AXENIC CULTURE OF THALASSIA TESTUDINUM BANKS EX KÖNIG (HYDROCHARITACEAE)

Cultures of Thalassia testudinum were established and maintained in the absence of other detectable organisms. Axenic cultures were initiated using surface sterilized seeds which were aseptically dissected from surface sterilized fruits. Seedlings were cultured in 75-ml (25-mm × 200-mm) culture tubes containing 30 ml of rooting substrate and 40 ml of chemically defined seawater media. Seedlings and culture media were analyzed for microbial contamination after 42 days of culture utilizing standard marine bacterial/fungal isolating procedures and by light and scanning electron microscopy. Axenic seagrass cultures allow physiological studies such as nutrient assimilation kinetics, rhizosphere and phyllosphere microbial interactions through mono- and poly-axenic seagrass-microbial cultures.     

TRACE METAL CYCLING IN TROPICAL-SUBTROPICAL ESTUARIES DOMINATED BY THE SEAGRASS THALASSIA TESTUDINUM

The present study was designed to determine the uptake and release rates of various trace metal cations by turtle grass and its community in order to provide the coefficients of our previously described computer model intended to simulate trace metal cycling in subtropical and tropical estuaries. The site of uptake in Thalassia was also examined.     

STUDIES OF A MARINE GRASS,THALASSIA TESTUDINUM. I. ULTRASTRUCTURE OF THE OSMOREGULATORY LEAF CELLS

Thalassia testudinum (Turtle Grass), a marine monocot which grows completely submerged, differs from intertidal and other halophytic angiosperms in that it has no specialized saltsecretory glands. Osmoregulation appears to be accomplished by the epidermal leaf cells which have highly invaginated plasmalemmas with numerous mitochondria situated in the interdigitations. The ultrastructure and proposed mode of secretion are similar to that of the salt-marsh monocot Spartina, but differ from that found in dicots. Evidence is presented to show why monocots are the only angiosperms which have adapted to a completely marine environment.     

POLLINATION ECOLOGY OF LABIATAE IN A PHRYGANIC (EAST MEDITERRANEAN) ECOSYSTEM

This study was conducted in a phryganic (East Mediterranean) ecosystem at Daphni, near Athens, Greece. The Labiatae, represented by ten species belonging to nine genera, dominate in this ecosystem type. They flower from February to July. Both flowering time and nectar quantity are related to the species ability to tolerate intense water stress. Labiatae are visited by 201 insect species. Of these, 43 are exclusively supported by the family and 37 are monotropous. Solitary bees (mainly Anthophoridae, Megachilidae, Halictidae) constitute 47.3% of pollinators. The family is important in hosting specialized bees (15 species) in phrygana, particularly late in the flowering season. Labiatae species form two equally represented groups in this system; namely, the late winter-early spring (early) flowering, visited by relatively few pollinator species, and the late spring-summer (late) flowering species, visited by numerous pollinators. This temporal distinction is accompanied by different pollination profiles that include duration of anthesis, reward to pollinators, floral attractiveness, and flower character differentiation. All of these attributes are maximized in the early flowering period. This strategy suggests a mechanism for resource partitioning at a time when the pollinator resource is limited and competition for the services of pollinators is expected to be intense. Contrary to the current theory concerning cornucopian species, the copiously rewarding flowers of Labiatae in phrygana are not those abundantly serviced by pollinators.     

