The allometric approach to species differences in brain size

Allometric methods can be used to test quantitative theories of the relationship between brain size and body size across species, and to search for ecological, behavioural, life history, and ontogenetic correlates of brain size. Brain size scales with an allometric exponent of around 0.75 against body size across mammals, but is closer to 0.56 for birds and for reptiles. The slope of the allometric line often varies depending upon the taxonomic level of analysis. However, this phenomenon, at least in mammals, may be a statistical artifact. Brain size for a given body size (relative brain size) varies among orders in birds and mammals, and some dietary associations with relative brain size have been found in particular taxa. Developmental status at birth is the most consistent correlate of relative brain size: precocial neonates have larger brains for a given maternal size than altricial neonates in both birds and mammals. Altricial neonates, however, have more brain growth following birth, and in birds also have larger relative adult brain sizes. Energetic explanations for differences in neonatal brain growth, although attractive on theoretical grounds, have largely failed to stand up to empirical tests.     

Ideal nutrient productivities and nutrient proportions in plant growth

Abstract I propose that one single formulation can be applied to relate growth and content of several nutrients, including the most important macronutrients, of most plant species. The plant growth rate is proportional to the nutrient content minus a given minimal concentration of the nutrient in minimum. The proportionality factor, the nutrient productivity, and the minimum concentration are species specific properties. The nutrient productivity formulation is shown to apply for very different plant species and for different nutrients.     

Modulation of lymphocyte nuclear matrix organization in vivo by 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole: an autoradiographic and immunofluorescence study

Assembly of active nuclei in lymphocytes stimulated by mitogen is paralleled by the elaboration of a structurally and biochemically complex nuclear matrix (NM). To examine the dynamics of individual NM polypeptide components during blastogenesis, we have applied immunofluorescence labelling with anti-NM antibodies to concanavalin A-stimulated mouse splenocytes. Whereas peripherin and PI2 antigens did not reorganize during stimulation, labelling of PI1 and small nuclear ribonucleoprotein (snRNP) antigens increased markedly in intensity and redistributed in concert with the previously reported NM restructuring. Double-labelling showed, furthermore, that snRNPs and the internal staining component of PI1 were largely co-localized. As an approach to studying the role of RNA and RNA synthesis in NM organization, we have further examined the effects of the inhibitor of RNA synthesis, 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB), on NM antigen distribution. The rapid inhibition of 3H-uridine incorporation by DRB was accompanied by coordinate aggregation of snRNPs and of the internal PI1 component into large, brightly stained patches. Both 3H-uridine incorporation levels and antigen localization were readily reversed upon removal of DRB. We conclude that NM antigens behave independently during nuclear and NM assembly and that NM organization, as reflected by NM antigen distribution, is modulated by con A- and DRB-induced alterations in RNA synthesis. We propose, furthermore, that the PI1 antigen plays a role in RNA metabolism, and is possibly involved in RNA transport to the nuclear periphery.     

Age and growth rate determinations of an intertidal bivalve, Phacosoma japonicum, using internal shell increments

A venerid bivalve Phacosoma japonicum (Reeve) occurring commonly in the Japanese coastal area preserves periodic growth lines in the shell cross-section. Long-term shell growth patterns of this species have been traced for many individuals on the intertidal flat of the Seto Inland Sea, west Japan. Sclerochronological analysis of these individuals and specimens collected monthly shows that several growth cessation marks within their shells are formed during the winter of each year prior to spawning. Hence the marks were used for age and growth rate determinations. As large individuals showed little shell growth for more than two years after the formation of 7 or 8 annual increments, this species probably has a lifespan of more than ten years. Shell growth patterns of this species based on annual increments can be accurately approximated by a von Bertalanffy curve. The number of microgrowth increments formed during a year tends to decrease with age, although it varies markedly among specimens of the same age. Furthermore, even in summer during rapid shell growth, the microgrowth increments do not represent daily and/or sub-daily tidal rhythms in many specimens. The results of this study and those by several authors strongly suggest that the annual increments are the key for age and growth rate determinations of both living and fossil bivalve species.     

Basal ppGpp level adjustment shown by new spoT mutants affect steady state growth rates and rrnA ribosomal promoter regulation in Escherichia coli

Summary This work describes an approach towards analyzing the regulatory effects of variation of guanosine 3,5-bispyrophosphate (ppGpp) basal levels in Escherichia coli during steady state growth. A series of strains was derived by mutating the spoT gene (which encodes the major cellular ppGppase) so as to obtain systematic increments in ppGpp basal levels. These strains differ genetically at the spoT locus and, in some cases, also at the relA locus because of the severity of spoT mutant alleles. Measurements of ppGpp revealed a ten-fold range of basal levels during growth on minimal medium. The empirical relationship between ppGpp concentration and growth rate is a simple linear inverse correlation. Tandem rrnA ribosomal RNA promoters, present on a multicopy plasmid, are shown to be differentially regulated over this range of basal levels. The upstream P ₁ promoter activity shows an inverse exponential relation to ppGpp concentration whereas the downstream P ₂ promoter is only weakly affected. We conclude that there are systematic regulatory consequences associated with small changes in ppGpp basal levels during steady state growth that probably are part of a continuum with more dramatic effects observed during the stringent response to amino acid deprivation.     

