title: Positive selection at the ASPM gene coincides with brain size enlargements in cetaceans.
abstract: The enlargement of cetacean brain size represents an enigmatic event in mammalian evolution, yet its genetic basis remains poorly explored. One candidate gene associated with brain size evolution is the abnormal spindle-like microcephaly associated (ASPM), as mutations in this gene cause severe reductions in the cortical size of humans. Here, we investigated the ASPM gene in representative cetacean lineages and previously published sequences from other mammals to test whether the expansion of the cetacean brain matched adaptive ASPM evolution patterns. Our analyses yielded significant evidence of positive selection on the ASPM gene during cetacean evolution, especially for the Odontoceti and Delphinoidea lineages. These molecular patterns were associated with two major events of relative brain size enlargement in odontocetes and delphinoids. It is of particular interest to find that positive selection was restricted to cetaceans and primates, two distant lineages both characterized by a massive expansion of brain size. This result is suggestive of convergent molecular evolution, although no site-specific convergence at the amino acid level was found.
authors.affiliation: Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing, People's Republic of China.
authors.forename: Shixia
authors.initials: S
authors.lastname: Xu
authors.forename: Yuan
authors.initials: Y
authors.lastname: Chen
authors.forename: Yuefeng
authors.initials: Y
authors.lastname: Cheng
authors.forename: Dan
authors.initials: D
authors.lastname: Yang
authors.forename: Xuming
authors.initials: X
authors.lastname: Zhou
authors.forename: Junxiao
authors.initials: J
authors.lastname: Xu
authors.forename: Kaiya
authors.initials: K
authors.lastname: Zhou
authors.forename: Guang
authors.initials: G
authors.lastname: Yang
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology*; D002591:Cetacea / Q000033:anatomy & histology* / Q000235:genetics*; D019143:Evolution, Molecular; D008322:Mammals / Q000033:anatomy & histology / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D011110:Polymorphism, Genetic; D011323:Primates / Q000033:anatomy & histology / Q000235:genetics; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D013045:Species Specificity
chemical_list: D009419:Nerve Tissue Proteins