Evo Devo

Evolutionary development - at the biological interface between genetic regulatory mechanisms and biological evolution.

gene regulation and biological evolution

Gene regulation, rather than genetic mutation plays an important role in some rapid adaptive speciations.

Most of the 50 or so species of freshwater stickleback fish are descendents of marine stickleback that colonized lakes and streams at the end of the last ice age about 10,000 years ago. Researchers have discovered that rapid speciation displaying different levels of armor plating in sticklebacks results not from gene mutations, but rather from different regulation of a single gene, the Eda gene that codes for the protein ectodermal dysplasin. "Evolution of the fish is based on how the Eda gene is used; how, when and where it is activated during embryonic growth." HHMI News Researchers Trace Evolution to Relatively Simple Genetic Changes.

Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles.
Major phenotypic changes evolve in parallel in nature by molecular mechanisms that are largely unknown. Here, we use positional cloning methods to identify the major chromosome locus controlling armor plate patterning in wild threespine sticklebacks. Mapping, sequencing, and transgenic studies show that the Ectodysplasin (EDA) signaling pathway plays a key role in evolutionary change in natural populations and that parallel evolution of stickleback low-plated phenotypes at most freshwater locations around the world has occurred by repeated selection of Eda alleles derived from an ancestral low-plated haplotype that first appeared more than two million years ago. Members of this clade of low-plated alleles are present at low frequencies in marine fish, which suggests that standing genetic variation can provide a molecular basis for rapid, parallel evolution of dramatic phenotypic change in nature.
Colosimo PF, Hosemann KE, Balabhadra S, Villarreal G Jr, Dickson M, Grimwood J, Schmutz J,
Myers RM, Schluter D, Kingsley DM. Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles. Science. 2005 Mar 25;307(5717):1928-33.
Comment in: Science. 2005 Mar 25;307(5717):1890-1..


How many genetic changes control the evolution of new traits in natural populations? Are the same genetic changes seen in cases of parallel evolution? Despite long-standing interest in these questions, they have been difficult to address, particularly in vertebrates. We have analyzed the genetic basis of natural variation in three different aspects of the skeletal armor of threespine sticklebacks (Gasterosteus aculeatus): the pattern, number, and size of the bony lateral plates. A few chromosomal regions can account for variation in all three aspects of the lateral plates, with one major locus contributing to most of the variation in lateral plate pattern and number. Genetic mapping and allelic complementation experiments show that the same major locus is responsible for the parallel evolution of armor plate reduction in two widely separated populations. These results suggest that a small number of genetic changes can produce major skeletal alterations in natural populations and that the same major locus is used repeatedly when similar traits evolve in different locations.
The Genetic Architecture of Parallel Armor Plate Reduction in Threespine Sticklebacks. (Free Full Text Research Article) PLos Biology Volume 2 Issue 5 MAY 2004.


Evolution. The synthesis and evolution of a supermodel. [Science. 2005] PMID: 15790836
The genetic architecture of parallel armor plate reduction in threespine sticklebacks. [PLoS Biol. 2004] PMID: 15069472
Parallel genetic basis for repeated evolution of armor loss in Alaskan threespine stickleback populations. [Proc Natl Acad Sci U S A. 2004] PMID: 15069186
The master sex-determination locus in threespine sticklebacks is on a nascent Y chromosome. [Curr Biol. 2004] PMID: 15324658
Lateral plate evolution in the threespine stickleback: getting nowhere fast. [Genetica. 2001] PMID: 11838781
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More HHMI articles: Genetic Control of Vertebrate Skeletal Development. Also Evolution's Mirror in a Fish's Spines (04.14.04) and Fish May Show How Nature Diversifies(12.19.01) and more HHMI Genes We Share: Focusing on Skeletons and New Gene Knockouts Reveal "Master Planners" of the Skeleton(07.17.03)

