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961.
THIERRY LENGAGNE FLORENT ARTHAUD MICKAËL CORMIER PIERRE JOLY 《Biological journal of the Linnean Society. Linnean Society of London》2007,92(4):755-762
When pairing with high quality females, a male increases its fitness through an increased number and/or quality of sired offsprings. In anurans, size has often been used as a measure of female quality. In the present study, we examined the effects of pairing with large females for small males in the common toad, Bufo bufo . For the first time in anurans, we show a fitness cost for males to maintain amplexus with a large female. Indeed, although we did not detect any effect of male size on male pairing success in a first breeding event in the presence of other competing males, when males that were successful in the first breeding event were tested for a second time, male pairing success strongly decreased when they had been first paired with a large female. However, the higher fecundity of large females (1.52-fold more than that of small females) may override this pairing cost, especially because high fertilization rate was not linked to male/female body size ratio. Indeed, we did not detect any difference in egg fertilization success between small males paired with large and small females. Our results suggest that predictable cues of female reproductive value exist in common toads, thus meeting a prerequisite of the occurrence of male mate choice. Male mate choice, probably underestimated in anurans, may be particularly important in species where the breeding season is short and the number of mating events for a male is limited. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 755–762. 相似文献
962.
Interspecific interactions can vary within and among populations and geographical locations, and this variation can influence
the nature of the interaction (e.g. mutualistic versus antagonistic) and its evolutionary stability. Globeflowers are exclusively
pollinated by flies whose larvae feed only on their seeds. Here we document geographical variability in costs and benefits
in globeflowers in sustaining their pollinating flies throughout the range of this arctic-alpine European plant over several
years. A total of 1,710 flower heads from 38 populations were analysed for their carpel, egg and seed contents. Individual
and population analyses control for the confounding influences of variation in both: (1) population traits, such as fly density
and egg distribution among flower heads; and (2) individuals traits, such as carpel and egg numbers per flower head. Despite
considerable variation in ecological conditions and pollinator densities across populations, large proportions (range 33–58%)
of seeds are released after predation, with a benefit-to-cost ratio of 3, indicating that the mutualism is stable over the
whole globeflower geographical range. The stability of the mutualistic interaction relies on density-dependent competition
among larvae co-developing in a flower head. This competition is revealed by a sharp decrease in the number of seeds eaten
per larva with increasing larval number, and is intensified by non-uniform egg distribution among globeflowers within a population.
Carpel number is highly variable across globeflowers (range 10–69), and flies lay more eggs in large flowers. Most plants
within a population contribute to the rearing of pollinators, but some pay more than others. Large globeflowers lose more
seed to pollinator larvae, but also release more seed than smaller plants. The apparent alignment of interests between fly
and plant (positive relationship between numbers of seeds released and destroyed) is shown to hide a conflict of interest
found when flower size is controlled for. 相似文献
963.
Mammalian mating systems are thought to be shaped by the spatial distribution and abundance of key resources, which in turn
influence the spacing behaviour of individuals. In particular, female home range size is predicted to reflect the availability
of key resources. We documented the availability and distribution of food and shelter resources for two neighbouring populations
of bobucks, or mountain brushtail possums, Trichosurus cunninghami, that were characterised by different mating systems: our “forest population” was socially monogamous, whereas the “roadside
population” was polygynous. Both silver wattle, Acacia dealbata, the main food resource for bobucks, and den-trees, which provided shelter, occurred at significantly higher density at the
roadside site. The pattern of distribution of these two resources also differed between the sites. Both food and den-trees
were scattered evenly throughout the roadside habitat. In contrast, den-trees were located predominantly at one end of the
forest site, while silver wattle trees were located at the other. There was no significant difference in the amount of silver
wattle, or in the number of den-trees, located within the home ranges of individual females at the two sites. However, forest
females had home ranges, on average, almost three times the size of those of roadside females. At the roadside site, the size
of female home ranges varied inversely with the density of silver wattle, indicating that these females ranged over as large
an area as necessary to gain access to sufficient silver wattle trees. There was no such relationship among forest females.
These populations provide a clear example of resource distribution determining female home range size. This influenced the
number of female home ranges a male’s home range overlapped with, which in turn determined the mating system. Such clear links
between resource availability and mating system have not previously been established in a marsupial. 相似文献
964.
