Abstract
Attempts to control invasive species using species-specific pheromones need to incorporate an understanding of interactive effects among those pathways. The larvae of invasive cane toads (Rhinella marina) utilise chemical cues to repulse, attract or suppress conspecific larvae. We can exploit these effects to reduce toad abundance, but the effects of each cue may not be additive. That is, exposure to one type of cue may lessen the impact of exposure to another cue. To assess this possibility, we exposed toad larvae to combinations of cues. Tadpoles that had been exposed to the suppression cue during larval development exhibited no response to the attraction cue, resulting in lower capture rates in attractant-baited traps. Suppression, however, did not affect a tadpole’s response to the alarm cue, and exposure to the alarm cue during tadpole development did not affect response to the attraction cue. Tadpoles exposed to the suppression cue were smaller than control tadpoles at 10 days post-exposure, and consequently were more vulnerable to gape-limited invertebrate predators. Our results demonstrate that the responses by toad tadpoles to chemical cues interact in important ways, and are not simply additive when combined. Control efforts need to incorporate an understanding of such interactions if we are to most effectively use chemical-communication pathways to control invasive amphibians.
Highlights
Increasing rates of international commerce and exchange are translocating more and more species into areas far outside their native ranges [1]
The current paper addresses a critical question that must be answered before we can work out how to utilise these chemically-mediated responses for toad control: how do responses to these cues interact? Plausibly, for example, toad tadpoles exposed to the alarm cue might focus on escaping the perceived threat of predation rather than searching out and consuming newly-laid toad eggs; or tadpoles whose developmental trajectories have been modified by exposure to the suppression cue might thereafter fail to respond to alarm or attraction cues
The number of tadpoles trapped was affected by a significant interaction between suppression treatment and trapping treatment (t = 2.21, df = 1, P = 0.03; Fig 1A)
Summary
Increasing rates of international commerce and exchange are translocating more and more species into areas far outside their native ranges [1]. Most of the species that are transported fail to establish in their new homes, invasions can impose substantial ecological, evolutionary and economic impacts [1,2,3,4]. We urgently need effective ways to eradicate or manage invasive populations [5] without deleteriously affecting native species that occupy the same habitat [6]. To achieve species-specificity and avoid collateral damage, we may be able to exploit species-specific communication pathways and competitive mechanisms [7,8,9,10]. Many aquatic species–including invasive taxa–utilise chemical communication systems, and chemicals that function in this way provide potential avenues with which to target aquatic.
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