title: Parallel adaptive origins of digestive RNases in Asian and African leaf monkeys.
abstract: Similar morphological or physiological changes occurring in multiple evolutionary lineages are not uncommon. Such parallel changes are believed to be adaptive, because a complex character is unlikely to originate more than once by chance. However, the occurrence of adaptive parallel amino acid substitutions is debated. Here I propose four requirements for establishing adaptive parallel evolution at the protein sequence level and use these criteria to demonstrate such a case. I report that the gene encoding pancreatic ribonuclease was duplicated independently in Asian and African leaf-eating monkeys. Statistical analyses of DNA sequences, functional assays of reconstructed ancestral proteins and site-directed mutagenesis show that the new genes acquired enhanced digestive efficiencies through parallel amino acid replacements driven by darwinian selection. They also lost a non-digestive function independently, under a relaxed selective constraint. These results demonstrate that despite the overall stochasticity, even molecular evolution has a certain degree of repeatability and predictability under the pressures of natural selection.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, 1075 Natural Science Building, 830 North University Avenue, Ann Arbor, Michigan 48109, USA. jianzhi@umich.edu
authors.forename: Jianzhi
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D016673:Colobinae / Q000235:genetics* / Q000378:metabolism; D003104:Colobus / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D020440:Gene Duplication; D006801:Humans; D008969:Molecular Sequence Data; D010179:Pancreas / Q000201:enzymology; D010802:Phylogeny; D012260:Ribonucleases / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D012260:Ribonucleases