Plant Ecol (2019) 220:457–466

https://doi.org/10.1007/s11258-019-00927-y (0123456789().,-volV)( 0123456789().,-volV)

Civet pollination in Mucuna birdwoodiana (: 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 . 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 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 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 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 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 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 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 . 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 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 , 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. This study was conducted in wild, self-seeded popu- The behaviors of animals visiting flowers were lations of M. birdwoodiana occurring in Kadoorie divided into six categories based on their effect on the Farm and Botanic Garden (KFBG) and Sai Kung in visited flowers (Kobayashi et al. 2015): (1) explosive Hong Kong in March and April 2018. In KFBG, we set opening with no damage to the flower (successful two study sites: one in semi-natural, managed wood- opening); (2) explosive opening with damage to the land within a botanic garden (denoted BG; flower (such as flower dropping), even though pollen 22°2505700N, 114°0700600E; 190 m elevation) and one may still be successfully transferred; (3) visitation of a in unmanaged mature secondary forest within a nature previously opened flower; (4) nectar robbing from an reserve (denoted NR; 22°2508–1400N, unopened flower; (5) destruction of a flower without 114°07018–2300E; 500–630 m elevation). A plant opening (tearing off, biting, or dropping); and (6) other studied in Sai Kung occurred in young secondary behavior such as touching flowers. Chi-square tests forest and grew near a path (denoted SK; 22°2403000N, were conducted to ascertain significance in the 114°1705500E; 110 m elevation). frequency among the different observed behaviors for each floral visitor. Observations of floral visitors Bagging experiment Motion-sensitive video camera traps (Ltl-5210A and Ltl-6210MC; Shenzhen Ltl Acorn Electronics Co., A bagging experiment was conducted at site NR to Ltd., China) were used for documenting floral visitors. ascertain the importance of explosive opening for fruit Video camera traps were strapped to trees by belt or set (i.e., to evaluate the possibility of autogamous self- wire. In total, 18 cameras were set to monitor 88 pollination). Forty-two inflorescences with 592 123 460 Plant Ecol (2019) 220:457–466 unopened flowers from four individuals were first sucrose, fructose, and glucose, and a sugar ratio was enclosed in fine mesh nets. Once all flowers within the calculated as sucrose/(glucose ? sucrose). nets had dropped, fruit set was checked. In addition, Nectar volume and concentration were compared the number of fruits produced by each inflorescence using the Kruskal–Wallis test and sugar ratios were monitored in the camera trapping experiment was compared using a Mann–Whitney U-test. All statisti- recorded (i.e., open fruit set), allowing us to compare cal analyzes were conducted in R version 3.5.0 (R fruit set rates following spontaneous autogamy and Core Team 2018). natural pollination. We calculated the fruit set rate (i.e., the number of fruits produced as a proportion of the total number of flowers) for the bagged inflores- Results cences but counted the rate of fruit production per inflorescence for the open pollinated inflorescences, Flower visitors and their behavior because we were unable to check all flower opening behaviors by explosive openers due to a time lag and Four mammal species were observed visiting flowers otherwise missed shots with the video equipment. of M. birdwoodiana (Table 1, Fig. 2). Pallas’s squir- Thus, for open pollination, there may be a tendency to rel, Callosciurus erythraeus styani, had the highest VR overestimate fruit set. Opened flowers that were eaten at the BG and NR sites in KFBG, but was not observed (or otherwise destroyed) by animals in the open visiting flowers at SK (Table 1). The second most pollination experiment were excluded from the frequent visitor at BG and NR was the masked palm analysis. civet, Paguma larvata, and this was the sole visitor at SK. Only these two visitors successfully opened Nectar survey flowers. Both explosive openers held one or both wing petals using their forelimbs and inserted their Due to its accessibility, nectar production was mon- snout through the gap formed between the banner and itored at the BG site by collecting five flowers from wing petals; they then pushed the banner petal upward five inflorescences from a single individual every three using their snout and simultaneously pressed down- hours starting from 1500 h, and then probing for ward on the wing petal(s) held between their forelimbs nectar inside the calyx. Total nectar volume was (Videos S1, S2). This released the stamens and pistil, measured using a microsyringe (MS-N100; Ito Cor- firing a plume of pollen forwards. Masked palm civets poration, Shizuoka, Japan) and sugar concentration were recorded visiting flowers only during the night was measured using a hand-held sugar refractometer (19:33–05:17), whereas Pallas’s squirrels visited in (HSR-500; Atago, Tokyo, Japan). the daytime (06:07–18:52). Masked palm civets In addition, sugar composition was analyzed by always opened flowers when they visited, while high-performance liquid chromatography (HPLC). Pallas’s squirrels did not open flowers on every visit Nectar was collected from five flowers from five (Table 1). Masked palm civets opened flowers more inflorescences on a single plant at 0900 h and 2100 h, frequently as compared with Pallas’s squirrels at BG, and this was transferred to Eppendorf microtubes and but both species opened flowers in similar numbers at stored in the freezer (- 20 °C) until analyzed. The NR (Fig. 3). The frequency of explosive opening nectar was first dissolved in acetonitrile solution behavior witnessed in the Masked palm civet did not (nectar:distilled water:acetonitrile = 2:33:65) and this differ significantly among the different study sites (v2 2 solution was percolated through a Mini-UniPrep test; v 2 = 0.73, P = 0.68), whereas that of Pallas’s 2 syringeless filter (UN203NPUAQU; GE Healthcare squirrels did (v 1 = 49.31, P \ 0.01). In addition, companies, UK). This percolated acetonitrile solution nectar robbing and other destructive behaviors were was then analyzed (LC-20AD; Shimadzu Corporation, observed far more frequently in Pallas’s squirrels as Kyoto, Japan). A Sugar-D column (Nacalai Tesque, compared with masked palm civets at all sites (Fig. 3). Kyoto, Japan) was used and 80% acetonitrile solution During explosive opening, the stamens were flung was delivered at a flow rate of 0.5 ml/min. Sugars forwards, depositing pollen grains onto the lower jaw were identified from the resulting chromatogram by of the masked palm civet and onto the throat and belly comparing against standard chromatograms for of the Pallas’s squirrel, and the stigma came to rest in a 123 Plant Ecol (2019) 220:457–466 461

