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Pollination efficiency of Potamogeton pectinatus L
Abstract
Fruit-set was measured on submerged inflorescences of Potamogeton pectinatus L. in Switzerland. Inflorescences that even when stretched could not have reached the surface were compared with those that could have reached the surface. The seed set (percentage of ovules to seeds) for totally submerged inflorescences was 3.95% and for inflorescences that may have reached the surface 25.35%. Pollination is clearly less efficient deep below the water surface than at the surface. However, it is surprising how constant the low seed-set is underwater (2.5–7.5%) and how variable and inefficient it is at the water surface (6.5–40%).
... Hydroautogamy have been reported in three hermaphroditic genera of Potamogetonaceae [4,17,18]. In these genera, another uncommon pollination phenomenon was reported. ...
Aquatic plants are phylogenetically well dispersed across the angiosperms. Reproductive and other life-history traits of aquatic angiosperms are closely associated with specific growth forms. Hydrophilous pollination exhibits notable examples of convergent evolution in angiosperm reproductive structures, and hydrophiles exhibit great diversity in sexual system. In this study, we reconstructed ancestral characters of aquatic lineages based on the phylogeny of aquatic angiosperms. Our aim is to find the correlations of life form, pollination mode and sexual system in aquatic angiosperms. Hydrophily is the adaptive evolution of completely submersed angiosperms to aquatic habitats. Hydroautogamy and maleflower-ephydrophily are the transitional stages from anemophily and entomophily to hydrophily. True hydrophily occurs in 18 submersed angiosperm genera, which is associated with an unusually high incidence of unisexual flowers. All marine angiosperms are submersed, hydrophilous species. This study would help us understand the evolution of hydrophilous pollination and its correlations with life form and sexual system.
... Potamogeton pectinatus and P. fiIiformis are self-compatible and produce hermaphrodite flowers. Pollination usually occurs at the water-surface (epihydrophily), although it can also occur underwater, albeit less successfully (Guo & COOK 1989). ...
Genetic variability in Potamogeton pectinatus and P. filiformis was studied by means of isozymes. The overall levels of variability were similar to some other well studied hydrophilous species, and were shown to be distributed more between than within populations. This partitioning of variability was attributed to three main factors. (1) Clonal growth (as measured by the frequency of multi-enzyme phenotypes) was shown to be a major factor in both species, although more important in P. pectinatus. (2) Low levels of sexual reproduction were shown to be a likely contributor to the partitioning of variability in P. pectinatus; such reproduction is probably limited by seedling recruitment rather than by infrequent flowering. (3) Geographical isolation was indicated as a factor regulating gene flow at distances of more than about 1000 km in both species, with the data suggesting that dispersal between populations is mainly by seed rather than by vegetative means.
Modes of pollination, the morphological and functional adaptations for selfing and outcrossing, the mechanism of the opening of thecae in water medium and self-incompatibility were studied in 12 species of Potamogeton. Species of the genus have different morphological and functional adaptations for anemophily, anemoephydrophily, ephydrophily and hyphydrophily via "hydroautogamy". Pollination and mating systems in different species are adaptive, variable and complicated processes. Seed production in species with submerged flowers is achieved in two ways. In Potamogeton obtusifolius (the subgenus Potamogeton) by agamospermy (gametophytic apomixis, diplospory of Taraxacum type). In hyphydrophilous P. filiformis (the subgenus Coleogeton) air bubbles bring about dehiscence of anthers and result in autogamy. Self-incompatibility present in some species is probably of the gametophytic type.
