No abstract

Invasive species are one of the main reasons for the ongoing global loss of biodiversity. Anoplolepis gracilipes is an invasive ant that has recently received significant attention due to its negative effect on the native fauna and flora of Christmas Island, Indian Ocean. This species has contributed to a drastic change in the structure of the Christmas Island rainforest through its negative impact on the island's endemic red land crab, the dominant consumer on the islands forest floor. In this study, we investigate the population structure of A. gracilipes on Christmas Island in order to determine whether multiple introductions occurred on the island and how they correspond to known infestations. We genotyped 578 individuals collected from 50 nests across the Island. We identify two distinct subgroups in the population that represent two different supercolonies. These supercolonies are interspersed across the island, however both nuclear (microsatellites) and mitochondrial markers strongly suggest that there is no gene flow between the two colonies. Significant heterozygote excess within the entire sampling area, with all but one worker examined being heterozygous for all seven microsatellite loci, suggests an unusual reproductive system in these ants. Our results are consistent with recent sociogenetic findings in a population of A. gracilipes in Northern Borneo.

The threat imposed by invasive species and difficulties associated with control and management places more impetus on trying to prevent their introduction. The identification of introduction pathways is a vital component towards this goal. In this study, we use a genetic marker‐based approach to retrospectively investigate the pathway of origin of the invasive Argentine ant (Linepithema humile) into New Zealand. We intensively sample the mitochondrial gene cytochrome b, from the entire known range of Argentine ants in New Zealand. No genetic variation was found in New Zealand. In order to identify likely introduction pathways, we use two alternative genetic analyses and suggest that a tcs approach that collapses identical haplotypes and calculates the probability of parsimony is superior to standard phylogenetic tree‐building algorithms. A minimum spanning network allowed relationships to be examined among sequences collated from previous international studies. The cytochrome b sequence, when compared to a global database, matched that from an Australian population. That Australia is the potential source of Argentine ants is in agreement with the New Zealand interception record, as goods from Australia have the highest number of interception records of Argentine ants. Our approach can easily be duplicated for other organisms and the methodology can be more widely applied to help aid further efforts to identify the routes of transmission for other invasive species and allow us to efficiently direct our biosecurity monitoring effort.

No abstract

Positive interactions play a widespread role in facilitating biological invasions. Here we use a landscape Áscale ant exclusion experiment to show that widespread invasion of tropical rainforest by honeydew-producing scale insects on Christmas Island (Indian Ocean) has been facilitated by positive interactions with the invasive ant Anoplolepis gracilipes . Toxic bait was used to exclude A. gracilipes from large (9 Á35 ha) forest patches. Within 11 weeks, ant activity on the ground and on trunks had been reduced by 98 Á100%, while activity on control plots remained unchanged. The exclusion of ants caused a 100% decline in the density of scale insects in the canopies of three rainforest trees in 12 months (Inocarpus fagifer , Syzygium nervosum and Barringtonia racemosa ), but on B. racemosa densities of scale insects also declined in control plots, resulting in no effect of ant exclusion on this species. This study demonstrates the role of positive interactions in facilitating biological invasions, and supports recent models calling for greater recognition of the role of positive interactions in structuring ecological communities.