Reading CJ 《Oecologia》2007,151(1):125-131
There is general consensus that climate change has contributed to the observed decline, and extinction, of many amphibian
species throughout the world. However, the mechanisms of its effects remain unclear. A laboratory study in 1980–1981 in which
temperate zone amphibians that were prevented from hibernating had decreased growth rates, matured at a smaller size and had
increased mortality compared with those that hibernated suggested one possible mechanism. I used data from a field study of
common toads (Bufo bufo) in the UK, between 1983 and 2005, to determine whether this also occurs in the field. The results demonstrated two pathways
by which global warming may cause amphibian declines. First, there was a clear relationship between a decline in the body
condition of female common toads and the occurrence of warmer than average years since 1983. This was paralleled by a decline
in their annual survival rates with the relationship between these two declines being highly correlated. Second, there was
a significant relationship between the occurrence of mild winters and a reduction in female body size, resulting in fewer
eggs being laid annually. Climate warming can, therefore, act on wild temperate zone amphibians by deleteriously affecting
their physiology, during and after hibernation, causing increased female mortality rates and decreased fecundity in survivors. 相似文献
965.
A test of the effect of floral color change on pollination effectiveness using artificial inflorescences visited by bumblebees 总被引:2,自引:0,他引:2
Floral color change has been recognized as a pollination strategy, but its relative effectiveness has been evaluated insufficiently
with respect to other floral traits. In this study, effects of floral color change on the visitation pattern of bumblebees
were empirically assessed using artificial flowers. Four inflorescence types were postulated as strategies of flowering behavior:
type 1 has no retention of old flowers, resulting in a small display size; type 2 retains old flowers without nectar production;
type 3 retains old flowers with nectar; and type 4 retains color-changed old flowers without nectar. Effects of these treatments
varied depending on both the total display size (single versus multiple inflorescences) and the pattern of flower-opening.
In the single inflorescence experiment, a large floral display due to the retention of old flowers (types 2–4) enhanced pollinator
attraction, and the number of flower visits per stay decreased with color change (type 4), suggesting a decrease in geitonogamous
pollination. Type-4 plants also reduced the foraging time of bees in comparison with type-2 plants. In the multiple inflorescence
experiment, the retention of old flowers did not contribute to pollinator attraction. When flowering occurred sequentially
within inflorescences, type-4 plants successfully decreased the number of visits and the foraging time in comparison with
type-2 plants. In contrast, floral color change did not influence the number of visits, and it extended the foraging time
when flowering occurred simultaneously within inflorescences but the opening of inflorescences progressed sequentially within
a plant. Therefore, the effectiveness of floral color change is highly susceptible to the display size and flowering pattern
within plants, and this may limit the versatility of the color change strategy in nature. 相似文献
966.
Urban MC 《Oecologia》2007,154(3):571-580
Theoretical efforts suggest that the relative sizes of predators and their prey can shape community dynamics, the structure
of food webs, and the evolution of life histories. However, much of this work has assumed static predator and prey body sizes.
The timing of recruitment and the growth patterns of both predator and prey have the potential to modify the strength of predator–prey
interactions. In this study, I examined how predator size dynamics in 40 temporary ponds over a 3-year period affected the
survival of spotted salamander (Ambystoma maculatum) larvae. Across communities, gape-limited predator richness, but not size, was correlated with habitat duration (pond permanence).
Within communities, mean gape-limited predator size diminished as the growing season progressed. This size reduction occurred
because prey individuals grew into a body size refuge and because the largest of the predators left ponds by mid-season. Elevated
gape-limited predation risk across time and space was predicted by the occurrence of two large predatory salamanders: marbled
salamander larvae (Ambystoma opacum) and red-spotted newt adults (Notophthalmus viridescens). The presence of the largest gape-limited predator, A. opacum, predicted A. maculatum larval survival in the field. The distribution of large predatory salamanders among ponds and across time is expected to
lead to differing community dynamics and to generate divergent natural selection on early growth and body size in A. maculatum. In general, a dynamic perspective on predator size often will be necessary to understand the ecology and evolution of species
interactions. This will be especially true in frequently disturbed or seasonal habitats where phenology and ontogeny interact
to determine body size asymmetries.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
967.
