In a variety of taxa, male reproductive success is positively related to the expression of costly traits such as large body
size, ornaments, armaments, and aggression. These traits are thought to improve male competitive ability and, thus, access
to limited reproductive resources. Females of many species also express competitive traits. However, we know very little about
the consequences of individual variation in competitive traits and the mechanisms that regulate their expression in females.
Consequently, it is currently unclear whether females express competitive traits owing to direct selection or as an indirect
result of selection on males. Here, we examine females of a mildly dimorphic songbird (Junco hyemalis) to determine whether females show positive covariance in traits (morphology and behavior) that may be important in a competition.
We also examine whether trait expression relates either to testosterone (T) in terms of mechanism or to reproductive success
in terms of function. We found that larger females were more aggressive and that greater ability to produce T in response
to a physiological challenge consisting of a standardized injection of gonadotropin-releasing hormone predicted some measures
of female body size and aggression. Finally, we found that aggressive females had greater reproductive success. We conclude
that T may influence female phenotype and that females may benefit from expressing a competitive phenotype. We also suggest
that the mild dimorphism observed in many species may be due in part to direct selection on females rather than simply a correlated
response to selection in males. 相似文献
Twenty-five strains of filamentous fungi, encompassing 14 different species and belonging mainly to Ascomycetes, were tested for their ability to degrade benzo[a]pyrene (BaP) in mineral liquid medium. The most performing isolates for BaP degradation (200 mg?l?1) in mineral medium were Cladosporium sphaerospermum with 29 % BaP degradation, i.e., 82.8 μg BaP degraded per day (day?1), Paecilomyces lilacinus with 20.5 % BaP degradation, i.e., 58.5 μg BaP day?1, and Verticillium insectorum with 22.3 % BaP degradation, i.e., 64.3 μg BaP day?1, after only 7 days of incubation. Four variables, e.g., biomass growth on hexadecane and glucose, BaP solubilization, activities of extracellular- and mycelium-associated peroxidase, and polyethylene glycol degradation, were also studied as selective criteria presumed to be involved in BaP degradation. Among these variables, the tests based on polyethylene glycol degradation and on fungal growth on hexadecane and glucose seemed to be the both pertinent criteria for setting apart isolates competent in BaP degradation, suggesting the occurrence of different mechanisms presumed to be involved in pollutant degradation among the studied micromycetes. 相似文献
Summary. Surrogate leaves treated with methanolic leaf
surface extracts of Brassica napus L. (cv Express) plants
that received three different sulphur fertilisation treatments
showed even more marked differences by the oviposition
choice of Delia radicum L. than the potted plants. This
confirms that the oviposition preference of D. radicum is
mediated by chemical compounds on the leaf surface and
that the quality of host-plants in terms of their nutrition
status can be perceived by the female insect.The oviposition data were positively correlated with the
content of fractionated surface extracts containing either
CIF (cabbage identification factor; 1,2-dehydro-3-thia-
4,10,10b-triaza-cyclopenta[.a.]fluorine-1-carboxylic acid)
or glucosinolates. Electrophysiological recordings from the
tarsal chemoreceptor sensilla C5 and D3,4 showed that receptor
neurons react to glucosinolate- and CIF-fractions. We
found that the chemosensory activity of specific glucosinolate-
and CIF-receptor neurons corresponded with the
respective behavioural activity in the oviposition choice
assays. The responses of D. radicum to glucosinolates in
the electrophysiological recordings studies corresponded
to the observed oviposition preference on plants or artificial
leaves characterised with an higher amount of glucosinolates
on leave surfaces. The presented data suggested
that CIF and glucosinolates are involved in host-plant
preference of D. radicum and are perceived by tarsal
chemoreceptors. 相似文献
This paper describes a study examining the potential of mineral magnetic, geochemical and organic properties to determine
if a 2003 wildfire in a catchment in British Columbia, Canada, caused a change in the sources of the suspended sediment transported
in the channel relative to a nearby unburnt (reference) catchment. The results show that some of the properties offer the
potential to determine sediment sources in the unburnt catchment. However, the 2003 wildfire modified the concentrations of
some properties and this can either compromise or enhance their ability as tracers in the burnt catchment. At present, the
source tracing results are inconclusive. This has implications for the use of certain properties as fingerprints and raises
important issues about approaches to sediment source identification. 相似文献
Injection molded nanocomposites have been successfully fabricated from cellulose acetate (CA), eco-friendly triethyl citrate
(TEC) plasticizer, and organically modified clay with and without maleic anhydride grafted cellulose acetate butyrate (CAB-g-MA)
as a compatibilizer. The effects of processing conditions such as mixing methods, pre-plasticizing times, extruder retention
times (RT) and addition of compatibilizer on the performance of these nanocomposites have been evaluated. The cellulosic plastic
with CA/TEC (80/20 wt%) was used as the polymer matrix for nanocomposite fabrication. The morphologies of these nanocomposites
were evaluated through X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. The mechanical properties
of the nanocomposites were measured and have been correlated with the XRD and TEM observations. From all of the sequential
mixing methods used, powder–powder mixing leads to the most transparent nanocomposites. Cellulosic plastic-based nanocomposites
obtained using increased pre-plasticizing times and RT showed better exfoliated structures. In the system containing compatibilizer,
the minimum retention time required for obtaining almost completely exfoliated hybrid nanocomposites was shorter than in the
system without compatibilizer. 相似文献
The dugong is classified as vulnerable to extinction by the World Conservation Union on the basis of declines in area or extent
of occupancy, habitat quality, and actual or potential levels of exploitation. In Thailand, the largest groups of dugongs
are found near islands off the Andaman coast. The authors conducted a 2-year project that included dugong population and habitat
assessment as well as interviews with local fishers. The results indicate declining populations of dugongs. The largest threat
to dugongs is incidental catch in fishing nets. The numbers of deaths reported place the dugong population along the Andaman
Sea in danger of extirpation. Other threats include seagrass destruction both from fishing and coastal development and the
use of dugong parts for medicinal purposes. Villagers still show strong ties with dugongs, and the majority favor establishing
more large protected areas for the species. These should arise from an integrated national dugong and seagrass conservation
strategy formulated by concerned stakeholders from government, nongovernmental organizations, scientists, and local communities.
