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53 results for “cichlid radiations”
Replicated functional evolution in cichlid adaptive radiations
<p>Adaptive radiations highlight the mechanisms by which species and traits diversify and the extent to which these patterns are predictable. We used 1,110 high-speed videos of suction feeding to study functional and morphological diversification in 300 cichlid species from three African Great Lake radiations of varying ages (Victoria, Malawi and Tanganyika) and an older, spatially dispersed continental radiation in the Neotropics. Among African radiations, standing diversity was reflective of time. Morphological and functional variance in Lake Victoria, the youngest radiation, was a subset of that within Lake Malawi, which itself was nested within the older Tanganyikan radiation. However, functional diversity in Neotropical cichlids was often lower than in Lake Tanganyika, despite being much older. These two radiations broadly overlapped, but each diversified into novel trait spaces not found in the youngest lake radiations. Evolutionary rates across radiations were inversely related to age, suggesting extremely rapid trait evolution at early stages, particularly in lake radiations. Despite this support for early bursts, other patterns of trait diversity were inconsistent with expectations of adaptive radiations. This work suggests that cichlid functional evolution has played out in strikingly similar fashion in different radiations, with contingencies eventually resulting in lineage-specific novelties.</p>
Visual opsin gene expression evolution in the adaptive radiation of cichlid fishes of Lake Tanganyika
<p>Tuning the visual sensory system to the ambient light is essential for survival in many animal species. This is often achieved through duplication, functional diversification, and/or differential expression of visual opsin genes. Here, we examined 753 new retinal transcriptomes from 112 species of cichlid fishes from Lake Tanganyika to unravel adaptive changes in gene expression at the macro-evolutionary and ecosystem level of one of the largest vertebrate adaptive radiations. We found that, across the radiation, all seven cone opsins – but not the rhodopsin – rank among the most differentially expressed genes in the retina, together with other vision-, circadian-rhythm-, and haemoglobin-related genes. We propose two new visual palettes characteristic of very shallow- and deep-water living species, respectively, and show that visual system adaptations along two major ecological axes, macro-habitat and diet, occur primarily via gene expression variation in a subset of cone opsin genes.</p>
Data from: Metagenomic insights into the dietary diversity of the adaptive radiation of cichlid fishes in Lake Tanganyika
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Replicated functional evolution in cichlid adaptive radiations
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Widespread temporal niche partitioning in an adaptive radiation of cichlid fishes
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Visual opsin gene expression evolution in the adaptive radiation of cichlid fishes of Lake Tanganyika
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Drivers and dynamics of a massive adaptive radiation in cichlid fishes
<p>Adaptive radiation is the likely source of much of the ecological and morphological diversity of life. How adaptive radiations proceed and what determines their extent remains elusive in most cases. Here we report the in-depth examination of the spectacular adaptive radiation of cichlid fishes in African Lake Tanganyika. Based on whole-genome phylogenetic analyses, multivariate morphological measurements of three ecologically relevant trait complexes (body shape, upper oral jaw morphology, and lower pharyngeal jaw shape), scoring of pigmentation patterns, and approximations of the ecology of virtually all ~240 cichlid species endemic to Lake Tanganyika, we show that the radiation occurred within the confines of the lake and that morphological diversification proceeded in consecutive trait-specific pulses of morphospace expansion. We provide empirical support for two theoretical predictions on how adaptive radiations proceed, the 'early-burst' scenario (for body shape) and the stages model (for all traits investigated). Through the analysis of two genomes per species and by taking advantage of the uneven distribution of species in subclades of the radiation, we further show that species richness scales positively with per individual heterozygosity, but is not correlated with transposable element content, number of gene duplications, or genome-wide levels of selection in coding sequences.</p>
Implementing large genomic SNP datasets in phylogenetic network reconstructions: a case study of particularly rapid radiations of cichlid fish
<p><span><span><span><span><span><span><span><span><span><span><span>The Midas cichlids of the <i>Amphilophus</i> <i>citrinellus </i>spp<i>.</i> species complex from Nicaragua, are an extraordinary adaptive rapid radiation (<24,000 years old; 13 described species). These cichlids are a very challenging group to infer its evolutionary history in phylogenetic analyses, due to the apparent prevalence of ILS, as well as past and current gene flow. Assuming solely a vertical transfer of genetic material from an ancestral lineage to new lineages is not appropriate in many cases of genes transferred horizontally in nature. Recently developed methods to infer phylogenetic networks under such circumstances might be able to circumvent these problems. These models accommodate not just incomplete lineage sorting, but also gene flow, under the multispecies network coalescent model (MSNC), processes that are at work in young, hybridizing, and/or rapidly diversifying lineages. There are currently only a few programs available that implement MSNC for estimating phylogenetic networks. Here, we present a novel way to incorporate single nucleotide polymorphism (SNP) data into the currently available PhyloNetworks program. Based on simulations, we demonstrate that SNPs can provide enough power to recover the true phylogenetic network. Moreover, our approach results in a faster algorithm compared to the original pipeline in PhyloNetworks, without losing power. We also applied our new approach to infer the phylogenetic network of Midas cichlid radiation. We implemented the most comprehensive genomic dataset to date (RADseq dataset of 679 individuals and >37K SNPs from 19 ingroup lineages) <span><span>and present estimated phylogenetic networks for this extremely young and fast-evolving radiation of cichlid fish. </span></span>We demonstrate that the MSNC is more appropriate than the multispecies coalescent alone for the analysis of this rapid radiation. </span></span></span></span></span></span></span></span></span></span></span></p>
