School of Life and Environmental Sciences A08, University of Sydney, Sydney, NSW, 2006, Australia.
Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD, 4072, Australia.
J Chem Ecol. 2019 Oct;45(10):838-848. doi: 10.1007/s10886-019-01111-2. Epub 2019 Nov 1.
Many aquatic organisms detect and avoid damage-released cues from conspecifics, but the chemical basis of such responses, and the effects of prolonged exposure to such cues, remain poorly understood. Injured tadpoles of the cane toad (Rhinella marina) produce chemical cues that induce avoidance by conspecific tadpoles; and chronic exposure to those cues decreases rates of tadpole survival and growth, and reduces body size at metamorphosis. Such effects suggest that we might be able to use the cane toads' alarm cue for biocontrol of invasive populations in Australia. In the present study, we examined behavioral and ecological effects of compounds that are present in cane toad tadpoles and thus, might trigger avoidance of crushed conspecifics. Four chemicals (L-Arg, L-Leu-L-Leu-OH, L-Leu-L-Ile-OH and suberic acid) induced behavioral avoidance in toad tadpoles at some (but not all) dosage levels, so we then exposed toad larvae to these chemicals over the entire period of larval development. Larval survival and size at metamorphosis were decreased by chronic exposure to crushed conspecifics (consistent with earlier studies), but not by exposure to any of the four chemicals. Indeed, L-Arg increased body size at metamorphosis. We conclude that the behavioral response to crushed conspecifics by cane toad tadpoles can be elicited by a variety of chemical cues, but that consistent exposure to these individual chemical cues does not affect tadpole viability or developmental trajectory. The optimal behavioral tactic of a tadpole may be to flee if it encounters even a single chemical cue likely to have come from an injured conspecific (indicative of predation risk), whereas the continuing presence of that single chemical (but no others) provides a less reliable signal of predation risk. Our data are consistent with results from studies on fish, that suggest a role for multiple chemicals in initiating alarm responses to damage-released cues.
许多水生生物能探测并回避同种个体释放的受损线索，但此类反应的化学基础以及长时间暴露于此类线索的影响仍知之甚少。蔗蟾（Rhinella marina）受伤的蝌蚪会产生化学线索，诱使同种蝌蚪回避；而长期接触这些线索会降低蝌蚪的存活率和生长率，并降低变态时的体型。这些影响表明，我们或许可以利用蔗蟾的警报线索来控制澳大利亚的入侵种群。在本研究中，我们研究了存在于蔗蟾蝌蚪体内的化合物的行为和生态效应，这些化合物可能会引发对同类受挤压个体的回避。四种化学物质（L-Arg、L-Leu-L-Leu-OH、L-Leu-L-Ile-OH 和琥珀酸）在某些（但不是所有）剂量水平下会引起蟾蝌蚪的行为回避，因此我们在整个幼体发育期间使蟾蝌蚪接触这些化学物质。慢性接触被压碎的同类会降低幼体的存活率和变态时的体型（与早期研究一致），但接触这四种化学物质均无影响。事实上，L-Arg 增加了变态时的体型。我们的结论是，蔗蟾蝌蚪对被压碎的同类的行为反应可以被多种化学线索引发，但持续暴露于这些单个化学线索不会影响蝌蚪的生存能力或发育轨迹。如果遇到单个可能来自受伤同类的化学线索（表明存在捕食风险），蝌蚪的最佳行为策略可能是逃离，而该单个化学物质（而不是其他物质）的持续存在则提供了一个不太可靠的捕食风险信号。我们的数据与鱼类研究的结果一致，表明多种化学物质在引发对受损线索释放的警报反应中起作用。
