Plant Ecology & Diversity, 2013 http://dx.doi.org/10.1080/17550874.2013.777133 Divergent seed production responses of white and blue flowers of Gentiana leucomelaena (Gentianaceae) to warming and watering Junpeng Mu a,b , Youhong Peng c and Kechang Niu a * a Department of Biology, Nanjing University, Nanjing, China; b Ecological Security and Protection Key Laboratory of Sichuan Province, Mianyang Normal University, Mianyang, China; c Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chinese Academy of Sciences, Chengdu, China (Received 14 April 2012; final version received 13 February 2013) Background: The adaptation, evolution and function of flower colour diversity in response to changing environments are one of the oldest puzzles in plant ecology. It is logical that comparative studies on fitness of flower colour would be the most meaningful if they were conducted on the same genotype. Aims: We used Gentiana leucomelaena, which produces both white and blue flowers on different tillers of the same individual, as a model species to test adaption and fitness differences of contrasting flowers in contrasting environments. Methods: We examined seed production by white and blue flowers in response to increased temperatures (28 ◦ C/2 ◦ C vs. 12 ◦ C/2 ◦ C; 12 h light/12 h dark) in a climate chamber study and to watering in the field (+1.5 l m -2 d -1 vs. control with no supplementary irrigation). Results: For white and blue flowers warming decreased but watering increased seed number. Increased temperature and watering increased the size of seeds from white flowers, but neither warming nor watering significantly changed seed size of blue flowers. Seed size was significantly negatively correlated with seed number in the temperature treatments but positively correlated in watering treatments. The positive correlation was strong in white flowers, but the negative correlation was stronger in blue than in white flowers. Conclusions: Water availability and low temperature confer an advantage to white flowers, while warming and dry habitats favour blue flowers. These divergent responses may influence total plant fitness and thus help explain the adaptive value and evolution of flower colour diversity. Keywords: adaptation; flower diversity; reproductive strategy; seed number; seed size Introduction The evolution and function of flower diversity (e.g. colour, size, shape) is one of the oldest puzzles in plant ecol- ogy, and there has been much research on the different exogenous and endogenous determinants of flower diversity (Darwin 1859; Stebbins 1974; Galen 1999; Dormont et al. 2010). Previous studies on flower colour diversity often have focused on the effect of biotic factors on the evolu- tion of the colour diversity, e.g. attracting insect pollinators (Ida and Kudo 2003; Chittka and Raine 2006; Kudo et al. 2007). Recently, with global climate change, an increasing number of studies have been concerned with the rapid adap- tation and evolution of flower colour diversity to changing abiotic factors (Orenshamir and Levinissim 1997; Grace and Logan 2001; Steyn et al. 2002). However, there is a scarcity of experimental studies on the relative fitness of different flower colours under varying environmental conditions. The results of such studies would help us to bet- ter understand the evolution and function of flower colour diversity. Previous studies on the function of flower colour diver- sity often have compared the fitness of individuals in different species or populations that had contrasting flower colours; however, due to genetic differences it is difficult to *Corresponding author. Email: kechangniu@nju.edu.cn determine the functional role of flower colour as a determi- nant of fitness. Theoretically, comparing the fitness between phenotypes within the same genotype (e.g. between tillers of the same individual) with contrasting coloured flowers is better than comparing genetically different members of a species with different colours. In plants with the same genotype, genetic variation would not be a constraining fac- tor in determining the fitness of different flower colours. However, there are very few studies comparing the adap- tation and fitness of contrasting flowers among individuals within a population or among tillers in the same individ- ual. Flower polymorphisms are common in nature, e.g. both blue and white flowers are produced by Linanthus parryae (A. Gray) Greene, a California desert annual (Schemske and Bierzychudek 2007). Examples of species with tillers on the same plant that produce different colours of flow- ers are not common, but one example of such a species is Gentiana leucomelaena Maximowicz ex Kusnezow. In this species some tillers produce white flowers and others produce blue flowers (Figure 1). The use of G. leucome- laena as our experimental organism allowed us to control for the effect of genetic variation in comparative studies on the fitness (e.g. seed number and seed size) of flower colour and on responses of contrasting flower colours to climate © 2013 Botanical Society of Scotland and Taylor & Francis Downloaded by [Nanjing University] at 23:22 17 March 2013