Plant Reproductive Biology Research Articles

Influence of Environmental Quality on Pollen Competitive Ability in Wild Radish

Pollen of Raphanus raphanistrum produced under low nutrient conditions sired fewer seeds than pollen produced under better conditions when the two types were applied on a stigma together. No difference was seen in single-donor crosses. Male mating success can be strongly influenced by the environmental conditions of pollen-bearing plants, a factor overlooked in studies of plant reproductive biology and in standard quantitative genetic crossing designs, where effects of male parent are equated with heritable genetic variation.

Studies on Plant Demography, A Festschrift for John L. Harper.

Contributors. Foreword. Preface. Profile of John L. Harper. Scientific Publications of John L. Harper Dynamics and Evolution of Plant Populations in Natural or Seminatural Environments: Past, Present and Future: Studies on the Population Dynamics of Some Long-lived Trees, J. Ogden. Plant Demography: A Community-level Interpretation, J. Sarukhan, D. Pinero and M. Martinez-Ramos. Fires and Emus: The Population Ecology of Some Woody Plants in Arid Australia, J.C. Nobel. Differences in Life Histories between Two Ecotypes of Plantago lanceolata L., J.M. van Groenendael. Variation and Differentiation in Population of Trifolium repens in Permanent Pastures, . Disasters and Catastrophies in Populations of Halimione portulacoides, Ad H.L. Huiskes and A.W. Stienstra. Establishment and Peri-establishment Mortality, R.E.L. Naylor. Population Biology and the Conservation of Rare Species, H.J. Harvey. Biology of Invasive and Weedy Species: Invading Plants: Their Potential Contribution to Population Biology, R.N. Mack. Proso Millet (Panicum miliaceum L.): A Crop and a Weed, P.B. Cavers and M.A. Bough. Population Dynamics of a Few Exotic Weeds in North-east India, R.S. Tripathi. Weeds and Agriculture: A Question of Balance, B.R. Trenbath. The Demographic Interpretation of Plant Form: Application to Plant Competition and Production: On the Astogeny of Six-cornered Clones: An Aspect of Modular Construction, A.D. Bell. The Importance of Plant form as a Determining Factor in Competition and Habitat Exploitation, P.H. Lovell and P.J. Lovell. Modular Demography and Form in Silver Birch, M. Jones. Modular Demography and Growth Patterns of Two Annual Weeds (Chenopodium album L. and Spergula arvenis L.) in Relation to Flowering, L. Maillette. A Modular Approach to Tree Production, M. Franco. Plant Interference: The Effects of Neighbours: Plant Responses to Crowding, A.R. Watkinson. The Thinning Rule and Its Application to Mixtures of Plant Populations, J. White. The Influence of Pathogens and Predators on Plant Populations: Pathogens and the Genetic Structure of Plant Populations, J.J. Burdon. Sex Ratios, Clonal Growth and Herbivory in Rumex acetosella, J.L. Doust and L.L. Doust. The Role of Grazing Animal, R. Dirzo. Plant Reproductive Biology: Islands and Dioecism: Insights from the Reproductive Ecology of Pandanus tectorius in Polynesia, P.A. Cox. The Meaning and Measurement of Reproductive Effort in Plants, F.A. Bazzaz and E.G. Reekie. Index.

EVOLUTION OF THE SEED PLANTS AND INCLUSIVE FITNESS OF PLANT TISSUES.

Here we put forward a new interpretation of the significance of some major features of vascular plant reproductive biology. These features are the integuments of maternal tissue surrounding the offspring, which distinguish seed plants from vascular cryptogams, and the (usually) triploid endosperm produced by double fertilization, which characterizes angiosperms. Maternal integuments and double fertilization are generally regarded as key innovations in plant evolution, and are usually given as the most fundamental characters which distinguish seed plants and angiosperms respectively (Cronquist, 1968; Takhtajan, 1969; Bold, 1973; Foster and Gifford, 1974; Stebbins, 1974; Sporne, 1975; Darlington, 1976). Our interpretation draws together an evolutionary-ecology model on maternal investment, inclusive-fitness calculations from population genetics, and information from comparative plant morphology and embryology. Each of these elements of our interpretation is well-known within the relevant discipline, but the elements have not previously been combined and applied to interpreting plant evolution.1 In this paper we first summarize how mother plants support their offspring in different groups of vascular plants. We show that this support is committed later, with respect to meiosis and fertilization, in more advanced groups of plants. Second, we describe available interpretations, to which our interpretation is an alternative, of the integuments and of double fertilization. Deficiencies of the available interpretations are pointed out, and the points to be explained by our interpretation are defined more exactly. Third, we argue that the advantage achieved by deferring investment in more advanced groups is that mothers can cause a limited total investment to be directed selectively to better offspring genotypes. Fourth, we show that the pattern of investment allocation which maximizes inclusive fitness for the mother is not the same as that which maximizes inclusive fitness for any one offspring. Fifth, we put forward our interpretation, which briefly is that the integuments and endosperm allow the mother to retain control of how her investment is allocated, while deferring the investment until offspring with genotypes different from her own (and therefore with potentially conflicting interests) have been created. Finally, we consider some relatively minor features of comparative plant reproductive biology, which are relevant to assessing our interpretation and other published interpretations.