Molecular evolution and depth-related adaptations of rhodopsin in the adaptive radiation of cichlid fishes in Lake Tanganyika
<p><span>The visual sensory system is essential for animals to perceive their environment and is thus under strong selection. In aquatic environments, light intensity and spectrum differ primarily along a depth gradient. Rhodopsin (RH1) is the only opsin responsible for dim-light vision in vertebrates and has been shown to evolve in response to the respective light conditions, including along a water depth gradient in fishes. In this study, we examined the diversity and sequence evolution of RH1 in the virtually entire adaptive radiation of cichlid fishes in Lake Tanganyika, focusing on adaptations to the achromatic environment with respect to depth. We show that Tanganyikan cichlid genomes contain a single copy of RH1. The 76 variable amino acid sites detected in RH1 across the radiation were not uniformly distributed along the protein sequence, and 31 of these variable sites show signals of positive selection. Moreover, the amino acid substitutions at 15 positively selected sites appeared to be depth-related, including three key tuning sites that directly mediate shifts in the peak spectral sensitivity, one site involved in protein stability, and 11 sites that may be functionally important on the basis of their </span><span>physicochemical properties. Among the strongest candidate sites for deep-water adaptations are two known key tuning sites (positions 292 and 299) and three newly identified variable sites (37, 104 and 290). Our study, which is th first compralehensive analysis of RH1 evolution in a massive adaptive radiation of cichlid fishes, provides novel insights into the evolution of RH1 in a freshwater environment.</span></p>
Molecular evolution and depth-related adaptations of rhodopsin in the adaptive radiation of cichlid fishes in Lake Tanganyika
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Drivers and dynamics of a massive adaptive radiation in cichlid fishes
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Implementing large genomic SNP datasets in phylogenetic network reconstructions: a case study of particularly rapid radiations of cichlid fish
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Data from: Parallel and non-parallel changes of the gut microbiota during trophic diversification in repeated young adaptive radiations of sympatric cichlid fish
<p><b>Background:</b> Recent increases in understanding the ecological and evolutionary roles of microbial communities has underscored their importance for their hosts' biology. Yet, little is known about gut microbiota dynamics during early stages of ecological diversification and speciation. We sequenced the V4 region of the 16s rRNA gene to study the gut microbiota of extremely young adaptive radiations of Nicaraguan Midas cichlid fish (<i>Amphilophus</i> cf. <i>citrinellus</i>) from two crater lakes to test the hypothesis that parallel divergence in trophic ecology is associated with parallel changes of the gut microbiota.</p> <p><b>Results:</b> Bacterial communities of the water and guts were highly distinct, indicating that the gut microbiota is shaped by host-specific factors. Across individuals of the same crater lake, differentiation in trophic ecology was associated with gut microbiota differentiation, suggesting that diet, to some extent, affects the gut microbiota. However, differences in trophic ecology were much more pronounced across than within species whereas similar patterns were not observed for taxonomic and functional differences of the gut microbiota. Across two crater lakes, we could not detect evidence for parallel changes of the gut microbiota associated with trophic ecology.</p> <p><b>Conclusions:</b> Similar cases of non-parallelism have been observed in other recently diverged fish species and might be explained by a lack of clearly differentiated niches during early stages of ecological diversification.</p>
Data from: Selection towards different adaptive optima drove the early diversification of locomotor phenotypes in the radiation of Neotropical geophagine cichlids
Background: Simpson envisaged a conceptual model of adaptive radiation in which lineages diversify into "adaptive zones" within a broad adaptive landscape. However only a handful of studies have actually investigated the adaptive landscape and its implication for our interpretation of the underlying mechanisms of phenotypic evolution. In fishes the evolution of locomotor phenotypes may represent an important dimension of ecomorphological diversification during an adaptive radiation given its implications for feeding and habitat use. Neotropical geophagine cichlids represent a newly identified adaptive radiation and provide a useful system for studying patterns of locomotor diversification and the implications of selective constraints on phenotypic divergence in general. Results: We use multivariate ordination models of phenotypic evolution and posterior predictive approaches to investigate the adaptive landscape and test for evidence of early diversification of locomotor phenotypes in Geophagini. The evolution of locomotor phenotypes was characterized by divergent selection towards two distinct adaptive peaks and the early divergence of modern morphological disparity. Evolutionary models and posterior predictive approaches favoured constant-rate divergent selection over decreasing rates of phenotypic evolution as the underlying process driving the early divergence of locomotor phenotypes. Conclusions: The influence of multiple adaptive peaks on the divergence of locomotor attributes in Geophagini is compatible with the expectations of an ecologically-driven adaptive radiation. This study confirms that the diversification of locomotor morphology represents an important dimension of phenotypic evolution in the geophagine adaptive radiation. It also suggests that the commonly observed early burst of phenotypic evolution during adaptive radiations is best explained by a model that incorporates divergent selection deep in the phylogeny.