Table 1 Inflorescence visitation rates (VR) of vertebrate visitors to Mucuna birdwoodiana inflorescences and explosive opening rates of the inflorescences (EOR) at three sites Species name Common name Visited time Garden in KFBG Forest in KFBG Sai Kung (n = 15) (n = 88) (n = 26) VR (%) EOR VR (%) EOR VR (%) EOR (%) (%) (%)

Callosciurus erythraeus Pallas’s squirrela Daytime 52.3 9.1 88.5 73.1 0.0 0.0 styania Macaca mulatta Rhesus macaque Daytime 2.3 0.0 23.1 0.0 0.0 0.0 Niviventer fulvescens Chestnut spiny rat Nighttime 4.5 0.0 3.8 0.0 0.0 0.0 Paguma larvata Masked palm Nighttime 10.2 10.2 53.8 53.8 20.0 20.0 civet VR = (number of inflorescences visited by each visitor/number of targeted inflorescences) 9 100. EOR = (number of inflorescences with open flowers opened by each visitor/number of targeted inflorescences) 9 100. Sample sizes indicate the number of monitored inflorescences aExotic subspecies

Fig. 2 Flower visitors of Mucuna birdwoodiana. a Masked palm civet (Paguma larvata) b Pallas’s squirrel (Callosciurus erythraeus styani) c Rhesus macaque (Macaca mulatta) d Chestnut spiny rat (Niviventer fulvescens)

123 462 Plant Ecol (2019) 220:457–466

Nectar secretion patterns

Nectar was stored at the base of the calyx. The Kruskal–Wallis test revealed that neither nectar vol- ume nor sugar concentration varied significantly 2 throughout the day (volume: v 7 = 2.51, P = 0.93, 2 Fig. 4a; concentration: v 7 = 5.01, P = 0.66, Fig. 4b). Mean nectar volume was 882.9 ± 75.0 ll and mean sugar concentration was 24.3 ± 0.6% (n = 40). HPLC revealed the dominant sugar to be sucrose. The sugar ratio was 1.45 ± 0.10 at 9:00 and 1.52 ± 0.11 at 21:00; these values are not significantly different (Mann–Whitney U-test; W =8,P=0.42, Table 3).

