Primary Mode Of Reproduction Research Articles

PALEOECOLOGIC AND TAXONOMIC IMPLICATIONS OFSPHENOTHALLUSANDSPHENOTHALLUS-LIKE SPECIMENS FROM OHIO AND AREAS ADJACENT TO OHIO

Sphenothallus and fossils similar to Sphenothallus are found in Ordovician, Devonian, and Mississippian rock units in Ohio and adjacent states and provinces. Although the Ordovician of Québec, Ontario, and Indiana has yielded parts of tubes, Ordovician specimens from southwest Ohio and nearby areas consist almost entirely of holdfasts on hardgrounds and shelly fossils. Sphenothallus is abundant in the Chagrin Shale (Famennian) of northeast Ohio where it is found in about four percent of concretions that contain identifiable fossils. The Chagrin specimens, usually parts of tubes, are occasionally preserved three-dimensionally. The rate of distal expansion of Chagrin Sphenothallus tubes varies intraspecifically; thus, this rate cannot be used to distinguish species. Some Chagrin specimens are attached to larger, conspecific specimens and to articulate brachiopods. Brachiopods have also been found attached to Chagrin Sphenothallus. Bedford-Berea sequence (Famennian) specimens from northern Kentucky and Meadville Member (Kinderhookian or Osagian) specimens from the Cuyahoga Formation of northeast Ohio are usually preserved as flattened tubes. In both occurrences tubes are similar in width, indicating that individuals in each assemblage are probably the same age. Meadville tubes possess characteristics diagnostic of Sphenothallus, but Bedford-Berea specimens, which lack longitudinal thickenings and exhibit little tube tapering, cannot be assigned to Sphenothallus sensu strictu.Sphenothallus was a gregarious, opportunistic species, tolerant of dysaerobic conditions and able to colonize environments ranging from hardgrounds to soft, muddy sea bottoms. No distinct branching was observed among the Chagrin, Bedford-Berea, or Meadville specimens, suggesting that larval dispersal was the primary mode of reproduction for the genus.

Paleoecologic and taxonomic implications of Sphenothallus and Sphenothallus-like specimens from Ohio and areas adjacent to Ohio

Sphenothallus and fossils similar to Sphenothallus are found in Ordovician, Devonian, and Mississippian rock units in Ohio and adjacent states and provinces. Although the Ordovician of Québec, Ontario, and Indiana has yielded parts of tubes, Ordovician specimens from southwest Ohio and nearby areas consist almost entirely of holdfasts on hardgrounds and shelly fossils. Sphenothallus is abundant in the Chagrin Shale (Famennian) of northeast Ohio where it is found in about four percent of concretions that contain identifiable fossils. The Chagrin specimens, usually parts of tubes, are occasionally preserved three-dimensionally. The rate of distal expansion of Chagrin Sphenothallus tubes varies intraspecifically; thus, this rate cannot be used to distinguish species. Some Chagrin specimens are attached to larger, conspecific specimens and to articulate brachiopods. Brachiopods have also been found attached to Chagrin Sphenothallus. Bedford-Berea sequence (Famennian) specimens from northern Kentucky and Meadville Member (Kinderhookian or Osagian) specimens from the Cuyahoga Formation of northeast Ohio are usually preserved as flattened tubes. In both occurrences tubes are similar in width, indicating that individuals in each assemblage are probably the same age. Meadville tubes possess characteristics diagnostic of Sphenothallus, but Bedford-Berea specimens, which lack longitudinal thickenings and exhibit little tube tapering, cannot be assigned to Sphenothallus sensu strictu.Sphenothallus was a gregarious, opportunistic species, tolerant of dysaerobic conditions and able to colonize environments ranging from hardgrounds to soft, muddy sea bottoms. No distinct branching was observed among the Chagrin, Bedford-Berea, or Meadville specimens, suggesting that larval dispersal was the primary mode of reproduction for the genus.

Population dynamics of an association between a coral reef sponge and a red macroalga