Factors Determining Fruit Set in Heterostylous Bluets, Houstonia caerulea (Rubiaceae)

Subpopulations of heterostylous Houstonia caerulea consist of both pin and thrum plants (heterogeneous) or of plants of a single morph (homogeneous). Crossing experiments demonstrate that pollination between morphs is essential for maximal fruit set. In heterogeneous subpopulations percent fruit set increases as the ratio of pins to thrums approaches unity. Fruit set also is positively correlated with subpopulation size but shows little relationship with distance to the nearest compatible subpopulation. In homogeneous subpopulations, however, fruit set decreases with increasing subpopulation size, and distance to the nearest compatible subpopulation is more important in determining percent fruit set. Substructuring, therefore, may profoundly affect the reproductive biology of plant populations. Heterostylous plants present population biologists with a unique tool for examining problems concerned with plant reproductive biology and spatial patterns in natural populations. Individuals of such species can easily be segregated morphologically into two genetic incompatibility groups. In Houstonia caerulea members of the long-styled group, commonly known as have anthers attached low in the corolla tube, small pollen grains, and large stigmatic papillae (Rothrock, 1868; Darwin, 1877; Meehan, 1880; Lewis, 1962, 1976; Ornduff, 1977). have short styles, anthers attached high in the corolla tube, large pollen grains, and small stigmatic papillae. Thrums usually represent the Ss heterozygote and pins, the ss homozygote, in terms of the genetics of the incompatibility system (Vuilleumier, 1967; Yeo, 1975). Such a system of enforced outcrossing should maintain an equal ratio of pins to thrums. The comparative ease in working witha visible genetic polymorphism such as heterostyly has allowed researchers to gather much information on disassortative pollination and pollination efficiencies in natural systems (Levin, 1968; Mulcahy & Caporello, 1970; Ornduff, 1970a, 1970b, 1971, 1975a, 1975b, 1976; Ganders, 1974, 1975a, 1975b, 1976; Dulberger, 1975). It also has made possible the demonstration of spatial patterning in plant populations (e.g., Levin, 1974; Ornduff & Weller, 1975). One question which has not been approached in heterostylous plants however, is the identification and quantification of extrinsic factors determining levels of fruit set. In non-heterostylous plant populations such factors as plant spacing (Levin & Kerster, 1968; Levin, 1972), plant density (Levin & Kerster, 1969a, 1969b), inflorescence size and form (Willson & Rathcke, 1974; Willson & Price, 1977; Wyatt, 1978, 1980) and ' Botany, Duke University, Durham, NC 27706; Present address of RW: Botany, University of Georgia, Athens, GA 30602.

Differential Seed Dispersal by Birds of the Tree Casearia nitida (Flacourtiaceae)

