Abstract
The native forests of the central and eastern Pacific Islands were extensively modified by Polynesian settlers, but our understanding of these processes is generalised. In the first large study of anthropogenic forest change in the Marquesas Islands, the identification of two members of the Sapotaceae family in prehistoric archaeological charcoal assemblages was notable. Extant species from this family are poorly represented in East Polynesia, and the findings of Planchonella and another taxon (cf. Sideroxylon) indicate their geographical distribution was once more extensive than it is today. They further suggest some Sapotaceae may have been common elements of the indigenous lowland forests of the eastern high islands of Polynesia. Charcoal from the aforementioned taxa were found in early cultural contexts at archaeological sites in three Marquesan valleys, but were almost undetectable in late prehistoric contexts. These declines could be attributed to overexploitation of the wood, forest clearance and seed predation by introduced rats. Data from another archaeological site in the archipelago also suggest that links with reductions in native frugivorous bird populations should be explored. This study has informed on a group of plants that are not well-represented in pollen spectra in the region, and further highlights the usefulness of archaeobotanical data in studying palaeoecological processes in the Holocene.
Introduction
As people settled in the islands of central Polynesia in the late Holocene, they affected widespread and long-lasting changes to vegetation and landforms. Forest alterations in the early settlement period, and the composition of native lowland forests that were encountered by the earliest colonists, are better understood in some locations than others. Pollen studies have provided some insights into lowland vegetation dynamics. It has been found that some lowland areas were once home to large expanses of native forest and, at times, previously unknown vegetation formations have been indicated. Extinct and extirpated indigenous taxa are often encountered in these records; examples include large palms and in some instances a number of angiosperm trees, which have been identified in cores from the Hawaiian Islands, Rapa Nui and the Austral Islands (e.g. Athens and Ward, 1993; Flenley et al., 1991; Prebble and Dowe, 2008).
Macro-remains from archaeological contexts provide a different vegetation record, one that informs on a temporal and spatial scale that is complimentary to palynological data. Wood charcoal in particular can provide direct evidence of forest elements that once existed near a site, and also inform on vegetation conditions around the time of first settlement. The remains of hearths and ovens often contain charcoal, and features such as these are abundant in lowland archaeological sites in many parts of Polynesia. Strata with high concentrations of charcoal, frequently the remains of vegetation clearance or regeneration, are also sometimes encountered in excavation. Despite the abundance of these materials at many sites, the number of large wood charcoal studies in southeastern Polynesia is limited (e.g. Orliac, 2000) and early contexts have been poorly represented in these analyses. I report here on a study of archaeological wood charcoal from multiple locations in the Marquesas Islands, where the identification of materials from early occupation sites allows for an assessment of vegetation at a time of human arrival (or shortly thereafter). In particular, I discuss the identification of two extirpated or extinct members of the Sapotaceae family that occur in archaeological contexts at several study locations.
Study site
The Marquesas Islands are an archipelago of nine high volcanic islands and a number of small islets and seamounts in the central eastern Pacific Ocean near the equator, located at approximately 7°5′–10°35′S and 138°30′–140°45′W, 1500 km to the northeast of the Society Islands (Figure 1). The larger Marquesan islands are remarkable for their high-elevation ridges, deep valleys, and rugged coastal cliffs that drop sharply into the ocean. The Marquesan climate is tropical and the northern islands are more arid, with mean annual rainfall between 1000 and 1800 mm at sea level, and mean temperatures range from 26°C to 27°C (Laurent et al., 2004). Permanent streams run through most of the larger valleys and intermittent streams are present in many places, but few ponds or swampy areas exist.
Location of the Marquesas Islands and map of Nuku Hiva with study locations indicted in bold (modified from Allen and McAlister, 2013).
The Marquesan archipelago hosts an indigenous vascular flora of 362 species, of which 45% are endemic (Lorence and Wagner, 2011). Although the flora was first described in the late 19th and early 20th centuries (Brown, 1935; Brown and Brown, 1931; Del Castillo, 1892), until recently it was not well explored or documented. Today, many Marquesan plants have been catalogued and described as part of an extensive research programme (Smithsonian National Museum of Natural History, n.d.; Wagner and Lorence, 1997; and see Florence, 1997, 2004; Florence and Lorence, 1997).