Sponges are often as abundant as corals on tropical coral reefs and many species are symbiotic with algae. These associations may contribute significantly to reef primary productivity. This paper describes the first study ever made of the population biology of any of the known associations between sponges and macroalgae. Populations of the symbiotic association between the sponge, Haliclona cymiformis (Esper), and the red macroalga, Ceratodictyon spongiosum Zanardini, were studied in One Tree Lagoon, southern Great Barrier Reef. The association primarily occurs in areas where the substratum consists of dead coral rubble (rubble banks), at the edge of the lagoon, where it can reach a biomass of up to 270 g wet weight m−2. Fragmentation is the primary mode of reproduction of the Haliclona/Ceratodictyon association at One Tree Reef. Although algal sporangia were frequently encountered during the summer, sperm cysts were infrequently found in the sponge, and oocytes and larvae were never observed. The size-frequency distribution of the clumps at the rubble bank sites was strongly skewed toward small individuals (longest branch length generally ≤80 mm). Haliclona/Ceratodictyon was also abundant at one site in the centre of the lagoon; at this site, which was not affected by strong currents or wave energy, the size-frequency distribution of the association was normal. Populations of the association at the rubble bank sites are very mobile, with intact clumps moved more than 30 cm per day under calm conditions and up to 1 m per day during rough weather. Survivorship of fragments or mobile clumps of the association is very high. At one site, the biomass of the association was not affected by two cyclones and at least one severe storm. At another site, up to 50% of the biomass of the population was lost following each of these storms, but the recovery of the biomass was largely complete within 9 months. The Haliclona/Ceratodictyon association has a rapid growth rate, of 8 mg (g wet weight)−1 day−1, which exceeds that of many other coral reef sponges, but it is within the range of growth rates reported for other species of marine macroalgae.

Population Structure and Growth Patterns of Opuntia echios var. gigantea along an Elevational Gradient in the Galápagos Islands1

Abstract Cacti growing in forests potentially experience growth limitation due to reduced light availability. To test this hypothesis, we studied the population structure of Opuntia echios var. gigantea at 15 sites on the south side of Isla Santa Cruz, Galapagos Islands, Ecuador. Populations were located in communities ranging from arid scrub at low elevations to closed-canopy tropical dry forest at higher elevations. Ordination confirmed the existence of a strong elevation–vegetation gradient. Opuntia abundance peaked at lower elevations (<ca 30 m), with lower densities in closed-canopy sites. For populations in scrub vegetation, density declined fairly regularly with plant height. Populations in forested sites had few plants of intermediate height, suggesting periodic recruitment. Scrub populations had random dispersion, while those in forests were aggregated. The change in spatial pattern may be related to a change in primary reproductive mode from asexual propagation via fallen fruits to propagation v...

Sperm competition in the absence of fertilization in Caenorhabditis elegans.

Hermaphrodite self-fertilization is the primary mode of reproduction in the nematode Caenorhabditis elegans. However, when a hermaphrodite is crossed with a male, nearly all of the oocytes are fertilized by male-derived sperm. This sperm precedence during reproduction is due to the competitive superiority of male-derived sperm and results in a functional suppression of hermaphrodite self-fertility. In this study, mutant males that inseminate fertilization-defective sperm were used to reveal that sperm competition within a hermaphrodite does not require successful fertilization. However, sperm competition does require normal sperm motility. Additionally, sperm competition is not an absolute process because oocytes not fertilized by male-derived sperm can sometimes be fertilized by hermaphrodite-derived sperm. These results indicate that outcrossed progeny result from a wild-type cross because male-derived sperm are competitively superior and hermaphrodite-derived sperm become unavailable to oocytes. The sperm competition assays described in this study will be useful in further classifying the large number of currently identified mutations that alter sperm function and development in C. elegans.

Pollination dynamics of arctic dwarf birch (Betula glandulosa; Betulaceae) and its role in the loss of seed production

At the northern limit of its distribution, arctic dwarf birch, Betula glandulosa, shows nearly complete absence of sexual reproduction (i.e., &lt;;0.5% viable samaras) and maintains its populations vegetatively. To investigate the possible role of pollination dynamics in the loss of sexual reproduction, pollination biology of arctic dwarf birch was compared at two locations: Tarr Inlet on Baffin Island, Northwest Territories near the northern limit of the species, and Kuujjuaq, Quebec in the center of its distribution where sexual reproduction is the primary mode of reproduction. Relative production of staminate and pistillate flowers, pollen rain, pollen viability, and stigmatic pollen loads throughout pollen dispersal were compared. Plants at Tarr Inlet produced 15%–30% of pollen produced at Kuujjuaq, both as a result of a lower density of staminate catkins and less pollen per catkin. Potential seed productivity is limited at the northern limit because pistillate catkins produce 50% fewer flowers in the north than in the south. While stigmatic pollen loads were similar at both sites, lower pollen viability (68% vs. 93%) and a higher probability of geitonogamous pollen due to clonal growth pattern reduced fertilization success at the northern site. These data suggest that lack of sexual reproduction in B. glandulosa at its northern limit is in part due to pollen limitation.

