Population structure and cryptic speciation in bonnethead sharks Sphyrna tiburo in the south-eastern U.S.A. and Caribbean.

Population structure and lineage diversification within a small, non-dispersive hammerhead shark species, the bonnethead shark Sphyrna tiburo, was assessed. Sphyrna tiburo is currently described as one continuously distributed species along the Atlantic continental margins of North, Central and South America, but recent genetic analysis of an insular population (Trinidad) suggests the possibility of cryptic speciation. To address this issue S. tiburo were sampled at six sites along c. 6200 km of continuous, continental coastline and from one island location (Grand Bahama) across a discontinuity in their distribution (the Straits of Florida), in order to test if they constitute a single lineage over this distribution. A total of 1030 bp of the mitochondrial control region (CR) was obtained for 239 S. tiburo, revealing 73 distinct haplotypes, high nucleotide diversity (0·01089) and a pair of highly divergent lineages estimated to have separated 3·61-5·62 million years ago. Mitochondrial cytochrome oxidase I and nuclear internal transcribed spacer loci show the same pattern. Divergence is similar within S. tiburo to that observed between established elasmobranch sister species, providing further evidence of cryptic speciation. A global AMOVA based on CR confirms that genetic diversity is primarily partitioned among populations (ΦST = 0·828, P < 0·001) because the divergent lineages are almost perfectly segregated between Belize and North America-The Bahamas. An AMOVA consisting solely of the North American and Bahamian samples is also significantly different from zero (ΦST = 0·088, P < 0·001) and pairwise FST is significantly different between all sites. These findings suggest that S. tiburo comprises a species complex and supports previous research indicating fine population structure, which has implications for fisheries management and biodiversity conservation.

Membrane transport of Tc-99m-labeled radiopharmaceuticals, I. Brain uptake by passive transport.

The membrane transport properties of twelve Tc-99m complexes were studied by determining each complex's brain uptake index (BUI), extent of protein binding, and octanol-to-saline partition coefficient. The chelating agents used were classified as either N-substituted carbamoylmethyliminodiacetates, substituted oxines, N,N'-diesters of EDTA, or N-substituted derivatives of DTPA. The Tc-99m complexes were found to cross the blood--brain barrier in proportion to their lipophilicity. Of the four types of chelating agents tested, substituted oxines appear to be most suitable for the development of diffusible Tc-99m-labeled compounds for imaging nonexcretory organs.

Tissue distribution of technetium-99m and carbon-14 labeled N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid.

The synthesis, radiochemical labeling, and tissue distribution characteristics of N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid are described. The radiopharmaceutical prepared by labeling with 99mTc was rapidly eliminated through the hepato-biliary system of mice. Parent 14C compound was eliminated primarily through the kidney. The 99mTc ion appears to have a greater influence than the organic carrier molecule on the distribution of the radiopharmaceutical.