The mitochondrial genome of the hammerhead Sphyrna zygaena

Possible female philopatry of the smooth hammerhead shark Sphyrna zygaena revealed by genetic structure patterns

We assessed the spatial pattern of genetic structure of smooth hammerhead shark Sphyrna zygaena in 10 localities from the Northern Mexican Pacific. A total of 35 haplotypes were identified in 129 sequences of the mtDNA control region. The results showed slight but significant genetic structure among localities (Φ_ST = 0.044, P < 0.001). In addition, the localities with highest number of juveniles were genetically different (Φ_ST = 0.058, P < 0.024), which may be representative of nursery areas. The genetic differentiation pattern can be associated to female philopatry and preference for particular birthing sites. Finally, historical demography shows that S. zygaena populations present a recent demographic expansion that occurred during glacial events in the late Pleistocene to early Holocene.

Complete mitogenome sequences of smooth hammerhead sharks, Sphyrna zygaena, from the eastern and western Atlantic

We report the first mitogenome sequences of the circumglobally distributed, highly mobile, smooth hammerhead shark, Sphyrna zygaena, from the eastern and western Atlantic. Both genomes were 16,729 bp long with 13 protein-coding genes, two rRNAs, 22 tRNAs and a non-coding control region. The two Atlantic shark sequences differ from each other by 13 SNPs, and by 43 and 44 SNPs from the published mitogenome of an S. zygaena specimen from the eastern Pacific Ocean. The cross-Atlantic mitogenome sequences reported here provide a resource to assist with population genetics studies of this widely exploited species of conservation concern.

Complete mitochondrial DNA genome of bonnethead shark, Sphyrna tiburo, and phylogenetic relationships among main superorders of modern elasmobranchs

Elasmobranchs are one of the most diverse groups in the marine realm represented by 18 orders, 55 families and about 1200 species reported, but also one of the most vulnerable to exploitation and to climate change. Phylogenetic relationships among main orders have been controversial since the emergence of the Hypnosqualean hypothesis by Shirai (1992) that considered batoids as a sister group of sharks. The use of the complete mitochondrial DNA (mtDNA) may shed light to further validate this hypothesis by increasing the number of informative characters. We report the mtDNA genome of the bonnethead shark Sphyrna tiburo, and compare it with mitogenomes of other 48 species to assess phylogenetic relationships. The mtDNA genome of S. tiburo, is quite similar in size to that of congeneric species but also similar to the reported mtDNA genome of other Carcharhinidae species. Like most vertebrate mitochondrial genomes, it contained 13 protein coding genes, two rRNA genes and 22 tRNA genes and the control region of 1086 bp (D-loop). The Bayesian analysis of the 49 mitogenomes supported the view that sharks and batoids are separate groups.