Population modelling and genetics of a critically endangered Madagascan palm Tahina spectabilis

Abstract Madagascar is home to 208 indigenous palm species, almost all of them endemic and >80% of which are endangered. We undertook complete population census and sampling for genetic analysis of a relatively recently discovered giant fan palm, the Critically Endangered Tahina spectablis in 2008 and 2016. Our 2016 study included newly discovered populations and added to our genetic study. We incorporated these new populations into species distribution niche model (SDM) and projected these onto maps of the region. We developed population matrix models based on observed demographic data to model population change and predict the species vulnerability to extinction by undertaking population viability analysis (PVA). We investigated the potential conservation value of reintroduced planted populations within the species potential suitable habitat. We found that the population studied in 2008 had grown in size due to seedling regeneration but had declined in the number of reproductively mature plants, and we were able to estimate that the species reproduces and dies after approximately 70 years. Our models suggest that if the habitat where it resides continues to be protected the species is unlikely to go extinct due to inherent population decline and that it will likely experience significant population growth after approximately 80 years due to the reproductive and life cycle attributes of the species. The newly discovered populations contain more genetic diversity than the first discovered southern population which is genetically depauperate. The species appears to demonstrate a pattern of dispersal leading to isolated founder plants which may eventually lead to population development depending on local establishment opportunities. The conservation efforts currently put in place including the reintroduction of plants within the species potential suitable habitat if maintained are thought likely to enable the species to sustain itself but it remains vulnerable to anthropogenic impacts.

newly discovered populations and added to our genetic study. We incorporated these new populations into species distribution niche model (SDM) and projected these onto maps of the region. We developed population matrix models based on observed demographic data to model population change and predict the species vulnerability to extinction by undertaking population viability analysis (PVA). We investigated the potential conservation value of reintroduced planted populations within the species potential suitable habitat. We found that the population studied in 2008 had grown in size due to seedling regeneration but had declined in the number of reproductively mature plants, and we were able to estimate that the species reproduces and dies after approximately 70 years. Our models suggest that if the habitat where it resides continues to be protected the species is unlikely to go extinct due to inherent population decline and that it will likely experience significant population growth after approximately 80 years due to the reproductive and life cycle attributes of the species. The newly discovered populations contain more genetic diversity than the first discovered southern population which is genetically depauperate. The species appears to demonstrate a pattern of dispersal leading to isolated founder plants which may eventually lead to population development depending on local establishment opportunities.
The conservation efforts currently put in place including the reintroduction of plants within the species potential suitable habitat if maintained are thought likely to enable the species to sustain itself but it remains vulnerable to anthropogenic impacts.

K E Y W O R D S
conservation genetics, demographic population growth modelling, population viability analysis, species distribution modelling

