Seasonal Dynamics of Plant Diversity on lnselbergs in the Ivory Coast (West Africa)

Inselbergs are isolated monolithic outcrops which are characterized by large areas of exposed crystalline rock. Due to harsh edaphic and microclimatic conditions, inselbergs are completely differentiated from their surroundings. Consequently they host a very distinct vegetation which is being investigated on a global scale over a six year period. The seasonal dynamics of Selected plant communities (Afrotrilepis pilosa mat, shallow depression, ephemeral flush vegetation) on granitic inselbergs in the Comoe National Park (NE Ivory Coast) were studied during the rainy period from May to November 1991 by recording all vascular plant species at 12 intervals. For the habitats investigated, the seasonal vegetation dynamics were related to the rainfall pattern. Maximum values both in species diversity and richness were attained in the first third of the rainy period. Drought in August and September caused a decline in species number and diversity in the shallow depression and ephemeral flush vegetation, resulting in mortality of more than 20% of the species. The individual communities studied differed considerably in species diversity and richness. We conclude that ephemeral flush and shallow depression communities are more species rich than the mat community which is dominated by the highly competitive and specialized K-strategist Afrotrilepis pilosa (a poikilohydric Cyperaceae) due to stochastic climatic perturbations which allow the maintenance of species rich non-equilibrium assemblages with r-strategists as major components.     

RELATIONSHIP BETWEEN SELF-FERTILITY,ALLOCATION OF GROWTH,AND INBREEDING DEPRESSION IN THREE CONIFEROUS SPECIES

Mortality and growth of self and outcross families of three wind-pollinated, mixed-mating, long-lived conifers, Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and noble fir (Abies procera) were followed from outplanting to age 26 (25 for noble fir) in spaced plantings at a common test site. Response to inbreeding differed greatly among species over time and in all regards. Only Douglas-fir and noble fir will be contrasted here, because ponderosa pine usually was intermediate to the other two in its response to inbreeding. In earlier reports, compared to noble fir Douglas-fir had a higher rate of primary selfing and larger inbreeding depression in seed set. Douglas-fir continued to have higher inbreeding depression in nursery and early field survival. The species differed in time courses of inbreeding depression in height and in allocation of growth due to crowding. Between ages 6 and 12, the relative elongation rate (dm · dm^?1 · yr^?1) of Douglas-fir was significantly greater in the selfs than in the outcrosses. The response was not observed in noble fir. At final measurement, inbreeding depression in diameter relative to inbreeding depression in height was greater in Douglas-fir than in noble fir. At final measurement inbreeding depression in height was inversely related to inbreeding depression in survival. Cumulative inbreeding depressions from time of fertilization to final measurement were 0.98, 0.94, and 0.83 for Douglas-fir, ponderosa pine, and noble fir, respectively, which indicates that selfs will not contribute to the mature, reproductive populations.     

PHOTOINHIBITION OF TEMPERATE LAKE PHYTOPLANKTON BY NEAR-SURFACE IRRADIANCE: EVIDENCE FROM VERTICAL PROFILES AND FIELD EXPERIMENTS1

To evaluate the in situ occurrence of phytoplankton photoinhibition, the light-mediated depression of chlorophyll in vivo fluorescence (IVF) and of the cellular fluorescence capacity (CFC) of phytoplankton was determined in three southeastern United States reservoirs. Vertical profiles of a fluorescence depression index (FDI) and of the CFC for reservoir phytoplankton showed that near-surface photoinhibition of fluorescence properties occurred in association with high surface irradiance and weak vertical mixing of the water column. To characterize the time scales of photochemical and photosynthetic responses to and recovery from exposure to supraoptimal light intensity, phytoplankton IVF responses and ¹⁴C-fixation rates were measured infield experiments. Phytoplankton chlorophyll IVF, CFC, and photosynthetic ¹⁴C fixation were rapidly (20–40 min) depressed when reservoir phytoplankton were exposed to surface irradiances (1700–2000 μE·m^?2·s^?1). Light-mediated increases in the FDI declined rapidly (20–40 min) to pre-exposure levels during a subsequent low-light (75–200 μE·m^?2·s^?1) period, but CFC and ¹⁴C fixation recovered more slowly (>40 min). Exposure of reservoir phytoplankton to a light-intensity gradient revealed both intensity and time thresholds for IVF and CFC depression. Phytoplankton photochemical responses to bright light operate on time scales that, in conjunction with vertical mixing, should limit the occurrence of photoinhibition to extreme irradiance environments. Our results support the hypothesis that the photoinhibition of phytoplankton productivity occurs less commonly than is indicated by fixed-depth incubation measurements.     

