More than a single species: Aetobatus Narinari

Results from a recent study suggests that one vulnerable species, Aetobatus narinari, may in fact constitute a species complex (a monophyletic group of similar species that do not differ enough from others in the genus to warrant separation at the the genus or subgenus level).





The Spotted Eagle Ray is a is a large, coral-reef dwelling batoid which is currently causing conservation concern. As a species, it has relatively low recruitment and is subject to intense and unregulated inshore fisheries. It is therefore considered highly vulnerable to sustained harvest. Currently, it is classified as a single, circumglobally distributed species. However, results from this study reveal that A. narinari is composed of at least 3 distinct lineages, with no genetic exchange among individuals from the Central Atlantic, Eastern Pacific, and Western/Central Pacific regions. These findings support the recognition of at least 2 distinct species within "A. narinari" and 2 lineages that should arguably be provided subspecies status.

The experiment obtained tissue samples from 36 A. narinari individuals from globally distributed regions. Aetobatus flagellum obtained from Ariake Bay, Japan, was used as an outgroup for intraspecifit phylogenetic analysis. The genomic DNA from the samples was amplified and sequenced using the Polymerase Chain Reaction and DNA Sequencing, and the data was analysed using computer software. Evolutionary relationships between the individuals were then estimated by constructing unrooted statistical parsimony networks for each locus using the Templetion et all. method as implemented in the software package TCS version 1.13 (more computer software). Phylogenetic analyses were conducted on concatenated mitochondrial and nuclear sequence data sets to further explore the evolutionary relationships among the A. narinari sequences. To assess the genetic divergence thresholds that might be informative for species delineation, divergence between the 3 major A. narinari phylogeographic lineages obtained (Western/Central Pacific, Eastern Pacific, and Central Atlantic) were compared with that between other taxonomically uncontested batoid and shark congener pairs. A likelihood ratio test was also performed to test for the existence of a molecular clock on the A. narinari data sets.

The study utilised a combination of genealogical concordance and genetic distance criteria to delineate the globally distributed species of A. narinari into at least 2 distinct species. One species was found to range through the Western and Central Pacific, while the other was found to range the Central Atlantic and the Eastern Pacific. The latter species was further divided into 2 subspecies separated by the Isthmus of Panama. These findings not only providing taxonomic clarification and insight into evolutionary history, but they also have direct management implications. The reduced population sizes and ranges of the delineated species reinforce concerns about the already threatened and vulnerable status of the Spotted Eagle Ray.

Submitted by 41714805.

Source: Richards, VP, Henning, M, Witzell, W, Shivji, MS 2009, 'Species delineation and evolutionary history of the globally distributed Spotted Eagle Ray (Aetobatus narinari)',
Journal of Heredity, vol. 100, no. 3, pp. 273-283, viewed 20 May 2009,

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