Effects Of "Public Information" On Offspring Sex Ratio In Great Tit (Parus Major)

When the population sex ratio deviates from 1:1, it will occur compensatory changes, and always skewed toward the rare sex. Based on the study status of the theory of public information and bird sex ratio adjustment, we test that whether the Great Tit (Parus major) have the ability to adjust their offspring sex ratio according to public information in the study. The hypothesis is that the Great Tits is able to gather the public information by acoustical signals, this is, according to different individuals'songs, and the Great Tits could judge whether the population sex ratio deviated from 1:1 and make decisions to adjust offspring sex ratio. The study was conducted from March to July during the period from 2008 to 2009 in Zuojia Nature Reserve. A modified playback system was used to continuously exaggerate the amount of colony sound available to the Great Tit throughout their pre-reproductive period and breeding period respectively. We collected 897 blood samples of nestlings or embryo samples from 108 broods for analyzing primary sex ration of offspring, and we collected 772 blood samples of nestlings from 108 broods for analyzing secondary sex ration of offspring. Our results showed that the primary and secondary sex ratio of offspring in population level in female sounds playback plots during the period of pre-reproductive was 1.09: 1 (♂:♀) and 1.03: 1 respectively; the primary and secondary sex ratio of offspring in population level in male sounds playback plots during the period of pre-reproductive was0.87: 1 and 0.78: 1 respectively; the primary and secondary sex ratio of offspring in population level in female sounds playback plots during breeding seasons was 0.95: 1 and 0.81: 1 respectively; the primary and secondary sex ratio of offspring in population level in male sounds playback plots during breeding seasons was 1.04: 1 and 1.17: 1 respectively; and the primary and secondary offspring sex ratios in population level in control plot was 1.22: 1 and 1.41: 1 respectively. Our results indicated that, to a certain extent, the Great Tit could adjust their premary and secondary sex ratio of offsoring according to public information. Playbacking sounds of males during pre-reproductive period will make the premary sex ratio of Great Tit to skew to female, however, contrary to the predication that playbacking sounds of females will make the offspring sex ratio of Great Tit to skew to male, the offspring sex ration in female sounds playbacking plots skewed to female, those results showed that the Great Tit could judge the population sex ratio and adjust their offspring sex ratio according to male sounds, and the adjustment of offspring sex ration mainly occurred during pre-reproductive period. An increasing number of studies have provided strong evidence that female birds can adjust the primary sex-ratio of their offspring by laying sex-biased clutches, however, our results did not find that the clutch size correlated to offspring sex ratio in Great Tit, but, the clutch size of Great Tit increased in female sounds playback plots during breeding period, mean clutch size for female sounds playback plot was 12.6±1.942 eggs (n = 19), for male sounds playback plot was 9.82±2.31 eggs (n = 26), for control plot was 10.55±1.703 eggs (n = 11). The clutch size in plots with sounds playback during breeding seasons did not differ significantly. Before breeding season, the mean laying date for male sounds playback is April 24th±10.17(n = 25).it is 13 days earlier than the plots with male song playback, 11 days earlier than the control plot, although the difference between them was not significant; it is a significant between palyback and laying date during the breeding seasons, the mean laying date for female sounds playback is April 20th±8.09(n = 15), it is 18 days earlier than the plots with female song playback and 15 days earlier than the control plot.Linear mixed models (LMM) calculated and indicated that clutch size and laying date and interaction between them have no significant effects on the primary and secondary offspring sex ratio at broods level,and laying sequence and egg mass and interaction also have no significant effects on offspring sex ratio of Great Tit.