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1.
Heike Pröhl  Olaf Berke 《Oecologia》2001,129(4):534-542
In many species with a resource-based mating system, males defend resources to increase their attractiveness to females. In the strawberry poison frog, Dendrobates pumilio, suitable tadpole-rearing sites appear to be a limited resource for females. Territorial males have been suggested to defend tadpole-rearing sites to increase their access to females. In this study we investigate the spatial association between tadpole-rearing sites and the sexes as well as the spatial association of males and females. If strawberry poison frogs have resource defense polygyny, we expect males and females to be associated with tadpole-rearing sites and that females will deposit their offspring in tadpole-rearing sites inside the territories of their mates. To test this hypothesis, home range and core area sizes were calculated for both sexes and the association patterns were compared in two areas that differed in their abundance of tadpole-rearing sites. Home ranges and core areas of females were much larger than male home ranges. Females showed a clumped distribution in the vicinity of tadpole-rearing sites. Males were not clumped and were less associated with tadpole-rearing sites. Females generally did not use tadpole-rearing sites in the territory of their mates and we therefore conclude that males did not defend tadpole-rearing sites for females. Our data are consistent with the general assumption that female distribution is influenced by resource distribution and that male distribution depends on female distribution. Nevertheless, the distribution of D. pumilio females was also influenced by male spacing patterns. Males probably initially establish their core areas where female density is high and then females move among territories to sample males. Males compete vigorously for places with high female density, the defense of which is likely important for enhancing their mating success. In general, the spacing patterns did not differ between populations but the sex ratio was strongly female biased in the habitat with more tadpole-rearing sites, reflecting the direct reliance of females on these resources.  相似文献   

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Wistar male rats received an intratesticular injection (at 114 and 265 days of age) of 3 mg of partially purified bull seminal ribonuclease (AS RNase) or saline. It was found that sexual behaviour (initiation of copulation as well as copulatory behavioural pattern) of experimental males was not changed, but the ability of these males to fertilize females was evidently suppressed. In addition to significantly lower weights of testes and epididymis, inhibition of seminiferous epithelium development (aspermatogenesis) associated with the absence of spermatozoa was determined in cauda epididymidis in experimental animals. However, Leydig cells remained without changes. Plasma testosterone levels of AS RNase treated males were not altered in comparison with the controls. Thus AS RNase specifically impaired spermatogenesis but did not influence androgen action and sexual behaviour.  相似文献   

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Larger signal size is known to facilitate the learning process of predators to warning signals. Further, smaller objects are generally harder to detect than large, which suggests that smaller sized prey are less likely to benefit from an aposematic strategy compared to crypsis. However, whether body size changes in concert with shifts between crypsis and aposematism in natural populations, remains largely unexplored. I tested whether body size was larger in visually conspicuous population than in cryptic populations among recently diverged populations of the Strawberry Poison frog, Oophaga pumilio. By analysing spectral reflectance and body size data from individuals from 18 discrete populations I found a larger mean body size in conspicuous populations, which was confirmed by an analysis of a subset of 12 populations accounting for phylogenetic history. This shows that the loss of conspicuous colour likely co-evolved repeatedly with a decrease in body size. Thus, selection on body size may influence evolutionary shifts between aposematism and crypsis and vice versa.  相似文献   

