Kin selection and the evolution of sexual conflict

Males and females do not always share the same evolutionary interests. This is particularly true in the case of multiple mating, where male–male competition can often lead to adaptations that are harmful to the female, and females can evolve counter adaptations to reduce the benefits males gain from such traits. Although social evolution has made substantial progress from kin selection theory, most studies of sexual conflict have ignored the effects of genetic relatedness. Here, I use a model of male harm and female resistance to investigate how kin selection affects the evolution of sexual conflict. Building on models of social evolution, I show that relatedness inhibits sexual conflict, in terms of male harm, whereas it has no effect on the evolution female resistance. This study examines a previously neglected mechanism that can potentially help to resolve sexual conflict over mating and highlights the potential importance of considering relatedness in empirical studies of sexual conflict.     

Diffusible signal factor‐dependent quorum sensing in pathogenic bacteria and its exploitation for disease control

Cell‐to‐cell signals of the diffusible signal factor (DSF) family are cis‐2‐unsaturated fatty acids of differing chain length and branching pattern. DSF signalling has been described in diverse bacteria to include plant and human pathogens where it acts to regulate functions such as biofilm formation, antibiotic tolerance and the production of virulence factors. DSF family signals can also participate in interspecies signalling with other bacteria and interkingdom signalling such as with the yeast Candida albicans. Interference with DSF signalling may afford new opportunities for the control of bacterial disease. Such strategies will depend in part on detailed knowledge of the molecular mechanisms underlying the processes of signal synthesis, perception and turnover. Here, I review both recent progress in understanding DSF signalling at the molecular level and prospects for translating this knowledge into approaches for disease control.     

H-NOX proteins in the virulence of pathogenic bacteria

Nitric oxide (NO) is a toxic gas encountered by bacteria as a product of their own metabolism or as a result of a host immune response. Non-toxic concentrations of NO have been shown to initiate changes in bacterial behaviors such as the transition between planktonic and biofilm-associated lifestyles. The heme nitric oxide/oxygen binding proteins (H-NOX) are a widespread family of bacterial heme-based NO sensors that regulate biofilm formation in response to NO. The presence of H-NOX in several human pathogens combined with the importance of planktonic–biofilm transitions to virulence suggests that H-NOX sensing may be an important virulence factor in these organisms. Here we review the recent data on H-NOX NO signaling pathways with an emphasis on H-NOX homologs from pathogens and commensal organisms. The current state of the field is somewhat ambiguous regarding the role of H-NOX in pathogenesis. However, it is clear that H-NOX regulates biofilm in response to environmental factors and may promote persistence in the environments that serve as reservoirs for these pathogens. Finally, the evidence that large subgroups of H-NOX proteins may sense environmental signals besides NO is discussed within the context of a phylogenetic analysis of this large and diverse family.     

Kin selection and evolution of infectious disease resistance

Discoveries of mutations conferring resistance to infectious diseases have led to increased interest in the evolutionary dynamics of disease resistance. Several recent papers have estimated the historical strength of selection for mutations conferring disease resistance. These studies are based on simple population genetic models that do not take account of factors such as spatial and family structure. Such factors may have a substantial impact on the strength of natural selection through inclusive fitness effects. That is, people have a strong tendency to live with relatives and therefore have a high probability of transmitting infectious diseases to them. Thus, an allele that protects an individual against disease infection also protects that individual's family members. Because some of these family members are likely to also be carrying the allele, selection for that allele is magnified by family structure. In this paper, I use mathematical modeling techniques to explore the impact of such kin selection on the strength of selection for infectious disease resistance alleles. I show that if the resistance allele has the same proportional effect on both within- and between-family transmission, then the impact of kin selection is relatively minor. Selection coefficients are increased by 5-35%, with a greater benefit for weaker alleles. The reason is that an individual with a strong resistance allele does not need much protection from infection by family members and thus does not benefit much from their alleles. The effect of kin selection can be dramatic, however, if the resistance allele has a larger effect on between-family transmission than within-family transmission (which can occur if between-family infection rates are much smaller than within-family rates), increasing selection coefficients by as much as two- to threefold. These results show conditions when it is important to consider family structure in estimates of the strength of selection for infectious disease resistance alleles.     

