Die grenzüberschreitende Übertragung von Wissen über Transitional Justice und ihre Akteure in historischer Perspektive

Historische Ansätze sind in der Betrachtung von Transitional Justice rar geblieben. Den weitreichenden Veränderungen, die das Feld im Zuge seiner Ausdehnung zum weltweit dominierenden Reflexions- und Handlungszusammenhang im Umgang mit historischem Unrecht erfahren hat, ist deshalb in aller Regel keine angemessene Beachtung geschenkt worden. Der vorliegende Beitrag widmet sich aus historischer Sicht den Fragen, wie seit den späten 1980er Jahren über die Grenzen nationaler Aufarbeitungsschauplätze hinaus Wissen über Transitional Justice generiert und übertragen worden ist, welche die beteiligten Akteursgruppen waren und welche Auswirkungen der Wandel in den Wissenstransfers und im Verhältnis zwischen den Akteuren auf die Entwicklungen im Feld hatte. Im Mittelpunkt der Analyse steht dabei das Instrument der Wahrheitskommissionen. Historical approaches to the study of transitional justice are rare. In the process of its expansion to the dominating paradigm in dealing with past injustices, the field experienced far reaching changes. Scholarship about transitional justice, however, has hardly taken into account these shifts in appropriate ways. This article examines from a historical point of view how knowledge about transitional justice was generated and transferred across the borders of the national sites of dealing with the past, what were the groups of actors involved and what effects the transformations of the knowledge circulation as well as of the relationship between the actors since the late 1980s had on the development of the field. The focus of the analysis, thereby, is on the instrument of truth commissions.

Ecological speciation and phenotypic plasticity affect ecosystems

Phenotypic differences among closely related populations and species can cause contrasting effects on ecosystems; however, it is unknown whether such effects result from genetic divergence, phenotypic plasticity, or both. To test this, we reared sympatric limnetic and benthic species of whitefish from a young adaptive radiation in a common garden, where the benthic species was raised on two distinct food types. We then used these fish in a mesocosm experiment to test for contrasting ecosystem effects of closely related species and of plastically induced differences within a species. We found that strong contrasting ecosystem effects resulted more frequently from genetic divergence, although they were not stronger overall than those resulting from phenotypic plasticity. Overall, our results provide evidence that genetically based differences among closely related species that evolved during a young adaptive radiation can affect ecosystems, and that phenotypic plasticity can modify the ecosystem effects of such species.

Speciation in Freshwater Fishes

The extraordinary species richness of freshwater fishes has attracted much research on mechanisms and modes of speciation. We here review research on speciation in freshwater fishes in light of speciation theory, and place this in a context of broad-scale diversity patterns in freshwater fishes. We discuss several major repeated themes in freshwater fish speciation and the speciation mechanisms they are frequently associated with. These include transitions between marine and freshwater habitats, transitions between discrete freshwater habitats, and ecological transitions within habitats, as well as speciation without distinct niche shifts. Major research directions in the years to come include understanding the transition from extrinsic environment-dependent to intrinsic reproductive isolation and its influences on species persistence and understanding the extrinsic and intrinsic constraints to speciation and how these relate to broad-scale diversification patterns through time.

Mechanisms of rapid sympatric speciation by sex reversal and sexual selection in cichlid fish

Mechanisms of speciation in cichlid fish were investigated by analyzing population genetic models of sexual selection on sex-determining genes associated with color polymorphisms. The models are based on a combination of laboratory experiments and field observations on the ecology, male and female mating behavior, and inheritance of sex-determination and color polymorphisms. The models explain why sex-reversal genes that change males into females tend to be X-linked and associated with novel colors, using the hypothesis of restricted recombination on the sex chromosomes, as suggested by previous theory on the evolution of recombination. The models reveal multiple pathways for rapid sympatric speciation through the origin of novel color morphs with strong assortative mating that incorporate both sex-reversal and suppressor genes. Despite the lack of geographic isolation or ecological differentiation, the new species coexists with the ancestral species either temporarily or indefinitely. These results may help to explain different patterns and rates of speciation among groups of cichlids, in particular the explosive diversification of rock-dwelling haplochromine cichlids.