Data from: Testing for ancient adaptive radiations in Neotropical cichlid fishes
Most contemporary studies of adaptive radiation focus on relatively recent and geographically restricted clades. It is less clear whether diversification of ancient clades spanning entire continents is consistent with adaptive radiation. We used novel fossil calibrations to generate a chronogram of Neotropical cichlid fishes and to test whether patterns of lineage and morphological diversification are congruent with hypothesized adaptive radiations in South and Central America. We found that diversification in the Neotropical cichlid clade and the highly diverse tribe Geophagini was consistent with diversity-dependent, early bursts of divergence followed by decreased rates of lineage accumulation. South American Geophagini underwent early rapid differentiation in body shape, expanding into novel morphological space characterized by elongate-bodied predators. Divergence in head-shape attributes associated with trophic specialization evolved under strong adaptive constraints in all Neotropical cichlid clades. The South American Cichlasomatini followed patterns consistent with constant rates of morphological divergence. Although morphological diversification in South American Heroini was limited, Eocene invasion of Central American habitats was followed by convergent diversification mirroring variation observed in Geophagini. Diversification in Neotropical cichlids was influenced by the early adaptive radiation of Geophagini, which potentially limited differentiation in other cichlid clades.
Data from: Evaluating genomic divergence and parallelism in replicate ecomorphs from young and old cichlid adaptive radiations
Comparative genomic studies of closely related species typically focus on single species pairs at one given stage of divergence. That makes it difficult to infer the continuum of evolutionary process during speciation and beyond. Here, we use whole-genome resequencing to examine genomic patterns of divergence in three sympatric cichlid species pairs with very similar functional and ecological differentiation, but different ages. We find a strong signature of increasing genomic divergence with time in both the mitochondrial genome and the nuclear genome. In contrast to many other systems, we find that in these cichlids regions of elevated relative differentiation also exhibit increased absolute differentiation. We detect a signature of convergent evolution in a comparison of outlier regions across all three species pair comparisons but the extent of it is modest, and regions that are strongly divergent in any one pair tend to be only slightly elevated in the other pairs, consistent with a repeatable but polygenic basis of traits that characterize the ecomorphs. Our results suggest that strong functional phenotypic differentiation, as seen in all three species pairs, is generally associated with a clear signature of genomic divergence, even in the youngest species pair.
Data from: Testing the potential of DNA barcoding in vertebrate radiations: the case of the littoral cichlids (Pisces, Perciformes, Cichlidae) from Lake Tanganyika
We obtained 398 cytochrome c oxidase subunit I barcodes of 96 morphospecies of Lake Tanganyika (LT) cichlids from the littoral zone. The potential of DNA barcoding in these fishes was tested using both species identification and species delineation methods. The best match (BM) and best close match (BCM) methods were used to evaluate the overall identification success. For this, three libraries were analysed in which the specimens were categorized into Operational Taxonomic Units (OTU) in three alternative ways: (A) morphologically distinct, including undescribed, species, (B) valid species and (C) complexes of morphologically similar or closely related species. For libraries A, B and C, 73, 73 and 96% (BM) and 72, 70 and 94% (BCM) of the specimens were correctly identified. Additionally, the potential of two species delineation methods was tested. The General Mixed Yule Coalescent (GMYC) analysis suggested 70 hypothetical species, while the Automatic Barcode Gap Discovery (ABGD) method revealed 115 putative species. Although the ABGD method had a tendency to oversplit, it outperformed the GMYC analysis in retrieving the species. In most cases where ABGD suggested oversplitting, this was due to intraspecific geographical variation. The failure of the GMYC method to retrieve many species could be attributed to discrepancies between mitochondrial gene trees and the evolutionary histories of LT cichlid species. Littoral LT cichlids have complex evolutionary histories that include instances of hybridization, introgression and rapid speciation. Nevertheless, although the utility of DNA barcoding in identification is restricted to the level of complexes, it has potential for species discovery in cichlid radiations.
