Interspecific host discrimination and competition in Apoanagyrus (Epidinocarsis) lopezi and A.(E.)diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti

Abstract.

• 1 Choice experiments on interspecific host discrimination in A.lopezi and A. diversicornis were carried out on discs of cassava leaf containing four hosts (P.manihoti) that had been parasitized by the other species and four unparasitized hosts.
• 2 A.lopezi accepted both host types equally for oviposition, whereas A.diversicornis accepted fewer hosts that had been parasitized by A.lopezi than unparasitized ones. A.diversicornis is therefore capable of interspecific host discrimination, but such a capability was not demonstrated for A.lopezi.
• 3 Survival probability in singly parasitized hosts was 0.85 for both parasitoid species. When the time interval between ovipositions was 2 h or less, survival in multiparasitized hosts was 0.68 for A.lopezi and 0.17 for A.diversicornis, irrespective of priority. Increasing A.lopezi priority to 24±2h did not increase A.lopezi survival. A.diversicornis survival, however, increased to 0.43 when A.diversicornis was given 24 ± 2 h priority. A.diversicornis eggs took 19 h longer than A.lopezi eggs to hatch. This could explain the difference in competitive abilities in multiparasitized hosts.
• 4 The observed difference in host selection behaviour between A.lopezi and A.diversicornis is in accordance with the different benefits of multiparasitism: A.lopezi gains more than A.diversicornis because of its superior within-host competitive abilities.
• 5 Neither species avoided multiparasitism completely. The low survival probability of A.diversicornis in multiparasitized hosts may partly explain its failure to establish when introduced into Africa as part of a biological control programme of P.manihoti.

     

The Use of Quantitative Electron Microscopy in the Study of Lipid Composition of Membranes

It is argued that a knowledge of the extent of individual cellmembrane systems is of crucial importance to the understandingof results obtained from lipid analysis of tissues and isolatedmembrane systems. In this preliminary study stereological methodshave been applied to electron micrographs of cucumber leavesat different stages of expansion, to assess the area of eachmembrane system present. The equivalent phospholipid-proteinmembrane area for the largest leaf was found to be 500 x 10⁹µm² compared with a value of 961 x 10⁹ µm² calculatedfrom published data on the phospholipid content of a similarleaf. Possible applications of quantitative electron microscopyto certain lipid studies are reviewed and it is concluded thatthis approach should be more widely adopted.     

The Histophysiology of the Prolactin Cell in Non-Mammalian Vertebrates

With the exception of the agnathan fishes, a prolactin cellhas been identified in all vertebrates in which it has beensought. This review examines the structure of the prolactin-producingpituitary cell in non-mammalian vertebrates, the manner in whichit responds to natural and artificial stimuli, and its controlby neural and humoral factors. Fundamental similarities anddifferences are described in an attempt to understand betterits method of operation. Given our present state of knowledge, there is, among all theapparent diversity, a similarity in the basic structure andmorphological response of this cell in teleosts, amphibians,reptiles, and birds. One can identify and speak with relativecertainty about a specific adenohypophysial cell called a "prolactincell." More profound differences may be found at the level ofcontrol mechanisms, chemistry of the hormone(s), and the natureof receptivity and response of target tissues. It appears that although there are basic similarities in thedesign of the prolactin cell, the systems that control its activitiesmay differ and the similar products produced by the cell maybe used toward different ends.     

Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration

Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site‐years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two‐stream albedo submodel provided accurate predictions of boreal needle‐leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two‐stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r²=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r²=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two‐stream albedo model and foliage nitrogen concentration. These nitrogen‐based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.     

