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South African Journal of Botany 78 (2012) 63–74 www.elsevier.com/locate/sajb

Nectar properties of the -pollinated Impatiens sakeriana: A comparison with six other co-flowering ⁎ M. Bartoš a,b, , Š. Janeček b, E. Padyšáková a,b, E. Patáčová b, J. Altman a,b,M.Pešata b, J. Kantorová b, R. Tropek a,c

a Faculty of Science, University of South Bohemia, Branišovská 31, CZ-370 05 České Budějovice, Czech Republic b Institute of Botany, Academy of Sciences of the Czech Republic, Dukelská 135, CZ-379 82 Třeboň, Czech Republic c Institute of Entomology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31, CZ-370 05 České Budějovice, Czech Republic

Received 20 December 2010; received in revised form 9 May 2011; accepted 11 May 2011

Abstract

Adaptations of the nectar traits in -pollinated flowers are amongst the most discussed aspects of floral evolution. In the case of sunbird- pollinated , data on nectar traits originate almost exclusively from the South African region and are very scarce for tropical Africa, where paradoxically the highest sunbird diversity occurs. Here we present a study on the nectar properties of a sunbird-pollinated plant, Impatiens sakeriana, growing in the West African mountains, including the nectar production, diurnal changes in the nectar standing crop, the nectar concentrations, the nectar volumes, total sugar amounts and sugar composition. Moreover we compare the nectar traits of I. sakeriana with six other co-flowering insect-visited plant species. Our results showed that many nectar properties, including high volume (approx. 38 μL in flowers unvisited by ), low sugar concentration (approx. 30% w/w) and high sucrose content (95%), are specific to I. sakeriana, compared to the insect-visited plants. These are in accordance with the most recent theory that nectar properties of the sunbird-pollinated plants are similar to those pollinated by . © 2011 SAAB. Published by Elsevier B.V. All rights reserved.

Keywords: Cameroon; Impatiens sakeriana; Nectar; Pollination; Sunbird

1. Introduction Plants pollinated by are expected to produce higher volumes of more diluted nectar than insect-pollinated plants Nectarivory in birds is a widespread phenomenon, especially (Bolten and Feinsinger, 1978; Nicolson and Fleming, 2003a; in the tropical and subtropical areas with long flowering Goldblatt and Manning, 2006). The higher nectar amount is seasons. It has been estimated that around 10% of all bird believed to be related to the high energetic requirements of the species may use nectar as a resource (Wolf and Gill, 1986). The birds (Heinrich, 1981). The function of low sugar concentration most famous nectar feeders in the New World are humming- in the bird-pollinated flowers is much more debatable. Two birds, representing the most specialised bird pollinators (Stiles, hypotheses have been offered to explain the low concentrations 1978; Arizmendi and Ornelas, 1990; Stiles and Freeman, 1993; in regard to the evolution of the most appropriate nectar Schuchmann, 1999). In the Old World the most specialised properties for the birds. Baker (1975) noticed that nectar with a nectarivorous birds are sugarbirds, flowerpeckers, sunbirds and low sugar concentration has also a low viscosity, which spiderhunters (Cheke et al., 2001). facilitates more efficient extraction from flowers. Calder (1979) suggested that the dilute nectars can support bird water requirements in warm to hot environments, but at the same time ⁎ Corresponding author at: Tel.: +420 384721156; fax: +420 384721136. he pointed to possible problems with excessive water input E-mail address: [email protected] (M. Bartoš). under lower temperatures. More recent studies show that just

