Genetic mapping of the many cases of parallel adaptive traits can address whether these traits involve mutations in the same genes (or chromosomal regions), whether the traits arise through selection of new mutations or are based on standing genetic variation ( 30), and other fundamental questions in adaptation genetics. Related species can often evolve similar phenotypes using different genetic bases, and distant species can converge using the same genes, thus blurring the distinction between parallelism and convergence ( 4, 30).Ĭichlids offer a great opportunity to investigate these questions because multiple adaptive phenotypes have evolved repeatedly. Given these findings, it is not surprising that most of the regions identified through QTL or association mapping cannot be replicated across studies. Epistasis probably plays a much stronger role in the genetic architecture of complex traits than was previously thought, and this will impact the effect size in different genetic backgrounds ( 54). The genetic basis of most quantitative traits investigated so far does not seem to be shared across species ( 9, 39). Recent research in quantitative genetics has shown that the underlying genetics or genomic architecture of such traits might be even more complex than was previously appreciated ( 54). The last concerns the extent of gradualism in adaptive evolution.
#Ob red zebra cichlid genetics free
The first three address the fundamental issue of how free evolution is to explore phenotypic space. This is well captured by the German common name for this family of fishes, Buntbarsche, or “colorful perches.”ĭo parallel phenotypes evolve through parallel evolution at the molecular genetic level? Is there a bias toward coding or noncoding variation in adaptation? What is the role of genetic constraints in adaptive evolution? Does adaptation proceed by the gradual fixation of small-effect loci ( 39, 109, 120)? These are some of the major questions in the field of adaptation genetics, and all of them have a direct bearing on long-standing questions in evolutionary biology. Cichlids are famous for being extremely diverse in terms of not only body shape but also body coloration. Ecological model systems can now become genetically accessible.Ĭichlid fish have long attracted the attention of evolutionary biologists because of their extraordinary species richness and phenotypic adaptive diversity ( Figure 1). New technological advances in DNA-sequencing technology now enable researchers to study evolutionarily interesting lineages from a genetic and genomic standpoint. We are still far from understanding more generally or being able to predict common evolutionary patterns and processes at the level of the gene or the genome that explain adaptation and speciation.Īlthough identifying generalities of adaptation and speciation has been a major goal of evolutionary biologists since the inception of the field, until recently, this line of research was limited to a few genetic model systems studied in the laboratory using species whose ecology typically remained unknown. But only now, more than 150 years after the publication of On the Origin of Species, are evolutionary biologists beginning to understand (in a few cases) the genomics and genetics of adaptation and speciation ( 22, 100, 101). Here, we review the results of genetic and genomic research on cichlids in the past decade and suggest some potential avenues to further exploit the potential of the cichlid model system to provide a better understanding of the genomics of adaptation and speciation.Ĭharles Darwin recognized that extinction, adaptation, and speciation are the most fundamental evolutionary outcomes. These recent findings also show that the sharing of older DNA polymorphisms is extensive and suggest that linage sorting is incomplete and that adaptive introgression played a role in the African radiation. Genetic mapping, genome-wide analyses, and genome projects have flourished in the past decade and have added new insights on the question of why there are so many cichlids.
Their broad phenotypic variation coupled with recent divergence makes cichlids an ideal model system for understanding speciation, adaptation, and phenotypic diversification.
This extraordinary diversity has attracted considerable interest from researchers across several biological disciplines. With more than 1,500 species, cichlid fishes provide textbook examples of recent and diverse adaptive radiations, rapid rates of speciation, and the parallel evolution of adaptive phenotypes among both recently and distantly related lineages.
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