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211.
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213.
The local resource enhancement (LRE) model predicts that in cooperatively breeding species, sex ratios will be biased in favor
of the more helpful sex. In this study, we assess the assumptions underlying the LRE model in a population of cooperatively
breeding wild dogs (Lycaon pictus) in Northern Botswana monitored over a 15-year period. In this population, litter size and pup survival to 1 year are strongly
affected by pack size and the breeding female’s age, but adult males have a stronger and more linear effect on females’ reproductive
performance than do adult females. This asymmetry in the benefits derived from male and female helpers is reflected in male-biased
sex ratios in litters at the time pups emerge from the den. Sex ratio biases are most pronounced in the litters of the youngest
mothers who live in significantly smaller packs than older females. The presence of potential rivals for the dominant female’s
position depresses pup production at the time of emergence, suggesting that competition among females for breeding positions
may also contribute to the selective forces affecting birth sex ratios. 相似文献
214.
Tug-of-war over reproduction in a cooperatively breeding cichlid 总被引:1,自引:0,他引:1
In group-living animals, dominants may suppress subordinate reproduction directly and indirectly, thereby skewing reproduction
in their favour. In this study, we show experimentally that this ability (‘power’) is influenced by resource distribution
and the body size difference between unrelated dominants and subordinates in the cichlid Neolamprologus pulcher. Reproduction was strongly skewed towards the dominant female, due to these females producing more and larger clutches and
those clutches surviving egg eating better than those of subordinate females, but was not so when subordinates defended a
patch. If breeding shelters were provided in two patches, subordinate females were more likely to exclusively defend a patch
against the dominant female and breed, compared to when the same breeding resource was provided in one patch. Relatively large
subordinate females were more likely to defend a patch and reproduce. Females also directly interfered with each other’s reproduction
by eating the competitors’ eggs, at which dominants were more successful. Although dominant females benefited from subordinate
females due to alloparental care and an increase in egg mass, they also showed costs due to reduced growth in the presence
of subordinates. The results support the view that the dominant’s power to control subordinate reproduction determines reproductive
partitioning, in agreement with the predictions from tug-of-war models of reproductive skew. 相似文献
215.
216.
主要从深圳市农业对水体的陆源污染包括农田化肥流失和畜禽养殖业排污等污染源出发,通过对农业化肥施用量和施用强度、畜禽养殖业排污变化趋势分析,估算出二者各自污染物排放量,探讨其与深圳近海水体污染变化趋势间的关系。对相关数据分析表明:(1)深圳市农业化肥流失是深圳近海水体富营养化成因之一,其在1994年之后对近海水体污染程度加大;(2)深圳市畜禽养殖业排污是深圳近海水体富营养化主要成因之一,其在1997年之后对近海水体污染程度加大;(3)农业化肥流失和畜禽养殖业排污主要受农业用地面积、农业政策的影响。 相似文献
217.
纤维素酶产生菌的选育及发酵条件优化 总被引:1,自引:0,他引:1
通过紫外线和化学诱变方法对一株纤维素酶产生菌--绿色木霉他进行了菌株选育,提高了产酶能力,变异株T211的CMCase和FPA分别达到19.17 IU/mL和1.94 IU/mL.进一步对其发酵条件进行研究,优化了培养基和培养条件.优化的培养基为:微晶纤维素10 g/L,麸皮10 g/L,蛋白胨0.4 g/L,尿素0.4 g/L,硫酸铵2.0 g/L,吐温-80 2.0 mL/L,其他同Mandel's营养盐液;培养条件包括温度、摇瓶装量、转速和接种量分别为:27~28℃、50 mL/250 mL、180 r/min和4%~6%.在上述条件下,CMCase达到25 IU/mL,FPA达到2.5 IU/mL. 相似文献
218.
In the cooperatively breeding red-cockaded woodpecker (Picoides borealis), male helpers are subordinate to male breeders and do not mate with females, even when unrelated to the breeding female
within their group or through extra-group matings, yet exhibit reproductive hormone profiles similar to those of breeders.
We investigated whether reproduction might be suppressed in helper males via high levels of the stress hormone corticosterone.
We also examined effects of group size and season on corticosterone levels by comparing baseline and maximal plasma levels
of corticosterone between helper males and breeding males, and among helper males and breeders of both sexes living in groups
of different sizes throughout the reproductive cycle. We also measured plasma levels of estrogen, progesterone, and testosterone
to examine other potential hormonal differences between helpers and breeders. Male status did not explain variation in any
hormones; therefore, our data do not support the hypothesis that helper males are reproductively suppressed via corticosterone
or the other hormones investigated. However, the presence of two or more helper males in a group tended to reduce baseline
corticosterone in breeding and helper males, but not breeding females, suggesting that helper males reduce parental effort
of other male group members. Seasonally, maximal corticosterone peaked during the nestling provisioning phase for breeding
and helper males, but not breeder females, suggesting that males show an increased response to stressors posing a potential
threat to survival of offspring. 相似文献
219.
Walter D. Koenig Eric L. Walters Joseph Haydock 《Behavioral ecology and sociobiology》2009,63(11):1659-1665
In cooperatively breeding acorn woodpeckers (Melanerpes formicivorus), helper males have a large positive effect on fledging success in good acorn crop years but only a small positive effect
in poor acorn crop years, while helper females exhibit the opposite pattern. Based on these findings, we tested the “concealed
helper effects” hypothesis, which proposes that laying females reduce investment in eggs (with respect to their size, number,
or quality) in a way that confounds helper effects and results in an absence of a relationship between helpers and breeding
success. Results generally failed to support the hypothesis. Mean egg size was positively related to temperatures during the
10 days prior to egg-laying and negatively related to the food supply as indexed by the prior fall’s acorn crop, but there
were no significant differences vis-à-vis helpers except for interactions with the acorn crop that only partly corresponded
to those predicted. With respect to clutch size, females laid larger clutches when assisted by female helpers, opposite the
pattern predicted. Although our results suggest that egg size is adjusted to particular ecological circumstances, we conclude
that neither egg nor clutch size is adjusted in a way that confounds the apparent effects of helpers, as proposed by the concealed
helper effects hypothesis. 相似文献
220.
油菜的自交不亲和性和杂种优势育种 总被引:5,自引:0,他引:5
官春云 《湖南环境生物职业技术学院学报》2001,7(1):1-6
本文综述了油菜自交不亲和性的特征特性、遗传特点、分子机制、甘蓝型油菜自交不亲和性的选育方法、油菜自交不亲和性繁殖和油菜自交不亲和杂种优势利用途径与方法。 相似文献