Explosive speciation rates and unusual species richness in haplochromine cichlid fishes: Effects of sexual selection

Ancient lakes are often unusually species rich, mostly as a result of radiation and species-flock formation having taken place in only one or a few of many taxa present. Understanding why some taxa radiate and others do not is at the heart of understanding biodiversity. In this chapter I discuss possible explanations for disproportionally large species numbers in some cichlid fish lineages in East African Great Lakes: the halochromine cichlid fishes in Lakes Victoria and Malawi. I show that speciation rates in this group are higher than in any other lacustrine fish radiation. Against this background, I review hypotheses put forward to explain diversity in cichlid species flocks. The evolution of species diversity requires three processes: speciation, ecological radiation and anatomical diversification, and it is wrong to consider hypotheses that are relevant to different processes as alternatives to each other. The African cichlid species flocks show unusually high ecological species packing in several phylogenetic groups and unusually high speciation rates in haplochromines. Therefore, it maybe concluded that at least two evolutionary models are required to explain the difference between cichlid diversity and other fish diversity in East African Lakes: one for speciation in haplochromines and one for coexistence. Subsequently I review work on speciation in haplochromines, and in particular studies aimed at testing the hypothesis of speciation by sexual selection. Haplochromines have a polygynous mating system, conducive to sexual selection, but other polygynous cichlids are not particularly species rich. This suggests that more than just strong sexual selection is required to explain haplochromine species richness. Recent palaeoecological evidence undermines the previously popular hypotheses that explained the species richness of Lake Victoria in terms of speciation under varying natural or sexual selection regimes in satellite lakes or in isolated lake basins. I summarize experimental and comparative studies, which provide evidence for two mechanisms of sympatric speciation by disruptive sexual selection on polymorphic coloration. Such modes of speciation may explain (i) the high speciation rates in colour polymorphic lineages of haplochromine cichlids under conditions where colour variation is visible in clear water, and (ii) in combination with factors that affect population survival, the unusual species richness in haplochromine species flocks. I argue that sexual selection, if disruptive, can accelerate the pace of adaptive radiation because the resultant genetic population fragmentation allows a much increased rate of differential response to disruptive natural selection. Hence, the ecological pattern of diversity resembles that produced by disruptive natural selection, with the difference that disruptive sexual selection continues to cause (gross) speciation even after niche space is saturated. This may explain the unusually high numbers of very closely related and ecologically similar species in haplochromine species flocks. The role of disruptive sexual selection is twofold: it not only causes speciation, but also maintains reproductive isolation in sympatry between species that have evolved in sympatry or allopatry. Therefore, the maintenance of diversity in species flocks that originated through sexual selection depends on the persistence of the selection regime within the environmental signal space under which that diversity evolved.

Color polymorphism and sex ratio distortion in a cichlid fish as an incipient stage in sympatric speciation by sexual selection

We investigated a Lake Victoria cichlid with a complex colour polymorphism that apparently represents one original species and two incipient species, all of which are sympatric. In laboratory breeding experiments we observed sex ratio distortion in certain matings between original and incipient species. Mate choice experiments show that males of the incipient species exhibit mating preferences against the original species, and males and females of the original species exhibit strong mating preferences against the incipient species. Mating preferences might evolve by sex ratio selection to avoid matings with distorted progeny sex ratios. Phenotype frequencies in nature suggest that mating preferences translate into mating frequencies, thus restricting gene flow and exerting disruptive sexual selection between the original and incipient species. The incipient species do not differ in morphology or ecology from the original species, implying that colour polymorphism, associated with sex ratio distortion, can be an incipient stage in sympatric speciation, and that disruption of gene flow can precede ecological differentiation

Can sympatric speciation by disruptive sexual selection explain rapid evolution of cichlid diversity in Lake Victoria?

Rapid speciation can occur on ecological time scales and interfere with ecological processes, resulting in species distribution patterns that are difficult to reconcile with ecological theory. The haplochromine cichlids in East African lakes are an extreme example of rapid speciation. We analyse the causes of their high speciation rates. Various studies have identified disruptive sexual selection acting on colour polymorphisms that might cause sympatric speciation. Using data on geographical distribution, colouration and relatedness from 41 species endemic to Lake Victoria, we test predictions from this hypothesis. Plotting numbers of pairs of closely related species against the amount of distributional overlap between the species reveals a bimodal distribution with modes on allopatric and sympatric. The proportion of sister species pairs that are heteromorphic for the traits under disruptive selection is higher in sympatry than in allopatry. These data support the hypothesis that disruptive sexual selection on colour polymorphisms has caused sympatric speciation and help to explain the rapid radiation of haplochromine species flocks.