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111.
Christine H. Petersen 《Marine Biology》2007,150(6):1289-1300
Discrete estuary subpopulations of the mud crab Hemigrapsus oregonensis (Dana, 1851) are connected via larval dispersal. Sequence variation at the mtDNA COI locus was examined in eight populations
sampled in 2001–2002 from central California through northern Oregon in the northeast Pacific (36.6–45.8°N) to infer patterns
of dispersal and historical connectivity in the region. Strong evidence for persistence since the mid-Pleistocene, with no
range truncation resulting from southward shifting temperature isoclines, was provided by a phylogeographic pattern of haplotypes
of an older clade distributed throughout the sampled range. A recently derived clade became widespread only north of Cape
Blanco after the last glacial maximum. Its clear pattern of restriction to the northern area, in the absence of similarly
restricted southern clades, suggests that contemporary dispersal around Cape Blanco is rare (population F
ST = 0.192). Low pairwise differentiation within Oregon and within central California, as well as contrasts between northern
and southern groups in the shape of the pairwise mismatch distribution, nucleotide diversity, and Tajima’s D suggest that these regions reflect different demographic histories. Potential mechanisms explaining this latitudinal break
include contemporary coastal circulation patterns, selection, and ancient patterns of larval dispersal in the California Current. 相似文献
112.
Organochlorine pesticides were widely used in the past in Sumas Prairie, British Columbia, Canada. In the 1990s, the hatching success of amphibians from agricultural sites was significantly depressed in the Sumas Prairie compared to reference sites. Therefore, in this study, organochlorine pesticides and polychlorinated biphenyls (PCBs) were measured in eggs of red-legged frogs (Rana aurora) and northwestern salamanders (Ambystoma gracile) from the Sumas Prairie. Egg masses were sampled from three agricultural sites that were exposed to agricultural runoff, and three reference sites that had lower agricultural runoff exposures. Not only was there little difference in contamination between agricultural and reference sites, but the levels of pesticides and PCBs found were lower than the concentrations reported to cause developmental or behavioural problems in amphibians. 相似文献
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114.
The kinetics of oxidation of methylhydrazine () and 1,1-dimethylhydrazine () by dissolved oxygen in water has been measured at various acidities as a function of catalyst (cupric ion) concentration. In dilute solutions the oxidation occurs through a cupric ion catalyzed process as well as by an uncatalyzed step. The extent of formation of nitrosodimethylamine () depends upon the initial concentration. In dilute solutions is not formed, but in more concentrated solutions, formation increases with increasing content, reaches a maximum at 60–80% (by volume) and then decreases. The yield appears to approximately parallel the viscosity of the medium, and it is speculated that the factors which control viscosity may also be responsible for governing formation. 相似文献
115.
B. Sango Otieno Christine M. Anderson-Cook 《Environmental and Ecological Statistics》2006,13(3):311-324
Circular or angular variables indicating direction or cyclical time can be of great interest to scientists studying ecology,
biology or environmental issues. A common problem of interest in circular data is estimating a preferred direction and its
corresponding distribution. This problem is complicated by the so-called “wrap-around effect” on the circle, which exists
because there is no natural minimum or maximum. The usual statistics employed for linear data are inappropriate for directional
data, as they do not account for its circular nature. Three choices for summarizing the preferred direction (the sample circular
mean, sample circular median and a circular analog of the Hodges–Lehmann estimator) are discussed, with examples from environmental
and ecological applications. Similar to the linear data case, the relative emphases of different methods sometimes yield different
measures of preferred direction in the presence of outliers or lack of symmetry in the original data.
Received: November 2003 / Revised: June 2004 相似文献
116.
Christine A. Nalepa 《Behavioral ecology and sociobiology》1984,14(4):273-279
Summary Adult pairs of the woodroach Cryptocercus punctulatus were reported to be incapable of founding colonies independently because the presence of a recently molted juvenile was required to transfer encysted symbiotic gut protozoa to newly hatched roaches. Field and laboratory evidence presented here shows that adult pairs of C. punctulatus do found colonies and that juveniles are generally not present to provide neonates with protozoan cysts. Newly hatched nymphs acquire their intestinal symbionts by feeding on the anal fluids of the adult roaches, i.e., by proctodeal trophallaxis. Conditions other than a symbiotic association with protozoans may have contributed to the evolution of eusociality in termites (Isoptera). 相似文献
117.
Vespine wasps have been shown to deposit an attractive chemical in the nest entrance. Foragers use this to help locate the nest when returning to it. We determined how many individuals need to track (pass through) the entrance before the chemical is recognized. We found a logistic response as the number of tracks increased. At 200 tracks and above there was a 75–90% positive response rate to the chemical. We found no evidence of trail-marking behavior performed by foragers inside the nest entrance. We conclude that the trail is not an evolved signal, but is a cue composed of an accumulation of hydrocarbons deposited from the legs or feet of workers as they walk on a substrate. This is the first quantitative measurement of the attractiveness of the nest-entrance chemical in a social wasp. 相似文献
118.
Claude Stoll MD Marie-Christine Ehret-Mentre Alain Treisser Christine Tranchant 《黑龙江环境通报》1991,11(1):17-22
We studied two children born to a myasthenic mother. The first child, a female, had multiple flexion contractures. She died 1 h after birth. In the second pregnancy, 3 years later, ultra-sonographic examination at 20 weeks showed decreased fetal movements and multiple flexion contractures. The pregnancy was interrupted. Eight other cases of congenital rnyasthenia with arthrogryposis are known; four of them are siblings. The recurrence risk may be as high as 100 per cent. Our second case demonstrates that prenatal diagnosis is possible early enough to allow termination of pregnancy. 相似文献
119.
120.