THE MOTION OF WINDBORNE POLLEN GRAINS AROUND CONIFER OVULATE CONES: IMPLICATIONS ON WIND POLLINATION

Comparisons are presented between the three-dimensional airflow patterns created around and by a scale model of a conifer ovulate cone and the trajectories of windborne pollen grains around Picea, Larix, and Pinus ovulate cones. Three general components of the airflow pattern around an ovulate cone model are 1) doldrum-like eddies, rotating over the adaxial surfaces of cone scales and directed toward attached ovules, 2) airflow spiralling around the cone axis along cone scale orthostichies and parastichies, and 3) a complex pattern of vortices (“umbilicus”) directed toward the leeward surface of the ovulate cone. The observed trajectories of pollen grains around cones of Picea, Larix, and Pinus conform to two of these three airflow components: 1) pollen grains are seen to roll along cone scales toward the distal scale margin and to become reentrained in airflow directed backward toward attached ovules, and 2) pollen grains passing around the cone are deflected into the “umbilicus” airflow pattern, where they either settle on or impact with cone scales (approach trajectories), or where they approach the leeward cone surface but are deflected away by airflow passing under the cone (Z-shaped trajectories). Vectoral analyses of pollen grain motion reveal a complex pattern of trajectories influenced by boundary layer conditions defined by ovulate cone geometry and ambient airflow speed. Wind tunnel studies of ovulate cones subtended by leaves and stem indicate that leaves circumscribing the cone act as a snowfence, deflecting windborne pollen toward the cone. Vectoral analyses of airflow patterns and pollen grain trajectories close to ovulate cones indicate that wind pollination in conifers is a non-stochastic aerodynamic process influenced by cone-leaf morphology and the behavior of pollen grains as windborne particles.     

POLLINATION AND SEED SET IN DIERVILLA LONICERA (CAPRIFOLIACEAE): TEMPORAL PATTERNS OF FLOWER AND OVULE DEPLOYMENT

Ovule development in Diervilla lonicera (Caprifoliaceae) is limited by insufficient pollination early in the blooming period and during extensive rainy periods. Production of flowers is skewed in time; an initial burst of flowering is followed by a long period of sparse flower production. Ovule number per flower increases through the blooming period. I discuss the interactions of fruit and seed set, ovule number, and bumble bee pollinator visitation patterns. When certain flowers have a higher a priori probability of successful pollination, it may be advantageous for plants to put more ovules in those flowers. Selective ovule deployment may be a general adaptive phenomenon that has received little attention.     

POLLEN CAPTURE AND WIND-INDUCED MOVEMENT OF COMPACT AND DIFFUSE GRASS PANICLES: IMPLICATIONS FOR POLLINATION EFFICIENCY

The motion induced by wind of Setaria geniculate (Lam.) Beauv. and Agrostis hiemalis (Walt.) B.S.P. panicles is shown to have harmonic characteristics that can influence pollination. During each cycle of its motion, the panicle of S. geniculata repeats a sequence of reorientations to the direction of ambient airflow. This repetition is correlated with a reiteration of airflow patterns through which airborne pollen grains must pass to reach floral surfaces. The panicle decelerates as it moves toward either of the two extreme positions of its oscillatory motion. The decelerations introduce a bias in the time the panicle spends in each of its orientations. This bias generates “preferred orientations” to the direction of ambient airflow which in turn results in biasing the aerodynamics of pollen capture. Similar phenomena are reported for the panicle of A. hiemalis, although a more complex pattern of oscillatory motion is observed. The reciprocity between the mechanics of oscillatory motion and the aerodynamics of pollen capture is shown to have deterministic properties which may surface above the “noise” produced by other, stochastic features influencing wind pollination.     

FLOWER,FRUIT AND SEED ABORTION IN TROPICAL FOREST TREES: IMPLICATIONS FOR THE EVOLUTION OF PATERNAL AND MATERNAL REPRODUCTIVE PATTERNS

Flower, fruit and immature seed abortion was studied in seven self-incompatible species of trees in a tropical lowland semideciduous forest. The species showed considerable variability in fruit and seed set and the rate at which flowers and fruits were aborted. The amount of flower and fruit abortion also varied over time within species. Small samples of open-pollinated flowers in three species showed adequate amounts of pollen on the stigma, but it could not be determined whether the pollen was compatible or incompatible. In a species with multiseeded fruits, the aborted fruits contained significantly fewer seeds than those retained on the plant. Position of fruit within the inflorescence and of seed within the ovary also had a marked effect on abortion: fruits and seeds at certain positions had a higher probability of abortion than those at other positions. Experiments to test the effect of pollen source on abortion were inconclusive. The factors underlying abortions were evaluated in the context of three mutually non-exclusive hypotheses. It is concluded that selection for increased pollen dispersal and uncertainty in paternity of the zygotes are major factors underlying abortions.     

