Review and Advances in Style Curvature for the Malvaceae Cheng-Jiang Ruan*
Total Page:16
File Type:pdf, Size:1020Kb
® International Journal of Plant Developmental Biology ©2010 Global Science Books Review and Advances in Style Curvature for the Malvaceae Cheng-Jiang Ruan* Key Laboratory of Biotechnology & Bio-Resources Utilization, Dalian Nationalities University, Dalian City, Liaoning 116600, China Correspondence : * [email protected] ABSTRACT The flowers of the Malvaceae with varying levels of herkogamy via style curvature have long intrigued evolutionary botanists. This review covers the flower opening process, approach herkogamy, style curvature and character evolution based on molecular phylogenetic trees, adaptive significances of style curvature and the mating system in some portions of the genera in this family. Hermaphroditic flowers of some species have showy petals and pollen and nectar rewards to pollinators. Approach herkogamy, in which stigmas are located on the top of a monadelphous stamen, has evolved as a mechanism to reduce the frequency of intra-floral self-pollination or the interference between male-female organs. Protandrous or monochogamous flowers in the fields open at about 5-7 days and 1-2 days respectively, and pollination is conducted by insects and birds. Interestingly, un-pollinated styles in some species curve when pollination fails. According to our observations and published or internet data, this curvature occurs in 23 species distributed in eight genera of four tribes (Malvavisceae, Ureneae, Hibisceae, Malveae) and appears to have evolved at least eight times. A shift to use style curvature is associated with a shift to annual or perennial herbs, and an unpredictable pollinator environment is likely an important trigger for this evolution. The adaptive significances of style curvature in the Malvaceae include delayed selfing, promotion of outcrossing or reduction in intrafloral male-female interference, sometimes two or three of which simultaneously occur in style curvature of one species (e.g., Kosteletzkya virginica). Delayed selfing via style curvature represents reproductive assurance and a mixed mating system, but the relationship between them is still an evolutionary enigma. _____________________________________________________________________________________________________________ Keywords: adaptive significance, character evolution, floral structure, mating system, phylogenetic approach, reproductive assurance CONTENTS INTRODUCTION........................................................................................................................................................................................ 98 FLORAL MORPHOLOGY AND POLLINATION BIOLOGY................................................................................................................... 99 Floral structure......................................................................................................................................................................................... 99 Flower opening process........................................................................................................................................................................... 99 Approach herkogamy .............................................................................................................................................................................. 99 Pollination biology ................................................................................................................................................................................ 101 STYLE CURVATURE AND COROLLA CLOSURE................................................................................................................................ 102 Style curvature....................................................................................................................................................................................... 102 Corolla closure promotes delayed selfing.............................................................................................................................................. 102 EVOLUTION OF STYLE CURVATURE AND ITS CORRELATED CHARACTERS ........................................................................... 103 Evolution of morphological characters.................................................................................................................................................. 104 Evolution of style curvature and correlated traits .................................................................................................................................. 106 Evolutionary relationship of style curvature and plant type-habit ......................................................................................................... 106 Unpredictable pollinator environments triggering the evolution of style curvature............................................................................... 106 Biogeographical history of style curvature ............................................................................................................................................ 107 ADAPTIVE SIGNIFICANCE OF STYLE CURVATURE ........................................................................................................................ 107 Adaptive significance ............................................................................................................................................................................ 107 Promotion of outcrossing....................................................................................................................................................................... 107 Delayed selfing pollination.................................................................................................................................................................... 107 Reduction in intrafloral male–female interference ................................................................................................................................ 107 Reproductive assurance ......................................................................................................................................................................... 108 Mixed mating system............................................................................................................................................................................. 108 CONCLUSION.......................................................................................................................................................................................... 109 FUTURE RESEARCH .............................................................................................................................................................................. 109 ACKNOWLEDGEMENTS ....................................................................................................................................................................... 109 REFERENCES........................................................................................................................................................................................... 109 _____________________________________________________________________________________________________________ INTRODUCTION Juncosa and Webster 1989; Dole 1990; Lyon 1992; Rathcke and Real 1993; Donnelly et al. 1998; Eckhert and Schaeffer Since Darwin (1862) observed reconfiguration in orchid 1998; Traveset et al. 1998; Fetscher and Kohn 1999; Kalisz pollinia, the dramatic movement of floral structures in many et al. 1999; Kennedy 1999; Bynum and Smith 2001; Fet- angiosperms, which influence plant pollination and mating scher 2001; Li et al. 2001; Wang et al. 2004; Edwards et al. systems, has long intrigued evolutionary botanists (Buttrose 2005; Liu et al. 2006; Peter and Johnson 2006). Meanwhile, et al. 1977; Faegri and van der Pijl 1979; Schlessman 1986; the reproductive assurance of maximum seed production Received: 8 July, 2009. Accepted: 21 April, 2010. Invited Review International Journal of Plant Developmental Biology 4 (Special Issue 1), 98-111 ©2010 Global Science Books and the evolutionary relationship between them presented FLORAL MORPHOLOGY AND POLLINATION by floral movements in response to unpredictable pollinator BIOLOGY environments has always been an evolutionary enigma to the mixed mating system (Herlihy and Eckert 2002; Kalisz Floral structure et al. 2004; Goodwillie et al. 2005; Cheptou and Schoen 2007). The interesting curvature of un-pollinated styles The Malvaceae contains herbs, shrubs, or less often trees, towards the anthers is known to occur in several species of and usually have an indumentum with peltate scales or stel- the Malvaceae family, including Hibiscus trionum (Buttrose late hairs (Tang et al. 2007). Leaves are alternate, stipulate et al. 1977), Hibiscus laevis (Klips and Snow 1997) and and petiolate (e.g. leaves of different types of K. virginica, Kosteletzkya virginica (Ruan et al. 2005a), which may in- Fig. 1A); the palmate leaf blade is usually veined, entire or volve different adaptive significances that include achieve- various lobed. Flowers are usually hermaphroditic and ento- ment of delayed selfing (Blanchard 1976), promotion of mophilous, unisexual in Kydia (Tang et al. 2007) and outcrossing (Stephens 1948), and supplies for outcrossing female flowers are rare (vestigial stamens, Fig. 1B) in K. the highest priority, while retaining the ability