Polynesians colonised the Marquesan archipelago by the 11th to 12th centuries, or perhaps earlier, and the analysis of radiocarbon results from short-lived materials (⩽10 years) places settlers unquestionably in the archipelago in the 13th century (see Allen, 2014). After settlement, lowland areas were extensively modified and by contact, groves of economically important introduced plants such as breadfruit (Artocarpus altilis, Moraceae) had become frequent in many of these locations (e.g. Krusenstern, 1813: 124–125).
Archaeological sites in three valleys on the windward side of Nuku Hiva, the largest of the Marquesas Islands with ca. 340 km2 of terrestrial surface, were selected to be part of this study (Figure 1). Hakaea, Hatiheu and Anaho fall within a 15-km radius and are broadly similar in elevation and overall topography, having steep walls and narrow coastal plains. Each valley does, however, have some variation in size, shape, hydrology and local climate conditions. Hatiheu is large and more uniformly moist and well-watered, while Anaho and Hakaea are smaller and parts have variable and at times dry conditions (Cauchard and Inchauspe, 1978; ORSTOM, 1993).
Materials and methods
Given the few fossil pollen records from Nuku Hiva (e.g. Allen et al., 2011), archaeological wood charcoal has provided a rich source of data to study human–forest interactions (Huebert, 2014). Samples for this analysis were collected at stratified sites near the coast in each of the three valleys, and at numerous test units placed adjacent to stone structures throughout the Anaho Valley, during a long-term archaeological programme directed by Melinda Allen (Allen, 2004, 2009; Allen and McAlister, 2010, 2013). Charcoal was retained systematically during these excavations, resulting in a large quantity of samples. Most was recovered by dry screening using 6.4- and 3.2-mm sieves or as in situ collections; others were recovered by wet screening when sediments were compacted, or using a simple bucket flotation method with heavy fractions screened using 3.2-mm mesh and light fractions strained through finely woven fabric. These materials represent at least a 600-year prehistoric sequence from an early occupation of the archipelago in the 12th century AD (or possibly earlier) to the late 18th century.
The availability, selection and use of plant materials by past people are important considerations when choosing archaeobotanical samples for interpretation. Much of the archaeological wood charcoal encountered in this region derives from fuel use in domestic contexts, and selection of these materials could have been influenced by factors ranging from the need to procure any available dry wood to a preference for hard, long-burning material that produced little smoke. Other activities may have introduced woods into these assemblages when materials had a secondary use as fuel, and vegetation clearance and the burning of structures can also introduce charcoal into an archaeological deposit. Cooking fires and burning regimes create different types of deposits, and each informs on local vegetation in a different way. Dispersed charcoal in cultural contexts where material has accumulated from domestic fires over long periods of time has been shown to inform on local vegetation formations (e.g. Chabal et al., 1999; Dotte-Sarout et al., 2014; Théry-Parisot et al., 2010). Charcoal from burned structures and certain types of domestic heating and cooking features are a more biased representation of these vegetation communities, containing more common forest elements and potentially highly selected material. For example, wood charcoal collected in situ from earth oven features in this archipelago has been shown to contain a restricted number of dense hardwood species that meet the demanding fuel needs necessary to heat oven stones (Huebert et al., 2010). In consideration of these potential biases, samples for the present study were selected from several context types to obtain information on both major and minor components of past vegetation in the study areas. They include occupation debris that accumulated on living surfaces, strata with high concentrations of charcoal where vegetation burning was indicated (burn layers), and features such as earth ovens and hearths.
A comparative collection was created to aid in charcoal identifications. Some materials were selected from the archives at the University of Auckland Anthropology Department, which houses collections of several hundred wood, fruit, seeds and various other plant parts from islands in the central and eastern Pacific including the Marquesas, Cook, Austral and Society Islands, Henderson (Pitcairn Islands), Fiji, and the Hawaiian archipelago. An additional 105 samples of wood and other plant parts were collected from Nuku Hiva by the author and deposited into this archive. Vouchers for these specimens were also collected, verified by botanists, and archived at the Auckland War Memorial Museum and the Herbarium of French Polynesia. Thin sections of fresh wood were mounted on slides and a histological study was performed. In total, the primary comparative collection used in this study included 129 wood sections from 51 families, including two specimens of Sapotaceae wood. A charcoal reference was created from a portion of these materials to better understand how anatomical structures are affected by carbonisation. This research was further supported by additional references of digitised or loaned Pacific specimens, which included a number of Sapotaceae, shared with the author (see section ‘Acknowledgements’). A series of publications on the wood anatomy of the neotropical Sapotaceae (Kukachka, 1978–1982) and the InsideWood database (Wheeler, 2011) were also consulted. Identifications were performed by snapping fragments to expose transverse, tangential longitudinal and radial planes using a scalpel (method adapted from Leney and Casteel, 1975). Exposed faces were observed using an epi-illuminated microscope at magnifications of 50–500×, and select materials were examined with a JEOL JSM-6700F Scanning Electron Microscope.
