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71.
The developmental mechanisms by which the environment may alterthe phenotype during development are reviewed. Developmentalplasticity may be of two forms: developmental conversion orphenotypic modulation. In developmental conversion, organismsuse specific environmental cues to activate alternative geneticprograms controlling development. These alternative programsmay either lead to alternative morphs, or may lead to the decisionto activate a developmental arrest. In phenotypic modulation,nonspecific phenotypic variation results from environmentalinfluences on rates or degrees of expression of the developmentalprogram, but the genetic programs controlling development arenot altered. Modulation, which is not necessarily adaptive,is probably the common form of environmentally induced phenotypicvariation in higher organisms, and adaptiveness of phenotypicplasticity therefore cannot be assumed unless specific geneticmechanisms can be demonstrated. The genetic mechanisms by whichdevelopmental plasticity may evolve are reviewed, and the relationshipbetween developmental plasticity and evolutionary plasticityare examined. 相似文献
72.
Optimal Degree of Skew in Cooperative Societies 总被引:7,自引:0,他引:7
An optimization model is employed to determine the outcome ofwithin-group conflict in cooperative societies. The model assumesthat selection acts simultaneously on the stronger, dominantmembers of the group to secure more benefits for themselvesat the expense of subordinates, and on subordinates to leavethe group in response to this usurpation if they can do betterelsewhere. When it is in the interest of the dominant to maintainthe group, the dominant will be limited in its opportunity tobias the benefits in its favor by the options available to subordinatesoutside the group. The resulting differences in fitness or netpay-off among group members due to usurpation by dominants definethe degree of skew. Ecological factors affect both the net benefitof grouping and the options for leaving, and thus establishthe limits of skewing. The assumptions and rules governing thisinteraction are first outlined using a game theory approach.A continuous model for predicting the exact degree of skew isthen developed. This analysis shows that the degree of skewincreases when the benefit of group breeding relative to solitarybreeding increases, and when the degree of relatedness amonggroup members increases. Finally, the trade-offs between breedingwith relatives versus nonrelatives are analyzed from a dominantrelative's point of view. The results of two empirical studieson a social bird and a social wasp are compared to the predictionsof these models. The exceptionally good fit to the models isinterpreted as evidence in favor of the "social manipulation"approach to "helping" and "altruism" in cooperatively breedingspecies. 相似文献
73.
DANIELA MILANO DANIEL E. RUZZANTE VICTOR E. CUSSAC PATRICIO J. MACCHI RICARDO A. FERRIZ JUAN P. BARRIGA JUANA C. AIGO MARIA E. LATTUCA SANDRA J. WALDE 《Biological journal of the Linnean Society. Linnean Society of London》2006,87(1):69-82
We examined the morphological variability (23 morphometric traits) among individual Galaxias platei ( N = 380) collected from 20 postglacial lakes in the southern Andes. The lakes were chosen to cover the latitudinal range of the species in Patagonia. Diet examined for a subset of these fish ( N = 261) collected during the summer months (January through March), differed among river basins but there were no clear latitudinal trends in the consumption of any prey type. Diet may, however, have partially shaped morphology, as pelvic measures were negatively correlated with consumption of amphipods. Substantial differentiation among populations was observed, primarily in the shape and dimensions of the head, in caudal morphology and in fin length. Our results indicate that the morphology of G. platei varies with latitude, and may be related to risk of predation and diet. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 69–82. 相似文献
74.
Spatial and temporal variation in the diet of a predaceous stonefly (Plecoptera: Perlodidae) 总被引:1,自引:0,他引:1
SUMMARY. 1. Spatial and temporal variation in the diet of the univoltine predatory stonefly, Kogotus nonus , was studied over 3 years in a small Alberta stream to determine whether the relative abundance of prey types in the diet of Kogotus reflected relative prey densities in the stream and whether the variation in absolute feeding rate was related to either prey or predator density.
2. The seasonal shift from sole utilization of Orthocladiinae to inclusion of Baetis in the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.
3. Feeding rate on Baetis . as assessed by per capita gut contents, showed a seasonal shift from a positive correlation with Baetis density in winter to a negative relationship with predator density in spring. This suggested that feeding by small Kogotus is a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference. 相似文献
2. The seasonal shift from sole utilization of Orthocladiinae to inclusion of Baetis in the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.
3. Feeding rate on Baetis . as assessed by per capita gut contents, showed a seasonal shift from a positive correlation with Baetis density in winter to a negative relationship with predator density in spring. This suggested that feeding by small Kogotus is a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference. 相似文献
75.
