THE EVOLUTION OF REPRODUCTIVE EFFORT IN LIZARDS AND SNAKES

Life history theory suggests that the optimal evolved level of reproductive effort (RE) for an organism depends upon the degree to which additional current reproductive investment reduces future reproductive output. Future reproduction can be decreased in two ways, through (i) decreases in the organism's survival rate, and/or (ii) decreases in the organism's growth (and hence subsequent fecundity). The latter tradeoff–that is, the “potential fecundity cost”—should affect the evolution of RE only in species with relatively high survival rate, a relatively high rate of fecundity increase with body size, or a relatively high reproductive frequency per annum. Unless these conditions are met, the probable benefit in future fecundity obtained from decreasing present reproductive output is too low for natural selection to favor any reduction in RE below the maximum physiologically possible. Published data on survival rate, reproductive frequency and relative clutch mass (RCM) suggest that many lizard species fall well below the level at which natural selection can be expected to influence RE through such “potential fecundity” tradeoffs. Hence, the relative allocation of resources between growth and reproduction is unlikely to be directly optimized by natural selection in these animals. Instead, energy allocation should influence the evolution of RE only indirectly, via effects on an organism's probability of survival during reproduction. Survival costs of reproduction may be the most important evolutionary determinants of RE in many reptiles, and information on the nature and extent of such costs is needed before valid measures of reptilian RE can be constructed.     

FLORAL BIOLOGY OF MAGNOLIA

The floral biology of eight species of Magnolia native to the United States is described. The flowers are protogynous. They are pollinated by several species of beetles that enter buds as well as closed and open flowers to feed on nectar, stigmas, pollen, and secretions of the petals. Individual flowers persist from two to four days and undergo a series of petal, stigma, and stamen movements that assure pollination by beetles. It is suggested that the flowers of Magnolia are highly specialized for exclusive pollination by beetles. These specialization mechanisms produce large quantities of food for the beetles and deny other types of insects (bees, moths, etc.) access to the flowers at critical stages in the pollination process, i.e., when stigmas are mature and pollen is shed.     

植物实验生殖生物学与生殖细胞工程:现在与未来

植物实验生殖生物学是植物实验胚胎学发展的新阶段,其主要特征为操作技术水平的提高与多学科综合性研究的加强。花粉原生质体、生殖细胞、精子,胚囊、卵细胞的操作、雌雄配子体外融合、配子-体细胞杂交等,代表了当前的主要研究趋势。实验生殖生物学与基因工程相结合,开辟了植物生殖工程新技术领域的前景。对生殖工程的意义与内容提出了轮廓设想。     

FLORAL STRUCTURE AND EVOLUTION IN LOPEZIEAE (ONAGRACEAE)

The Lopezieae present an interesting mixture of ancestral and derived characters: some members of the tribe retain the basic onagraceous chromosome number (n = 11), but the flowers are advanced in that they are mostly zygomorphic and always have a two-merous androecium. Species differ in the position of the nectaries, also in the way in which floral parts are united above the inferior ovary. These differences, when analyzed with information from a new monograph of the Lopezieae, provide the basis for a phylogenetic tree. It is inferred that ancestral Lopezieae were bird-pollinated woody perennials with regular flowers, two fertile stamens, and no floral tube distal to the ovary. Evolutionary events accompanying the emergence of modern taxa included abortion of the abaxial stamen (all surviving Lopezieae except Lopezia lopezioides), development of an epigynous floral tube (L. riesenbachia, L. semeiandra), decrease in floral symmetry without conversion to insect pollination (in two independent lines), and decrease in floral symmetry with conversion to insect pollination (in at least two independent lines). The prominent tubercles on upper petals of certain insect-pollinated species apparently evolved from the less prominent swollen areas still present in some of the bird-pollinated species. The tubercles and an associated snapping mechanism arose in response to increasing selection for fly pollination. Densely staining areas in some specimens may be osmophores; if so, scent plays a supplementary role in the orienting of insects to the upper petals. Interstaminal nectaries and the absence of a floral tube link the Lopezieae to Ludwigia; the relationship of these two taxa to Epilobium is presently unclear. Fossil records indicate that the Onagraceae had evolved by the beginning of the Tertiary Period and that the Ludwigia line is very old. The family's ancestral features are retained to a greater degree in Fuchsia, however, than in Ludwigia.     

北江间(鱼骨)的繁殖生物学

间(鱼骨)(Hemibarbus medius Yue,1995)属鲤形目,鲤科,(鱼句)亚科,(鱼骨)属,为1995年报到的一个新种[1].在此之前,学者一直将其归为唇(鱼骨)[2-5].间(鱼骨)广泛分布于华南及西南部分地区,如珠江、南盘江、乌江和万泉河等水系[6].其肉质鲜嫩、营养价值高、产量较大,一直为产区的重要经济鱼类.     

REPRODUCTIVE BIOLOGY OF ASCLEPIAS EXALTATA

An analysis of the relationships between plant size and survivorship and reproductive success was carried out by sampling four populations of the herbaceous perennial milkweed Asclepias exaltata in Virginia from 1980 to 1982. The annual survivorship rate (about 65%) is the lowest measured for any species of Asclepias. Survivorship was strongly size-dependent but showed no clear relationship with previous history of fruit production. Non-flowering plants were significantly smaller than flowering plants and showed very strong (r > 0.87) correlations between root dry weight and stem or leaf dry weight. Flowering plants were similar to nonflowering plants in root: shoot ratio (approximately 1:1) but differed in that root dry weight was not strongly correlated with stem or leaf dry weight. Components of inflorescence size were strongly correlated within a given level of comparison (e.g., stems per plant with flowers per plant) but less strongly correlated between levels (e.g., stems per plant with flowers per stem). Number of fruits per plant and percentage fruit-set were positively correlated with every component of inflorescence size. Although overall fruit-set was low (about 2%), fruits that were initiated had a high probability of surviving to maturity. There was no evidence of an early period of high fruit abortion: a relatively constant proportion of fruits aborted between each age class.     

THE REPRODUCTIVE BIOLOGY OF RASPBERRIES AND PLANT-POLLINATOR COMMUNITY STRUCTURE

Rubus idaeus and Rubus pubescens are congeners which differ with respect to their life history patterns. Rubus idaeus is locally important in the Northeast in areas subject to windthrow, fire, and man-made disturbances, while R. pubescens often forms a significant portion of the ground cover of shaded, damp, woodland areas. The life history pattern of R. idaeus is based upon the short term build up and slow decay of a large seed bank. Vegetative reproduction is more important in the eventual spread of R. pubescens. The reproductive traits of the two species reflect many of the above mentioned constraints and differences. Rubus pubescens produces relatively small quantities of nectar and flowers during a brief 1–2-wk period late in May. Synchronous flowering probably minimizes the incidence of floral predation and makes the low nectar flowers more attractive by reducing the pollinators' flight time. Rubus idaeus is an abundant species, which offers almost unlimited supplies of nectar during at least part of its extended 3–4-month flowering season. It is attractive to a wide range of pollinators and has figured prominently in the design, phenology, and reward structure of the early successional northern hardwoods plant-pollinator community.     

REPRODUCTIVE BIOLOGY OF TROPICAL LOWLAND RAIN FOREST TREES. II. POLLINATION SYSTEMS

The reproductive biology of tree species of a tropical rain forest was investigated to determine the relative frequency and spatial distribution of different types of pollination mechanisms. Species pollinated by medium-sized to large bees were most frequent, followed by those pollinated by moths, small diverse insects and small bees, in that order. Almost one half the total species were found to have pollinators with wide foraging ranges. Species pollinated by various groups of pollinators were distributed non-randomly. The greatest diversity of pollination systems was found in the subcanopy. As compared to the subcanopy, pollination mechanisms in the canopy were monotonous, consisting primarily of species pollinated by bees and small diverse insects. The hummingbird- and sphingid moth-pollinated species were found mainly in the subcanopy. The factors underlying the non-random distribution of pollinators are discussed and the potential implications of such distribution on the forest structure are explored.     

PATTERNS OF FLORAL DEVELOPMENT IN AGALINIS AND ALLIES (SCROPHULARIACEAE). II. FLORAL DEVELOPMENT OF AGALINIS DENSIFLORA

Initiation of floral primordia begins in Agalinis densiflora with production of two lateral adaxial calyx lobe primordia followed by a midadaxial primordium, and then primordia of two abaxial calyx lobes. Initiation of three abaxial corolla lobe primordia is succeeded by that of two stamen pairs and then by primordia of two adaxial corolla lobes. The primordium of the abaxial carpel appears before the adaxial one. Except for the calyx, initiation of primordia proceeds unidirectionally from the abaxial to the adaxial side of the floral apex. Zygomorphy in the calyx, corolla, and androecium is evident during initiation of primordia and is accentuated during organogenesis. The calyx undergoes comparatively rapid organogenesis, but the inner three floral series undergo a protracted period of organogenesis. The perianth series reach maturation prior to meiosis in the anthers. Maturation of the androecium and gynoecium are postmeiotic events.     

