower number per umbel exists within, rather than among, plants in natural populations. Thus, plants consist of both reproductively male (large) and female (small) inflorescences, which act to increase total reproductive success. It is therefore inappropriate to explain the evolution of large floral displays in milkweeds solely in terms of potential male reproductive success.     

Growth,plant quality and leaf damage patterns in a dioecious tree species: is gender important?

Frequently, female plants allocate more resources to reproductive structures and defense-related secondary compounds in comparison with male plants that invest more resources to growth, reflecting trade-offs between reproduction, growth and defense. Therefore, differences in herbivory can be expected between genders. In this study, over two years, we analyzed the differences in plant chemical defense, nutritional quality, plant size and herbivory between genders in the dioecious tree, Spondias purpurea in a Mexican tropical dry forest. We estimated the total leaf area and the area consumed by folivory using a digital image of each leaf. The nutritional quality was estimated as water content, and the concentration of chlorophyll and total nonstructural carbohydrates. The secondary metabolites analyzed were total content of soluble phenolics, flavonoids, protein precipitation capacity of tannins, gallotannins, soluble proanthocyanidins, hydrolyzable tannins and ellagitannins. Our results differ from most of studies that analyze the differential herbivory patterns in dioecious plants. We found that female trees had higher levels of herbivory than male trees of S. purpurea. In the same way, female trees showed higher size and nutritional quality than males, while chemical defense was higher in male trees. The higher percentage of folivory in female trees of S. purpurea is associated with greater nutritional quality and lower chemical defenses. Our results show that male-biased herbivory might not be universal in dioecious species. Therefore, studies of fitness components affected by herbivory are necessary to understand the evolution of dioecy and the importance of herbivores as selective agents on breeding system features.     

Differences in environmental response between the sexes of the dioecious shrub Baccharis halimifolia (Compositae)

Summary Baccharis halimifolia (Compositae) is a dioecious shrub which grows on the upland fringe of tidal marshes along the Atlantic and Gulf Coasts of North America. We examined the responses of the two sexes to variation in nutrient and moisture availability plant density, and defoliation. By growing plants from seedlings to flowering adults under various combinations of soil type, fertilization rate and plant density, we were able to establish different rates of plant growth and mortality. Plants grown at high density and low nutrient and water supply grew the least, incurrent the most mortality and showed a male-biased sex ratio (73% male). At low density with abundant nutrients and water, plants grew more, survived well, flowered frequently, and were female-biased (75% female). Changes in sex ratio were probably the result of sex-related mortality rather than sexual lability of the seedlings. While changes in sex ratio occurred under experimental conditions in the green-house, no evidence for differences in habitat utilization between the sexes were found in the field and the sex ratio (59% female) did not vary across habitats. In the marsh habitats we sampled where water and nutrients were apparently available, there was no evidence for differential mortality between the sexes. When defoliated (75% of leaf tissue), both sexes showed similar reductions in reproductive effort (number of flower heads/shoot). Our results indicate that differences between the sexes of Baccharis in their response to environmental growing conditions is an important ecological factor associated with the separation of male and female function into separate individuals.     

DIFFERENCES IN BIOMASS ALLOCATION TO REPRODUCTIVE AND VEGETATIVE STRUCTURES OF MALE AND FEMALE PLANTS OF A DIOECIOUS,PERENNIAL HERB,SILENE ALBA (MILLER) KRAUSE

The pattern of biomass allocation of males and females and the sex ratio and growth characteristics of plants from three seed-size classes in Silene alba were investigated in a greenhouse study. Seed size significantly affected adult plant size and flower production of both male and female plants, but there was no significant difference in the proportion of males and females emerging in three seed-size categories. Male and female plants differed in the proportion of total biomass allocated to vegetative and reproductive structures and these differences were consistent across all seed-size categories. Males allocated a greater proportion of their biomass to flowers than did females. Female reproductive effort was dependent upon the percentage of flowers producing mature capsules. Only females with greater than 20% fruit set have a higher reproductive expenditure than males. Consequently, female expenditure is potentially greater than males, but is spread out over a longer portion of the growing season. This difference in the timing of reproductive expenditures by males and females allows females to allocate more biomass to growth during the early flowering period and may therefore account for the common pattern in herbaceous perennial dioecious species in which adult females are larger than adult males.     

How to be an attractive male: floral dimorphism and attractiveness to pollinators in a dioecious plant

Background  

Sexual selection theory predicts that males are limited in their reproductive success by access to mates, whereas females are more limited by resources. In animal-pollinated plants, attraction of pollinators and successful pollination is crucial for reproductive success. In dioecious plant species, males should thus be selected to increase their attractiveness to pollinators by investing more than females in floral traits that enhance pollinator visitation. We tested the prediction of higher attractiveness of male flowers in the dioecious, moth-pollinated herb Silene latifolia, by investigating floral signals (floral display and fragrance) and conducting behavioral experiments with the pollinator-moth, Hadena bicruris.     

