排序方式: 共有68条查询结果,搜索用时 140 毫秒
1.
The role of fecundity and sexual selection in the evolution of size and sexual size dimorphism in New World and Old World voles (Rodentia: Arvicolinae)
下载免费PDF全文
![点击此处可从《Oikos》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Evolutionary ecologists dating back to Darwin (1871) have sought to understand why males are larger than females in some species, and why females are the larger sex in others. Although the former is widespread in mammals, rodents and other small mammals usually exhibit low levels of sexual size dimorphism (SSD). Here, we investigate patterns of sexual dimorphism in 34 vole species belonging to the subfamily Arvicolinae in a phylogenetic comparative framework. We address the potential role of sexual selection and fecundity selection in creating sex differences in body size. No support was found for hyperallometric scaling of male body size to female body size. We observed a marginally significant relationship between SSD and the ratio of male to female home range size, with the latter being positively related to the level of intrasexual competition for mates. This suggests that sexual selection favours larger males. Interestingly, we also found that habitat type, but not mating system, constitutes a strong predictor of SSD. Species inhabiting open habitats – where males have extensive home ranges in order to gain access to as many females as possible – exhibit a higher mean dimorphism than species inhabiting closed habitats, where females show strong territoriality and an uniform distribution preventing males to adopt a territorial strategy for gaining copulations. Nonetheless, variation in the strength of sexual selection is not the only selective force shaping SSD in voles; we also found a positive association between female size and litter size across lineages. Assuming this relationship also exists within lineages (i.e. fecundity selection on female size), this suggests an additional role for variation in the strength of fecundity selection shaping interspecific differences in female size, and indirectly in SSD. Therefore our results suggest that different selective processes act on the sizes of males and females, but because larger size is favoured in both sexes, SSD is on average relatively small. 相似文献
2.
Depth of soil water uptake by tropical rainforest trees during dry periods: does tree dimension matter? 总被引:1,自引:0,他引:1
Clément Stahl Bruno Hérault Vivien Rossi Benoit Burban Claude Bréchet Damien Bonal 《Oecologia》2013,173(4):1191-1201
Though the root biomass of tropical rainforest trees is concentrated in the upper soil layers, soil water uptake by deep roots has been shown to contribute to tree transpiration. A precise evaluation of the relationship between tree dimensions and depth of water uptake would be useful in tree-based modelling approaches designed to anticipate the response of tropical rainforest ecosystems to future changes in environmental conditions. We used an innovative dual-isotope labelling approach (deuterium in surface soil and oxygen at 120-cm depth) coupled with a modelling approach to investigate the role of tree dimensions in soil water uptake in a tropical rainforest exposed to seasonal drought. We studied 65 trees of varying diameter and height and with a wide range of predawn leaf water potential (Ψpd) values. We confirmed that about half of the studied trees relied on soil water below 100-cm depth during dry periods. Ψpd was negatively correlated with depth of water extraction and can be taken as a rough proxy of this depth. Some trees showed considerable plasticity in their depth of water uptake, exhibiting an efficient adaptive strategy for water and nutrient resource acquisition. We did not find a strong relationship between tree dimensions and depth of water uptake. While tall trees preferentially extract water from layers below 100-cm depth, shorter trees show broad variations in mean depth of water uptake. This precludes the use of tree dimensions to parameterize functional models. 相似文献
3.
M. Bonal 《Andrologie》1995,5(4):512-515
Therapies of cancer have markedly changed the evolution and prognosis of the cancer illness in its various forms and locatioins. Thus, the future of the sexual life of the men with a cancer is now a question. Sexuality of men is expressed herein in its physiological, intra psychological and relational aspects. Cancer and its therapies affect the sexual response, the body image and the sexual identity. The various factors responsible for the differents as aspects of sexual dysfunction induced by the cancer and its treatments are analysed. 相似文献
4.
Certain characters are more susceptible to increased fluctuating asymmetry (FA) than others. This trait-specific susceptibility has normally been attributed to different degrees of developmental stability, which could be caused by different modes of selection, functionality, or the stress experienced during the development process. Recently, it has also been suggested that the expression of FA not only depends on developmental stability, but also on the cost of growth of the trait, defined as the amount of structural components necessary to form a unit of length of a given character. In accordance with this argument, a trait with more structural components per unit of length should show lower asymmetry than a simpler one. To test this hypothesis, we examine the structure (number of barbs, barb length, and rachis width) and asymmetry of the longest tail feathers in 26 bird species. Regression analyses using phylogenetically independent contrasts show that FA is negatively correlated with the number of barbs and feather rachis width in males (including species with elongated tails subjected to sexual selection), and with rachis width in females, whose tails supposedly evolve by natural selection. Moreover, the negative correlation between FA and rachis width persisted when taking only the males of non-dimorphic species. These results confirm the hypothesis, suggesting that a trait's susceptibility to express developmental instability by fluctuating asymmetry depends on its structural composition. 相似文献
5.
