Comparative phylogeography of four Indo-Pacific moray eel species (Muraenidae) reveals comparable ocean-wide genetic connectivity despite five-fold differences in available adult habitat

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 homogene- ity within species whose adults differ in niche breadth. We tested this hypothesis using a compar- ative 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 iden- tical measurements previously published for habitat generalists Gymnothorax undulatus and Gymnothorax flavimarginatus. These 4 species share an ocean-wide distribution with adults occu- pying 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 vari- ation (h = 0.995 to 0.998) and low geographic-genetic differentiation (pairwise ΦST < 0.07 and not significant) for each species across 22 000 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 wide- spread gene flow despite a 5-fold difference in the habitat breadth occupied by adult populations.