Predominance of genetic monogamy by females in a hammerhead shark, Sphyrna tiburo: Implications for shark conservation.

There is growing interest in the mating systems of sharks and their relatives (Class Chondrichthyes) because these ancient fishes occupy a key position in vertebrate phylogeny and are increasingly in need of conservation due to widespread overexploitation. Based on precious few genetic and field observational studies, current speculation is that polyandrous mating strategies and multiple paternity may be common in sharks as they are in most other vertebrates. Here, we test this hypothesis by examining the genetic mating system of the bonnethead shark, Sphyrna tiburo, using microsatellite DNA profiling of 22 litters (22 mothers, 188 embryos genotyped at four polymorphic loci) obtained from multiple locations along the west coast of Florida. Contrary to expectations based on the ability of female S. tiburo to store sperm, the social nature of this species and the 100% multiple paternity observed in two other coastal shark species, over 81% of sampled bonnethead females produced litters sired by a single male (i.e. genetic monogamy). When multiple paternity occurred in S. tiburo, there was an indication of increased incidence in larger mothers with bigger litters. Our data suggest that sharks may exhibit complex genetic mating systems with a high degree of interspecific variability, and as a result some species may be more susceptible to loss of genetic variation in the face of escalating fishing pressure. Based on these findings, we suggest that knowledge of elasmobranch mating systems should be an important component of conservation and management programmes for these heavily exploited species.

Global mitochondrial DNA phylogeography and population structure of the silky shark, Carcharhinus falciformis

Globally, sharks are under enormous pressure from fishing efforts. One such species is the silky shark, Carcharhinus falciformis, which occurs in all the Earth’s tropical oceans and is captured in large numbers in pelagic fisheries. Regionally, the silky shark is listed as Vulnerable to Near Threatened by the International Union for the Conservation of Nature due to high levels of direct and by catch exploitation. Despite major conservation concerns about this species, little is known about its genetic status and level of demographic or evolutionary connectivity among its regional distributions. We report a genetic assessment of silky sharks sampled across a major portion of the species’ global range. We sequenced the complete mitochondrial DNA control region from 276 individuals taken from the western Atlantic and Indo-Pacific Oceans and the Red Sea. Overall, haplotype and nucleotide diversities were relatively large (0.93 ± 0.01 and 0.61 ± 0.32 %, respectively). Nucleotide diversity in Indo-Pacific sharks, however, was significantly lower and about half that in Atlantic sharks. Strong phylogeographic partitioning occurred between ocean basins. Furthermore, shallow but significant pairwise statistical differentiation occurred among most regional samples within the Indo-Pacific, but not the western Atlantic. Overall, at least five mitochondrial DNA populations of silky sharks were identified globally. Despite historically large population sizes, silky sharks appear to be isolated on relatively small spatial scales, at least in the Indo-Pacific, indicating that conservation and management efforts will need to be exerted at relatively small scales in a pelagic and highly vagile species.

Virgin birth in a hammerhead shark.

Parthenogenesis has been documented in all major jawed vertebrate lineages except mammals and cartilaginous fishes (Class Chondrichthyes: sharks, batoids, chimeras). Reports of captive female sharks giving birth despite being held in the extended absence of males have generally been ascribed to prior matings coupled with long-term sperm storage by the females. Here we provide the first genetic evidence for chondrichthyan parthenogenesis, involving a hammerhead shark. This finding also broadens the known occurrence of a specific type of asexual development (automictic parthenogenesis) among vertebrates, extending recently raised concerns about the potential negative effect of this type of facultative parthenogenesis on the genetic diversity of threatened vertebrate species.

Shark virgin birth produces multiple, viable offspring

Facultative automictic parthenogenesis has only recently been confirmed in the most ancient jawed vertebrates, the chondrichthyan fishes (sharks, batoids, and chimeras). To date, however, in both documented cases, the females have only produced a single parthenogen offspring, and none of these have lived for more than 3 days. We present a genetically verified case of automictic parthenogenesis by a white-spotted bamboo shark (Chiloscyllium plagiosum), in which at least 2 parthenogens were produced and survived for 5 years or more. These findings demonstrate that some female sharks are capable of producing, multiple, viable offspring through parthenogenesis.

Development and characterization of 10 polymorphic microsatellite loci for the blue shark, Prionace glauca, and their cross shark-species amplification.

Ten polymorphic nuclear microsatellite loci were developed from a microsatellite enriched genomic library of the blue shark, Prionace glauca. The utility of these markers for genetic studies of this globally distributed, heavily exploited, oceanic predator was assessed by screening 120 specimens sampled from six locations throughout the species’ range. Both moderately and highly polymorphic marker loci were identified. Three to 35 alleles were found to be segregating per locus (mean 10.1) with observed heterozygosities ranging from 24 to 91%. Evaluation of the cross-species amplification of these markers across 18 additional shark species indicates that these microsatellites are potentially useful for genetic studies of other species of conservation concern.

