DNA from historical and trophy samples provides insights into white shark population origins and genetic diversity

Characterizing genetic variation by retrospective genotyping of trophy or historical artifacts from endangered species is an important conservation tool. Loss of genetic diversity in top predators such as the white shark Carcharodon carcharias remains an issue, exacerbated in this species by declining, sometimes isolated philopatric populations. We successfully sequenced mitochondrial DNA (mtDNA) D-loop from osteodentine of contemporary South African white shark teeth (from 3 jaws), and from 34 to 129 yr old dried cartilage and skin samples from 1 Pacific Ocean and 5 Mediterranean sharks. Osteodentine-derived sequences from South African fish matched those derived from an individual’s finclips, but were generally of poorer quality than those from skin and cartilage of historical samples. Three haplotypes were identified from historical Mediterranean samples (n = 5); 2 individuals had unique sequences and 3 shared the contemporary Mediterranean haplotype. Placement of previously undescribed mtDNA haplotypes from historical material within both the Mediterranean and Pacific clades fits with the accepted intra-specific phylogeny derived from contemporary material, verifying our approaches. The utility of our methodology is in its provision of additional genetic resources from osteodentine (for species lacking tooth pulp) and cartilage of rare and endangered species held in often uncurated, contemporary and historical dry collections. Such material can usefully supplement estimates of connectivity, population history, and stock viability. We confirm the depauperate haplotype diversity of historical Mediterranean sharks, consistent with founding by a small number of Pacific colonizers. The consequent lack of diversity suggests serious challenges for the maintenance of this top predator and the Mediterranean ecosystem.

DNA from historical and trophy samples provides insights into white shark population origins and genetic diversity

Characterizing genetic variation by retrospective genotyping of trophy or historical artifacts from endangered species is an important conservation tool. Loss of genetic diversity in top predators such as the white shark Carcharodon carcharias remains an issue, exacerbated in this species by declining, sometimes isolated philopatric populations. We successfully sequenced mitochondrial DNA (mtDNA) D-loop from osteodentine of contemporary South African white shark teeth (from 3 jaws), and from 34 to 129 yr old dried cartilage and skin samples from 1 Pacific Ocean and 5 Mediterranean sharks. Osteodentine-derived sequences from South African fish matched those derived from an individual’s finclips, but were generally of poorer quality than those from skin and cartilage of historical samples. Three haplotypes were identified from historical Mediterranean samples (n = 5); 2 individuals had unique sequences and 3 shared the contemporary Mediterranean haplotype. Placement of previously undescribed mtDNA haplotypes from historical material within both the Mediterranean and Pacific clades fits with the accepted intra-specific phylogeny derived from contemporary material, verifying our approaches. The utility of our methodology is in its provision of additional genetic resources from osteodentine (for species lacking tooth pulp) and cartilage of rare and endangered species held in often uncurated, contemporary and historical dry collections. Such material can usefully supplement estimates of connectivity, population history, and stock viability. We confirm the depauperate haplotype diversity of historical Mediterranean sharks, consistent with founding by a small number of Pacific colonizers. The consequent lack of diversity suggests serious challenges for the maintenance of this top predator and the Mediterranean ecosystem.

Genetic and migratory evidence for sympatric spawning of tropical Pacific eels from Vanuatu

The spawning areas of tropical anguillid eels in the South Pacific are poorly known, and more information about their life histories is needed to facilitate conservation. We genetically characterized 83 out of 84 eels caught on Gaua Island (Vanuatu) and tagged 8 eels with pop-up satellite transmitters. Based on morphological evidence, 32 eels were identified as Anguilla marmorata, 45 as A. megastoma and 7 as A. obscura. Thirteen of these eels possessed a mitochondrial DNA sequence (control region, 527 bp) or nuclear haplotype (GTH2b, 268 bp) conflicting with their species designation. These individuals also had multi-locus genotypes (6 microsatellite loci) intermediate between the species, and 9 of these eels further possessed heterozygote genotypes at species-diagnostic nuclear single nucleotide polymorphisms (SNPs). We classified these individuals as possibly admixed between A. marmorata and A. megastoma. One A. marmorata and 1 A. megastoma migrated 634 and 874 km, respectively, towards the border between the South Equatorial Current and the South Equatorial Counter Current. Both species descended from around 200 m depth at night to 750 m during the day. Lunar cycle affected the upper limit of migration depths of both species. The tags remained attached for 3 and 5 mo and surfaced <300 km from the pop-up location of a previously tagged A. marmorata pop-up location. A salinity maximum at the pop-up locations corresponding to the upper nighttime eel migration depths may serve as a seamark of the spawning area. The similar pop-up locations of both species and the evidence for admixture suggest that these tropical eels share a sympatric spawning area.