排序方式: 共有44条查询结果,搜索用时 15 毫秒
31.
Contrary to classical sexual selection theories, females of many taxa mate with multiple males during one reproductive cycle. In this study, we conducted an experiment on the “trade-up hypothesis”, which proposes that females remate if a subsequently encountered male is potentially superior to previous mates to maximize the genetic quality of their offspring. We presented bank vole females (Clethrionomys glareolus) sequentially with two males of known dominance rank in different orders, i.e., either first subordinate and second dominant, first dominant and second subordinate, or two males that were equal in dominance (high ranking) and observed their mating behavior. We found that 92% of the females mated multiply and did not base their remating decision on male social status. Therefore, polyandry cannot be explained by the “trade-up hypothesis” based on dominance rank in this species. However, we found that dominant males sired significantly more offspring than subordinate males. This varied according to mating order: dominant males sired more offspring when they were second than when they were first. Moreover, litter sizes were significantly smaller when the dominant male was first (smallest relative success of dominant males) compared to litter sizes when mating order was reversed or both males equal in status. Our results suggest that even though multimale mating includes males that are of poorer quality and thus potentially decreases the fitness of offspring, most of a female’s offspring are sired by dominant males. Whether this is due to cryptic female choice, sperm competition, or a combination of both, remains to be tested. 相似文献
32.
Voluntary exercise at the expense of reproductive success in Djungarian hamsters (Phodopus sungorus)
Energy demands of gestation and lactation represent a severe challenge for small mammals. Therefore, additional energetic
burdens may compromise successful breeding. In small rodents, food restriction, cold exposure (also in combination) and wheel
running to obtain food have been shown to diminish reproductive outcome. Although exhibited responses such as lower incidence
of pregnancy, extended lactation periods and maternal infanticide were species dependent, their common function is to adjust
energetic costs to the metabolic state reflecting the trade-off between maternal investment and self-maintenance. In the present
study, we sought to examine whether voluntary exercise affects reproduction in Djungarian hamsters (Phodopus sungorus), which are known for their high motivation to run in a wheel. Voluntary exercise resulted in two different effects on reproduction;
in addition to increased infanticide and cannibalism, which was evident across all experiments, the results of one experiment
provided evidence that free access to a running wheel may prevent successful pregnancy. It seems likely that the impact of
voluntary wheel running on reproduction was associated with a reduction of internal energy resources evoked by extensive exercise.
Since the hamsters were neither food-restricted nor forced to run in the present study, an energetic deficit as reason for
infanticide in exercising dams would emphasise the particularly high motivation to run in a wheel. 相似文献
33.
The relative roles of the fish lateral line and inner ear for the perception of hydrodynamic stimuli are poorly investigated.
Here, we studied responsiveness to a 100 Hz vibrating sphere (dipole stimulus) of goldfish and oscars, two species that differ
in peripheral lateral line morphology, inner ear morphology, mechanical linkage between inner ear and swim bladder, and inner
ear sensitivity. We measured unconditioned dipole-evoked changes in breathing activity in still water and in the presence
of a 5-cm s−1 background flow. In still water, individuals from both species responded to sound pressure levels (SPLs) between 92 and 109 dB
SPL re 1 μPaRMS. Responsiveness was not affected by background flow or by temporary inactivation of the lateral line. The data suggest that
fish with different lateral line and inner ear morphologies have similar sensitivities to vibrating sphere stimuli and can
detect and respond to dipole sources equally well in still water and in moderate background flows. Moreover, behavioral responses
were not dependent on a functional lateral line, suggesting that in this type of experiment, the inner ear is the dominant
sense organ for the perception of hydrodynamic stimuli. 相似文献
34.
Zarfl C Hotopp I Kehrein N Matthies M 《Environmental science and pollution research international》2012,19(8):3152-3161
According to the European legislation, REACH, organic compounds are considered as substances of very high concern (SVHC) if they are persistent, bioaccumulative and toxic (PBT). A substance's long-range transport potential (LRTP) may also pose a risk to remote regions. This is, however, not yet explicitly included. For identification of compounds, which are not PBT according to REACH criteria, but show LRTP, we investigated 22,438 compounds from the Canadian Domestic Substance List (CDSL). The CDSL was searched for organic, neutral compounds. Substance properties were estimated with EPI Suite v4.00. Next, the substance list was edited in two ways: (1) The half-life criterion in air for LRTP as defined in the Stockholm Convention was applied. (2) For all compounds, indicators for persistence and LRTP were calculated with the multimedia model ELPOS v2.2. Applying the half-life criterion, we identified 594 substances, which are prone to LRT but are not PBT (non-PBT-L substances). In contrast, investigations with ELPOS lead to a shorter list of 188 substances, which are non-PBT-L substances. Finally, the list was compared with potential Arctic contaminants identified in previous literature. Our results show that there is a large number of organic chemicals which would not be considered as SVHC since they are not, at the same time, persistent, bioaccumulative and toxic according to REACH criteria. Nevertheless, they show LRTP according to different screening approaches and thus a potential hazard to remote regions. 相似文献
35.
