Gonzalez Cindy, Postaire Bautisse, Driggers William, Caballero Susana, Chapman Demian
Predator Ecology and Conservation Lab; Biological Sciences Department; Florida International University; 3000 NE 151 Street; MSB 350; North Miami; FL; 33181; USA.
Institut des Sciences de la Forêt Tempérée; Université de Quebec en Outaouais; Ripon; Québec; Canada. 58 Rue Principale; Ripon; QC J0V 1V0; Canada.
Zootaxa. 2024 Sep 23;5512(4):491-511. doi: 10.11646/zootaxa.5512.4.2.
Hammerhead sharks (Family Sphyrnidae) comprise a monophyletic Miocene radiation of carcharhiniform sharks characterized by their laterally expanded and dorsoventrally compressed head ('cephalofoil'). The bonnethead shark (Sphyrna tiburo) is currently described as a single amphi-American hammerhead species composed of the subspecies Sphyrna tiburo tiburo in the Western Atlantic Ocean (WA) and S. tiburo vespertina in the Eastern Pacific Ocean (EP). Variation in mitochondrial DNA and cephalofoil shape suggest a species complex, with S. tiburo occurring in the U.S., Mexico, and Bahamas; S. aff. tiburo occurring from Belize to Brazil; and S. vespertina occurring in the EP. Morphometric, meristic, and genetic variation was used to resolve the bonnethead shark complex in the Western Atlantic. Twenty-three specimens (12 S. aff. tiburo from Belize and 11 S. tiburo from U.S.) were subject to sixty-one morphometric measurements and three meristic characters (counts of the number of precaudal vertebrae, lower and upper rows of functional teeth). An allometric formula was used to standardize any effect caused by differences in size of the individuals and data were analyzed with univariate and multivariate statistics. Sphyrna aff. tiburo and S. tiburo have non-overlapping vertebral counts (80-83 and 71-74 respectively) but no morphometric differences were detected. Although not captured in morphometric analysis, the cephalofoil of S. aff. tiburo has a more pointed anterior margin than S. tiburo that together with lobule shaped posterior margins gives the cephalofoil a distinctive shovel-shaped appearance. Concatenated mitochondrial sequences and 12 nuclear microsatellite markers clearly separated S. aff. tiburo and S. tiburo. We conclude that this complex comprises two species in the Western Atlantic, S. tiburo and S. alleni sp. nov., and we provide a description of the latter, which is distinguished by precaudal vertebral counts (80-83), a shovel-shaped cephalofoil with rounded posterior margins, and robust differences in mitochondrial and nuclear genetic markers. We suggest nuclear genetic and meristic examination of EP bonnetheads is needed to update the taxonomical status and redescribe S. vespertina.
双髻鲨科（Sphyrnidae）包括中新世以来的一类单系群真鲨目鲨鱼，其特征是头部横向扩展且背腹扁平（“头翼”）。窄头双髻鲨（Sphyrna tiburo）目前被描述为一种分布于美洲两岸的单一双髻鲨物种，由西大西洋（WA）的窄头双髻鲨指名亚种（Sphyrna tiburo tiburo）和东太平洋（EP）的黄昏窄头双髻鲨（S. tiburo vespertina）组成。线粒体DNA和头翼形状的差异表明这是一个复合物种群，其中窄头双髻鲨分布于美国、墨西哥和巴哈马群岛；近似窄头双髻鲨（S. aff. tiburo）分布于伯利兹至巴西；黄昏窄头双髻鲨分布于东太平洋。利用形态测量、可数性状和遗传变异来解析西大西洋的窄头双髻鲨复合物种群。对23个标本（12个来自伯利兹的近似窄头双髻鲨和11个来自美国的窄头双髻鲨）进行了61项形态测量和3个可数性状（尾前椎骨数、功能性牙齿的下排和上排数量）的计数。使用异速生长公式来标准化个体大小差异所造成的任何影响，并运用单变量和多变量统计方法对数据进行分析。近似窄头双髻鲨和窄头双髻鲨的椎骨数不重叠（分别为80 - 83和71 - 74），但未检测到形态测量上的差异。尽管在形态测量分析中未体现，但近似窄头双髻鲨的头翼前缘比窄头双髻鲨更尖，其头翼后缘呈小叶状，使头翼呈现出独特的铲形外观。串联的线粒体序列和12个核微卫星标记清楚地将近似窄头双髻鲨和窄头双髻鲨区分开来。我们得出结论，这个复合物种群在西大西洋包括两个物种，即窄头双髻鲨和新物种艾伦双髻鲨（S. alleni sp. nov.），我们对后者进行了描述，其特征为尾前椎骨数（80 - 83）、后缘圆润的铲形头翼以及线粒体和核遗传标记上的显著差异。我们建议需要对东太平洋窄头双髻鲨进行核基因和可数性状检查，以更新其分类地位并重新描述黄昏窄头双髻鲨。