Size-selective fishing drives species composition in the Celtic Sea

Fishing alters community size structure by selectively removing larger individual fish and by changing the relative abundance of different-sized species. To assess the relative importance of individual-and species-level effects, two indices of fish community structure were compared, the relative abundance of large fish individuals (large fish indicator, LFI) and the relative abundance of large fish species (large species indicator, LSI). The two indices were strongly correlated for empirical data from the Celtic Sea and for data from simulated model communities, suggesting that much of the variability in the LFI is caused by shifts in the relative abundance of species (LSI). This correlation is explained by the observation that most of the biomass of a given species is spread over few length classes, a range spanning the factor 2 of individual length, such that most species contributed predominantly to either the small or the large component of the LFI. The results suggest that the effects of size-selective fishing in the Celtic Sea are mediated mainly through changes in community composition.

TACHYKININS WITH UNUSUAL STRUCTURAL FEATURES FROM A URODELE, THE AMPHIUMA, AN ELASMOBRANCH, THE HAMMERHEAD SHARK, AND AN AGNATHAN, THE RIVER LAMPREY

Tachykinins were purified from extracts of gastrointestinal tissues of the urodele, Amphiuma tridacrylum (three-toed amphiuma), and the elasmobranch Sphyrna lewini (hammerhead shark), and from the brain of the agnathan Lampetra fluviatilis (river lamprey). The amphiuma substance P (SP) (DNPSVGQFYGLM-NH2) contains 12 amino residues compared with 11 for mammalian SP and lacks the Arg/Lys-Pro-Xaa-Pro motif that is characteristic of NK, receptor-selective agonists. Lampetra SP (RKPHPKEFVGLM-NH2) is identical to SP from the sea lamprey and the shark SP-related peptide (AKFDKFYGLM-NH2) is identical to dogfish scyliorhinin L. Amphiuma neurokinin A (NKA) (HKDAFIGLM-NH2) and lamprey NKA (HFDEFVGLM-NH2) contain 9 amino acid residues compared with 10 for mammalian NKA. The shark NKA-related peptide (ASGPTQAGIV(10)GRKRQKGEMF(20)VGLM-NH2) shows limited structural similarity to mammalian neuropeptide gamma and the teleost tachykinin, carassin but contains 24 rather than 21 amino acid residues. The data show that the primary structures of the tachykinins have been very poorly conserved during vertebrate evolution and that pressure has acted only to maintain the functionally important sequence -Phe-Xaa-Gly- Leu-Met-NH2 at the COOH-termini of the peptides.

Why the size structure of marine communities can require decades to recover from fishing

A dynamic food-web model of more than 1000 species was used to quantify the recovery trajectory of marine community size-structure under different hypothetical fishing regimes, using the Northeast Atlantic as an example. Size-structure was summarised by four indicators: the Large Fish Indicator (LFI), the Large Species Indicator (LSI), the biomass-weighted mean maximum length of fish species (EMBED Equation.3) and the biomass-weighted mean maturation length of fish species (EMBED Equation.3). Time-series of these indicators recorded recovery following release from fishing with various size-selectivities, intensities and durations. In model simulations, fishing-induced trophic cascades were observed to distort fish community size-structure, but these did not have a large influence on recovery level or duration as measured by the four indicators. However, simulations showed that local extinctions of large fish species increased in number with both fishing intensity and duration, and could strongly limit the recovery level. Recovery of fish community size-structure to near equilibrium frequently took multiple decades in simulations; these long transient periods suggest that management interventions for size-structure recovery may require much longer than previously thought. Our results demonstrate the need for community-level modelling to set realistic targets for management of community size-structure.

The Eschatology of Global Warming in a Scottish Fishing Village

In Gamrie, an Aberdeenshire fishing village home to 700 people and six millennialist Protestant churches, global warming is more than just a 'hoax': it is a demonic conspiracy that threatens to bring about the ruin of the entire human race. Such a certainty was rendered intelligible to local Christians by viewing it through the lens of dispensationalist theology brought to the village by the Plymouth Brethren. In a play on Weberian notions of disenchantment, I argue that whereas Gamrie's Christians rejected global warming as a false eschatology, and environmentalism as a false salvationist religion, supporters of the climate change agenda viewed global warming as an apocalyptic reality and environmentalism as providing salvific redemption. Both rhetorics – each engaged in a search for 'signs of the end times' – are thus millenarian.