Cichlids of the lower Congo River - a new model system in speciation research?

Fishes account for the highest diversity of all vertebrate groups on our planet. Among them one group clearly outnumbers all the others - cichlids (Perciformes, Cichlidae). The present study focuses on cichlids of the lower Congo River, one of the most spectacular habitats for animal life on earth. One primary aim was to establish the lower Congo cichlids as the first model system in speciation research based on riverine species and to emphasize their contribution to general cichlid species diversity. The reconstruction of robust phylogenetic trees and reliable placement of the lower Congo cichlids within a framework of African cichlids were the first goals of the present thesis. The lower Congo cichlid genera are assigned to different cichlid tribes: “Haplochromis”, Lamprologus and Steatocranus belong to the haplotilapiines, a tribe comprising the megadiverse lacustrine radiations and tilapiine genera, and Nanochromis and Teleogramma to the chromidotilapiines, an ancient West/Central African mainly riverine cichlid lineage. Multi-locus phylogenetic trees of both haplotilapiines and chromidotilapiines and more detailed of haplochromines were reconstructed, allowing the identification of biogeographic coherences and general relationships of the lower Congo genera with the remaining African cichlids. Age estimates allowed setting phylogenetic splitting events in context with the palaeohistory of the African continent. Species differentiation along the lower Congo River and potential timing of initial colonization of the lower Congo rapids were inferred by including nearly all to date known species of the genera Steatocranus and Nanochromis. Intrageneric relationships were reconstructed based on extensive multi-locus AFLP datasets in combination with mitochondrial and nuclear sequence data. I could show, that Steatocranus and Nanochromis species predominantly differentiated allopatrically within the lower Congo River in about 5mya. The rapids were colonized in each genus at least twice from surrounding lakes (Nanochromis) and rivers. The existence of various levels of gene flow between adjacent and more distantly related species especially in Steatocranus species and within the haplochromines underlines the non-destructive and potentially even beneficial role of hybridization in cichlids. A rather web-like evolution in the genus Steatocranus doubts the general applicability of bifurcating trees especially in species known to hybridize

Einfluss probiotischer Substanzen auf den antioxidativen Status von neugeborenen Hundewelpen

In der vorliegenden Arbeit wurde erstmals der antioxidative Status von neugeborenen Hundewelpen bestimmt. Zusätzlich wurde untersucht, ob die Zufütterung von Lactoferrin bzw. Enterococcus faecium einen Einfluss auf den antioxidativen Status der Tiere ausübt. Dazu wurden 42 neonatale Beagle-Welpen am 3. Tag nach der Geburt von den Muttertieren getrennt und in zwei unabhängigen Fütterungsversuchen von Hand aufgezogen (Lactoferrin-Versuch und Ec. faecium-Versuch). Der antioxidative Status wurde als TEAC an Tag 3, 7, 14, 28, 56, 70, 84 und 98 im Blut der Welpen gemessen. Zusätzlich wurden die Plasmakonzentrationen des antioxidativ wirksamen Vitamin E bestimmt. Als Vergleich zur mutterlosen Aufzucht dienten 11 neugeborene Beagle-Welpen, die bei ihren Mutterhündinnen aufwuchsen. An Tag 1, 3, 7 und 14 wurden bei ihnen neben der TEAC die Vitamine E und C im Blut gemessen. Außerdem wurde freies Eisen, die latente Eisenbindungskapazität sowie Gesamteisen bestimmt und die totale Eisenbindungskapazität und Transferrinsättigung berechnet. Nach der Geburt kam es bei den neugeborenen Hundewelpen durch erhöhten oxidativen Stress zu einer deutlichen Verminderung des antioxidativen Status im Blut. Dabei konnte kein Einfluss der Lactoferrin- bzw. Ec. faecium-Supplementierung festgestellt werden. Es wurde kein Zusammenhang zwischen dem erniedrigten antioxidativen Status und einem vermehrten Auftreten von Neugeborenenerkrankungen oder einer erhöhten Welpensterblichkeit offensichtlich

The root of the East African cichlid radiations

<p>Abstract</p> <p>Background</p> <p>For decades cichlid fishes (Perciformes: Cichlidae) of the East African cichlid radiations (Teleostei: Cichlidae) have served as natural experimental subjects for the study of speciation processes and the search for potential speciation key factors. Despite numerous phylogenetic studies dealing with their intragroup relationships, surprisingly little is known about the phylogenetic placement and time of origin of this enigmatic group. We used multilocus DNA-sequence data from five nuclear and four mitochondrial genes and refined divergence time estimates to fill this knowledge gap.</p> <p>Results</p> <p>In concordance with previous studies, the root of the East African cichlid radiations is nested within the so called "Tilapias", which is a paraphyletic assemblage. For the first time, we clarified tilapiine intragroup relationships and established three new monophyletic groups:"Oreochromini", "Boreotilapiini" and a group with a distribution center in East/Central Africa, the "Austrotilapiini". The latter is the founder lineage of the East African radiations and emerged at the Miocene/Oligocene boundary at about 14 to 26 mya.</p> <p>Conclusion</p> <p>Our results provide the first resolved hypothesis for the phylogenetic placement of the megadiverse East African cichlid radiations as well as for the world's second most important aquaculture species, the Nile Tilapia, <it>Oreochromis niloticus</it>. Our analyses constitute not only a robust basis for African cichlid phylogenetics and systematics, but provide a valid and necessary framework for upcoming comparative phylogenomic studies in evolutionary biology and aquaculture.</p

