Behavioural variation and plasticity along an invasive ant introduction pathway

Abstract

Once established in new areas, introduced species may exhibit changes in their biology due to phenotypic plasticity, novel selection pressures and genetic drift. Moreover, the introduction process itself has been hypothesised to act as a selective filter for traits that promote invasiveness. We tested the hypothesis that behaviours thought to promote invasiveness-such as increased foraging activity and aggression-are selected for during invasion by comparing traits among native and introduced populations of the widespread Argentine ant (Linepithema humile). We studied Argentine ant populations in the native range in Argentina and in three invaded regions along an introduction pathway: California, Australia and New Zealand. In each region, we set up 32 experimental colonies to measure foraging activity and interspecific aggression in a subset of the study regions. These colonies were subject to experimental manipulation of carbohydrate availability and octopamine, a biogenic amine known to modulate behaviour in insects, to measure variation in behavioural plasticity. We found variation in foraging activity among populations, but this variation was not consistent with selection on behaviour in relation to the invasion process. We found that colonies with limited access to carbohydrates exhibited unchanged exploratory behaviour, but higher exploitation activity and lower aggression. Colonies given octopamine consistently increased foraging behaviour (both exploration and exploitation), as well as aggression when also sugar-deprived. There was no difference in the degree of behavioural response to our experimental treatments along the introduction pathway. We did not find support for selection of behavioural traits associated with invasiveness along the Argentine ant's introduction pathway or clear evidence for an association between the introduction process and variation in behavioural plasticity. These results indicate that mechanisms promote behavioural variation in a similar fashion both in native and introduced ranges. Our results challenge the assumption that introduced populations always perform better in key behavioural traits hypothesised to be associated with invasion success.

Native and introduced Argentine ant populations are characterised by distinct transcriptomic signatures associated with behaviour and immunity

“…We investigated if expression of genes related to the dopaminergic, octopaminergic and serotoninergic neural pathways could be associated with the Argentine ant range, potentially contributing to its invasion success through, for instance, increased foraging activity, increased interspecific aggression and/or lower intraspecific aggression. Interestingly, we did not find behavioural differences in foraging activity between native and invaded ranges, and we found no variation in sensitivity to OA supplementation in the diet provided to the experimental colonies (Felden et al 2018). Here, genes associated with biogenic amines, including OA, displayed clear range-specific expression pattern, suggesting an association with the introduction process.…”

“…We used worker ants collected in Argentina, California, Australia and New Zealand from colonies maintained in standardised conditions for 20 days prior to sampling as described in Felden et al (2018). Ants were collected at four different sites in each region, except in Europe that only included two distinct sites (Suppl.…”

“…not gene expression), we also included samples from colonies that were fed with one mealworm and octopamine in 1% sucrose solution (i.e. samples AR OTA-3 , CA RCH-3 , AU STA-2 , AU STA-3 ; see Felden et al 2018). Foraging workers were sampled and stored in ice-cold RNALater (Invitrogen, USA).…”

“…in birds: Fidler et al 2007;Korsten et al 2010) and can exhibit range-specific polymorphism (Mueller et al 2013;Holtmann et al 2016). Behavioural differences between the native and introduced Argentine ant populations might be restricted to specific behaviour in a specific context (Felden et al 2018). To gain further insight into variation in the molecular basis of the Argentine ant's behaviour across its native and introduced ranges, we measured expression of genes related to the main biogenic amine pathways.…”

Behavioural traits and feeding ecology of Mediterranean lionfish and native species naiveté to lionfish predation

“…dispersal, reproduction, feeding, competition) that individuals within an invading population must overcome to succeed (Blackburn et al 2011); only individuals with certain life-history and behavioural traits may then move forward between steps in the invasion process (Chapple et al 2012). As a result of such ‘filtering’ of individuals, the invading population is not a random subset of the native natal population (Felden et al 2018), while traits ‘selected’ for in individuals during one stage of the invading process may being maladaptive and lead to invasion failure in following stages (Chapple et al 2012, Felden et al 2018). Thus, the introduction or establishment of an invasive species in a novel region will not necessary lead to the species becoming invasive and to similar impacts on local biodiversity as observed elsewhere.…”