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

Abstract

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 (Φ = 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 (Φ = 0·088, P < 0·001) and pairwise F 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.

A new map of the tiger shark (Galeocerdo cuvier) genetic population structure in the western Atlantic Ocean: Hypothesis of an equatorial convergence centre

“…The highest level was found off the south‐eastern coast of Brazil, at a location close to São Paulo ( h = 0.874, π = 0.0026), and the lowest in the Gulf of Mexico ( h = 0.212, π = 0.0002), highlighting the unexpectedly high variability in Fernando de Noronha Archipelago (the highest value measured for the species until now), and the Gulf of Mexico as an area of lower genetic variability for the tiger shark. Compared with other coastal shark species—for example, bonnethead sharks (Fields, Feldheim, Gelsleichter, Pfoertner, & Chapman, ), blacktip sharks (Gledhill et al, ; Keeney & Heist, ), and Brazilian sharpnose sharks (Mendonça et al, )—tiger sharks exhibit moderate genetic variability.…”

Strong trans-Pacific break and local conservation units in the Galapagos shark (Carcharhinus galapagensis) revealed by genome-wide cytonuclear markers

“…In addition, no movement was recorded between Revillagigedo and the Galapagos Islands, despite including intermediate locations (potential stepping-stones). Bonnethead sharks (Sphyrna tiburo) show similar asymmetry between neutral SNPs and mtDNA in the west Atlantic region, possibly due to sexbiased dispersal (Portnoy et al 2015), and also exhibit strong population structure indicative of a species complex rather than a single species (Fields et al 2016).…”

Updated checklist of the extant Chondrichthyes within the Exclusive Economic Zone of Mexico

“…As a corollary to the above, recently published works or studies in progress can be cited. Thus, Fields et al (2016) proposed the existence of populations with possible cryptic speciation among hammerhead sharks ( Sphyrnidae ) from the Gulf of Mexico and the Caribbean Sea. Another study conducted by Hinojosa-Alvarez et al (2016) indicates the possibility of a third species of manta ray within the genus Mobula (sensu lato Manta , see Last et al 2016a ) for the Yucatan Peninsula.…”