Fred Ruhe
Well-known member
AUSTRALIAN ISLAND EMUS ARE HOLOCENE DWARFS
THOMSON, Vicki A., University of Adelaide, Adelaide, Australia; COOPER, Alan, University of Adelaide, Adelaide, Australia
At least six taxa of emus (flightless birds) inhabited Australia in the past: Dromaius gidju n. sp. from the Miocene; D. ocypus from the Pliocene; D. ater, D. baudinianus, and D. novaehollandiae diemenensis from the Holocene; as well as D. novaehollandiae, which is currently extant. Fossil evidence and reports from early European explorers suggest that at least three island emus, including the two dwarfed emus, were hunted to extinction only recently in the 19th century (D. ater, D. baudinianus, and D. novaehollandiae diemenensis from southern Australian offshore islands: King island, Kangaroo Island, and Tasmania, respectively). Although a previous study of the King Island emu found their genetic diversity fell within that of the mainland emu, little is known about how the Kangaroo Island emu or the Tasmanian emu relate to either of these forms, or even whether the Tasmanian emu was diminutive in size at all. By sequencing a short fragment of the mitochondrial control region from sub-fossil specimens of the King Island emu (n=8), Kangaroo Island emu (n=11) and Tasmanian emu (n=4), we were able to establish they all share the same or similar DNA markers with the extant mainland emu (n=81). Short damaged fragments of DNA are usually all that remain in sub-fossil and fossil bone remains, particularly from hot or wet regions of the world such as Australia. Measurements were also taken of the femur and tarsometatarsi bones of the King Island emu (n=16 and n=12), Kangaroo Island emu (n=13 and n=12), and mainland emu (n=8 for both) for length, proximal width, proximal depth, distal width, distal depth, shaft width, and shaft depth. Preliminary analyses of pairwise linear measurements show the Kangaroo Island emu were smaller than the mainland emu, with the King Island emu even smaller than the Kangaroo Island emu. By generating Mosimann shape variables for each individual, we were able to remove a substantial part of the isometric scaling. Principal component analyses of the Mosimann shape variables show some overlap of all three emu taxa, suggesting even though isometric size is largely removed some sizerelated shape (allometric) variability remains. Furthermore, the degree of dwarfism for each island emu appears to correlate with island size. By analyzing both genetic and morphological diversity of congeneric island/mainland taxa pairs, this work on the Australian emu provides a case study for examining island dwarfism as an evolutionary mechanism.
THOMSON, Vicki A., University of Adelaide, Adelaide, Australia; COOPER, Alan, University of Adelaide, Adelaide, Australia
At least six taxa of emus (flightless birds) inhabited Australia in the past: Dromaius gidju n. sp. from the Miocene; D. ocypus from the Pliocene; D. ater, D. baudinianus, and D. novaehollandiae diemenensis from the Holocene; as well as D. novaehollandiae, which is currently extant. Fossil evidence and reports from early European explorers suggest that at least three island emus, including the two dwarfed emus, were hunted to extinction only recently in the 19th century (D. ater, D. baudinianus, and D. novaehollandiae diemenensis from southern Australian offshore islands: King island, Kangaroo Island, and Tasmania, respectively). Although a previous study of the King Island emu found their genetic diversity fell within that of the mainland emu, little is known about how the Kangaroo Island emu or the Tasmanian emu relate to either of these forms, or even whether the Tasmanian emu was diminutive in size at all. By sequencing a short fragment of the mitochondrial control region from sub-fossil specimens of the King Island emu (n=8), Kangaroo Island emu (n=11) and Tasmanian emu (n=4), we were able to establish they all share the same or similar DNA markers with the extant mainland emu (n=81). Short damaged fragments of DNA are usually all that remain in sub-fossil and fossil bone remains, particularly from hot or wet regions of the world such as Australia. Measurements were also taken of the femur and tarsometatarsi bones of the King Island emu (n=16 and n=12), Kangaroo Island emu (n=13 and n=12), and mainland emu (n=8 for both) for length, proximal width, proximal depth, distal width, distal depth, shaft width, and shaft depth. Preliminary analyses of pairwise linear measurements show the Kangaroo Island emu were smaller than the mainland emu, with the King Island emu even smaller than the Kangaroo Island emu. By generating Mosimann shape variables for each individual, we were able to remove a substantial part of the isometric scaling. Principal component analyses of the Mosimann shape variables show some overlap of all three emu taxa, suggesting even though isometric size is largely removed some sizerelated shape (allometric) variability remains. Furthermore, the degree of dwarfism for each island emu appears to correlate with island size. By analyzing both genetic and morphological diversity of congeneric island/mainland taxa pairs, this work on the Australian emu provides a case study for examining island dwarfism as an evolutionary mechanism.