Estimating the effect of inbreeding on survival

Conservation biologists need to be able to estimate reliably the effects of inbreeding on survival, and need to be able to do so with a range of different data types. Kalinowski and Hedrick described a non-linear maximum likelihood estimation procedure for modelling relationships between survivorship and inbreeding. Although their method is useful for illustrating the concepts involved in modelling such relationships, it is only applicable to simple datasets. We illustrate that the parameter estimates generated by Kalinowski and Hedrick's method are easily obtained using generalized linear modelling procedures available in standard statistical packages, and that these offer several advantages even with simple datasets. We suggest procedures that can be used for modelling relationships between survival and inbreeding with more complex data types, including datasets with multiple and ragged encounters, uncertain detection and random effects.     

Large brood sizes of pied flycatcher, sparrowhawk and goshawk in peak microtine years: support for the mast depression hypothesis

The mast depression hypothesis (MDH) proposes that cyclic population fluctuations of microtines and other herbivores are an effect of cyclic seed cropping of plants. This is because high seed crops, termed masts, are produced at the expense of chemical defence against herbivores. It has generally been assumed that bird-hunting raptors produce high numbers of offspring when microtine prey are abundant because of reduced competition from generalist predators. However, this may also be caused by higher production of herbivorous insects, and thus insectivorous bird prey, because of lower contents of chemical defence compounds in some plant species, such as bilberry Vaccinium myrtillus and cowberry V. vitis-idaea. In Aust-Agder county, southern Norway, the mean brood size of pied flycatcher Ficedula hypoleuca, sparrowhawk Accipiter nisus and goshawk A. gentilis was higher in peak vole years than in other years. The effect was not due to variation in nest predation, as only successful nesting attempts were included in the analyses. For the pied flycatcher, the annual proportion of large broods (>6 fledglings) was positively correlated with the vole trapping index. No correlation was found between the offspring production of goshawks and the proportion of voles in their diet. During a 3-year light-trapping study of nocturnal moths prior to our study, four moth species whose larvae ate Vaccinium were commonest in the vole peak year. All these results are consistent with the MDH. Received: 16 March 1998 / Accepted: 20 April 1998     

The down-regulation of cardiac contractile proteins underlies myocardial depression during sepsis and is mitigated by carbon monoxide

The aim of this study is to investigate the mechanism underling cardiac dysfunction during sepsis, as well as the possible amelioration of this dysfunction by exogenous carbon monoxide (CO) administration. For this purpose, rats (six-week-old, male, Sprague-Dawley) were administered LPS (15 mg/kg body weight, i.p. 6 h) and/or CORM (30 mg/kg, i.p.). The decreased left ventricular ejection fraction (EF) observed in LPS group rats was recovered in the LSP + CORM group, confirming the protective role of CO against sepsis-induced myocardial depression. Proteomic as well as immunoblot analysis showed that the levels of myosin heavy and light chains (MHC and MLC) as well as α-cardiac actin (ACTC) were decreased in the LPS group, and these decreases were mitigated in the LSP + CORM group, suggesting that the amounts of major contractile proteins are decreased in depressed myocardium. Not only LPS-induced inflammatory cytokine (TNFα and IL-1β) production but also the decrease in myofilament proteins was mitigated by CORM. These results confirm the protective action of exogenously administered CO against myocardial depression during sepsis, and reveal a novel mechanism underling cardiac dysfunction during sepsis.     

Estimation of genetic purging under competitive conditions

Inbreeding depression for fitness traits is a key issue in evolutionary biology and conservation genetics. The magnitude of inbreeding depression, though, may critically depend on the efficiency of genetic purging, the elimination or recessive deleterious mutations by natural selection after they are exposed by inbreeding. However, the detection and quantification of genetic purging for nonlethal mutations is a rather difficult task. Here, we present two comprehensive sets of experiments with Drosophila aimed at detecting genetic purging in competitive conditions and quantifying its magnitude. We obtain, for the first time in competitive conditions, an estimate for the predictive parameter, the purging coefficient (d), that quantifies the magnitude of genetic purging, either against overall inbreeding depression (d ≈ 0.3), or against the component ascribed to nonlethal alleles (d_NL ≈ 0.2). We find that competitive fitness declines at a high rate when inbreeding increases in the absence of purging. However, in moderate size populations under competitive conditions, inbreeding depression need not be too dramatic in the medium to short term, as the efficiency of purging is also very high. Furthermore, we find that purging occurred under competitive conditions also reduced the inbreeding depression that is expressed in the absence of competition.     

