Mitochondrial DNA Diversity and Divergence Among Sharpnose Sharks, Rhizoprionodon Terraenovae, from the Gulf of Mexico and Mid-Atlantic Bight

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VIMS Articles Virginia Institute of Marine Science

1996

Mitochondrial DNA Diversity And Divergence Among Sharpnose Sharks, Rhizoprionodon Terraenovae, From The Gulf Of Mexico And Mid-Atlantic Bight

Edward J. Heist Virginia Institute of Marine Science

John Musick Virginia Institute of Marine Science

John Graves Virginia Institute of Marine Science

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Recommended Citation Heist, Edward J.; Musick, John; and Graves, John, "Mitochondrial DNA Diversity And Divergence Among Sharpnose Sharks, Rhizoprionodon Terraenovae, From The Gulf Of Mexico And Mid-Atlantic Bight" (1996). VIMS Articles. 590. https://scholarworks.wm.edu/vimsarticles/590

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Abstract.-The Atlantic sharpnose Mitochondrial DNA diversity and shark, Rhizoprionodon terraenovae, is a small coastal shark that is harvested divergence among sharpnose sharks, in both directed and nondirected fish eries throughout its range. Because Rhizoprionodon terraenovae, from the pups of this species are found both along the southeastern U.S. Atlantic Gulf of Mexico and Mid-Atlantic Bight* coast and the GulfofMexico, it is pos sible that multiple isolated breeding stocks exist. Restriction fragment Edward J. Heist·· length polymorphism analysis ofmito chondrial DNA was used to test the John A. Musick hypothesis that Atlantic sharpnose John E. Graves sharks from the U.S. Atlantic coast and the western GulfofMexico have iden School of Marine Science. Virginia Institute of Marine Science tical mitochondrial haplotype frequen College of William and Mary. Gloucester Point Virginia 23062 cies and therefore no apparent genetic e-mail address: [email protected] stock structure. Seven mitochondrial haplotypes were detected among 52 in dividuals. The distribution of haplo types between samples did not differ significantly from homogeneity (P= 0.694), indicatingthatthe null hypoth esis of a single breeding population The Atlantic sharpnose shark, parturition takes place from April could not be rejected. Rhizoprionodon terraenovae, is a to June in the northern Gulf of small (maximum length 110 cm to Mexico (Branstetter, 1981; Parsons, tal length) coastal shark that inhab 1983) and from May to June in its the east coast ofNorth America South Carolina (Castro, 1993). from New Brunswick, Canada, to The most recent fishery manage Yucatan, Mexico (Compagno, 1984). ment plan for sharks in the coastal This species is abundant along the Atlantic waters ofthe United States southern U.S. Atlantic coast and is (NMFS3) divides sharks into three second only to the sandbar shark, categories for management pur Carcharhinus plumbeus, inlongline poses: pelagic species, large coastal catches in Virginia (Musick et al., species, and small coastal species. 1993). It supports a large recre Currently catches of small coastal ational fishery offTexas (Parrackl ) species (predominantly theAtlantic and is an important species in the sharpnoseshark) are not regulated Mexican shark longline fishery (Applegate et al., 1993). In addition to being caught in directed fisher ies, theAtlantic sharpnose sharkis * Contribution 1933 ofthe Virginia Insti tute ofMarine Science, School ofMarine frequently taken by shark long Science, College of William and Mary, liners targeting large coastal spe Gloucester Point, Virginia 23062. cies (Branstetter and McEachran, ** Present address: Department ofWildlife 1986; Russell, 1993) as well as by and Fisheries Sciences, 'Thxas A&M Uni versity, College Station,Texas 77843-2258. commercial shrimp trawlers (Bran E-mail address: [email protected]. l stetter, 1981; Parrack ); however, 1 Parrack, M. L. 1990. A study ofshark the implementation of turtle ex exploitation in U.S. Atlantic coastal wa cluder devices (TED's) has produced ters during 1986-1989. NOAA, Natl. Mar. Fish. Serv., Southeast Fisheries the additional benefit of reducing Science Center, Miami, Florida. 2 bycatch of sharks (Branstetter ). 