Publications by authors named "Christoph Haag"
Two important characteristics of metapopulations are extinction-(re)colonization dynamics and gene flow between subpopulations. These processes can cause strong shifts in genome-wide allele frequencies that are generally not observed in "classical" (large, stable, and panmictic) populations. Subpopulations founded by one or a few individuals, the so-called propagule model, are initially expected to show intermediate allele frequencies at polymorphic sites until natural selection and genetic drift drive allele frequencies toward a mutation-selection-drift equilibrium characterized by a negative exponential-like distribution of the site frequency spectrum.
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- Obligate parthenogenesis (OP) in Daphnia pulex may not evolve solely from disruptions in meiosis or recombination, as some males still undergo normal meiosis with only minor changes in recombination rates.
- The study suggests that the mechanisms behind OP could involve sex-limited genetic changes or reuse of existing parthenogenesis pathways rather than just alterations in meiosis-related genes.
- Overall, this research highlights the complexity of asexuality evolution, indicating that a variety of genetic factors contribute to the transition from cyclical to obligate parthenogenesis.
Article Synopsis
- In some asexual species, rare males can be produced by parthenogenetic females, potentially affecting the persistence of asexual reproduction through gene transmission.
- This study focuses on Artemia parthenogenetica, testing whether these males arise from recombination between sex chromosomes during asexual reproduction.
- Results from RAD-sequencing indicate that males show loss of heterozygosity at the sex determination locus, supporting the idea that recombination is not entirely suppressed, thereby explaining the occasional appearance of males in asexual populations.
Article Synopsis
- The study investigates how extinction and recolonization in habitat patches affect the evolution of metapopulations, specifically comparing them to larger, stable populations.* -
- Using whole-genome pool-sequencing on 60 subpopulations of Daphnia magna, researchers found that metapopulations show lower genetic diversity and higher differentiation, supporting the propagule model which states that colonization leads to genetic bottlenecks.* -
- The results indicate that younger and more isolated subpopulations experience reduced effective population sizes and genetic drift, revealing that the evolutionary dynamics of metapopulations differ significantly from those of larger, stable populations.*
AbstractDetermining how and how often asexual lineages emerge within sexual species is central to our understanding of sex-asex transitions and the long-term maintenance of sex. Asexuality can arise "by transmission" from an existing asexual lineage to a new one through different types of crosses. The occurrence of these crosses, cryptic sex, variations in ploidy, and recombination within asexuals greatly complicates the study of sex-asex transitions, as they preclude the use of standard phylogenetic methods and genetic distance metrics.
View Article and Find Full Text PDFVisible light excitation of iodine(III)-BF complex enables the formation of carbocations from C(sp)-H bonds. The complexes are generated catalytically from iodoarene, carboxylate ligand, the oxidizing agent Selectfluor, and the Lewis acid BF. This modular catalytic system allows the formation of synthetically valuable amine derivatives without a metal- or photocatalyst.
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- Daphnia magna serves as a key model for studying host-parasite coevolution due to its interaction with microparasites, showing unique ecological and evolutionary traits compared to other arthropods like Drosophila.
- The study analyzed the genomes of 36 D. magna clones from Europe to investigate adaptive protein evolution, revealing high genetic diversity that is structured among populations but not as strongly adapted as seen in Drosophila.
- Findings indicate a prevalence of weakly deleterious genetic variants in D. magna, suggesting reduced selection effectiveness and emphasizing local adaptation instead of widespread adaptive fixation across its populations.
Article Synopsis
- The study investigates how different sex ratios, specifically in Daphnia magna (a type of water flea), impact mating competition and reproductive success among males and females.
- The experiments revealed that males' reproductive success decreases significantly as the number of females per male decreases, whereas females' success is primarily affected under extreme female-biased conditions.
- The findings suggest that mating competition and sexual selection can affect both sexes, particularly indicating that females may face limitations in mating opportunities in skewed sex ratios commonly found in nature.
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- Sexual species experience a "twofold cost of males," leading to the expectation that asexual mutants, which reproduce clonally, should outcompete them; however, the study of brine shrimp reveals complexities in this idea with asexuals potentially engaging in "cryptic sex."
- The brine shrimp, long thought to be a purely asexual species, shows evidence of recombination and parent-offspring differences, suggesting that they may not be strictly clonal despite their rare male production.
- Findings indicate that hybrid females can reproduce both sexually and asexually, challenging previous notions of asexuality and emphasizing the need for reevaluating models of sexual reproduction, asexuality, and gene flow within asexual lineages.
Article Synopsis
- A study on Daphnia pulex examines how asexual species can outperform sexual ones in the presence of parasites, contrary to common theories.
- During a parasite outbreak, asexual Daphnia, initially rare, overtook the pond, showing lower susceptibility to infection and less harm once infected compared to their sexual counterparts.
- The findings suggest that this dynamics shift, driven by the parasite, led to the eventual decline of the dominant sexual population, highlighting an overlooked aspect of the Red Queen Hypothesis regarding the advantages of rarity in asexual reproduction.
Article Synopsis
- Researchers found that some female organisms lost the ability to produce males due to a dominant allele in a specific gene.
- By studying genome sequences of different clones, they identified genetic markers linked to this non-male producing (NMP) trait on chromosome I.
- The gene responsible is thought to be influenced by Methyl farnesoate, a hormone that typically induces male production, suggesting that changes in the expression of this gene lead to the NMP phenotype.