谷子叶片光合速率日变化及水分利用效率

通过降低空气湿度（ 从约３０ ％ 减少到５ ％ ） 、增加ＣＯ２ 浓度（ 从４００ μｌ ＣＯ２／Ｌ增加到７３０ μｌ ＣＯ２／Ｌ） 、烫叶鞘破坏韧皮部等处理对谷子叶片光合速率日变化和水分利用效率（ＷＵＥ） 进行了研究, 发现中午光合速率降低与光合产物积累有关; 虽然低大气相对湿度（５ ％ ） 使光合速率有所降低,但提高了ＷＵＥ。而烫叶鞘使光合物质积累既抑制了光合速率,又降低了ＷＵＥ。     

Study of Diurnal Changes in Photosynthetic Rate and Quantum Efficiency of Grapevine Leaves and Their Utilization in Canopy Management

Photosynthetic rate and quatum efficiency of grapevine (Vitis vinifera L. cv. Sauvignon blanc) leaves were measured under the field with ample soil water supply, and in phytotron with ample supply of water and mineral nutrients, constant air humidity and CO2 concentration, and optimum air temperature, respectively. Under field conditions CO2 assimilation quantum efficiency of leaves reached its maximum in the morning, which was followed by continuous decrease and midday depression. The leaves intercepting more light energy in the morning showed a higher quantum efficiency. Those leaves subjected continuously to strong irradiance exhibited a more obvious and longer midday depression. Reduction of leaf light interception around midday could reduce midday depression. Shaded leaves had a higher quantum efficiency than leaves under direct sunlight. The diurnal changes in photosynthetic rate and quantum efficiency of leaves were shown to be closely related to the variations in mesophyll resistance to CO2. In phytotron experiments the photosynthetic quantum efficiency of leaves was reduced after a certain period of illumination not only at 1200 μmol · m-2 · s-1 PFD, higher than the saturating light of vine leaves (≈1000 μmol · m-2 · s-1), which was caused by "photoinhibition”, but also at 800 and 200μmol · m-2 · s-1, which was similar to "photoinhibition”. But photosynthetic quantum efficiency of leaves exposed continuously to a very weak PFD (100 μmol · m -2 · s-1) remained contant. The diurnal changes in mesophyll resistance to CO2 of vine leaves could be partly related to photoinhibition. It is considered that, under field conditions without soil water limitation, midday depression of vine leaf photosynthesis could be a result of an increase of the mesophyll resistance induced by multiple effects of strong light, high temperature and low humidity. A higher light interception by canopy plane in the morning may be advantageous to exploit higher photosynthetic potentiality of leaves, but a lower light interception in the middle of day may reduce midday depression. The north-south orientation plane can provide optimum light regime and improve photosynthetic environment in vineyards.     

Pollen transfer dynamics and the evolution of gametophytic self-incompatibility

Recent studies of mating system evolution have attempted to include aspects of pollination biology in analysis of both theoretical models and experimental systems. In light of this growing trend, we propose a simple population genetic model for the evolution of gametophytic self-incompatibility, incorporating parameters for pollen discounting and pollen export/capture. In this model, we consider several cases that span the spectrum for dominance of the mutant self-incompatibility allele and for the degree of incompatibility conferred by the allele. We confirm earlier results that inbreeding depression is required for successful invasion of the self-incompatibility allele and we demonstrate that, unless pollen discounting is very low, the level of inbreeding depression must be very high for an allele conferring self-incompatibility to become established. Finally, we show that the dominance of the mutant allele has a greater impact on the fate of a newly arisen self-incompatibility allele than the strength of the incompatibility conferred by the allele. In particular, the more recessive the self-incompatibility expression in heterozygote stigmas and the weaker the response induced, the easier it is for a self-incompatibility allele to invade.