2 Branstetter, S. 1995. Gulf and South Atlantic sharpnose sharks travel in Atlantic Fisheries Development Founda tion, Suite 997, Lincoln Center, 5401 W. sex-segregated schools, as noted by Kennedy, Tampa, Florida 33609. the disparate sex ratios of adults Personal commun. captured by longlines (Branstetter, 3 NMFS. 1993. Fishery management 1981; Musick et al., 1993). The ges plan for sharks of the Atlantic Ocean. U.S. Dep. Commer., NOAA, Southeast Manuscript accepted 14 May 1996. tation period for this species is Regional Office, St. Petersburg, FL, p. Fishery Bulletin 94:664-668 (1996). about ten to twelve months, and 1-167. Heist et al.: Mitochondrial DNA diversity and divergence among Rhizoprionodon terraenovae 665 because catch rates are assumed to be at or below maximum sustainable yield and because life history parameters predict a relatively high recruitmentrate ..<: ...... :..: for this species in comparison to the large coastal Summer 1990 ., species targeted by the U.S. Atlantic shark longline ...... <:<". '.' ',' .,.. .. >- . 1991 .. , ...... ~ ... ,~" .. fishery (NMFS3). Recently Cortes (1995) challenged 1992 " . . ,...... this assessment on the basis ofa reevaluation oflife ...... , , history characteristics relevant to recruitment (age ...... , '. N 30"- at maturity, fecundity, and longevity) and suggested ...:".•:: .. "... : i that the Atlantic sharpnose shark may be more vul nerable to overfishingthan was previously assumed. Proper management of this species requires not '.,. '~March only accurate estimates ofstandingstock and recruit < • 1993 ment values but also an understanding ofthe repro ductive population structure of the species. The ob servation that pups ofthis species are found both in the South Atlantic Bight as well as in the Gulf of ~ Mexico, coupled with the small size and apparent ...'. April lack ofsignificantlongshore migration, suggests that .'.':. ~ 1993 o 300 L.L...l...J there may be isolated breeding populations of this Kilometers species. Information on stock structure of marine fishes has traditionally relied on two approaches: tag and recapture studies and analyses ofgenetic varia tion. Although considerable information has been ob tained on the movements of large sharks by means Figure 1 of tagging (Casey and Kohler, 1990), these tagging Locations and dates for collection of sharpnose shark, Rhizo studies have generally neglected smaller species of prionodon terraenOl'ae. sharks. Furthermore, to our knowledge the genetic structure of any population of small coastal shark has not been investigated. This study tests the hy pothesis of genetic homogeneity in allele frequency BstE II, Dra I, Hind III, Hpa I, Sea I, and Xho I) by in Atlantic sharpnose sharks between the Gulf of following the manufacturers' instructions. Restric Mexico and Mid-Atlantic Bight by using restriction tion fragments were separated on 1.0% horizontal fragment haplotypes ofmitochondrial DNA (mtDNA). agarose gels runat 2V/cm overnight, then transferred after electrophoresis to a nylon membrane by means of Southern transfer according to the protocols of Materials and methods Sambrook et a1. (1989), Filters were hybridized with highly purified mtDNAfrom tiger shark, Galeoeerdo Atlantic sharpnose sharks were collected with re cuvier, nick-translated with biotin-14-dATP, and vi search longlines in the Mid-Atlantic Bight (n=23) as sualized with the BRL BlueGene Nonradioactive part of an ongoing shark research program of the Nucleic Acid Detection System. Virginia Institute ofMarine Science, from the recre Fragment patterns were scored for each restric ational fishery of southern Texas (n=21) and from tion enzyme and each individual was assigned a com artisanal longline vessels from Veracruz, Mexico posite genotype based on the fragment patterns for (n=8) (Fig. 1). Heart tissue samples from Atlantic all enzymes (Tables 1 and 2). The nucleon (haplo sharpnose sharks caught in the Mid-Atlantic Bight type) diversity was calculated for each sample and were placed into cryovials and stored under liquid for the composite ofall samples following Nei (1987). nitrogen in the field. In Texas and Mexico, whole Nucleotide sequence diversity was calculatedfollow hearts were collected on wet ice and stored frozen at ing the site approach ofNei and Miller (1990). Chi (-20°C) until shipped to Virginia. All samples were square significance ofthe difference in genotypic fre stored at -70°C. quencies between samples was computed by using Mitochondrial DNA was isolated from tissue by the randomization protocol of Roff and Bentzen following the rapidisolation protocol ofChapman and (1989). Nucleotide sequence diversities and diver Powers (1983). Aliquots ofmtDNAwere digested with gences were calculated by using the REAP statisti ten restriction enzymes (Ava I, Ava II, Ban I, Bel I, cal analysis package (McElroy et aI., 1991). 666 Fishery Bulletin 94(4). 1996

