摘要:

AbstractThe absorption of high kinetic energy by a small amount of material depends not only on the quality of the material but also on the structural design of the elements involved. Using a rapid response microbalance, we measured the tensions of radial threads in webs of the garden cross spider,Araneus diadematus. We also measured the stress‐strain characteristics of dry radius and wet spiral threads laid down byA. diadematus, as well as of the very different and dry spiral threads laid down by the hackled‐band weaver,Uloborus walckenaerius.The radius threads ofA. diadematusshowed good extensibility (e = 39. 4%), high tensile strength (s = 1153. 8 MPa) and large hysteresis (56%) which indicates that they can function as shock absorbers and structural elements. Although fewer radii were built in the upper than in the lower half of theAraneusweb, our method found no systematic difference between the average pretensions of individual radius threads in these two halves. However, pretension in the upper half of the web showed greater variation.Orb weavers employ two different mechanisms to increase the energy‐absorbing capacity of their respective capture spirals. The sticky spiral ofAraneus diadematusabsorbed energy by large extensibility (about 475%) of the wetted thread which developed substantial force only after 100–200% extension, and the entire thread failed suddenly. The hackled band ofUloborus walckenaeriushad shorter extensibility (about 125%) and it absorbed energy by friction of the fine hackled fibres, many of which needed to break in succession before a thread failed. © 1995 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402710102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ability of eel intestinal epithelial cells to recover from an acute acid load was analysed using the fluorescent dye 2′, 7′‐bis‐carboxy‐ethyl‐5, 6‐carboxyfluorescein (BCECF) and cell suspensions. Under these experimental conditions (bicarbonate‐free solutions) the resting pHiin cells prepared from sea‐water (7.52 ± 0.031) and fresh‐water (7.50 ± 0.094) adapted animals proved to be similar. The recovery rate (following an acid load) increases by increasing the Na ion concentration in the extracellular medium. This pHirecovery is competitively inhibited by the specific inhibitor dimethylamiloride (DMA) with a low Kiin sea‐ (1.2 μM) as well as in fresh‐water (1.3 μM) adapted animals, indicating the presence of a specific Na/H exchange activity in these cells. Using basolateral membrane vesicles it could be demonstrated that this activity is located on the basolateral side of the enterocyte membrane. The kinetic parameters (Kappand Jmax) of this exchanger are similar in fresh‐water and sea‐water adapted animals suggesting that no salinity adaptation occurs, thus excluding the involvement of the antiporter in the osmoregulatory processes. These results are in agreement with the presence in the plasma membrane of the eel enterocytes of a Na/H‐l (housekeeper) form of the a

ISSN:0022-104X    

DOI:10.1002/jez.1402710103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractRed‐toothed shrews of subfamily Soricinae are small mammals with very high mass‐specific metabolic rate. Owing to their high aerobic power they are interesting objects for studies concerning the limits and constraints of skeletal muscle adaptation. In order to clarify the correlation between metabolic rate and muscle properties, we have analyzed fiber types, fiber size, and myosin heavy chain composition of the common shrew(Sorex draneus)and compared them to those of rat (Rattus norvegicus).Three distinct differences between shrew and rat muscles were noted. 1) The fibers of shrew muscles are exceptionally small in comparison to rat myofibers. 2) Electrophoretic and histochemical analysis showed that shrew muscles are composed of only fast fibers (fiber types IIB and IID), the slow type I fibers being totally absent. 3) The shrew muscles are much more homogenous than rat muscles in regard to myosin heavy chain and fiber type composition. The shrew diaphragm consists exclusively myosin heavy chain type IId (MHCIId), while masseter and soleus are composed 95% and 87% of MHCIId, respectively. Other four studied muscles contain MHCIIb and MHCIId approximately in equal proportions.The present findings show that shrew muscles are composed of small, highly aerobic, fast type II fibers, which may be sufficiently fatigue‐resistant to function both as postural muscles and to power fast and high frequency movements of limbs and diaphragm. © 1995 Wiley‐L