Pollination and Floral Ecologyis the most comprehensive single-volume reference to all aspects of pollination biology--and the first fully up-to-date resource of its kind to appear in decades. This beautifully illustrated book describes how flowers use colors, shapes, and scents to advertise themselves; how they offer pollen and nectar as rewards; and how they share complex interactions with beetles, birds, bats, bees, and other creatures. The ecology of these interactions is covered in depth, including the timing and patterning of flowering, competition among flowering plants to attract certain visitors and deter others, and the many ways plants and animals can cheat each other.Pollination and Floral Ecologypays special attention to the prevalence of specialization and generalization in animal-flower interactions, and examines how a lack of distinction between casual visitors and true pollinators can produce misleading conclusions about flower evolution and animal-flower mutualism. This one-of-a-kind reference also gives insights into the vital pollination services that animals provide to crops and native flora, and sets these issues in the context of today's global pollination crisis.Provides the most up-to-date resource on pollination and floral ecologyDescribes flower advertising features and rewards, foraging and learning by flower-visiting animals, behaviors of generalist and specialist pollinators--and moreExamines the ecology and evolution of animal-flower interactions, from the molecular to macroevolutionary scaleFeatures hundreds of color and black-and-white illustrations.
Studies on floral ecology and flower evolutionary aspects have never been as broad as at present Research in biotic and abiotic pollination and nearly every facet of flowers, their biology and function has grown enormously. The reason for this was outlined in my last report (Prog Bot 50). The most fascinating perspectives are that floral ecologists, studying and measuring variation and morphological and behavioral modifications in the interactions they observe, are more and more in a position to evaluate directly selectional pressure, its dynamics in space and time, which then allows the understanding of the basic forces of adaptive evolution. In other words, many recent studies utilize animal-flower interactions to make quantitative tests of general hypotheses in evolutionary ecology (Feinsinger 1987; Armbruster 1992). Feinsinger (1987) proposes two major directions for future research, namely its application to agriculture and conservation biology. Barrett and Eckert (1990) expect that future studies will be even more comprehensive, as they will not concentrate on single life cycle stages only, but consider also the traits ex-pressed at different stages of the life history; selection does not act on isolated traits but “evaluates” the whole phenotype during its entire life.
The floral biology of the obligately aquatic plant species Groenlandia densa (L.) Fourreau was studied. It is effectively pollinated (1) in air above the water surface (anemophily), (2) at the water surface where the stigmas can pick up pollen grains directly from the surface of the water (epihydrophily), or (3) underwater with wet stigmas (hypohydrophily). Underwater, the pollen grains are associated with the air-water interface of bubbles, but they may be positioned on both sides of this interface. The breeding system is almost entirely autogamous with self-fertilization; a slight degree of proterogyny may permit some outbreeding.
Potamogeton subg. Coleogeton is elevated to generic level. A combination of morphological and anatomical features readily distinguishes the new genus Coleogeton from both Groenlandia and Potamogeton, the two other genera recognized in the Potamogetonaceae. All new combinations for taxa that occur in North America are proposed for use in the Flora of North America. These new combinations include Coleogeton striatus, C. pectinatus, C. filiformis, C. filiformis subsp. alpinus, C. filiformis subsp. occidentalis, and C. vaginatus.
Aquatic species represent fewer than two percent of all flowering plants, and only 18 aquatic genera have acquired true hydrophily (water-pollination) which is associated with an unusually high incidence of unisexual flowers. From the subset of submersed, hydrophilous angiosperms, only 13 genera have colonized marine habitats. The evolution of hydrophily, unisexuality, and marine habit in angiosperms was explored using estimates of phylogeny obtained by phylogenetic analyses of chloroplast (rbcL) gene sequence data. Despite what might appear to be difficult evolutionary transitions, hydrophiles are highly polyphyletic with independent origins in the monocotyledon subclass Alismatidae in addition to two derivations in Be dicotyledon families Ceratophyllaceae and Callitrichaceae. Yet, even in alismatids, hydrophily has evolved many times. Unisexuality has also evolved repeatedly in the Alismatidae, and is ancestral to the evolution of hydrophiles and marine plants in the Hydrocharitaceae, Marine angiosperms (known only from Alismatidae) have evolved in three separate lineages. The multiple origins of hydrophilous, marine plants offer an extraordinary example of convergent evolution in angiosperms.