Results Virginia Texas Veracruz

Ten restriction enzymes produced an average AAAAAAAAAA 14 14 4 of50 restriction fragments with a survey of288 base pairs (bp) or 1.74% ofthe 16.6 kb mtDNA AAAAAAABAA 0 0 molecule (Table 1). Seven haplotypes were de AAAAAAACAA 5 4 tected, resulting in a nucleon diversity of0.640 AAAAAAADAA 2 and an overall nucleotide sequence diversity AAAAAABAAA 0 0 (NSD) of0.13% (Table 2; Fig. 2). Four ofthe ten · restriction enzymes revealed multiple restric- · AAABAAAAAA tion patterns; one enzyme, Hpa I, detected four · BAAAAAAAAA - 0 0 different patterns. The single most common 23 21 B haplotype was found with similar frequencies in each sample and in each year within the At Figure 2 lantic sample (range=0.50-0.67), and three less Composite mtDNA haplotypes, inferred phylogenetic relation ships among haplotypes (vertical hatches represent restriction common haplotypes also occurred in all three site differences), and distribution of haplotypes in samples of geographic samples. Three rare haplotypes, Atlantic sharpnose shark, Rhizoprionodon terraenOlJae. Compos each found in a different individual, were ite haplotypes consist ofrestriction fragment patterns for the fol equally divided amongthe three samplingloca lowing enzymes (left to right): Ava I, Ava II, Ban I, Bel I, BstE II, tions. Each haplotype differed from the common Dra I, Hind III, Hpa I. Sca I. and ll.7w I. pattern by the gain or loss of a single restriction site (Fig. 2.) The chi-square probability of haplotype homogeneity among samples (Roff and Bentzen, 1989) was 0.694, indicating that the Table 2 samples could have been drawn from a single popu Nucleon diversity and percent nucleotide sequence diver sity in the Atlantic sharpnose shark, Rhizoprionodon lation ofmtDNAhaplotypes. The nucleotide sequence terraenovae. divergences between the three samples, corrected for within sample diversity, were all less than 0.01%. Nucleon Nucleotide Sample source diversity sequence diversity (%)