Allopatric speciation in the desert: diversification of cichlids at their geographical and ecological range limit in Iran

Cichlids are textbook examples for rapid diversification and high species diversity. While in South America, several hundred and in Africa, more than 1500 species of cichlid fish have been described, only one single cichlid species, Iranocichla hormuzensis Coad 1982, was known from Iran, the easternmost range margin of the species-rich African cichlids (Cichlidae: Pseudocrenilabrinae). The aim of our paper was to assess the genetic and phenotypic diversity among populations of Iranocichla across most of its geographical range in Southern Iran. For this, we sequenced two mitochondrial genes and collected color observation of male nuptial coloration in different habitats. Besides conspicuous differences in male nuptial coloration, we found considerable genetic differentiation among Iranocichla populations pointing to the existence of at least two allopatric species, with no evidence of more than one species at one site. Diversification within Iranocichla started, based on our data, in the middle or late Pleistocene and was followed by further population differentiation and bottlenecks during isolation events in the last glacial maximum. Population dispersal leading to the population structure observed today most likely occurred in the course of the early Holocene sea-level rise

A Dense Linkage Map of Lake Victoria Cichlids Improved the Pundamilia Genome Assembly and Revealed a Major QTL for Sex-Determination.

Genetic linkage maps are essential for comparative genomics, high quality genome sequence assembly and fine scale quantitative trait locus (QTL) mapping. In the present study we identified and genotyped markers via restriction-site associated DNA (RAD) sequencing and constructed a genetic linkage map based on 1,597 SNP markers of an interspecific F2 cross of two closely related Lake Victoria cichlids (Pundamilia pundamilia and P sp. 'red head'). The SNP markers were distributed on 22 linkage groups and the total map size was 1,594 cM with an average marker distance of 1.01 cM. This high-resolution genetic linkage map was used to anchor the scaffolds of the Pundamilia genome and estimate recombination rates along the genome. Via QTL mapping we identified a major QTL for sex in a ∼1.9 Mb region on Pun-LG10, which is homologous to Oreochromis niloticus LG 23 (Ore-LG23) and includes a well-known vertebrate sex-determination gene (amh)

Switching Between Bicyclic and Linear Peptides — The Sulfhydryl-Specific Linker TPSMB Enables Reversible Cyclization of Peptides

Phage display-selected bicyclic peptides have already shown their great potential for the development as bioactive modulators of therapeutic targets. They can provide enhanced proteolytic stability and improved membrane permeability. Molecular design of new linker molecules has led to a variety of new synthetic approaches for the generation of chemically constrained cyclic peptides. This diversity can be useful for the development of novel peptide-based therapeutic, diagnostic, and scientific tools. Herein, we introduce 1,3,5-tris((pyridin-2-yldisulfanyl)methyl)benzene (TPSMB) as a planar, trivalent, sulfhydryl-specific linker that facilitates reversible cyclization and linearization via disulfide bond formation and cleavage of bicyclic peptides of the format CXnCXnC, where X is any proteinogenic amino acid except cysteine. The rapid and highly sulfhydryl-specific reaction of TPSMB under physiological conditions is demonstrated by selecting bicyclic peptide binders against c-Jun N-terminal kinase 3 (JNK3) as a model target. While model peptides remain stably cyclized for several hours in presence of typical blood levels of glutathione in vitro, high cytosolic concentrations of glutathione linearize these peptides completely within 1 h. We propose that reversible linkers can be useful tools for several technical applications where target affinity depends on the bicyclic structure of the peptide

Time and Origin of Cichlid Colonization of the Lower Congo Rapids

Most freshwater diversity is arguably located in networks of rivers and streams, but, in contrast to lacustrine systems riverine radiations, are largely understudied. The extensive rapids of the lower Congo River is one of the few river stretches inhabited by a locally endemic cichlid species flock as well as several species pairs, for which we provide evidence that they have radiated in situ. We use more that 2,000 AFLP markers as well as multilocus sequence datasets to reconstruct their origin, phylogenetic history, as well as the timing of colonization and speciation of two Lower Congo cichlid genera, Steatocranus and Nanochromis. Based on a representative taxon sampling and well resolved phylogenetic hypotheses we demonstrate that a high level of riverine diversity originated in the lower Congo within about 5 mya, which is concordant with age estimates for the hydrological origin of the modern lower Congo River. A spatial genetic structure is present in all widely distributed lineages corresponding to a trisection of the lower Congo River into major biogeographic areas, each with locally endemic species assemblages. With the present study, we provide a phylogenetic framework for a complex system that may serve as a link between African riverine cichlid diversity and the megadiverse cichlid radiations of the East African lakes. Beyond this we give for the first time a biologically estimated age for the origin of the lower Congo River rapids, one of the most extreme freshwater habitats on earth