Intraspecific competition has long been considered a key driver of evolutionary diversification, but whether it can also promote evolutionary innovation is less clear. Here we examined the interplay between competition and phenotypic plasticity in fuelling the origins of a novel, complex phenotype – a distinctive carnivore morph found in spadefoot toad tadpoles (genus Spea) that specializes on fairy shrimp. We specifically sought to explore the possible origins of this phenotype by providing shrimp to Scaphiopus holbrookii tadpoles (the sister genus to Spea that does not produce carnivores) while subjecting them to competition for their standard diet of detritus. Previous research had shown that this species will eat shrimp when detritus is limited, and that these shrimp-fed individuals produce features that are redolent of a rudimentary Spea carnivore. In this study, we found that: (1) behavioural and morphological plasticity enabled some individuals to expand their diet to include shrimp; (2) there was heritable variation in this plasticity; and (3) individuals received a growth and development benefit by eating shrimp. Thus, novel resource use can arise via plasticity as an adaptive response to intraspecific competition. More generally, our results show how competition and plasticity may interact to pave the way for the evolution of complex, novel phenotypes, such as the distinctive carnivore morph in present-day Spea.

中文翻译：

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种内竞争和表型可塑性如何促进新型复杂表型进化的实验研究

种内竞争长期以来一直被认为是进化多样化的关键驱动力，但是它是否还能促进进化创新尚不清楚。在这里，我们研究了竞争与表型可塑性之间的相互作用，以助长一种新颖而复杂的表型的起源-一种独特的食肉动物形态，发现于专攻仙女虾的spa足蟾蜍t（Spea属）中。我们特别寻求通过提供虾探讨这一表型的可能来源Scaphiopus holbrookii蝌蚪（妹妹属以SPEA不会产生食肉动物），同时让它们竞争标准碎屑饮食。先前的研究表明，在碎屑受限的情况下，该物种会吃虾，而这些由虾喂养的个体产生的特征却是基本的豌豆食肉动物。在这项研究中，我们发现：（1）行为和形态可塑性使某些人能够扩大饮食，包括虾。（2）这种可塑性有可遗传的变化；（3）个体通过食用虾获得了生长发育的好处。因此，可以通过可塑性产生新的资源利用，作为对种内竞争的适应性反应。更广泛地说，我们的结果表明竞争和可塑性如何相互作用，从而为复杂的新表型（例如当今Spea中独特的食肉动物形态）的进化铺平道路。