Gleichgewichtsbewegungen von Blättern als Reaktion auf asymmetrische Belastung — Isoklinotropismus nach Härdtl (1927) — und ihre Beziehung zum Gravitropismus

1. Die anscheinend in Vergessenheit geratenen älteren Angaben von HÄRDTL (1927 und spärer) und PRINGSHEIM (1931), nach denen einseitig belastete Blätter Gleichgewichtsbewegungen ausführen können (Isoklinotropismus nach HÄRDTL), wurden an mehreren Arten (Chelidonium majus, Aegopodium podagra ria, Ranunculus repens, Sambucus nigra, Coleus blumei und Hibiscus rosa sinensis) bestätigt,— Die einseitige Belastung erfolgte durch Einstecken von Nadeln in die eine Hälfte der Blattspreite bzw. in eine Blattfieder. 2. Bei Blättern, die in Spreite oder Stiel epinastisch gekrtimmt sind (die überwiegende Mehrzahl) oder auch durch die Belastung abwärts gebogen sind, kommt es dabei zu zwei verschiedenen Reaktionen: a) zu einer sofort eintretenden rein physikalischen reversiblen Reaktion, da die einseitige Last eine Torsion der Spreite bewirkt, die die Spreitenspitze nach der der Last gegenüberliegenden Seite [führt, und b) zu einer spärer eintretenden physiologischen Reaktion durch eine Wachstumskrümmung nach derselben Seite, - Beide Komponenten der Bewegung ftihren zu einer Verringerung oder einem Ausgleich des Ungleichgewichtes. 3. Die physiologische Reaktion war meist nach einem oder einigen Tagen erkennbar, bei Chelidonium mitunter schon nach einigen Stunden, bei Hibiscus gelegentlich erst nach etwa einer Woche. Mitunter blieb die Reaktion auch aus. Bei den gefiederten Blattern erfolgte sie in der Rhachis, ober- und unterhalb der belasteten Fieder, mitunter auch im Blattstiel, bei Coleus im Spreitengrund und im Blattstiel, bei Hibiscus im oberen Gelenkpolster (“Sekundargelenk”) des Blattstiels. Auch ältere Blätter reagierten oft noch überraschend gut. Vielfach führte die physiologische Reaktion zu einer vollständigen Ausbalancierung der einseitig belasteten Blattspreite. Auf nachtragliche Entfernung der eingesteckten Nadeln gingen auch die Krtimmungen in 2–3 Tagen wieder weitgehend zurück. 4. Als Ursache ftir die Gleichgewichtsbewegungen der Blätter kommen zwei verschiedene Mechanismen in Betracht: a) Infolge der durch die einseitige Belastung hervorgerufenen Schräglage der Blattspreite sammelt sich das Auxin auf der tiefer liegenden Flanke von Mittelnerv bzw. Rhachis und Blattstiel an, was zu einem stärkeren Wachstum dieser Seite und einer Gleichgewichtskrümmung führen muß. Nach dieser Auffassung ordnet sich der Isoklinotropismus dem Gravitropismus ein. b) Die nach der Belastung sofort eintretende auf der Torsionsspannung beruhende rein physikalische und zunächst reversible Gleichgewichtsreaktion des Blattes wird nach einigen Stunden oder Tagen teilweise irreversibel. (Für die spannungsfreien Abschnitte der Rhachis eines gefiederten Blattes oberhalb der Belastung kann diese Erklärung natürlich nicht gelten). Vermutlich sind beide Mechanismen, vor allern wohl der erstgenannte, bei den einzelnen Arten in verschiedenem Maße, als Ursache der Gleichgewichtsbewegungen wirksam. 5. Der biologische Sinn der Ausbalancierung eines (größeren) Blattes (PRINGSHELM 1931, HÄRDTL 1927, 1937 a) liegt darin, daß a) ein ausbalanciertes Blatt den geringsten Aufwand an mechanischen Elementen erfordert, und b) Photo- und Gravitropismus nur ein ausbalanciertes Blatt ohne Komplikationen in die angestrebte Lage fuhren konnen.     

High KIR diversity in Amerindians is maintained using few gene-content haplotypes

Interaction between killer cell immunoglobulin-like receptors (KIR) and cognate HLA class I ligands influences the innate and adaptive immune response to infection. The KIR family varies in gene content and allelic polymorphism, thereby, distinguishing individuals and populations. KIR gene content was determined for 230 individuals from three Amerindian tribes from Venezuela: the Yucpa, Bari and Warao. Gene-content haplotypes could be assigned to 212 individuals (92%) because only five different haplotypes were present—group A and four group B. Six different haplotype combinations accounted for >80% of individuals. Each tribe has distinctive genotype frequencies. Despite few haplotypes, all 14 KIR genes are at high frequency in the three tribes, with the exception of 2DS3. Each population has an even frequency of group A and B haplotypes. Allele-level analysis of 3DL1/S1 distinguished five group A haplotypes and six group B haplotypes. The high frequency and divergence of the KIR haplotypes in the Amerindian tribes provide greater KIR diversity than is present in many larger populations. An extreme case being the Yucpa, for whom two gene-content haplotypes account for >90% of the population. These comprise the group A haplotype and a group B haplotype containing all the KIR genes, except 2DS3, that typify the group B haplotypes. Here is clear evidence for balancing selection on the KIR system and the biological importance of both A and B haplotypes for the survival of human populations.Electronic Supplementary Material Supplementary material is available for this article at     

Patterns of intermediate host use and levels of association between two conflicting manipulative parasites.

