SPATIAL PATTERNS OF SEED DISPERSAL AND POSTDISPERSAL SEED PREDATION OF CRYPTANTHA FLAVA (BORAGINACEAE)

I examined the spatial patterns of seed dispersal and postdispersal seed predation of the semidesert perennial Cryptantha flava (A. Nels.) Payson (Boraginaceae) at two sites in north-eastern Utah. Most flowers mature only one seed (nutlet) which is permanently retained within a pubescent calyx. The calyx and enclosed seed abscise from the plant as a unit. These dispersal units are effectively dispersed by wind as evidenced by the highly directional seed shadows and the long distances some of them travel (up to 31.3 m). Potential seed predators at the sites include five species of rodents, of which Peromyscus maniculatus is the most common, and two species of ants, Pogonomyrmex occidentalis and an undescribed species of Conomyrma. There were no strong spatial patterns of postdispersal seed predation. More seeds were removed from dishes placed at the bases of fruiting adults than from dishes ≥ 1.0 m away in one of three experiments. More seeds were removed from under shrubs or clumps of grass than in the open in one of four experiments. After 3–4 days, there was a consistent tendency for more seed removal from high density (75 seeds per .25 m²) quadrats than from low density (75 seeds per 6.25 m²) quadrats, but the difference was not always significant. There was a similar nonsignificant difference between high- and low-density quadrats exposed for 21 days. The pubescent calyx greatly discourages seed predation by ants, and probably also reduces predation by rodents. In addition, by increasing the surface area of the dispersal unit, the calyx may facilitate dispersal by wind.     

ON THE EVOLUTION OF MIGRATION IN HETEROGENEOUS ENVIRONMENTS

Populations often experience variable conditions, both in time and space. Here we develop a novel theoretical framework to study the evolution of migration under the influence of spatially and temporally variable selection and genetic drift. First, we examine when polymorphism is maintained at a locus under heterogeneous selection, as a function of the pattern of spatial heterogeneity and the migration rate. In a second step, we study how levels of migration evolve under the joint action of kin competition and local adaptation at a polymorphic locus. This analysis reveals the existence of evolutionary bistability, whereby a low or a high migration rate may evolve depending on the initial conditions. Last, we relax several assumptions regarding selection heterogeneity commonly made in previous studies and explore the consequences of more complex spatial and temporal patterns of variability in selection on the evolution of migration. We found that small modifications in the pattern of environmental heterogeneity may have dramatic effects on the evolution of migration. This work highlights the importance of considering more general scenarios of environmental heterogeneity when studying the evolution of life‐history traits in ecologically complex settings.     

杜仲胚发育过程的研究

西安地区栽培杜仲,4月中旬传粉,下旬受精。合子休眠35天左右。6月初形成原胚,6—8月胚分化发育,10月种子成熟。合子在休眠期,其体积增长1—1.5倍,极性渐显著。合子经两次横分裂,形成线形排列的四细胞原胚。其后基细胞衍生的细胞参与胚体的形成,胚的发育属藜型。胚柄单列细胞,靠珠孔端一个形大,具吸器作用。胚的后期发育与一般双子叶植物相同。     

A THEORY ON THE EVOLUTION OF THE EXINE IN ORCHIDACEAE

The development of secondarily derived features in orchid pollen precludes the possibility of applying evolutionary trends hypothesized for dicot pollen to orchid pollen and perhaps even monocot pollen. There are three lines of pollen wall development, all secondarily derived from a possible tectate-perforate ancestral type, i.e., tectate-imperforate with incipient columellae (Cypripedioideae), intectate lacking a foot layer (Orchidoideae), and tectate-imperforate with globular masses of sporopollenin (Vandoid Epidendroideae).     

THE EFFECTS OF 5-BROMODEOXYURIDINE ON YOLK SAC ERYTHROPOIESIS IN THE CHICK EMBRYO

The effects of the thymidine analog, 5-bromodeoxyuridine (BUdR), on the formation of red cells in the yolk sac of the chick embryo were examined. The prospective area opaca vasculosa from a definitive primitive streak embryo was excised, disaggregated, and deposited into a cell clump, and the cell clump was placed in organ culture. Hemoglobin synthesis is detectable after about 16 hr in culture. The formation of erythropoietic foci and incorporation of ⁵⁵Fe into heme were used to measure the extent of erythropoiesis. Exposure to 40 µg/ml of BUdR within 6 hr after explantation almost completely eliminated red cell formation; subsequent transfer to thymidine medium showed that the inhibition was reversible, and there was no histological evidence of analog toxicity. Between 6 and 12 hr after initiation of organ culture, the tissue became completely refractory to BUdR. DNA synthesis, as monitored by thymidine-³H and BUdR-³H pulses, was extensive both during and after the period of BUdR sensitivity. Hence, during both BUdR sensitive and insensitive periods the analog was incorporated into DNA of cells which had not yet synthesized hemoglobin. It is proposed that between 6 and 12 hr a crucial regulatory event for terminal differentiation is perturbed by the presence of BUdR in the chromosomes.     

