Prevailing theory predicts that lower levels of intra-clutch variation in host eggs facilitate the detection of brood parasitism.
We assessed egg matching using both human vision and UV-VIS spectrophotometry and then followed the nest fate of great reed
warblers naturally parasitised by European cuckoos. Rejection was predicted by the following three variables: matching between
cuckoo and host eggs on the main chromatic variable defined by principal components analysis of the egg spectra (which has
a strong loading in the UV); the number of host eggs in the nest; and human estimates of intra-clutch variation. The first
variable is not correlated to human estimates of matching, which do not predict rejection. In line with another recent study,
rejection rates were predicted by higher levels of intra-clutch variation in the host eggs, suggesting that higher rather
than lower levels of intra-clutch variation can facilitate the discrimination of cuckoo eggs by hosts. We suggest that the
importance of intra-clutch variation is context dependent, with intra-clutch variation being important when there is good
matching between the host and the cuckoo eggs. Our results also suggest that both spectrometric and human visual assessments
of egg matching and intra-clutch variation are prudent: the former provide the best method of estimating reflectance variation,
whereas the latter include some assessment of patterns of maculation. 相似文献
Hosts of the common cuckoo (Cuculus canorus), an avian brood parasite, develop antiparasite defense mechanisms to increase their reproductive success. Ejection of the
parasite egg and desertion of the parasitized nest are the most typical adaptations in response to brood parasitism, but nest
desertion may also occur in response to partial clutch reduction, independently from parasitism. Some great reed warblers
(Acrocephalus arundinaceus) showed both mechanisms in the same incidence of cuckoo parasitism: in 18% of successful ejections of the parasite eggs,
they deserted their nests. We studied if such cases of post-ejection nest-desertion are caused by brood parasitism or reduced
clutch value. We experimentally parasitized clutches consisting of five or three host eggs with two painted conspecific eggs
to mimic parasitic eggs, as multiple parasitism is frequent in the area. Although hosts ejected these parasitic eggs in both
clutch categories (100% and 67% for the larger and smaller inital clutch sizes, respectively), we found that after manipulation,
post-ejection nest-desertion frequently occurred at small (3-egg) clutches (40%), but rarely at large (5-egg) clutches (17%).
The same phenomenon also occurred when unparasitized 3-egg clutches were reduced by two eggs, but not when 5-egg clutches
were reduced in the same way. A logistic regression model revealed that only initial clutch size affected nest desertion of
parasitized nests in our experiments. Therefore, we conclude that post-ejection nest-desertion is not a second antiparasite
mechanism, which might serve as a redundant antiparasite defense, but a reaction to typically small and further decreased
clutch size. 相似文献
Abstract With the advent of hybrid electric vehicles, computer-based vehicle simulation becomes more useful to the engineer and designer trying to optimize the complex combination of control strategy, power plant, drive train, vehicle, and driving conditions. With the desire to incorporate emissions as a design criterion, researchers at West Virginia University have developed artificial neural network (ANN) models for predicting emissions from heavy-duty vehicles. The ANN models were trained on engine and exhaust emissions data collected from transient dynamometer tests of heavy-duty diesel engines then used to predict emissions based on engine speed and torque data from simulated operation of a tractor truck and hybrid electric bus. Simulated vehicle operation was performed with the ADVISOR software package. Predicted emissions (carbon dioxide [CO2] and oxides of nitrogen [NOx]) were then compared with actual emissions data collected from chassis dynamometer tests of similar vehicles. This paper expands on previous research to include different driving cycles for the hybrid electric bus and varying weights of the conventional truck. Results showed that different hybrid control strategies had a significant effect on engine behavior (and, thus, emissions) and may affect emissions during different driving cycles. The ANN models underpredicted emissions of CO2 and NOx in the case of a class-8 truck but were more accurate as the truck weight increased. 相似文献
This study presents a comprehensive characterization of occurrence and levels of 16 polycyclic aromatic hydrocarbons (PAHs) in arable soils used for conventional and organic production in northern and central part of Serbia as well as cross-border region with Hungary. Furthermore, this study includes a characterization of PAH sources and carcinogenic/non-carcinogenic human health risk for PAHs accumulated in analysed arable soils. The total concentration of 16 PAHs varied between 55 and 4584 µg kg?1 in agricultural soil used for conventional production and between 90 and 523 µg kg?1 in agricultural soil used for organic production. High molecular weight (HMW) PAHs were dominant compounds with similar contribution in both soil types (86% and 80% in conventional and in organic soil, respectively). Principal component analysis and diagnostic ratios of selected PAHs were used for identification of PAH sources in the analysed soils. Additionally, positive matrix factorization was applied for quantitative assessment. The results indicated that the major sources of PAHs were vehicle emissions, biomass and wood combustion, accounting for?~?93% of PAHs. Exposure of farmers assessed through carcinogenic (TCR) and non-carcinogenic (THQ) risk did not exceed the acceptable threshold (TCR?<?10–6 and THQ?<?1). Oral ingestion was the main exposure route which accounted for 57% of TCR and 80% of THQ. It was followed by dermal contact. This investigation gives a valuable data insight into the PAHs presence in arable soils and reveals the absence of environmental and health risk. It also acknowledges the importance of comprehensive monitoring of these persistent pollutants.
The current study represents a preliminary investigation made into the influence of cattle grazing in the area of a bauxite
quarry (Comarnic–Poieni, Romania) on the cow milk chemistry. Weathering and surface runoff in the bauxite quarry contaminate
the local chemistry of the soil, vegetation and water. During cattle transhumance, cyclic feeding patterns occur, with grazing
alternating between clean pastures and the area of the quarry. Soil and water samples were collected from the contaminated
area of the quarry. Raw milk samples were collected during two stages, corresponding to the periods of grazing on clean pasture
and the quarry area, respectively. Based on the obtained data, the relationship between cattle grazing and the composition
of milk was interpreted. Preliminary results indicated a direct correlation of increased concentration of Al in the milk,
following grazing in the bauxite quarry. 相似文献