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Marine Turtle Newsletter 89:20-22, © 2000

Marine Turtle Newsletter-Online

Meeting Report: Taxonomic Status of the East Pacific Green Turtle (Chelonia agassizii)

Brian W. Bowen1 & Stephen A. Karl2
1Department of Fisheries and Aquatic Sciences and Archie Carr Center for Sea Turtle Research, University of Florida, Gainesville, FL 32653 (E-mail: bowen@gnv.ifas.ufl.edu)
2Department of Biology, SCA 110, University of South Florida, Tampa, FL 33620 (E-mail: karl@chuma.cas.usf.edu)

Most of the uncertainties about sea turtle systematics and taxonomy have been resolved in the last 15 years, due to rigorous morphological, biochemical, and genetic assessments (see Bowen & Karl 1996; Dutton et al. 1996; and references therein). Perhaps the sole exception, and the last frontier in sea turtle taxonomy, is the status of the black turtle or East Pacific green turtle. To address this issue, a colloquium was held at the Annual Symposium on the Biology and Conservation of Sea Turtles (Feb. 29-March 4, 2000). The debate over taxonomy of the black turtle has been revitalized in recent years by the infusion of genetic data, the dire conservation status of the black turtle, and the publication of a forum in Conservation Biology (13:990-1016).

Opinions range from retention of species status to the possibility that this is a melanistic population (or group of populations) of Chelonia mydas. Here, we provide a summary of the conclusions from each presentation. The detailed arguments for each position are presented elsewhere (Bowen & Karl 1996, Carr 1961; Dutton et al. 1996; Figueroa & Alvarado 1991; Kamezaki & Matsui 1995; Karl & Bowen 1999; Mrosovsky 1983; Parham & Zug 1996; Pritchard 1996; Pritchard 1999; and references therein).

Presentations in this forum included the following:
B.W. Bowen (moderator): opening remarks.
P.C.H. Pritchard: Taxonomy and classification of the black turtle.
N. Kamezaki & K. Kuroyanagi: Morphology and osteology of Chelonia.
S.A. Karl & B. W. Bowen: Evolutionary genetics of Chelonia.
J. Alvarado & C. Delgado. Ecological and behavioral aspects of the black turtle (NB Presented by Jeff Seminoff)
P.A. Meylan: Systematics of green turtles, a phylogenetic perspective

Pritchard has consistently championed the species status of the black turtle. After presenting a review of the taxonomic history of C. agassizii, he cautioned against reassignment of the black turtle to subspecific status until more information is available. Until then, he argued that the current binomial assignments should take precedence. Pritchard also developed two themes that would emerge in several presentations: First, that reproductive isolation is the most important test of species status; and second, that the black turtle could be an emerging species, undergoing divergence in a peripheral, atypical habitat. Finally, Pritchard warned against over-reliance on lab machinery and modern technology in lieu of traditional classification and field observations.

Kamezaki and colleagues have previously advocated subspecies status for the black turtle based on cranial morphology. New data and ongoing studies of shell morphology, however, prompt the authors to tentatively support species status.

Karl and Bowen have maintained that the genetic differentiation of the black turtle is typical of populations, rather than species. We recognize, however, that this may be an incipient evolutionary entity.

Alvarado and colleagues have previously supported the species status of the black turtle, based on morphological considerations. Here Alvarado and Delgado raise the possibility of significant differences in ecology, reproductive biology, and trophic specialization that distinguish the black turtle from the green turtle. Furthermore, these authors emphasized that taxonomic issues are secondary to concerns about the dire decline of East Pacific populations.

Meylan, using a survey of available phylogenetic data, noted that if the black turtle is a valid subspecies, then several other regional aggregates of C. mydas might qualify as subspecies. He also pointed out the most prominent gaps in morphological and genetic assessments, and developed the recurrent theme that phylogenetic information on the Chelonia group is fragmentary at present.

Elsewhere in the Sea Turtle Symposium, Omar Chassin Noria and colleges presented new data on mitochondrial DNA differentiation of East Pacific turtles. These authors concluded that the genetic data do not support species status for the black turtle.

Following the presentations there was an open discussion by the speakers and attendees. Several people reiterated the need to collect phylogenetic data across the range of Chelonia. Particular emphasis should be placed on under-sampled regions. The need to share data across geopolitical boundaries also was emphasized.



Table 1. Results of attendee voting on the taxanomic status of the black turtle.

At the end of the presentations, ballots were distributed to determine the opinions of attendees. The results of voting indicate that a majority considers the black turtle to be either a population or a subspecies (Table 1). However, if we remove the half dozen ballots from our close associates (e.g., students, spouses, and collaborators), the results are approximately a three-way tie. A consensus clearly does not currently exist. There was a broad agreement, however, on two issues.

First, the black turtle is unique in some respect and is likely to be an emerging evolutionary lineage. Second, the taxonomic debate will be moot if population declines continue.

Acknowledgements: We thank the invited speakers and participants for making the colloquium a success. Jeff Seminoff filled in for Javier Alvarado at short notice, who being refused entry to the US was unable to attend the symposium. Thanks to the Florida Sea Turtle Protection Program, especially Blair Witherington and Allen Foley, for making this colloquium possible.

BOWEN, B.W. & S.A. KARL. 1996. Population structure, phylogeography, and molecular evolution. pp. 29-50 in P.L. Lutz and J.A. Musick, Editors. The Biology of Sea Turtles, CRC Press, Boca Raton, FL

CARR, A.F. 1961. Pacific turtle problem. Natural History 70:64-71.

DUTTON, P.H., S.K. DAVIS, T. GUERRA & D. OWENS. 1996. Molecular phylogeny for marine turtles based on sequences of the ND4-leucine tRNA and control regions of mitochondrial DNA. Molecular Phylogenetics and Evolution 5:511-521.

FIGUEROA, A. & J. ALVARADO. 1991. Morphometric comparison of the Chelonia populations of Michoacan, Mexico and Tortuguero, Costa Rica. NOAA Technical Memo. (NMFS-SEFC) 278:179-182.

KAMEZAKI, N. & M. MATSUI. 1995. Geographic variation in the skull morphology of the green turtle, Chelonia mydas, with a taxonomic discussion. Journal of Herpetology 29:51-60.

KARL, S.A. & B.W. BOWEN. 1999. Evolutionary significant units versus geopolitical taxonomy: molecular systematics of an endangered sea turtle (genus Chelonia). Conservation Biology 13: 990-999.

MROSOVSKY, N. 1983. Conserving sea turtles. British Herpetological Society, London.

PARHAM, J.F. & G.R. ZUG. 1996. Chelonia agassizii - valid or not? Marine Turtle Newsletter. 72:2-5.

PRITCHARD, P.C.H. 1996. Evolution, phylogeny, and current status. Pages 1-28 in P. L. Lutz and J. A. Musick, Editors. The Biology of Sea Turtles, CRC Press, Boca Raton, FL.

PRITCHARD, P.C.H. 1999. Status of the black turtle. Conservation Biology 13:1000-1003.