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421.
Field observations and model-presentation experiments have shown that yellow warblers (Dendroica petechia) produce seet calls preferentially in response to brood-parasitic brown-headed cowbirds (Molothrus ater). In this study, we investigated whether seet calls are functionally referential alarm calls denoting cowbirds by determining whether female warblers responded appropriately to seet calls in the absence of a cowbird, whether alarm calling by warblers varied with response urgency, and how warblers in a population allopatric with cowbirds responded to cowbird and avian predator models and seet playbacks. As a control, we presented chip calls, which are elicited by nest predators as well as by non-threatening intruders, but are not strongly associated with cowbirds. Yellow warblers responded differently to playbacks of seet than chip calls. To seet playbacks, almost 60% of females gave seet calls and rushed to sit in their nests, responses typically elicited by cowbirds, whereas these responses were given infrequently in response to chip calls. Yellow warblers seet called equally in situations that simulated low, medium and high risk of parasitism, which suggests that these calls did not vary with response urgency. In a population allopatric with cowbirds, seet calls were rarely produced in response to cowbird or avian nest predator models and never to seet playbacks. These results suggest that seet calls are functionally referential signals denoting cowbirds and that cowbird parasitism was a strong selective pressure in the evolution of functional referentiality in the seet call of yellow warblers.Communicated by W.A. Searcy 相似文献
422.
Testis size variation in frogs: testing the alternatives 总被引:1,自引:0,他引:1
Sharon B. Emerson 《Behavioral ecology and sociobiology》1997,41(4):227-235
While sperm competition may be a major factor affecting relative testis size in vertebrates as a whole, additional hypotheses
have not been given much attention in frogs. This is important because sperm competition is relatively uncommon in frogs and
relative testis size varies in frogs that do not have multiple-male breeding systems. This paper tests two additional hypotheses
for differences in relative testis size among frogs: relative clutch size (number of eggs/snout vent length) and androgen
level. Testis size was measured in 90 species of frogs belonging to five families. Relative testis size was found to be positively
correlated with relative clutch size in species that lack sperm competition. Mean androgen levels of species also positively
covaried with relative testis size. However, there was no correlation between relative testis size and level of male agonistic
behavior among species, despite other work indicating that testosterone levels are positively correlated with agonistic behavior
in at least some species. These findings suggest that a number of factors in addition to sperm competition are important in
the evolution of testis size in male frogs.
Received: 17 January 1997 / Accepted after revision: 23 June 1997 相似文献
423.
Polychlorinated biphenyl (PCB) effects on marine phytoplankton photosynthesis and cell division 总被引:1,自引:0,他引:1
Inhibition of photosynthesis and cell division by polychlorinated biphenyls (PCBs) was studied using 7 marine phytoplankton species representing 4 algal classes. PCB concentrations as low as 1.0 g l-1 reduced cell division of Thalassiosira pseudonana 3H and Isochrysis galbana. Both photosynthesis and cell division of T. pseudonana 3H, Chaetoceros socialis, Skeletonema costatum, T. pseudonana 13-1, Monochrysis, lutheri and I. galbana were inhibited at a PCB concentration of 10.0 g l-1. The effects on photosynthesis were immediate and probably resulted in reduced rates of cell division. Interspecific differences in susceptibility were observed. These differences have significance with respect to primary production and the species composition of phytoplankton communities. The initial slopes of photosynthesis-irradiance (P-I) curves for the diatoms S. costatum and T. pseudonana 3H were reduced in the presence of PCBs. These results suggest that PCBs affect the photosynthetic light reactions. 相似文献
424.
Lee P. Shulman MD Sherman Elias Richard N. Andersen Owen P. Phillips Aubrey Milunsky Karen A. Holbrook Lynne T. Smith Jo-David Fine Joe Leigh Simpson 《黑龙江环境通报》1991,11(11):813-818
Junctional epidermolysis bullosa, Herlitz variant (junctional EB-Herlitz) is a lethal autosomal recessive skin disorder currently amenable to prenatal diagnosis only by direct analysis of fetal skin. However, elevated levels of alpha-fetoprotein, as well as the presence of acetylcholinesterase in amniotic fluid, have been associated with other severe fetal genodermatoses. Fetal skin samplings were performed in ten pregnancies at risk for fetal junctional EB-Herlitz, with three fetuses affected on the basis of electron microscopic detection of blisters within the lamina lucida and abnormal hemidesmosomes. In neither affected nor unaffected pregnancies were maternal serum or amniotic fluid alpha-fetoprotein levels elevated. Moreover, alphafetoprotein levels in both maternal serum and amniotic fluid were not statistically different comparing affected and unaffected fetuses. Acetylcholinesterase was not present in the amniotic fluid samples of the three affected pregnancies. Unlike other severe fetal genodermatoses, neither alpha-fetoprotein nor acetylcholinesterase was predictive of junctional EB-Herlitz. 相似文献
425.
This research investigates how creativity is influenced by externally imposed structure (how structured the task is), internal, cognitively produced, structure (how structured the individuals' cognitive style is), and the interaction between these two factors. Reviewing past literature, we find a contradiction. Studies that focused on the situational perspective found that externally imposed structure increases creativity. In contrast, studies that focused on the individual found that systematic (structured) cognitive style decreases creativity. In two empirical studies we investigated this seeming contradiction. We focused on two aspects of externally imposed structure: The construction of the task (Study 1) and the instructions provided (Study 2). The findings of both studies revealed that creativity was higher under structured conditions. We also show that intuitive individuals are more creative than systematic individuals, but mainly under free conditions, where structure is not externally imposed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
426.
