1
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Lichilín N, Salzburger W, Böhne A. No evidence for sex chromosomes in natural populations of the cichlid fish Astatotilapia burtoni. G3 (BETHESDA, MD.) 2023; 13:6989787. [PMID: 36649174 PMCID: PMC9997565 DOI: 10.1093/g3journal/jkad011] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 09/14/2022] [Accepted: 12/16/2022] [Indexed: 01/18/2023]
Abstract
Sex determination (SD) is not conserved among teleost fishes and can even differ between populations of the same species. Across the outstandingly species-rich fish family Cichlidae, more and more SD systems are being discovered. Still, the picture of SD evolution in this group is far from being complete. Lake Tanganyika and its affluent rivers are home to Astatotilapia burtoni, which belongs to the extremely successful East African cichlid lineage Haplochromini. Previously, in different families of an A. burtoni laboratory strain, an XYW system and an XY system have been described. The latter was also found in a second laboratory strain. In a laboratory-reared family descending from a population of the species' southern distribution, a second XY system was discovered. Yet, an analysis of sex chromosomes for the whole species distribution is missing. Here, we examined the genomes of 11 natural populations of A. burtoni, encompassing a wide range of its distribution, for sex-linked regions. We did not detect signs of differentiated sex chromosomes and also not the previously described sex chromosomal systems present in laboratory lines, suggesting different SD systems in the same species under natural and (long-term) artificial conditions. We suggest that SD in A. burtoni is more labile than previously assumed and consists of a combination of non-genetic, polygenic, or poorly differentiated sex chromosomes.
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Affiliation(s)
- Nicolás Lichilín
- Zoological Institute, Department of Environmental Sciences, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland.,Department of Neuroscience and Developmental Biology, University of Vienna, Djerassiplatz 1, 1030 Vienna, Austria
| | - Walter Salzburger
- Zoological Institute, Department of Environmental Sciences, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland
| | - Astrid Böhne
- Zoological Institute, Department of Environmental Sciences, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland.,Leibniz Institute for the Analysis of Biodiversity Change, Museum Koenig Bonn, Adenauerallee 127, 53113 Bonn, Germany
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2
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Weber AAT, Rajkov J, Smailus K, Egger B, Salzburger W. Speciation dynamics and extent of parallel evolution along a lake-stream environmental contrast in African cichlid fishes. SCIENCE ADVANCES 2021; 7:eabg5391. [PMID: 34731007 PMCID: PMC8565912 DOI: 10.1126/sciadv.abg5391] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Understanding the dynamics of speciation is a central topic in evolutionary biology. Here, we investigated how morphological and genomic differentiation accumulated along the speciation continuum in the African cichlid fish Astatotilapia burtoni. While morphological differentiation was continuously distributed across different lake-stream population pairs, we found that there were two categories with respect to genomic differentiation, suggesting a “gray zone” of speciation at ~0.1% net nucleotide divergence. Genomic differentiation was increased in the presence of divergent selection and drift compared to drift alone. The quantification of phenotypic and genetic parallelism in four cichlid species occurring along a lake-stream environmental contrast revealed parallel and antiparallel components in rapid adaptive divergence, and morphological convergence in species replicates inhabiting the same environments. Furthermore, we show that the extent of parallelism was higher when ancestral populations were more similar. Our study highlights the complementary roles of divergent selection and drift on speciation and parallel evolution.