Kin selection, not group augmentation, predicts helping in an obligate cooperatively breeding bird

Kin selection theory has been the central model for understanding the evolution of cooperative breeding, where non-breeders help bear the cost of rearing young. Recently, the dominance of this idea has been questioned; particularly in obligate cooperative breeders where breeding without help is uncommon and seldom successful. In such systems, the direct benefits gained through augmenting current group size have been hypothesized to provide a tractable alternative (or addition) to kin selection. However, clear empirical tests of the opposing predictions are lacking. Here, we provide convincing evidence to suggest that kin selection and not group augmentation accounts for decisions of whether, where and how often to help in an obligate cooperative breeder, the chestnut-crowned babbler (Pomatostomus ruficeps). We found no evidence that group members base helping decisions on the size of breeding units available in their social group, despite both correlational and experimental data showing substantial variation in the degree to which helpers affect productivity in units of different size. By contrast, 98 per cent of group members with kin present helped, 100 per cent directed their care towards the most related brood in the social group, and those rearing half/full-sibs helped approximately three times harder than those rearing less/non-related broods. We conclude that kin selection plays a central role in the maintenance of cooperative breeding in this species, despite the apparent importance of living in large groups.     

Bacterial quorum sensing in symbiotic and pathogenic relationships with hosts*

Gram-negative bacteria communicate with each other by producing and sensing diffusible signaling molecules. This mechanism is called quorum sensing (QS) and regulates many bacterial activities from gene expression to symbiotic/pathogenic interactions with hosts. Therefore, the elucidation and control of bacterial QS systems have been attracted increasing attention over the past two decades. The most common QS signals in Gram-negative bacteria are N-acyl homoserine lactones (AHLs). There are also bacteria that employ different QS systems, for example, the plant pathogen Ralstonia solanacearum utilizes 3-hydroxy fatty acid methyl esters as its QS signals. The QS system found in the endosymbiotic bacterium associated with the fungus Mortierella alpina, the development of an affinity pull-down method for AHL synthases, and the elucidation of a unique QS circuit in R. solanacearum are discussed herein.     

Luminescence, virulence and quorum sensing signal production by pathogenic Vibrio campbellii and Vibrio harveyi isolates

Aims:  To study the relationship between luminescence, autoinducer production and virulence of pathogenic vibrios. Methods and Results:  Luminescence, quorum sensing signal production and virulence towards brine shrimp nauplii of 13 Vibrio campbellii and Vibrio harveyi strains were studied. Although only two of the tested strains were brightly luminescent, all of them were shown to produce the three different types of quorum sensing signals known to be produced by Vibrio harveyi. Cell-free culture fluids of all strains significantly induced bioluminescence in the cholerae autoinducer 1, autoinducer 2 and harveyi autoinducer 1 reporter strains JAF375, JMH597 and JMH612, respectively. There was no relation between luminescence and signal production and virulence towards brine shrimp. Conclusions:  There is a large difference between different strains of Vibrio campbellii and Vibrio harveyi with respect to bioluminescence. However, this is not reflected in signal production and virulence towards gnotobiotic brine shrimp. Moreover, there seems to be no relation between quorum sensing signal production and virulence towards brine shrimp. Significance and Impact of the Study:  The results presented here indicate that strains that are most brightly luminescent are not necessarily the most virulent ones and that the lower virulence of some of the strains is not due to a lack of autoinducer production.     

植物的亲缘选择

亲缘选择是指在一个随机交配群体中的个体基于亲缘关系而以一种非随机性的方式相互作用,其作用结果是亲缘个体得到更大的广义适合度。综述了亲缘选择和亲缘竞争两种观点以及各自的试验支持证据;分析了导致亲缘选择试验结果出现分歧的原因,认为这主要是由于对亲缘选择理解上的模糊以及试验设计的不严谨所致。植物间的亲缘选择研究不仅相对较少,对亲缘选择的机制研究更为欠缺,这就造成了目前对此问题在科学认识上出现不少盲点。综合前期研究,提出今后对亲缘选择的研究应该首先界定"亲缘"程度,同时改良试验设计方案,选择多种不同生境下的物种对亲缘选择进行深入研究,并且考虑环境因子对植物亲缘选择的影响。同时,对植物亲缘识别机制的研究应该从生理生化方面出发,通过定性定量地分析探索植物根系分泌物在植物亲缘识别中的作用和作用途径。     

Kin selection and the evolution of virulence

Social interactions between conspecific parasites are partly dependent on the relatedness of interacting parasites (kin selection), which, in turn, is predicted to affect the extent of damage they cause their hosts (virulence). High relatedness is generally assumed to favour less competitive interactions, but the relationship between relatedness and virulence is crucially dependent on the social behaviour in question. Here, we discuss the rather limited body of experimental work that addresses how kin-selected social behaviours affect virulence. First, if prudent use of host resources (a form of cooperation) maximizes the transmission success of the parasite population, decreased relatedness is predicted to result in increased host exploitation and virulence. Experimental support for this well-established theoretical result is surprisingly limited. Second, if parasite within-host growth rate is a positive function of cooperation (that is, when individuals need to donate public goods, such as extracellular enzymes), virulence is predicted to increase with increasing relatedness. The limited studies testing this hypothesis are broadly consistent with this prediction. Finally, there is some empirical evidence supporting theory that suggests that spiteful behaviours are maximized at intermediate degrees of relatedness, which, in turn, leads to minimal virulence because of the reduced growth rate of the infecting population. We highlight the need for further thorough experimentation on the role of kin selection in the evolution of virulence and identify additional biological complexities to these simple frameworks.     