Data from: Speciation in sympatry with ongoing secondary gene flow and an olfactory trigger in a radiation of Cameroon cichlids
The process of sympatric speciation in nature remains a fundamental unsolved problem. Cameroon crater lake cichlid radiations were long regarded as one of the most compelling examples; however, recent work showed that their origins were more complex than a single colonization event followed by isolation. Here, we performed a detailed investigation of the speciation history of a radiation of Coptodon cichlids from Lake Ejagham using whole-genome sequencing data. The existence of this radiation is remarkable since this 0.5 km2 lake offers limited scope for divergence across a shallow depth gradient, disruptive selection is weak, and the species are sexually monochromatic. We infer that Lake Ejagham was colonized by riverine cichlids soon after its formation 9,000 years ago, yet speciation occurred only in the last 1,000-2,000 years. We show that secondary gene flow from riverine species has been ongoing, into ancestral and extant Lake Ejagham lineages, and identify and date river-to-lake admixture blocks. One of these contains a cluster of olfactory receptor genes that introgressed close to the time of the first speciation event and coincides with a higher overall rate of admixture into the recipient lineages. Olfactory signaling is a key component of mate choice and species recognition in cichlids. A functional role for this introgression event is consistent with previous findings that assortative mating appears much stronger than ecological divergence in Ejagham Coptodon. We conclude that speciation in this radiation took place in sympatry, yet may have benefited from ongoing riverine gene flow.
Exon-based phylogenomics and the relationships of African cichlids: Tackling the challenges of reconstructing phylogenies with repeated rapid radiations
<p>African cichlids (subfamily: Pseudocrenilabrinae) are among the most diverse vertebrates, and their propensity for repeated rapid radiation has made them a celebrated model system in evolutionary research. Nonetheless, despite numerous studies, phylogenetic uncertainty persists, and riverine lineages remain comparatively underrepresented in higher-level phylogenetic studies. Heterogeneous gene histories resulting from incomplete lineage sorting (ILS) and hybridization are likely sources of uncertainty, especially during episodes of rapid speciation. We investigate relationships of Pseudocrenilabrinae and its close relatives while accounting for multiple sources of genetic discordance using species tree and hybrid network analyses with hundreds of single-copy exons. We improve sequence recovery for distant relatives, thereby extending the taxonomic reach of our probes, with a hybrid reference guided/<em>de novo</em> assembly approach. Our analyses provide robust hypotheses for most higher-level relationships and reveal widespread gene heterogeneity, including in riverine taxa. ILS and past hybridization are identified as sources of genetic discordance in different lineages. Sampling of various Blenniiformes (formerly Ovalentaria) adds strong phylogenomic support for convict blennies (Pholidichthyidae) as sister to Cichlidae, and points to other potentially useful protein-coding markers across the order. A reliable phylogeny with representatives from diverse environments will support ongoing taxonomic and comparative evolutionary research in the cichlid model system.</p>
Data from: Population genomic tests of models of adaptive radiation in Lake Victoria region cichlid fish.
Adaptive radiation is usually thought to be associated with speciation, but the evolution of intraspecific polymorphisms without speciation is also possible. The radiation of cichlid fish in Lake Victoria is perhaps the most impressive example of a recent rapid adaptive radiation, with 600+ very young species. Key questions about its origin remain poorly characterized, such as the importance of speciation versus polymorphism, whether species persist on evolutionary time scales, and if speciation happens more commonly in small isolated or in large connected populations. We used 320 individuals from 105 putative species from Lakes Victoria, Edward, Kivu, Albert, Nabugabo and Saka, in a radiation-wide AFLP genome scan to address some of these questions. We demonstrate pervasive signatures of speciation supporting the classical model of adaptive radiation associated with speciation. A positive relationship between the age of lakes and the average genomic differentiation of their species, and a significant fraction of molecular variance explained by above-species level taxonomy suggest the persistence of species on evolutionary time scales, with radiation through sequential speciation rather than a single starburst. Finally the large gene diversity retained from colonization to individual species in every radiation suggests large effective population sizes and makes speciation in small geographical isolates unlikely.
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Allen Brain Atlas
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