Does social structure drive genetic structure in Hawaiian spinner dolphins?

Map of the Hawaiian Archipelago with locations highlighted in pink where spinner dolphins regularly occur.

Social structure varies across the Hawaiian Archipelago for spinner dolphins: they have small populations (~100-300 dolphins) and high group stability in the far-northwestern Hawaiian Islands (Kure, Midway, and Pearl & Hermes), but they have larger population (~600 dolphins) and more fluid groups at the Big Island of Hawai‘i. We investigated the population genetic structure of spinner dolphins across the Hawaiian Archipelago, and, surprisingly, found evidence for high gene flow between the islands with stable groups (the far-northwestern islands), but limited gene flow to or from the island with the fluid social groups (Big Island ). High dispersal between the islands with strong group stability may be driven by evolutionary pressures to avoid inbreeding in very small populations.
To read more about this work, check out our publication:

Andrews KR, L Karczmarski, WWL Au, SH Rickards, CAVanderlip, BW Bowen, E Gordon Grau, RJ Toonen. 2010. Rolling stones and stable homes: Social structure, habitat diversity, and population genetics of the Hawaiian spinner dolphin (Stenella longirostris). Molecular Ecology 19:732-748.


Do ocean currents drive population structure in deepwater fish?


Map of the Hawaiian Archipelago and Johnston Atoll. The arrow illustrates larval dispersal from Johnston Atoll to the mid-archipelago.

Ocean currents are likely to play a major role in shaping the population genetic structure of fish by dispersing their larvae. To test this hypothesis for deepwater fish, we conducted population genetic analyses and oceanographic modeling of larval dispersal for three deepwater fish species across the Hawaiian Archipelago (“Ehu” Etelis marshi, “Onaga” Etelis coruscans, “Hawaiian grouper” Hyporthodus quernus). Genetic analyses indicated overall high connectivity across the Hawaiian Archipelago for all three fish species. However, a region in the middle of the archipelago (Gardner to Necker) had genetically distinct populations and/or high genetic diversity for all three fish. Our analyses indicated this pattern is likely driven by larval transport on ocean currents from Johnston Atoll, which is the closest landmass to Hawai‘i (~800km south).
To read more about this work, check out our publications:

Andrews KR, V Moriwake, C Wilcox, EG Grau, C Kelley, RL Pyle, BW Bowen. 2014 Phylogeographic analyses of submesophotic snappers Etelis coruscans and Etelis “marshi” (Family Lutjanidae) reveal concordant genetic structure across the Hawaiian Archipelago. PLoS ONE 9(4)e91665

River, MAJ,* Andrews KR*, D Kobayashi, J Wren, C Kelley, GK Roderick, RJ Toonen. 2011. Genetic analyses and simulations of larval dispersal reveal distinct populations and directional connectivity across the range of the Hawaiian Grouper (Epinephelus quernus). Journal of Marine Biology 2011: Article ID 765353. *Equal contribution


What ecological factors control gene flow in holoplankton?

Haloptilus longicornis. Photo credit: Emily Norton and Michelle Jungbluth

We might expect extensive gene flow across wide geographic areas for holoplanktonic species, because they spend their entire lives in the plankton, where ocean currents can disperse individuals widely and prevent the formation of isolated groups. However, our population genetic analyses found distinct populations separated by equatorial waters for the holoplanktonic copepod H. longicornis. Equatorial waters have high overall productivity, and we suspect these high productivity waters are poor habitat for this species, so that most individuals that enter these waters die. In this way, equatorial waters act as a barrier to gene flow, resulting in the presence of distinct populations on either side of the equator across the globe.

To read more about this work, check out our publication:

Andrews KR, E Norton, I Fernandez-Silva, E Portner, E Goetze. 2014. Multilocus evidence for globally-distributed cryptic species and distinct populations across ocean gyres in a mesopelagic copepod. Molecular Ecology 23(22):5462-79.