Defining the genetics of the widely used G3 strain of the mosquito, Anopheles gambiae

Mosquito species in the Anopheles gambiae complex have been referred to as "the deadliest animals in the world" due to their role as vectors of malaria throughout sub-Saharan Africa. Consequently, An. gambiae was among the first species to have its whole genome sequenced in 2002 and it continues to be the subject of intense study. An. gambiae is one member of a nine member species complex and, along with its sister species, An. coluzzii, is among the most important vectors of human malaria. Laboratory research on malaria vectors across a broad range of disciplines utilizes a strain known as G3, which was established in 1975 from mosquitoes collected from McCarthy Island, The Gambia. This strain is well known to be a mongrel strain, nonetheless it is often referred to as An. gambiae, which it is not. The issue with G3 goes far beyond the typical inbreeding associated with long-standing laboratory colonies. G3 is an An. gambiae/An. coluzzii interspecific hybrid. Although these two species are known to hybridize in nature, the pattern of interspecific introgression in G3 we describe in this paper is unlike any observed in natural populations. In this report we provide an in-depth analysis of the genetics of the G3 strain and compare it with natural populations of its two parental species. We discuss potential concerns that results obtained from research using the G3 strain may not apply to populations of these mosquito species as they occur in nature.