For many parasites with complex life cycles, manipulation of intermediate host phenotypes is often regarded as an adaptation to increase the probability of successful transmission. This phenomenon creates opportunities for either synergistic or conflicting interests between different parasite species sharing the same intermediate host. When more than one manipulative parasite infect the same intermediate host, but differ in their definitive host, selection should favour the establishment of a negative association between these manipulators. Both Polymorphus minutus and Pomphorhynchus laevis exploit the amphipod Gammarus pulex as intermediate host but differ markedly in their final host, a fish for P. laevis and a bird for P. minutus. The pattern of host use by these two conflicting manipulative parasites was studied. Their incidence and intensity of infection and their distribution among G. pulex were first examined by analysing three large samples of gammarids collected from the river Tille, Eastern France. Both parasites had low prevalence in the host population. However, temporal fluctuation in the level of parasitic infection was observed. Overall, prevalence of both parasite species was higher in male than in female G. pulex. We then assessed the degree of association between the two parasites among their intermediate hosts, using two different methods: a host-centred measure and a parasite-centred measure. Both measures gave similar results; showing random association between the two acanthocephalan species in their intermediate hosts. We discuss our results in relation to the selective forces and ecological constraints that may determine the pattern of association between conflicting manipulative parasites.     

Diversification of porcine MHC class II genes: evidence for selective advantage

The major histocompatibility complex (MHC) is an immunological gene-dense region of high diversity in mammalian species. Sus scrofa was domesticated by at least six independent events over Eurasia during the Holocene period. It has been hypothesized that the level and distribution of MHC variation in pig populations reflect genetic selection and environmental influences. In an effort to define the complexity of MHC polymorphisms and the role of selection in the generation of class II gene diversity (DQB, DRB1, and pseudogene ΨDRB3), DNA from globally distributed unrelated domestic pigs of European and Asian origins and a Suidae out-group was analyzed. The number of pseudogene alleles identified (ΨDRB3 33) was greater than those found in the expressed genes (DQB 20 and DRB1 23) but the level of observed heterozygosity (ΨDRB3 0.452, DQB 0.732, and DRB1 0.767) and sequence diversity (ΨDRB3 0.029, DQB 0.062, and DRB1 0.074) were significantly lower in the pseudogene, respectively. The substitution ratios reflected an excess of d _N (DQB 1.476, DRB1 1.724, and ΨDRB3 0.508) and the persistence of expressed gene alleles suggesting the influence of balancing selection, while the pseudogene was undergoing purifying selection. The lack of a clear MHC phylogeographic tree, coupled with close genetic distances observed between the European and Asian populations (DQB 0.047 and DRB1 0.063) suggested that unlike observations using mtDNA, the MHC diversity lacks phylogeographic structure and appears to be globally uniform. Taken together, these results suggest that, despite regional differences in selective breeding and environments, no skewing of MHC diversity has occurred. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

In search of the missing subject: narrative identity and posthumous wronging

With the advanced methods of analysing old biological material, it is pressing to discuss what should be allowed to be done with human remains, particularly for well documented historical individuals. We argue that Queen Christina of Sweden, who challenged the traditional gender roles, has an interest in maintaining her privacy when there are continued attempts to reveal her ‘true’ gender. In the long-running philosophical debate on posthumous wronging, the fundamental question is: Who is wronged? Our aim is to find this ‘missing subject’ using narrative theory.Narrative identity emphasises the fact that no person is alone in knowing or telling their life story. People’s lives are entangled and parts of the life story of a deceased person can remain in the living realm. Since the narrative identity of a person does not necessarily end upon their death, and this narrative continues to relate directly to the person who once existed, it is the narrative subject that can continue to be posthumously wronged. Queen Christina can no longer maintain her own identity, but we maintain it by our research into her life. We propose three duties relevant for posthumous wronging: the duty of truthfulness, the duty of recognition and the duty to respect privacy.     

