Comparative ecology and phylogeography in east African cichild fishes

Since almost two decades speciation outbursts, so-called adaptive radiations, have been put forward as a major reason for a large portion of the bio-diversity we see today. Adaptive radiations are indisputably very complex processes with many factors to consider. They are, however, not separable from the concept of ecological speciation by the means of natural selection. Hence the concept of convergent evolution, which states that different organisms independently evolve similar morphological or behavioral traits as a result of similar ecological selection regimes, was put forward as an essential indicator of the ‘adaptiveness’ of respective species differences and/or similarities. In the exceptionally species rich and eco-morphologically highly diverse assemblages of the East African Rift lakes, the paradox was put forward that competitive ecological exclusion of converging species seems to require a temporal and special separation (allopatry) of the different lineages in order for them to coexist. Recent phylogenetic framework and molecular dating seem to indicate though that in fact many lineages formed very rapidly thus not allowing the avoidance of competitive exclusion. These are questions addressed in the first part of my thesis (“Comparative ecology”) consisting of two Chapters. 1: “Convergent evolution within an adaptive radiation of cichlid fishes” where we investigated ecologically based convergence within the Lake Tanganyika cichlid radiation and 2. “The ecological and genetic basis of convergent thick-lipped phenotypes in cichlid fishes” where we investigated the convergent occurrence of a conspicuous trait which is thought to be highly adaptive, the thick lipped phenotype of cichlid fishes. Considering the strong connectivity of convergent evolution with the ecological properties of a habitat mediated by natural selection it is apparently crucial to study ecological parameters of habitats connected by convergent phenotypes which we did in Chapter 3: "Depth-dependent abundance of Midas Cichlid fish (Amphilophus spp.) in two Nicaraguan crater lakes". Here we characterised effective population sizes by means of transect methods in order to compare two lakes exhibiting convergent phenotypes. In a second part (“Phylogeography”) I combine different studies dealing with a combination of distributional patterns, patterns of phylogenetic relationships and ecological factors of east African riverine cichlids since they have become increasingly important in the understanding of large-scale relations of African cichlid fishes. In Chapter 4: “Back to Tanganyika: a case of a recent immigration into a species flock of East African cichlid fishes” we investigate a recently discovered dispersal event of a modern cichlid lineage (Haplochromis spp.) across major watershed barriers in Eastern Africa. In Chapter 5: “Divergence between lake and stream habitats in an East African cichlid fish” we investigate the degree of ecological divergence of a riverine cichlid species, which also occurs in pure lake habitats (Astatotilapia burtoni). In Chapter 6: “Admixture between divergent mitochondrial lineages and greater phenotypic variation in a basal haplochromine cichlid fish from Lake Chila, Zambia” we investigate the phylogeographic history of a basal haplochormine clade (genus: Pseudocrenilabrus). Morphological diversity within natural populations is a crucial prerequisite for natural selection to act on and to enable ecological adaptive evolution. A special case of such morphological variation, the mouth asymmetry of scale eating cichlid fish of Lake Tanganyika, was the main topic of the third part of my thesis (“Asymmetrical Polymorphism”) and Chapter 7: “A field based assessment of attack strategies and feeding success in the scale eating cichlid fish Perissodus microlepis (Perciformes)”

Fear of cyber-identity theft and related fraudulent activity

Identity theft and related fraudulent activities affect approximately one in twenty-five adults each year across western societies. The Internet provides a new avenue for obtaining identity tokens and identifying information and increases the scale on which identity theft can be perpetrated. Recent research has suggested that fear of these types of crimes now matches or exceeds the fear of traditional place-based crimes, and has the potential to curtail online activities and hinder the further development of e-commerce applications. In this article, we conduct exploratory research identifying predictors of fear of cyber-identity theft and related fraudulent activities, based on the analysis of items included in the Australian Survey of Social Attitudes (2007). Fear was predicted by a generalized fear of crime component and a specific Internet exposure component. Traditional predictors of fear of crime were insignificant or weak predictors, highlighting the need for further research

Traubenwelke - eine neue Hypothese

Die Traubenwelke führte in den letzten Jahren auch in der Schweiz vermehrt zu Ertragsausfällen. Nach ihrem starken Auftreten im Jahr 2005 führte Hans Jüstrich, Rebbaukommissär des Kantons Graubünden, eine Umfrage in der Deutschschweiz durch. Im Rahmen einer Diplomarbeit wurden die Antworten ausgewertet. Die Ergebnisse wurden ergänzt durch Resultate von Betriebsbesuchen im Spätsommer 2006. In einer Semesterarbeit folgte dann eine Literaturrecherche zur Überprüfung einer neuen Theorie: Die verfrühte Verstopfung der Siebröhren (Phloem) durch Kallose unterbricht die Versorgung der Beeren und lässt diese schrumpfen

Spatial variation in abiotic and biotic factors in a floodplain determine anuran body size and growth rate at metamorphosis

Body size at metamorphosis is a critical trait in the life history of amphibians. Despite the wide-spread use of amphibians as experimental model organisms, there is a limited understanding of how multiple abiotic and biotic factors affect the variation in metamorphic traits under natural conditions. The aim of our study was to quantify the effects of abiotic and biotic factors on spatial variation in the body size of tadpoles and size at metamorphosis of the European common toad (Bufo b. spinosus). Our study population was distributed over the riverbed (active tract) and the fringing riparian forest of a natural floodplain. The riverbed had warm ponds with variable hydroperiod and few predators, whereas the forest had ponds with the opposite characteristics. Spatial variation in body size at metamorphosis was governed by the interactive effects of abiotic and biotic factors. The particular form of the interaction between water temperature and intraspecific tadpole density suggests that abiotic factors laid the foundation for biotic factors: intraspecific density decreased growth only at high temperature. Predation and intraspecific density jointly reduced metamorphic size. Interspecific density had a negligible affect on body size at metamorphosis, suggesting weak inter-anuran interactions in the larval stage. Population density at metamorphosis was about one to two orders of magnitudes higher in the riverbed ponds than in the forest ponds, mainly because of lower tadpole mortality. Based on our results, we conclude that ponds in the riverbed appear to play a pivotal role for the population because tadpole growth and survival is best in this habita

Where Am I? Niche constraints due to morphological specialization in two Tanganyikan cichlid fish species

Food resource specialization within novel environments is considered a common axis of diversification in adaptive radiations. Feeding specializations are often coupled with striking morphological adaptations and exemplify the relation between morphology and diet (phenotype-environment correlations), as seen in, for example, Darwin finches, Hawaiian spiders, and the cichlid fish radiations in East African lakes. The cichlids' potential to rapidly exploit and occupy a variety of different habitats has previously been attributed to the variability and adaptability of their trophic structures including the pharyngeal jaw apparatus. Here we report a reciprocal transplant experiment designed to explore the adaptability of the trophic structures in highly specialized cichlid fish species. More specifically, we forced two common but ecologically distinct cichlid species from Lake Tanganyika,; Tropheus moorii; (rock-dweller), and; Xenotilapia boulengeri; (sand-dweller), to live on their preferred as well as on an unpreferred habitat (sand and rock, respectively). We measured their overall performance on the different habitat types and explored whether adaptive phenotypic plasticity is involved in adaptation. We found that, while habitat had no effect on the performance of; X. boulengeri; ,; T. moorii; performed significantly better in its preferred habitat. Despite an experimental duration of several months, we did not find a shift in the morphology of the lower pharyngeal jaw bone that would be indicative of adaptive phenotypic plasticity in this trait

The taxonomic diversity of the cichlid fish fauna of ancient Lake Tanganyika, East Africa

Ancient Lake Tanganyika in East Africa houses the world's ecologically and morphologically most diverse assemblage of cichlid fishes, and the third most species-rich after lakes Malawi and Victoria. Despite long-lasting scientific interest in the cichlid species flocks of the East African Great Lakes, for example in the context of adaptive radiation and explosive diversification, their taxonomy and systematics are only partially explored; and many cichlid species still await their formal description. Here, we provide a current inventory of the cichlid fish fauna of Lake Tanganyika, providing a complete list of all valid 208 Tanganyikan cichlid species, and discuss the taxonomic status of more than 50 undescribed taxa on the basis of the available literature as well as our own observations and collections around the lake. This leads us to conclude that there are at least 241 cichlid species present in Lake Tanganyika, all but two are endemic to the basin. We finally summarize some of the major taxonomic challenges regarding Lake Tanganyika's cichlid fauna. The taxonomic inventory of the cichlid fauna of Lake Tanganyika presented here will facilitate future research on the taxonomy and systematics and the ecology and evolution of the species flock, as well as its conservation

Back to Tanganyika: a case of recent trans-species-flock dispersal in East African haplochromine cichlid fishes

The species flocks of cichlid fishes in the East African Great Lakes are the largest vertebrate adaptive radiations in the world and illustrious textbook examples of convergent evolution between independent species assemblages. Although recent studies suggest some degrees of genetic exchange between riverine taxa and the lake faunas, not a single cichlid species is known from Lakes Tanganyika, Malawi and Victoria that is derived from the radiation associated with another of these lakes. Here, we report the discovery of a haplochromine cichlid species in Lake Tanganyika, which belongs genetically to the species flock of haplochromines of the Lake Victoria region. The new species colonized Lake Tanganyika only recently, suggesting that faunal exchange across watersheds and, hence, between isolated ichthyofaunas, is more common than previously thought

Homogenized finite element analysis of distal tibia sections: Achievements and limitations.

High-resolution peripheral quantitative computed tomography (HR-pQCT) based micro-finite element (μFE) analysis allows accurate prediction of stiffness and ultimate load of standardised (∼1 cm) distal radius and tibia sections. An alternative homogenized finite element method (hFE) was recently validated to compute the ultimate load of larger (∼2 cm) distal radius sections that include Colles' fracture sites. Since the mechanical integrity of the weight-bearing distal tibia is gaining clinical interest, it has been shown that the same properties can be used to predict the strength of both distal segments of the radius and the tibia. Despite the capacity of hFE to predict structural properties of distal segments of the radius and the tibia, the limitations of such homogenization scheme remain unclear. Therefore, the objective of this study is to build a complete mechanical data set of the compressive behavior of distal segments of the tibia and to compare quantitatively the structural properties with the hFE predictions. As a further aim, it is intended to verify whether hFE is also able to capture the post-yield strain localisation or fracture zones in such a bone section, despite the absence of strain softening in the constitutive model. Twenty-five fresh-frozen distal parts of tibias of human donors were used in this study. Sections were cut corresponding to an in-house triple-stack protocol HR-pQCT scan, lapped, and scanned using micro computed tomography (μCT). The sections were tested in compression until failure, unloaded and scanned again in μCT. Volumetric bone mineral density (vBMD) and bone mineral content (BMC) were correlated to compression test results. hFE analysis was performed in order to compare computational predictions (stiffness, yield load and plastic deformation field pattern) with the compressive experiment. Namely, strain localization was assessed based on digital volume correlation (DVC) results and qualitatively compared to hFE predictions by comparing mid-slices patterns. Bone mineral content (BMC) showed a good correlation with stiffness (R2 = 0.92) and yield (R2 = 0.88). Structural parameters also showed good agreement between the experiment and hFE for both stiffness (R2 = 0.96, slope = 1.05 with 95 % CI [0.97, 1.14]) and yield (R2 = 0.95, slope = 1.04 [0.94, 1.13]). The qualitative comparison between hFE and DVC strain localization patterns allowed the classification of the samples into 3 categories: bad (15 sections), semi (8), and good agreement (2). The good correlations between BMC or hFE and experiment for structural parameters were similar to those obtained previously for the distal part of the radius. The failure zones determined by hFE corresponded to registration only in 8 % of the cases. We attribute these discrepancies to local elastic/plastic buckling effects that are not captured by the continuum-based FE approach exempt from strain softening. A way to improve strain localization hFE prediction would be to use longer distal segments with intact cortical shells, as done for the radius. To conclude, the used hFE scheme captures the elastic and yield response of the tibia sections reliably but not the subsequent failure process

Structural manipulations of a shelter resource reveal underlying preference functions in a shell-dwelling cichlid fish

Many animals can modify the environments in which they live, thereby changing the selection pressures they experience. A common example of such niche construction is the use, creation or modification of environmental resources for use as nests or shelters. Because these resources often have correlated structural elements, it can be difficult to disentangle the relative contribution of these elements to resource choice, and the preference functions underlying niche-construction behaviour remain hidden. Here, we present an experimental paradigm that uses 3D scanning, modelling and printing to create replicas of structures that differ with respect to key structural attributes. We show that a niche-constructing, shell-dwelling cichlid fish,; Neolamprologus multifasciatus; , has strong open-ended preference functions for exaggerated shell replicas. Fish preferred shells that were fully intact and either enlarged, lengthened or had widened apertures. Shell intactness was the most important structural attribute, followed by shell length, then aperture width. We disentangle the relative roles of different shell attributes, which are tightly correlated in the wild, but nevertheless differentially influence shelter choice and therefore niche construction in this species. We highlight the broad utility of our approach when compared with more traditional methods (e.g. two-choice tasks) for studying animal decision-making in a range of contexts

Diet and habitat as determinants of intestine length in fishes

Fish biologists have long assumed a link between intestinal length and diet, and relative gut length or Zihler’s index are often used to classify species into trophic groups. This has been done for specific fish taxa or specific ecosystems, but not for a global fish dataset. Here, we assess these relationships across a dataset of 468 fish species (254 marine, 191 freshwater, and 23 occupy both habitats) in relation to body mass and fish length. Herbivores had significantly relatively stouter bodies and longer intestines than omni- and faunivores. Among faunivores, corallivores had longer intestines than invertivores, with piscivores having the shortest. There were no detectable differences between herbivore groups, possibly due to insufficient understanding of herbivorous fish diets. We propose that reasons for long intestines in fish include (i) difficult-to-digest items that require a symbiotic microbiome, and (ii) the dilution of easily digestible compounds with indigestible material (e.g., sand, wood, exoskeleton). Intestinal indices differed significantly between dietary groups, but there was substantial group overlap. Counter-intuitively, in the largest dataset, marine species had significantly shorter intestines than freshwater fish. These results put fish together with mammals as vertebrate taxa with clear convergence in intestine length in association with trophic level, in contrast to reptiles and birds, even if the peculiar feeding ecology of herbivorous fish is probably more varied than that of mammalian herbivores