Genetic sex determination (GSD) can evolve from environmental sex determination (ESD) via an intermediate state in which both coexist in the same population. Such mixed populations are found in the crustacean Daphnia magna, where non-male producers (NMP, genetically determined females) coexist with male producers (MP), in which male production is environmentally inducible and can also artificially be triggered by exposure to juvenile hormone. This makes Daphnia magna a rare model species for the study of evolutionary transitions from ESD to GSD.
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- * Contrary to predictions that asexual organisms accumulate mutations, findings indicate that LOH is rare during asexual reproduction in D. magna, suggesting genetic homogeneity.
- * High-throughput sequencing and follow-up Sanger re-sequencing were used to assess genetic variation, leading to the conclusion that asexual lineages remain largely genetically stable over relevant time periods.
Article Synopsis
- Species with wide geographic ranges, like Daphnia magna, pose challenges for phylogeographic research due to sampling difficulties, particularly in underrepresented areas like Eastern Asia.
- This study utilizes mitochondrial COI sequences to explore the phylogeography of Daphnia magna across populations from Western Europe to Eastern Asia, revealing a significant divide between Eastern and Western haplotypes.
- The findings indicate a narrow contact zone in Western Siberia where these two groups co-exist, but do not suggest they are separate species; instead, they may have reconnected after expanding from different refuges, highlighting Central Siberia's role in Eurasian freshwater invertebrate studies.
Article Synopsis
- - The study focuses on a life cycle characterized by cyclic-parthenogenesis, which alternates between asexual and sexual reproduction, allowing for comparison of gene expression in genetically identical males and females.
- - Researchers found that 42% of annotated genes exhibited sex-biased expression, a rate consistent with estimates from other species, indicating that environmental sex determination does not reduce this bias.
- - A total of 707 ortholog genes showed consistent sex-biased expression across three species, with many involved in sex determination pathways, and notably, 75% of these genes were overexpressed in females.
Low recombination rates in sexual species and sex-asex transitions.
Philos Trans R Soc Lond B Biol Sci
December 2017
Article Synopsis
- In sexual diploid eukaryotes, at least one crossover generally occurs between homologous chromosomes during meiosis for proper segregation, but exceptions exist, such as species where one sex doesn’t recombine.
- The study examines species with low recombination rates, exploring whether these rates promote transitions between sexual and asexual reproduction or if they are a result of such transitions.
- A newly identified brine shrimp species from Kazakhstan shows notably short genetic linkage maps, indicating minimal crossovers, underscoring the significance of studying recombination in lesser-known species to understand evolutionary implications.
Article Synopsis
- * Daphnia magna, a small freshwater crustacean, exhibits a unique case where a dominant female sex-determining locus exists alongside its typical ESD, mapping to a low-recombining region in its genome.
- * The identified genomic region, which functions similarly to a sex-related supergene and contains key genes for sex differentiation, may offer insights into the evolutionary processes behind the development of sex chromosomes.
Article Synopsis
- Recombination rate is crucial for genetic research, showing significant variability between species, populations, and genomic regions, which is important for understanding genetic diversity and evolution.
- A high-density genetic map for the water flea Daphnia magna was created using advanced sequencing techniques, resulting in over 4,000 genetic markers and revealing a genome-wide recombination rate of 6.78 cM/Mb.
- This new linkage map coupled with the draft genome allows for detailed studies of recombination across D. magna's genome, paving the way for future research on genome evolution and trait mapping.
Article Synopsis
- Meiosis is a crucial process in sexual reproduction for eukaryotes, with complex mechanics revealed in different model organisms.
- The article explores the origin and various modifications of meiosis, including how it functions in different organisms and its role in their life cycles.
- It discusses the evolutionary interpretations of meiosis features and emphasizes that many aspects of their evolutionary significance remain unclear, highlighting the need for further research.
Article Synopsis
- The study focuses on using the waterflea Daphnia magna as a model organism to investigate gene-environment interactions due to its ecological relevance and unique reproductive traits.
- The STRESSFLEA consortium created a detailed RNA-Seq dataset by exposing different genotypes of D. magna to various environmental stressors.
- This research provides valuable genetic and transcriptomic resources, which will aid future studies in environmental genomics and the understanding of how genes respond to ecological changes.
Article Synopsis
- Reduced population sizes amplify genetic drift, impacting evolutionary dynamics and leading to increased genetic load and changes in inbreeding depression and hybrid vigor.
- A study on Daphnia magna shows that higher genetic diversity correlates with lower genetic load and inbreeding depression, while hybrid vigor decreases as genetic diversity diminishes.
- The findings suggest that genetic variation for traits related to fitness varies significantly between large and small populations, affecting key evolutionary processes like selection, adaptation, and reproduction in natural environments.
Local adaptation is a key process for the maintenance of genetic diversity and population diversification. A better understanding of the mechanisms that allow (or prevent) local adaptation constitutes a key in apprehending how and at what spatial scale it occurs. The production of resting stages is found in many taxa and reflects an adaptation to outlast adverse environmental conditions.
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- Many organisms have cryptic breeding systems that influence their ecology and evolution, making them hard to study through traditional observational methods.
- Genomic approaches, such as analyzing genetic transmission from parents to offspring, can help understand these systems, especially in cases like Daphnia magna where self-fertilization and automictic parthenogenesis are compared.
- This study confirms that offspring produced by automixis, primarily through terminal fusion, can be distinguished from those produced by self-fertilization using genome-wide heterozygosity data, highlighting the value of genomic techniques in revealing breeding mechanisms.