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Inertial load can affect the control of a dynamic system whenever parts of the system are accelerated ordeclerated. During steady-state pedating, because within-cycle variations in crank angular acceleration still exist, the amount of crank inertia present (which varies widely with road-riding gear ratio) may affect the within-cycle coordination of muscles. However, the effect of inertial load on steady-state pedaling coordination is almos always assumed to be negligible, since the net mechanical energy per cycle developed by muscles only depends on the constant cadence and workload. This study tests the hypothesis that under steady-state conditions, the net joint torques produced by muscles at the hip, knee, and ankle are unaffected by crank inertial load. To perform the investigation, we constructed a pedaling apparatus which could emulate the low inertial load of a standard ergometer or the high inertial load of a road bicycle in high gear. Crank angle and bilateral pedal force and angle data were collected from ten subjects instructed to pedal steadily (i.e. constant speed across cycles) and smoothly (i.e. constant speed within a cycle) against both inertias at a constant workload. Virtually no statistically significant changes were found in the net hip and knee muscle joint torques calculated from an inverse dynamics analysis. Though the net ankle muscle joint torque, as well as the one- and two-legged crank torque, showed statistically significant increases at the higher inertia, the changes were small. In contrast, large statistically significant reductions were found in crank kinematic variability both within a cycle and between cycles (i.e. cadence), primarily because a larger inertial load means a slower crank dynamic response. Nonetheless, the reduction in cadence variability was somewhat attenuated by a large statistically significant increase in one-legged crank torque variability. We suggest, therefore, that muscle coordination during steady-state pedaling is largely unaffected, though less well regulated, when crank inertial load is increased.  相似文献   

6.
Exchange-transferred nuclear Overhauser enhancement (etNOE) provides a useful method for determining the 3-dimensional structure of a ligand bound to a high-molecular-weight complex. Some concern about the accuracy of such structures has arisen because indirect relaxation can occur between the ligand and macromolecule. Such indirect relaxation, or spin diffusion, would lead to errors in interproton distances used as restraints in structure determination. We address this concern by assessing the extent of intermolecular spin diffusion in nineteen peptide-protein complexes of known structure. Transferred NOE intensities were simulated with the program CORONA (Calculated OR Observed NOESY Analysis) using the rate-matrix approach to include contributions from indirect relaxation between protein-ligand and intraligand proton pairs. Intermolecular spin diffusion contributions were determined by comparing intensities calculated with protonated protein to those calculated with fully deuterated protein. The differences were found to be insignificant overall, and to diminish at short mixing times and high mole ratios of peptide to protein. Spin diffusion between the peptide ligand and the protein contributes less to the etNOE intensities and alters fewer cross peaks than the well-studied intramolecular spin diffusion effects. Errors in intraligand interproton distances due to intermolecular relaxation effects were small on average and can be accounted for with the restraint functions commonly used in NMR structure determination methods. In addition, a rate-matrix approach to calculate distances from etNOESY intensities using a volume matrix comprising only intraligand intensities was found to give accurate values. Based on these results, we conclude that structures determined from etNOESY data are no less accurate due to spin diffusion than structures determined from conventional NOE intensities.  相似文献   

7.
Multimodal signals facilitate communication with conspecifics during courtship, but they can also alert eavesdropper predators. Hence, signallers face two pressures: enticing partners to mate and avoiding detection by enemies. Undefended organisms with limited escape abilities are expected to minimize predator recognition over mate attraction by limiting or modifying their signalling. Alternatively, organisms with anti-predator mechanisms such as aposematism (i.e. unprofitability signalled by warning cues) might elaborate mating signals as a consequence of reduced predation. We hypothesize that calls diversified in association with aposematism. To test this, we assembled a large acoustic signal database for a diurnal lineage of aposematic and cryptic/non-defended taxa, the poison frogs. First, we showed that aposematic and non-aposematic species share similar extinction rates, and aposematic lineages diversify more and rarely revert to the non-aposematic phenotype. We then characterized mating calls based on morphological (spectral), behavioural/physiological (temporal) and environmental traits. Of these, only spectral and temporal features were associated with aposematism. We propose that with the evolution of anti-predator defences, reduced predation facilitated the diversification of vocal signals, which then became elaborated or showy via sexual selection.  相似文献   

