Phylogeography of Mesophotic Coral Ecosystems: Squirrelfish and Soldierfish (Holocentriformes: Holocentridae)

Mesophotic coral ecosystems (MCEs: similar to 30 to 100+ m depth) may be older and more stable than shallow coral ecosystems that are more prone to disturbances in both the long term (glacial sea level cycles) and short term (heavy weather and anthropogenic activities). Here, we assess the phylogeography of two MCE fishes, the soldierfish Myripristis chryseres (N = 85) and the squirrelfish Neoniphon aurolineatus (N = 74), with mtDNA cytochrome oxidase C subunit I. Our goal is to resolve population genetic diversity across the Central and West Pacific and compare these patterns to three shallow-reef species in the same taxonomic family (Holocentridae). Significant population structure (phi(ST) = 0.148, p = 0.01) was observed in N. aurolineatus, while no structure was detected in M. chryseres (phi(ST) = -0.031, p = 0.83), a finding that matches the shallow-water congener M. berndti (phi(ST) = -0.007, p = 0.63) across the same range. Nucleotide diversity in the MCE fishes was low (pi = 0.0024-0.0028) compared to shallow counterparts (pi = 0.003-0.006). Coalescence times calculated for M. chryseres (similar to 272,000 years) and N. aurolineatus (similar to 284,000 years) are more recent or comparable to the shallow-water holocentrids (similar to 220,000-916,000 years). We conclude that the shallow genetic coalescence characteristic of shallow-water marine fishes cannot be attributed to frequent disturbance. We see no evidence from holocentrid species that MCEs are older or more stable habitats.