Unexpected Patterns of Global Population Structure in Melon-Headed Whales (Peponocephala electra)

Foraging specialization, environmental barriers, and social structure have driven the development of strong genetic differentiation within many marine species, including most of the large dolphin species commonly referred to as ‘blackfish’ (subfamily Globicephalinae).  We used mitochondrial sequence data (mtDNA) and genotypes from 14 nuclear microsatellite loci (nDNA) to examine patterns of genetic population structure in melon-headed whales (MHWs, Peponocephala electra), a poorly known member of the blackfish family for which genetic structuring is unknown.  MHWs are globally distributed in tropical and subtropical waters, and have formed resident populations around oceanic islands.  They frequently mass strand, suggesting strong social cohesion within groups.  Based on these characteristics, we hypothesized that MHWs would exhibit strong regional genetic differentiation, similar to that observed in other members of the Globicephalinae subfamily.  Instead we found only moderate differentiation (median mtDNA ΦST = 0.204, median nDNA FST = 0.012) among populations both within and between ocean basins.  Our results suggest that populations of MHWs that are resident to oceanic islands maintain a higher level of genetic connectivity than is seen in most other blackfish. MHWs may be more behaviorally similar to delphinids from the Delphininae subfamily (particularly the spinner dolphin, Stenella longirostris), which are known to form coastal and island-associated resident populations that maintain genetic connectivity either through occasional long-distance dispersal or gene flow with larger pelagic populations.  Our results suggest that differences in social organization may drive different patterns of population structure in social odontocetes.

Citation:

Martien, K.K., B.L. Hancock-Hanser, R.W. Baird, J.J. Kiszka, J.M. Aschettino, M. Oremus, and M.C. Hill. 2017. Unexpected Patterns of Global Population Structure in Melon-Headed Whales (Peponocephala electra). Marine Ecology Progress Series 577: 205-220. doi: 10.3354/meps12203