THE DEVELOPMENT AND SURVIVAL OF PODISUS SAGITTUS (HEMIPTERA: PENTATOMIDAE) ON ARTIFICIAL DIETS

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The effects of 4 diets on population parameters of Podisus sagittus (L.), a pentatomid predator of Lepidoptera, were compared. Direct comparisons were made of survival, stadial lengths, generation times and predator weights at 20, 25, and 33°C. Temperature influenced stadial lengths, generation time and survival but not weight. Improved survival compared with controls was recorded for diet I at 20°C and diet I and II at 25°C. On diet III adults were produced only at 33°C, in which survival was similar to that in the controls.     

EFFECTS OF SALINITY,NITROGEN, AND POPULATION DENSITY ON THE SURVIVAL,GROWTH, AND REPRODUCTION OF ATRIPLEX TRIANGULARIS (CHENOPODIACEAE)

Populations of Atriplex triangularis were grown under laboratory conditions in a growth chamber and manipulated in an inland Ohio saline pond in order to examine the relative effects of salinity, nitrogen fertilization, and population density on growth, reproduction, and survival. For laboratory plants, nitrogen fertilization was the most important variable, with biomass and reproductive effort being greatest at the high nitrogen level. As salinity increased, biomass decreased only in plants not limited by nitrogen. Increasing density caused biomass per plant to decrease at both high and low nitrogen levels. For field plants, density was the most important variable, with biomass per plant and survival both decreasing as density increased. As density increased, size inequality among individuals increased but biomass per unit area and individual reproductive effort remained relatively constant. Nitrogen fertilization slightly enhanced survival, but did not affect biomass. It is suggested that density-dependent processes may be significant even in relatively harsh physical environments.     

EFFECTS OF FIRE IN TALLGRASS PRAIRIE ON GROWTH AND REPRODUCTION OF PRAIRIE CONEFLOWER (RATIBIDA COLUMNIFERA: ASTERACEAE)

Effects of fire on growth and reproduction of the perennial forb Ratibida columnifera were studied on the Konza Prairie Research Natural Area in northeastern Kansas, USA. Populations were sampled in seven different tallgrass prairie watersheds that varied in fire frequency and in the number of years elapsed since the last fire. Plants from sites not burned for many years were 2.6 times larger and produced 50% more stems than plants from recently burned sites. Number of seeds per plant was also higher in long-unburned sites due to greater numbers of flower heads per plant and greater numbers of achenes produced per head. Reproductive effort (ratio of inflorescence biomass to total vegetative biomass) was 33% lower in annually burned prairie than in any of the other sites. Significant differences in the relationships of inflorescence biomass to vegetative plant biomass in burned vs. unburned sites indicated that burning causes direct changes in plant reproductive effort independent from its effects on plant size. There was no clear relationship between patterns of seed production among sites and patterns of R. columnifera abundance. Ratibida columnifera responses to fire are most likely a result of changes in the relative competitive abilities of forbs and the dominant perennial grasses due to post-fire changes in abiotic conditions rather than a result of direct effects of fire on the fate of buds and subsequent vegetative and floral development.     

INTERACTIVE EFFECTS OF OFFSPRING SIZE AND TIMING OF REPRODUCTION ON OFFSPRING REPRODUCTION: EXPERIMENTAL,MATERNAL, AND QUANTITATIVE GENETIC ASPECTS

We demonstrate that egg size in side-blotched lizards is heritable (parent-offspring regressions) and thus will respond to natural selection. Because our estimate of heritability is derived from free-ranging lizards, it is useful for predicting evolutionary response to selection in wild populations. Moreover, our estimate for the heritability of egg size is not likely to be confounded by nongenetic maternal effects that might arise from egg size per se because we estimate a significant parent-offspring correlation for egg size in the face of dramatic experimental manipulation of yolk volume of the egg. Furthermore, we also demonstrate a significant correlation between egg size of the female parent and clutch size of her offspring. Because this correlation is not related to experimentally induced maternal effects, we suggest that it is indicative of a genetic correlation between egg size and clutch size. We synthesize our results from genetic analyses of the trade-off between egg size and clutch size with previously published experiments that document the mechanistic basis of this trade-off. Experimental manipulation of yolk volume has no effect on offspring reproductive traits such as egg size, clutch size, size at maturity, or oviposition date. However, egg size was related to offspring survival during adult phases of the life history. We partitioned survival of offspring during the adult phase of the life history into (1) survival of offspring from winter emergence to the production of the first clutch (i.e., the vitellogenic phase of the first clutch), and (2) survival of the offspring from the production of the first clutch to the end of the reproductive season. Offspring from the first clutch of the reproductive season in the previous year had higher survival during vitellogenesis of their first clutch if these offspring came from small eggs. We did not observe selection during these prelaying phases of adulthood for offspring from later clutches. However, we did find that later clutch offspring from large eggs had the highest survival over the first season of reproduction. The differences in selection on adult survival arising from maternal effects would reinforce previously documented selection that favors the production of small offspring early in the season and large offspring later in the season—a seasonal shift in maternal provisioning. We also report on a significant parent-offspring correlation in lay date and thus significant heritable variation in lay date. We can rule out the possibility of yolk volume as a confounding maternal effect—experimental manipulation of yolk volume has no effect on lay date of offspring. However, we cannot distinguish between genetic effects (i.e., heritable) and nongenetic maternal effects acting on lay date that arise from the maternal trait lay date per se (or other unidentified maternal traits). Nevertheless, we demonstrate how the timing of female reproduction (e.g., date of oviposition and date of hatching) affect reproductive attributes of offspring. Notably, we find that date of hatching has effects on body size at maturity and fecundity of offspring from later clutches. We did not detect comparable effects of lay date on offspring from the first clutch.     

