Fundamental to many theories of sexual selection is the expectation that sexual traits, which males use in an attempt to increase mating success, confer costs as well as benefits to individual males. Although evolution of exaggerated male traits is predicted to be halted, by costs applied by natural selection, there is a lack of empirical work devoted to quantitatively establishing whether natural selection opposes sexual selection generated by the preferences of females. In this study, we quantified natural and sexual selection gradients on breeding values for cuticular hydrocarbon (CHC) components of male contact pheromones in Drosophila serrata. As male sexual traits may often be environmentally condition dependent, breeding values were used in the selection analysis to remove the possibility of environmental correlations between the measured trait and fitness biasing estimates of selection. The direction of natural selection was found to oppose sexual selection on a subset of CHCs examined. Opposing natural and sexual selection suggests that further evolution of the male pheromone may in part be limited by costs associated with attractive male CHC blends. 相似文献
Restoration models and practise to date have been applied mainly to ecosystems. More recently, there has been a focus on the “landscape perspective” of ecosystem restoration in order to improve nature conservation and management effectiveness.
Here, we clarify some of the differences between ecosystem- and landscape-oriented restoration, and propose four components that should be considered in planning and conceptualising: (a) landscape composition and configuration; (b) traditional land management techniques; (c) linear and point features; and (d) other heritage features. We further discuss the concept of reference landscapes, and the contrasts between restoration and rehabilitation. Spatial approaches to restoration are explored, comparing small areas with complete restoration (“museum landscapes”) from large areas with rehabilitation of landscape physiognomy or point and linear features. The linkages with nature conservation and the sustainable use and management of natural resources are examined in the context of a rapidly changing world. 相似文献
Adventitious sprouting from the hypocotyle and roots in monocarpic herbs has been confirmed in previous experimental studies as a means to avoid bud limitation after severe injury in annual and biennial plants. Data regarding the role of adventitious sprouting in natural populations, however, were lacking. The aim of the present study was to assess whether adventitious sprouting occurs in natural populations and how it is affected by plant size, plant injury, plant cover and environmental characteristics.
Methods
Data were sampled from 14 037 individual plants from 389 populations belonging to 22 annual and biennial species. Growth parameters were measured in individual plants, species composition and plant cover in communities were evaluated, and environmental characteristics were estimated using Ellenberg indicator values.
Key Results
It was confirmed that adventitious sprouting occurs in natural populations of all but five species examined. Adventitious sprouting was positively affected by plant size and plant injury. Environmental factors including availability of soil nitrogen were not shown to affect adventitious sprouting. Annual and biennial plants did not differ in sprouting, but upright annuals had a lower number of and longer adventitious shoots than prostrate annuals.
Conclusions
Adventitious bud formation is used to overcome meristem limitation when stem parts are lost due to injury, and thus resprouting in short-lived monocarps should not be overlooked. 相似文献
Intention, Goal, Scope, Background It has gained growing acceptance in recent years that there are values in LCA, and several authors have discussed how value
orientations can influence LCA models and results. The aim of this article is to continue this discussion and to focus on
value choices in LCA.
Objectives To find a way of describing value orientations in relation to choices in LCA.
Methods This objective has been pursued in this paper by investigating the relationship between values and traditional science, exploring
the concept of values, investigating the relationship between values and choice, and suggesting a way to describe the value
base for specific choices in LCA.
Results and Discussion Research on how to improve the environmental performance of products resembles peace research in that it aims to achieve
a certain value-laden situation in society. The epistemological basis for peace research also seems to apply to LCA research.
The term value has many meanings. There are several classification methods for values and I claim that one is more suitable
for choices in LCA than the others. The correlation between values and choice is not straightforward, and values can only
partially explain choices.
Conclusions Describing the value base for choices in LCA increases the consistency and transparency of the value choices and offers a
means of justifying them.
Recommendations and Outlook It is recommended that the value base is described in terms of 1) what is included in the concern for the environment 2)
how tradeoffs are made and 3) how uncertainty is handled. 相似文献
The photosynthetic pathway of plant species collected at Menyuan, Henan, and Maduo sites, east of Tibetan Plateau, China,
during the growing season were studied using stable carbon isotopes in leaves. The 232 samples leaves analyzed belonged to
161 species, 30 families, and 94 genera. The δ13C values (from −24.6 to − 29.2 ‰) indicated that all the considered species had a photosynthetic C3 pathway. The absence of plant species with C4 photosynthetic pathway might be due to the extremely low air temperature characterizing the Tibetan Plateau. The average
δ13C value was significantly (p<0.05) different between annuals and perennials at the three considered study sites. Hence the longer-lived species had greater
water-use efficiency (WUE) than shorter-lived species, that is, longer-lived species are better adapted to the extreme environmental
conditions of the Tibetan Plateau. 相似文献
Recent work on the coding of spatial information in the brain has significantly advanced our knowledge of sensory to motor transformations on several fronts. The encoding of information referenced to the retina (eye-centered) but modulated by eye position, called a gain field representation, has proved to be very common throughout parietal and occipital cortex. The use of an eye-centered representation as a working memory of spatial location is problematic if the eyes move during the memory period. Details regarding the manner in which the brain solves this problem are beginning to emerge. Finally, the discovery of eye-centered representations of ongoing or intended arm movements has changed the way we think about the order of operations in the sensory to motor coordinate transformation. 相似文献