| Domestic animal offspring of one gender may be preferred over the other. The skewing of offspring sex ratio might have important application in the animal husbandry. At present, sex-ratio skewing occurs in some mammalian species under both field and laboratory conditions, and these alterations might be adaptive. However, the underlying mechanisms are likely to be complex and are still not well understood. From April to August2009and2010, the characteristics of offspring sex ratio skewing and causative factors were researched in plateau pikas(Ochotona curzoniae), a small herbivorous mammal lives in Qinghai-Tibet Plateau, at Haibei Alpine Meadow Ecosystem Research Station, the Chinese Academy of Sciences. The population density dynamic, sex ratio and offspring sex ratio were studied by mark-recapture and direct observation methods during different reproductive periods. Adult females were bred in laboratory to make sure of the amount and sex ratio of newly born offspring of each pair. The concentration of plasma Adrenocorticotropic hormone (ACTH), Corticosterone (CORT), Estradiol (E2), Testosterones (TESTO), Immunoglobulin G (IgG) and Glucagon (Glu) of plateau pikas were measured by enzyme-linked Immunosorbent assay (ELISA) and the relationships between the adult females reproductive quality, reproductive time, plasma hormonal concentrations and their newly birth offspring number and sex ratio were analyzed by stepwise regression for determining the causative factors in skewing offspring sex ratio. Family structure, paternal-infant kinship, mating strategy, and different behavioral time activity budget of plateau pikas’adults were studied by mark-recapture, microsatellite technology and direct observation techniques. The relationships among the offspring amount and sex ratio of every male adult and its behavior, rank and the concentration of plasma hormone were studied. The main results were reported as follows:1. The sex ratio of young plateau pikas born in May was significant differ from those born in June (P<0.01). The sex ratio of young pikas born in May at higher density population was significant differ from1:1(x2=5.579, P=0.018), however, the sex ratio of young pikas in lower density population and born in June at higher density population was not significant differ from1:1(P>0.05)2. The birth weight of young males born in May were significantly higher than young females (F=6.567, P=0.016), also significantly higher than young males born in June (F=6.791, P=0.034). The birth weight of young males born in June were not significantly differ from young females (F=1.036, P=0.547), and the birth weight of young females born in May were not significant differ from young females born in June (F=1.356,P=0.213)3. At August, the male weight of first litter was significantly higher than second litter (F=9.456, P=0.001), but the female weight of first litter was not significantly differ from second litter (F=2.341, P=0.136); Survival rate of first litter males from August2009to April2010were significantly higher than that of second litter male (x2=4.609, P=0.032), but there was a significant difference between the female of first and second litter, which means the young male quality of first litter was higher than second litter. These results support the first cohort advantage hypothesis.4. The litter size of female adult was affected by reproductive time and population density. The litter size of female adult born in May was significance higher than born in June (F=4.072, P=0.022), and the litter size of female adult in lower population density was also higher than the higher population density (F=13.588, P=0.001)5. By stepwise regression, the reproductive time, year and litter size were determined as the main causative factors in the offspring sex ratio skewing(R=5.293, F=14.307, P<0.001). The concentration of female adult plasma IgG and Glu at gestation, and body weigh, ear length, rear foot length, and body length of female adult after reproductive did not affect the offspring sex ratio.6. Predator amount have affected the concentration of plasma ACTH, CORT, E2, TESTO, IgG and Glu, and also affected the ratio of male young birth in May.7. The concentration of female adult plasma ACTH has a significant positive correlation with that of the CORT (P<0.001). The concentration of female adult plasma ACTH, CORT have a significant positive correlation with that of the E2and TESTO respectively (P<0.05), but without a significant correlation with that of IgG and Glu respectively (P>0.05). The concentration of female adult plasma E2has a significant positive correlation with that of the TESTO (P=0.004), but with no significant correlation with that of IgG and Glu respectively (P>0.05). However, concentration of female adult plasma IgG has a significant positive correlation with that of the Glu (P=0.004)8. By stepwise regression, the concentration of female adult plasma TESTO at the period of around conception or pregnancy were evaluated as the causative factor in skewing the offspring sex ratio (F=16.149, P<0.001). The proportion of male young increased with plasma TESTO around conception, and decreased with plasma TESTO at pregnancy. These results support maternal testosterone levels govern mammalian sex ratio deviations hypothesis.9. By stepwise regression, the concentration of female adult plasma Glu at the period of around conception were found as the causative factor in skewing offspring sex ratio. The proportion of male young increased with plasma Glu around conception. This result supports maternal glucose levels govern mammalian sex ratio deviations hypothesis.10. Averages percentage of observation and aggressive behaviors of dominant male adults were significantly higher than that of subordinate male adult, respectively (P<0.05), but the averages percentage of feeding, locomotion and familiarly behaviors of dominant male adult were not significantly differ from that of subordinate male adult respectively (.P>0.05).11. Concentration of dominant male plasma TESTO were significantly higher than that of subordinate male adult (F=33.453, P<0.001), but the concentration of ACTH, CORT, E2, IgG and Glu of dominant male plasma showed no significance difference from that of subordinate male adult respectively (P>0.05).12. The offspring amount of dominant male at May was significantly higher than that of subordinate male adult (F=54.009, P<0.001), and the sex ratio of offspring of dominant male was significantly different form subordinate (F=8.411, P=0.009).13. By stepwise regression, averages of percentages of observation and the concentration of male adult plasma TESTO at the time of impregnation were determining as the causative factors for offspring numbers at May. The averages of percentages of aggressive behavior of male adult was determining as the causative factor skewed the offspring sex ratio. The proportion of male offspings increased with the averages of percentages of aggressive behavior of adult males (P=0.004).14. Summary, plateau pikas could regulate the sex ratio of their offsprings according to the fitness of male and female offsprings. Adult females regulate their offspring sex ratio by modulating the concentration of plasma TESTO and Glu at the time around conception and the concentration of plasma TESTO at pregnancy; Adult males got the dominant rank and increased their reproductive success by improving the percentage of observation and aggressive behavior. Male adult also could affect their offspring sex ratio by modulating their aggressive behavior. |
PDF Full Text Request