Notes on the flowering and pollination of the endemic grassland Aloe reitzii var . reitzii ( Asphodelaceae )

Pollination systems in the genus Aloe are diverse, with numerous recent studies identifying unique and often unexpected mutualisms (Arena, Symes & Witkowski 2013; Botes, Johnson & Cowling 2009a; Botes, Wragg & Johnson 2009b; Hargreaves, Harder & Johnson 2008; Johnson 2004). While the perception remains that many Aloe species are pollinated by birds, relatively few studies have quantified the contributions of different pollinator guilds. Furthermore, in cases where a specific pollinator guild (e.g. birds) is identified as the most important contributor to pollination, fewer studies have addressed the specific roles of each species in that guild.


Introduction
Pollination systems in the genus Aloe are diverse, with numerous recent studies identifying unique and often unexpected mutualisms (Arena, Symes & Witkowski 2013;Botes, Johnson & Cowling 2009a;Botes, Wragg & Johnson 2009b;Hargreaves, Harder & Johnson 2008;Johnson 2004).While the perception remains that many Aloe species are pollinated by birds, relatively few studies have quantified the contributions of different pollinator guilds.Furthermore, in cases where a specific pollinator guild (e.g.birds) is identified as the most important contributor to pollination, fewer studies have addressed the specific roles of each species in that guild.
Many Aloe species can potentially hybridise and given the diversity of the genus it is important to understand how the species integrity of co-occurring taxa is maintained.Botes, Johnson & Cowling (2008) proposed that the problem of Aloe species coexistence may be explained by a greater diversity of bird pollination systems in the genus than previously documented.In five co-occurring Aloe species that flower together during winter there was a partitioning of pollinators, with short-billed generalist nectar feeders pollinating species with large amounts of dilute nectar in short corolla tubes, and long-billed specialist nectar feeders, that is, sunbirds, pollinating species with small amounts of concentrated nectar in long corolla tubes (Botes et al. 2008).
Many species-specific studies have provided valuable data regarding the widely distributed Afrotropical genus Aloe, where the diversity of species, with respect to (1) nectar characteristics, including volume and concentration, (2) flowering season and duration, (3) inflorescence, raceme and flower arrangement, (4) floral morphology, including structure, colour and position, (5) distribution and habitat preferences and (6) population size, is important in determining plant-pollinator associations (Botes et al. 2008(Botes et al. , 2009a(Botes et al. , 2009b;;Hargreaves, Johnson & Nol 2004;Hargreaves, Harder & Johnson 2012;Hoffman 1988;Johnson 2004;Pailler, Warren & Labat 2002; Background: Aloe reitzii var.reitzii is a succulent with a restricted distribution in the montane grassland of eastern South Africa.It is a summer (late January-March) flowering succulent that grows on rocky outcrops at 1000 m-1600 m, and the conspicuous inflorescences suggest a pollination system focused towards birds.

Conclusion:
Because birds are important pollinators for many Aloe species, it is assumed that the bird species detected visiting A. reitzii var.reitzii are similarly important pollinators.At least 10 invertebrate species and sengi (Elephantulus sp.) were also recorded as visitors to flowers, but they may be less important pollinators than specialist and generalist avian nectarivores.This study provides further insight into the pollination biology of a diverse, and ecologically important, succulent genus in Africa.

Notes on the flowering and pollination of the endemic grassland Aloe reitzii var. reitzii (Asphodelaceae)
Read online: Scan this QR code with your smart phone or mobile device to read online.Ratsirarson 1995;Stokes & Yeaton 1995;Wilson et al. 2009).While species-specific predictions of pollinators can be made on the basis of pollination syndromes, it is clear that determination of pollinator assemblages requires thorough field study (Fenster et al. 2004;Geerts & Pauw 2009;Johnson & Steiner 2000).An important tool in this regard is the application of camera traps, which in recent years have provided important and detailed information on plantpollinator interactions (Melidonis & Peter 2015;Steenhuisen et al. 2015;Zoeller et al. 2016).
Aloe reitzii Reynolds (1937) 1a and b).It grows on rocky areas, but is by no means confined to them (Glen & Hardy 2000;Reynolds 1969).It is known from 12 to 15 locations, with most populations confined to a small area (Raimondo et al. 2005).
Plants The objective of this study was to investigate potential pollinators of A. reitzii var.reitzii as inferred by visitation events captured by remote camera traps, as well as by field observations.