外源基因表达造成的群体感应细菌生存压力的建模分析

外源基因的表达及其对细菌种群的影响对于群体感应系统和合成生物学产业的研究具有重要意义。然而,人们对于表达外源蛋白的细菌本身的行为模式仍然知之甚少。为了研究菌落生长和外源基因表达的过程究竟受到哪些因素的影响,文中测量了受Lux类受体调控的外源基因在N-酰基高丝氨酸内酯 (N-acyl homoserine lactone,N-AHL) 信号分子诱导下的表达,并模拟了其对细菌种群动态的影响。文中建立了一个假设性的数学模型,对信号分子诱导表达下细菌种群生长受影响的现象进行了分析。先前的研究通常将细菌种群生长受群体感应系统影响的现象归咎于合成群体感应信号分子的消耗与N-AHL信号分子的毒性,文中提供了对于这种生存压力的另一种可能的解释。     

Reproductive skew in cooperative breeding: Environmental variability,antagonistic selection,choice, and control

A multitude of factors may determine reproductive skew among cooperative breeders. One explanation, derived from inclusive fitness theory, is that groups can partition reproduction such that subordinates do at least as well as noncooperative solitary individuals. The majority of recent data, however, fails to support this prediction; possibly because inclusive fitness models cannot easily incorporate multiple factors simultaneously to predict skew. Notable omissions are antagonistic selection (across generations, genes will be in both dominant and subordinate bodies), constraints on the number of sites suitable for successful reproduction, choice in which group an individual might join, and within‐group control or suppression of competition. All of these factors and more are explored through agent‐based evolutionary simulations. The results suggest the primary drivers for the initial evolution of cooperative breeding may be a combination of limited suitable sites, choice across those sites, and parental manipulation of offspring into helping roles. Antagonistic selection may be important when subordinates are more frequent than dominants. Kinship matters, but its main effect may be in offspring being available for manipulation while unrelated individuals are not. The greater flexibility of evolutionary simulations allows the incorporation of species‐specific life histories and ecological constraints to better predict sociobiology.     

Kin selection under blending inheritance

Why did Darwin fail to develop his insights on kin selection into a proper theory of social adaptation? One suggestion has been that his inadequate understanding of heredity kept the problem out of focus. Here, I determine whether it is possible to develop a quantitative theory of kin selection upon the assumption of blending inheritance. I find that, whilst Hamilton's rule of kin selection can be readily derived under the assumption of blending inheritance, this mechanism complicates the computation of relatedness coefficients, and can even cause them to fluctuate over generations. Nevertheless, I show that the ultimate criterion for selection to favour any social trait - i.e. a time-average of Hamilton's rule - remains the same as under particulate inheritance. By eliminating the gene from the theory of kin selection, I clarify the role that it plays in the theory of social adaptation.     

Kin and familiarity influence association preferences and aggression in the mangrove killifish Kryptolebias marmoratus

Association preferences and aggression intensity were investigated in relation to kin and familiarity in the self-fertilizing, clonal vertebrate, the mangrove killifish Kryptolebias marmoratus. Results indicated that fish preferentially associated with and exhibited less intense aggression towards members of their own genotype (kin), compared to members of a different genotype (non-kin). Furthermore, when fish were presented with stimulus groups of the same genotype that were familiar or unfamiliar, fish preferentially associated with and exhibited lower aggression intensity directed towards familiar groups. These results indicate that this species prefer to associate with both kin and familiar individuals and modulate aggression accordingly. These results are discussed with reference to the adaptive benefits of kin recognition and preferences for familiars, and place results within the context of current knowledge of the ecology of K. marmoratus.     

Perspectives: Hamilton's Legacy: Mechanisms of Kin Recognition in Humans

The behavior literature is replete with examples of individuals exhibiting costly acts that benefit someone else. These examples troubled Darwin so much so that he thought they would be fatal to his theory of natural selection. A century later, W. D. Hamilton refined that theory by showing, quantitatively, that such acts could be favored if the individuals involved were relatives. His theory of inclusive fitness is generally considered one of the greatest theoretical advances in evolution since Darwin's time. Less appreciated from Hamilton's 1964 paper is the hypothesis that mechanisms favoring accurate kin recognition will also be selected. Here, I review those recognition mechanisms and survey the literature on human kin recognition. Although not often considered, humans both produce cues to kinship that vary with genetic relatedness and have perceptual abilities to detect these cues in others and assess that relatedness. The potential functions of these abilities are discussed. Importantly, gaps in our understanding of the development and use of recognition mechanisms are noted.     