| INTRODUC TI ON
There have been a startling number of plant species extinctions recorded in recent times, but equally, the number of species discovered and rediscovered indicates more field studies are needed to document what we have and where it grows (Humphreys, Govaerts, Fininski, Lughadha, & Vorontsova, 2019). Madagascar is one of the countries identified as having lost a disproportionately high number of plant species in modern times (Humphreys et al., 2019). It is one of the world's most threatened biodiversity hotspots with over 80 percent of its flora being endemic, coupled with widespread habitat degradation (Gautier & Goodman, 2003;Meyers, Mittermeier, Mittermeier, Fonseca, & Kents, 2000;Rakotoarinivo, Dransfield, Bachman, Moat, & Baker, 2014). Palms have been identified as approximately four times more at risk of extinction than other plant groups in Madagascar (Rakotoarinivo et al., 2014). A total of 41 species of endemic palms have been discovered since 1995 in Madagascar (Govaerts, Dransfield, Zona, Hodel, & Henderson, 2019), one of the most significant being the Critically Endangered Tahina spectabilis (tribe Chuniophoeniceae of subfamily Coryphoideae), due to its phylogenetic distinctiveness within the Madagascan palm flora (Baker et al., 2009;Dransfield & Rakotoarinivo, 2011;Dransfield, Uhl, et al., 2008;Rakotoarinivo et al., 2014). While the protected areas encompass many species, those with highly restricted distributions such as T. spectabilis are frequently missed (Heywood, 2019;Rakotoarinivo et al., 2014).
Endangered species recovery programs for plants now increasingly add translocations and reintroductions to secure species survival as well as in situ and ex situ conservation approaches, particularly where populations are critically small, restricted, and unprotected (Godefroid et al., 2011;Heywood, 2019;Silcock et al., 2019;Weeks et al., 2011). Success of translocations for reintroduction of threatened species will depend on knowledge of species' habitat distribution, biology and ecology, genetic diversity, and population dynamics (Godefroid et al., 2011;Heywood, 2019;Silcock et al., 2019;Weeks et al., 2011). Tahina spectabilis, while only recently discovered and named in 2008, was quickly secured with ex situ conservation measures which involved seed harvesting and international distribution Gardiner, Rabehevitra, Letsara, & Shapcott, 2017). This regulated local collection of seed also resulted in the opportunistic planting of specimens within the expected suitable habitat of the species  close to the original population location (Gardiner, Rabehevitra, Letsara, et al., 2017). The recent discovery of a second population location to the north of the known and originally predicted habitat has led to the need to revise the original species habitat distribution model as well as to reassess the species extent of occurrence (EOO and area of occupancy (AOO) for IUCN conservation assessments Gardiner, Rabehevitra, Letsara, et al., 2017;.
Tahina specatabilis is a hapaxanthic species, producing a massive terminal inflorescence that can give rise to many thousands of pale green fruits approximately 3 cm long and 2 cm in diameter before the plant subsequently dies . The many thousands of small flowers on the inflorescence attract large numbers of insects (X. Metz, pers. obs.) that could be potential pollinators. Seeds could be dispersed by lemurs, bats, or parrots, which have been observed in the area (A. Shapcott, pers. obs.). Given this life cycle, small populations of adults can potentially be lost if plants reproduce too infrequently or if the resulting seed crop is aborted or destroyed by predation as the species depends of successful regeneration of seedlings. Palms play a particularly important role in human lives in poorer countries, such as Madagascar; however, they are often destructively harvested, for example, for palm heart consumption or construction materials, and in the case of T. spectabilis, that would lead to loss of reproductive potential as well as adult population size (Gruca, Blanch-Overgaard, Dransfield, & Balslev, 2016;Melito, Faria, Amorim, & Cazetta, 2014;Rakotoarinivo et al., 2014;Shapcott, Quinn, Rakotoarinivo, & Dransfield, 2012).
The area in which T. spectabilis is found is known for its strongly seasonal climate that can support relatively few palm species compared to the species-rich eastern rainforests of Madagascar (Dransfield & Rakotoarinivo, 2011;Jury, 2003). The vegetation is savannah interspersed with seasonally dry deciduous western forest often associated with tertiary karst limestone outcrops (tsingy); small scale cattle grazing is common in the area, and due to a combination of local politics and agricultural practices, landscape level fires are common (Jury, 2003;Kull, 2002). While many palm species which occupy a savannah landscape are thought to be fire resistant, the combination of changed fire regimes and cattle grazing has been shown to impact the demographic growth of populations of some species (Abrahamson, 1999;Arneaud, Farrell, & Oatham, 2017;Mandle & Ticktin, 2012). Some local measures have been put in place at the original locations first visited in 2008 to protect T. spectabilis from fire and cattle trampling, considered to be threats to this species in situ (Gardiner, Rabehevitra, Letsara, et al., 2017;Gardiner, Rabehevitra, & Rajaonilaza, 2017).
This study surveyed T. spectabilis populations in 2008 and again in 2016 to assess the demographic structure, population size, genetic diversity, and relationships, across the known species distribution in Madagascar. The viability and threats to the species were assessed with the assistance of population demographic matrix modelling PVA, and the impacts of the expanded known distribution since discovery were investigated. Specifically, we asked if the species populations were increasing, stable, or decreasing and what variables are most likely to impact on its long-term viability? Are the newly discovered populations genetically distinct from the original known population and what do the patterns of genetic diversity tell us about the species at a landscape level? In addition, we asked what contribution are the locally planted individuals likely to have for the conservation of this species and how long is it likely to take before these or other isolated individuals contribute to develop new populations?

| ME THODS
All known populations of T. spectabilis were visited in 2008, and the coordinates of their locations recorded with a GPS. The relative locations of all individuals were systematically mapped as X Y coordinates along contiguous belt transects (20 m × 30 m) encompassing the entire population. The GPS location was taken at the start and finish of each transect as well as the compass direction. These data were later used to construct georeferenced maps of the relative locations of each plant by using trigonometry to adjust for variable transect direction. For each plant, the following data were recorded: height of the trunk to the base of the lowest leaf sheath or if no trunk, the total height of the plant; diameter or number of fronds if larger than seedling and lacking a trunk. The locations of three adult plants that had flowered and died in previous years (pre 2006, 2006, and 2007) were also recorded. Samples from mature leaves were collected from every plant above 15 cm height except one for genetic analysis. Samples were collected from a subsample of seedlings <15 cm. Samples were surface cleaned with paper towel, cut into smaller pieces, and stored in individually labelled sealed plastic bags with silica gel. In addition, silica gel-dried leaf material from 25 seedlings propagated at RBG Kew from seed collected from the 2006 mother tree was also obtained to be included in the genetic analysis.
The original three populations were relocated in 2016 and resurveyed using the same systematic belt-transect methods as used previously (Gardiner, Rabehevitra, Letsara, et al., 2017). However, to enable ongoing population recording by the local village personnel, we classified the plants into simple size classes (estimated using body dimensions) as follows where: Seedling 1 (S1): seedlings up to 30 cm; As a result of local searches, additional populations (TS4-TS7; Figure 1) were also located (Gardiner, Rabehevitra, Letsara, et al., 2017), and these entire populations systematically surveyed as de-