Data are presented which demonstrate (1) flight patterns of frugivorous birds are responsible for directional patterns of seed dispersal, (2) these patterns influence seed mortality, and (3) dispersal of seeds away from the parent tree is more likely to result from behaviors characteristic of obligate frugivores (Ramphastos sulfuratus and R. swainsonii) than frugivore/insectivores (Myiozetetes similts and M. granadensis). Investment by the parent tree in a seed carried by a frugivore is less likely to be wasted than investment in a seed carried by an frugivore because specialists are more likely to carry seeds away from areas of high seed mortality than opportunists. PLANTS HAVE A VARIETY OF CHARACTERISTICS which result in dispersal of their seeds by fruiteating animals. These involve the structure of the fruit (van der Pijl 1969) or other aspects of plant reproductive biology (Snow 1965; Smythe 1970; Snow 1971). Previous studies consider the effects of treatment by the digestive tract on the germination of seeds (Darwin 1859; Kerner 1897; Rick and Bowman 1961), the effects of long-distance dispersal on the biogeography of plants (Cruden 1966; Carlquist 1974), effects of dispersal on the survivorship of seeds which suffer high levels of animal predation (janzen 1971), and the expected influence of such predation on the local dispersion of plants (Janzen 1970). The variety and abundance of fruits in the tropics is correlated with a diverse bird fauna showing varying degrees of specialization for frugivory and seed dispersal (Wetmore 1914; Keast 1958; Orians 1969; Karr 1971; Morton 1973). Absent frcm previous studies are quantitative data showing the patterns of seed distribution produced by movements of different kinds of dispersers and the effects of this dispersal on the survivorship of seeds. Such information is particularly desirable in view of McKey's (1975) argument that the dispersal of seeds by specialized birds which are obligate frugivores should be qualitatively different from dispersal by opportunistic birds which facultatively feed on fruit or insects. If this point of view accurately reflects close coevolutionary relationships between obligate frugivores and the plants upon which they feed, we predict that specialists should also produce patterns of seed distribution and resulting seed mortality more beneficial to the plant than those produced by birds with less dependence on fruit. This paper offers a partial test of this prediction and suggests further research which will elucidate relationships between plants and their dispersal

Observations on Seed Dispersal by Bats in a Tropical Humid Region in Veracruz, Mexico

The study of the seeds rejected during a year by a colony of Artibeus jamaicensis Leach in a cave located in Los Tuxttlas Region of Veracruz, Mexico, gave us information concerning the fruit species on which these bats feed, their degree of utilization and bats' preference for some fruits. Information was also obtained on some peculiarities in the reproductive biology of plants, for example, the length of fruiting seasons and the possible role played by bats in the interchange of seeds between primary and secondary growth vegetation in a tropical humid evergreen forest area. FRUGIVOROUS BATS play an important role in the dispersal of several tropical plant species whose

Comparative Phenological Studies of Trees in Tropical Wet and Dry Forests in the Lowlands of Costa Rica

The dearth of plant phenological studies in tropical latitudes has been pointed out by various authors (Gibbs & Leston 1970; McClure 1966; Nevling 1971; Rees 1964). A review and brief evaluation of the few available investigations is presented by Frankie, Baker & Opler (1974). In most of these studies, a partial analysis of leafing, flowering or fruiting data is offered for a limited number of species and for limited time periods only. The results of a comparative phenological investigation of the trees in Wet and Dry forest sites in lowland Costa Rica are reported here. An attempt has been made to provide a unified analysis of the leafing, flowering, and fruiting periodicities of most species at both sites. The Wet forest site, Finca La Selva, is situated in the Atlantic watershed, while the Dry forest site, Comelco Property, is situated in the Pacific watershed. The study, which began in 1968, is part of a larger investigation aimed at analysing the biological organization of Wet and Dry forest ecosystems from the standpoint of plant reproductive biology. In this study the definition of a tree put forward by Lindley & Moore (1884, p. 1161) as 'any woody plant of perennial duration which rises from the ground with a trunk' has been adopted in part. To this we have added a minimum height qualification of approximately 3 m. We were unable to recognize distinct layers within the forest canopy at either site. Stratification, in which three or more tiers are generally designated, has been described by investigators working in various Tropical Rain forests (Beard 1955; Jones 1955; Lundell 1937; Richards 1952; Webb 1959). Other workers have been unable to discern definite layers clearly (Cain & Castro 1959; Grubb et al. 1963; Paijmans 1970; Schulz 1960). However, because trees are subject to different environmental conditions depending upon their position in the canopy and also for ease in recording data, tree species at the Wet forest site were arbitrarily divided into two categories: overstorey and understorey species. The first group consisted of canopy and subcanopy species, with the understorey comprising trees generally less than 15 m in height. Croat (1969) also divided trees at Barro Colorado Island into two layers for similar reasons. No layering effect was observed in the Dry forest and, because of the lesser tree heights, all trees in this forest were considered to belong to a single layer.

Bees as Tools in Studies of Reproductive Biology of Plants

Bees as Tools in Studies of Reproductive Biology of Plants