The strategy needs to be both top down and bottom up in its formation to balance existing and potential uses as well as conflicts
between artisanal and commercial fishers. The strategy should include the development of educational materials and enforceable
regulations, as well as the designation of community-protected seagrass beds and a system of dugong sanctuaries along the
Andaman coast. An integrated management plan is needed urgently, with the continued input of concerned scientists, to monitor
and increase knowledge of dugong behavior and distribution. 相似文献
The objective of this study was to assess the time variation of mineral and water stress levels across the life of a declining, Mg-deficient, spruce stand, in order to clarify the factors that caused the decline. Since 1985, strong soil acidification linked to a large leaching of nitrate and base cations was measured at the study site. In 1994, 5 trees were felled and tree rings were measured and analysed for Ca, Mg, K, Sr, 13C12C and 87Sr/86Sr isotopic ratios. Strontium pools and fluxes as well as root Sr isotope ratio in relation to depth were also measured. Wood chemical concentrations and isotope ratios were strongly related to the dominance status of each tree. On average during the study period, the 87Sr/86Sr ratio of spruce wood decreased. Using a mechanistic model computing long term variations of 87Sr/86Sr ratio in trees and soils, we reproduced the observed trend by simulating soil acidification – increasing Sr drainage from the whole profile, and particularly from the organic horizon –, and root uptake becoming more superficial with time. Between 1952 and 1976, tree ring 13C decreased strongly and continuously, which, in addition to other factors, might be related to an increase in water stress. Thus, a decrease in rooting depth, possibly related to soil acidification, appeared as a possible cause for the long term increase in water stress. The extreme drought event of 1976 appears to have revealed and triggered the decline. 相似文献
A field investigation conducted on Boulder Creek in Boulder, Colorado evaluated impacts of flood control maintenance activities on flood conveyance, water quality, and fish habitat. Thirty-nine transects were monitored at one control site and two maintenance sites over a period of eight months. Each site was visited on more than 50 occasions in order to characterize pre- and post-maintenance conditions, and to monitor maintenance activities. Measurements along the transects included substrate composition, flow depth, velocity, and elevation. Reach-average values were assigned to variables such as in-stream vegetation, streambank stability, and woody vegetation before and after maintenance. Water temperature, dissolved oxygen, pH, specific conductance, and turbidity were sampled, and habitat suitability indices were developed pre- and post-maintenance for seven indicator fish species. Water quality impacts during maintenance consisted of high turbidity levels (> 400 NTU), which returned to background levels (0.1–15 NTU) overnight, as well as changes in mean temperature and pH. Alteration of physical channel characteristics as a result of maintenance had limited effects on habitat quality for four of seven fish species, but caused improvements in habitat quality for three fish species. The main implications of this study for floodplain management are that: (1) Flood control maintenance practices can be in direct conflict with water quality and fish habitat objectives, and should be carefully designed and implemented by an interdisciplinary team. (2) Physical habitat for some fish species can be improved as well as reduced by maintenance activities. Habitat suitability curves may be useful tools for evaluating limiting factors of the habitat and for identifying opportunities for habitat improvements as part of maintenance. 相似文献
Petroleum products are generally volatile hydrocarbon mixtures. These mixtures may contaminate land surfaces, the unsaturated zone and ground waters at numerous sites and thus represent a long-term source of environmental subsurface pollution. Based on laboratory and field evidence obtained by our research groups and others we emphasize in the present review paper the effect of leaching on the abiotic processes controlling the fate of volatile petroleum hydrocarbon mixtures (VPHMs) in the soil environment. The modification of petroleum hydrocarbon mixtures due to changes in the soil water content is considered the result of a “leaching phenomenon”. The experimental evidence of VPHM behavior in the porous media is linked to four major processes: retention, redistribution and attenuation in the subsurface, and dissolution in the soil water.
Once VPHMs reach the soil surface, their residual concentration and composition is influenced by the amount and quality of the leaching water. The transport and natural attenuation of the VPHMs in the unsaturated zone is affected by the amount and rate of leaching. Since VPHM are a mixture of volatile and non-volatile hydrocarbons whose components differ by several orders of magnitude in their vapor pressure and water solubility, their fates in the soil environment under leaching will be diverse too. This will influence the temporal concentrations of the VPHM components and their distributions with depth, as vapors, solutes, or water-immiscible solutions. Wetting the soil before or after the VPHMs reach it, differentially affects the abiotic processes governing petroleum products behavior into the porous media. 相似文献