ON THE EVOLUTION OF DISPERSAL AND ALTRUISM IN APHIDS

How competitive interactions and population structure promote or inhibit cooperation in animal groups remains a key challenge in social evolution. In eusocial aphids, there is no single explanation for what predisposes some lineages of aphids to sociality, and not others. Because the assumption has been that most aphid species occur in essentially clonal groups, the roles of intra- and interspecific competition and population structure in aphid sociality have been given little consideration. Here, I used microsatellites to evaluate the patterns of variation in the clonal group structure of both social and nonsocial aphid species. Multiclonal groups are consistent features across sites and host plants, and all species—social or not—can be found in groups composed of large fractions of multiple clones, and even multiple species. Between-group dispersal in gall-forming aphids is ubiquitous, implying that factors acting ultimately to increase between-clone interactions and decrease within-group relatedness were present in aphids prior to the origins of sociality. By demonstrating that between-group dispersal is common in aphids, and thus interactions between clones are also common, these results suggest that understanding the ecological dynamics of dispersal and competition may offer unique insights into the evolutionary puzzle of sociality in aphids.     

OBSERVATIONS ON FIBRILLOGENESIS IN THE CONNECTIVE TISSUE OF THE CHICK EMBRYO WITH THE AID OF SILVER IMPREGNATION

A technique is described which combines silver impregnation and ultrathin sectioning for the electron microscopic demonstration of fibrils in the connective tissue of the chick embryo. The electron micrographs presented in this paper provide evidence for the specificity and completeness of the silver-impregnation technique. It has been shown that, in this particular tissue after fixation in neutral formalin and at the stage of development represented by our material, the argyrophil fibers are embedded in a material which is continuous with the body of the fibroblasts.     

ON THE EVOLUTION OF PSEUDOGAMY

A. density- and frequency-dependent model for the evolution and maintenance of pseudogamous females is developed and analyzed. Ecological as well as evolutionary aspects of pseudogamy are discussed. Criteria are described for the stable coexistence of sexual females and pseudogamous females under natural conditions. The conditions for invasion of a normal bisexual population by pseudogamous females are less stringent than the conditions for stable coexistence. Hence, we expect that some populations will be characterized by unstable sex ratios over time (with the resulting local extinction due to lack of males) while other populations will be characterized by stable sex ratios over time. If high population sex ratios (i.e., many females to few males) are to be stable, the net population growth rate must be large, and there can be no successful male preference for sexual females.     

ON THE EVOLUTION OF MEGACERINES

<正> The megacerine deer (the tribe Megacerini of the subfamily Cervinae) is a rather ancient extinct group, known from the end of the Miocene, The tribe comprises 8 genera: Megaceros Owen, 1844, Sinomegaceros Dietrich, 1933, Praemegaceros Portis, 1920, Praedama Portis, 1920, Arvernoceros Heintz, 1970, Neomegaloceros Korotkevitch, 1971, Orchonoceros Vislobokova, 1979 and Praesinomegaceros Vislobokova, 1983. The Pleistocene history of megacerines is much studied regarding the evolutionary stage of these deer. Almost all students recognize the existence of two branches of megacerines in the Pleistocene of Europe: one of these connected with Megaceros giganteus (Blumenbach, 1803) and the other with Praemegaceros verticornis (Dawkins, 1872), although the estimations of the systematic range of these cervids are different (Azzaroli,     

多胚水稻胚位与苗位的观察研究

多胚水稻是进行水稻无融合生殖研究的重要材料,通过对4个多胚水稻品系种子胚位及萌发后的苗位观察发现这些品系中存在着多种胚位及苗位类型,其中以双-13的类型最为丰富。认为不定胚在与合子胚共存的情况下难以萌发表达,而只有当合子胚败育时才有可能得以萌发,并且认为反向单苗,侧向单苗及倒序单苗可能起源于不定胚,因而可能成为进行水稻无融合生殖筛选的重要标志。