Darwin's beautiful contrivances: evolutionary and functional evidence for floral adaptation

• Published in: The New phytologist Vol. 183; no. 3; pp. 530 - 545
• Main Authors: Harder, Lawrence D., Johnson, Steven D.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.08.2009; Blackwell Publishing; Blackwell Publishing Ltd
• Subjects: adaptation; Adaptation, Physiological; Biodiversity; Biological adaptation; Biological Evolution; Darwin; diversification; Ecological genetics; Evolution; Flowers; Flowers - physiology; heritability; natural selection; outcrossing; Phenotypic selection; Phenotypic traits; Plants; Pollinating insects; Pollination; Tansley Review
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2009.02914.x

Summary 530 I. Introduction 530 II. The process of floral and inflorescence adaptation 532 III. Experimental studies of flowers as adaptations 538 IV. Floral diversification: microevolution writ large? 539 V. Concluding comments 541 Acknowledgements 542 References 542 Although not 'a professed botanist', Charles Darwin made seminal contributions to understanding of floral and inflorescence function while seeking evidence of adaptation by natural selection. This review considers the legacy of Darwin's ideas from three perspectives. First, we examine the process of floral and inflorescence adaptation by surveying studies of phenotypic selection, heritability and selection responses. Despite widespread phenotypic and genetic capacity for natural selection, only one-third of estimates indicate phenotypic selection. Second, we evaluate experimental studies of floral and inflorescence function and find that they usually demonstrate that reproductive traits represent adaptations. Finally, we consider the role of adaptation in floral diversification. Despite different diversification modes (coevolution, divergent use of the same pollen vector, pollinator shifts), evidence of pollination ecotypes and phylogenetic patterns suggests that adaptation commonly contributes to floral diversity. Thus, this review reveals a contrast between the inconsistent occurrence of phenotypic selection and convincing experimental and comparative evidence that floral traits are adaptations. Rather than rejecting Darwin's hypotheses about floral evolution, this contrast suggests that the tempo of creative selection varies, with strong, consistent selection during episodes of diversification, but relatively weak and inconsistent selection during longer, 'normal' periods of relative phenotypic stasis.