Predators and parasitoids may contribute to controlling the population sizes of phytophagous insects, and this has been shown
to benefit plants. Phytophagous insects may also be killed by other herbivores (intraguild predation), usually larger-sized
vertebrates that ingest insects accidentally while feeding on common food sources. We studied the intraguild predation on
acorn weevils by ungulates and assessed the consequences for weevil populations. Infested acorns are prematurely abscised
and the weevil larvae finish their development inside the acorns after being dropped. Our results show that weevil larvae
were killed by ungulates eating the infested acorns on the ground. Ungulates did not discriminate between infested and sound
acorns, and the probability of a larva being incidentally eaten was inversely related to acorn availability. Thus, predation
risk was enhanced by the premature drop of infested acorns when acorn availability on the ground was low. Predation rates
on infested acorns were much higher where ungulates were present, and acorn infestation rates were significantly lower. However,
ungulates did not provide the oaks any net benefit, since the reduction of infestation rates was not enough to compensate
for the large amounts of sound acorns eaten by ungulates. Seed predation is usually studied as a progressive loss of seeds
by pre- and post-dispersal predators, but the interactions between them are usually not considered. We show that intraguild
predation on insects by large ungulates had an effect on the structure of the foraging guild, as the proportion of acorns
predated by insects decreased; however, replicating the same experimental design in different ecological scenarios would increase
the strength of these results. In conclusion, the present study shows the importance of considering the multi-trophic interactions
between seed predators in order to have a complete picture of granivory. 相似文献
6.
The formation of colonies and the evolution of coloniality have been suggested to be a by-product of the use of public information
to select breeding habitats. In this study we performed an experimental test to investigate whether the Lesser Kestrel (Falco naumanni) uses breeding success of conspecifics as a source of public information to select a breeding colony. We considered four
potential cues based on reproductive performance of conspecifics in each colony: mean and variance of breeding success measured
in both all pairs (TRS, total reproductive success), and only successful pairs (PRS, partial reproductive success). Both mean
PRS and mean TRS could be predictive cues of the future reproductive output at a given site, because they varied among colonies
and were autocorrelated from one year to the next. To dissociate any relationship between habitat quality and reproductive
success we manipulated the mean brood sizes by transferring chicks among ten colonies. In five colonies, all the broods with
at least two nestlings were reduced in one chick and in other five colonies all broods were enlarged by one chick. In the
following year, we found that the number of adult immigrant kestrels settled at a colony was only explained by mean PRS in
the previous year. We also examined the settlement of yearlings, which lack of information on breeding success in previous
years. Unlike adult immigrant kestrels, yearlings tended to settle more frequently in those colonies with low mean PRS in
the previous year, probably because of the lower pressure for occupation in those colonies. A multiple regression analysis
showed that the growth of colonies was positively dependent on the mean PRS in the experimental year, and negatively on the
number of predated nests. This study provides a solid support to the hypothesis that colonial species can use mean breeding
success of successful pairs as a source of public information to make settlement decisions. 相似文献
7.
Shen TH Gladoun N Castillo-Martin M Bonal D Domingo-Domenech J Charytonowicz D Cordon-Cardo C 《PloS one》2012,7(4):e35243
Cre-loxp mediated conditional knockout strategy has played critical roles for revealing functions of many genes essential for development, as well as the causal relationships between gene mutations and diseases in the postnatal adult mice. One key factor of this strategy is the availability of mice with tissue- or cell type-specific Cre expression. However, the success of the traditional molecular cloning approach to generate mice with tissue specific Cre expression often depends on luck. Here we provide a better alternative by using bacterial artificial chromosome (BAC)-based recombineering to insert iCreERT2 cDNA at the ATG start of the Upk2 gene. The BAC-based transgenic mice express the inducible Cre specifically in the urothelium as demonstrated by mRNA expression and staining for LacZ expression after crossing with a Rosa26 reporter mouse. Taking into consideration the size of the gene of interest and neighboring genes included in a BAC, this method should be widely applicable for generation of mice with tissue specific gene expression or deletions in a more specific manner than previously reported. 相似文献
8.
Insulin-expressing cells that have been differentiated from human pluripotent stem cells in vitro lack the glucose responsiveness characteristic of mature beta cells. Beta-cell maturation in mice was studied to find genetic markers that enable screens for factors that induce bona fide beta cells in vitro. We find that functional beta-cell maturation is marked by an increase in the glucose threshold for insulin secretion and by expression of the gene urocortin 3. 相似文献
9.
High variation in foliage and leaf litter chemistry among 45 tree species of a neotropical rainforest community 总被引:1,自引:0,他引:1
Distinct ecosystem level carbon : nitrogen : phosphorus (C : N : P) stoichiometries in forest foliage have been suggested to reflect ecosystem-scale selection for physiological strategies in plant nutrient use. Here, this hypothesis was explored in a nutrient-poor lowland rainforest in French Guiana. Variation in C, N and P concentrations was evaluated in leaf litter and foliage from neighbour trees of 45 different species, and the litter concentrations of major C fractions were also measured. Litter C ranged from 45.3 to 52.4%, litter N varied threefold (0.68-2.01%), and litter P varied seven-fold (0.009-0.062%) among species. Compared with foliage, mean litter N and P concentrations decreased by 30% and 65%, respectively. Accordingly, the range in mass-based N : P shifted from 14 to 55 in foliage to 26 to 105 in litter. Resorption proficiencies indicated maximum P withdrawal in most species, but with a substantial increase in variation in litter P compared with foliage. These data suggest that constrained ecosystem-level C : N : P ratios do not preclude the evolution of highly diversified strategies of nutrient use and conservation among tropical rainforest tree species. The resulting large variation in litter quality will influence stoichiometric constraints within the decomposer food web, with potentially far-ranging consequences on nutrient dynamics and plant-soil feedbacks. 相似文献
10.