EXPERIMENTAL STUDIES OF THE EVOLUTIONARY SIGNIFICANCE OF SEXUAL REPRODUCTION. III. MATERNAL AND PATERNAL EFFECTS DURING SEEDLING ESTABLISHMENT

To determine whether genetic differences in fitness components exist among seeds and seedlings in a natural population, weighed propagules of six parents of Anthoxanthum odoratum from a reciprocal diallel cross were planted into the parental source population, a mown field. Seed families of maternal genotypes differed in germination success, while paternal families showed no detectable differences. Differential germination success could not be attributed to propagule weight. Seed families ranked differently in germination percentage in different blocks. No survivorship differences among parental seed families could be detected. There were significant cross × block × germination and cross × block × survivorship interactions; different crosses performed better or worse in different blocks. In some cases, crosses sired by different fathers within a maternal seed family differed in germination or survivorship, suggesting that natural selection may be capable of discriminating among juvenile genotypes within a maternal family despite the presence of large overall maternal effects. These results indicate that seedling establishment may differ according to genotype and that microsite heterogeneity may maintain genetic variation in juvenile traits in natural plant populations.     

EXPERIMENTAL STUDIES OF THE EVOLUTIONARY SIGNIFICANCE OF SEXUAL REPRODUCTION II. A TEST OF THE DENSITY-DEPENDENT SELECTION HYPOTHESIS

This study tests the hypothesis that one evolutionary advantage of sexual reproduction is that it produces genetically variable progeny with a density-dependent advantage mediated by resource partitioning or pest pressure. Our experimental approach involved planting separate plots of sexually-derived and asexually-derived tillers of the grass Anthoxanthum odoratum in density gradients at the two natural sites from which the source material was taken. The sexual progeny displayed a significant fitness advantage compared to the asexual progeny. But, in contrast to the expectations of the density-dependent selection hypothesis, the advantage of the sexually produced progeny is most marked at lower densities. Thus, the results of this experiment and our previous report (Antonovics and Ellstrand, 1984) seem to best support the frequency-dependent selection hypothesis for the advantage of sexual reproduction.     

EXPERIMENTAL STUDIES OF THE EVOLUTIONARY SIGNIFICANCE OF SEXUAL REPRODUCTION. V. A FIELD TEST OF THE SIB-COMPETITION LOTTERY HYPOTHESIS

Sexually and asexually derived tillers of Anthoxanthum odoratum were planted directly in the field to test the hypothesis that competition among groups of sexual and asexual siblings favors the maintenance of sexual reproduction in populations. The results showed a substantial fitness advantage for sexual tillers. However, in contrast with the models, the advantage of sex did not increase with increasing numbers of colonists in the patch, there were multiple survivors among colonists, and an advantage was observed even for singly planted tillers. When a truncation-selection scheme was imposed ex post facto on the data, the relative performance of sexual tillers was similar to that predicted by the Bulmer (1980) model, suggesting that sib-competition models fail due to the violation of the assumption of truncation selection. The advantage of sex was not correlated with the presence of other species, total percentage cover, or species diversity, although sites where sex was favored were physically clustered.     

EXPERIMENTAL STUDIES ON THE FUNCTIONAL SIGNIFICANCE OF HETEROSTYLY

Heterostyly has been viewed as both an antiselfing device and a mechanism that increases the proficiency of pollen transfer between plants. We used experimental manipulation of the morph structure of garden populations of self-compatible, tristylous Eichhornia paniculata to investigate the function of floral polymorphism. Outcrossing rates (t), levels of intermorph mating (d), and morph-specific male and female reproductive success were compared in replicate trimorphic and monomorphic populations. In trimorphic populations, t and d averaged 0.81 (2 SE = 0.03) and 0.77 (2 SE = 0.03) respectively, with no difference in either parameter among morphs. Ninety-five percent of outcrossed seeds were therefore the result of intermorph fertilizations. Male reproductive success of the long-styled morph was low, especially in comparison with plants of the short-styled morph. Outcrossing rates for each morph were higher in trimorphic than monomorphic populations where t averaged 0.71 (2 SE = 0.01), 0.30 (2 SE = 0.04) and 0.43 (2 SE = 0.1) for the long-, mid-, and short-styled morphs, respectively. Seed set was lower in monomorphic populations, particularly those composed of the L morph, reflecting reduced pollen deposition. Floral polymorphism therefore increased both outcrossing rate and fecundity but the magnitude of the differences varied among morphs. If the ancestral condition in heterostylous groups resembled the L morph, as has been suggested, data from this study suggests that the selective basis for the establishment of floral polymorphism could have been increased pollen transfer rather than higher levels of outcrossing.     

ON THE EVOLUTIONARY CONSEQUENCES OF SEXUAL IMPRINTING

The idea that sexual imprinting may generate sexual selection and possibly lead to speciation has been much discussed in the ethological literature. Here the feasibility of three such hypotheses is investigated using mathematical models of sexual selection in which mating preferences are acquired through imprinting and hence dependent upon the parental phenotypes. The principal findings are the following. (1) Sexual imprinting reduces the likelihood of novel adaptive traits spreading through a population, except in some circumstances in which there is heterozygote advantage. (2) Asymmetrical mating preferences, acquired through imprinting, can generate sexual selection for traits that impair survival. (3) The conditions under which sexual imprinting will maintain a genetic polymorphism in a population are fairly restricted. (4) Sexual imprinting can act as a barrier to gene flow minimizing the impact of migration and preserving and accentuating genetic differences between populations. The findings suggest that sexual imprinting may be of considerable evolutionary significance.     