Results
In total, 6138 charcoal fragments were analysed and a minimum of 57 taxa were identified. Two taxa of interest were found in assemblages from all three valleys. Each displayed a combination of features characteristic of many Sapotaceae woods, which include axial parenchyma in narrow bands or lines up to three cells wide, very thick-walled fibres, vessel diameters 50–100 µm and ray widths of one to three cells. Additional features observed include thin rays with short multiseriate portions comprising small procumbent body cells and multiple rows of upright and/or square marginal cells, intervessel pits that are alternate and small, rounded or angular vessel-ray pits (sometimes difficult to examine in charcoal), and in some specimens, tyloses that appear to be thickened or sclerified. One of the identified taxa is a member of the genus Planchonella, displaying vessels in radial multiples of four or more (Figure 2A). The other (Figure 2B) matches many characteristics of the wood of Sideroxylon, most notably the charred reference specimen of Sideroxylon st.-johnianum (Figure 2C) from Henderson (Pitcairn Islands), and also a sample of Sideroxylon polynesicum from the Hawaiian Islands.
Sapotaceae wood charcoal of (A) Planchonella sp. and (B) cf. Sideroxylon sp. from Nuku Hiva archaeological assemblages and (C) charred reference specimen of Sideroxylon st.-johnianum. Distinctive features of Sapotaceae wood indicated with white arrows: (1) axial parenchyma in narrow bands or lines up to three cells wide; (2) ray width one to three cells; (3) vessel diameters 50–100 µm, radial multiples of 4 or more common in Planchonella (3a) and vessels frequent in Sideroxylon (3b, c); (4) fibres very thick-walled. Tangential longitudinal section: (5) thin rays with short multiseriate portions comprising small procumbent body cells and multiple rows of upright and/or square marginal cells; (6) intervessel pits alternate and small; (7) thickened tyloses (B only).
Sapotaceae wood charcoal was most abundant and occurred frequently in the 52 samples examined from the Hakaea Beach site. This site is notable as one of the most securely dated pre-14th century AD occupations in the Marquesas, and in the excavated area the cultural sequence spans approximately 300 years from the 12th to the 15th centuries AD (Allen and McAlister, 2010). The three main cultural layers at this site produced an exceptional charcoal assemblage in that more than a dozen woody taxa were identified in the lower cultural strata that were not found in the uppermost cultural layer. Many occurred in only a few samples, but Planchonella and several others were present in a quarter of the samples from early contexts, and cf. Sideroxylon was notably frequent (found in 81% of samples) and abundant (18% of total fragment count, Table 1) in early contexts at this site. Although charcoal from cf. Sideroxylon was a frequent contributor to the large assemblage from early contexts (which totalled 1114 fragments), it was found in much lower relative abundances (2–3%) in middle and late period contexts. Planchonella occurred in only one sample from late contexts.
Counts and relative percentages of Sapotaceae charcoal fragments identified at sites in three Nuku Hiva study locations.
These woods were also identified at the Pahumano-o-te-tai site, located in Hatiheu Valley. Cultural activities at this site commenced in the late 13th or late 14th century AD and continued into the contact period (Allen and McAlister, 2013). Several charcoal-rich sediments encountered here indicate vegetation clearance accompanied initial occupation of the area and burning played a role in landscape evolution over the next several centuries. In the 21 samples examined from this site, the wood of cf. Sideroxylon was present in the earliest cultural zone where it occurred in 60% of the samples and accounted for a significant proportion (16%, Table 1 centre rows) of the assemblage from that temporal zone. Some material was also present in middle period contexts, and it was absent from late prehistoric contexts, though this may not be significant as the sample sizes from these zones are smaller. Planchonella occurred at Pahumano in only one sample, which was from the earliest temporal zone.