0254-6299/$ - see front matter © 2011 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2011.05.015 64 M. Bartoš et al. / South African Journal of Botany 78 (2012) 63–74 the excess water from dilute nectars represents the prevailing evaporation (Plowright, 1987). Pyke and Waser (1981) speculated osmoregulatory challenge to nectar-feeding birds. As a on the hypothesis that nectar properties evolved to affect pollinator consequence, the potential advantages related with more diluted foraging behaviour. nectars of bird-pollinated plants are debatable (Martinez del Rio The relation of the nectar sugar composition to the pollinator et al., 2001). The daily water intake of birds feeding on dilute class has also been repeatedly questioned (e.g. Galetto and nectar can be several times higher than their body weight Bernardello, 2004; Chalcoff et al., 2006; Wolff, 2006; Schmidt- (McWhorter and Martinez del Rio, 1999; Lotz and Nicolson, Lebuhn et al., 2007). A long-standing paradigm has been that 1999). The nectar-feeding birds are well adapted for elimination hummingbirds and birds differ in preferences of of surplus water. A South American , Sephanoides nectar sugar composition in the plants pollinated by them. sephanoides, can regulate the redundant water by decreasing Hummingbirds were generally regarded as sucrose-dominant water reabsorption in its kidneys (Hartman Bakken and Sabat, nectar consumers in comparison with the Old World nectar- 2006). Another studied nectarivorous bird, the Palestine sunbird ivorous birds, which prefer hexose-dominant nectar (Bruneau, (Nectarinia osea), is moreover able to regulate intestinal water 1997; Baker et al., 1998; Nicolson and Fleming, 2003a; absorption (McWhorter et al., 2003; McWhorter et al., 2004). Schmidt-Lebuhn et al., 2007). The hypothesis on this The higher ability of the Whitebellied Sunbird (Nectarinia dichotomy is however controversial, as there are large groups talatala) to produce highly diluted cloacal fluid when feeding of sunbird-pollinated plants in the Old World which produce on a dilute sucrose solution was manifested by Fleming and sucrose-rich nectar (Vos et al., 1994; Barnes et al., 1995). The Nicolson (2003). Besides avoiding over-hydration during the broader synthesis of Nicolson and Fleming (2003a) showed that feeding on more diluted nectars, the nectar-feeding birds face the passerine-pollinated plants embody a bimodal pattern with a dehydration during times of fasting (naturally during the night) high number of plants with high sucrose content and many (Hartman Bakken et al., 2004; Hartman Bakken and Sabat, species with hexose-rich nectar. Moreover, the dichotomy was 2006; Fleming et al., 2004a). Different bird groups solve this also put into doubt by several experimental studies showing that dilemma in different ways: whereas sunbirds are able to produce the specialised Old World are able to absorb sucrose concentrated cloacal fluid (Fleming and Nicolson, 2003), effectively (Lotz and Nicolson, 1996; Downs, 1997; Jackson hummingbirds conserve water balance only by remarkable et al., 1998) and did not prefer hexoses (or in extremely diluted reduction of their glomerular filtration rate (Hartman Bakken solutions only) using equicaloric (Fleming et al., 2004b; Brown et al., 2004; Hartman Bakken and Sabat, 2006). Dehydration et al., 2008) or equiweight (Lotz and Nicolson, 1996; Brown during the day activity is rather improbable as the birds can et al., 2008) solutions. Recently, Johnson and Nicolson (2008) consume supplementary water (Nicolson and Fleming, 2003b). have proclaimed this dichotomy as false, and suggested a more Nevertheless the plants produce nectar to increase their fitness useful distinction between specialised (i.e. including just and not to satisfy altruistically birds' requirements (Pyke, 1981; hummingbirds or sunbirds) and generalised (i.e. including Pyke and Waser, 1981; Martinez del Rio et al., 2001). In bulbuls, weavers, orioles and others) bird pollination systems. consequence, we need to consider the nectar properties as a Moreover, recent experiments show that the generalist avian compromise between plant and bird concerns. This could be the nectarivores prefer hexose solutions of concentrations similar as reason why the plants specialised to opportunistic nectarivores those found in the plants adapted to these birds (Fleming et al., produce relatively less concentrated nectar (8–12%) than plants 2008; Odendaal et al., 2010; Brown et al., 2010a,b). specialised to specialist nectarivores (15–25%), as they need to The theories on the nectar properties of the Old World plants satisfy the highly different requirements of their pollinators pollinated by specialised sunbirds can be nevertheless strongly (Johnson and Nicolson, 2008; Botes et al., 2008; Symes et al., affected by unbalanced geographical data acquisition. In most 2008; Brown et al., 2010a,b; Odendaal et al., 2010; Symes et al., of the synthesising studies the data predominates from the South 2010). On the other hand, it has been shown that plants pollinated African region (Baker et al., 1998; Johnson and Nicolson, by specialised birds produce a bit more diluted nectar than 2008), which represents just a marginal area of sunbird expected from the birds' preferences (Tamm and Gass, 1986; distribution (Cheke et al., 2001). Only a few studies have Roberts, 1996; Blem et al., 1997; Blem et al., 2000; Johnson et al., been done on the plant nectar properties in tropical Africa (Vos 2006). This disproportion can be explained considering that a et al., 1994; Burd, 1995; Evans, 1996; Johnson and Brown, different force other than ornithocentricity can modify the 2004; Ley and Claßen-Bockhoff, 2009), where paradoxically nectar properties. The plant aims to reduce the costs related the highest diversity of sunbirds occurs (Cheke et al., 2001). with nectar production and hence to produce less nectar volume Moreover, the scarce data from the Afrotropical areas seems to and/or lower nectar concentrations (Bronstein, 2001). Bolten and be quite inconsistent. It has been shown that sunbird-pollinated Feinsinger (1978) proposed that diluted nectar in the humming- telekii growing on Mt. Kenya have nectar concentrations of bird-accessible flowers evolved not to attract hummingbirds but around 60% (Evans, 1996), whereas Lobelia deckenii, growing on to avoid attracting bees. Other ecologists explain the relatively Mt. Kilimanjaro and visited by the sunbird Nectarinia johnstoni low nectar concentrations of the bird-pollinated flowers by and the mountain chat Cercomela sordida,haveonlyaround8% specific nectar composition and secretion patterns (Nicolson, nectar (Burd, 1995). However, the study of Burd (1995) did not 2002; Nicolson and Fleming, 2003a). Alternatively, the dilute determinate the pollination effectiveness of both birds and if the nectars can be also a solely secondary consequence of deep tubular generalist chat is the more effective pollinator, the extremely flowers of the bird-pollinated plants, which minimise water dilute nectar in L. deckenii corresponds to the Johnson and M. Bartoš et al. / South African Journal of Botany 78 (2012) 63–74 65

