Civet Pollination in Mucuna Birdwoodiana (Fabaceae: Papilionoideae)
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Plant Ecol (2019) 220:457–466 https://doi.org/10.1007/s11258-019-00927-y (0123456789().,-volV)( 0123456789().,-volV) Civet pollination in Mucuna birdwoodiana (Fabaceae: Papilionoideae) Shun Kobayashi . Stephan W. Gale . Tetsuo Denda . Masako Izawa Received: 26 October 2018 / Accepted: 18 March 2019 / Published online: 28 March 2019 Ó Springer Nature B.V. 2019 Abstract Inferring pollinators from floral traits is larvata, and introduced Pallas’s squirrels, Callosciu- problematic because many flowers do not conform to a rus erythraeus styani, were observed opening flowers, prescribed phenotype by which they may be assigned and fruits were found to form on flowers opened by to any one particular pollination ‘syndrome.’ This both species. Paguma larvata opened flowers more necessitates empirical investigation to confirm polli- frequently and less destructively than C. e. styani. The nator relationships. Mucuna birdwoodiana is thought nectar is sucrose-dominant with no variation in nectar to be fruit bat-pollinated on account of its malodorous, volume nor sugar concentration throughout the day. pale green, gullet-type flowers, but we sought to Pollination success in M. birdwoodiana is dependent clarify its pollination system through direct examina- on flower-opening animals. The primary pollinator of tion. This study was conducted in Hong Kong. Flowers M. birdwoodiana is P. larvata, not fruit bats as had of this species undergo ‘‘explosive opening’’ during been suggested by a suite of supposedly adaptive floral pollination. Bagging experiments were conducted to traits. check the necessity of this mechanism to achieve fruit set. Floral visitors were recorded by video camera Keywords Explosive opening Á Mucuna Á Non- traps and nectar secretion patterns were surveyed. flying mammal Á Paguma larvata Á Pollination Á Flowers do not open automatically and unopened Tropical Asia flowers do not fructify. Masked palm civets, Paguma Communicated by Elizabeth Pringle. Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11258-019-00927-y) con- Nearly 90% of angiosperms are pollinated by animals tains supplementary material, which is available to authorized (Ollerton et al. 2011). Animal-pollinated plants users. exhibit an array of adaptive features which together define a floral presentation that is thought to be under S. Kobayashi (&) Á T. Denda Á M. Izawa Faculty of Science, University of the Ryukyus, 1 Senbaru, strong selective pressure by pollinators (Parachnow- Nishihara, Okinawa 903-0213, Japan itsch and Kessler 2010). Convergence among such e-mail: [email protected] phenotypes has been interpreted as evidence of distinct pollination syndromes, in which even distantly S. W. Gale Kadoorie Farm and Botanic Garden, Lam Kam Road, Tai related plants pollinated by the same pollinator (or Po, New Territories, Hong Kong, China 123 458 Plant Ecol (2019) 220:457–466 groups of pollinators) exhibit a similar suite of floral been taken as evidence of discrete bat- and bird- traits (e.g., Fægri and van der Pijl 1979). Following pollination syndromes, respectively (Fægri and van this concept, some researchers have inferred pollina- der Pijl 1979; Willmer 2011). Another distinctive tors based on observations of floral traits alone. feature of Mucuna flowers is their explosive opening. Although some predictions based on such observa- In this mechanism, the stamens and pistil, retained tions have proven to be correct (e.g., Kay and under tension by a pair of keeled petals in the Schemske 2003; Hargreaves et al. 2004; Rosas- unopened state, are rapidly released when the petals Guerrero et al. 2014), several exceptions have also are parted, catapulting the pollen grains onto the been found (e.g., Ollerton et al. 2009; Amorim et al. inadvertent foraging animal (i.e., the explosive 2013). For example, Rivera-Marchand and Ackerman opener). Specifically, an explosive opener must press (2006) demonstrated that, despite its white, bell- down on the wing petals and push up the banner petal shaped flowers that secrete copious amounts of nectar in order to spring the trigger (Agostini et al. 2006; at night, Pilosocereus royenii is pollinated predomi- Toyama et al. 2012). Once opened, the flower parts do nantly by carpenter bees, not bats as initially predicted. not return to their original position. Because observa- The notion of prescriptive pollination syndromes is tions suggest Mucuna species do not produce seeds therefore increasingly giving way to an understanding without opening (Kobayashi 2017), and that consid- that quantitative surveys are needed to clarify the role erable force is needed for explosive opening (Kobaya- of potential pollinators. shi et al. 2018d), the explosive opener is