EFFECTS OF HEAVY METALS ON SURVIVAL AND GROWTH OF BIOMPHALARIA GLABRATA SAY (GASTROPODA: PULMONATA) AND INTERACTION WITH SCHISTOSOME INFECTION

The effects of dissolved Pb, Cd and Hg on growth and survivalof adult Biomphalaria glabrata Say. uninfected and infectedwith Schistosoma mansoni Sambon, were examined. Pb at concentrationsfrom 0.25–100 µM, Cd from 0.075–0.25 µMand Hg from 0.25–1 µM significantly reduced growthand survival of normal snails. With each metal the effects increasedwith increasing concentration. The LC 25 at 2 wks exposure was82 ± 19, 0.22 ± 0.04 and 0.94 ± 0.13 µM(x ± S.E.) for Pb, Cd and Hg, respectively. Snails exposedto heavy metals continued to be reproductively active, but theegg production was highly variable and no significant effectof heavy metal exposure was demonstrated. Infection also decreasedsurvival and growth of snail hosts and infected individualsexposed to heavy metals displayed the greatest mortality. TheLC 25 for infected snails at 2 wks exposure was 8 ± 3,0.9 ± 0.02 and 0.29 ± 0.08 for Pb, Cd and Hg respectively.A significant interaction between heavy metal exposure and infectionwas apparent. Infected snails were not reproductively active.Cercarial shedding by infected snails was significantly reducedin the presence of heavy metals and by 6 wks shedding had ceasedat the highest metal concentrations. (Received 20 May 1996; accepted 31 July 1996)     

POPULATION DEMOGRAPHY OF PASTINACA SATIVA (APIACEAE): EFFECTS OF SEED MASS ON EMERGENCE,SURVIVAL, AND RECRUITMENT

The effect of seed mass on emergence, survival, and recruitment to flowering in Pastinaca sativa, a species that produces progressively smaller seeds on the primary, secondary, and tertiary umbels, was analyzed in two field experiments begun in 1982 and 1983. In both experiments, overall emergence was positively related to seed mass, but the effects of seed mass on emergence in fall cohorts was relatively unimportant. Initial seed mass was positively related to overwintering survival in one experiment but not the other, possibly due to differences in winter conditions. Survival to flowering was positively related to seed mass in the 1982 experiment but negatively related to seed mass in the 1983 experiment. This difference is due to greater survival of seedlings from small seeds during short-term droughts, a previously unrecognized advantage of small seeds. Because of differences in survival in the two experiments, recruitment (number of flowering plants/number of seeds sown) was positively related to seed mass in the 1982 experiment but not in the 1983 experiment. The effects of timing of emergence on survival generally disappeared within 12 months. Our results suggest that the relationship between initial seed mass and recruitment in Pastinaca represents a distribution of outcomes, variable from year to year. However, because short-term droughts in Iowa are common, we hypothesize that in most years, seed mass has little impact on recruitment. Furthermore, small scale heterogeneity may often overwhelm any potential effects of seed mass and timing of emergence on recruitment.     

温度对喜马拉雅低额溞生长与生殖的影响

对采自中国云南省高海拔地区-稀有低额溞-喜马拉雅低额溞(Simocephalus himalayensis)在低海拔地区实验室内不同温度梯度下的生长及生殖能力进行了研究.结果表明:高海拔地区生活的低额溞在低海拔地区的相应环境中同样生长繁殖良好,其繁殖率、最大生殖量及种群的增长能力不受海拔高度及不同环境条件的影响.在一定温度条件下(15-31℃,误差为±1℃),喜马拉雅低额溞的发育速率随温度的升高而加快,但在32℃时减慢.在通常培养条件下,喜马拉雅低额溞一般有4个幼龄期(15℃时部分溞体有5个幼龄),16-19个成龄,平均寿命通常为74d(15℃)、54d(20℃)、39d(25℃)和24d(30℃).平均总产仔量在15-25℃最高,分别为449个(15℃)、482个(20℃)和447个(25℃).各温度梯度下的体长增长模型都表明,其体长与龄期之间存在显著的对数关系.每溞平均生殖量以20℃时最高,种群的内禀增长率(rm)和一生的生殖次数都以25℃时最高,净增殖率(R0)以20℃最高.喜马拉雅低额溞最适合的繁殖温度范围在15-25℃.研究还对该种与相应种类在不同温度条件下的生殖量和生物学特性进行了比较.     

