Hybridization between sympatric hammerhead sharks in the western North Atlantic Ocean

Abstract

Hybridization between closely related species has been documented across a wide range of taxa but has not been well studied in elasmobranchs. Hammerhead sharks have drawn global conservation concern because they experience some of the highest mortality rates among sharks when interacting with fisheries. Here we report on the detection of hybrids between the globally distributed scalloped hammerhead ( Sphyrna lewini ) and recently described Carolina hammerhead ( S. gilberti ) which are only known from the western Atlantic Ocean. Using a genomics approach, 10 first-generation hybrids and 15–17 backcrosses were detected from 554 individuals. The identification of backcrosses demonstrates hybrids are viable, and all backcrosses but one involved a scalloped hammerhead. All hybrids but one possessed Carolina hammerhead mtDNA, indicating sex-biased gene flow between species. Repeated hybridization and backcrossing with scalloped hammerheads could lead to the loss of endemic Carolina hammerheads.

Phylogeography and population genetics of the cryptic bonnethead shark Sphyrna aff. tiburo in Brazil and the Caribbean inferred from mtDNA markers

“…Indeed, vicariant events caused by sea‐level changes (maximum 130 m) during this geological time have been recognized as responsible for speciation in several plant and animal lineages (Briggs & Bowen, 2013), including sharks (Domingues et al ., 2018, 2019). Nonetheless, there is no contemporary physical barrier to dispersal preventing contact between the two lineages, so more sampling between Belize and Mexico (Yucatan Peninsula) could reveal the extent of sympatry and possibly hybridization between these species, as has been seen in other shark species complexes (Barker et al ., 2019; Morgan et al ., 2012).…”

Maternal provisioning gives young-of-the-year Hammerheads a head start in early life

“…data) were beyond the scope of this study, and thus not reported here. Since S. lewini and S. gilberti are a cryptic species pair, fin clips were taken from every animal and preserved in a dimethyl sulfoxide solution for subsequent species genetic identification following the protocols of Barker et al (2019). Hybrid individuals and those with indeterminant genetic discrimination where liver samples were taken for lipid extraction were removed from the data set (n = 14; Supplemental Table 1).…”

“…Temporal and geographical growth patterns in YOY were explored using a larger data set from Barker et al (2019). Since this data set did not include scar healing or condition information, only date of sampling, fork length, location and species identification information were used.…”

“…Using a larger data set from Barker et al (2019), the effect of time (DOY) and coastal region on growth dynamics for each species were tested (Supplemental Table 3). Both S. lewini (n = 128) and S. gilberti (n = 146) experienced an initial lag from time of first appearance (~ DOY 115), where fork length did not show appreciable increases with time until around end of June (~ DOY 175).…”

Hexabothriidae and Monocotylidae (Monogenoidea) from the gills of neonate hammerhead sharks (Sphyrnidae) Sphyrna gilberti, Sphyrna lewini and their hybrids from the western North Atlantic Ocean

“…Their divergence was estimated to have occurred 4.5 million years ago (Pinhal et al ., 2012; Quattro et al ., 2013). In addition, these species are capable of hybridization (Barker et al ., 2019). Because of the morphological similarity, S. gilberti was described only recently from the Carolina coasts (South and North Carolina states, USA) in the western North Atlantic Ocean (Quattro et al ., 2013).…”