Differential reproductive success among subfamilies in queenless honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) colonies

With very rare exceptions, queenright worker honeybees (Apis mellifera L.) forego personal reproduction and suppress reproduction by other workers, preferring to rear the queens sons. This is in stark contrast to colonies that have lost their queen and have failed to rear a replacement. Under these conditions workers activate their ovaries and lay many eggs that develop parthenogenetically into a final brood of males (drones) before the colony perishes. Interestingly, not all workers contribute equally to this final generation of drones in queenless colonies. Some subfamilies (workers that share the same father) contribute a disproportionately greater number of offspring than other subfamilies. Here we explore some of the mechanisms behind this reproductive competition among subfamilies. We determined the relative contribution of different subfamilies present in colonies to laying workers, eggs, larvae and pupae by genotyping samples of all life stages using a total of eight microsatellite loci. Our colonies were headed by free-mated queens and comprised 8–17 subfamilies and therefore differed significantly from colonies used in an earlier study investigating the same phenomena where colonies comprised an artificially low number of subfamilies. We show that, first, subfamilies vary in the speed with which they activate their ovaries after queen-loss and, second, that the survival of eggs to the larval stage is unequal among subfamilies suggesting that some subfamilies lay eggs that are more acceptable than others. However, there is no statistically significant difference among subfamilies in the survival of larvae to pupae, indicating that ovary activation and egg survival are the critical components to reproductive competition among subfamilies of queenless honeybee workers.Communicated by R. Page     

Specificity of odour-mediated avoidance of competition in Drosophila parasitoids

Although there are many examples of the role of volatile infochemicals in interactions between trophic levels of insect communities, surprisingly little is known of volatile interactions between species within the third trophic level. Recently it was found that Leptopilina heterotoma, an endoparasitoid that attacks Drosophila larvae, avoids one type of patches (decaying stinkhorn mushrooms) when parasitoids of another species (L. clavipes) are present on these patches. L. heterotoma is able to smell the presence of L. clavipes from a distance (Fig. 1). In this paper we investigate the source of the odour that induces avoidance behaviour, by varying the host species and parasitoid species present on stinkhorn mushrooms, and by using another type of patch (sap-fluxes of wounded trees). L. heterotoma was found to avoid stinkhorn patches with conspecific as well as heterospecific parasitoids (Fig. 2). Hosts had to be present in the patch to elicit avoidance, but avoidance behaviour was also found with another host species present in the patch (Fig. 3). No avoidance behaviour was found with sap-flux patches with hosts and parasitoids on them (Fig. 4). Avoidance of stinkhorn patches only occurred when the parasitoids present on the patch were able to contact hosts (Figs. 5 and 6). The exact source of the odour that elicits avoidance is still unclear, so that one can only speculate on the function of the signal. However, there is a clear benefit to the receiver, because it is able to avoid superior competitors. Avoidance can lead to non-aggregated parasitoid distributions. The importance of avoidance behaviour for population dynamics and stability of parasitoid-host systems is discussed.     

The scent of dominance: female field crickets use odour to predict the outcome of male competition

Pheromones may convey information about mate quality and social status. In the field cricket Gryllus integer, females mount the males for copulation, such that males cannot coerce females to mate. We examined whether virgin G. integer females preferred the scent of potentially dominant males to that of subordinate males. First, we collected pheromones by confining males on filter paper. Next, we offered filter paper from each of two size-matched males and control paper to females that had never been exposed to males, and measured the time spent by the female on each kind of paper. Finally, dominance status of the males in each size-matched pair was determined by pitting the two males against one another in agonistic contests. When offered filter paper from subsequently dominant versus subsequently subordinate males, females spent more time on the paper from the dominant male than the subordinate male, and much less time on control paper. Thus, pheromones may inform female G. integer about a male's potential to achieve dominant social status. Male pheromones were also associated with the female's tendency to mount a male. In contrast to cockroaches, where females prefer the scent of subordinate males (presumably to avoid risk of injury), female crickets prefer the scent of potentially dominant males and are more likely than males to wound their mating partners.     