8.
Aposematic signals represent one of the most accessible traits to evaluate the interaction of natural and sexual selection on signal evolution. Here we investigate the contributions of these two selective forces on the aposematic signal evolution of the highly polytypic strawberry poison frog, Oophaga pumilio, of Bocas del Toro, Panama. Previous research has shown that the brightness of O. pumilio warning coloration can inform predators of the toxicity levels associated with different populations of the archipelago. Other studies suggest that sexual selection may be influencing warning signal brightness within populations via female mate choice (Isla Solarte, Isla Bastimentos, and Aquacate Peninsula populations) and male–male competition (Isla Solarte). Here we present two non-exclusive scenarios for how natural and sexual selection interact to drive phenotypic variation across this archipelago: (1) predators impose a selective regime whereby populations above a toxicity-brightness threshold are at liberty to diversify via sexual selection and below which populations are constrained to maintain a stricter resemblance to a more cryptic population mean, and (2) synergistic/additive effects of inter- and intrasexual selection drive the evolution of brighter males within populations above this toxicity threshold. We investigate whether aposematic patterns of divergence across the archipelago relative to the common mainland phenotype meet these predictions using existing data on O. pumilio morph toxicity measures and overall conspicuousness estimates to an avian predator. Using standardized z-scores to evaluate the range of trait values, we find that indeed the population representative of the common mainland phenotype (Almirante) represents an intermediate level of both toxicity and conspicuousness, and that derived Bocas del Toro populations vary in each of those components in directions predicted by the proposed scenarios. Furthermore, we find greater divergence towards conspicuousness than crypsis, a pattern suggestive of sexual and natural selection acting synergistically in morphs with high toxicity.  相似文献   

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Amazonia is famous for high biodiversity, and the highlands of the transition zone between the Andes and the lowlands of the Amazon basin show particularly high species diversity. Hypotheses proposed to explain the high levels of diversity in the highlands include repeated parapatric speciation across ecological gradients spanning the transition zone, repeated allopatric speciation across geographic barriers between the highlands and lowlands, divergence across geographic barriers within the transition zone, and simple lineage accumulation over long periods of time. In this study, we investigated patterns of divergence in frogs of the genus Epipedobates (family Dendrobatidae) using phylogenetic and biogeographic analyses of divergence in mitochondrial DNA (1778 aligned positions from genes encoding cyt b, 12S and 16S rRNA for 60 Epipedobates and 11 outgroup specimens) and coloration (measured for 18 specimens representing nine species in Epipedobates). The majority of phenotypic and species diversity in the poison frog genus Epipedobates occurs in the transition zone, although two morphologically conserved members of the genus are distributed across the lowlands of the Amazon basin. Phylogenetic analysis reveals that there is a single highland clade derived from an ancestral colonization event in northern Peru by a population of lowland ancestry. Epipedobates trivittatus, a widespread Amazonian species, is a member of the highland clade that reinvaded the lowlands. Comparative analyses of divergence in coloration and mtDNA reveals that divergence in coloration among populations and species in the highlands has been accelerated relative to the lowlands. This suggests a role for selection in the divergence of coloration among populations and species.  相似文献   

13.
HeLa cells were grown in the presence of 10 mM sodium butyrate and soluble chromatin containing hyperacetylated histones was prepared by mild micrococcal nuclease digestion and sucrose gradient fractionation. Sedimentation and electric dichroism were used to study the cation-induced folding of this acetylated chromatin from the 10 nm filament to the 30 nm solenoid conformation. Although under some conditions acetylated chromatin appears slightly less condensed than control chromatin, the major conclusion is that hyperacetylation of histones does not in itself prevent the formation of the higher order chromatin solenoid.  相似文献   

14.
The objective of the study was to determine the individual differences in sexual activity of rams. In total, 374 observations were made on 17 rams (22 for each ram). The average duration of mating for all rams was 70.9 s, ranging from 30.0 to 166.7 s for particular rams. The average duration of mating for a group of ten more active rams (MAR) was 49.3 s, while for a group of seven less active rams (LAR) it was 101.8 s, the difference being highly significant. Significant differences were also found with respect to the average number of mounts per ejaculation, both between individual rams (mean 2.36) and between group MAR (2.20) and LAR (2.60). The percentage of failure, defined as copulations without ejaculation, was significantly higher in group LAR (11.1%) than in group MAR (2.5%), indicating that the rams of group MAR copulate much more efficiently than the other males. The lambing results obtained from service during the first oestrus did not show significant differences between groups MAR and LAR, neither with respect to their fertility nor to the lambing rate.  相似文献   

