Abstract
The blacklegged tick (Ixodes scapularis) and the invasive European fire ant (Myrmica rubra) are both expanding throughout their sympatric range in coastal New England. Ixodes scapularis is the primary vector of the bacterium Borrelia burgdorferi, which is the causative agent of Lyme disease, and Mount Desert Island, Maine, home to Acadia National Park, currently is affected by a high Lyme disease burden. Ticks have many natural predators, including ants, although no previous studies have investigated interactions between these two species. To test the hypothesis that the presence of M. rubra alters I. scapularis abundance, we collected ticks by drag-sampling at eight ant-infested sites and eight uninfested control sites in Acadia National Park. We found that nymph density was significantly higher at ant-infested sites, while larval density was significantly higher at control sites. In addition, we conducted a laboratory bioassay to measure M. rubra aggression against I. scapularis larvae, nymphs, and adults and Dermacentor variabilis adults, and found that ant aggression was significantly higher against D. variabilis adults than I. scapularis adults. Our findings support the hypothesis that M. rubra has divergent effects across I. scapularis life stages, and we discuss possible ecological mechanisms, including optimal microclimate and predation, that could promote density of nymphs while inhibiting density of larvae.
Highlights
Invasive species are transforming ecosystems worldwide at an unprecedented scale with negative outcomes for biodiversity [1,2,3], animal and human health [4], agriculture [5], and forestry [6]
We collected a total of 232 I. scapularis nymphs and 3,778 I. scapularis larvae throughout the field study (Fig 3A and 3B)
M. rubra displayed greater aggression toward D. variabilis adults than toward I. scapularis adults (Z = 5.79, P < 0.001), and overall, aggression was higher within Nest 1 than within Nest 2 (Z = 7.91, P < 0.001; Fig 4)
Summary
Invasive species are transforming ecosystems worldwide at an unprecedented scale with negative outcomes for biodiversity [1,2,3], animal and human health [4], agriculture [5], and forestry [6]. Invasive species interact with sympatric native species through a variety of mechanistic pathways [7, 8]. In the case of invasive or geographically expanding disease vectors, these interspecific interactions may have important impacts on the ecology of vector-borne infectious disease and human and wildlife health [4].
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