Fire ant origins and genetics

The fire ant Wasmannia auropunctata is one of the most annoying things in the Solomon Islands. They have a very irritating and itchy bite, are so small as to be invisible, and they have a penchant for living in your underwear draw. Not pleasant. Unfortunately, they are another of the invasive species that have invaded the islands from elsewhere, in this case South America. They are found naturally through a large part of South America, from Argentina to the Caribbean islands. They have been introduced to a number of places, including Hawaii and the United States, Gabon in West Africa, and in the South Pacific both the Solomon Islands and New Caledonia.

To investigate where these ants came from, Alexander Mikheyev and Ulrich Mueller conducted a genetic study on a bunch of both natural and introduced populations of the fire ant. Looking at a little bit of the mitochondrial COI gene, they discovered that the Solomon Island populations have affinities with US and Hawaiian, and Northern South America and Caribbean populations. New Caledonian specimens were quite different, originating from southern natural populations in Argentina and Brazilian populations. Gabon has also been invaded by this group. This suggests that the two Pacific populations sampled were independantly derived, probably through trade or troop movements during WWII.

An assumption that I've usually made with invasive species in the Pacific is that they tend to do a bit of island-hopping, and in this case I would've hypothesised that the New Caledonian and Solomon Island populations would be the same. This is obviously not the case here, and it is a reminder that it's worth keeping in mind that there are many ways for organisms to get from place to place.

References:
Mikheyev AS, Mueller UG. 2007. Genetic relationships between native and introduced populations of the little fire ant Wasmannia auropunctata. Diversity and Distributions 13:573-579.