First case of parthenogenesis in an intersexual zebra shark (Stegostoma tigrinum) having incomplete claspers.

Abstract

Parthenogenesis, where reproduction occurs without fertilization by a male, and intersexuality, where an individual exhibits both male and female characteristics, have occasionally been observed in elasmobranchs. Although parthenogenesis has been previously documented in zebra sharks (Stegostoma tigrinum), no individual with intersexuality has been reported. The female S. tigrinum [2060 mm total length (TL)], with incomplete claspers, laid 30 eggs in 2018 at the Osaka Aquarium NIFREL after 2 years and 5 months of monosex rearing. Embryonic development was confirmed in eight of these eggs, resulting in the successful hatching of one individual (253.8 mm TL). Its claspers exhibited incomplete external and internal structures, and its ovary contained scattered sperm duct-like structures without any evidence of spermatogenesis. Consequently, the present specimen was classified as having basic intersexuality. Furthermore, an analysis of 14 microsatellite loci in the hatching juvenile revealed complete maternal homozygosity across all loci, indicating parthenogenesis. This is the first report of parthenogenesis in an intersex individual. Our results play an important role in enhancing our understanding of the diversity of shark reproduction.