Abstract
We present genetic and morphometric support for a third, distinct, and recently diverged group of Manta ray that appears resident to the Yucatán coastal waters of the Gulf of Mexico. Individuals of the genus Manta from Isla Holbox are markedly different from the other described manta rays in their morphology, habitat preference, and genetic makeup. Herein referred to as the Yucatán Manta Ray, these individuals form two genetically distinct groups: (1) a group of mtDNA haplotypes divergent (0.78%) from the currently recognized Manta birostris and M. alfredi species, and (2) a group possessing mtDNA haplotypes of M. birostris and highly similar haplotypes. The latter suggests the potential for either introgressive hybridization between Yucatán Manta Rays and M. birostris, or the retention of ancestral M. birostris signatures among Yucatán Manta Rays. Divergence of the genetically distinct Yucatán Manta Ray from M. birostris appears quite recent (<100,000 YBP) following fit to an Isolation-with-Migration model, with additional support for asymmetrical gene flow from M. birostris into the Yucatán Manta Ray. Formal naming of the Yucatán Manta Ray cannot yet be assigned until an in-depth taxonomic study and further confirmation of the genetic identity of existing type specimens has been performed.
Highlights
The genus Manta currently comprises two recently re-described species, Manta alfredi (Krefft, 1868) and M. birostris (Walbaum, 1792), that occur circumglobally in tropical and subtropical seas (Marshall, Compagno & Bennett, 2009)
We argue that this supports M. birostris as the likely ancestral manta to Yucatán Manta Rays, with the likelihood of ongoing or recent interspecific gene flow between these two Manta groups
We propose that if the divergent Yucatán Manta Ray genetic group represents a truly distinctive species, the mechanisms driving this separation from the other two manta ray species are likely similar to the proposed ecological barriers that led to the separation between M. birostris and M. alfredi (Kashiwagi et al, 2012)
Summary
The genus Manta currently comprises two recently re-described species, Manta alfredi (Krefft, 1868) and M. birostris (Walbaum, 1792), that occur circumglobally in tropical and subtropical seas (Marshall, Compagno & Bennett, 2009). Recent genetic evidence supports Marshall, Compagno & Bennett (2009) morphological and ecological separation of M. birostris and M. alfredi (Kashiwagi et al, 2012). Several specimens visually identified in the field as M. alfredi (iv and v in Kashiwagi et al, 2012), separated out genetically as M. birostris. These anomalies indicate that visual identification is not as accurate as Marshall, Compagno & Bennett (2009) suggest. Using visual identification as the sole method for identification of Manta spp. is further complicated by their ability to display rapid (within minutes), reversible changes to their external color morphology, especially along the dorsal surface (Ari, 2014)
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