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111.
112.
Yung Hang Lam Mary Hoi Yin Tang Chin Peng Lee Sai Yuen Sin Rebecca Tang Hong Soo Wong Sai Fun Wong 《黑龙江环境通报》2001,21(8):627-629
Recent data have suggested that fetal nuchal translucency (NT) is affected by fetal gender. We investigated the size of this effect in 12 189 unselected pregnancies with known normal outcomes that had undergone NT measurements between 10 and 14 weeks of gestation. NT increased with gestation and was converted to multiples of the median (MoM) for the gestational day. The median NT MoM (95% CI) for female fetuses was 0.98 (0.97–0.99). This was significantly lower than that of the male fetuses (1.03; range1.02–1.04) (p<0.0005; Wilcoxon rank-sum test). The gender difference was not observed at 10 weeks but was observed from 11 weeks onwards. There is no obvious explanation for the above findings. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
113.
Summary. Individual variations in pheromone emission patterns were examined in a scarab beetle, Anomala cuprea Hope (Coleoptera: Scarabaeidae), by headspace collection of airborne volatiles from individual females. The amount of pheromone
obtained varied among virgin females, and about 16% of these females (“silent” females) did not emit detectable amount of
pheromone throughout the experimental period. There was no clear temporal pattern of peak pheromone emission for 19 days after
the onset. More than half of the laboratory mated females completely stopped releasing pheromone after the first mating, while
the rest of them continued releasing pheromone, frequently followed by additional mating.
Received 26 March 2001; accepted 28 January 2002. 相似文献
114.
Chad C. Smith 《Behavioral ecology and sociobiology》2007,61(9):1349-1358
Operational sex ratio (the ratio of sexually active males to fertilizable females) has a major influence on male competition
for mates and male–female interactions. The contributions of male and female density per se to mating system dynamics, however,
are rarely examined, and the fitness consequences are often inferred rather than quantified. Male mosquitofish (Gambusia affinis) compete aggressively and frequently harass females for copulations, a behavior thought to reduce female fitness. Female
fitness can also be reduced by increases in female density, which may affect food availability, cannibalism rates, and chemical
interactions between females. I manipulated male and female densities of G. affinis to measure their effects on male–male aggression, male harassment toward females, and female fitness. I found that males
chased rivals more often and attempted fewer copulations when female density decreased, but surprisingly male density had
no significant effect on the frequency of these male behaviors. In contrast, males’ agonistic displays toward other males
increased with male density, but display behavior was unaffected by female density. These results suggest that male and female
density do not always contribute equally or at all to the patterns of behavior we observe. Female fitness declined as female
density increased, the opposite pattern expected if male harassment is costly to females. This suggests that a strong, negative
effect of female density overwhelmed any potential costs of male harassment. Sources of female density dependence and the
consequences of changes in male and female density to patterns of male behavior are discussed. 相似文献
115.
116.
117.
Results of laboratory experiments on the effects of population density of Aedes communis Deg. larvae on their growth, survival, and sex ratio are presented. At the highest density, larval mortality increased by factors of 1.5 and 2.2, the duration of preimaginal development increased significantly, and the weight of pupae was 11 and 14.7% smaller than in low-density populations. The sex ratio was the same in both cases. The absolute numbers and the biomass of insects per cultivation vessel were greater in high-density populations. 相似文献
118.
S. Balshine-Earn 《Behavioral ecology and sociobiology》1996,39(2):107-116
Operational sex ratio (OSR) theory predicts that sexual differences in potential reproductive rates (PRRs) create biases
in the OSR and thus determine the relative strength of sexual selection (competition and choice) operating on each sex. Although
this theory is well accepted, empirical studies that quantify it are still lacking. This paper presents such a study. I measured
the natural OSR of Galilee St. Peter’s fish (Sarotherodon galilaeus) in the field (Lake Kinneret) and examined the direction of mate choice in the laboratory. The OSR in Lake Kinneret was male
biased. Both a male-biased sex ratio and higher male reproductive rates (twice as fast as females) contributed to the skew
in the OSR, but the sexual differences in PRR were shown to be the main factor causing variation in the OSR. Females, the
sex with the lower PRR, were more selective for mates. The faster male reproductive rate may explain why females are more
selective for mates despite varying less in quality.
Received: 29 May 1995/Accepted after revision: 13 April 1996 相似文献
119.
Summary. Under field conditions significantly more black
chafer, Holotrichia loochooana loochooana (Sawada)
(Coleoptera: Scarabaeidae) males landed on black and gray
sources than white ones containing 10 mg of female
pheromone, anthranilic acid. When a broader spectrum of
colours was tested the frequency of male landing was intensively
proportional to as the lightness of the colour of the
lures. These findings demonstrated that mate location by
H. l. loochooana males is dependent on
both olfactory and visual stimuli of the source. In contrast, female aggregation was not
affected by colour. 相似文献
120.
洞庭平原褐家鼠种群动态和繁殖特性 总被引:8,自引:1,他引:7
褐家鼠是洞庭平原稻作区的主要害鼠之一,在房舍区数量动态复杂,季节消长基本上属春冬双峰型,在农田区数量季节消长为夏秋双峰型。褐家鼠总雌性比为52.0%,全年繁殖.3~10月为繁殖盛期,盛期平均怀孕率为34.91±8.69%,平均胎仔数为8.2±l.0,4、7、9月出现怀孕高峰,11月至翌年2月为繁殖低潮期。褐家鼠在洞庭平原70年代数量较低,80年代初暴发成灾,80年代后期数量有逐步下降趋势。针对种群特征,提出了控制褐家鼠种群数量的对策。 相似文献