The present paper reviews the literature on reproduction, survial, dispersion and competition in aquatic plants of mostly European rivers. The specificity of the strategies of colonization in aquatic plants in comparison with terrestrial plants is noted. The importance of the knowledge of these life history traits in the control of the harmful effects caused by aquatic plants and for ecosystem management is also considered. The difficulty of applying current ecological theories concerning adaptative strategies to aquatic plants is discussed, focusing on the great interest of studying the species traits of aquatic macrophytes for testing such theories and interpreting recolonization patterns of disturbed areas. Knowledge of strategies of reproduction, dispersion and competition among aquatic plants remains very fragmentary, particularly from a quantitative view-point, and further studies are required both for theoretical and practical applications.
Reproduction is central to changes in distribution and abundance patterns of submersed freshwater macrophytes. In this paper we seek to identify potential ‘bottlenecks’ limiting sexual or vegetative reproduction or its predictability for these plants. To this end we consider the regulation of seed production, seed fate, vegetative propagule production, and vegetative propagule fate in turn, both in general terms and for the perennial Vallisneria americana Michx. in particularPlant biomass appears to be an important determinant of the incidence of flowering for greenhouse-grown Vallisneria americana: 88% of 425 plants either failed to flower if below a threshold dry weight of 0.75 g, or flowered if above it. The number of flowers (in females) or inflorescences (in males), however, was only moderately well correlated with Vallisneria biomass, and the flowering ‘threshold rule’ weakened considerably in the field. Closer examination of the dependence of seed output on plant biomass and pollination intensity, and of the importance of seed or fruit abortion is needed for submersed species.Our ignorance of seed fate is exemplified by the paucity of quantitative studies on dispersal distances and seed deposition patterns, on seed banks, and on features of seed microenvironments pertinent to germination, although the sensitivity of seed dormancy and germination to a variety of environmental conditions has been tested in the laboratory for many species. Further, losses of seeds and seedlings as a result of unfavorable environments, sediment disturbance, flotation, pathogens, and herbivores are generally not well characterized. Overall, the principal limiting step for sexual reproduction may in some cases be lack of floral induction, and in others, ineffective pollination, but dispersal away from the local population, failure of seeds to germinate, and the challenges of seedling establishment cannot be ruled out.Plant size is well correlated with vegetative propagule production for both greenhouse and field Vallisneria populations. As with seed germination, the germination of vegetative propagules has been relatively well studied in the laboratory, but important regulators of germination and establishment in the field warrant further study.We suggest that more investigations at two interfaces of physiological ecology and demography may be particularly fruitful. Regarding propagule production, experimental focus on allocation patterns which ‘translate’ accumulated resources into seeds or vegetative propagules should prove rewarding. Regarding propagule fate, post-dispersal mortality of seeds and vegetative propagules may be rooted in phytiological tolerance limits, but could also be attributable to pathogen or herbivore attack.
Four leaf morpha groups (floating-leaved, submerged broad-leaved, submerged linear-leaved and filiform-leaved) and three inflorescences type groups (erect, facultative floating and floating) can be found in the genus Potamogeton. Life forms in the genus correlate with pollination types (anemophily, epihydrophily and hydroautogamy). Floral traits vary greatly among different life forms and pollination types. Both floating and submerged broad-leaved species produce erect inflorescences that are suited for anemophilous pollination. These flowers also have the highest pollen/ovule (P/O) ratio (25,013) and the smallest pollen grain volume (6046 μm3). On the contrary, submerged filiform-leaved species produce only floating inflorescences and their flowers produce the largest pollen grains (17,567 μm3) and have the lowest P/O ratio (6752), which is typical of the syndromes of hydroautogamy and epihydrophily. The relatively prolific seed production (about 70%) and wide dispersal in the floating and submerged broad-leaved species and the submerged filliform-leaved species indicate that these two groups are well adapted to the aquatic environment. This is in contrast with the less well-adapted complex and unstable pollination system found in linear-leaved species. We propose that the pollination systems and life forms in the Potamogeton, have undergone modification in response to the demands imposed by the aquatic environment during the evolutionary process in the genus.
