Understanding the emergence of the Animal Kingdom is one of the major challenges of modern evolutionary biology. Many genomic changes took place along the evolutionary lineage that gave rise to the ...Metazoa. Recent research has revealed the role that co-option of old genes played during this transition, but the contribution of genomic novelty has not been fully assessed. Here, using extensive genome comparisons between metazoans and multiple outgroups, we infer the minimal protein-coding genome of the first animal, in addition to other eukaryotic ancestors, and estimate the proportion of novelties in these ancient genomes. Contrary to the prevailing view, this uncovers an unprecedented increase in the extent of genomic novelty during the origin of metazoans, and identifies 25 groups of metazoan-specific genes that are essential across the Animal Kingdom. We argue that internal genomic changes were as important as external factors in the emergence of animals.
The evolution of winged insects revolutionized terrestrial ecosystems and led to the largest animal radiation on Earth. However, we still have an incomplete picture of the genomic changes that ...underlay this diversification. Mayflies, as one of the sister groups of all other winged insects, are key to understanding this radiation. Here, we describe the genome of the mayfly Cloeon dipterum and its gene expression throughout its aquatic and aerial life cycle and specific organs. We discover an expansion of odorant-binding-protein genes, some expressed specifically in breathing gills of aquatic nymphs, suggesting a novel sensory role for this organ. In contrast, flying adults use an enlarged opsin set in a sexually dimorphic manner, with some expressed only in males. Finally, we identify a set of wing-associated genes deeply conserved in the pterygote insects and find transcriptomic similarities between gills and wings, suggesting a common genetic program. Globally, this comprehensive genomic and transcriptomic study uncovers the genetic basis of key evolutionary adaptations in mayflies and winged insects.
Gene duplications and gene losses have been frequent events in the evolution of animal genomes, with the balance between these two dynamic processes contributing to major differences in gene number ...between species. After gene duplication, it is common for both daughter genes to accumulate sequence change at approximately equal rates. In some cases, however, the accumulation of sequence change is highly uneven with one copy radically diverging from its paralogue. Such ‘asymmetric evolution’ seems commoner after tandem gene duplication than after whole-genome duplication, and can generate substantially novel genes. We describe examples of asymmetric evolution in duplicated homeobox genes of moths, molluscs and mammals, in each case generating new homeobox genes that were recruited to novel developmental roles. The prevalence of asymmetric divergence of gene duplicates has been underappreciated, in part, because the origin of highly divergent genes can be difficult to resolve using standard phylogenetic methods.
This article is part of the themed issue ‘Evo-devo in the genomics era, and the origins of morphological diversity’.
The animal kingdom shows an astonishing diversity, the product of over 550 million years of animal evolution. The current wealth of genome sequence data offers an opportunity to better understand the ...genomic basis of this diversity. Here we analyse a sampling of 102 whole genomes including >2.6 million protein sequences. We infer major genomic patterns associated with the variety of animal forms from the superphylum to phylum level. We show that a remarkable amount of gene loss occurred during the evolution of two major groups of bilaterian animals, Ecdysozoa and Deuterostomia, and further loss in several deuterostome lineages. Deuterostomes and protostomes also show large genome novelties. At the phylum level, flatworms, nematodes and tardigrades show the largest reduction of gene complement, alongside gene novelty. These findings paint a picture of evolution in the animal kingdom in which reductive evolution at the protein-coding level played a major role in shaping genome composition.
Resolving the relationships among animal phyla is a key biological problem that remains to be solved. Morphology is unable to determine the relationships among most phyla and although molecular data ...have unveiled a new evolutionary scenario, they have their own limitations. Nuclear ribosomal genes (18S and 28S rDNA) have been used effectively for many years. However, they are considered of limited use for resolving deep divergences such as the origin of the bilaterians, due to certain drawbacks such as the long-branch attraction (LBA) problem. Here, we attempt to overcome these pitfalls by combining several methods suggested in previous studies and routinely used in contemporary standard phylogenetic analyses but that have not yet been applied to any bilaterian phylogeny based on these genes. The methods used include maximum likelihood and Bayesian inference, the application of models with rate heterogeneity across sites, wide taxon sampling and compartmentalized analyses for each problematic clade. The results obtained show that the combination of the above-mentioned methodologies minimizes the LBA effect, and a new Lophotrochozoa phylogeny emerges. Also, the Acoela and Nemertodermatida are confirmed with maximum support as the first branching bilaterians. Ribosomal RNA genes are thus a reliable source for the study of deep divergences in the metazoan tree, provided that the data are treated carefully.