The large assemblages from Anaho Valley sites also contained Sapotaceae charcoal. At the Anaho coastal sites, the cultural sequence commenced in the 13th century AD, but the most intensive occupation dates to between the 15th and 17th century AD (Allen, 2004, 2009). At the stone structures in this valley, the corpus of associated dates suggests they were initially used no earlier than the mid-17th century AD (Allen, 2009), though in some locations there was evidence of earlier pre-structural activity. In total, there were 27 samples each from two stratified coastal occupation sites and 48 samples from test units adjacent to stone structures located throughout the valley. In these assemblages, the two taxa of interest occurred only infrequently in middle and late contexts, despite the large quantity of fragments identified (Table 1, lower rows). A small amount of cf. Sideroxylon was identified in samples from each of the cultural strata in the coastal sites, but it was very infrequent in the numerous test units associated with late prehistoric residential foundations. A small amount of Planchonella occurred in several samples from middle period contexts in the coastal sites, but it was otherwise absent in samples from this valley.
Discussion
Taxonomy, habit and associates
The Sapotaceae family is an important component of tropical forests in many areas worldwide, and it produces timbers of commercial significance, latex, oils and fats (Govaerts et al., 2001). The wood is heavy and hard, and many neotropical genera have been documented by wood anatomists (e.g. Kukachka, 1978–1982). Members of the family have been subject to reorganisation for decades, though recent genetic studies have clarified some of their evolutionary relationships (Swenson and Anderberg, 2005), especially of those taxa found in Oceania (Bartish et al., 2005; Smedmark and Anderberg, 2007; Swenson et al., 2013). Several East Polynesian taxa were described by botanists in the early 20th century (Brown, 1935; Lam, 1938, 1954). Today, some are rare and protected in their native range (Meyer and Butaud, 2009) and none are (or were historically) listed for the Marquesas group (Smithsonian National Museum of Natural History, n.d.).
Sideroxylon L. (syn. Nesoluma in this region) has three recognised members in Polynesia (Smedmark and Anderberg, 2007). Sideroxylon nadeaudii (Drake) Smedmark & Anderb. can be found in the mesic forests of the Society Islands from 400 to 800 m in elevation, where it ranges from 5- to 15-m in height, may be long-lived, and is considered critically endangered because of fruit predation by rats (Meyer and Butaud, 2009). Sideroxylon polynesicum (Hillebr.) Smedmark & Anderb. is a shrub to medium size tree. Its native range includes the Cooks (Mangaia), Australs (Rapa and Raivavae, J-Y Meyer, 2014, personal communication) and all of the main Hawaiian Islands. It was once found in the region from near the coast to approximately 450 m (Lam, 1938), though it is now considered threatened and vulnerable in some areas (IUCN, 2014). Early in the 20th century, Sideroxylon polynesicum was a component of the typical dry forests of the Hawaiian Islands along with Planchonella, Nothocestrum, Nestegis, Polyscias, Antidesma, Bobea, Rauvolfia and others (Rock, 1913: 380–381), and today it has been noted on slopes, lava fields and in remnant patches of dry forest in this archipelago, though it is rare (Wagner et al., 1999). Sideroxylon st.-johnianum (HJ Lam & Meeuse) Smedmark & Anderb. is a small endemic tree that is co-dominant with Pisonia grandis and Xylosma suaveolens on the plateau forest of Henderson, an uninhabited island, where it also occurs in scrub vegetation and on cliff slopes (Waldren et al., 1995).
Planchonella is a polymorphic species of wide distribution that is adapted to many habitat types, which is a characteristic of the family as a whole (see Swenson et al., 2013). Several species are indigenous to the western archipelagos of Polynesia, and on the largest islands of Samoa, Planchonella torricellensis (K Schum.) H J Lam is dominant in some lowland to montane forests (Whistler, 2004). In East Polynesia, Planchonella tahitensis (Nadeaud) Pierre ex Dubard can be found today from sea level to mid-elevations on the high volcanic islands of Tahiti, Mo’orea and Raiatea in the Society Islands, and also in the raised limestone atolls of the Tuamotu (Anaa, Makatea and Niau) and Austral (Rurutu, Tubuai and Raivavae) archipelagos (Butaud et al., 2008). Its largest concentrations are in moist and transitional forests, and it can grow to 40-m height. Planchonella sandwicensis (A Gray) Pierre is endemic to the main islands of Hawaii, where it grows as shrubs or trees to 20-m tall in dry to mesic forests above 240 m (Wagner et al., 1999). It once occurred in a variety of locations in the Hawaiian Islands with associates such as Sideroxylon, Bobea and Nestegis in the forests of Lāna‘i, Polyscias and Antidesma in lava fields, and with Myoporum, Rauvolfia and Nothocestrum in dry areas (Rock, 1913: 381–392).