JEFFREY A. RADDING MARTINE Y. K. ARMSTRONG M. SANDRA BOGUCKI FRANK F. RICHARDS 《The Journal of eukaryotic microbiology》1989,36(1):61S-62S
Pneumocystis carinii is an opportunistic pathogen of man, carried as a commensal in healthy subjects. It frequently causes a fatal pneumonia in the immunosupprcssed host. It is a major complication of HIV-1 infection in man (AIDS). Using surface radioiodination of rat-denved P. carinii trophozoites obtained from in vitro culture, a major surface glycoprotein (gp120) has been identified. The glycoprotein exhibits adherent behavior similar to that of the intact organism. Purification of gp120 by conventional methods was unsuccessful as the glycoprotein irreversibly bound lo numerous column matrices. A combination of gel chromatography and hydroxyapatile chromatography in sodium dodecylsulfaie v. as utilized to purify the glycoprotein. Some preliminary characterization of the glycoprotein is presented. 相似文献
76.
NATALIA PREZ‐HARGUINDEGUY SANDRA DÍAZ FERNANDA VENDRAMINI DIEGO E. GURVICH ANA M. CINGOLANI MELISA A. GIORGIS MARCELO CABIDO 《Austral ecology》2007,32(7):749-757
Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central‐western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems. 相似文献
77.
EMILY G. HARDING PAUL D. CURTIS SANDRA L. VEHRENCAMP 《The Journal of wildlife management》2007,71(6):2061-2066
Abstract: Woodpecker damage to homes and buildings is a widespread and locally severe problem in vertebrate pest control. Woodpeckers may cause an average of $300 (United States currency) in damage to affected houses, resulting in millions of dollars of property damage annually in the United States. However, there is no known, practical, consistently effective technique to prevent woodpecker damage. We tested the effectiveness of 6 woodpecker control techniques available commercially, used anecdotally by homeowners, and recommended by wildlife specialists in different Cooperative Extension publications. These deterrents included Prowler Owls, Irri-TapeTM, the Bird Pro Sound System, Scare-Eyes (all manufactured by Bird-X, Inc., Chicago, IL), suet feeders, and roost boxes. We conducted our study in late spring and autumn during August 2003 through December 2004 in the Town of Ithaca, Tompkins County, New York, USA. We evaluated 16 homes with active woodpecker damage, and visited each house about 3 times per week to determine a rate of new woodpecker holes per day. We then placed a deterrent at the house and monitored the rate of new holes per day. Although none of the deterrents that we tested was completely successful in keeping woodpeckers from creating new holes in house siding, homes where Irri-Tape was installed exhibited the greatest reduction in woodpecker damage. Avoiding earth-tone stain and paint colors may be the best long-term solutions for preventing woodpecker damage in wooded areas. Homeowners should avoid using natural-colored stains, as brightly painted houses (white, light blue, pastels) were less likely to attract woodpeckers. 相似文献
78.
ENRIQUE E. MONTAMAT SANDRA DURAND JOSE L. BOCCO GLORIA M. DE LUCA D'ORO ANTONIO BLANCO 《The Journal of eukaryotic microbiology》1999,46(2):155-159
Analysis of zymograms of extracts of Trypanosoma cruzi isolated from different hosts in Argentina allowed characterization of 12 zymodemes or "isozymic strains," only six of which were found in human patients. Two of these six zymodemes (Z1 and Z12) were widely distributed and found in more than 80% of human patients. These two "major natural clones" differed significantly in pathogenic activity. Because the groupings obtained by studying enzymes and kinetoplast DNA (kDNA) were similar, it is possible to identify the zymodeme by analyzing kDNA. A 290-bp fragment was amplified by PCR using primers for the sequences flanking the hypervariable regions of kDNA minicircles. Labeled probes for this fragment, prepared from Z1 and Z12 reference stocks, hybridized specifically with PCR-amplified kDNA from parasite stocks, allowing identification of zymodemes. 相似文献
79.
SANDRA KNAPP F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1991,105(2):179-210
KNAPP, S., 1991. A revision of the Solatium sessile species (sectio Geminata pro parte : Solanaceae ). The taxonomy of the Solanum sessile species group (a part of the large and unwieldy section Geminata) is reviewed, based on detailed field and herbarium studies. Members of the group are found from Mexico to Bolivia in a variety of habitats. Ten species are recognized: S. obovalifolium, S. sessile, S. monadelphum, S. turgidum, S. triste, S. chlamydogynum, S. rovirosanum, S. palmillae, S. oppositifolium and conferliseriatum. 相似文献
80.