POLLINATION AND SEED PRODUCTION IN IPOMOPSIS AGGREGATA: DIFFERENCES AMONG AND WITHIN FLOWER COLOR MORPHS

The pollination of red, pink, and white color morphs of Ipomopsis aggregata was evaluated to assess whether ethological isolation based on pollinator color discrimination may occur. We observed animal visitors, assessed pollen delivery, seed set per fruit, percentage of flowers setting fruit, nectar production, and timing of flower opening for different color morphs in the Front Range of Colorado. Based on traditional zoophilous flower classifications, we expected hummingbirds to pollinate red-flowered I. aggregata subsp. collina and hawkmoths to pollinate white-flowered I. aggregata subsp. Candida. However, ethological isolation does not appear to occur among color morphs of I. aggregata in the Front Range. Hummingbirds visited red-flowered plants in excess overall, and, to a lesser extent, so did hawkmoths. Both hummingbirds and hawkmoths visited all color morphs and probably transferred pollen among them. Pollen delivery data and a day-night bagging experiment also suggest that pollinators do not necessarily behave as predicted by flower classifications. In addition, there is little evidence for major differences between red, white, and pink flowers in any aspects of reproductive biology. Indeed, most variation occurs within a given color morph.     

PARENTAL EFFECTS ON SEED DEVELOPMENT AND SEED YIELD IN RAPHANUS RAPHANISTRUM: IMPLICATIONS FOR NATURAL AND SEXUAL SELECTION

The possibility that sexual selection operates in angiosperms to effect evolutionary change in polygenic traits affecting male reproductive success requires that there is additive genetic variance for these traits. I applied a half-sib breeding design to individuals of the annual, hermaphroditic angiosperm, wild radish (Raphanus raphanistrum: Brassicaceae), to estimate paternal genetic effects on, or, when possible, the narrow-sense heritability of several quantitative traits influencing male reproductive success. In spite of significant differences among pollen donors with respect to in vitro pollen tube growth rates, I detected no significant additive genetic variance in male performance with respect to the proportion of ovules fertilized, early ovule growth, the number of seeds per fruit, or mean individual seed weight per fruit. In all cases, differences among maternal plants in these traits far exceeded differences among pollen donors. Abortion rates of pollinated flowers and fertilized ovules also differed more among individuals as maternal plants than as pollen donors, suggesting strong maternal control over these processes. Significant maternal phenotypic effects in the absence of paternal genetic or phenotypic effects on reproductive traits may be due to maternal environmental effects, to non-nuclear or non-additive maternal genetic effects, or to additive genetic variance in maternal control over offspring development, independent of offspring genotype. While I could not distinguish among these alternatives, it is clear that, in wild radish, the opportunity for natural or sexual selection to effect change in seed weight or seed number per fruit appears to be greater through differences in female performance than through differences in male performance.     

FREQUENCY-DEPENDENT SEED PRODUCTION AND HYBRIDIZATION RATES: IMPLICATIONS FOR GENE FLOW BETWEEN LOCALLY ADAPTED PLANT POPULATIONS

Gene flow between genetically distinct plant populations can have significant evolutionary consequences. It can increase genetic diversity, create novel gene combinations, and transfer adaptations from one population to another. This study addresses the roles of frequency-dependent selection and mating system in gene exchange between two subspecies of Gilia capitata (Polemoniaceae). Long-distance migrants are likely to be rare in new habitats, and the importance of immigrant frequency to fitness, gene exchange, and ultimately introgression, has not been explored. To test for the importance of frequency in migration, a field experiment was conducted in which artificial populations (arrays) composed of different mixtures of the two subspecies were placed in the home habitats of both. Female function (seed production) and a portion of male function (hybridization rate) were compared for the two subspecies to assess the potential for gene exchange and introgression between them. Individual fitness (through both hybridization and seed production) for the inland subspecies varied with its frequency as an immigrant at the coastal site. Rare immigrants produced fewer seeds and fathered fewer hybrid offspring. In contrast, both forms of reproductive function were frequency independent for the coastal subspecies when it was an immigrant at the inland site. Seed production was high and insensitive to frequency, and immigrants from the coast never successfully fertilized the inland subspecies' seeds. To control for the effects of frequency-dependent pollinator behavior in the field, hand crosses were performed in the greenhouse using a range of pollen mixtures. The greenhouse experiment demonstrated that cross-fertilization is possible in only one direction, that cross-pollination in the other direction is only partially successful, and that pollen from the coastal subspecies has a strong negative effect on seed production by the inland subspecies. Experimental pollen supplementation in the field verified both the unilateral incompatibility and the negative effect of coastal pollen on inland plant seed production observed in the greenhouse. Contrasts between field array and greenhouse results suggest that pollinator behavior and other ecological factors act to exaggerate reproductive barriers between the two subspecies. In this system, immigrant frequency interacts with reproductive biology and pollinator ecology to enhance gene flow between the populations in one direction, while restricting gene establishment and introgression in the other direction.     