Nicolson (2008) conclusions, that plants adapted to generalised et al. unpublished results); the insect visitors are covered by bird pollinators have very diluted nectars. Other studied species Table 1 (for more details see the next paragraph). have nectar concentrations more typical for the sunbird-pollinated I. sakeriana Hook.f. (Balsaminaceae) is a 3 m erect herb of plants (approx. 15–25% w/w; Johnson and Nicolson, 2008). Such the mountain forest or its edge. Deeply red zygomorphic concentrations have been also demonstrated for several other flowers, presented year-round, are long pediculate. Flower specialised plants, such as several Maranthaceae species from longevity is about six days. I. sakeriana is pollinated only by Gabon (Ley and Claßen-Bockhoff, 2009), South-African, East- two sunbird species ( oritis, reichenowi); African and pantropical species of the Leonotus (Vos et al., no insect visitors were observed (Janeček et al., 2011) 1994), and a sunbird-pollinated orchid, Disa satyriopsis, from (Fig. 1a). Malawi (Johnson and Brown, 2004). Lobelia columnaris Hook.f. () is a 3 m erect It this study, we focused on the nectar properties of Impatiens herb of the mountain forest edges and the mountain grasslands. sakeriana, which grows in montane forest and along streams in the Blue or pink-purple flowers are comprised to the terminal Cameroonian mountains, and is fully dependent upon sunbird pyramidal panicle. The flowers live about ten days and are pollination (Janeček et al., 2011). Moreover, we analysed nectar presented in the dry season. L. columnaris is visited by many properties of six other co-flowering plants visited by insects to insect functional groups and also by sunbirds (Cynnyris reveal if these properties are unique in the wider community bouvieri, C. reichenowi). This species forms the monophyletic context. group with the pachycaul of East Africa, which are strongly adapted to bird pollinators (Evans, 1996; Antonelli, 2009)(Fig. 1b). 2. Materials and methods Hypoestes aristata (Vahl) Roem. & Schult. (Acanthaceae) is a 1 m erect herb of the mountain forest or its edge. Pale mauve 2.1. Study area flowers with darker markings are clustered to the whorls. The flowers live about five days and are presented in the dry season. Fieldwork was carried out in the Mendong Buo area, near the H. aristata is visited by many insect functional groups and also Big Babanki village, the Bamenda Highlands, North-West by sunbirds, especially C. reichenowii (Fig. 1c). Province, Cameroon (06°05′26″ N, 10°18′09″ E; 2200 m a.s.l.) Hypericum revolutum Vahl. (Gutifereae) is an up to 12 m from November 2007 to January 2008. The study area shrub or tree of the mountain forest edges and the stream experiences a single wet season from March/April to mid- mantels. Its flat yellow flowers develop solitarily on shoot November, with the precipitation ranging from 1780 to apices. Flower longevity is about two days. H. revolutum is 2290 mm/year (Cheek et al., 2000). Work started at the visited by many insect functional groups and also by all beginning of the dry season, with the start of the target plants' presented sunbird species, which, however, contribute little to flowering peaks. The studied area was composed of a mosaic of its pollination (Janeček et al., 2007)(Fig. 1d). Afromontane forest remnants, extensive and intensive pastures, Brillantaisia lamium (Nees) Benth. (Acanthaceae) is a 1.5 m forest clearings and abandoned pastures dominated by Pteridium erect herb of the mountain forest edges. Flowers are purple to aquilinum, and scrubby stream mantle vegetation (for more blue-coloured and form the lax panicle. Flower longevity is details see Reif et al., 2007; Tropek and Konvicka, 2010; Hořák et about three days. It is visited just by a few specialised insect al., 2010). The studied plant species were concentrated mainly functional groups (Fig. 1e). within the forest edges and along streams. Pycnostachys eminii Gürke (Lamiaceae) is an up to 3 m herb of the mountain forest edges and the mountain grasslands. Pale 2.2. Study plant species and their visitors blue flowers are conglobated into cylindrical spikes. Flower longevity is about two days. The flowers are visited by bees and The nomenclature and known species characteristics follow sporadically by C. bouvieri and C. reichenowi, but the birds Cheek et al. (2000). Information on the sunbird visitors showed negative selection to the plant and their visits are just originates from our previous studies (Riegert, 2011; Janeček accidental (Janeček et al., unpublished results) (Fig. 1f).

