1Marine Biodiversity Division, ICAR- Central Marine Fisheries Research Institute, Kochi, Kerala, India
2Kanyakumari Turtle NEWS Club, Palapetty, Thrissur, Kerala, India
A clutch of 126 olive ridley (Lepidochelys olivacea) turtle eggs was laid at Palapetty Beach, Thrissur District, Kerala on 15th January 2016 and relocated by members of the Kanyakumari Turtle NEWS Club to the hatchery at Palapetty. On 02ndMarch 2016, after 46 days of incubation, 58 hatchlings emerged from the nest unaided in the early morning. The nest was excavated three hours after emergence of the first hatchling, at which time 14 more hatchlings emerged from the exposed egg including two pairs of twins (Table 1; for example see Figure 1) which emerged from the eggshells on their own. The hatchlings were transported to a holding tank 15min post-hatching. The twin hatchlings were unable to remain afloat and their movement on land was also impaired as they remained connected by the respective yolk sacs. The first pair of twin hatchlings died half an hour after hatching, while the second pair of twins survived for six hours. Four other hatchlings which emerged from the exposed eggs died before being introduced to the holding tank. The surviving hatchlings were released to sea approximately nine to thirteen hours after hatching.
Twinning is a rare phenomenon amongst sea turtles, and aberrant embryos usually die before the pipping stage or even if they pip, seldom emerge (Miller, 1985). This is the first published report of twin sea turtle hatchlings being alive at pipping, although Hewavisenthi (1989) described a single hatchling leatherback turtle (Dermochelys coriacea) that emerged live from the egg after its smaller twin died prior to term. Twin embryos that did not reach the pipping stage have been recorded in olive ridley (Hewavisenthi, 1990), green (Chelonia mydas; Fowler, 1979; Kaska & Downie, 1999; Diong et al., 2003), hawksbill (Eretmochelys imbricata; Junchompoo et al., 2013), leatherback (Deraniyagala ,1930, 1932; Hughes et al., 1967; Chan, 1985; Eckert, 1990) and loggerhead (Caretta caretta; (Caldwell, 1959; Fujiwara, 1964; Blanck & Sawyer, 1981; Limpus, 1985, Peters et al., 1994; Piovano et al., 2011) turtles.
The twin hatchlings found in this study were of nearly equal size, but much smaller in comparison to the other hatchlings in the clutch, perhaps the result of having to share the resources available in the egg. No external developmental abnormalities were observed.
Fertilisation of sea turtle eggs occurs in the oviduct, with the deposition of albumin and formation of egg shell beginning within 72 hours of ovulation. Over the successive seven days, the zygote undergoes discoidal meroblastic cleavage to form a gastrula by Day 9; embryonic development is suspended at middle gastrulation until after the eggs are laid (Miller, 1982). Whether the formation of twins took place by the inclusion of two zygotes in one eggshell in the oviduct post-fertilisation and pre-oviposition, or due to cleavage of one zygote into two within an egg post-fertilisation is beyond the scope of this study and would require parental DNA investigations to ascertain.
Both pairs of twin hatchlings were deposited in the National Designated Repository of the Central Marine Fisheries Research Institute, Kochi, Kerala, India and have been assigned the accession number Lepidochelys olivacea Misc.38.
The authors would like to thank Dr. A. Gopalakrishnan, Director, ICAR-Central Marine Fisheries Research Institute, Kochi for his support for the study, all individuals associated with the Kanyakumari Turtle NEWS Club, Palapetty, for their efforts towards locating the nesting site and running of the Palapetty hatchery, and The Kerala Forests and Wildlife Department, GoI, and Shri Ravi Panakkal of NEWS India for support and encouragement during the conservation activities and field study.
Blanck, C.F. & R.H. Sawyer. 1981. Hatchery practices in relation to early embryology of the loggerhead sea turtle, Caretta caretta (Linné). Journal of Experimental Marine Biology and Ecology 49: 163–177.
Caldwell, D.K. 1959. The loggerhead turtles of Cape Romain, South Carolina. Abridged and annotated. Bulletin of the Florida State Museum 4: 319–348.
Chan, E.H. 1985. Twin embryos in unhatched egg of Dermochelys coriacea. Marine Turtle Newsletter 32: 2–3.
Deraniyagala, P.E.P. 1930. The Testudinata of Ceylon. Ceylon Journal of Science B 16: 43–88.
Deraniyagala, P.E.P. 1932. Notes on the development of the leathery turtle, Dermochelys coriacea. Ceylon Journal of Science B 17: 73–102.
Diong, C.H., L.K.A. Tan & C.M.U. Leh. 2003. Axial bifurcation in a bicephalic Chelonia mydas embryo. Chelonian Conservation and Biology 4: 725–727.
Eckert, K.L. 1990. Twinning in leatherback sea turtle (Dermochelys coriacea) embryos. Journal of Herpetology 24: 317–320.
Fowler, L.E. 1979. Hatching success and nest predation in the green sea turtle, Chelonia mydas, at Tortuguero, Costa Rica. Ecology 60: 946–955.
Fujiwara, M. 1964. Some cases of spontaneous twinning in the loggerhead turtle. Acta Herpetologica Japonica 2: 7–8.
Hewavisenthi, S. 1989. Twin green turtle hatchlings in Sri Lanka. Marine Turtle Newsletter 46: 9.
Hewavisenthi, S. 1990. Abnormal hatchlings of green and olive ridley turtles, Victor Hasselblad Hatchery, Sri Lanka. Marine Turtle Newsletter 50: 15–16.
Hughes, G.R., A.J. Bass & M.T. Mentis. 1967. Further studies on marine turtles in Tongaland II. The Lammergeyer 7: 5-54.
Junchompoo, C., C. Penpian & W. Tarkoolrangsi. 2013. First report of twinning in the hawksbill sea turtle (Eretmochelys imbricata) from Khram Island, Chonburi Province, Thailand. In: Proceedings of the Design Symposium on Conservation of Ecosystem (The 12th SEASTAR2000 workshop 2013). Pp 17-20.
Kaska, Y. & R. Downie. 1999. Embryological development of sea turtles (Chelonia mydas, Caretta caretta) in the Mediterranean. Zoology in the Middle East 19: 55–69.
Limpus, C.J. 1985. A study of the loggerhead turtle, Caretta caretta, in eastern Australia. Ph.D. thesis. University of Queensland, Brisbane, Australia.
Miller, J.D. 1982. Development of marine turtles. Ph.D. thesis. University of New England, Armidale, Australia.
Miller, J.D. 1985. Embryology of marine turtles. In: Biology of the Reptilia: Development A. Volume 14. (eds. Gans C, F. Billet & P.F.A. Maderson). Pp 269-328. John Wiley & Sons, New York, USA.
Peters, A., K.J.F. Verhoeven & H. Strijbosch. 1994. Hatching and emergence in the Turkish Mediterranean loggerhead turtle, Caretta caretta: natural causes for egg and hatchling failure. Herpetologica 50: 369–373.
Piovano, S., Y. Kaska, E. Prazzi, S. Nannarelli & C. Giacoma. 2011. Low incidence of twinning in the loggerhead sea turtle. Folia Zoologica 60: 159–166.
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