Regulation of seed number and female incitation of mate competition by a pH-dependent proteinaceous inhibitor of pollen grain germination in Leucaena leucocephala

Summary Leucaena leucocephala generally produces pods with more than 7–9 seeds. This is regulated by the stigmatic inhibition of pollen grain germination when the pollen grains are less than a critical number in the stigma. This number-dependent inhibition of pollen grain germination is effected by a pH-dependent proteinaceous inhibitor active at the stigmatic pH. Only when the pollen grains in the stigma exceed the critical number, they inactivate the inhibitor by collectively raising the stigmatic pH and thus overcoming the inhibition. The adaptive significance of such pre-fertilization mechanism for the female in inciting mate competition among the pollen grains is discussed. The evolution of en masse pollen grain dispersal units is explained as a sexual selection strategy by males in response to such stigmatic inhibition by females.     

Filtration rate capacities in 6 species of European freshwater bivalves

Summary Filtration rate capacities in undisturbed freshwater bivalves were determined by means of two different methods (indirect clearance and suction methods) in Anodonta anatina (L.), Unio tumidus Philipsson, Unio pictorum (L.), Unio crassus Philipsson, Dreissena polymorpha (Pallas) and Sphaerium corneum (L.). In A. anatina, D. polymorpha, and S. corneum the filtration rate (FR, 1 h^-1) at 19–20°C as a function of dry tissue weight (DW, g) or ash-free dry weight (AFDW, g) could be expressed by the equations: 1.10 DW^0.78, 6.82 DW^0.88, and 2.14 AFDW^0.92, respectively. In U. tumidus, U. pictorum, and U. crassus filtration rates were comparable with those of A. anatina. In D. polymorpha the b value of the corresponding regression of gill area on dry weight was 0.87. The rates of water transport in freshwater bivalves are 2–8 times lower than in marine bivalves of comparable size. A corresponding difference in the filtration rate per gill area unit is found. The measured filtration rates in undisturbed bivalves are substantially higher (at least 4 times) than previously reported. This indicates that the impact of bivalve water processing on freshwater ecosystems is greater than hitherto suggested.     

Cultivar differences in the rate of nitrate uptake by intact wheat plants as related to growth rate

Six Argentinian wheat ( Triticum aestivum L.) cultivars grown in nutrient solutions in controlled environment were compared for their nitrate uptake rates on a root dry weight basis. Up to 3-fold differences were observed among the cultivars at 16, 20 and 24 days from germination, either when measured by depletion from the nutrient solution in short-term experiments, or by total N accumulation in the tissue during 8 days.
No differences in total N concentration in root or shoots were found among cultivars. Although the different cultivars showed significant differences in shoot/root ratio and nitrate reductase activity (EC 1.6.6.1) in the roots, none of these parameters was correlated with the nitrate uptake rate. However, nitrate uptake was found to be positively correlated (r = 0.99) with the shoot relative growth rate of the cultivars. The three cultivars with the highest nitrate uptake rates and relative growth rates showed a positive correlation between root nitrate concentration and uptake. However, this correlation was not found in the cultivars with the lowest growth and uptake rates.
Our results indicate that the difference in nitrate uptake rate among these cultivars may only be a consequence of their differences in growth rate, and it is suggested that at least two mechanisms regulate nitrate uptake, one working when plant demand is low and another when plant demand is high.     

温度对亚东璃眼蜱发育的影响

亚东璃眼蜱的卵、饱食的幼虫和若虫分放在四个等级的温度、相对湿度90%和黑暗的条件下,观察温度对各期发育的影响.在20°、25°、30°和35℃条件下,卵期发育的平均日数分别为71.87±0.05、31.55±0.03、21.02±0.03和16.47±0.03天;幼虫蜕化期分别为25.02±0.05、13.01±0.03、8.75±0.02和6.40±0.02天;若虫蜕化期分别为47.32±0.22、24.2±0.13、14.36±0.08和10.78±0.06天.在各种温度条件下若虫蜕化为成虫的时间,雄虫比雌虫长.卵期发育的积温为321.77日度,而幼虫和若虫蜕化期分别为129.97和212.39日度.卵期发育的温度低阈为15.07℃,而幼虫和若虫蜕化期分别为14.88和15.58℃.