MEASUREMENTS OF SELECTION IN A HERMAPHRODITIC PLANT: VARIATION IN MALE AND FEMALE POLLINATION SUCCESS

I measured phenotypic selection of floral traits through both male and female functions of the hermaphroditic flowers of Ipomopsis aggregata (Pursh) V. Grant subsp. aggregata (Polemoniaceae). Fluorescent powdered dyes were used to track movement of pollen by hummingbirds and to measure pollen delivery to individual plants as well as pollen receipt. A phenotypic selection analysis revealed that selection due to male-male competition during pollination was capable of delaying flowering date and widening corolla tubes by 0.22 and 0.24 standard-deviation units, respectively, in a single generation. Several floral traits were highly correlated with each other. Multivariate selection analysis suggested that selection through male function directly favored late flowering as well as a sexual expression characterized by a short pistillate phase and long corollas. Selection intensities through male and female functions were of similar overall magnitude during the pollination stage of the life cycle, but different traits were favored, and selection sometimes acted in opposing directions. In 1985, selection through female function favored increased time spent in the pistillate phase and exserted stigmas (unlike selection through male function). As a result, individual plants varied greatly in functional gender. Plants that had exserted stigmas and narrow corollas and that spent a disproportionately long time in the pistillate phase achieved greater pollination success as females, while plants with the opposite traits achieved greater success as males. Moreover, female pollination success tended to increase, and male pollination success to decrease, with time spent in the pistillate phase, supporting a critical assumption of sex-allocation theory. Selection in the populations studied fluctuated from year to year and was highly sex-specific.     

REPRODUCTION IN POLEMONIUM: PATTERNS AND IMPLICATIONS OF FLORAL NECTAR PRODUCTION AND STANDING CROPS

Patterns of floral nectar production and standing crop were measured in four populations of the herbaceous perennial plant species Polemonium foliosissimum. Contrary to prediction (Pleasants, 1983), individual flowers in this mass-flowering species were found to produce equivalent nectar volumes every day of their lives. Alternative methods of increasing the reward variability presented to pollinators are evaluated for P. foliosissimum and the relationship between that variability and risk-aversive foraging by pollinators is discussed. Significant spatial and temporal variability in rate of nectar production was found. Populations separated by approximately 200 m exhibited different rates. Nectar production declined significantly as a function of time of the flowering season in two populations but not in a third. In spite of such variability, individual plants showed consistency in production both within a single blooming season and across successive seasons. Because of the variability found in the present study, care should be taken to design appropriate sampling protocols in future nectar studies. Patterns of standing nectar crop were consistent with those expected if pollinators were using an area-restricted searching pattern.     

CUTANEOUS GAS EXCHANGE IN VERTEBRATES: DESIGN, PATTERNS, CONTROL AND IMPLICATIONS

1. The exchange of oxygen and carbon dioxide between skin and environment is commonplace in the vertebrates. In many lower vertebrates, the skin is the major or even sole avenue for respiration.
2. As implied by the physical laws governing diffusion of gases, the skin diffusion coefficient, surface area, gas diffusion distance and transcutaneous gas partial pressures may independently or jointly affect cutaneous respiration. In vertebrates, each of these variables has undergone modification that may be related to dependence upon cutaneous gas exchange.
3. Both theoretical models and experimental data suggest that cutaneous gas exchange is limited by the rate of diffusion. However, changes in convection of the respiratory medium and of blood may partially compensate for diffusion limitation, and potentially function in the regulation of cutaneous gas exchange.
4. Typically, the skin is one of several gas exchangers, although many salamanders and some species in other vertebrate groups breathe solely through the skin. The cutaneous contribution to overall gas exchange is often most important in small animals, at cool temperatures, at low levels of activity and in normoxic and normocapnic conditions. Branchial and pulmonary respiration increasingly predominate in other circumstances.
5. Often, the skin figures more prominently in CO₂, excretion than in O₂, uptake.
6. Cutaneous gas exchange emerges in vertebrates as a process perhaps less effective and more constrained than branchial or pulmonary exchange but also less energetically costly. Its utility is indicated by its wide and successful exploitation in vertebrates occupying a diverse array of habitats.     

