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41.
The semen of many primate species coagulates into a mating plug believed to prevent the sperm of subsequent mating events from accessing the ova. The texture of the coagulum varies among species: from a semisoft mass in humans to a firm plug in chimpanzees. In humans, a component of the coagulum, semenogelin I, also inhibits sperm motility. We tested the hypothesis that polymorphism and divergence at semenogelin I differ among hominoid species with different mating systems. Sequence data for the semenogelin I locus were obtained from 12 humans, 10 chimpanzees, 7 gorillas, and 1 bonobo. Mitochondrial D-loop data were collected from a subset of individuals to assess levels of variation at an unlinked locus. HKA tests using D-loop sequence data revealed a significant reduction of polymorphism at semenogelin I in chimpanzees, consistent with predictions of a selective sweep at this locus. This result was supported by independent HKA tests using polymorphism data from a putatively neutral locus from the literature. Humans show a similar trend toward reduced polymorphism, although HKA tests were only marginally significant. Gorilla sequence data show evidence of functional loss at the semenogelin I locus, indicated by stop codons within the putative open reading frame as well as high levels of polymorphism. Elevated K
a/K
s ratios within the Pan–Homo clade suggest a history of positive selection at semenogelin I. Our results suggest that there is a positive relationship between the intensity of sperm competition in a species and the strength of positive Darwinian selection on the seminal protein semenogelin I. 相似文献
42.
Female preferences for male mating signals are often evaluated on single parameters in isolation or small suites of characters. Most signals, however, are composites of many individual parameters. In this study we quantified multivariate traits in the advertisement call of the túngara frog, Physalaemus pustulosus. We represented the calls in multidimensional scaling space and chose nine test calls to represent the range of population variation. We then tested females for phonotactic preference between calls in each pair of the nine test calls. We used statistics developed for paired comparisons in such "round robin" competitions to evaluate the null hypothesis of equal attractiveness, and to examine the degree to which females responded to calls as being different from or similar to one another in attractiveness. We then examined the attractiveness of each test call relative to all other test calls as a function of their location in multivariate acoustic space (the acoustic landscape) to visualize sexual selection on calls. Finally, we used methods from cognitive psychology to illustrate the females' perception of call attractiveness in multivariate space, and compared this perceptual landscape to the acoustic landscape of quantitative call variation. We show that correlations between individual call characters are not strong and thus there are few biomechanical constraints on their independent evolution. Most call variables differed among males, and there was high repeatability of call characters within males. Females often discriminated between pairs of calls from the population, and there were significant differences among calls in their attractiveness. Female preferences for calls were not stabilizing. The region of the acoustic landscape that was most attractive to females included the mean call but was not centered around it. The females' perceptual or preference landscape did not correlate with the call's acoustic landscape, and female perception of calls decreased rather than enhanced call differences. 相似文献
43.
Triggering of the T cell receptor (TCR) may be antagonized by ligands that are slight variants of the immunogenic peptide.
This paper proposes a mathematical model to quantify the strength of the antagonistic effect. The model is based on the kinetics
of association and dissociation of TCR and peptide/major histocompatibility (pMHC) molecules, and incorporates TCR triggering
according to a kinetic proofreading mechanism. Model analysis indicates that while the average lifetime of the TCR/pMHC complex
is the basic determinant of the contribution to TCR triggering made by the ligand, the affinity of the ligand and its MHC
presentation level are also important. However, these contributions depend on the kinetic limitation regime. There is a continuum
of limitation regimes, at the extremes of which are found TCR limitation and MHC limitation. Both ligand affinity and TCR
and pMHC densities determine whether TCR triggering is TCR limited or MHC limited. The changing importance of affinity and
antigen presentation level under various kinetic limitation regimes may explain the respective roles of antagonistic and agonistic
self peptides in thymic selection. Moreover, TCR down-regulation under TCR-limited conditions may allow the T cell to differentiate
between the average lifetime of the TCR/pMHC complex and the presentation level of the ligand. A method for experimental differentiation
between passive and active antagonistic effects is proposed which exploits the differences between TCR and MHC limitation. 相似文献
44.
Ecological Genetics of Mpi and Gpi Polymorphisms in the Acorn Barnacle and the Spatial Scale of Neutral and Non-neutral Variation 总被引:1,自引:0,他引:1
Different allozyme genotypes at the mannose phosphate isomerase(Mpi) locus in the northern acorn barnacle (Semibalanus balanoides)show a strong association with distinct intertidal microhabitats.In estuaries along the Maine Coast, the FF homozygote has higherfitness in exposed, high-tide level microhabitats while theSS homozygote has higher fitness under algal cover or at low-tidemicrohabitats. These patterns are consistent with a Levene (1953)model of balancing selection. In these same samples, polymorphismsat the glucose phosphate isomerase locus (Gpi) and mitochondrialDNA (mtDNA) show no fitness differences among microhabitats,providing intra-genomic controls supporting selection at ornear Mpi. Here we report a similar analysis of genotype-by-microhabitatassociations at sites in Narragansett Bay, Rhode Island, closeto the southern range limit of S. balanoides. Genotype zonationat Mpi between high- and low-tide microhabitats is significantlydifferent between Maine and Narragansett Bay due to oppositezonation patterns for the SF and FF genotypes. Enzyme activitydata are consistent with this "reverse" zonation. At Gpi, thereis significant microhabitat zonation in Narragansett Bay, whilethis locus behaves as a neutral marker in Maine. Mt DNA showsno significant microhabitat zonation in either Rhode Islandor Maine. The Mpi data suggest that Levene-type selection foralternative genotypes in alternative habitats may operate atscales of both 10's of meters and 100's of kilometers. The Gpidata show how an apparently neutral locus can exhibit non-neutralvariation under different environmental conditions. We arguethat both Mpi and Gpi provide important genetic variation foradaptation to environmental heterogeneity that is recruitedunder distinct conditions of stress and carbohydrate substrateavailability. 相似文献
45.