Seasonal variation in feeding behavior, competition and female social relationships in a forest dwelling guenon, the blue monkey (Cercopithecus mitis stuhlmanni), in the Kakamega Forest, Kenya

Socioecological models relate differences in feeding strategies to variation in the nature of female social relationships. Among the African forest guenons, females consume large quantities of fruit and other plant reproductive parts, resources which are thought to promote contest competition, yet these monkeys have been characterized as having agonistically undifferentiated relationships in which rank, if discernible at all, does not correlate with fitness benefits. To determine whether female relationships become more hierarchical under relevant ecological conditions, we monitored the adult females of two blue monkey groups (Cercopithecus mitis stuhlmanni) over a complete annual cycle in the Kakamega Forest, Kenya. Females competed aggressively for plant reproductive parts more often than any other resource type, and in both groups we detected linear dominance hierarchies. Nonetheless, agonism rates remained low throughout our study, and did not vary with changes in ecological conditions. Rather, when plant reproductive parts were scarce, subordinate females spent more time feeding and less time resting in an apparent attempt to compensate for a reduced efficiency of food intake. The effects of rank and food abundance were not reflected, however, in the distribution of grooming. The use of alternative feeding strategies appeared to blunt competition – females of all ranks were unlikely to be near others while feeding and spent more time consuming alternative resources when plant reproductive parts were scarce. The diverse diet of this species may allow females to avoid conflict so that dominance has only subtle effects that are difficult to detect. While socioecological models often simplify the connection between resources and female interactions, our results emphasize that the behavior of animals consuming particular resources, and not the resources themselves, are critical predictors of social patterns.     

Rank differences in energy intake rates in white-faced capuchin monkeys, Cebus capucinus: the effects of contest competition

The effect of aggressive competition over food resources on energy intake rate is analyzed for individuals of three groups of 25–35 white-faced capuchin monkeys, Cebus capucinus, living in and near Lomas Barbudal Biological Reserve, Costa Rica. An individuals energy intake rate on a given food species was affected by its rank and the number of agonistic interactions within the feeding tree. Dominant group members had higher energy intake rates relative to subordinate group members whether or not there was agonism within the feeding tree. Low- and mid-ranked individuals had lower energy intake rates in trees with higher amounts of aggression, while energy intake rate of high-ranked individuals was not affected by the amount of aggression in the feeding tree. Energy intake was not influenced by the sex of the individual when rank was held constant statistically. Energy intake was positively correlated with total crown energy (measured in kilojoules) within the feeding tree for two of three study groups. This difference may be explained by the quality of each groups territory. Finally, high-ranked individuals are responsible for the majority of agonism within feeding trees and target middle- and low-ranked individuals equally. These findings fit the predictions of current socioecological models for within-group contest competition over food resources. The results of this study suggest that within-group competition affects energy intake rate in white-faced capuchin monkeys.     

Alternative reproductive tactics in male common shrews: relationships between mate-searching behaviour,sperm production,and reproductive success as revealed by DNA fingerprinting

The common shrew (Sorex araneus) is a solitary small mammal with a promiscuous mating system. Previous studies of this species suggest that females typically mate multiply, and that males may adopt alternative mate-searching tactics. We studied two generations of common shrews in a population near Oxford, England. Males were found to adopt two different mate-searching tactics. Those classed as type A occupied relatively small exclusive ranges during March, and made repeated long-distance movements to visit female ranges around the time of first oestrus in April. Males classed as type B established large overlapping ranges in areas of relatively high female density during March, and maintained these ranges throughout April. Type B males were larger than type A males at an early stage of sexual maturation, but there was no difference in the adult body size of the two types of male. Type A males had significantly higher epididymal sperm counts than type B males. Paternity analyses of litters born during the first year of the study reveal that the mean number of offspring fathered by type B males was greater than the mean number fathered by type A males. It is concluded that different mate-searching tactics may be conditional upon the timing of sexual maturation. Differences in sperm production are discussed in relation to sperm competition theory.     