Table 1 Summary of visits of the morphotaxonomical functional insect groups in the individual plant species. Col-s Col-n Hym-t Hym-e Hym-s Hym-p Thy Lep Dip-s Dip-n Het Auc Nr. guilds Impatiens sakeriana 0 Hypoestes aristata 69 75 14 9 5 4 6 Lobelia columnaris 813485 4 Hypericum revolutum 795 235 32 507 53 14 129 6 11 9 Pycnostachys eminii 64 2 Brillantaisia lamium 54 4 3 Virectaria major 5883275 6 7 COL-S — highly specialised beetles; COL-N — other nectarivorous and pollenivorous beetles; HYM-T — highly specialised bees with long tongue; HYM-E — bees with large societies; HYM-S — bees with small societies and solitary species; THY — thrips; LEP — butterflies and hawk moths; DIP-S — specialised flies; DIP-N — other flies; HYM-P — parasitoid hymenopterans; HET — true bugs; AUC — leafhoppers. 66 M. Bartoš et al. / South African Journal of Botany 78 (2012) 63–74

Virectaria major (K. Schum.) Verds. (Rubiaceae) is a 2 m insect groups. The visitation of the target plants by individual insect weak-stemmed shrub of the mountain forest edges and the functional groups was recorded in sixteen 15 m transects of the mountain grasslands. Pale purple flowers form the erect terminal stream edge vegetation. Each plant species was observed 5 min per clusters. Flower longevity is about two days. It is visited by many each transect (if present) and visit (if actually flowering). The insect functional groups (Fig. 1g). observations were equally distributed within the day and the study period. The recording was limited from 09 h00 to 16 h00, the 2.3. Insect visitors—the pilot study activity peak of the most insect pollinators, and to suitable weather (at least partly cloudy). We observed each plant species from 4 to To explore the spectrum of insects visiting the target plants we 18 h, depending on its abundance in the studied community and its performed a pilot-study where we observed individual functional phenology. In spite of the relatively different sampling effort, the

Fig. 1. The studied plant species. Scale bars=1 cm; (a) Impatiens sakeriana; (b) Lobelia columnaris; (c) Hypoestes aristata; (d) Hypericum revolutum; (e) Brillantaisia lamium; (f) Pycnostachys eminii; (g) Virectaria major. M. Bartoš et al. / South African Journal of Botany 78 (2012) 63–74 67 insect functional group number is saturated for all studied plants, sugar concentration was measured using a Pal-1 (Atago co.) which allowed us to compare the individual plant species (see pocket refractometer. Small amounts of nectar (mostly highly Supplementary Fig. 1). concentrated and highly viscous) were diluted by distilled water Each specimen was classified into one of the 12 morphotax- on the refractometer and the concentration was calculated for onomical functional groups according to their relation to the the original amount. Total amount of sugar per flower was pollination process (modified after Williams et al., 2001 and calculated from sugar concentration per unit volume (mg/μL) Fenster et al., 2004): highly specialised beetles (Coleoptera: and sugar volume (Bolten et al., 1979). For calculation of sugar Lycidae); the other nectarivorous and pollenivorous beetles amount per μL from w/w concentration (the concentration (Coleoptera); highly specialised bees with long tongues measured by refractometer) we used exponential regression (Hymenoptera: Apinae); bees with large societies (Hymenop- equation (Galetto and Bernardello, 2005). tera: Apinae); bees with small societies and solitary species (Hymenoptera: Apinae); thrips (Thysanoptera); butterflies and 2.7. Nectar sugar composition hawk moths (Lepidoptera); specialised flies (Diptera: Syrphidae and Bombyliidae); other flies (Diptera); parasitoid hymenop- For assessment of the nectar sugar composition, 25 randomly terans (Hymenoptera: Parasitica); true bugs (Heteroptera); and selected flowers of each st