Virginia 0.597 0.120 Discussion Texas 0.538 0.105 Veracruz 0.788 0.175 The results of this study indicate that historically Total 0.640 0.133 there has been sufficientgene flow among sharpnose Heist et al.: Mitochondrial DNA diversity and divergence among Rhizoprionodon terraenovae 667 sharks from the Gulf of Mexico to the Mid-Atlantic neity in allele frequencies (Allendorf and Phelps, Bight to prevent significant divergence in mitochon 1981). Therefore fishery-relevant stocks canbemain drial DNA haplotypes. The frequencies of the most tained in the absence of statistically significant ge common alleles, as well as the occurrences of rare netic divergence. Furthermore, ifa single population alleles, were nearly identical in each of the three has recently diverged into multiple stocks, there may samples. The nucleon and nucleotide sequence di not have been sufficient time for a significant level versities were also similar among samples. The hy of genetic divergence to have become established. pothesis that Atlantic sharpnose sharks collected Perhapsby examininggenetic characters that evolve from locations as distant as Veracruz and Virginia more rapidly than whole mitochondrial DNA (such were members of a single homogeneous gene pool as direct sequencing ofthe mitochondrial control re could not be rejected. gion or microsatellite analysis) stock structure may The distribution of mtDNA haplotypes has been be eventually detected in this species. The only way, used previously to infer patterns ofgene flow in sev however, to determine the current level ofgene flow eral other commercially important shark species in in this species may be through a tag and recapture the GulfofMexico and southeastern (U.S.) Atlantic program. This information is necessary to determine coast (reviewed in Avise, 1992). Gene flow in fishes whether regional exploitation ofthis species will be is accommodated both by the active movement ofju compensated by immigration from other regions and veniles and adults, as well as by the passive move whether regional (state) regulations will be an effec ment of eggs and larvae. Significant differences in tive means ofconservation. mtDNAhaplotype frequencies have been detected in In orderto perform robusttests ofhypotheses con species with limited adult migration and demersal cerning gene flow in organisms, the markers used eggs (marine toadfishes, Opsanus spp.; Avise et aI., must have sufficient intraspecific variation so that 1987) as well as in those with pelagic eggs and lar differences in the frequencies of alleles can be as vae (black sea bass, Centropristis striata; Bowen and sessed between regions. The level of intraspecific Avise, 1990; and menhaden, Brevoortia spp., Bowen variation in the Atlantic sharpnose shark (NSD= and Avise, 1990). 0.13%)is considerably higher thanthe NSD of0.036% Sharpnose sharks are nektonic from the moment reported by Heist et al. (1995) in the sandbar shark, ofparturition; therefore, gene flow is accommodated Carcharhinus plumbeus, although lower than that only bythe active movements ofjuveniles and adults. detected by Heist et al. (1996) in the shortfin mako, Significant differences in haplotype frequencies were Isurus oxyrinchus (NSD=0.38%). Although the num detected in redfish (Scianops ocellatus; Gold et aI., ber of individuals surveyed in this study is small, 1993) of the Gulf of Mexico and southeast U.S. At the similaramount ofvariation detected within each lantic coast but not in the hardhead catfish (Arius sample and the close agreement in frequencies be felis; Avise et aI., 1987), two species with large active tween regions strongly suggest mtDNA haplotype adults but with presumably little passive transport homogeneity between sharpnose sharks ofthe Mid of eggs and larvae. In addition, Heist et al. (1995) Atlantic Bight and Gulf of Mexico. This study has detected no heterogeneity in mtDNA haplotype fre demonstrated that this small coastal shark, with no quencies in the sandbar shark, Carcharhinus passive larval transport, nevertheless exhibits plumbeus, over the same geographic range. mtDNA haplotype homogeneity across a broad geo In menhaden, the presence of two groups of ge graphic range. netically divergent mtDNA haplotypes in the Atlan tic was interpreted as indicating complete isolation of these two groups in the past, followed by a mix Acknowledgments ture of stocks with divergent mtDNA haplotypes (Bowen and Avise, 1990). The close relationships The authors wish to thank Shelton Applegate, among all haplotypes detected in the Atlantic Fernando. Farias, and Leonardo Castillo for help in sharpnose shark is consistent with the hypothesis obtaining samples from Mexico. Rocky Ward, Randy of a single evolutionary lineage with no historical Blankenship, and Ivonne Blandon provided samples subdivision. from Texas, and Captain J. A. "Tony" Penello and The lack ofgenetic divergence amongAtlantic and Steve Branstetter provided assistance in Virginia. GulfofMexico sharpnose sharks can not prove that This project was supportedbytheWallop Breaux pro separate stocks do not exist. An exchange rate of a gram of the U.S. Department ofInterior, U.S. Fish small number «20) of females per generation be and Wildlife Service, with additional funds distrib tween isolated breeding populations is enough to uted by the Virginia Marine Resources Commission prevent drift from establishing significant heteroge- of the Commonwealth ofVirginia. 668 Fishery Bulletin 94/4), J996

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