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3
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Rajkov J, El Taher A, Böhne A, Salzburger W, Egger B. Gene expression remodelling and immune response during adaptive divergence in an African cichlid fish. Mol Ecol 2020; 30:274-296. [PMID: 33107988 DOI: 10.1111/mec.15709] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 10/08/2020] [Accepted: 10/19/2020] [Indexed: 11/29/2022]
Abstract
Variation in gene expression contributes to ecological speciation by facilitating population persistence in novel environments. Likewise, immune responses can be of relevance in speciation driven by adaptation to different environments. Previous studies examining gene expression differences between recently diverged ecotypes have often relied on only one pair of populations, targeted the expression of only a subset of genes or used wild-caught individuals. Here, we investigated the contribution of habitat-specific parasites and symbionts and the underlying immunological abilities of ecotype hosts to adaptive divergence in lake-river population pairs of the cichlid fish Astatotilapia burtoni. To shed light on the role of phenotypic plasticity in adaptive divergence, we compared parasite and microbiota communities, immune response, and gene expression patterns of fish from natural habitats and a lake-like pond set-up. In all investigated population pairs, lake fish were more heavily parasitized than river fish, in terms of both parasite taxon composition and infection abundance. The innate immune response in the wild was higher in lake than in river populations and was elevated in a river population exposed to lake parasites in the pond set-up. Environmental differences between lake and river habitat and their distinct parasite communities have shaped differential gene expression, involving genes functioning in osmoregulation and immune response. Most changes in gene expression between lake and river samples in the wild and in the pond set-up were based on a plastic response. Finally, gene expression and bacterial communities of wild-caught individuals and individuals acclimatized to lake-like pond conditions showed shifts underlying adaptive phenotypic plasticity.
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Affiliation(s)
- Jelena Rajkov
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| | - Athimed El Taher
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| | - Astrid Böhne
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| | - Walter Salzburger
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| | - Bernd Egger
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
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4
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Li YL, Xing TF, Liu JX. Genome-wide association analyses based on whole-genome sequencing of Protosalanx hyalocranius provide insights into sex determination of Salangid fishes. Mol Ecol Resour 2020; 20:1038-1049. [PMID: 32315505 DOI: 10.1111/1755-0998.13172] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Revised: 03/28/2020] [Accepted: 04/09/2020] [Indexed: 12/22/2022]
Abstract
Identification of sex determination system and sex-determining genes have important implications in conservation, ecology and evolution. However, much remains to be discovered about the evolution of different sexual determination systems in teleost fishes, of which the mechanisms of sex determination are remarkably variable. In the present study, the whole genomes of 20 males and 20 females of a Salangid fish, Protosalanx hyalocranius, were sequenced and genome wide association analyses were conducted to uncover its sex determination system and putative sex-determining genes. A total of 150 SNPs were significantly associated with sex, which showed high differentiation between sexes (FST ranged from 0.245 to 0.556). Of the 150 sex-associated SNPs, 76 SNPs displayed sex specificity with even coverage of depth and were female heterogametic, which suggested a ZZ/ZW sex determination system. Interestingly, one scaffold containing sex-specific SNPs displayed synteny to the sex chromosome of medaka. Annotations of sex-associated loci suggested that both transcriptional regulators (e.g., FOX genes) and secreted hormones and their receptors might be involved in the sex determination/differentiation of P. hyalocranius. More strikingly, we found a nonsense mutation in one copy of GALNT homology gene of all females, which suggested that "Z dosage" effect might play a vital role in the processes of sex determination/differentiation. These sex-specific loci could be a valuable resource for further research on sex determination of Salangid fishes and the results could contribute to the understanding of sex determination mechanisms and the evolution of sex chromosome in teleost fishes.
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Affiliation(s)
- Yu-Long Li
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China
| | - Teng-Fei Xing
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Jin-Xian Liu
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China
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5
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Svardal H, Quah FX, Malinsky M, Ngatunga BP, Miska EA, Salzburger W, Genner MJ, Turner GF, Durbin R. Ancestral Hybridization Facilitated Species Diversification in the Lake Malawi Cichlid Fish Adaptive Radiation. Mol Biol Evol 2020; 37:1100-1113. [PMID: 31821500 PMCID: PMC7086168 DOI: 10.1093/molbev/msz294] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The adaptive radiation of cichlid fishes in East African Lake Malawi encompasses over 500 species that are believed to have evolved within the last 800,000 years from a common founder population. It has been proposed that hybridization between ancestral lineages can provide the genetic raw material to fuel such exceptionally high diversification rates, and evidence for this has recently been presented for the Lake Victoria region cichlid superflock. Here, we report that Lake Malawi cichlid genomes also show evidence of hybridization between two lineages that split 3-4 Ma, today represented by Lake Victoria cichlids and the riverine Astatotilapia sp. "ruaha blue." The two ancestries in Malawi cichlid genomes are present in large blocks of several kilobases, but there is little variation in this pattern between Malawi cichlid species, suggesting that the large-scale mosaic structure of the genomes was largely established prior to the radiation. Nevertheless, tens of thousands of polymorphic variants apparently derived from the hybridization are interspersed in the genomes. These loci show a striking excess of differentiation across ecological subgroups in the Lake Malawi cichlid assemblage, and parental alleles sort differentially into benthic and pelagic Malawi cichlid lineages, consistent with strong differential selection on these loci during species divergence. Furthermore, these loci are enriched for genes involved in immune response and vision, including opsin genes previously identified as important for speciation. Our results reinforce the role of ancestral hybridization in explosive diversification by demonstrating its significance in one of the largest recent vertebrate adaptive radiations.