NEIGHBOR RELATEDNESS AND COMPETITIVE PERFORMANCE IN IMPATIENS CAPENSIS (BALSAMINACEAE): A TEST OF THE RESOURCE PARTITIONING HYPOTHESIS

The Elbow Room hypothesis for the maintenance of sex depends upon the assumption that intraspecific resource partitioning occurs and increases in magnitude with decreasing genetic similarity of competitors. This assumption leads to the prediction that plants should have greater fitness in competition with nonrelatives than in competition with siblings. Moreover, if a population displays fine scale genetic structure and genetic similarity declines with distance, then resource partitioning should increase with increasing geographical distance between the source locations of the competing genotypes. We tested these predictions in a greenhouse experiment by subjecting inbred Impatiens capensis seedlings to four types of competitors: 1) inbred full sibs; 2) inbred nonrelatives from the same source location; 3) inbred nonrelatives from a source location 30 m away; and 4) inbred nonrelatives from another population approximately 1 km distant. Plant dry weight at harvest increased significantly with seed weight and earlier emergence date, decreased significantly with seed weight and earlier emergence date of the competitor, and varied significantly among maternal seed families. However, there was no significant effect of competitor relatedness or distance between parental locations. The experiment therefore failed to support the resource partitioning hypothesis.     

正颤蚓的生长发育及繁殖生物学的研究

在实验室饲养的条件下,研究了正颤蚓在15℃、20℃、25℃水温的生长发育和繁殖过程。结果表明正颤蚓从其受精卵在蚓茧内发育,孵出生长到产卵,在15℃水温需100—123d,在20℃水温需70—90d,在25℃水温需48—64d。蚓自蚓茧内孵出后的165d生长期内,其15℃、20℃、25℃水温的体重生长回归方程分别是W=6.87/［1+136.48     

COMPARATIVE STUDIES ON RESPIRATION : IV. THE EFFECT OF ETHER ON THE RESPIRATION OF WHEAT.

These experiments show that 7.3 and 3.65 per cent ether solutions cause an increase in respiration followed by a decrease. The results agree with those of Haas on Laminaria, of Gustafson on higher fungi, and of Mrs. Brooks on bacteria. They do not agree with the theory of Verworn that anesthesia is a kind of asphyxia and that it decreases respiration.     

裂叶沙参和泡沙参种群有性生殖和无性繁殖的比较

通过对裂叶沙参(Adenophora lobophylla Hong)和泡沙参(A.potaninii Korsh.)种群有性生殖和无性繁殖特性的对比,揭示濒危植物裂叶沙参的种群内部致濒机制。结果表明:裂叶沙参种群幼苗抢占草本层上层空间能力弱于泡沙参种群;裂叶沙参种群是以相对长的生殖期和高产籽量来适应环境;裂叶沙参种群开花结实量虽高于泡沙参种群,但其中成熟种子少,种子质量差,致使其种群由种子到一年生幼苗的转化率极低,并且幼苗生活力弱,是导致其种群濒危的重要内部原因。裂叶沙参种群除有性生殖外还兼有较弱的无性繁殖,是对其有性生殖的一个重要补充。     

OBSERVATIONS ON THE MORPHOLOGY AND SEXUAL REPRODUCTION OF COOLIA MONOTIS (DINOPHYCEAE)1

The surface morphology of the dinoflagellate Coolia monotis Meunier was compared with the surface morphology of Ostreopsis, The apical pore of C. monotis is similar in architecture to that of Ostreopsis but considerably longer (12 μm) than in O. heptagona (8–9 μm) and O. ovata (6–7 μm). A ventral pore in C. monotis is located on the right ventral margin between apical plate l′ and precingular plate 6″ and is similar in appearance and location to the ventral pore of O. ovata. The longitudinal flagellum (20 μm) in C. monotis is longer than in O. ovata (12 μ). Although Coolia and Ostreopsis appear to be distinctly different and should remain as two separate genera, they appear to be related. Cells of C. monotis divided by binary fission. Doubling time was 3–4 days in the logarithmic phase of growth at 23°C, 12:12 h L:D, 30–90 μE-m^?2·s^?1, and a salinity of 36%. Cultures reached cell densities of 2.5 × 10³ cells·L^?1 after 15 days of growth. The sexual process in C. monotis occurred in Erdschreiber's medium when Danish soil extract was substituted with mangrove sediment extract under the culture conditions described above. Gamete fusion produced large biflagellated planozygotes (70–75 μm diam). Planozygote maturation involved cytoplasmic reorganization, loss of motility, development of a spherical shape (80–90 μm diam), and two to three orange accumulation bodies. The cells at this stage appeared to be thin-walled cysts. Further development included reorganization of cyst contents, emergence of non-motile gametes, and development of chloroplasts, sulcus, and girdle. The nucleus of the newly formed cells occupied 50% or more of the total cell volume. Meiosis occurred in the cyst, but nuclear cyclosis was not observed. Four daughter cells were produced within 36–48 h, and motile gametes developed. The gametes exhibited sexuality for 2 months and completed the sexual life cycle by going through a thin-walled cyst stage.     

根田鼠生命表和繁殖的研究

根据229((?)(?)124,♀♀105)只实验室出生的幼鼠生长、繁殖和死亡观察根田鼠雄性和雌性的期望寿命(c_0)分别为3.040(即39周)和3.176(即41周);平均死亡率((?))分别为0.283和0.272,两者很接近。妊振期平均为20.6天,哺乳期在15—20天,产仔数平均为4.56只。实验种群经一世代后的净增殖率(R_0)为2.0456,内禀增长率(r_m)为0.0787/月。