ISSN:0022-104X    

DOI:10.1002/jez.1402710104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe plasma levels of glucocorticoid hormones (e. g., corticosterone and cortisol) are often used as an index of physiological stress. However, under natural conditions, glucocorticoid secretion can respond to both environmental influences (e. g., extreme climatic conditions) and internal influences (populational differences and annual seasonal cycles). To distinguish between these kinds of influences, we examined seasonal variation in basal levels of corticosterone and the adrenocortical response to acute stress in six populations of western fence lizardsSceloporus occidentalis. Three populations (Mojave CA, Lone Pine CA, and Tulalip WA) were near the periphery of the species distribution, and three were in the central part of the range (Ojai CA, Hopland CA, and Bend OR). Basal corticosterone showed no consistent pattern of variation, but the adrenocortical response to acute stress was consistently highest 1) in populations living at the margin of the species range, 2) during the hottest and driest seasons, and 3) in individuals with the largest decrements in physiological condition (length‐adjusted mass). Thus, basal adrenal secretion and adrenal responsiveness to acute stress were dissociated, and the latter more likely reflected the physiological condition of an individual and the severity of its environment. However, further analysis showed that physiological condition only partially explains the variation in adrenocortical responsiveness and that intrinsic seasonal and population differences may be as important as the external influences of the physical environment. After factoring out seasonal changes in physiological condition, adrenocortical response of two populations under identical controlled laboratory conditions also showed that a peripheral population (Mojave, CA) maintained a higher response than a central population (Bend, OR) that was not attributable to population differences in physiological condition. © 1995 Wiley‐Liss,

ISSN:0022-104X    

DOI:10.1002/jez.1402710105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe blastoderm of the fruit flyDrosophila melanogasteris unusually well suited for analysis of fundamental questions in animal development. One such question is how genes specify the positional information which determines the developmental pathways (fate) of cells at appropriate spatial locations. In this paper we propose a dynamical model of gene regulation which explicitly describes how positional information is used in the blastoderm. The model is applied to analyze important experimental findings on the dependence of cell fate on the concentration of the Bicoid morphogen. The model shows that positional information in the presumptive middle body is cooperatively determined by maternal products of thebicoidandhunchbackgenes. © 1995 Wiley‐Liss, I

ISSN:0022-104X    

DOI:10.1002/jez.1402710106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractA Ca2+ionophore (A23187, 3 μM) and inhibitor of protein synthesis (cycloheximide, 10 μg/ml) were used sequentially as a unique method for activating mouse oocytes in vitro. Brief exposure of oocytes to A23187 followed by 6 hr in cycloheximide resulted in a higher activation rate (93.8%) compared to A23187 or cycloheximide alone (37.7% and 36.5%, respectively) or the two reagents in reverse order (29.8%). The parthenogenones consistently contained a single pronucleus and second polar body, and showed a high degree of developmental potential, as assessed by transfer to recipient females or addition of a male pronucleus followed by transfer to recipients. This method is a useful way of obtaining large numbers of activated haploid mammalian oocytes for further developmental studies. © 1995 Wiley‐Liss,

ISSN:0022-104X    

DOI:10.1002/jez.1402710107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractImmunohistochemical staining of tissue sections prepared from gonads and gonad‐associated tissues obtained from adult chickens was performed in order to assess the possibility that these tissues may be sites of enrichment with IgM‐containing cells in various B lineages. Evidence is presented which suggests that IgM‐containing B lineage cells are present in 1) the ovarian stroma and subcapsular areas of the ovary and 2) the interstitium and subcapsular areas of the epididymis of the testes. These represent new sites reported for B lineage cells in adult chickens. Some questions relevant to the physiologic, ontogenetic, and phylogenetic implications of these observations relative to vertebrate hematolymphopoietic processes are included. © 1995 Wiley‐L

ISSN:0022-104X    

DOI:10.1002/jez.1402710108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:0022-104X    

DOI:10.1002/jez.1402710101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY