First evidence for postzygotic reproductive isolation between two populations of Eurasian perch (Perca fluviatilis L.) within Lake Constance

<p>Abstract</p> <p>Background</p> <p>The evolution of reproductive traits, such as hybrid incompatibility (postzygotic isolation) and species recognition (prezygotic isolation), have shown their key role in speciation. Theoretical modeling has recently predicted that close linkage between genes controlling pre- and postzygotic reproductive isolation could accelerate the conditions for speciation. Postzygotic isolation could develop during the sympatric speciation process contributing to the divergence of populations. Using hybrid fitness as a measure of postzygotic reproductive isolation, we empirically studied population divergence in perch (<it>Perca fluviatilis </it>L.) from two genetically divergent populations within a lake.</p> <p>Results</p> <p>During spawning time of perch we artificially created parental offspring and F₁hybrids of the two populations and studied fertilization rate and hatching success under laboratory conditions. The combined fitness measure (product of fertilization rate and hatching success) of F₁hybrids was significantly reduced compared to offspring from within population crosses.</p> <p>Conclusion</p> <p>Our results suggest intrinsic genetic incompatibility between the two populations and indicate that population divergence between two populations of perch inhabiting the same lake may indeed be promoted by postzygotic isolation.</p

Інтертекстуальна деміургія: спроба порівняльного аналізу оповідання Дж. Р. Р. Толкієна "Листок Ніггля" та роману М.Булгакова «Майстер і Маргарита»

(uk) Одним з найяскравіших прикладав інтертекстуального творення є роман М. Булгакова «Майстер та Маргарита». Ця стаття є спробою порівняльного аналізу твору російського письменника і казки Дж. Толкієна «Листок Ніггла», найповніше простежуються особливості деміургійного процесу. Дж. Толкієн у короткій казці оповідає долю генія, в алегоричній формі розкриває його (генія) здібності до створення та перетворення світу.(en) The article is devoted to the comparative analysis of J. Tolkien's and M. Bulgakov's creative conception that is mostly embodied in the works «Leaf by Niggle» and «Master and Margaret». The main character of the tale «Leaf by Niggle» resembles other J. Tolkien's heroes and the author himself. The tale is devoted to the fate of a genius, opens his abilities for creation and transformation o f the world

Kin and population recognition in sympatric Lake Constance perch (Perca fluviatilis L.) : can assortative shoaling drive population divergence?

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer-Verlag GmbH for personal use, not for redistribution. The definitive version was published in Behavioral Ecology and Sociobiology 59 (2006): 461-468, doi:10.1007/s00265-005-0070-3.Prior studies have shown that perch (Perca fluviatilis L.) of Lake Constance belong to two genetically different but sympatric populations, and that local aggregations of juveniles and adults contain closely related kin. In this study we analysed the genetic structure of pelagic perch larvae to investigate, if kin structured shoals already exist during early ontogenetic development or might be the result of homing to natal sites. Analysis of the gene frequencies at five microsatellite loci revealed that 3 out of 5 pelagic aggregations of larvae showed significant accumulation of kin. To investigate possible mechanisms of shoal formation, we tested if perch use olfactory cues to recognize their kin. Choice tests in a fluviarium showed preference for odours of unfamiliar kin versus unfamiliar non-kin. Additionally, we showed that perch could differentiate between the odours of the two sympatric populations and significantly preferred unfamiliar and unrelated conspecifics of their own over the foreign population. Our results present a behavioural mechanism that could lead to the observed formation of kin structured shoals in perch. We further discuss if the ability to discriminate between the own and the foreign population could result in assortative mating within populations and thus form the basis of “socially mediated speciation” in perch.Funding was provided by Deutsche Forschungsgemeinschaft within the collaborative research center SFB 454, Littoral of Lake Constance, the “Fonds der Chemischen Industrie”, University of Konstanz, and the “Konrad Adenauer-Stiftung”

Evolutionäre Mechanismen der Populationsaufspaltung beim Flussbarsch (Perca fluviatilis L.)

The central issue of this thesis is the understanding of evolutionary mechanisms, that maintain and drive the divergence of populations and can lead to sympatric speciation. A former study showed that two populations of perch (Perca fluviatilis L.) co-exist in Lake Constance. For the first time I provide empirical evidence, that socially mediated divergence (kin- and population preference) in combination with ecological factors (difference in spawning times) could explain the origin and persistence of the perch subpopulations. Divergence between perch populations could be reinforced by reduced hybrid fitness.My results support that both populations originated from a single source population because analysis of the variability of mitochondrial DNA (mtDNA D-loop sequencing) showed no difference in haplotype frequencies between the eastern and western subpopulations of perch in Lake Constance. Moreover, perch originated most likely from the Danube River because Danube and Lake Constance perch share the same distinct haplotype, whereas perch from the Rhine (the second possible refuge) lack this special haplotype. This is consistent with the geological history of Lake Constance with a known connection between the lake and the Danube during lake formation in the Pleistocene (app. 15 000 years ago). Subsequent upstream colonization from the Rhine is unlikely because there has always been a impassable waterfall.A microsatellite analysis on the genetic structure of larval perch in the pelagic zone of Lake Constance showed that perch form shoals of closely related conspecifics. To test if this behaviour is due to a preference for members of their own subpopulation, including kin, I investigated active choice for olfactory cues in laboratory reared perch. Juvenile perch were tested in a two-channel flume for preference of odours from different conspecifics of known relatedness. Three different choice experiments were conducted: holding water from kin (three different sibling groups were tested: full-sibs, maternal half sibs or paternal half sibs) was always tested vs. holding water of non-kin belonging to the same subpopulation. Perch significantly preferred kin over non kin, there was no difference between the different kinship tests. In a second experiment population recognition was tested. Juvenile perch significantly preferred unrelated members of their own versus members of the foreign population. From these experiments I conclude that kin and population coherence can be an active choice based on olfactory preference, which could easily lead to assortative mating.An important constraint on disruptive population divergence is selection against hybrids. Therefore I measured the fertilization and hatching success of F1 hybrids of the two populations compared to those within each parental population. Two different F1 hybrids (mother eastern population, father western population and vice versa) were produced by artificial fertilization. Compared to the eastern and western populations, fitness was significantly lower for both hybrids. These laboratory measures of hybrid fitness suggest that some genetic incompatibility has already accumulated in the parental populations. Therefore, genetic divergence between the two perch populations in Lake Constance seems to be underway and is reinforced by reduced hybrid fitness.Differences in lake basin morphology could lead to ecological separation of the two subpopulations based on asynchrony in spawning time/location. In a preliminary morphological analysis slight but significant differences could be found between the two subpopulations. Differences in morphological traits did not affect characters, that are commonly driven by ecological speciation but reflect an accumulation of neutral genetic differences between reproductively isolated subpopulations.To conclude, I provide empirical evidence for a socially mediated divergence, that may drive sympatric speciation of perch: asynchrony in spawning time and location cause ecological separation of perch into subpopulations. The resulting disruptive population divergence is enhanced by olfactory preference for kin and conspecifics of the same population, and is reinforced by selection against hybrids

Parasite identification, succession and infection pathways in perch fry (Perca fluviatilis) : new insights through a combined morphological and genetic approach

Identification of parasite species is particularly challenging in larval and juvenile hosts, and this hampers the understanding of parasite acquisition in early life. The work described here employs a new combination of methods to identify parasite species and study parasite succession in fry of perch (Perca fluviatilis) from Lake Constance, Germany. Classical morphological diagnostics are combined with sequence comparisons between parasite life-stages collected from various hosts within the same ecosystem. In perch fry at different stages of development, 13 different parasite species were found. Incomplete morphological identifications of cestodes of the order Proteocephalidea, and trematodes of the family Diplostomatidae were complemented with sequences of mitochondrial DNA (cytochrome oxidase 1) and/or nuclear (28 s rDNA) genes. Sequences were compared to published data and used to link the parasites in perch to stages from molluscs, arthropods and more easily identifiable developmental stages from other fishes collected in Lake Constance, which both aided parasite identification and clarified transmission pathways. There were distinct changes in parasite community composition and abundance associated with perch fry age and habitat shifts. Some parasites became more abundant in older fish, whereas the composition of parasite communities was more strongly affected by the ontogenetic shifts from the pelagic to the littoral zone

Multiple isotope analyses of the pike tapeworm Triaenophorus nodulosus reveal peculiarities in consumer–diet discrimination patterns

Previous studies of dietary isotope discrimination have led to the general expectation that a consumer will exhibit enriched stable isotope levels relative to its diet. Parasite–host systems are specific consumer–diet pairs in which the consumer (parasite) feeds exclusively on one dietary source: host tissue. However, the small numbers of studies previously carried out on isotopic discrimination in parasite–host (ΔXP-HT) systems have yielded controversial results, showing some parasites to be isotopically depleted relative to their food source, while others are enriched or in equilibrium with their hosts. Although the mechanism for these deviations from expectations remains to be understood, possible influences of specific feeding niche or selection for only a few nutritional components by the parasite are discussed. ΔXP-HT for multiple isotopes (δ13C, δ15N, δ34S) were measured in the pike tapeworm Triaenophorus nodulosus and two of its life-cycle fish hosts, perch Perca fluviatilis and pike Esox lucius, within which T. nodulosus occupies different feeding locations. Variability in the value of ΔXP-HT calculated for the parasite and its different hosts indicates an influence of feeding location on isotopic discrimination. In perch liver ΔXP-HT was relatively more negative for all three stable isotopes. In pike gut ΔXP-HT was more positive for δ13C, as expected in conventional consumer–diet systems. For parasites feeding on pike gut, however, the δ15N and δ34S isotope values were comparable with those of the host. We discuss potential causes of these deviations from expectations, including the effect of specific parasite feeding niches, and conclude that ΔXP-HT should be critically evaluated for trophic interactions between parasite and host before general patterns are assumed

Genotyping MHC classIIB in non-model species by reference strand-mediated conformational analysis (RSCA)

Major histocompatibility complex (MHC)diversity is described in many species and, in particular, is germane to the conservation of endangered species. However, studies addressing the functional link between individual MHC-variation and, for example, disease susceptibility are underrepresented. This is most likely due to the complex nature of MHC in most species, which hampers reliable individual typing. To date MHC-genotyping by reference strand-mediated conformational analysis (RSCA) has been used in only a few model species where extensive prior information on MHC-gene sequences was available. In those cases, RSCA was found to be a highly accurate and reliable method. Here we adapt this method to two non-model species, Eurasian perch (Perca fluviatilis) and Alpine whitefish (Coregonus spp.). We show that RSCA can be quickly applied as a flexible genotyping method to any species, even with only limited prior information about its MHC-genes

Do Visual Experiences Have Contents?

Philosoph

Evolutiv junge europäische Höhlenfische

A population of loaches (Barbatula spec.) from the Aach Cave in Germany represents the first cave fish in Europe and the northernmost cave fish worldwide. Reasons for the evolution of this fish may include that its cave is fed by surface water that percolates from the upper Danube and enhances the habitat. Cave Barbatula are evolutionarily young and may serve to generalize findings about the well-studied Mexican cave tetra (Astyanax mexicanus).publishe