THE POLLINATION ECOLOGY OF AQUILEGIA ELEGANTULA AND A. CAERULEA (RANUNCULACEAE) IN COLORADO

Aquilegia elegantula Greene and A. caerulea James occur in montane and subalpine habitats in the southern Rocky Mountains of western North America. The red and yellow flowers of A. elegantula are nodding, odorless, protogynous, and secrete a concentrated (44%) sucrose nectar in the floral spurs. Seed set in flowers under pollinator exclosures was 12% while seed set in open-pollinated flowers was 65%. The flowers of A. elegantula are pollinated primarily by the Broad-tailed Hummingbird (Selasphorus platycercus [Swainson]) and by at least three species of pollen-foraging bumblebees, of which Bombus occidentalis Greene is the most common. The blue and white flowers of A. caerulea are erect, mildly fragrant, protandrous, and secrete a 26% sucrose nectar. Seed set in caged flowers in the field averaged 39%. in uncaged flowers 54%. The most important pollinators of A. caerulea are the crepuscular hawkmoth, Hyles (=Celerio) lineata (Fabricius) and ten species of pollen-foraging Bombus. The most abundant bumblebee species, B. occidentalis, is also a frequent nectar thief. Differences in pollination systems alone probably do not constitute an effective anti-hydridization mechanism between A. elegantula and A. caerulea, but do serve to reinforce differences in habitat and flowering time that distinguish the two species.     

POLLINATION ECOLOGY OF PYRRHOPAPPUS CAROLINIANUS (COMPOSITAE)

Pyrrhopappus carolinianus and Hemihalictus lustrans constitute a mutualistic association: the early morning flowering of Pyrrhopappus provides the matinal bee with a nearly exclusive pollen source, although other plants must be visited for nectar. Female Hemihalictus, the primary pollen vector, tear open the anthers and remove the pollen before it is available to other bees. The foraging behavior of the bee insures cross-pollination. The flight pattern of the bees generally restricts the pollen dispersal range. If cross-pollination fails, then autogamy results from twisting of the styles that brings the stigmas in contact with the pollen presented on the styles of other florets. Schinia mitis is an important predator of the capitulae of P. carolinianus.     

THE POLLINATION ECOLOGY OF ZENOBIA (ERICACEAE)

Zenobia is a shrub endemic to the coastal plain of the Carolinas and southeastern Virginia. The sole species, Zenobia pulverulenta, appears to be weakly self-compatible and partially self-pollinating. Fruit set was reduced, but not eliminated by excluding insect floral visitors. Insect visitors were collected and their pollen loads examined for Zenobia and foreign pollen. Analysis of these pollen loads and observations of insect-foraging behavior indicate that workers of three species of bumblebee (Bombus bimaculatus, B. griseocollis and B. impatiens) are. the principal pollinators of Zenobia. However, pollinator density and composition appear to be strongly influenced by the habitats in which Zenobia grows. Pollen and nectar serve as the primary rewards for pollinators.     

POLLINATION ECOLOGY OF FOUR DALECHAMPIA SPECIES (EUPHORBIACEAE) IN NORTHERN NATAL,SOUTH AFRICA

The pollination ecology of four Dalechampia species was studied in three areas in northern Natal, South Africa. All species were pollinated by resin- and/or pollen-collecting megachilid bees (Hymenoptera: Megachilidae). The most common of these at all study sites was Heriades sp. (Megachilini), which collected both pollen and resin. This bee was the primary pollinator of D. galpinii and D. volubilis, and a secondary pollinator of D. aff. parvifolia and D. capensis. The primary pollinators of these latter two Dalechampia were Pachyanthidium near cucullatum and P. cordatum (Anthididiini), respectively. These are larger bees that collected mainly resin. Other visitors varied among Dalechampia species and among sites. Pairs of Dalechampia species were often found in sympatry (within 30 m of each other) and shared pollinators to varying extents. “Transfer experiments,” in which we placed inflorescences of two Dalechampia species together, reinforced observations of flower discrimination by bees foraging among naturally occurring sympatric pairs. Heriades sp. showed no obvious discrimination between Dalechampia species, but Pachyanthidium spp. “preferred” the Dalechampia species with the greater resin reward. Occasionally, however, Pachyanthidium would visit less rewarding species. Thus, although sympatric African Dalechampia species showed some pollinator partitioning, it was much weaker than found among New World species, and cannot alone explain the general absence of Dalechampia hybrids in northern Natal.     