Discussion

Effective pollinator of M. birdwoodiana

As has been documented for other Mucuna species (e.g., M. macrocarpa; Kobayashi 2017), our study reveals that M. birdwoodiana does not produce fruits if Fig. 3 Frequencies of observed behaviors by flower visitors of its flowers are not explosively opened. Therefore, the Mucuna birdwoodiana at the three study sites. a BG at Kadoorie Farm and Botanic Garden (KFBG) b NR at KFBG c Sai Kung. explosive opening mechanism is essential for pollina- ‘‘X’’ indicates that the species did not visit flowers at that study tion success in this species. Once the stamens and site pistil have been exposed in this way, they remain free of the keel petals, indicating that a flower can achieve position that directly contacted these parts of the successful pollination in a single opening. These animal visitors. However, in some cases, pollen grains observations conform with the mechanism described were also observed on the head or back of Pallas’s for the closely related M. macrocarpa (Toyama et al. squirrels. Once a flower had been opened, the stamens 2012). Moreover, our camera trap footage suggests and pistil remained exposed and free of the petals. that a large number of pollen grains are fired onto and Observation of explosively opened flowers confirmed therefore inadvertently removed by explosive openers, that many pollen grains had been removed by the and that the stigma makes contact with more-or-less visitors. the same position on the body of the explosive opener Asian honeybees (Apis cerana cerana) were fre- to which the pollen grains adhere. These findings quently seen visiting both opened and unopened confirm that explosive openers are the primary polli- flowers. Although they did not collect pollen, they nator in this species. In the present study, the number were observed foraging for nectar. of flowers opened by masked palm civets was similar to that of Pallas’s squirrel at one study site, but was Fruit set markedly greater at the two other study sites (Fig. 3). In addition, masked palm civets were less destructive No fruits formed on bagged inflorescences (Table 2), when interacting with flowers of M. birdwoodiana as and no flowers opened automatically. However, fruits compared with Pallas’s squirrels. Therefore, we infer did form from flowers opened by masked palm civets that masked palm civets are the most important or Pallas’s squirrels. Fruit set was observed on 27.9% pollinator of M. birdwoodiana, at least in this part of of monitored inflorescences (6.6% of flowers) and on the species’ range, although our sample size was 78.3% of monitored inflorescences with opened flow- small. ers (42.2% of opened flowers) (Table 2). 123 Plant Ecol (2019) 220:457–466 463

Table 2 Fruit set rate of bagged and targeted Mucuna birdwoodiana inflorescences and flowers monitored in the video camera trap experiments Bagged experiment Camera trap experiment Inflorescences Flowers Inflorescences Flowers All targeted Inflorescences All targeted Opened inflorescences with opened flowers (including flowers flowers opened and unopened flowers) n Rate (%) n Rate (%) n Rate (%) n Rate (%) n Rate (%) n Rate (%)

Garden in KFBG (BG) – – – – 88 15.9 19 73.7 1116 4.1 46 55.4 Forest in KFBG (NR) 42 0.0 592 0.0 26 73.1 24 79.2 314 17.5 55 35.3 Sai Kung (SK) – – – – 15 20.0 3 100.0 175 2.9 5 41.7 Total 129 27.9 46 78.3 1605 6.6 106 42.2

The Pallas’s squirrel is considered an introduced species in Hong Kong (Ho 1994), with naturalized populations of two subspecies (styani and thai) thought to have established within the last 50–60 years from released or escaped pets (Shek 2006). However, the species has an extensive native distribution across southern China and throughout much of continental Southeast Asia (Duckworth et al. 2017), suggesting that it probably occurred naturally in Hong Kong prior to landscape-level forest clear- ance, as is inferred for other squirrel species (Dudgeon and Corlett 2004). Therefore, it is plausible that Pallas’s squirrels may have contributed as a diurnal pollinator of M. birdwoodiana historically, and that they continue to do so throughout the latter’s range in southeast China, although their efficacy is likely to be lower than that of masked palm civets. In a previous study, the fruit bat of Leschenault’s rousette, Rousettus leschenaulti, was observed visiting Fig. 4 Nectar secretion patterns of Mucuna birdwoodiana. M. birdwoodiana flowers in Hong Kong (Lau 2004), a Volume b Nectar sugar concentration. Error bars indicate SD and it therefore remains possible that this species also serves as an occasional pollinator. Indeed, two fruit bat Table 3 Sugar components (%) and sugar ratio of Mucuna species (R. leschenaultia and Cynopterus sphinx) birdwoodiana flowers occur in Hong Kong and both are known to roost in Fructose Glucose Sucrose Sugar ratio urban parks and countryside where M. birdwoodiana is commonly found (Corlett 2005; Shek 2006; Hong 9:00 24.4 ± 1.4 15.4 ± 0.6 60.2 ± 1.8 1.45 ± 0.10 Kong Herbarium and South China Botanical Garden 21:00 24.2 ± 1.2 16.6 ± 0.6 59.2 ± 1.8 1.52 ± 0.11 2008). However, explosive opening behavior by R. leschenaultia was not observed in the earlier study (Lau pers. comm.), and neither of the two fruit bat species were observed visiting flowers of M.