We show that explicit mathematical and biological relationships exist among the scaling exponents and the allometric constants (α and β, respectively) of log–log linear tree‐community size frequency distributions, plant density NT, and minimum, maximum and average stem diameters (Dmin, Dmax, and , respectively). As individuals grow in size and Dmax increases, NT is predicted to decrease as reflected by a decrease in the numerical value of α and an increase in the value of β. Our derivations further show that NT decreases as increases even if Dmin or Dmax remain unchanged. Because Dmax and the age of the largest individuals in a community are correlated, albeit weakly, we argue that the interdependent relationships among the numerical values of α, β, NT, and shed light on the extent to which communities have experienced recent global disturbance. These predicted relationships receive strong statistical support using two large datasets spanning a broad spectrum of tree‐dominated communities. 相似文献
46.
47.
In many species of bacteria most inducible DNA repair genes are regulated by LexA homologues and are dependent on RecA for induction. We have shown previously by analysing the induction of recA that two mechanisms for the induction of gene expression following DNA damage exist in Mycobacterium tuberculosis. Whereas one of these depends on RecA and LexA in the classical way, the other mechanism is independent of both of these proteins and induction occurs in the absence of RecA. Here we investigate the generality of each of these mechanisms by analysing the global response to DNA damage in both wild-type M. tuberculosis and a recA deletion strain of M. tuberculosis using microarrays. This revealed that the majority of the genes that were induced remained inducible in the recA mutant stain. Of particular note most of the inducible genes with known or predicted functions in DNA repair did not depend on recA for induction. Amongst these are genes involved in nucleotide excision repair, base excision repair, damage reversal and recombination. Thus, it appears that this novel mechanism of gene regulation is important for DNA repair in M. tuberculosis. 相似文献
48.
Contrasting patterns of nonneutral evolution in proteins encoded in nuclear and mitochondrial genomes 总被引:4,自引:0,他引:4
We report that patterns of nonneutral DNA sequence evolution among published nuclear and mitochondrially encoded protein-coding loci differ significantly in animals. Whereas an apparent excess of amino acid polymorphism is seen in most (25/31) mitochondrial genes, this pattern is seen in fewer than half (15/36) of the nuclear data sets. This differentiation is even greater among data sets with significant departures from neutrality (14/15 vs. 1/6). Using forward simulations, we examined patterns of nonneutral evolution using parameters chosen to mimic the differences between mitochondrial and nuclear genetics (we varied recombination rate, population size, mutation rate, selective dominance, and intensity of germ line bottleneck). Patterns of evolution were correlated only with effective population size and strength of selection, and no single genetic factor explains the empirical contrast in patterns. We further report that in Arabidopsis thaliana, a highly self-fertilizing plant with effectively low recombination, five of six published nuclear data sets also exhibit an excess of amino acid polymorphism. We suggest that the contrast between nuclear and mitochondrial nonneutrality in animals stems from differences in rates of recombination in conjunction with a distribution of selective effects. If the majority of mutations segregating in populations are deleterious, high linkage may hinder the spread of the occasional beneficial mutation. 相似文献
49.
Cooperation is central to human existence, forming the bedrock of everyday social relationships and larger societal structures. Thus, understanding the psychological underpinnings of cooperation is of both scientific and practical importance. Recent work using a dual-process framework suggests that intuitive processing can promote cooperation while deliberative processing can undermine it. Here we add to this line of research by more specifically identifying deliberative and intuitive processes that affect cooperation. To do so, we applied automated text analysis using the Linguistic Inquiry and Word Count (LIWC) software to investigate the association between behavior in one-shot anonymous economic cooperation games and the presence inhibition (a deliberative process) and positive emotion (an intuitive process) in free-response narratives written after (Study 1, N = 4,218) or during (Study 2, N = 236) the decision-making process. Consistent with previous results, across both studies inhibition predicted reduced cooperation while positive emotion predicted increased cooperation (even when controlling for negative emotion). Importantly, there was a significant interaction between positive emotion and inhibition, such that the most cooperative individuals had high positive emotion and low inhibition. This suggests that inhibition (i.e., reflective or deliberative processing) may undermine cooperative behavior by suppressing the prosocial effects of positive emotion. 相似文献
50.
Shiran Shapira Oded Ben-Amotz Osnat Sher Dina Kazanov Jacob Mashiah Sarah Kraus Eyal Gur Nadir Arber 《PloS one》2015,10(10)