New insights into the evolution of clonality and its implications on southern range expansion in native populations of the little fire ant

CHIFFLET, L.; CALCATERRA, L. A.; CONFALONIERI, V.

Curitiba, Paraná, Brasil

Simposio; XXIII Simpósio de Mirmecología, An International Ant Meeting; 2017

Universidad Federal de Paraná

The little fire ant, Wasmannia auropunctata, is native form the Neotropics and has became invasive outside its native range. This ant species most probably originated in central Brazil and then each of two clades, A and B, expanded northward and southward respectively. There is evidence that during the last 50 years clade B suffered a recent southern expansion presumably mediated by human activity, reaching central Argentina. This ant species also exhibits a polymorphism in its reproductive system, in which queens and males of introduced populations and anthropic habitats are mostly produced clonally while in native populations they can reproduce either sexually (mostly in natural environments) or clonally (in anthropic environments). Here we evaluated if clonality is associated to the recent range expansion of clade B, since all the populations within the southernmost limit of native distribution are established in anthropic habitats. We amplified 12 microsatelite loci by PCR multiplex from a total of 194 reproductive individuals (185 females and 9 males) from 101 nests in 37 sites with different degree of disturbance (e.g. primary forests, floodplains and human disturbed habitats) in southern South America and inferred the reproductive system of each population using GeneClone v.2.0 software. We combined our dataset with the one of Foucaud et al. (2009) who analysed 17 sites from northern South America, having a total dataset of 54 sites/populations. Clonality was the most common reproductive system, occurring in 38 of 54 sites, mostly in human disturbed habitats. All the populations present along the recently colonized area were clonal, suggesting an association between clonality and the southern range expansion suffered by the little fire ant during the last 50 years. Floodplains contained, almost at the same frequency, sexual populations and populations with both clonal and sexual reproductive systems, called hereafter as ?mixed populations?. No clonality was recorded in this type of habitat. Within primary forests, sexual populations were the most common, though a clonal and a mixed population were also found in two forests in northern South America. Because flooding is known to represent an important selective pressure, and a variety of ant species have evolved several responses to flooding, the high frecuency of mixed reproductive system in this kind of habitat could constitute valuable evidence of the origin of clonality during the evolutionary history of the little fire ant within its native range. (CONICET; ANPCYT, USDA-ARS).