FLORAL BIOLOGY OF NEPENTHES GRACILIS (NEPENTHACEAE) IN SUMATRA

Nepenthes gracilis, a dioecious carnivorous plant, has inconspicuous flowers lacking petals. Nectaries distributed on the upper surface of four sepals secrete dilute nectar (3%–12% sugar concentration) at night, but the nectar immediately disappears during the day by evaporation in the sunny environment of Sumatra. Male flowers have a higher nectar production rate but lower sugar concentration of nectar than female flowers. Flowers of both sexes were visited by pyralid moths at night and by calliphorid flies in the evening. Pollen was found attached on these insects visiting Nepenthes flowers. The pattern of nectar production of sepals is regarded as attracting nocturnal flying insects and avoiding ants, while the pitchers attract ants by nectar secreted on the pitcher rim.     

FLORAL BIOLOGY AND REGULATION OF SEED SET AND SEED SIZE IN THE LILY,CLINTONIA BOREALIS

We studied the reproductive ecology of Clintonia borealis, a clonal understory species, in eastern Ontario. Flowers are protogynous and require insect pollination for outcrossing and maximum seed set. Most pollination is done by nectar-gathering bumble bees. We recorded pollen deposition and flowering patterns in 1983. Flowering lasted for about 10 days in mid-June. Stigmatic pollen loads were lowest at the onset of blooming, reflecting the scarcity of male-phase flowers. Pollination increased significantly by peak bloom and subsequently remained high. However, since bees fly mostly between neighboring stems, much of the pollen transferred may have been geitonogamous. In 1983, seed set per flower was not increased by supplementing pollination or by reducing the number of fruits competing for resources per stem. Rather, flowers set more seeds (14%) only if both treatments were performed simultaneously. Seed size was increased by 25% when competitive fruits were removed and by 5% more when pollen was added under the removal treatment. Further work in 1984 showed that pollination effects may be related to changes in pollen source. Selfed flowers set fewer and smaller seeds than outcrossed ones when screened from insects and hand pollinated. Outcrossing distance had little effect on seed set or seed size. Thus, in C. borealis seed number and seed size are limited by a balance between maternal resource availability and the amount of outcrossing provided by pollinators.     

EXPERIMENTAL PLANT REPRODUCTIVE BIOLOGY AND REPRODUCTIVE CELL MANIPULATION IN HIGHER PLANTS: NOW AND THE FUTURE

Experimental plant reproductive biology has recently emerged as a new form of experimental embryology characterized by the direct experimental isolation and manipulation of reproductive cells and protoplasts. This work is fostered by current multidisciplinary trends in the sciences and serves to deepen our knowledge about the control of reproductive processes by providing novel in vitro material. The techniques of experimental plant reproductive biology also show great potential in providing new means for biotechnology, leading to significant refinements in plant breeding in higher plants that may eventually permit direct reproductive cell engineering. Recent achievements by our research group in experimental manipulation and biological studies of pollen protoplasts, generative cells, sperm cells, and embryo sacs are reviewed, and some ideas about future developments in this new area are presented.     

THE FLORAL BIOLOGY OF CASSIA DIDYMOBOTRYA AND C. AURICULATA (CAESALPINIACEAE)

The flowers of Cassia didymobotrya and C. auriculata have three types of fertile anthers that differ in orientation, size, shape, and pollen production. Flowers with right-handed or left-handed style deflections, i.e., enantiostylous flowers, occur in the same raceme. In Israel, both species are pollinated by pollen collecting buzzing females of Xylocopa pubescens. Vibrations of the carpenter bee are necessary for release of pollen from poricidal anthers and, in C. didymobotrya, also for absorption of pollen through the stigmatic opening into a cavity of the style tip. The largest anthers supply pollen for pollination. Pollen for consumption by the bee, on the other hand, appears to be supplied by all fertile anthers. This is in contrast to the accepted view of a complete separation of functions in the heteromorphic anthers in Cassia. The pollen/ovule ratio in C. didymobotrya was 55,200, and that in C. auriculata 32,000. Only 0.01% of the pollen produced by a flower was found in the stigmatic pollen load, and this fraction allows for high seed sets. From a comparison of the pollen production and utilization in the Cassia species and in certain distylous plants, it is concluded that heteranthery in Cassia does not confer an advantage in pollen economy. The high pollen/ovule ratios are explained by lack of nectar as well as by the large area on which pollen is deposited on the bee's body relative to the small size of the stigma. Enantiostyly in Cassia is considered as part of a pollination syndrome whose characteristics are outlined. The function of enantiostyly as an outbreeding strategy is discussed. In the two Cassia species, opportunities for self- and geitonogamous pollinations and self-compatibility minimize an effect of enantiostyly in promotion of outcrossing. Instead, it is proposed that style deflections may clear access of the pollinator to the anthers and protect female parts from injury by a vibrating heavy-bodied visitor.