RESUMEN
Bipolarity, the presence of a species in the high latitudes separated by a gap in distribution across the tropics, is a well-known pattern of global species distribution. But the question of whether bipolar species have evolved independently at the poles since the establishment of the cold-water provinces 16-8 million years ago, or if genes have been transferred across the tropics since that time, has not been addressed. Here we examine genetic variation in the small subunit ribosomal RNA gene of three bipolar planktonic foraminiferal morphospecies. We identify at least one identical genotype in all three morphospecies in both the Arctic and Antarctic subpolar provinces, indicating that trans-tropical gene flow must have occurred. Our genetic analysis also reveals that foraminiferal morphospecies can consist of a complex of genetic types. Such occurrences of genetically distinct populations within one morphospecies may affect the use of planktonic foraminifers as a palaeoceanographic proxy for climate change and necessitate a reassessment of the species concept for the group.
Asunto(s)
Evolución Molecular , Plancton/genética , Animales , Regiones Antárticas , Regiones Árticas , Secuencia de Bases , Clima Frío , ADN Ribosómico/genética , Genética de Población , Genotipo , Datos de Secuencia Molecular , Océanos y Mares , Filogenia , Plancton/clasificación , ARN Ribosómico/genéticaRESUMEN
Phylogenetic analysis of five partial planktic foraminiferal small subunit (SSU) ribosomal (r) DNA sequences with representatives of a diverse range of eukaryote, archaebacterial, and eubacterial taxa has revealed that the evolutionary origin of the foraminiferal lineage precedes the rapid eukaryote diversification represented by the "crown" of the eukaryotic tree and probably represents one of the earliest splits among extant free-living aerobic eukaryotes. The foraminiferal rDNA sequences could be clearly separated from known symbionts, commensals, and food organisms. All five species formed a single monophyletic group distinguished from the "crown" group by unique foraminiferal specific insertions as well as considerable nucleotide distance in aligned regions.
Asunto(s)
Evolución Biológica , ADN Ribosómico/genética , Eucariontes/genética , Filogenia , Plancton/fisiología , Animales , Cartilla de ADN , ADN Protozoario/genética , Diplomonadida/clasificación , Diplomonadida/fisiología , Eucariontes/clasificación , Eucariontes/fisiología , Células Eucariotas , Kinetoplastida/clasificación , Kinetoplastida/fisiología , Modelos Biológicos , Plancton/clasificación , Reacción en Cadena de la Polimerasa/métodos , Homología de Secuencia de Ácido NucleicoRESUMEN
Hepatic portal and arterial blood flow and the net hepatic uptake of individual free fatty acids (FFA) were measured in sheep during intravenous infusions of saline and noradrenaline (2 mu kg-minus 1 min-minus 1). During noradrenaline infusion in FFA increased in the circulating (arterial) plasma in amounts oleate greater than palmitate greater than stearate. Changes in the hepatic uptake of FFA opposed these changes in plasma FFA composition; the hepatic uptake of oleate increased more than that of palmitate, and the uptake of stearate fell slightly, but not significantly.