It is commonly known that drought stress is a major constraint limiting crop production. Drought stress and associated drought tolerance mechanisms are therefore under intense investigation with the ...view to future production of drought tolerant crops. With an ever-growing population and variable climate, novel approaches need to be considered to sustainably feed future generations. In this context, definitions of drought tolerance are highly variable, which poses a major challenge for the systematic assessment of this trait across the plant kingdom. Furthermore, drought tolerance is a polygenic trait and understanding the evolution of this complex trait may inform us about patterns of gene gain and loss in relation to diverse drought adaptations. We look at the transition of plants from water to land, and the role of drought tolerance in enabling this transition, before discussing the first drought tolerant plant and common drought responses amongst vascular plants. We reviewed the distribution of a combined “drought tolerance” trait in very broad terms to encompass different experimental systems and definitions used in the current literature and assigned a binary trait “tolerance vs. sensitivity” in 178 extant plant species. By simplifying drought responses of plants into this “binary” trait we were able to explore the evolution of drought tolerance across the wider plant kingdom, compared to previous studies. We show how this binary “drought tolerance/sensitivity” trait has evolved and discuss how incorporating this information into an evolutionary genomics framework could provide insights into the molecular mechanisms underlying extreme drought adaptations.
Novel and divergent genes in the evolution of placental mammals Dunwell, Thomas L.; Paps, Jordi; Holland, Peter W. H.
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
10/2017, Letnik:
284, Številka:
1864
Journal Article
Recenzirano
Odprti dostop
Analysis of genome sequences within a phylogenetic context can give insight into the mode and tempo of gene and protein evolution, including inference of gene ages. This can reveal whether new genes ...arose on particular evolutionary lineages and were recruited for new functional roles. Here, we apply MCL clustering with all-versus-all reciprocal BLASTP to identify and phylogenetically date ‘Homology Groups’ among vertebrate proteins. Homology Groups include new genes and highly divergent duplicate genes. Focusing on the origin of the placental mammals within the Eutheria, we identify 357 novel Homology Groups that arose on the stem lineage of Placentalia, 87 of which are deduced to play core roles in mammalian biology as judged by extensive retention in evolution. We find the human homologues of novel eutherian genes are enriched for expression in preimplantation embryo, brain, and testes, and enriched for functions in keratinization, reproductive development, and the immune system.
One of the hallmarks of multicellular organisms is the ability of their cells to trigger responses to the environment in a coordinated manner. In recent years primary cilia have been shown to be ...present as 'antennae' on almost all animal cells, and are involved in cell-to-cell signaling in development and tissue homeostasis; how this sophisticated sensory system arose has been little-studied and its evolution is key to understanding how sensation arose in the Animal Kingdom. Sponges (Porifera), one of the earliest evolving phyla, lack conventional muscles and nerves and yet sense and respond to changes in their fluid environment. Here we demonstrate the presence of non-motile cilia in sponges and studied their role as flow sensors.
Demosponges excrete wastes from their body with a stereotypic series of whole-body contractions using a structure called the osculum to regulate the water-flow through the body. In this study we show that short cilia line the inner epithelium of the sponge osculum. Ultrastructure of the cilia shows an absence of a central pair of microtubules and high speed imaging shows they are non-motile, suggesting they are not involved in generating flow. In other animals non-motile, 'primary', cilia are involved in sensation. Here we show that molecules known to block cationic ion channels in primary cilia and which inhibit sensory function in other organisms reduce or eliminate sponge contractions. Removal of the cilia using chloral hydrate, or removal of the whole osculum, also stops the contractions; in all instances the effect is reversible, suggesting that the cilia are involved in sensation. An analysis of sponge transcriptomes shows the presence of several transient receptor potential (TRP) channels including PKD channels known to be involved in sensing changes in flow in other animals. Together these data suggest that cilia in sponge oscula are involved in flow sensation and coordination of simple behaviour.
This is the first evidence of arrays of non-motile cilia in sponge oscula. Our findings provide support for the hypothesis that the cilia are sensory, and if true, the osculum may be considered a sensory organ that is used to coordinate whole animal responses in sponges. Arrays of primary cilia like these could represent the first step in the evolution of sensory and coordination systems in metazoans.
Animals display a diversity of life cycles, including larvae in some lineages but not in others. A new study reveals a shared genetic toolkit in many animals that regulates the transition to the ...juvenile form, from an embryo or a larva.
Animals display a diversity of life cycles, including larvae in some lineages but not in others. A new study reveals a shared genetic toolkit in many animals that regulates the transition to the juvenile form, from an embryo or a larva.
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