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Affiliation(s)
- Hannes Svardal
- Department of Biology, University of Antwerp, Antwerp, Belgium
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- Wellcome Sanger Institute, Hinxton, United Kingdom
- Naturalis Biodiversity Center, Leiden, The Netherlands
| | | | - Milan Malinsky
- Zoological Institute, University of Basel, Basel, Switzerland
| | | | - Eric A Miska
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- Wellcome Sanger Institute, Hinxton, United Kingdom
- Gurdon Institute, University of Cambridge, Cambridge, United Kingdom
| | | | - Martin J Genner
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
| | - George F Turner
- School of Biological Sciences, Bangor University, Bangor, United Kingdom
| | - Richard Durbin
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
- Wellcome Sanger Institute, Hinxton, United Kingdom
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6
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Rapid niche expansion by selection on functional genomic variation after ecosystem recovery. Nat Ecol Evol 2018; 3:77-86. [DOI: 10.1038/s41559-018-0742-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 11/02/2018] [Indexed: 11/08/2022]
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7
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Beichman AC, Huerta-Sanchez E, Lohmueller KE. Using Genomic Data to Infer Historic Population Dynamics of Nonmodel Organisms. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2018. [DOI: 10.1146/annurev-ecolsys-110617-062431] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Genome sequence data are now being routinely obtained from many nonmodel organisms. These data contain a wealth of information about the demographic history of the populations from which they originate. Many sophisticated statistical inference procedures have been developed to infer the demographic history of populations from this type of genomic data. In this review, we discuss the different statistical methods available for inference of demography, providing an overview of the underlying theory and logic behind each approach. We also discuss the types of data required and the pros and cons of each method. We then discuss how these methods have been applied to a variety of nonmodel organisms. We conclude by presenting some recommendations for researchers looking to use genomic data to infer demographic history.
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Affiliation(s)
- Annabel C. Beichman
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA
| | - Emilia Huerta-Sanchez
- Department of Molecular and Cell Biology, University of California, Merced, California 95343, USA
- Current affiliation: Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912, USA
| | - Kirk E. Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA
- Interdepartmental Program in Bioinformatics and Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
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8
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Rajkov J, Weber AAT, Salzburger W, Egger B. Immigrant and extrinsic hybrid inviability contribute to reproductive isolation between lake and river cichlid ecotypes. Evolution 2018; 72:2553-2564. [DOI: 10.1111/evo.13612] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 09/14/2018] [Indexed: 12/25/2022]
Affiliation(s)
- Jelena Rajkov
- Zoological Institute; University of Basel; Vesalgasse 1 CH-4051 Basel Switzerland
| | | | - Walter Salzburger
- Zoological Institute; University of Basel; Vesalgasse 1 CH-4051 Basel Switzerland
| | - Bernd Egger
- Zoological Institute; University of Basel; Vesalgasse 1 CH-4051 Basel Switzerland
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9
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Salzburger W. Understanding explosive diversification through cichlid fish genomics. Nat Rev Genet 2018; 19:705-717. [DOI: 10.1038/s41576-018-0043-9] [Citation(s) in RCA: 138] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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10