123 464 Plant Ecol (2019) 220:457–466 birdwoodiana in present study despite their known nocturnal, bat-pollinated M. urens in South America, occurrence at our study sites (Shek 2006). Fruit bats which secretes nectar only at night (Agostini et al. are therefore not regarded as primary pollinators. 2011). However, a similar pattern has been docu- The Rhesus macaque and chestnut spiny rat were mented in the Asian M. macrocarpa, a diurnal also observed visiting flowers in our study, but they squirrel- and nocturnal bat-pollinated species failed to trigger explosive opening. As explosive (Kobayashi et al. 2018b). In addition, the sugar opening is necessary for reproduction in M. birdwood- composition of M. birdwoodiana nectar is also similar iana, these visitors do not appear to contribute to to that of M. macrocarpa (Kobayashi et al. 2018b). pollination success. Formosan rock macaques, Ma- These features may suggest that M. birdwoodiana is caca cyclopis, and spinous country rats, Niviventer not strongly adapted for nocturnal palm civet pollina- coxingi, visited M. macrocarpa, a sister species in tion, but our data do provide support for the hypothesis Taiwan, but they also failed to open flowers and thus that the species also benefits from more opportunistic cannot be regarded as effective pollinators of that diurnal squirrel pollination. species (Kobayashi et al. 2017). In contrast, the Japanese macaque, Macaca fuscata, frequently Viverridae as pollinators opened flowers of M. macrocarpa and contributed to pollination success at the northern limit of this species Many Viverridae species are arboreal, have an in Kyushu, Japan (Kobayashi et al. 2015). These omnivorous but fruit-rich diet (Goswami and Friscia findings indicate that the effectiveness of different 2010), and correspondingly are important dis- Macaca species as pollinators of Mucuna varies persers in tropical forests (Rabinowitz 1991; Corlett geographically, even within single widespread species 1998; Zhou et al. 2008). Despite the equally critical of the latter. On the other hand, available evidence role played by pollinators in forest ecosystems, suggests that rats (Muridae) do not open Mucuna Viverridae have not been confirmed as main pollina- flowers (Kobayashi et al. 2018c), although they have tors, although some Viverridae species visit flowers been shown to be effective pollinators of other plants and may contribute to pollination (Lack 1977; Steen- (e.g., Wester et al. 2009; Johnson and Pauw 2014). huisen et al. 2015; Kobayashi et al. 2017). Given their nocturnal lifestyle and diet, in reality civet pollination Adaptive floral characters for civet pollination may be more widespread than currently recognized. Furthermore, nectariferous lianas such as M. bird- The keel length of M. birdwoodiana (7.5–8.5 cm) is woodiana are likely to constitute an important food greater than that of known squirrel- and bat-pollinated source for arboreal mammals in disturbed and sec- Mucuna species ( \ 7.0 cm) (Wilmot-Dear 1984). ondary tropical forest (Dudgeon and Corlett 2004). Although its pale green flowers have been interpreted While fruit bats are frequently regarded as the most as characteristic of bat-pollinated species (Lau 2004; important mammal pollinators in tropical Asia (Cox Willmer 2011), the vine is otherwise robust and woody et al. 1991; Corlett 2004), squirrels also play a (frequently exceeding 15 cm diameter in mature valuable role (van der Pijl 1961; Corlett 2004). The individuals; pers. obs.; Wilmot-Dear 1984), and taken confirmation of specialized non-flying mammal pol- in combination these traits could therefore be viewed lination systems among Mucuna species (Chen et al. as adaptive, promoting visits by bulky (3–6 kg body 2012; Kobayashi et al. 2017; this study) and other trees weight), nocturnally active palm civets (Shek 2006). and lianas (Yumoto et al. 2000; Tandon et al. 2003)in The nectar volume confirmed in the present study is tropical Asia strengthens this perspective. Both squir- more than twice as large as has been documented in rels and civets are known to have radiated in tropical any bat-, squirrel- or bird-pollinated Mucuna species Asia (Corlett 2007), and our results suggest that (Agostini et al. 2011; Chen et al. 2012). Such a large unique pollination systems involving non-flying mam- nectar volume is likely to be effective for attracting a mals have similarly diversified in the region. large-bodied mammal, such as a palm civet. More- over, the nectar secretion pattern in M. birdwoodiana Acknowledgements We are grateful to Michael Lau for is notable for providing a nutritive store throughout the providing advice and to Kadoorie Farm and Botanic Garden for allowing us to conduct this study. We also thank Shinichi Gima day, which differs markedly from the purely 123 Plant Ecol (2019) 220:457–466 465

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