A genetic perspective on rapid evolution in cane toads (Rhinella marina)

The process of biological invasion exposes a species to novel pressures, in terms of both the environments it encounters and the evolutionary consequences of range expansion. Several invaders have been shown to exhibit rapid evolutionary changes in response to those pressures, thus providing robust opportunities to clarify the processes at work during rapid phenotypic transitions. The accelerating pace of invasion of cane toads (Rhinella marina) in tropical Australia during its 80-year history has been well characterized at the phenotypic level, including common-garden experiments that demonstrate heritability of several dispersal-relevant traits. Individuals from the invasion front (and their progeny) show distinctive changes in morphology, physiology and behaviour that, in combination, result in far more rapid dispersal than is true of conspecifics from long-colonized areas. The extensive body of work on cane toad ecology enables us to place into context studies of the genetic basis of these traits. Our analyses of differential gene expression from toads from both ends of this invasion-history transect reveal substantial upregulation of many genes, notably those involved in metabolism and cellular repair. Clearly, then, the dramatically rapid phenotypic evolution of cane toads in Australia has been accompanied by substantial shifts in gene expression, suggesting that this system is well suited to investigating the genetic underpinnings of invasiveness.

生物入侵过程会使入侵物种面临全新的选择压力，既涵盖其所遭遇的环境条件，也包含种群扩张所带来的进化后果。多项研究已证实，诸多入侵物种会针对这些压力快速产生进化适应性改变，这为解析快速表型转变过程中的内在作用机制提供了极佳的研究契机。在80年的入侵历程中，澳大利亚热带地区的甘蔗蟾蜍（Rhinella marina）的入侵扩散速率不断加快，其表型特征已得到充分解析，相关研究包括通过同质园实验（common-garden experiments）证实了多个与扩散相关性状的遗传力。来自入侵前沿的个体（及其后代）在形态、生理与行为层面均表现出显著特征变化，这些变化共同使其扩散速率远高于来自长期定居区域的同种个体。针对甘蔗蟾蜍生态学的大量研究成果，为解析这些性状的遗传基础提供了研究语境支撑。我们对该入侵历史梯度两端的甘蔗蟾蜍开展的差分基因表达（differential gene expression）分析显示，大量基因出现了显著上调，其中尤以参与代谢与细胞修复过程的基因为代表。由此可见，澳大利亚甘蔗蟾蜍所经历的极快速表型进化，伴随着基因表达层面的显著改变，这表明该研究体系非常适合用于解析入侵性的遗传基础。