体验中的美丽瞬间活动参与者感想摘录

“在城市里,接触大自然的机会和条件都很少。作为城市的生态屏障,草原到底面临着怎样的沙化、退化等问题？自然保护区的工作是怎么开展的？他们遇到了怎样的艰难？城市人应该为自然保护做些什么？如果没有身临其境的体验,就不会有深切的体会。”     

The Mu Transpososome Through a Topological Lens

ABSTRACT

Phage Mu is the most efficient transposable element known, its high efficiency being conferred by an enhancer DNA element. Transposition is the end result of a series of well choreographed steps that juxtapose the enhancer and the two Mu ends within a nucleoprotein complex called the ‘transpososome.’ The particular arrangement of DNA and protein components lends extraordinary stability to the transpososome and regulates the frequency, precision, directionality, and mechanism of transposition. The structure of the transpososome, therefore, holds the key to understanding all of these attributes, and ultimately to explaining the runaway genetic success of transposable elements throughout the biological world. This review focuses on the path of the DNA within the Mu transpososome, as uncovered by recent topological analyses. It discusses why Mu topology cannot be analyzed by standard methods, and how knowledge of the geometry of site alignment during Flp and Cre site-specific recombination was harnessed to design a new methodology called ‘difference topology.’ This methodology has also revealed the order and dynamics of association of the three interacting DNA sites, as well as the role of the enhancer in assembly of the Mu transpososome.     

Kin Discrimination in a Macropod Marsupial

Differential treatment of kin is ubiquitous in social animals. Parents often behave preferentially towards their dependent offspring. Species in several taxa also bias behaviour towards non-descendent kin. This latter phenomenon has not been demonstrated in marsupials, which are reportedly less social than eutherian mammals. We report the first evidence of non-parental kin-biased behaviour in a macropodid marsupial. Experimental pairing of individuals based on kinship reliably altered the rate of aggression between individuals in pairs of female tammar wallabies ( Macropus eugenii ). This effect is probably attributable to relatedness rather than to familiarity. Marsupial sociality may be substantially more complex than is currently recognized.     

Kin recognition in a social spider

Social spiders accept immigrant spiders into their kin-based groups, suggesting that spiders cannot recognise kin and may lose inclusive fitness benefits. A field and two laboratory experiments on Diaea ergandros, a social crab spider, demonstrated that younger and older instar D. ergandros do discriminate siblings, but potential benefits were variable and not equally distributed. First, proportional survival was greater in large groups regardless of the within-group relatedness, so accepting immigrants increases probability of group survival (although relatedness was more important among smaller groups). Second, juvenile D. ergandros ate unrelated spiders instead of siblings when starved, so immigrants might represent a food reserve in times of food shortage. Third, subadult resident, sibling females cannibalised unrelated, immigrant females and their brothers instead of immigrant males when starved, suggesting that subadult female spiders may maximise outbreeding opportunities. These benefits provide selective pressure for groups to accept immigrants, but as benefits are realised differentially, conflict and cooperation will exist within spider groups similar to that shown in other group-living taxa.     

Kin selection is the key to altruism

Kin selection theory, also known as inclusive fitness theory, has been the subject of much debate and misunderstanding. Nevertheless, the idea that relatedness among individuals can drive the evolution of altruism has emerged as a central paradigm in evolutionary biology. Or has it? In two recent articles, E.O. Wilson argues that kin selection should no longer be considered the main explanation for the evolution of altruism in insect societies. Here, we discuss what these articles say about kin selection and how it relates to the theory. We conclude that kin selection remains the key explanation for the evolution of altruism in eusocial insects.     

Human Ability to Recognize Kin Visually Within Primates

The assessment of relatedness is a key determinant in the evolution of social behavior in primates. Humans are able to detect kin visually in their own species using facial phenotypes, and facial resemblance in turn influences both prosocial behaviors and mating decisions. This suggests that cognitive abilities that allow facial kin detection in conspecifics have been favored in the species by kin selection. We investigated the extent to which humans are able to recognize kin visually by asking human judges to assess facial resemblance in 4 other primate species (common chimpanzees, western lowland gorillas, mandrills, and chacma baboons) on the basis of pictures of faces. Humans achieved facial interspecific kin recognition in all species except baboons. Facial resemblance is a reliable indicator of relatedness in at least chimpanzees, gorillas, and mandrills, and future work should explore if the primates themselves also share the ability to detect kin facially.     

Kin and sex recognition in a dioecious grass

Plants have evolved complex mechanisms to recognize and respond to the presence of neighboring plants, and the genetic identity of a neighbor has been shown to make a difference in this response. Studies have found that plants are able to differentiate among self- versus non-self and among sibling (kin) competitors. Here, we present data for the dioecious grass Distichlis spicata on seedling recognition of kin and sex. D. spicata exhibits extreme spatial segregation of the sexes (SSS) in the field, and previous work has shown that intra-sexual competition is less than inter-sexual competition in the field. In this experiment, we conducted experiments in the lab, exposing the seedlings to liquid media in which seedlings had been previously grown, rather than have the seedling physically contact one another. We found that inter-sexual interactions caused a decrease in the total dry weight and an increase in root/shoot ratio of the plants compared with intra-sexual interactions. These findings suggest that D. spicata plants can recognize and respond to plant sex and that inter-sexual competition contributes to SSS, even when additional interactions, such as mycorrhizal fungi are controlled, and physical interactions between plants are removed. In the kin recognition analysis, we found that plants paired with another plant from the same mother had significantly greater lateral root number and length than plants paired with non-kin, suggesting that in this highly clonal grass, kin recognition may be an important mechanism in competitive interactions.     