Study site
Field

Flowering biology
A single meandering transect (~1.5 km), that avoided recounting the same individual, was walked through the areas where plants occurred at Site 1, and flowering recorded.
The number of racemes was counted on 109 flowering plants.

Inflorescence visitors
Nine camera traps (Bushnell, model 119456, China) were set up on tripods (ht.~1.5 m), at least 1 m distant from each plant, to record visitors to flowering plants.Cameras were set at high sensitivity to take three photographs when motion sensors were activated, with 3-s intervals between activations.
Cameras were erected on the afternoon of 19 February and collected mid-morning on 21 February.A light rain fell on the night of 20 February.Any animal perched on the inflorescence, or photographed in flight close to the inflorescence, was defined as a flower visitor.If successive photographs captured what appeared to be the same individual, these were recorded as a single visit.Visits to plants ranged from an individual perched on a raceme and captured in only one photograph to an individual moving between racemes and photographed in successive images.While the presence of a visitor does not define its role as a pollinator, the records, together with observations at the site, do provide a basis from which to make interpretations regarding pollination of A. reitzii var.reitzii.Because different sized organisms may have different effects on the triggering mechanisms, and camera trapping is less likely to record all insects, no comparisons regarding visitation rates were made between birds and insects.For birds the proportion of visits by each species was calculated by dividing the total number of visits per species by the sum of all visits.For each plant, and for each hour during the day, the accumulative number of minutes (05:00-19:00) that cameras were set was determined.
The number of visits for each plant was then used to calculate an hourly visitation rate (number of visits/plant/hour).To calculate visitation rates only daylight hours were considered although cameras were active during night hours.All values are given as mean ± SD.

Flowering biology
A total of 726 plants (only sampled at Site 1) were recorded for the presence or absence of flowering.In total, 18.9% of plants were recorded flowering.The number of racemes per plant ranged from 1 to 10 (median = 3; mean = 2.9 ± 1.2; n = 109) and measured 44 cm ± 3 cm in length (n = 6 mature racemes).On all plants there were open flowers.The mean hourly visitation rate was 0.36 ± 0.19 visits/plant/ hour.Cape Weaver, Malachite Sunbird and Greater Doublecollared Sunbird visitation rates were 0.22 ± 0.15, 0.11 ± 0.11 and 0.03 ± 0.10 visits/plant/hour, respectively.These species were all observed probing flowers for nectar, by either perching below (Figure 1c) or above (Figure 1e) the open flowers.

Inflorescence visitors and behaviour
At least nine invertebrate species were observed and photographed on camera traps (Figure 1) and visited throughout the day from mid-morning to late-afternoon (Table 1).The only nocturnal visitors recorded were moths (Lepidoptera) during 19:00-20:59.Invertebrates were observed drinking nectar (e.g.Camponotus sp.) or removing pollen (e.g.Apis mellifera) while others were observed simply perched on flowers (e.g.Maura sp.) or inflorescence stems (e.g.Odontomutilla sp.) (Table 1).With values for A. reitzii var.reitzii at the lower end of the concentrations predicted for specialist nectarivores, and volumes extending into the range expected for generalist nectarivores, it is not surprising that the majority of floral visits were by Cape Weavers, which are generalist nectarivores and are adept at feeding on nectar (Craig 2014;Johnson & Nicolson 2008).Malachite Sunbirds were recorded on as many study plants as Cape Weavers, suggesting that these two species may both be important pollinators of A. reitzii var.reitzii.Malachite Sunbirds are ubiquitous throughout southern Africa and have been identified as primary pollinators of an entire guild of plant species -the 'Malachite Syndrome' (Geerts & Pauw 2009).
Many of the study plants received significant visitation from invertebrates.While it is possible that several of these were nectar robbers (Richardson 2004), honeybees were recorded in this study and have been shown as important pollinators of other Aloe species, (Botes et al. 2009a;Symes et al. 2009).They made up by far the greatest proportion of recorded insect visitors so, like in A. greatheadii var.davyana, they may be important pollinators when they occur in large numbers (Symes et al. 2009).Interestingly, observations of a wide variety of insects visiting study flowers contrasts findings in winter-flowering Aloe species which, unless they are visited by honeybees, are less likely to be visited by insects (Botes et al. 2009a;Hoffman 1988;Kuiper et al. 2015;Payne, Symes & Witkowski 2016;Symes et al. 2009).
Aloe peglerae, an endemic grassland Aloe of the Magaliesberg Mountain Range, is pollinated mainly by Cape Rock Thrush Monticola rupestris, a diurnal generalist nectarivore, with > 60% of pollination made by this species (Arena et al. 2013;Payne et al. 2016).However, pollination is also supplemented by nocturnal mammals such as Namaqua Rock Mouse Micaelamys namaquensis and Eastern Rock Sengi Elephantulus myurus (Payne et al. 2016).Anecdotal reports from the landowner at Site 2 suggest that sengi (Elephantulus sp.) have been observed visiting flowers during the day (B.Struwig, pers.comm.).However, no photographs were obtained of small mammals visiting flowers during this study.Thus, while visits by small mammals, such as sengi (Wester 2010), may be more common in rocky areas at our study sites, this mammal-plant association remains to be investigated.