Kin distribution of amphibian larvae in the wild

According to kin selection theory, the location of an individual with respect to its relatives can have important ramifications for its fitness. Perhaps more than any other vertebrate group, anuran amphibian larvae have been the subject of many experiments on this topic. Some anuran species have been shown in the laboratory to recognize and associate with their siblings and half-siblings. However, due to the difficulty of identifying sibships, no kinship studies with anuran larvae have been conducted in the wild. Here, we use microsatellite analysis to show that wood frog (Rana sylvatica) tadpoles were nonrandomly distributed in two ponds with respect to their relatives. In one pond, the tadpoles were significantly clumped with their siblings or half-siblings as expected from other published laboratory studies on this species. However, in another pond, the tadpoles were significantly nonrandomly dispersed from their siblings or half-siblings. This is the first example of kin repulsion of nonreproductive animals in the wild and the first time a species has been shown to display both aggregation and repulsion under different circumstances. These results suggest that kin distribution is context dependent and demonstrate the importance of testing kin selection hypotheses under natural conditions.     

黄河鲤水产细菌的分离及其毒力因子和群体感应信号分子的检测

[背景]水产细菌病害制约水产养殖业健康发展,群体感应与细菌毒力因子的产生密切相关,群体感应调控细菌的毒力因子特性值得进一步研究.[目的]探究群体感应与黄河鲤细菌病害的关系,明确群体感应对细菌毒力因子特性的影响.[方法]通过16SrRNA基因测序并构建系统进化树确定筛选菌株的进化地位,通过脱脂牛奶平板法和偶氮酪蛋白法检测...     

Siderophore-mediated cooperation and virulence in Pseudomonas aeruginosa

Why should organisms cooperate with each other? Helping close relatives that are likely to share the same genes (kin selection) is one important explanation that is likely to apply across taxa. The production of metabolically costly extracellular iron-scavenging molecules (siderophores) by microorganisms is a cooperative behaviour because it benefits nearby conspecifics. We review experiments focusing on the production of the primary siderophore (pyoverdin) of the opportunistic bacterial pathogen, Pseudomonas aeruginosa, which test kin selection theories that seek to explain the evolution of cooperation. First, cooperation is indeed favoured when individuals interact with their close relatives and when there is competition between groups of cooperators and noncooperators, such that the benefit of cooperation can be realized. Second, the relative success of cheats and cooperators is a function of their frequencies within populations. Third, elevated mutation rates can confer a selective disadvantage under conditions when cooperation is beneficial, because high mutation rates reduce how closely bacteria are related to each other. Fourth, cooperative pyoverdin production is also shown to be favoured by kin selection in vivo (caterpillars), and results in more virulent infections. Finally, we briefly outline ongoing and future work using this experimental system.     

青岛近海沉积物生物被膜中密度感应及密度感应淬灭细菌多样性

【背景】细菌密度感应(Quorum sensing,QS)是指细菌利用分泌的信号分子进行相互交流的现象,而密度感应淬灭(Quorumquenching,QQ)是指通过干扰信号分子的产生、释放、积累或应答从而阻抑密度感应通路。【目的】探究青岛近海沉积物生物被膜中密度感应和密度感应淬灭细菌的多样性。【方法】采用海水培养基2216E从青岛近海沉积物生物被膜中分离获取可培养细菌,采用平板交互划线和高通量筛选的方法分别筛选具有密度感应和密度感应淬灭的菌株。【结果】共分离获得83株共54种具有密度感应和密度感应淬灭的细菌,分属于四大细菌门类:变形菌门、拟杆菌门、厚壁菌门和放线菌门。其中,38株(45.8%)可以产生酰基高丝氨酸内酯(Acyl-homoserine lactone,AHL)类信号分子,它们分属于变形菌门(37株,15种)和拟杆菌门(1株,1种),优势属为弧菌属和鲁杰氏菌属;能够降解AHL类信号分子的有57株(68.7%),在变形菌门(41株,23种)、拟杆菌门(14株,10种)、厚壁菌门(5株,5种)以及放线菌门(1株,1种)中均有分布。【结论】在青岛近海沉积物生物被膜可培养细菌中,具有密度感应和密度感应淬灭现象的菌株具有很高的丰度和多样性,为后续生态学意义的研究与海洋微生物的开发提供了参考。