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Cyanovirin-N can exist in solution in monomeric and domain-swapped dimeric forms, with HIV-antiviral activity being reported for both. Here we present results for CV-N variants that form stable solution dimers: the obligate dimer [DeltaQ50]CV-N and the preferential dimer [S52P]CV-N. These variants exhibit comparable DeltaG values (10.6 +/- 0.5 and 9.4 +/- 0.5 kcal.mol(-1), respectively), similar to that of stabilized, monomeric [P51G]CV-N (9.8 +/- 0.5 kcal.mol(-1)), but significantly higher than wild-type CV-N (4.1 +/- 0.2 kcal.mol(-1)). During folding/unfolding, no stably folded monomer was observed under any condition for the obligate dimer [DeltaQ50]CV-N, whereas two monomeric, metastable species were detected for [S52P]CV-N at low concentrations. This is in contrast to our previous results for [P51G]CV-N and wild-type CV-N, for which the dimeric forms were found to be the metastable species. The dimeric mutants exhibit comparable antiviral activity against HIV and Ebola, similar to that of wild-type CV-N and the stabilized [P51G]CV-N variant.  相似文献   

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Oxidative DNA damage plays a role in disease development and the aging process. A prominent participant in orchestrating the repair of oxidative DNA damage, particularly single-strand breaks, is the scaffold protein XRCC1. A series of chronological and biological aging parameters in XRCC1 heterozygous (HZ) mice were examined. HZ and wild-type (WT) C57BL/6 mice exhibit a similar median lifespan of ~26 months and a nearly identical maximal life expectancy of ~37 months. However, a number of HZ animals (7 of 92) showed a propensity for abdominal organ rupture, which may stem from developmental abnormalities given the prominent role of XRCC1 in endoderm and mesoderm formation. For other end-points evaluated-weight, fat composition, blood chemistries, condition of major organs, tissues and relevant cell types, behavior, brain volume and function, and chromosome and telomere integrity-HZ mice exhibited by-and-large a normal phenotype. Treatment of animals with the alkylating agent azoxymethane resulted in both liver toxicity and an increased incidence of precancerous lesions in the colon of HZ mice. Our study indicates that XRCC1 haploinsufficiency in mammals has little effect on chronological longevity and many key biological markers of aging in the absence of environmental challenges, but may adversely affect normal animal development or increase disease susceptibility to a relevant genotoxic exposure.  相似文献   

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Retinoid X receptors (RXRs) function as homo- or heterodimers with other nuclear receptors, such as peroxisome proliferator-activated receptors (PPARs), which are targets for treatment of hyperlipidemia and type 2 diabetes, or liver X receptors (LXRs), which are involved in glucose/lipid metabolism. PPAR/RXR or LXR/RXR are known as permissive RXR-heterodimers because they are activated by RXR agonists alone. Interestingly, the pattern of RXR-heterodimer activation is different depending on the RXR agonist structure, but the structure–activity relationship has not been reported. Here we show that modification or replacement of the carboxyl group in the acidic domain of RXR agonists has little or no effect on permissive RXR-heterodimer activation. Phosphonic acid (9), tetrazole (10), and hydroxamic acid (12) analogues were synthesized from the common bromo intermediate 7. Except for 9, these compounds showed RXR full-agonistic activities in the concentration range of 1–10 μM. The order of agonistic activity toward both PPARγ/RXRα and LXRα/RXRα was the same as it was for RXR, that is, 11 > 10 > 12. These results should be useful for the development of RXR agonists with improved bioavailability.  相似文献   

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