Résumé
Phylogeographic structure was investigated in the blue-spotted maskray,
Neotrygon kuhlii, focusing on the Coral Triangle region. We used as
genetic marker a 519-bp fragment of the cytochrome c-oxidase subunit I
(COI) gene, sequenced in a total of 147 individuals from 26 sampling
locations. The parsimony network of COI haplotypes was split into seven
distinct clades within the Coral Triangle region. Different clades had
exclusive but contiguous geographic distributions, indicating
parapatric-like phylogeographic structure. Strong genetic differences were
also inferred between local populations within a clade, where reciprocal
monophyly between geographically adjacent samples was observed on several
instances. Nearly 25% of the total molecular variance could be ascribed to
differences between geographic samples within a clade, whereas interclade
variation accounted for >65% of the total variance. The strong
phylogeographic structure observed within a clade can be explained by
either sedentarity or female philopatry. We interpret the parapatric
distribution of clades as the joint result of 1) expansion from refuge
populations at times of low sea level, and 2) possible enhanced
competition between individuals from different clades, or assortative
mating, or hybrid zones, along lines of secondary contact. The
parapatric-like structure uncovered in the present study parallels
regional differences at nuclear marker loci, thus pointing to incipient
speciation within Coral Triangle N. kuhlii.