非稳态条件下藻类种间非生物资源竞争理论及研究进展

从理论及实验研究的角度论述了藻类非稳态种间资源竞争研究进展。实验室内稳态条件下的竞争理论得到了大量实验验证,由于自然水体处于非稳状态,非稳态条件下藻类种间资源竞争日益成为藻类水华形成机制研究的重点。主要理论包括Tilman的R*法则和资源比假说,Grover的拾遗者-机会主义者交替竞争假说(VIS),中度干扰假说(IDH)及关键光强(CLIH)假说。这些假说的提出丰富了藻类资源竞争的理论体系,为研究自然状态下藻类增殖和竞争行为奠定理论基础。今后的藻类种间资源竞争的研究重点为非稳态下物理条件变化以及物理、化学和生物资源共同变化下藻类种间关系及生物多样性的研究。     

Copulation behavior and paternity in the chaffinch

Summary We investigated two aspects of sperm competition in a wild population of chaffinches Fringilla coelebs: copulation behavior and genetic parentage determined by DNA fingerprinting. Pairs copulated at a high rate before laying, peaking at 4.4 copulation attempts per hour on day –3 relative to laying, with an average of 207 copulation attempts (83 behaviorally successful) per clutch. Extra-pair copulation attempts (n = 20) made up 7.8% of all copulation attempts that females were involved in. The rate at which pairs copulated was lower during egg-laying, but there was no evidence that this was due to the male of the pair timing copulations to coincide with an insemination window; it was more likely due to the fact that females solicited copulations at a lower rate. Both sexes solicited copulations but males solicited mainly extra-pair copulations. DNA fingerprinting showed that 17.0% of chicks (n = 47) in 23% of broods (n = 13) were fathered by a male other than the one paired to their mother. There was no evidence of intraspecific brood parasitism. In three cases where we were able to identify the father of extra-pair offspring it proved to be a neighboring male.Correspondence to: B.C. Sheldon     

MBBR泥膜复合系统泥膜竞争关系的影响因素

为探究MBBR泥膜复合硝化系统内泥膜竞争关系，通过小试试验研究了水处理过程中常规因素（污泥浓度、DO、温度、C/N）对MBBR泥膜复合系统硝化效果的影响，分析了系统内污泥容积负荷和移动床生物膜反应器（MBBR，Moving-Bed Biofilm Reactor）生物膜容积负荷变化趋势，进而得出泥膜竞争规律.结果表明，MBBR泥膜复合系统容积负荷均大于单一污泥或MBBR生物膜系统的容积负荷.在一定范围内，污泥浓度、DO、温度与MBBR泥膜复合系统容积负荷呈现正相关，且系统内活性污泥在与MBBR生物膜在竞争DO和基质时优势明显，而MBBR生物膜则具有更强的耐低温能力.进水C/N与MBBR泥膜复合系统硝化负荷呈负相关，且活性污泥在应对进水C/N过高时较MBBR生物膜更具优势，MBBR的“镶嵌”则强化了系统SND效果.微生物群落变化显示MBBR泥膜复合系统内的硝化细菌优势菌属为Nitrospira，且悬浮载体生物膜对其富集能力明显高于活性污泥.     

战略管理在企业管理中的重要性

面对激烈变化、严峻挑战的经营环境,企业欲求得长期生存和不断发展就必须进行总体性谋划。而战略管理便是这种总体性谋划的关键一环。本文主要从战略管理的意义和实施两方面介绍企业应在充分利用环境中存在的各种机会和创造新机会的基础上,确定企业和环境的关系,规定企业从事的经营范围,合理地调动企业结构和分配企业的全部资源,从而使企业获得某种竞争优势。