My Mom is a Green Sea Turtle, and my Dad is a Loggerhead!

         

          During our awesome class field trip to the South Carolina Aquarium Sea Turtle Hospital a peculiar chart caught my eye. It was a bar graph, organized by species along the X-axis illustrating the number of successful sea turtles releases. Though I do not fully recollect the actual number of released turtles from each species, I do remember the Loggerhead Sea Turtle and the Green Sea Turtle were the most common visitors to the hospital. However, it wasn’t the amazing amount of successful releases this incredible institution preformed that drew my attention. It was the category on the bar graph that was labeled by a very peculiar species name; the species was entitled “Other”. In all my years of profound interest in herpetology, I had never run across any “Other” Sea Turtles, so I had to inquire more about what this meant. It turns out the South Carolina Aquarium Sea Turtle Hospital had been visited by a few hybrid sea turtles.

            I found this to be extremely interesting and my lack of knowledge of this subject inspired me to do further research on the hybridization sea turtles. In the Journal of Heredity I came across an article entitled “Hybridization Among the Ancient Mariners: Characterization of Marine Turtle Hybrids With Molecular Genetic Assays”. The hybridization of marine sea turtles isn’t a recent phenomenon; there have been alleged recorded sightings of hybrid sea turtles dating back to the 19^th century. However, advancements in molecular and DNA genetic analyses have only been applicable in the last half century. Furthermore, the endangered status of every species of marine sea turtle has made it challenging to formulate any comprehensive scientific data on these hybrid turtles. Thus this study, orchestrated and developed by S. A. Karl, B. W. Bowen, and J. C. Avise, poses as very informative basis for this area of study.

            This study was essentially a collection of blood and tissue from juvenile sea turtles that resembled intermediates between sea turtle species. Then they assessed the mitochondrial genotype of these samples and compared it to the known fragment patterns of the six Cheloniid species. This study resulted in the confirmation of hybrid crosses of Chelonia X Caretta (Green Sea turtle and Loggerhead Sea turtle), Caretta X Eretmochelys (Loggerhead and Hawksbill), Caretta X Lepidochelys (Loggerhead and Kemps Ridely), and Chelonia X Eretmochelys (Green and Hawksbill).

            Hybridization isn’t an exclusive ability in Sea Turtles. There are hybridizations found in different mammalian species, other reptiles, as well as amphibians. However, this proof of sea turtle hybridization could potentially be recognized as the oldest natural hybridization of vertebrate lineages. The phylogenetic divergence of Caretta caretta and Eretmochelys imbricata is estimated to be over 50 million years ago.

How this event occurs and why it occurs is not yet fully understood. What has been further hypothesized from this study is that this phenomenon will typically occur between species that have an overlap of mating grounds. For example, the Green Sea Turtle and Loggerhead Sea Turtle have common mating grounds witnessed off the coast of Brazil. In this study all of the confirmed hybrid crosses between Green and Loggerhead Sea Turtles were found in this area off Brazil.  It is further hypothesized that it is typically the larger species in the hybridization that puts forth the male contributor. This is because it is assumed that a male’s inability to mount a mate of his or her own species would drive him to seek a smaller sea turtle as a potential mate.

This concept of hybridization in sea turtles is extremely intriguing to me. This study further provides proof not only that hybridization in sea turtles is possible, but also that it is a natural occurrence. This study also sets a foundation for future studies in this subject area. I do hope to see further information on this unique ability in the future, yet I do understand the limitations to preforming significant studies on these endangered species. However, studies on the breeding behavior of sea turtles may spark solutions for increasing their future populations. As a developing herpetologist and an inhabitant of this earth, I do hope these majestic reptiles continue to exist on this plant for centuries to come

Here is the link to the study if anybody wants to check it out: http://www.seaturtle.org/pdf/KarlSA_1995_JHered.pdf