THE POLLINATION ECOLOGY OF DICENTRA CUCULLARIA

In northeastern Iowa and southwestern Wisconsin the flowers of Dicentra cuculiarla were found to be pollinated almost exclusively by Bombus bimaculatus nectar-foraging queens, which were phenologically synchronized in their emergence from hibernation with the flower's anthesis. Cinematographic and stereophotographic evidence indicated that pollen transfer was effected by the ventral side of the insect's head and anterior thorax contacting essential flower parts and to a lesser degree by the front and middle legs contacting pollen-laden edges of the inner petals. Lepidoptera, Diptera, and small Hymenoptera occasionally encountered on the flowers were ineffective in pollination. Abundant Apis mellifera pollen-foraging workers regularly effected pollination, but being an introduced species it exhibits no naturally developed pollination adaptation to the flower. Nectar spur perforation by B. affinis nectar-foraging queens did not affect plant fertility, and this behavior was related only in part to forager tongue length. Nectar-foraging behavior of B. bimaculalus queens on the flowers was correlated with the phenological development of the annual insect colonies.     

COMMUNITY STUDIES IN POLLINATION ECOLOGY IN THE HIGH TEMPERATE ANDES OF CENTRAL CHILE. I. POLLINATION MECHANISMS AND ALTITUDINAL VARIATION

Pollination mechanisms and pollinators are reported for a total of 137 species (75% of the non-abiotically pollinated flora) as they occur at three altitudinal levels (subandean scrub: 2,200–2,600 m; cushion-plant zone: 2,700–3,100 m; subnival feldfield: 3,200–3,600 m) in the Andean (alpine) zone on the Cordon del Cepo (33°17'S) in central Chile as part of community oriented research in reproductive biology in the high temperate Andes of South America. Only around 4% of the species studied failed to be visited by potential pollinators. Hymenopterans (principally bees) are important pollinators of 50% of the biotically pollinated flora, butterflies of 24% and flies of 46%. Other vectors include beetles, moths, and hummingbirds. An estimated 17% of the flora is anemophilous. Bee species-richness, specialist feeding, and melittophily reach maxima in the subandean scrub; thereafter, bees diminish rapidly in number, with bees pollinating only 13% of the subnival flora as contrasted with 68% of the subandean flora. Although fly and butterfly species-richness also decline with increasing altitude, the proportions of species pollinated by these vectors actually increases. High-altitude populations of melittophilous species with broad altitudinal ranges are invariably serviced by fewer bee species as compared with lower populations. The rich bee fauna at the lower end of the Andean zone in central Chile appears to have resulted from upward colonization from that of the subtending lowland Mediterranean sclerophyllous woodland vegetation. Altitudinal variation in pollination spectra is discussed in relation to contrasting life history characteristics and different modes of thermoregulation in the insect groups involved.     

THE POLLINATION ECOLOGY OF SOLANUM ROSTRATUM (SOLANACEAE)

The pollination mechanisms and pollen vectors of Solarium rostratum have been examined by greenhouse experiments and field studies. Although the capacity for autogamy exists in this weedy annual, it rarely occurs because of two factors: (1) the morphology of the flower and (2) the foraging behavior of the various species of Bombus, the primary pollen vector in the regions studied. The percentages of geitonogamy and xenogamy are dependent on the flight pattern of the bees and the number of open flowers on a plant.     

NUTRITIONAL STUDIES OF THE SUBMERGED MARINE ANGIOSPERM THALASSIA TESTUDINUM I. GROWTH RESPONSES OF AXENIC SEEDLINGS TO NITROGEN ENRICHMENT

Algae- and bacteria-free seedling cultures of the seagrass Thalassia testudinwn Banks ex König were utilized to evaluate effects of nutrient enrichment on growth and chemical composition. Seedlings cultured in media based on both synthetic seawater and NH-15 medium amended with inorganic nitrogen (NH₄⁺) and organic nitrogen (glutamine, glutamate, urea and yeast extract) exhibited no growth enhancement relative to controls in the growth parameters measured. General decreases in green leaf areas and leaf widths after one month coupled with relatively high C:N ratios after 3 months in culture suggest utilization and depletion of stored reserves with little or no assimilation of exogenous nutrients. These observations coupled with previous results in non-axenic seedling cultures indicate microbial associations may play a critical role in the nutrient physiology of this species.     