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Evolutionary biology: lost and found. [Nature. 2004] PMID: 15085113
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The master sex-determination locus in threespine sticklebacks is on a nascent Y chromosome. [Curr Biol. 2004] PMID: 15324658
The genetic architecture of parallel armor plate reduction in threespine sticklebacks. [PLoS Biol. 2004] PMID: 15069472
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Fishing for the secrets of vertebrate evolution in threespine sticklebacks. [Dev Dyn. 2005] PMID: 16252286
Parallel genetic basis for repeated evolution of armor loss in Alaskan threespine stickleback populations. [Proc Natl Acad Sci U S A. 2004] PMID: 15069186
Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles. [Science. 2005] PMID: 15790847
Genetic and developmental basis of evolutionary pelvic reduction in threespine sticklebacks. [Nature. 2004] PMID: 15085123
The master sex-determination locus in threespine sticklebacks is on a nascent Y chromosome. [Curr Biol. 2004] PMID: 15324658
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The master sex-determination locus in threespine sticklebacks is on a nascent Y chromosome. [Curr Biol. 2004] PMID: 15324658
Fishing for the secrets of vertebrate evolution in threespine sticklebacks. [Dev Dyn. 2005] PMID: 16252286
How much of the variation in adaptive divergence can be explained by gene flow? An evaluation using lake-stream stickleback pairs. [Evolution Int J Org Evolution. 2004] PMID: 15562693
Adaptive divergence and the balance between selection and gene flow: lake and stream stickleback in the Misty system. [Evolution Int J Org Evolution. 2002] PMID: 12144020
Speciation in reverse: morphological and genetic evidence of the collapse of a three-spined stickleback (Gasterosteus aculeatus) species pair. [Mol Ecol. 2006] PMID: 16448405
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1 Comments:

Blogger qtr said...

Glossary of terms: classification systems and population mechanisms in speciation:

Allopatric speciation occurs when a geographical barrier sub-divides a parent species, resulting in geographic and reproductive isolation such that the descendent species can no longer interbreed upon removal of the barrier.

Anagenesis differs from cladogenesis in that one species progressively transforms into a replacement species when sufficient gene mutations fix in the descendant population. At this point, the ancestral species has become extinct. This mechanism is distinct from the increase in numbers of species generated by cladogenetic branching events.

Cladogenesis is the mechanism of speciation in which one or more lineages (clades) arise from an ancestral line. Such speciation events increase the variety of plants or animals through branching of the phylogenetic tree. Cladogenesis is differentiated from anagenesis, which is the in toto replacement of one species by an anatomically distinct species.

Monophyletic taxon or clade: an accurate grouping of only (opp. polyphyletic) and all (opp. paraphyletic) descendents of a shared common ancestor. A monopyletic group is genetically homogeneous and reflects evolutionary relationships.

Paraphyletic taxon or clade: a monophyletic group that excludes one or more discrete groups descended from the most recent common ancestral species of the entire group. Other descendent species of the most recent common ancestor have been excluded from the paraphyletic taxon, usually because of morphologic distinctiveness.

Phenetic system: groupings of organisms based on mutual similarity of phenotypic (physical and chemical) characteristics. Phenetic groupings may or may not correlate with evolutionary relationships.

Phylogenetic system: groups organisms based on shared evolutionary heritage. DNA and RNA sequencing techniques are considered to give the most meaningful phylogenies.

Phylogenetic separation into evolutionary relationships (clades), based on comparison of genomes is likely to supplant phenotypical (phenetic) taxonomies of the prokaryotes.

Peripatry (paripatry) is a subset of allopatry in which an isolated group has a smaller population than the parent group. Ernst Mayr introduced the term. Peripatric speciation occurs when the smaller sub-group of a species enters a novel niche within the range of the parent species, becoming geographically and reproductively isolated. Peripatric speciation (paripatric) is distinguished from allopatric speciation by the smaller size of the isolate group, and from sympatric speciation, which involves no barrier to breeding.

Polyphyletic taxon: opposite to monophyletic taxon: A polyphyletic group is mistakenly or improperly erected on the basis of homoplasy — characteristics that have arisen despite not sharing a common ancestor. Homoplasy arises because of convergent evolution, parallelism, evolutionary reversals, horizontal gene transfer, or gene duplications. Polyphyletic taxa are genetically heterogeneous because members do not share a common ancestor.

Neontology is a branch of biology that emphasizes the study of modern biota (living or recent organisms) rather than fossilized organisms (paleontology).

Numerical Taxonomies are a common approach to phenetic taxonomy that employ a number of phenotypic characteristics to generate similarity coefficients that may be mapped in dendrograms. Groupings based on numerical taxonomy may or may not correlate with evolutionary relationships.

Taxonomies aim to group organisms according to shared characteristics against the background of biological diversity.

Sympatry involves no geographical separation of sub-populations of individuals. Sympatric speciation events occur most often in plants by the mechanism of polyploidy in which the number of chromosomes is doubled or tripled. John Maynard Smith proposed a model called disruptive speciation, in which homozygotes might have greater fitness than heterozygotes under some environmental conditions.

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