Potamogetonaceae (Alismatales) comprises about three genera, including
Potamogeton, a near cosmopolitan genus of about 80-100 species. The
understanding of its floral unit is quite controversial, being interpreted as a reduced
inflorescence or a true flower. In the current circumscription of Potamogetonaceae
there is scarce embryological information of Potamogeton and complementation of
data is needed. It is known that the pollen in this genus is inaperturate and it has
been suggested by some authors that in this type of pollen there is a release of
constraint on tetrad shape, as in other Monocotyledons. The aims of the present
study were to investigate the development of the androecium and the gynoecium in
three Potamogeton species in order to: understand the relationship between
microsporogenesis features and inaperturate pollen formation; elucidate the nature of
the floral unit; verify whether organ initiation patterns occur in the flower or not; and
complement the embryological data. Inflorescences at various developmental stages
were collected and fixed in 1% glutaraldehyde and 4% formaldehyde in 0.1 M sodium
phosphate buffer, pH 7.2. for both light (LM) and scanning electron microscopy
(SEM). The samples for LM were embedded in hydroxyethyl methacrylate, then
sectioned, stained and mounted according to standard procedures. Samples for SEM
were also processed according standard procedures. For TEM examination, anthers
were fixed in 2.5% glutaraldehyde and 2% paraformaldehyde in 0.1 M sodium
phosphate buffer, pH 7.2, then embedded in epoxy resin, sectioned and stained. At
microsporogenesis, cytokinesis is successive and the callosic cell wall formation was
achieved by centrifugal cell plates, with simultaneous deposition of additional callose.
The resulting tetrads were of various shapes. The inflorescences of the three species
studied were similar, varying only in flower number and shape of the floral organs.
The initiation order of floral organs was similar: lateral tepals, median tepals, followed
by lateral stamens, median stamens and carpels. The carpels of P. illinoensis
developed in a different way compared to the other species. The embryological
characters were constant among the three species and some of them are as follows:
anther wall of the monocotyledonous-type, and ascidiate carpels with a single
campylotropous ovule that develop a Polygonum type of embryo sac. The present
data indicate that the lack of specific points of additional callose deposition during
microsporogenesis is the probable reason to the lack of apertures in the
Potamogeton pollen. The floral unit of Potamogeton should be interpreted as a true
flower. Moreover, two patterns of floral organ initiation were pointed out, which are
not correlated to specific clades. The stigma shape, and both position and shape of
carpel opening were identified as potential characters to taxonomy. This study
presented some new and complementary information for the embryology of
Potamogeton. The data also contribute to a better understanding of the embryology
of Potamogetonaceae as a whole and shed light on conflicting information caused by
the use of old circumscription of the family.
Several pollination systems including anemophily, ephydrophily, and hyphydrophily have been reported for the aerial and/or submerged flowers of Potamogeton. Anemophily is generally believed to characterize the aerial-flowered taxa. The supposition that hyphydrophily characterizes submerged-flowered taxa derives from observations of underwater seed production. Hyphydrophily is often associated with larger pollen and, like anemophily, generally implies xenogamy and stochastic pollen delivery-features predicting high pollen/ovule (P/O) ratios. Relative to this, we present data from limited breeding studies and extensive analyses of pollen size and P/O ratios of North American species. The species tested were partly autogamous. Aerial-flowered species bear larger pollen and show significantly higher P/O ratios than those with submerged flowers. Thus, we suggest autogamy as an alternative to hyphydrophily for the submerged-flowered species of Potamogeton. Hydroautogamy is proposed to define a special class of autogamy; e.g., in Potamogeton, wherein self pollination is effected by pollen moving from anthers to stigmas over the surface of air bubbles. Autogamy is posited as a more likely first hypothesis in studies of breeding systems of submerged-flowering angiosperms with bisexual flowers. We also suggest that in Potamogeton P/O ratios reflect both breeding and pollination systems. A model is presented that shows how higher P/O ratios, than the breeding system of a taxon would imply, could be generated by the added effect of the pollination system.
It is evident that underwater outcrossing (hypohydrophily) arose from aerial pollination systems. However, no mechanism to explain this transition has been proposed. Herein I suggest a system involving bubble pollination, similar to hydroautogamy in Potamogeton, as an intermediate in the transition from aerial to submerged pollination systems. Such an intermediate would provide the opportunity for the gradual evolution of characters that are needed for underwater outcrossing without sacrificing seed production during the transition.