Kin Recognition and Inbreeding Avoidance in a Butterfly

Owing to the risk of inbreeding depression, the evolution of inbreeding avoidance by means of kin recognition is expected for many biological systems. Nevertheless, an ability to distinguish among relatives and non‐relatives has been only rarely demonstrated, especially so in non‐social organisms. We here show that, in the non‐social tropical butterfly Bicyclus anynana, females discriminate against relatives by preferentially mating with non‐relatives. Inbreeding avoidance was more pronounced in inbred as compared with outbred butterflies, suggesting that it is partly condition dependent. We argue that, in our system, the evolution of inbreeding avoidance is related to carrying a high genetic load and thus to being particularly sensitive to inbreeding depression. We suggest that kin recognition might be more widespread than currently thought and that future studies may possibly benefit from considering condition dependence, especially by paying attention to and/or manipulating population history, genetic load, and the risk of inbreeding depression. We further suggest that kin recognition in B. anynana might be based on cuticular hydrocarbons used for self‐referencing.     

Kin recognition and cannibalism in a subsocial spider

Evolution of cooperation and group living in spiders from subsocial family groups may be constrained by their cannibalistic nature. A tendency to avoid cannibalizing kin may facilitate tolerance among spiders and implies the ability to identify relatives. We investigated whether the subsocial spider Stegodyphus lineatus discriminates kin by recording cannibalism among juveniles in experiments during which amount of food and size difference among spiders in groups were varied. We hypothesized that family groups should be less cannibalistic than groups of mixed‐parental origin. Further, we tested whether food‐stress would influence cannibalism rates differently in kin and nonkin groups and the effect of relatedness on cannibalism within groups of spiders of variable size compared with those of homogenous size. In groups of six spiders, more spiders were cannibalized in nonsib groups than in sib groups under low food conditions. A tendency for nonkin biased cannibalism in starved spider pairs supported that kin recognition in S. lineatus is expressed when food is limited. Size variance of individuals within well‐fed groups of siblings and unrelated spiders had no influence on cannibalism rates. Apparently, both hunger and high density are important promoters of cannibalism. In addition to inclusive fitness benefits, we suggest that an ability to avoid cannibalizing kin will favour the evolution of cooperation and group living in phylogenetically pre‐adapted solitary species.     

Additive,Epistatic, and Environmental Effects Through the Lens of Expression Variability QTL in a Twin Cohort

The expression of a gene can vary across individuals in the general population, as well as between monozygotic twins. This variable expression is assumed to be due to the influence of both genetic and nongenetic factors. Yet little evidence supporting this assumption has been obtained from empirical data. In this study, we used expression data from a large twin cohort to investigate the influences of genetic and nongenetic factors on variable gene expression. We focused on a set of expression variability QTL (evQTL)—i.e., genetic loci associated with the variance, as opposed to the mean, of gene expression. We identified evQTL for 99, 56, and 79 genes in lymphoblastoid cell lines, skin, and fat, respectively. The differences in gene expression, measured by the relative mean difference (RMD), tended to be larger between pairs of dizygotic (DZ) twins than between pairs of monozygotic (MZ) twins, showing that genetic background influenced the expression variability. Furthermore, a more profound RMD was observed between pairs of MZ twins whose genotypes were associated with greater expression variability than the RMD found between pairs of MZ twins whose genotypes were associated with smaller expression variability. This suggests that nongenetic (e.g., environmental) factors contribute to the variable expression. Lastly, we demonstrated that the formation of evQTL is likely due to partial linkages between eQTL SNPs that are additively associated with the mean of gene expression; in most cases, no epistatic effect is involved. Our findings have implications for understanding divergent sources of gene expression variability.     

Kin recognition in rattlesnakes

Snakes are often regarded as the least social of all vertebrate groups, but this assumption stems from the fact that they are secretive and difficult to observe in nature, rather than direct evidence. Recent studies have revealed a surprising degree of social complexity in snakes. Here, I examine the ability of captive-raised timber rattlesnakes (Crotalus horridus) to recognize siblings by measuring the mean separation distance and frequency of contact between pairs of individuals housed together. The results show that female siblings associate more closely with each other than nonsibling pairs. Previous studies have shown that timber rattlesnakes occupying the same hibernacula have higher relatedness than snakes using neighbouring hibernacula, and frequently form social aggregations. Rattlesnakes exhibit other characteristics consistent with advanced sociality, including group defence, conspecific alarm signals and maternal defence of young. These findings reinforce the notion that, rather than being solitary and asocial, some snake species may form family groups.