Phylogeography of the Indo-West Pacific maskrays (Dasyatidae, Neotrygon): a complex example of chondrichthyan radiation in the Cenozoic

Maskrays of the genus Neotrygon (Dasyatidae) have dispersed widely in the
Indo-West Pacific being represented largely by an assemblage of narrow-ranging
coastal endemics. Phylogenetic reconstruction methods reproduced nearly identical
and statistically robust topologies supporting the monophyly of the genus
Neotrygon within the family Dasyatidae, the genus Taeniura being consistently
basal to Neotrygon, and Dasyatis being polyphyletic to the genera Taeniurops
and Pteroplatytrygon. The Neotrygon kuhlii complex, once considered to be an
assemblage of color variants of the same biological species, is the most derived
and widely dispersed subgroup of the genus. Mitochondrial (COI, 16S) and
nuclear (RAG1) phylogenies used in synergy with molecular dating identified
paleoclimatic fluctuations responsible for periods of vicariance and dispersal
promoting population fragmentation and speciation in Neotrygon. Signatures of
population differentiation exist in N. ningalooensis and N. annotata, yet a largescale
geological event, such as the collision between the Australian and Eurasian
Plates, coupled with subsequent sea-level falls, appears to have separated a once
homogeneous population of the ancestral form of N. kuhlii into southern
Indian Ocean and northern Pacific taxa some 4–16 million years ago. Repeated
climatic oscillations, and the subsequent establishment of land and shallow sea
connections within and between Australia and parts of the Indo-Malay Archipelago,
have both promoted speciation and established zones of secondary contact
within the Indian and Pacific Ocean basins.

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