molecular decay of the tooth gene enamelin (enam) mirrors the loss of enamel in the fossil record of placental mammals牙基因的分子衰变enamelin(enam)镜子搪瓷的损失在胎盘类哺乳动物的化石记录.pdfVIP

Molecular Decay of the Tooth Gene Enamelin (ENAM) Mirrors the Loss of Enamel in the Fossil Record of Placental Mammals 1 1 2 3 1 Robert W. Meredith , John Gatesy , William J. Murphy , Oliver A. Ryder , Mark S. Springer * 1 Department of Biology, University of California Riverside, Riverside, California, United States of America, 2 Department of Veterinary Integrative Biosciences, Texas AM University, College Station, Texas, United States of America, 3 San Diego Zoo’s Institute for Conservation Research, Escondido, California, United States of America Abstract Vestigial structures occur at both the anatomical and molecular levels, but studies documenting the co-occurrence of morphological degeneration in the fossil record and molecular decay in the genome are rare. Here, we use morphology, the fossil record, and phylogenetics to predict the occurrence of ‘‘molecular fossils’’ of the enamelin (ENAM) gene in four different orders of placental mammals (Tubulidentata, Pholidota, Cetacea, Xenarthra) with toothless and/or enamelless taxa. Our results support the ‘‘molecular fossil’’ hypothesis and demonstrate the occurrence of frameshift mutations and/or stop codons in all toothless and enamelless taxa. We then use a novel method based on selection intensity estimates for codons (v) to calculate the timing of iterated enamel loss in the fossil record of aardvarks and pangolins, and further show that the molecular evolutionary history of ENAM predicts the occurrence of enamel in basal representatives of Xenarthra (sloths, anteaters, armadillos) even though frameshift mutations are ubiquitous in ENAM sequences of living xenarthrans. The molecular decay of ENAM parallels the morphological degeneration of enam