Lifetime selection on adult body size and components of body size in a waterstrider: opposing selection and maintenance of sexual size dimorphism

Abstract.— Sexual size dimorphism (SSD), the difference in body size between males and females, is common in almost all taxa of animals and is generally assumed to be adaptive. Although sexual selection and fecundity selection alone have often been invoked to explain the evolution of SSD, more recent views indicate that the sexes must experience different lifetime selection pressures for SSD to evolve and be maintained. We estimated selection acting on male and female adult body size (total length) and components of body size in the waterstrider Aquarius remigis during three phases of life history. Opposing selection pressures for overall body size occurred in separate episodes of fitness for females in both years and for males in one year. Specific components of body size were often the targets of the selection on overall body size. When net adult fitness was estimated by combining each individual's fitnesses from all episodes, we found stabilizing selection in both sexes. In addition, the net optimum overall body size of males was smaller than that of females. However, even when components of body size had experienced opposing selection pressures in individual episodes, no components appeared to be under lifetime stabilizing selection. This is the first evidence that contemporary selection in a natural population acts to maintain female size larger than male size, the most common pattern of SSD in nature.     

Footprints of intragenic recombination at HLA loci

 To evaluate the effect of balancing selection and intragenic recombination (or gene conversion) at six individual HLA loci, synonymous nucleotide diversity in different exon groups is examined within (π_w) and between (π_b) allelic lineages that may be defined by either serological or DNA sequence differences. Both π values are high in exons which encode for the peptide binding region (PBR) and tend to decrease in other exons. The value of π_w is significantly smaller than that of π_b in any exon of any locus. However, even π_w is much greater than nucleotide diversity at non-HLA loci. These observations provide additional strong evidence for the operation of balancing selection in PBR-encoding exons and its indirect effects on polymorphism at linked neighboring regions. It appears that allelic lineages have generally evolved in isolation but the linkage relationships within and between exons are incomplete throughout the long evolutionary history. To quantify intragenic recombination and account for the large discrepancy between the HLA and non-HLA diversity, a population genetics model is analyzed with special reference to the evolution of modern humans. The analysis suggests that the recombination rate between two sites 1000 base pairs apart is about 10^–5 per generation and that the effective size of human populations (equivalent roughly to the number of breeding individuals in a randomly mating population) has dropped from 10⁵ to 10⁴ in most of the Quaternary. One possibility for this reduction is discussed. Received: 11 August 1997 / Revised: 8 October 1997     

多措并举 激发兴趣 提高教学效果

针对高职招生文理兼收和学生学习基础实际,在细胞生物学与医学遗传学课程教学中,通过案例引导丰富感性认识,创设问题情境培养主动学习能力,运用网络优势培养获取信息和解读问题能力,设计趣味性开放实验提高实践能力,促进知识理解和技能提高,提高教学实效.     

Molecular mechanisms of dominance evolution in Müllerian mimicry

Natural selection acting on dominance between adaptive alleles at polymorphic loci can be sufficiently strong for dominance to evolve. However, the molecular mechanisms underlying such evolution are generally unknown. Here, using Müllerian mimicry as a case‐study for adaptive morphological variation, we present a theoretical analysis of the invasion of dominance modifiers altering gene expression through different molecular mechanisms. Toxic species involved in Müllerian mimicry exhibit warning coloration, and converge morphologically with other toxic species of the local community, due to positive frequency‐dependent selection acting on these colorations. Polymorphism in warning coloration may be maintained by migration–selection balance with fine scale spatial heterogeneity. We modeled a dominance modifier locus altering the expression of the warning coloration locus, targeting one or several alleles, acting in cis or trans, and either enhancing or repressing expression. We confirmed that dominance could evolve when balanced polymorphism was maintained at the color locus. Dominance evolution could result from modifiers enhancing one allele specifically, irrespective of their linkage with the targeted locus. Nonspecific enhancers could also persist in populations, at frequencies tightly depending on their linkage with the targeted locus. Altogether, our results identify which mechanisms of expression alteration could lead to dominance evolution in polymorphic mimicry.     

FEMALE PROMISCUITY IS POSITIVELY ASSOCIATED WITH NEUTRAL AND SELECTED GENETIC DIVERSITY IN PASSERINE BIRDS

Passerine birds show large interspecific variation in extrapair paternity rates. There is accumulating evidence that such promiscuous behavior is driven by indirect, genetic benefits to females. Sexual selection theory distinguishes between two types of genetic benefits, additive and nonadditive effects, mediated by preferences for good and compatible genes, respectively. Good genes preferences should imply directional selection and mating skew among males, and thus reduced genetic diversity in the population. In contrast, compatible genes preferences should give balancing selection that retains genetic diversity. Here, we test how well these predictions fit with patterns of variation in genetic diversity and promiscuity levels among passerine birds. We found that more promiscuous species had higher nucleotide diversity at autosomal introns, but not at Z‐chromosome introns. We also found that major histocompatibility complex (MHC) class IIB alleles had higher sequence diversity, and therefore should recognize a broader spectrum of pathogens, in more promiscuous species. Our results suggest that female promiscuity targets a multitude of autosomal genes for their nonadditive, compatibility benefits. Also, as immunity genes seem to be of particular importance, we hypothesize that interspecific variation in female promiscuity among passerine birds has arisen in response to the strength of pathogen‐mediated selection.