Ecological specialisation is hypothesised to play a major role in the evolution of phenotypic diversity, especially following the colonisation of novel habitats. For example, cichlid fishes provide some of the most remarkable evidence for rapid ecological diversification. Here, we capitalised on a recently (≤ 40 years ago) introduced population of red devils (Amphilophus labiatus) in Australia to investigate adaptive phenotypic responses to a novel environment. We used stomach content analyses, morphometrics and laboratory experiments to test for covariation between diet and size of an important trophic trait, lip size. We found that, while maximum lip size in the study population was smaller than in the species’ natural range, the proportions of algae, insects and fish remains in the diet covaried with lip size. However, contrary to predictions, we found no evidence for lip development to be plastic under laboratory conditions in relation to substrate complexity or food manipulation, nor did we find any relationship between lip morphology and feeding performance in adults. Single nucleotide polymorphism data, in turn, suggested that the introduced population has reduced standing genetic variation, which potentially influences both phenotypic plasticity and diversity, in comparison to native populations. Together, the results suggest that morphological variation in a key trophic trait can respond rapidly to diet in a novel environment, despite reduced genetic diversity in the population.

据推测，生态专业化在表型多样性的演变中起主要作用，尤其是在新的栖息地定殖之后。例如，丽鱼科鱼类为快速的生态多样化提供了一些最杰出的证据。在这里，我们利用了最近（≤40年前）引入的红色魔鬼种群（Amphilophus labiatus）在澳大利亚调查对新型环境的适应性表型反应。我们使用了胃内容物分析，形态计量学和实验室实验来测试饮食和重要营养特征的大小（嘴唇大小）之间的协变。我们发现，虽然研究人群的最大嘴唇尺寸小于该物种的自然范围，但饮食中藻类，昆虫和鱼类的比例仍然与嘴唇尺寸相关。但是，与预测相反，我们没有发现在实验室条件下与基质复杂性或食物处理有关的唇部发育为可塑性的证据，也没有发现成人的唇部形态与摄食性能之间的任何关系。反过来，单核苷酸多态性数据表明，引入的种群减少了常设遗传变异，与本地人口相比，这可能会影响表型可塑性和多样性。总之，这些结果表明，尽管种群中的遗传多样性降低了，但在关键的营养性状上的形态变化却可以在新型环境中对饮食做出快速反应。