Sapotaceae in East Polynesian prehistory
Little was known about the process of Marquesan forest transformation from settlement to the contact period, or about the lowland forests that were encountered by settlers, but this study has provided some important information on these topics. Most notably, it is evident that populations of Sapotaceae were once growing in coastal and lowland areas, but they were greatly reduced after human settlement. The co-occurrence of Planchonella and (cf.) Sideroxylon in these assemblages could further suggest that lowland vegetation communities shared some characteristics of the historic Hawaiian forests described by Rock (1913: 380–392).
The results of this study indicate Sapotaceae woods were used as fuel early in the occupation sequences. This finding adds to what little has been documented about the traditional uses of these trees and their historic distribution in East Polynesia. Sapotaceae received infrequent mention in the early contact literature of the region written by botanically inclined visitors. The family was, for example, poorly covered in the botanical collections made during Cook’s voyages (Nicolson and Fosberg, 2004; S Cafferty, personal communication, 2014), suggesting the trees were rare or absent in lowland vegetation formations in many areas by the late 18th century. In Hawaii, P. sandwicensis sap was once used as an adhesive to snare birds (Rock, 1913: 385), and the hardwood was also said to have been used for house construction and digging sticks (Wagner et al., 1999: 1234). Less is known about the traditional uses of Sideroxylon. Native Hawaiians made no use of any part of S. polynesicum (keahi) in the early 20th century, despite the wood being quite hard and durable (Rock, 1913: 380–381). It was, however, an esteemed fuelwood on Rapa (where it was called kalaka and karaka) in the early 20th century (Brown, 1935; Lam, 1938; Prebble and Anderson, 2012 citing unpublished field notes of J Stokes) and karaka was inventoried as a fuelwood in the Rapan ethnology manuscript (Stokes, n.d.: 236–243A). It should be noted that the trees of this family do have uses in western Polynesia, especially Planchonella and Palaquium, the latter of which is an important commercial timber, and in Samoa they have construction and craft uses that include houseposts, carved artefacts and canoes (Whistler, 2004).
While some extant Sapotaceae in East Polynesia are threatened by predation from introduced rats today (Meyer and Butaud, 2009), large reductions in frugivorous pigeon and dove populations after human settlement in the Marquesas (Steadman, 2006) may have also been a factor contributing to their decline. Many Pacific Island trees rely on the actions of animals for seed distribution and pollination (e.g. Franklin and Steadman, 2010; McConkey and Drake, 2002; Meehan et al., 2002) and the fruits of the Sapotaceae are fleshy and particularly attractive to birds (Pennington, 1991; Waldren et al., 1995). Some, such as S. polynesicum, are very prolific and produce large quantities of reddish-purple olive-shaped fruits (Rock, 1913: 380–381). Mutualistic relationships between indigenous flora and fauna such as these were undoubtedly disrupted after human settlement, and an important dispersal mechanism could have been lost. The temporal trends in faunal assemblages observed at another Marquesan archaeological site are therefore of particular interest: at Hanamiai on Tahuata, several native landbirds were shown to have declined significantly only a few hundred years after the initial occupation period (Rolett, 1998; Steadman and Rolett, 1996). The tempo and intensity of that trend corresponds to the reduction of Sapotaceae observed in the present analysis. While such a correlation does not imply causation in complex ecosystem interactions, and several large frugivorous birds can still be found on Nuku Hiva, these findings do suggest the integrated analysis of archaeobotanical and avifaunal materials are an important direction of future research in human palaeoecology in this region.
