Data from: Differences in developmental strategies between long-settled and invasion front populations of the cane toad in Australia

Phenotypic plasticity can enhance a species’ ability to persist in a new and stressful environment, so that reaction norms are expected to evolve as organisms encounter novel environments. Biological invasions provide a robust system to investigate such changes. We measured rates of early growth and development in tadpoles of invasive cane toads (Rhinella marina) in Australia, from a range of locations and at different larval densities. Populations in long-colonised areas have had the opportunity to adapt to local conditions, whereas at the expanding range edge, the invader is likely to encounter challenges that are both novel and unpredictable. We thus expected invasion-vanguard populations to exhibit less phenotypic plasticity than range-core populations. Compared to clutches from long-colonised areas, clutches from the invasion front were indeed less plastic (i.e., rates of larval growth and development were less sensitive to density). In contrast, those rates were highly variable in clutches from the invasion front, even among siblings from the same clutch under standard conditions. Clutches with highly variable rates of growth and development under constant conditions had lower phenotypic plasticity, suggesting a trade-off between these two strategies. Although these results reveal a strong pattern, further investigation is needed to determine whether these different developmental strategies are adaptive (i.e., adaptive phenotypic plasticity versus bet-hedging), or instead are driven by geographic variation in genetic quality or parental effects.

表型可塑性（phenotypic plasticity）可提升物种在全新胁迫环境中的存续能力，因此当生物接触新环境时，反应规范（reaction norms）理应发生演化。生物入侵（biological invasions）为研究这类演化变化提供了可靠的实验体系。我们测定了澳大利亚境内入侵性蔗蟾（Rhinella marina）不同采样点位、不同幼体密度条件下蝌蚪的早期生长与发育速率。长期定居区域的种群已有充足时间适应当地环境，而在分布区扩张边缘地带，入侵物种往往会面临全新且不可预测的生存挑战。据此我们推测，入侵先锋种群（invasion-vanguard populations）的表型可塑性低于分布区核心种群（range-core populations）。与长期定居区域的卵块相比，入侵前线的卵块确实表现出更低的表型可塑性（即幼体生长与发育速率对密度的敏感性更弱）。与之相反，入侵前线卵块的生长与发育速率在标准化实验条件下仍存在极高变异，即便在同一卵块的同胞个体间亦是如此。在恒定环境下生长与发育速率变异度较高的卵块，其表型可塑性更低，这表明两种策略间存在进化权衡。尽管本研究结果揭示了显著的规律，但仍需进一步探究以明确：这些不同的发育策略究竟是适应性的（即适应性表型可塑性与风险分摊策略（bet-hedging）的差异），还是由遗传质量的地理差异或亲本效应（parental effects）所驱动。