427.
Schwede Donna B. LeDuc Sharon K. Otte Tanya L. 《Water, Air, & Soil Pollution: Focus》2001,1(5-6):59-66
The National Oceanic and Atmospheric Administration's Multi-Layer Model (NOAA-MLM) is used by several operational dry deposition networks for estimating the deposition velocity of O3, SO2, HNO3, and particles. The NOAA-MLM requires hourly values of meteorological variables. Since collection of on-site meteorology can be expensive, a study was performed to compare NOAA-MLM predicted deposition velocitiesusing modeled meteorological data in lieu of on-site meteorological data. NOAA-MLM was run for three sites in the Clean Air Status and Trends Network using on-site data as well as the output of two mesoscale meteorological models, Eta and MM5. The differences between the deposition velocities predictedusing the mesoscale models and those predicted using the on-sitemeteorological measurements ranged from –0.001 to 0.106 cm s-1 and were within the model error determined in NOAA-MLM evaluation studies. This research shows that the NOAA-MLM is particularly sensitive to differences in atmospheric turbulence,soil moisture budget, and canopy wetness.(On assignment to the National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina.) (author for correspondence, e-mail 相似文献
428.
Jennifer L. Phillips Jill Ory Andr Talbot 《Journal of the American Water Resources Association》2000,36(6):1287-1308
ABSTRACT: The Umatilla River Basin Fisheries Restoration Plan was initiated in the early 1980s to mitigate salmonid losses caused by hydroelectric development and habitat degradation. The objectives are to enhance the abundance of endemic steelhead and reintroduce extirpated chinook and coho salmon. The project prompted collaborative effort among federal, state, and tribal agencies, and local water users. It has incorporated habitat restoration, flow enhancement, fish passage improvements, and population supplementation through artificial production. Water exchanges have successfully increased minimum flows during spring and fall migration. While flows remain depressed compared to historic conditions, there is potential for improved habitat, passage, and homing. The mean adult‐to‐adult return rate of hatchery‐reared steelhead exceeded replacement and that of the naturally‐spawning population. Although the smolt‐to‐adult survival rates of hatchery‐reared fish fluctuate, salmonid escapement has increased in recent years, permitting steelhead and spring chinook harvest. Enumeration of potential spawners and observed redds reveals an increase in natural production of all supplemented species. Comparison of hatchery‐reared and naturally‐spawning steelhead populations revealed differences in life history characteristics (in age composition and sex ratios) though run timing and genetic stock compositions of the two components of the populations have not differed. Sustained monitoring is needed to determine benefits of integrating habitat restoration and artificial production in restoring salmonid populations. 相似文献
429.
Jay Willis John Phillips Rachel Muheim Francisco Javier Diego-Rasilla Alistair J. Hobday 《Behavioral ecology and sociobiology》2009,64(1):57-68
Tunas make sharp descents and ascents around dawn and dusk called spike dives. We examine spike dives of 21 southern bluefin
tuna (Thunnus maccoyii) implanted with archival tags in the Great Australian Bight. Using a new way to categorize this behavior, we show that spike
dives are similar among all the fish in the study. The dive profiles are mirror images at dawn and dusk and are precisely
timed with respect to sunrise and sunset. We analyze the possible reasons for spike dives, considering the timing of spike
dives, the characteristic dive profile, and the tuna's magnetic habitat. In addition, we present anatomical evidence for elaboration
of the pineal organ, which is light mediated and has been implicated in navigation in other vertebrates. The new evidence
presented here leads us to suspect that spike dives represent a survey related to navigation. 相似文献
430.
Toxicity of emerging energetic soil contaminant CL-20 to potworm Enchytraeus crypticus in freshly amended or weathered and aged treatments 总被引:1,自引:0,他引:1
Kuperman RG Checkai RT Simini M Phillips CT Anthony JS Kolakowski JE Davis EA 《Chemosphere》2006,62(8):1282-1293
We investigated the toxicity of an emerging polynitramine energetic material hexanitrohexaazaisowurtzitane (CL-20) to the soil invertebrate species Enchytraeus crypticus by adapting then using the Enchytraeid Reproduction Test (ISO/16387:2003). Studies were designed to develop ecotoxicological benchmark values for ecological risk assessment of the potential impacts of accidental release of this compound into the environment. Tests were conducted in Sassafras Sandy Loam soil, which supports relatively high bioavailability of CL-20. Weathering and aging procedures for CL-20 amended into test soil were incorporated into the study design to produce toxicity data that better reflect soil exposure conditions in the field compared with the toxicity in freshly amended soils. Concentration-response relationships for measurement endpoints were determined using nonlinear regressions. Definitive tests showed that toxicities for E. crypticus adult survival and juvenile production were significantly increased in weathered and aged soil treatments compared with toxicity in freshly amended soil, based on 95% confidence intervals. The median effect concentration (EC50) and EC20 values for juvenile production were 0.3 and 0.1 mg kg-1, respectively, for CL-20 freshly amended into soil, and 0.1 and 0.035 mg kg-1, respectively, for weathered and aged CL-20 soil treatments. These findings of increased toxicity to E. crypticus in weathered and aged CL-20 soil treatments compared with exposures in freshly amended soils show that future investigations should include a weathering and aging component to generate toxicity data that provide more complete information on ecotoxicological effects of emerging energetic contaminants in soil. 相似文献