36.
37.
The operational sex ratio (OSR) may influence the intensity of competition for mates and mate choice and is therefore thought
to be a major factor predicting the intensity and direction of sexual selection. We studied the opportunity for sexual selection,
i.e., the variance in male reproductive success and the direction and intensity of sexual selection on male body mass in bank
vole (Clethrionomys glareolus) enclosure populations with experimentally manipulated sex ratios. The opportunity for sexual selection was high among male-biased
OSRs and decreased towards female-biased OSRs. Paradoxically, selection for large male body mass was strongest in female-biased
OSRs and also considerable at intermediate OSRs, whereas at male-biased OSRs, only a weak relationship between male size and
reproductive success was found. Litters in male-biased OSRs were more likely to be sired by multiple males than litters in
female-biased OSRs. Our results suggest that the intensity and direction of sexual selection in males differs among different
OSRs. Although the direction of sexual selection on male body mass was opposite than predicted, large body mass can be favored
by sexual selection. Naturally varying OSRs may therefore contribute to maintain variation in male sexually selected traits. 相似文献
38.
Webster L Walsham P Russell M Hussy I Neat F Dalgarno E Packer G Scurfield JA Moffat CF 《Chemosphere》2011,83(6):839-850
Halogenated persistent organic pollutants [polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs)] along with total lipid, were measured in the liver and muscle of three species of deep water fish (black scabbard, black dogfish (liver only) and roundnose grenadier) collected from the Rockall fishing area, to the west of Scotland, between 2006 and 2008. Both contaminant groups were detected in the muscle and liver, with concentrations of PCBs being higher than PBDEs. There were no significant differences in the PCB or PBDE concentrations between the three species, or different sampling locations in the Rockall fishing area. PCB concentrations (ΣICES (International Council for the Exploration of the Sea)7 PCBs) greater than 500 μg kg−1 lipid weight were found in 26 of the 106 liver samples. PCB concentrations were compared to OSPAR assessment criteria, concentrations were above background but below Environmental Assessment Criteria. Estimated Toxic Equivalent (TEQ) concentrations, calculated using published models, in the fish muscle and liver indicated that consumption of deep water fish is unlikely to represent a risk to human health. The high squalene content in some of the black dogfish liver necessitated an additional clean-up step, involving gel permeation chromatography, when analyzing for PBDEs. Concentrations of PBDEs were low with many congeners being below detection limits, particularly in the muscle. There are currently no assessment criteria available for PBDEs. Furthermore, there is only very limited data on PBDEs in deep water fish. However, the concentrations observed in this study were similar to the concentrations recently reported in Mediterranean deep water fish. 相似文献
39.
Ines Dombrowsky Ram Almog Nir Becker Eran Feitelson Simone Klawitter Stefan Lindemann Natalie Mutlak 《Environmental management》2010,45(5):1112-1126
The basin scale has been promoted universally as the optimal management unit that allows for the internalization of all external
effects caused by multiple water uses. However, the basin scale has been put forward largely on the basis of experience in
temperate zones. Hence whether the basin scale is the best scale for management in other settings remains questionable. To
address these questions this paper analyzes the economic viability and the political feasibility of alternative management
options in the Kidron/Wadi Nar region. The Kidron/Wadi Nar is a small basin in which wastewater from eastern Jerusalem flows
through the desert to the Dead Sea. Various options for managing these wastewater flows were analyzed ex ante on the basis
of both a cost benefit and a multi-criteria analysis. The paper finds that due to economies of scale, a pure basin approach
is not desirable from a physical and economic perspective. Furthermore, in terms of political feasibility, it seems that the
option which prompts the fewest objections from influential stakeholder groups in the two entities under the current asymmetrical
political setting is not a basin solution either, but a two plant solution based on an outsourcing arrangement. These findings
imply that the river basin management approach can not be considered the best management approach for the arid transboundary
case at hand, and hence is not unequivocally universally applicable. 相似文献
40.
The paper discusses the role of visions within sustainability assessment and governance for sustainable development in Europe.
Currently, our societies (still) develop along an unsustainable path, which results in a number of persistent problems (climate
change, loss of biodiversity, poverty, etc.). Integrated sustainability assessment (ISA) is one approach designed to initiate
transitions towards sustainability. Visions of a sustainable future form an important part of ISA. These visions support the
process of discussing how the transition from today’s societies/systems to a sustainable future can be achieved. According
to the principles of ISA, visions should be developed in a participatory way, thus including the ideas and perceptions of
stakeholders, decision-makers, experts and/or citizens. The paper starts with an introduction of the concepts of visions and
scenarios and describes exemplary methods for their participatory development. Then, the main concepts for integrated sustainability
assessment in comparison with other impact assessments are discussed. The main body of the paper presents experiences in three
projects (ARTEMIS, ALARM, ECOCHANGE) in which visions and scenarios of sustainable futures were developed with stakeholders.
The paper concludes with lessons learned and suggestions for future applications for participatory scenario development. 相似文献