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1.
Coevolution between male and female traits can result from correlatedresponses to selection or correlated selection on geneticallyindependent traits. This study examines the possibility thattraits involved in precopulatory sexual selection may influencethe evolution of traits involved in postcopulatory sexual selectiondue to the existence of correlated selection or correlated responsesto selection. Artificial selection on male eye span in Cyrtodiopsisdalmanni, a sexually dimorphic stalk-eyed fly, is used to testfor correlated changes in reproductive traits of male and femaleflies. Flies from replicate lines that had been under selectionfor 57 generations were matched for age and genotyped at fourX-linked microsatellite loci. Egg number and testis size increasedwith age, but did not differ among lines. Spermathecal areasand duct lengths differed among replicates, but not among selectiontreatments. Female relative eye span, size of the ventral receptacleand egg size exhibited significant correlated responses to selectionon male relative eye span. The absence of any change in spermlength or testis size between lines indicates that changes infemale traits are unlikely due to correlated selection mediatedby sperm competition. Significant effects of X-linked microsatellitegenotypes indicate instead that the correlated responses toselection were due, in part, to X-linked genes in linkage disequilibriumor that exhibit pleiotropy. The presence of nonadditive alleliceffects on genetically correlated female traits combined withadditive allelic effects on a male ornament provides a previouslyunrecognized mechanism by which genetic variation could be maintaineddespite strong sexual selection.  相似文献   

2.
Estrogen attenuates postexercise HSP70 expression in skeletal muscle   总被引:5,自引:0,他引:5  
Exercise has been demonstrated as aphysiological inducer of heat shock protein (HSP)70. Many of theproposed signals of this response exhibit sexual dimorphism. Thus thepresent objectives were to determine whether HSP70 induction afterexercise exhibits gender specificity and to elucidate the mechanismsunderlying such a phenomenon. Postexercise HSP70 induction in skeletalmuscle was greater in male than female rats at the level of protein and mRNA (P = 0.005). Moreover, placebo-treatedovariectomized animals demonstrated a greater HSP70 response toexercise than those treated with estrogen (P = 0.015 and 0.019 for protein and mRNA, respectively). These findings indicatethat the gender-specific HSP70 response to exercise is mediated by thefemale-specific hormone estrogen. Compounds structurally related to17-estradiol, the major endogenous estrogen, but which do notactivate the estrogen receptor, also attenuated HSP70 induction withexercise (P < 0.01), indicating a nongenomic hormonalmechanism. These findings highlight a specific example of thebiological differences between males and females and reiterate thephysiological effects of sex hormones extending beyond their roles inreproductive function.

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3.
Heat stress prior to diving has been shown to confer protection against endothelial damage due to decompression sickness. Several lines of evidence indicate a relation between such protection and the heat shock protein (HSP)70 and HSP90 and the major cellular red-ox determinant, glutathione (GSH). The present study has used human endothelial cells as a model system to investigate how heat stress and simulated diving affect these central cellular defense molecules. The results demonstrated for the first time that a simulated dive at 2.6 MPa (26 bar) had a potentiating effect on the heat-induced expression of HSP70, increasing the HSP70 concentration on average 54 times above control level. In contrast, a simulated dive had no significant potentiating effect on the HSP90 level, which might be due to the higher baseline level of HSP90. Both 2 and 24-h dive had similar effects on the HSP70 and HSP90, suggesting that the observed effects were independent of duration of the dive. The rapid HSP response following a 2-h dive with a decompression time of 5 min might suggest that the effects were due to compression or pressure per se rather than decompression and may involve posttranslational processing of HSP. The exposure order seemed to be critical for the HSP70 response supporting the suggestion that the potentiating effect of dive was not due to de novo synthesis of HSP70. Neither heat shock nor a simulated dive had any significant effect on the intracellular GSH level while a heat shock and a subsequent dive increased the total GSH level approximately 62%. Neither of these conditions seemed to have any effect on the GSH red-ox status.  相似文献   

4.
Testosterone has recently been proposed as a link between male quality and health and the expression of sexual traits. We investigated the relationship between testosterone and measures of the individual condition and health of males in a natural population of house finches (Carpodacus mexicanus). We also conducted a captive experiment in order to test for the effects of testosterone on resistance to coccidia, which is a common parasite of house finches. Free-living males in better condition had higher testosterone levels and lower corticosterone levels than free-living males in poor condition. In our captive experiment, increased testosterone accelerated the rate of coccidial infection as compared with sham-implanted or gonadectomized males. Although the differences were not significant, free-living males infected with coccidia had lower levels of testosterone and higher levels of corticosterone than males that were not infected. Thus, experimentally elevating testosterone levels in captive males resulted in a higher percentage of infected males, while free-living males with coccidial infection had low testosterone levels. This apparent discrepancy between captive and free-living males in the association of testosterone and disease may be explained by the condition dependence of testosterone. These results suggest that the testosterone-dependent sexual traits reliably indicate male overall condition and health and, thus, females could benefit from assessing potential mates based on these traits.  相似文献   

