Genetic structure and congeneric range overlap among sharpnose sharks (genusRhizoprionodon) in the Northwest Atlantic Ocean

Abstract

Sharpnose sharks (genus Rhizoprionodon) experience extensive fishing pressure throughout their ranges in the Atlantic Ocean. As such, it is important to understand the degree to which intraspecific populations interact across a spatial gradient. The Atlantic sharpnose shark (Rhizoprionodon terraenovae) and Caribbean sharpnose shark (Rhizoprionodon porosus) share a similar appearance and spatial presence within the Gulf of Mexico, though until recently only R. terraenovae was observed north of the Bahamas. We assessed the population structure of R. terraenovae using the mitochondrial control region (650 bp). Our results indicate significant genetic structure (FST = 0.049, P < 0.001; ΦST = 0.017, P = 0.008) between the Gulf of Mexico and the rest of the Atlantic. In addition, we observed R. porosus outside their known range, in South Carolina, Virginia, and northern Florida. Given the overlapping range with R. terraenovae, we assessed the potential for congeneric hybridization with the addition of the nuclear ribosomal internal transcribed spacer 2 gene (1260 bp). Results designate these specimens to be true R. porosus specimens, indicating the need for reevaluation of this species’ range.

Age-Dependent Dispersal and Relatedness in Tiger Sharks (Galeocerdo cuvier)

“…Polymerase chain reactions (PCR) were completed using the touch-down protocol described in Holmes et al (Holmes et al, 2017) on a C1000 ThermoCycler from BioRad (Hercules, CA). Products were visualized with the microsatellite plugin for Geneious v7.1.8 (Kearse et al, 2012), and quality control was conducted following Davis et al (2019). We used Arlequin v3.5.2.2 (Excoffier and Lischer, 2010) to test for Hardy-Weinberg Equilibrium and calculate diversity statistics, and calculated the likelihood of error due to mistyping, null alleles, and allele dropout in Microchecker (van Oosterhout et al, 2004).…”

Spatial variability in the fecundity of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) in the northern Gulf of Mexico

“…neighboring systems (Tyminski et al 4 ; Portnoy et al, 2015;Fields et al, 2016). Unlike for bonnetheads, no fine-scale population structure has been observed for Atlantic sharpnose sharks in the northern GOM (Heist et al, 1996;Davis et al, 2019) and tag-recapture data show relatively larger scale movements in the region compared with those of bonnetheads (Tyminski et al 4 ; Deacy 5 ). If brood size is affected by temperature, the phenomenon would be expected to be most evident in a species, such as bonnetheads, that has been shown to make limited movements outside of spatially discrete areas along a latitudinal cline.…”

“…Portnoy et al (2014) went on to speculate that the outflow of freshwater from the Mississippi River created a barrier to movement across the GOM for the stenohaline blacknose shark. Results of genetic analyses of Atlantic sharpnose sharks indicates that there is one genetic stock of the Atlantic sharpnose shark throughout the northern GOM (Heist et al, 1996;Todd et al, 2004;Davis et al, 2019). However, of the 118 tagged Atlantic sharpnose sharks for which recapture data were available from previous studies, only 3 individuals moved between the eastern and western GOM (Kohler et al, 1998; Bethea and Grace 7 ; Hendon et al 8 ).…”

“…An essential component for appropriately assessing and effectively managing populations of elasmobranchs (sharks, skates, and rays) is accurate species-specific information pertaining to reproductive biology (Walker, 2005). However, intraspecific differences in important reproductive characteristics, such as size at maturity, size at birth, and reproductive periodicity, have been shown to occur within some shark species (e.g., Lombardi-Carlson et al, 2003;Sulikowski et al, 2007;Driggers and Hoffmayer, 2009), complicating the management process. For example, Yamaguchi et al (2000) examined the reproductive biology of starspotted smooth-hounds (Mustelus manazo) at 5 locations in the eastern Pacific Ocean and found that individuals at the northernmost sampling location had a higher age and size at maturity and longer reproductive cycle than conspecifics at lower latitudes.…”

Observations on heterodonty within the dentition of the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), from the north-central Gulf of Mexico, USA, with implications on the fossil record

“…The Atlantic Sharpnose Shark, Rhizoprionodon terraenovae ( Richardson, 1836 ), is the most common small coastal requiem shark in the north-central Gulf of Mexico, USA ( Drymon, Powers & Carmichael, 2012 ). Consequently, much is known about the distribution ( Drymon et al, 2010 ; Bethea et al, 2014 ), movement ( Gurshin & Szedlmayer, 2004 ; Carlson et al, 2008 ), age and growth ( Carlson & Baremore, 2003 ), reproduction ( Parsons, 1983 ; Hoffmayer et al, 2013 ), sexual segregation ( Drymon et al, 2020 ), and population structure ( Davis, Suárez-Moo & Daly-Engel, 2019 ) of this species. The dietary habits of Atlantic Sharpnose Sharks have been particularly well studied and demonstrate that the trophic niche of this species varies spatially ( Drymon, Powers & Carmichael, 2012 ; Plumlee & Wells, 2016 ; Seubert et al, 2019 ) and ontogenetically ( Bethea, Buckel & Carlson, 2004 ; Bethea et al, 2006 ; Harrington et al, 2016 ).…”