THE INTERPHOTORECEPTOR RETINOID-BINDING PROTEIN GENE IN THERIAN MAMMALS - IMPLICATIONS FOR HIGHER-LEVEL RELATIONSHIPS AND EVIDENCE FOR LOSSOF FUNCTION IN THE MARSUPIAL MOLE

The subclass Theria of Mammalia includes marsupials (infraclass Metath eria) and placentals (infraclass Eutheria). Within each group, interor dinal relationships remain unclear. One limitation of many studies Is incomplete ordinal representation. Here, we analyze DNA sequences for part of exon 1 of the interphotoreceptor retinoid binding protein gene , including 10 that are newly reported, for representatives of ail the rian orders. Among placentals, the most robust clades are Cetartiodact yla, Paenungulata, and an expanded African clade that includes paenung ulates, tubulidentates, and macroscelideans. Anagalida, Archonta, Altu ngulata, Hyracoidea + Perissodactyla Ungulata, and tl ic ''flying prim ate'' hypothesis are rejected by statistical tests. Among marsupials, the most robust clade includes all orders except Didelphimorphia. The phylogenetic placement of the monito dcl monte and the marsupial mole remains unclear However, tile marsupial mole sequence contains three f rameshift indels end numerous siop codons in ail three reading frames, Given that the interphotoreceptor retinoid binding protein gene is a single-copy gene that functions in the visual cycle and that the marsu pial mole is blind with degenerate eyes, this finding suggests that ph enotypic degeneration of the eyes Is accompanied by parallel changes a t the molecular level as a result of relaxed selective constraints.