EVOLUTIONARY EFFECTS OF SELECTION ON AGE AT REPRODUCTION IN LARVAL AND ADULT: DROSOPHILA MELANOGASTER

Two sets of three replicate lines of Drosophila melanogaster were artificially selected by reproduction at either a ‘young’ or an ‘old’ age. The pure lines, the hybrids between the lines within a selection regimen and the base stock from which the lines were derived were compared for longevity, early and late fertility, development time, larval viability and adult thorax length. Comparison of hybrid with pure lines showed some evidence for inbreeding depression in the lines from both selection regimes. Comparison of hybrid lines with the base stock did not provide evidence for any trade-off in either males or females between early fertility on the one hand and late life fertility and longevity on the other. Nor was there any clear evidence of a trade-off between pre-adult and adult fitness components. There was evidence of inadvertent selection for rapid development in both selection regimens, especially in the females of the ‘young’ lines, and this complicated the interpretation of the responses and correlated responses to selection. An improvement in adult performance in the ‘old’ line males relative to the base stock appeared to be attributable to reversal of mutation accumulation. Comparison of the hybrid ‘young’ and ‘old’ lines with the base stock did not support the idea that the superior longevity and late life fertility of the ‘old’ lines relative to the ‘young’ lines could be accounted for by the effects of mutation accumulation in the ‘young’ lines. The results point to the need to compare selected lines with their base stock when deducing responses and correlated responses to selection and to avoid unintentional selection. In this type of experiment, larval density should be standardized during selection, and adults should not be under pressure for rapid maturation.     

水温对正颤蚓繁殖的影响

正颤蚓 [Tubifextubifex(Mller,1774 ) ]是水栖寡毛类的普生种类 ,此类动物在自然界中喜生活于水中较黑暗的淤泥等沉积物中。由于该动物具有典型的环节动物特征及易于获取 ,历来为国内外学者所钟爱的实验动物。为了研究其生活史及其各种生物学特征 ,许多学者在实验室中模拟该动物天然的生活环境 ,利用淤泥、沙子等做基质进行喂养[1— 3 ] ,但由于这些基质仍较黑暗 ,影响细致的观察 ,故给研究造成诸多不便 ,如对蚓茧和幼蚓难以做到准确的计数。故选用一种透明的基质则十分必要。有人指出颤蚓科在繁殖过程中 ,具有可逆的生殖系统退化特征 ,…     

EFFECTS OF ACIDIC SOLUTIONS ON SEXUAL REPRODUCTION OF PTERIDIUM AQUILINUM

Experiments were performed to determine the effects of acidic solutions on spermatozoid motility and fertilization of gametophytes of Pteridium aquilinum. Buffered solutions (0.0025 m ) were used to simulate exposures to acidic precipitation for up to a 3.5 hr exposure. Experimental results suggest that the spermatozoid population can be subdivided into several groups with respect to pH sensitivity; about 25% spermatozoids are immobile one min after exposure to pH 6.1 buffer while about an equal percentage remain motile after 30 min exposure to buffer of pH 5.1. Between these two response extremes are two other subpopulations. One is quite sensitive to pH but shows some recovery if pH is between 5.6 and 6.1, while the second subpopulation does not seem to exhibit any motility recovery at all but is more resistant to acidity than the first subpopulation. To complement experiments that evaluate spermatozoid responses, experiments were performed to view the process of fertilization under controlled environmental conditions as well as under the canopy of a forest. Fertilization of gametophytes in uncovered petri dishes under a forest canopy was similar to results in aseptic culture after gametophytes were exposed to various pH levels and 86.6 μM sulfate. Although there were some differences between results obtained under aseptic culture conditions and cultures maintained under a forest canopy, it is evident that a lower buffer pH decreased fertilization. Fertilization at pH 4.5 and 3.6 was about one-half that occurring at pH 6.1. Fertilization in gametophytes exposed to pH 3.0 was about 10-20% of that occurring at pH 6.1. Addition of 86.6 μM sulfate decreased fertilization under all culture conditions. These experimental results suggest that fertilization in P. aquilinum may be used as a bioindicator of contaminants in rainwater. The results demonstrate that spermatozoid motility (and the process of fertilization) is more acid sensitive than gametophytic and sporophytic tissues.