THE POLLINATION ECOLOGY OF DELPHINIUM TRICORNE (RANUNCUL ACEAE)

The pollination ecology of Delphinium tricorne, a spring-ephemeral herb of eastern deciduous forests, was studied at eight sites in the Ohio River basin from West Virginia to southern Illinois. The plant was found to be obligately dependent for its pollination on queen bumblebees (Bombus Latr. spp.) and hummingbirds, to which the flowers are closely adapted in form, color, function, and blooming phenology. Other bees, including Anthophora ursina, Osmia bucephala, Ptilothrix bombiformis, and Xylocopa virginica; Lepidoptera, including Amphion nessus, Danaus plexippus, Epargyreus clams, Erynnis juvenalis, Hemaris thysbe, Papilio glaucus, P. philenor, P. troilus, Poanes zabulon, Vanessa atalanta, and V. cardui; and the beefly Bombylius major foraged for nectar and/or pollen on the flowers without pollinating them. Techniques employed in the study included insect exclosures to test fertility of plants in the absence of pollinators, analysis of floral colors by reflectance spectrophotometry and ultraviolet photography, analysis of pollinator behavior by cinematography and close-range stereophotography, collection and identification of visitors to flowers, and identification of pollen types carried by foragers on the flowers.     

POLLINATION ECOLOGY OF MONARDA DIDYMA,M. CLINOPODIA,AND HYBRIDS (LAMIACEAE) IN THE SOUTHERN APPALACHIAN MOUNTAINS

Monarda didyma L. and M. clinopodia L. occasionally form introgressive populations in the mountains of eastern Tennessee and western North Carolina. Monarda didyma produces large red scentless nectar-rich flowers and is pollinated primarily by the Ruby-throated Hummingbird (Archilochus colubris [Linnaeus]). The smaller, white, scented flowers of Monarda clinopodia produce small amounts of nectar and are pollinated mainly by bumblebees (Bombus spp.). The two species are highly interfertile and have strongly overlapping flowering periods. Differences in pollinator sets and pollinator constancy appear to be only partial barriers to hybridization. Lack of suitable habitats for the establishment of hybrid progeny might be the most important isolating mechanism between the two species.     

SEM COMPARISON OF FRUITS OF A SEAGRASS,HALODULE (CYMODOCEACEAE), FROM AUSTRALIA AND TEXAS

Fruits of Halodule were collected from marine sediments in Shark Bay, Western Australia, and in Laguna Madre, Texas, and compared using scanning electron microscopy. The fruits of the Australian collection had a more deeply furrowed wall surface, and the fruits of the Texas collection had a more prominent stylar beak. The fruits of both collections had walls that were composed of irregularly interlocking cells, each with multilayered, concentric cell walls. The fruit wall separates into nearly equal halves along a cleavage line composed of cells that are not interlocked. The seed coats are composed of flattened cells with annular thickenings and the oblong hypocotyls are composed of large, polygonal cells that contain starch grains. The cotyledon and plumule are folded into a hypocotylary invagination along the line of wall separation. A radicle hump or short radicle develops during germination in seawater. Although the taxonomy of Halodule has been based on a vegetative feature, the leaf tips, fruit differences may be of diagnostic value.     

STUDIES ON THE POLLINATION ECOLOGY OF TIPULARIA DISCOLOR (ORCHIDACEAE)

Tipularia discolor, a woodland orchid, flowers in mid-summer when reproductive activity is minimal within the herb synusia. Tipularia is insect-pollinated, and artificial crosses showed that seeds are produced after self-pollination, intra-inflorescence pollination, and outcrossing. The single nocturnal pollinator, Pseudaletia unipuncta (Noctuidae), located Tipularia populations within a day or two of anthesis. Pollinators were shown to be capable of utilizing portions of the inflorescences that contained the most nectar. After total nectar resources declined, pollinators were no longer active on the inflorescences, even though flowers and nectar were still available. The mode of pollinator activity seems to be closely related to floral morphology, although the moths are able, early in the flowering phenophase, to successfully obtain nectar without effecting any change in the reproductive status of flowers.