Patterns of sex ratio variation and genetic diversity in the dioecious forest perennial <Emphasis Type="Italic">Mercurialis perennis</Emphasis>

In small populations of plant species with separate sexes, it can be expected that besides the local environment also stochastic events influence population sex ratios. Biased sex ratios may in turn negatively affect genetic diversity due to increased genetic drift and, in clonal plants, due to reduced sexual reproductive output. Empirical evidence for these processes is scarce, however. We investigated the pattern of sex ratio variation and the distribution of genetic variation of the dioecious clonal forest herb Mercurialis perennis using AFLP markers. Analysis of molecular variance indicated a pronounced genetic structure. Overall within-population genetic diversity was moderate and local sex ratios were slightly male biased. The proportion of male to female plants in large populations slightly increased with increasing light penetration to the herb layer. Small populations, on the contrary, displayed high variability in sex ratios, unrelated to the local light environment. Genotypic diversity decreased with more male-biased sex ratios. We conclude that stochastic events related to small population size and the local forest environment, related to canopy closure, affect the proportion of female plants and indirectly influence local genotypic diversity, likely through the degree of sexual reproduction. This is one of the first studies to report a clear association between gender proportions and genetic diversity of a dioecious plant species in a fairly large survey.     

Variation of morphological and chemical traits in sexes of the dioecious perennial grass Poa ligularis in relation to shrub cover and aridity in Patagonian ecosystems

Sexes of dioecious species may have dimorphic responses to environmental variation due to differences in resource requirements and reproductive costs. We analyzed the effect of aridity/relative shrub cover, and vicinity to shrub patches on morpho-chemical traits of sexes of the dioecious perennial grass Poa ligularis in patchy arid ecosystems in northern-central Patagonia. We hypothesized that sexes of P. ligularis have dimorphic responses in morpho-chemical traits in relation to the environmental variation induced by aridity/relative shrub cover and vicinity to shrub patches. We selected seven sites across a gradient of increasing aridity and relative shrub cover. We randomly collected 5–10 P. ligularis plants per site registering the sex (female or male) and location with respect to shrub patches (shrub patch or inter-patch). For each plant, we assessed morpho-chemical traits (height of the vegetative tillers, length/dry weight/area of blades, specific blade area, nitrogen and soluble phenol concentration in blades). Sexes showed dimorphic responses in height of vegetative tillers, blade length, and blade area with respect to vicinity to shrub patches; and in variation of soluble phenolics in blades in relation to aridity/relative shrub cover. Responses in both sexes were opposite to those expected by aridity, highlighting the role of favorable environments induced by shrub canopies on dimorphic responses of sexes of P. ligularis. Resource-rich microsites associated with shrub canopies promoted increased plant performance of females with high reproductive costs while resource-poor open areas, favorable for pollen dispersal, induced improved chemical defenses of males. These results are consistent with the resource availability hypothesis.     

Sex‐specific interaction between arbuscular mycorrhizal and dark septate fungi in the dioecious plant Antennaria dioica (Asteraceae)

Male and female plants of dioecious species often differ in their resource demands and this has been linked to secondary sexual dimorphism, including sex‐specific interactions with other organisms such as herbivores and pollinators. However, little is known about the interaction between dioecious plants and fungal root endophytes. Plants may be simultaneously colonised by arbuscular mycorrhizal (AM) and dark septate (DS) fungi. While it is well established that AM mutualism involves reciprocal transfer of photosynthates and mineral nutrients between roots of host plants and these fungi, the role of DS fungi remains controversial. Here, we report the temporal and spatial variation in AM and DS fungi in female, male and non‐reproductive Antennaria dioica plants in three natural populations in Finland during flowering and after seed production. Females had higher colonisation by AM fungi, but lower colonisation by DS fungi than male and non‐reproductive plants. The higher AM colonisation was observed during flowering, and this difference varied among populations. Our results suggest that females and males of A. dioica interact with AM and DS fungi differently and that this relationship is dependent on soil fertility.     

Interactions in the patterns of vegetative growth and reproduction in woody dioecious plants

Summary Interactions between vegetative growth and reproduction were evaluated in Peumus boldus, Lithraea caustica and Laretia acaulis, three woody dioecious species in central Chile. Phenological observations were made periodically on marked branches of male and female plants, and biomass allocation (dry weight) to vegetative and reproductive tissues was measured. The magnitude of flowering was evaluated in groups of plants in three successive seasons. The patterns of activities are species- and sex-dependent, and cycles of 2–4 years have been established. Branches that produce flowers either do not grow or grow less than branches without flowers, and males and females have differential resource allocation: male branches attain higher biomass values. Groups of plants show seasonal behavior that suggest synchrony in their reproductive activities.