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Rajkov J, Weber AA, Salzburger W, Egger B. Adaptive phenotypic plasticity contributes to divergence between lake and river populations of an East African cichlid fish. Ecol Evol 2018; 8:7323-7333. [PMID: 30151152 PMCID: PMC6106192 DOI: 10.1002/ece3.4241] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 05/03/2018] [Accepted: 05/04/2018] [Indexed: 01/01/2023] Open
Abstract
Adaptive phenotypic plasticity and fixed genotypic differences have long been considered opposing strategies in adaptation. More recently, these mechanisms have been proposed to act complementarily and under certain conditions jointly facilitate evolution, speciation, and even adaptive radiations. Here, we investigate the relative contributions of adaptive phenotypic plasticity vs. local adaptation to fitness, using an emerging model system to study early phases of adaptive divergence, the generalist cichlid fish species Astatotilapia burtoni. We tested direct fitness consequences of morphological divergence between lake and river populations in nature by performing two transplant experiments in Lake Tanganyika. In the first experiment, we used wild-caught juvenile lake and river individuals, while in the second experiment, we used F1 crosses between lake and river fish bred in a common garden setup. By tracking the survival and growth of translocated individuals in enclosures in the lake over several weeks, we revealed local adaptation evidenced by faster growth of the wild-caught resident population in the first experiment. On the other hand, we did not find difference in growth between different types of F1 crosses in the second experiment, suggesting a substantial contribution of adaptive phenotypic plasticity to increased immigrant fitness. Our findings highlight the value of formally comparing fitness of wild-caught and common garden-reared individuals and emphasize the necessity of considering adaptive phenotypic plasticity in the study of adaptive divergence.
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Affiliation(s)
- Jelena Rajkov
- Zoological InstituteUniversity of BaselBaselSwitzerland
| | | | | | - Bernd Egger
- Zoological InstituteUniversity of BaselBaselSwitzerland
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11
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Pauquet G, Salzburger W, Egger B. The puzzling phylogeography of the haplochromine cichlid fish Astatotilapia burtoni. Ecol Evol 2018; 8:5637-5648. [PMID: 29938080 PMCID: PMC6010872 DOI: 10.1002/ece3.4092] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Revised: 03/15/2018] [Accepted: 03/27/2018] [Indexed: 12/14/2022] Open
Abstract
Astatotilapia burtoni is a member of the "modern haplochromines," the most species-rich lineage within the family of cichlid fishes. Although the species has been in use as research model in various fields of research since almost seven decades, including developmental biology, neurobiology, genetics and genomics, and behavioral biology, little is known about its spatial distribution and phylogeography. Here, we examine the population structure and phylogeographic history of A. burtoni throughout its entire distribution range in the Lake Tanganyika basin. In addition, we include several A. burtoni laboratory strains to trace back their origin from wild populations. To this end, we reconstruct phylogenetic relationships based on sequences of the mitochondrial DNA (mtDNA) control region (d-loop) as well as thousands of genomewide single nucleotide polymorphisms (SNPs) derived from restriction-associated DNA sequencing. Our analyses reveal high population structure and deep divergence among several lineages, however, with discordant nuclear and mtDNA phylogenetic inferences. Whereas the SNP-based phylogenetic hypothesis uncovers an unexpectedly deep split in A. burtoni, separating the populations in the southern part of the Lake Tanganyika basin from those in the northern part, analyses of the mtDNA control region suggest deep divergence between populations from the southwestern shoreline and populations from the northern and southeastern shorelines of Lake Tanganyika. This phylogeographic pattern and mitochondrial haplotype sharing between populations from the very North and the very South of Lake Tanganyika can only partly be explained by introgression linked to lake-level fluctuations leading to past contact zones between otherwise isolated populations and large-scale migration events.