Pollination Dynamics of Arctic Dwarf Birch (Betula glandulosa; Betulaceae) and Its Role in the Loss of Seed Production

At the northern limit of its distribution, arctic dwarf birch, Betula glandulosa, shows nearly complete absence of sexual reproduction (i.e., <;0.5% viable samaras) and maintains its populations vegetatively. To investigate the possible role of pollination dynamics in the loss of sexual reproduction, pollination biology of arctic dwarf birch was compared at two locations: Tarr Inlet on Baffin Island, Northwest Territories near the northern limit of the species, and Kuujjuaq, Quebec in the center of its distribution where sexual reproduction is the primary mode of reproduction. Relative production of staminate and pistillate flowers, pollen rain, pollen viability, and stigmatic pollen loads throughout pollen dispersal were compared. Plants at Tarr Inlet produced 15%–30% of pollen produced at Kuujjuaq, both as a result of a lower density of staminate catkins and less pollen per catkin. Potential seed productivity is limited at the northern limit because pistillate catkins produce 50% fewer flowers in the north than in the south. While stigmatic pollen loads were similar at both sites, lower pollen viability (68% vs. 93%) and a higher probability of geitonogamous pollen due to clonal growth pattern reduced fertilization success at the northern site. These data suggest that lack of sexual reproduction in B. glandulosa at its northern limit is in part due to pollen limitation.

Isozyme Variability and Breeding Systems in Populations of Yellow Nutsedge (Cyperus esculentus)

The importance of seeds in the reproduction and maintenance of yellow nutsedge (Cyperus esculentusL. # CYPES) populations was evaluated. Isozyme analysis using starch gel electrophoresis was performed on 20 individuals of each of 10 widely separate populations in California. Genetic variation among individuals served as an indicator of the relative importance of asexual and sexual reproduction in each population. Eight enzyme systems were assayed from which 12 loci were resolvable, with four of those loci exhibiting variability. A maximum of four isozyme genotypes appeared in any population; only nine of 81 total potential genotypes were identified. Five populations were isozymically uniform, apparently composed of a single genotype. The remaining five populations were genotypically variable; these frequently deviated strongly from the genotype frequencies expected of a sexually reproducing population. These results indicate that sexually produced seeds are unimportant in the maintenance of yellow nutsedge populations in agricultural environments. Although viable seed may be produced, tubers appear to be the primary mode of reproduction in this species.

Reproduction and morphogenesis of Rickettsiella chironomi, an unusual intracellular procaryotic parasite of midge larvae.

The reproduction and morphogenesis of Rickettsiella chironomi, an unusual procaryotic parasite of midge larvae, was studied with electron microscopy. The morphogenic cycle was similar to that found in chlamydia and consisted of four major cell types: (i) medium-sized spherical initial bodies (ca. 1 micrometers in diameter), (ii) large spherical initial bodies (1.5-2 micrometers), (iii) spherical intermediate bodies (600 to 700 nm), and (iv) disk-shaped elementary bodies (60 X 600 nm). The primary mode of reproduction involved binary fission of initial bodies to form other initial bodies or intermediate bodies. Each intermediate body condensed, forming an elementary body. The morphogenesis of R. chironomi is compared with that of several other organisms to which it is possibly related, including vertebrate chlamydia and invertebrate pathogens of the genera Rickettsiella and Porochlamydia, and its taxonomic position in regard to these is discussed. Additionally, a brief description of the pathology caused by the development of R. chironomi in larvae of Chironomus decorus and Chironomus frommeri is given.

Pollination of Cnidoscolus texanus (Euphorbiaceae) in South-Central Oklahoma

The pollination phase in the reproduction of the monoecious Cnidoscolus texanus is primarily nocturnal: pollen and nectar production, peak fragrance emission, and most intense insect visitation to the blossoms all commence with dusk and conclude at dawn. The two principal visitors, the night foraging hawkmoths Hyles lineata and Manduca quinquemaculata, visit both the carpellate and staminate flowers for nectar and carry copious quantities of pollen on their proboscises. Although the plant species is self-compatible, the pattern of flowering for each plant essentially precludes self-fertilization. Therefore the primary mode of reproduction in Cnidoscolus is sphingophilous outcrossing. Bull nettle, Cnidoscolus texanus (Muel. Arg.) Small, is a common plant of sandy wastelands in south-central USA and north-central Mexico. Its floral biology was investigated for three populations of abandoned fields near The University of Oklahoma Biological Station, 2 mi E of Willis, Marshall County, Oklahoma over the summer of 1972. Cnidoscolus texanus, is monoecious with the flowers borne in numerous, terminal cymes. Each cyme includes one, very rarely zero or three, carpellate flowers subtended by 6-12, typically 9, staminate ones. The perianth is 5-lobed and corollalike, and in the staminate flowers, united to form a trumpet blossom (Faegri and van der Pijl 1971) with a tube 14-20 mm deep and a limb of five free lobes 10-16 mm long. The 10 stamens typically are arranged in two numerically equal but morphologically dissimilar and distinct series. The filaments of the inner whorl are basally coalescent and their anthers extend only to the mid-level of the perianth tube. Stamens of the outer whorl are free with the anthers slightly exserted. Occasional plants differ with respect to the numerical distribution of anthers between the series; a few are monadelphous; and finally in some, the central anthers are exserted and the outer series shorter.