全北区古近纪的鸟类动物群(英文)

中国的较高纬度地区有着丰富且交通无阻的含化石地层,故在全北区生物地理的研究中占有独特的位置。它提供了欧洲和北美新生代早期沉积之间的联系。这些动物群中所含丰富多样的鸟类动物群,直到目前才得到足够的关注。早始新世时,在全球范围内,甚至在高纬度地区,都遍布着热带森林;在怀俄明州的绿河湖区,还发现了棕榈叶的化石。因而,德国Messel的鸟类动物群表现出与非洲热带森林较近的亲缘关系,怀俄明州绿河的鸟类动物群与南美洲热带地区关系密切,也就不足为奇了。实际上,古近纪的标志性特征是温暖潮湿的生态系统在全球广泛分布,削弱了高纬度地区对生物分布所起的屏障作用。晚始新世-渐新世全球温度的下降,致使新近纪加剧了大陆隔离并促成了生态变化,进而导致了现代鸟类在分类上的多样性。     

Cystolith Development and Structure in Pilea cadierei (Urticaceae)

Cystolith formation, structure and composition have been investigatedin leaves and stem internodes of Pilea cadierei (Urticaceae)using a variety of techniques at the light and electron microscopelevels. The development of lithocysts from epidermal cells hasbeen followed. These cells are cytoplasmically similar to otherepidermal cells but possess a much more active Golgi apparatusand more numerous mitochondria. The cystolith is a spindle-shapedbody composed of concentric layers of longitudinally orientatedcellulose microfibrils associated with pectins and other cellwall polysaccharides. At maturity it is heavily impregnatedwith calcium carbonate. Some cystoliths also contain siliconand are covered in a sheath of siliceous material. Cystolithformation occurs at the tip of a peg that grows in from thelithocyst wall. Evidence from ultrastructure suggests that thelithocytst cytoplasm transports carbohydrates to the cystolithvia Golgi vesicles, and organizes the deposition of cystolithcellulose microfibrils via a system of microtubules lying beneaththe plasma membrane that envelopes the growing cystolith. Thepeg is composed of heavily staining amorphous material likethat of an apoplastically sealed cell wall. It is incapableof supporting the migration of lanthanum ions into the cystolith.We conclude that cystoliths are isolated volumes of apoplastthat act as repositories for inorganic salts, principally calciumcarbonate. We propose that calcium ions move into the lithocystprotoplast from surrounding cells and are then transported acrossthe plasma membrane boundary into the cystolith. This proposalconflicts with previous suggestions that calcium enters by diffusionthrough the peg. Cystolith, lithocyst, cell wall, calcium, silicon, cytochemistry, electron probe analysis, Pilea cadierei     

Morphological Modifications of Oocyte Vitelline Envelope from Bufo arenarum during Different Functional States

The submicroscopic morphology of the vitelline envelope of Bufo arenarum's oocyte change significantly during the maturation and fertilization processes. The morphological changes are related to physiological activity in vivo and can be triggered in vitro by experimental procedures. It is our scope to present the ultrastructure differences of fascicular components of the vitelline envelope in coelomic, "pars recta" conditioned, oviductal, oviposited and fertilized oocytes. Our experimental results indicate that artificial "pars recta" treatment of coelomic oocytes arrange the fascicular components as those of oviposited oocyte, although differences still remain indicating that additional maturation processes take place while the egg pass througth the oviduct. Fertilized or activated oocytes which are refractary to sperm penetration, change the vitelline envelope fascicular components orientation giving a submicroscopical image quite different to those of none fertilized oocytes. These ultrastructural changes define in a clear cut manner the functional states of Bufo arenarum's oocyte.     

A bioassay for screening materials influencing feeding in the field slug Deroceras reticulatum (Müller) (Mollusca: Pulmonata)

Test materials were incorporated in wheatflour pellets to measure their effect on slug feeding. The dry weights of individual pellets were measured before and after exposure for 24 h to starved slugs. The method gave consistent results, and can accommodate test materials with different physical properties. The phagostimulant effect of sucrose was confirmed. An extract of the herb tarragon (Artemisia dracunculus) was the most effective antifeedant of the materials used at the concentrations tested. The method is compared with other published techniques.