Potential selection driving evolution of long corolla tubes and case studies

Diverse corolla morphologies are thought to function in protecting sexual organs within flowers and attracting pollinators. The transition from open to tubular flowers is considered a key innovation in the evolution of corollas. A classic question that scholars have tried to answer since Darwin is: was the evolution of long corolla tubes caused by an arms-race relationship between the proboscis of the pollinator and the length of the corolla tube? Phenotypic manipulations have been conducted across multiple species with long corolla tubes to elucidate the mechanisms underlying the co-evolution between flowers and their interacting animal agents, driven by reciprocal selection. In this review, we summarize both the biotic and abiotic factors affecting corolla tube length, including the effects of pollinators, nectar robbers, and herbivores, as well as environmental factors like light and water availability. Moreover, we propose four potential evolutionary pathways for the development of pollinator-mediated long-tubed corollas. This review aims to provide insights and guidance for future studies on the evolution of tubular flowers.