Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity

Lions were the most widespread carnivores in the late Pleistocene, ranging from southern Africa to the southern USA, but little is known about the evolutionary relationships among these Pleistocene populations or the dynamics that led to their extinction. Using ancient DNA techniques, we obtained mitochondrial sequences from 52 individuals sampled across the present and former range of lions. Phylogenetic analysis revealed three distinct clusters: (i) modern lions, Panthera leo ; (ii) extinct Pleistocene cave lions, which formed a homogeneous population extending from Europe across Beringia (Siberia, Alaska and western Canada); and (iii) extinct American lions, which formed a separate population south of the Pleistocene ice sheets. The American lion appears to have become genetically isolated around 340 000 years ago, despite the apparent lack of significant barriers to gene flow with Beringian populations through much of the late Pleistocene. We found potential evidence of a severe population bottleneck in the cave lion during the previous interstadial, sometime after 48 000 years, adding to evidence from bison, mammoths, horses and brown bears that megafaunal populations underwent major genetic alterations throughout the last interstadial, potentially presaging the processes involved in the subsequent end-Pleistocene mass extinctions.     

Dense Crithidia Growth and Heme Sparing: Relation to Fe,Cu, Mo Chelation*

SYNOPSIS. Heme, intrinsically required by Trypanosomatidae, is unstable, especially in conventional alkaline (pH 7.2–8.0) media. Low solubility of heme in a pH 6.5 basal medium (developed to assay biopterin with Crithidia fasciculata) posed a problem: in media acidified during growth because of glycolysis, heme precipitated, perhaps contributed to acid-limited growth and interfered with densitometric estimation of growth. The remedy was to: replace glucose with less rapidly metabolized mannitol; distribute media in thin layers to promote oxidation of acetate, fumarate, and malate (presumably leaving an alkaline residue); and buffer heavily with histidine + Good zwitterionic buffers, and superimpcse physiological buffering by arginine + asparagine whose catabolism appeared to yield an excess of NH⁺₄ over acid. Thereupon, Fe and Cu deficiencies sharply limited growth in the medium whose main chelators were: (a) 2,3–dihydroxybenzoic + 5-sulfosalicylic acids (which preferentially bind transitional elements at their higher valences; (b) malic and gluconic acids; and (c) histidine. With unconventionally heightened concentrations of Fe, Cu, and Mo (the latter serving as Cu buffer as well as nutrient per se), the hemin concentration could be lowered, widening the margin of safety for heme solubility. Growth then reached 1.4 × 10⁸ cell/ml. This medium may serve to screen for ligands promoting uptake or release of Fe and Cu. The increased growth is a step towards improving the assay medium for biopterin and practical use of Crithidia to assay several B vitamins and essential amino acids for metazoa.