SEED PRODUCTION AND DISPERSAL IN DALECHAMPIA (EUPHORBIACEAE): DIVERGENT PATTERNS AND ECOLOGICAL CONSEQUENCES

Patterns of capsule development and methods of seed dispersal are described and compared for 16 neotropical species of Dalechampia. In 15 species all the capsules in a single inflorescence develop simultaneously. In one species, D. spathulata, the capsules develop sequentially. I suggest that the difference between D. spathulata and the other species is the result of the fact that D. spathulata occurs in a low-light, rainforest environment, whereas the other species grow in high-light environments. Sequential development of capsules appears to reduce the loss of seeds to seed predators in species that occur in light-limited environments. The seeds of all 16 species of Dalechampia are dispersed by explosive dehiscence of the capsules. Within the genus there are several different adaptations that increase the average dispersal distance for the seed crop.     

PATTERNS AND PROCESSES OF DIVERSIFICATION: SPECIATION AND HISTORICAL CONGRUENCE IN SOME NEOTROPICAL BIRDS

This paper documents congruence in geographical patterns of speciation for four clades of birds having taxa endemic to the same areas within the Neotropics. Two genera, Pionopsitta parrots and Selenidera toucans, corroborate a well known biogeographic disjunction in which taxa endemic to southern Central America and the Chocó region of northwestern South America are the sister-group to a radiation within the Amazon basin. These two genera, along with two lineages within the toucan genus Pteroglossus, also document a pattern of historical interrelationships for four well known areas of endemism within Amazonia: Guyanan + (Belém-Pará + (Inambari + Napo)). These generalized historical patterns are interpreted to have arisen via fragmentation (vicariance) of a widespread ancestral biota. A review of the paleogeographic evidence suggests that these vicariance events could have originated as a result of several different mechanisms operating at various times during the Cenozoic. The inference that diversification of the Neotropical biota is primarily the result of the most recent of these possible vicariance events, namely isolation within Quaternary forest refugia, is unwarranted, given present data. These patterns of historical congruence are also interpreted as direct evidence against the hypothesis that diversification of the forest biota was a consequence of parapatric differentiation along recently established ecological gradients.     

POLLINATION AND FRUIT-SET IN ASCLEPIAS: A REAPPRAISAL

Experimental pollinations of Asclepias tuberosa L., the first for this species and second large-scale effort for the genus, reveal trends toward local population differentiation. The species possesses a low level of self-compatibility, the first documented report for the genus. Analysis of flowers visited by natural pollinators in populations across the eastern half of the United States demonstrated a linear relationship between pollinia removal and pollinia insertion. Clarifications in older literature regarding the specificity of the pollination mechanism, effective levels of pollination in natural populations, and the performance of experimental manipulations are made, and it is concluded that fruit-set in Asclepias is regulated by the interaction of both mechanical aspects of pollination and physiological aspects of fertilization and fruit development. A model incorporating these restraints is seen to predict fairly well the observed fruit to flower ratio of about 1:100 in natural populations.     

贵州新元古代到寒武纪早期特异埋藏后生生物群及其研究意义

贵州化石丰富,素有古生物王国之称,其中早期特异埋藏后生生物十分发育,由老至新有埃迪卡拉系的瓮安生物群、江口庙河生物群、寒武系第1统的小壳动物群、第2统下部的牛蹄塘生物群及中上部的杷榔动物群、第3统底部的凯里生物群。这些特异埋藏生物群与云南寒武系的澄江动物群、关山生物群及陕南埃迪卡拉系高家山生物群构成了我国早期后生生物的演化链,反映了从动物起源（瓮安生物群）、可疑多门类动物出现（江口庙河生物群）、动物骨骼化（高家山生物群）、生物矿化质和量的变化或骨骼动物爆发性辐射（小壳动物群）及海绵动物辐射（牛蹄塘生物群）再到动物主要门类出现的寒武纪大爆发（澄江动物群）、海洋生物多样化及生态复杂化（凯里生物群）的演化过程。     

大青沟森林植物群落主要木本植物种群分布格局及动态的研究

本文运用方差／均值比率法及聚集强度的某些指数研究了大青沟森林植物群落主要木本植物种群的分布格局及其动态。主要木本植物种群的分布格局大多为集群型,只有部分群落中大果榆、色木槭及家榆种群为随机分布。格局动态的分析表明,水曲柳、黄菠萝、春榆、大果榆种群幼苗—幼树—小树—中树—大树分布格局由集群分布逐渐变为随机分布,而蒙古栎由于较强的萌生性,大树阶段仍为集群分布。分析表明影响种群分布格局的因子大致可归纳为两类：一是物种本身的生物学特性,二是由环境条件引起的种内种间竞争;方差／均值比率法是一种较好的分析种群分布格局的方法。