Little information on the past distribution of Sapotaceae in the region has been gathered from fossil pollen records. Members of the family have been reported as rare elements in spectra from lowland situations on O‘ahu, Hawaii (Athens et al., 2002) and coastal sites in Tonga (Fall, 2005). In a study of sediment cores from catchments in the Samoan, Cook and Society Islands, Sapotaceae pollen was only identified at one site, in the lowest stratum of a core from an inland lake on Upolu (Parkes, 1994). A Sapotaceae was also reported as extirpated from Rimatara in the Austral Islands <900 cal. BP (Prebble and Dowe, 2008: Table 1). Archaeological wood charcoal has been somewhat more informative, as fragments of material from this family have been identified at several other sites in Polynesia. Planchonella charcoal was identified in several samples from Kahikinui, Maui, in contexts dating to before AD 1650 (Coil, 2004). Sapotaceae charcoal was also identified by the author in samples from the basal occupation zone of the Moturakau Rockshelter site, located on an islet in the Aitutaki lagoon, Cook Islands (Allen and Huebert, 2014: Table 4). Several fragments of cf. Planchonella were also identified by G Murakami in a pre-15th century context at the Ureia site on Aitutaki, and it was suggested that the absence of this material from later contexts at this site was notable (Allen, 1992: 96–97; R Wallace, unpublished data). When these findings are considered together with those of the present study, it is evident that human settlement had an impact on the trees and shrubs of the Sapotaceae family in several parts of eastern Polynesia.
Conclusion
The results of this study demonstrate that the natural distribution of plants in the Sapotaceae family was once more extensive than it is today, and it identifies two taxa that were frequent in the native lowland forests of windward Nuku Hiva at the time of human arrival. It is evident that wood from an indeterminate member of the family in particular, comparable to other Sideroxylon of the region, was once frequently used as a fuelwood and was probably a common element of the vegetation communities in these areas. A member of Planchonella was also present but may have been less frequent, though it is also possible the wood was not often used. Overall, it is evident that the trees and shrubs of the Sapotaceae family did not thrive as settlers remodelled the lowland vegetation communities of windward Nuku Hiva, and the decline of these woods to almost undetectable levels in late prehistoric contexts suggests the trees became rare in the surrounding vegetation. This trend is notable for the Hakaea Beach sequence in particular, and suggests the shift may have occurred within a few hundred years after settlement. These trees may have declined in the Marquesan lowland vegetation communities through seed predation by rats, and also by the reduction of indigenous bird populations, which were an important dispersal mechanism that decreased rapidly after human settlement of the archipelago. Present evidence further suggests that their decline and disappearance can be attributed to the overexploitation of tree species that have very hard wood, a quality that is especially favoured in the region for some utilitarian and construction uses, and also to fuel the traditional earth oven.
Footnotes
Acknowledgements
These data are part of a larger analysis of prehistoric arboriculture, agronomic development and landscape domestication in the Marquesas Islands. I thank Melinda S Allen for granting access to a substantial archive of material excavated from sites on Nuku Hiva, and for inviting me to participate in the 2011 field season. The reference collection was assembled with the assistance of Tioka Puhetini, Moetai Huioutu and Dadou Teikiehuupoko of Nuku Hiva, Ewen Cameron and Rhys Gardner of the Auckland Museum Herbarium, Jean-François Butaud and Rod Wallace. A collection of Scanning Electron Microscope (SEM) images of native Hawaiian woods, documented by the late Charles Lamoureux, were shared with the author by Michael Thomas of the Joseph F Rock Herbarium at the University of Hawaii, and microphotographs of several Hawaiian Sapotaceae were also supplied by Deborah Woodcock. Lloyd Donaldson provided advice on wood identification, as well as access to a SEM and several Sapotaceae specimens archived at Scion (New Zealand Forest Research Institute Ltd). Steve Cafferty of the Natural History Museum, London, supplied detailed information on the Sapotaceae collected by Banks & Solander. Jean-Yves Meyer, Melinda Allen and two anonymous reviewers are thanked for their helpful comments on earlier drafts of the manuscript.
Funding
This research was funded by a Doctoral Scholarship and Faculty of Arts Doctoral Research Fund Grant from the University of Auckland, and a Royal Society of New Zealand Skinner Grant. Funding and/or grant number: FundRef Funding Sources University of Auckland (Grant/Award Number: ‘Doctoral Scholarship’, ‘Faculty of Arts Doctoral Research Fund Grant’), Royal Society of New Zealand (Grant/Award Number: ‘Skinner Grant’).