Conclusion
In conclusion, A. reitzii var.reitzii is visited primarily by generalist and specialist avian nectarivores, as well as by invertebrates.Although the latter cannot be confirmed as legitimate pollinators, the fact that (1) birds and insects have been shown to be successful pollinators of numerous Aloe species and (2) fruit set at the site is abundant each year (landowners, pers.obs.) suggests that these organisms are important role players in the pollination of A. reitzii var.reitzii.A generalist pollination system might contribute to fitness of A. reitzii var.reitzii, a range-restricted, summerflowering endemic occurring in fire-dominated grasslands; this remains to be investigated further.Furthermore, this study shows the usefulness of remote camera traps in testing predictive floral syndromes in the diverse genus Aloe.

:
Nectar standing crop (flower volume and concentration) and the proportion of plants flowering were recorded.Camera traps and observations were used to record visitors to A. reitzii var.reitzii inflorescences.
reach a height of up to 1.0 m and produce multiple racemes that can reach 2.5 m in height (Glen & Hardy 2000; Reynolds 1969; Van Wyk & Smith 2003).The immature unopened flowers are dark red, becoming orange to pale yellow when mature (Van Wyk & Smith 2003), and are incurved and relatively long (32 mm-50 mm), suggesting pollination by birds (Figure 1a and b) (Glen & Hardy 2000; Reynolds 1969; Symes, Human & Nicolson 2009; Van Wyk & Smith 2003).
Photos taken by Craig Symes

Table 1
). http://www.abcjournal.orgOpen Access Nectar characteristics A total of 48 visits were made by three bird species during 155 hours of camera trap observations.Most visits were by Cape Weaver, Ploceus capensis (60.4%), with fewer visits by Malachite Sunbird, Nectarinia famosa (27.1%) and Greater Double-collared Sunbird, Cinnyris afer (12.5%) (Table1).Cape Weaver and Malachite Sunbird visited eight and six of the nine monitored plants, respectively.Greater Double-collared Sunbird only visited a single plant, located near a bushclump in a rocky outcrop.The earliest bird visitor was at 05:40 and the latest at 18:26.Plants were visited by birds during all hours of the day except mid-afternoon.

TABLE 1 :
Visitors recorded at Aloe reitzii var.reitzii flowers, Houtenbek farm, Dullstroom, from 19 to 21 February 2014, by camera trap (155 camera trap hours; n = 9 camera traps) and visual observations.'-'for number of visits indicates species not recorded on camera traps.While this study considers visitation data from only three days of a flowering season, camera traps and field observations provided information on the most likely pollinators of A. reitzii var.reitzii.In the grassland environment in which A. reitzii var.reitzii occurs there are a Source: Author's own work http://www.abcjournal.orgOpenAccessDiscussion