PAFAH1B1 and NDEL1 in the Cetartiodactyla superorder: Investigating adaptive evolution in two cerebral gyrification genes in Orcinus orca and Tursiops truncatus
Cerebral gyrencephaly, distinguished by the convoluted folds and grooves in the cerebral cortex, occurs in many animals in Class Mammalia. The highest rates of cerebral gyrification occur in Order Cetacea within the Superorder Cetartiodactyla. Of all cetaceans, two members of Family Delphinidae, Orcinus orca (killer whales) and Tursiops truncatus (Atlantic bottlenose dolphins) have exceptionally high indices of cerebral gyrification. Research has shown that mutation in two genes, PAFAH1B1 and NDEL1, both located on human chromosome 17, disrupt gyrencephaly normally observed in human brains. Based on this research, PAFAH1B1 and NDEL1 were evaluated for positive selection in Orcinus orca and Tursiops truncatus, to test the hypothesis that these genes are undergoing adaptive evolution against the background of purifying selection. The results of multiple selection tests supported a set of null hypotheses, indicating that these genes were under purifying, not positive, selection, which supports the hypothesis that delphinid cerebral gyrification is not under the control of either PAFAH1B1 or NDEL1.