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Affiliation(s)
| | | | - Bernd Egger
- Zoological InstituteUniversity of BaselBaselSwitzerland
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12
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Jacobs A, Hughes MR, Robinson PC, Adams CE, Elmer KR. The Genetic Architecture Underlying the Evolution of a Rare Piscivorous Life History Form in Brown Trout after Secondary Contact and Strong Introgression. Genes (Basel) 2018; 9:genes9060280. [PMID: 29857499 PMCID: PMC6026935 DOI: 10.3390/genes9060280] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 05/16/2018] [Accepted: 05/17/2018] [Indexed: 01/17/2023] Open
Abstract
Identifying the genetic basis underlying phenotypic divergence and reproductive isolation is a longstanding problem in evolutionary biology. Genetic signals of adaptation and reproductive isolation are often confounded by a wide range of factors, such as variation in demographic history or genomic features. Brown trout (Salmo trutta) in the Loch Maree catchment, Scotland, exhibit reproductively isolated divergent life history morphs, including a rare piscivorous (ferox) life history form displaying larger body size, greater longevity and delayed maturation compared to sympatric benthivorous brown trout. Using a dataset of 16,066 SNPs, we analyzed the evolutionary history and genetic architecture underlying this divergence. We found that ferox trout and benthivorous brown trout most likely evolved after recent secondary contact of two distinct glacial lineages, and identified 33 genomic outlier windows across the genome, of which several have most likely formed through selection. We further identified twelve candidate genes and biological pathways related to growth, development and immune response potentially underpinning the observed phenotypic differences. The identification of clear genomic signals divergent between life history phenotypes and potentially linked to reproductive isolation, through size assortative mating, as well as the identification of the underlying demographic history, highlights the power of genomic studies of young species pairs for understanding the factors shaping genetic differentiation.
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Affiliation(s)
- Arne Jacobs
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
| | - Martin R Hughes
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
- Scottish Centre for Ecology and the Natural Environment, University of Glasgow, Rowardennan, Loch Lomond, Glasgow G63 0AW, Scotland, UK.
| | - Paige C Robinson
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
| | - Colin E Adams
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
- Scottish Centre for Ecology and the Natural Environment, University of Glasgow, Rowardennan, Loch Lomond, Glasgow G63 0AW, Scotland, UK.
| | - Kathryn R Elmer
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
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13
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Haenel Q, Laurentino TG, Roesti M, Berner D. Meta-analysis of chromosome-scale crossover rate variation in eukaryotes and its significance to evolutionary genomics. Mol Ecol 2018; 27:2477-2497. [PMID: 29676042 DOI: 10.1111/mec.14699] [Citation(s) in RCA: 99] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Revised: 03/23/2018] [Accepted: 03/26/2018] [Indexed: 01/02/2023]
Abstract
Understanding the distribution of crossovers along chromosomes is crucial to evolutionary genomics because the crossover rate determines how strongly a genome region is influenced by natural selection on linked sites. Nevertheless, generalities in the chromosome-scale distribution of crossovers have not been investigated formally. We fill this gap by synthesizing joint information on genetic and physical maps across 62 animal, plant and fungal species. Our quantitative analysis reveals a strong and taxonomically widespread reduction of the crossover rate in the centre of chromosomes relative to their peripheries. We demonstrate that this pattern is poorly explained by the position of the centromere, but find that the magnitude of the relative reduction in the crossover rate in chromosome centres increases with chromosome length. That is, long chromosomes often display a dramatically low crossover rate in their centre, whereas short chromosomes exhibit a relatively homogeneous crossover rate. This observation is compatible with a model in which crossover is initiated from the chromosome tips, an idea with preliminary support from mechanistic investigations of meiotic recombination. Consequently, we show that organisms achieve a higher genome-wide crossover rate by evolving smaller chromosomes. Summarizing theory and providing empirical examples, we finally highlight that taxonomically widespread and systematic heterogeneity in crossover rate along chromosomes generates predictable broad-scale trends in genetic diversity and population differentiation by modifying the impact of natural selection among regions within a genome. We conclude by emphasizing that chromosome-scale heterogeneity in crossover rate should urgently be incorporated into analytical tools in evolutionary genomics, and in the interpretation of resulting patterns.