Flood tolerance is commonly regarded as the main factor explaining low diversity and monodominance in tropical swamps. In this study we examined seedling mortality in relation to seasonality, i.e., flooding versus drought, of the dominant tree species (Prioria copaifera), and three associated species (Pterocarpus officinalis, Carapa guianensis and Pentaclethra macroloba), in seasonally flooded forests (SFF) in Darien, Panama. Seedling mortality differed among species, years and seasons. Prioria seedlings experienced the lowest overall mortality, and after 3 years many more Prioria seedlings remained alive than those of any of the associated species. In general, within species, larger seedlings had greater survival. Seed size, which can vary by close to 2 orders of magnitude in Prioria, had a confounding effect with that of topography. Large-seeded Prioria seedlings experienced 1.5 times greater mortality than small-seeded seedlings, as large-seeded Prioria seedlings were more likely to be located in depressions. This finding suggests that seed size, plant size and topography are important in understanding SFF regeneration. For all species, seedling mortality was consistently greater during the dry season than during flooding. For Prioria, dry season seedling mortality was correlated with drought stress, that is, high mortality during the long El Niño dry season of 1998 and the normal dry season of 2000, but very low dry season mortality during the mild dry season of 1999. Prioria’s ability to dominate in seasonally flooded forest of Central America is partly explained by its low drought-related mortality in comparison to associated species. 相似文献
968.
Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to
the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality
models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive
season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high
inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation
(CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%).
Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally
support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season
should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings
emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence
success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal
hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate
that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability
and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks
probably reflect compensation for high and unpredictable mortality during early life history stages in this species. 相似文献
969.
A range of traits, including metabolic costs, biomass allocation and seed reserves, may contribute to interspecific variation
in the shade tolerance of tree seedlings. In addition, shade tolerance may be affected by differential responses of species
to soil resource availability at low light. We used a custom-built whole-plant gas-exchange chamber to quantify instantaneous
whole-plant light compensation point (WPLCP) and to parameterize whole-plant daily C gain models for seedlings of eight temperate
deciduous tree species. We examined the relationship of WPLCP to growth, biomass allocation and gas-exchange under high and
low light and nutrient availabilities and compared it to WPCLP of naturally recruited saplings. For species showing a response,
both increased light and nutrient availability resulted in increased WPLCP. However, species’ responses to resource availability
did not correspond closely with shade tolerance as has generally been predicted. Variation in WPLCP within species was best
predicted by whole-plant dark respiration rates, leaf-level light compensation point and leaf mass per area. Among species,
seed size was a strong negative correlate of WPLCP, explaining 66% of the variation. Species with the lowest WPLCP maintained
lower growth rates across treatments but greater biomass in the low-light treatment compared with more light-demanding species.
These data suggest that a number of traits, in particular metabolic costs and seed size, contribute to WPLCP. However, gas-exchange-based
WPLCP was 1.5–3.5 times lower than corresponding growth-based field estimates of WPLCP, suggesting that other factors such
as biotic interactions or ontogenetic shifts in whole-plant light requirements may substantially increase species’ WPLCP under
natural conditions. 相似文献
970.
Falke KC Flachenecker C Melchinger AE Piepho HP Maurer HP Frisch M 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2007,114(5):765-776
Selection and random genetic drift are the two main forces affecting the selection response of recurrent selection (RS) programs
by changes in allele frequencies. Therefore, detailed knowledge on allele frequency changes attributable to these forces is
of fundamental importance for assessing RS programs. The objectives of our study were to (1) estimate the number, position,
and genetic effect of quantitative trait loci (QTL) for selection index and its components in the base populations, (2) determine
changes in allele frequencies of QTL regions due to the effects of random genetic drift and selection, and (3) predict allele
frequency changes by using QTL results and compare these predictions with observed values. We performed QTL analyses, based
on restriction fragment length polymorphisms (RFLPs) and simple sequence repeats (SSRs), in 274 F2:3 lines of cross KW1265 × D146 (A × B) and 133 F3:4 lines of cross D145 × KW1292 (C × D) originating from two European flint maize populations. Four (A × B) and seven (C × D)
cycles of RS were analyzed with SSRs for significant allele frequency changes due to selection. Several QTL regions for selection
index were detected with simple and composite interval mapping. In some of them, flanking markers showed a significant allele
frequency change after the first and the final selection cycles. The correlation between observed and predicted allele frequencies
was significant only in A × B. We attribute these observations mainly to (1) the high dependence of the power of QTL detection
on the population size and (2) the occurrence of undetectable QTL in repulsion phase. Assessment of allele frequency changes
in RS programs can be used to detect marker alleles linked to QTL regions under selection pressure.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献