MEPS 437:269-277 (2011)  -  DOI: https://doi.org/10.3354/meps09248

ABSTRACT: Most coral reef fishes have non-migratory adults and depend on a pelagic larval stage for dispersal. Species with long pelagic larval duration (PLD) can have tremendous dispersal potential and thus display little geographic-genetic differentiation among reef habitats. Restricted adult niche breadth due to habitat specialization can have the opposite effect of fragmenting populations and increasing geographic-genetic differentiation. If long PLD suffices to ensure widespread gene flow among reef populations, we predict similar geographic-genetic homogeneity within species whose adults differ in niche breadth. We tested this hypothesis using a comparative phylogeographic study of 4 sympatric moray eel species that differ in the amount of available habitat within their reported ranges. We generated molecular genetic data for Echidna nebulosa (N = 79) and Gymnomuraena zebra (N = 67) to measure geographic-genetic structure within these species, whose adult habitat is very restricted for moray eels, and compared these results to identical measurements previously published for habitat generalists Gymnothorax undulatus and Gymnothorax flavimarginatus. These 4 species share an ocean-wide distribution with adults occupying the same reefs; however, adults of E. nebulosa and G. zebra are restricted to shallow waters and occupy only 20% of the area occupied by the Gymnothorax species. Mitochondrial (632 bp of cytochrome b and 596 bp of cytochrome oxidase I) genomic sequences revealed high genetic variation (h = 0.995 to 0.998) and low geographic-genetic differentiation (pairwise Φ_ST < 0.07 and not significant) for each species across 22000 km of the Indo-Pacific. Nuclear genomic sequences (420 bp of RAG-1 and 746 bp of RAG-2) demonstrated 16 to 25 haplotypes per marker within each species with minimal geographic-genetic differentiation among populations. This suggests that in cosmopolitan and highly dispersive species such as morays, larval life history can ensure widespread gene flow despite a 5-fold difference in the habitat breadth occupied by adult populations.

KEY WORDS: Gene flow · Phylogeography · Connectivity · Reef fish · Leptocephalus · Moray eel