regarded as Beyond confirming functional pollinators, direct the main pollinator in Mucuna (van der Pijl 1941; observations are also vital for characterizing the Hopkins and Hopkins 1993; Agostini et al. 2006; behavior of floral visitors. This is especially important Kobayashi et al. 2015, 2017, 2018a). for mammal-pollinated plants or flowers with a However, inferences on plant–pollinator interac- complex pollination mechanism. For example, pri- tions have largely been drawn from studies of Central mate flower visitors do not always contribute to and South American members of the genus. Despite pollination because they sometimes pick and eat the Asia accounting for around 70% of total species flowers of supposedly primate-pollinated plants diversity in Mucuna (Moura et al. 2016), the pollina- (Grand 1972; Janson et al. 1981; Kobayashi et al. tion biology of few Asian species has been studied (M. 2015). Therefore, the contribution of potential polli- macropoda: Hopkins & Hopkins 1993; M. semper- nators to pollination success cannot be evaluated virens: Chen et al. 2012; M. macrocarpa: Kobayashi without documenting their precise interaction with et al. 2015, 2017, 2018a). Mucuna birdwoodiana is floral presentation. restricted to southern China (Wu et al. 2010) and Mucuna (Fabaceae) is a genus of evergreen lianas produces large inflorescences, each with 5–27 flowers, that are mainly distributed in the tropics, with more that hang directly from the vine, often several meters than 100 species known worldwide (Schrire 2005). above ground level (Fig. 1a). The flowers are large Species possess papilionaceous ‘gullet’-type flowers, and all petals are pale green in color (Fig. 1b, c). This although floral size, color, and nectar secretion combination of floral characters, together with their patterns differ markedly among species (Wilmot-Dear pungent, musky smell, has led to the presumption that 1984, 1990). To date, several purple- or pale green- flowers of this species are pollinated by bats (Lau flowered species (M. holtonii, M. pruriens, M. sloanei, 2004). Although casual observations suggest that a and M. urens) have been confirmed as bat-pollinated number of mammals, including fruit bats, routinely (Fleming et al. 2009), while several red- or yellow- visit the species (Lau 2012), the necessity of explosive flowered species (M. rostrata and M. japira) have been opening for fruit set and the means by which the confirmed as bird-pollinated (Cotton 2001; Agostini putative pollinator may achieve this remains unclear. et al. 2006). This dichotomy in pollination systems Moreover, detailed observations of the behavior of within the genus is supported by the observation that flower visitors have not previously been conducted bat-pollinated species bloom and secrete nectar only at and so the adaptive significance of floral color, size, night, whereas bird-pollinated species bloom for a and other floral traits, if any, has yet to be confirmed. period of several days and secrete nectar continuously Thus, the aim of the present study was to characterize throughout the day (Agostini et al. 2011). This has the pollination system of M. birdwoodiana. 123 Plant Ecol (2019) 220:457–466 459 inflorescences (1110 flowers) of one plant at BG, nine cameras were set to monitor 26 inflorescences (314 flowers) of four plants at NR, and two cameras were set to monitor 15 inflorescences (175 flowers) of one plant at SK. At the time of setting the camera traps, 10 flowers on three inflorescences at BG and seven flowers on three inflorescences at NR had already been opened. The monitored inflorescences were located at various heights (0–8 m) above ground level. All cameras were kept in position until all flowers on the inflorescences had withered and dropped. The record- ing mode was set for 30-s video clips with no interruption between clips, and sensitivity set to normal (Kobayashi et al. 2015, 2017). Visitation rate (VR) was calculated as the percent- age of observed inflorescences visited by a given species and Explosive Opening Rate (EOR) was calculated as the percentage of observed inflores- cences that had one flower triggered by a visitor. We used VR and EOR instead of absolute flower counts, Fig. 1 Inflorescences (a), unopened flower (b) and opened and calculated the flower visitation rate as the number flower (c)ofMucuna birdwoodiana.(A) calyx (B) banner of visits per hour per flower, which is a common index (C) wing (D) keel (carina) (E) pistil (stigma) (F) stamens in pollination ecology, because the flowers within an inflorescence mature at different times, making it Materials and methods difficult to determine each individual flowering period using video camera traps. It is also easier to calculate Study sites visiting frequency for a whole inflorescence rather than that of an individual flower.