5.
The study of oxidative stress is a potential tool for studying the functional interactions among life history traits, sexual traits and physiological status in animals. In this study, we investigated relationships between measures of plasma oxidative status and male sexual traits, female reproductive investment and three other life history traits, in a wild population of collared flycatchers (Ficedula albicollis). Flycatcher males with a larger white forehead patch had higher level of plasma antioxidant capacity. For females, clutch size was not associated with plasma oxidative status, but egg size was positively correlated with antioxidant capacity. The relationship between age and levels of plasma oxidative damage remains controversial in this species: young female flycatchers showed higher levels of hydroperoxides compared to antioxidants, whereas age did not predict oxidative status of males. Males had higher levels of oxidative damage than females, although the concentration of antioxidant compounds was similar between the sexes. Females that mated with more ornamented males had higher plasma antioxidant capacity. Our results suggest that, for males and females, greater investment in sexual signal and reproduction, respectively, does not reduce the capacity for self-maintenance or avoidance of oxidative stress. Finally, our data support indirectly the occurrence of assortative mating in our species, since females with higher plasma antioxidant capacity mated with more ornamented males.  相似文献   

6.
Negative relations between trait size and levels of fluctuatingasymmetry in secondary sexual traits have been claimed to beindicative of honest signaling of male quality. Comparativestudies of beetle horns have been used to illustrate the requirednegative relation between trait size and asymmeiry However,such studies may be confounded by measurement error or samplingbias due to population differences or differences within speciesin the phenotypic expression of hornedness. We examined thepatterns of fluctuating asymmetry within two species of hornedbeetle. We found that, in agreement with theory, horns exhibitgreater asymmetry than naturally selected traits. However, wefound a strong positive relation between horn size and asymmetryin Onthophagus taurs, a species with male dimorphisms, and aflat relation in Bubas bison, a species with continuous variationin horn size. We suggest that these differences may reflectfunctional differences in horns. We conclude that patterns ofasymmetry in horned beetles do not support the notion of honestsignaling.  相似文献   

7.
Sexual selection has traditionally been divided into competitionover mates and mate choice. Currently, models of sexual selectionpredict that sexual traits are expressed in proportion to thecondition of their bearer. In horned beetles, male contestcompetition is well established, but studies on female preferencesare scarce. Here I present data on male mating success and condition dependence of courtship rate in three species of horn-dimorphicdung beetles, Onthophagus taurus, Onthophagus binodis, andOnthophagus australis. I found that in the absence of malecontest competition, mating success of O. taurus and O. australiswas unrelated to their horn length and body size, whereas inO. binodis horn size had a negative effect but body size hada positive effect on male mating success. Overall, in O. binodismajor morph males had greater mating success than minor morphmales. In all three species male mating success was affectedby courtship rate, and the courtship rate was condition dependent such that when males were manipulated to be in poor conditionthey had lower courtship rates than males that were manipulatedto be in good condition. My findings provide new insight intothe mating systems of horned dung beetles and support an importantassumption in indicator models of sexual selection.  相似文献   

8.
Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.  相似文献   

9.
Few studies have focused on the expression of heat shock proteins (HSPs) after chronic heat stress. The objective of this study was to investigate the effect of chronic high temperature–humidity index treatment on the expressions of HSP60, HSP70, HSP90, HSPA2 and HSC70, in the Rex rabbit testis and the expressions of these proteins after recovery from the chronic heat shock. Thirty mature male rabbits of the same age were randomly divided into three groups: control, heat stress, and recovery. The western blot results showed that the expressional levels of HSP60, HSP90, and HSC70 increased significantly and HSPA2 was elevated slightly after a 9-week heat treatment. HSP70 was absent in the control testis and had a high level of expression after heat stress. All of these proteins partially reverted back to normal levels after a 9-week recovery. The immunohistochemical results indicated that the expression patterns of HSP60, HSP90, HSPA2, and HSC70 did not change.  相似文献   

10.
One postulated mechanism for the reduction in stress tolerance with aging is a decline in the regulation of stress-responsive genes, such as inducible heat shock protein 72 (HSP70). Increased levels of oxidative stress are also associated with aging, but it is unclear what impact a prooxidant environment might have on HSP70 gene expression. This study utilized a superoxide dismutase/catalase mimetic (Eukarion-189) to evaluate the impact of a change in redox environment on age-related HSP70 responses to a physiologically relevant heat challenge. Results demonstrate that liver HSP70 mRNA and protein levels are reduced in old compared with young rats at selected time points over a 48-h recovery period following a heat-stress protocol. While chronic systemic administration of Eukarion-189 suppressed hyperthermia-induced liver HSP70 mRNA expression in both age groups, HSP70 protein accumulation was blunted in old rats but not in their young counterparts. These data suggest that a decline in HSP70 mRNA levels may be responsible for the reduction in HSP70 protein observed in old animals after heat stress. Furthermore, improvements in redox status were associated with reduced HSP70 mRNA levels in both young and old rats, but differential effects were manifested on protein expression, suggesting that HSP70 induction is differentially regulated with aging. These findings highlight the integrated mechanisms of stress protein regulation in eukaryotic organisms responding to environmental stress, which likely involve interactions between a wide range of cellular signals.  相似文献   

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