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Affiliation(s)
- Quiterie Haenel
- Zoological Institute, University of Basel, Basel, Switzerland
| | | | - Marius Roesti
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada
| | - Daniel Berner
- Zoological Institute, University of Basel, Basel, Switzerland
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14
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Keller IS, Salzburger W, Roth O. Parental investment matters for maternal and offspring immune defense in the mouthbrooding cichlid Astatotilapia burtoni. BMC Evol Biol 2017; 17:264. [PMID: 29262789 PMCID: PMC5738712 DOI: 10.1186/s12862-017-1109-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 12/06/2017] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND Parental care, while increasing parental fitness through offspring survival, also bears cost to the care-giving parent. Consequentially, trade offs between parental care and other vitally important traits, such as the immune system seem evident. In co-occurring phases of parental care and immunological challenges negative consequences through a resource allocation trade off on both the parental and the offspring conditions can be predicted. While the immune system reflects parental stress conditions, parental immunological investments also boost offspring survival via the transfer of immunological substances (trans-generational immune priming). We investigated this relationship in the mouthbrooding East African cichlid Astotatilapia burtoni. Prior to mating, females were exposed to an immunological activation, while others remained immunologically naïve. Correspondingly, the immunological status of females was either examined directly after reproduction or after mouthbrooding had ceased. Offspring from both groups were exposed to immunological challenges to assess the extent of trans-generational immune priming. As proxy for immune status, cellular immunological activity and gene expression were determined. RESULTS Both reproducing and mouthbrooding females allocate their resources towards reproduction. While upon reproduction the innate immune system was impeded, mouthbrooding females showed an attenuation of inflammatory components. Juveniles from immune challenged mouthbrooding females showed downregulation of immune and life history candidate genes, implying a limitation of trans-generational plasticity when parents experience stress during the costly reproductive phase. CONCLUSION Our results provide evidence that both parental investment via mouthbrooding and the rise of the immunological activity upon an immune challenge are costly traits. If applied simultaneously, not only mothers seem to be impacted in their performance, but also offspring are impeded in their ability to react upon a potentially virulent pathogen exposure.
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Affiliation(s)
- Isabel S. Keller
- Evolutionary Ecology of Marine Fishes, GEOMAR - Helmholtz Centre for Ocean Research, Kiel, Germany
| | | | - Olivia Roth
- Evolutionary Ecology of Marine Fishes, GEOMAR - Helmholtz Centre for Ocean Research, Kiel, Germany
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15
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Burress ED, Alda F, Duarte A, Loureiro M, Armbruster JW, Chakrabarty P. Phylogenomics of pike cichlids (Cichlidae: Crenicichla): the rapid ecological speciation of an incipient species flock. J Evol Biol 2017; 31:14-30. [PMID: 29044782 DOI: 10.1111/jeb.13196] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 08/13/2017] [Accepted: 10/12/2017] [Indexed: 12/18/2022]
Abstract
The rapid rise of phenotypic and ecological diversity in independent lake-dwelling groups of cichlids is emblematic of the East African Great Lakes. In this study, we show that similar ecologically based diversification has occurred in pike cichlids (Crenicichla) throughout the Uruguay River drainage of South America. We collected genomic data from nearly 500 ultraconserved element (UCEs) loci and >260 000 base pairs across 33 species, to obtain a phylogenetic hypothesis for the major species groups and to evaluate the relationships and genetic structure among five closely related, endemic, co-occurring species (the Uruguay River species flock; URSF). Additionally, we evaluated ecological divergence of the URSF based on body and lower pharyngeal jaw (LPJ) shape and gut contents. Across the genus, we recovered novel relationships among the species groups. We found strong support for the monophyly of the URSF; however, relationships among these species remain problematic, likely because of the rapid and recent evolution of this clade. Clustered co-ancestry analysis recovered most species as well delimited genetic groups. The URSF species exhibit species-specific body and LPJ shapes associated with specialized trophic roles. Collectively, our results suggest that the URSF consists of incipient species that arose via ecological speciation associated with the exploration of novel trophic roles.
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Affiliation(s)
- E D Burress
- Department of Biological Sciences and Auburn University Museum of Natural History, Auburn University, Auburn, AL, USA
| | - F Alda
- Museum of Natural Science, Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA
| | - A Duarte
- Sección Zoología Vertebrados, Departmento de Ecología y Evolución, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - M Loureiro
- Sección Zoología Vertebrados, Departmento de Ecología y Evolución, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay.,Sección Ictología, Departmento de Zoología, Museo Nacional de Historia Natural, Montevideo, Uruguay
| | - J W Armbruster
- Department of Biological Sciences and Auburn University Museum of Natural History, Auburn University, Auburn, AL, USA
| | - P Chakrabarty
- Museum of Natural Science, Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA
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