Colony Fusion in Argentine Ants is Guided by Worker and Queen Cuticular Hydrocarbon Profile Similarity

Abstract

Introduced populations of the Argentine ant, Linepithema humile, have experienced moderate to severe losses of genetic diversity, which may have affected nestmate recognition to various degrees. We hypothesized that cuticular hydrocarbons (CHC) serve as nestmate recognition cues, and facilitate colony fusion of unrelated L. humile colonies that share similar CHC profiles. In this study, we paired six southeastern U.S. L. humile colonies in a 6-month laboratory fusion assay, and determined if worker and queen CHC profile similarity between colonies was associated with colony fusion and intercolony genetic similarity. We also compared worker and queen CHC profiles between fused colony pairs and unpaired controls to determine if worker and queen chemical profiles changed after fusion. We found that colony fusion correlated with the CHC similarity of workers and queens, with the frequency of fusion increasing with greater CHC profile similarity between colonies. Worker and queen CHC profile similarity between colonies also was associated with genetic similarity between colonies. Queen CHC profiles in fused colonies appeared to be a mix of the two colony phenotypes. In contrast, when only one of the paired colonies survived, the CHC profile of the surviving queens did not diverge from that of the colony of origin. Similarly, workers in non-fused colonies maintained their colonyspecific CHC, whereas in fused colonies the worker CHC profiles were intermediate between those of the two colonies. These results suggest a role for CHC in regulating interactions among mutually aggressive L. humile colonies, and demonstrate that colony fusion correlates with both genetic and CHC similarities. Further, changes in worker and queen chemical profiles in fused colonies suggest that CHC plasticity may sustain the cohesion of unrelated L. humile colonies that had fused.

Colony fusion and worker reproduction after queen loss in army ants

“…The mixing of worker CHC profiles in merged colonies after fusion indicates that the label representing the colony odour is highly dynamic, which allows workers originating from two merging colonies to become chemically similar and thus fully integrated in a relatively short time. The same has recently been shown for Argentine ants (Linepithema humile) under laboratory conditions (Vásquez et al 2009).…”

“…In addition to backtracking behaviour, orphaned workers could in theory seek out and recognize related colonies for fusion (Vásquez et al 2009). That this is not the case is clearly demonstrated by the fact that most merging colonies had different mitochondrial haplotypes and therefore lacked recent maternal co-ancestry in five out of six unambiguous fusions.…”

Communication and Social Regulation in Termites

“…The CHC data confirm the DNA data. They also show that the cuticular signature of the R. flavipes population found in France is strongly chemically homogenous, which may explain the lack of agonistic behavior among colonies; a similar pattern has been observed in other invasive species, such as the Argentine ant (Vasquez et al 2009). Temperate subterranean termites belonging to Reticulitermes, Coptotermes, and Heterotermes live in a wide variety of ecosystems.…”

Variations in Worker Cuticular Hydrocarbons and Soldier Isoprenoid Defensive Secretions Within and Among Introduced and Native Populations of the Subterranean Termite, Reticulitermes flavipes

“…One of the characteristics that appear essential for colony fusion is the absence of intraspecific aggression among individuals of the two parental colonies. The CHC homogeneity in introduced populations of R. flavipes could explain the lack of intraspecific aggression and, indirectly, the high rate of colony fusion within these introduced populations, as has been recently proposed for the Argentine ant, Linepithema humile (Vasquez et al, 2009). This study also revealed that CHC profiles differed significantly among U.S. populations, whereas the three French populations exhibited similar CHC profiles.…”