| Habitat extent and modelling
The geographic coordinates of each site location was input to Google Earth Pro (www.earth.google.com), and the geographic distances between the populations were then determined using the ruler func- In order to refine the potential distribution of T. spectabilis, a species distribution model was created with Maxent 2.2 using the current known occurrence sites and 24 ecological variables including 19 climatic parameters (Hijmans, Cameron, Parra, Jones, & Jarvis, 2005) such as temperature, precipitation and five layers related to habitat characteristics: elevation, slope (USGS, 2015), geology (Besairie, 1964), vegetation map (Moat & Smith, 2007), and the vegetation cover fraction (Jiang et al., 2006). The variables having the most influence in the model were then hypothesized to be the most significant for the distribution of the palm.
In order to provide good distribution models, SDM was carried out in two steps: firstly, a model involving all of the 24 environmental layers, and secondly, a model based on the 10 first responsive layers from the first operation (Table 1)

| Demographic modelling
The raw frequencies in each developmental stage were transformed to percentage of the population in each size category and plotted to investigate the shape of the population structure. The plants at TS1 were classified according to the seven developmental stages described above, and this field data were used to quantify the parameters and  , 1999). Note that standard deviations for these estimates are also calculated. Fecundity was zero for all stages except A3 (F A3S1 ) and was given as the estimated average number of seedlings produced per reproductive tree based on field data. As these data are based on seedling numbers per reproductive tree after seed harvesting has taken place, all models incorporate seed harvesting.
We used the number of known trees that did or did not fruit successfully over the total time period since record keeping began for this species, to estimate the average frequency of reproduction.  were set to 1,000, density dependence was set to be ceiling (also ran exponential), and stage specific to S1, S2, J1, J2 developmental stages affecting survival rates to simulate self-thinning of high density seedling populations. The eight year time step was used to ensure our model parameters were consistent with the field observations.
The maximum carrying capacity (Kmax) was set to approximately 10 times the TS1 population size (5,000) to allow for maximum capacity of seedling production and probably overestimates the potential for the habitat to accommodate this species. Maximum growth rate (λ) was set at 1.5 based on the observed overall population growth rate of 1.47 over the eight year time period at TS1. A 10 percent standard deviation in the stage matrix (also tried 20% SD) was used to account to sampling error in calculations and is the program default.
Environmental stochasticity was set to normal in the model de- the models input data more robust for chance annual fluctuations.

| Genetic analysis
All samples collected during the 2008 survey were used in the initial genetic study (James, 2010 Thirty-eight microsatellite primers previously developed for other palm species were trialed for successful amplification of T. spectabilis for the initial genetic study using a subset of samples (James, 2010) as per Shapcott et al. (2012). Of those that successfully amplified product within the expected size range further standard optimization of PCR conditions were trialed as needed such as altering MgCl 2 the number of PCR cycles and testing for optimal annealing temperature to obtain repeatable clean product. Following this process, nine primers that gave optimal results within the expected size range were used for genetic analysis. These were; Pd15, Pd32, Pd50, Pd57  ), and the fixation index (F) was also calculated using GenAlEx 6.4 (Peakall & Smouse, 2006  4% trunked) at a total of seven sites including the original three locations ( Figure 1, Table 2). The majority of plants were found at TS1

| Demographics and habitat
( of which the trunks were 2 m or taller (A2, A3; Table 2). In 2016, we counted 27 trees with trunks, but only 14 of those had trunks 2 m or taller; five mature trunked trees had died after initiating flowering ( Table 2). The population TS4, discovered in 2010, was composed entirely of 170 seedlings in 2016 ( Figure 1; Table 2). Observations from the TS4 and TS1 populations suggest high seedling survivorship from S1 to S2 stages. The highly disturbed sites, TS5 and TS6, each consist of a single plant (Figure 1, Table 2). TS7 was located in a more intact vegetation patch nearby, consisting of 23 plants and occupying approx. 350 m 2 , but only has three trunked trees and only one with a trunk >2 m ( Table 2).
The revised SDM indicates that the potential areas suitable for the species remain restricted to coastal areas in small parts of the northwest of Madagascar, between Analalava in the north and to the southern part of the Antsanifera peninsula ( Figure 1). Of the two predicted models created, the one involving only 10 environ- There is considerable potential suitable habitat within the northern region, particularly closer to the coast. The total Extent of Occurrence EOO of wild populations is 206,751 km 2 and the AOO based on a 2 km grid is 24 km 2 ; there is a considerable disjunction between the two known areas of occurrence (Table 3) although suitable areas are relatively predicted between the known occurrence sites (Figure 1).
There has been some fencing to reduce cattle trampling, and there was evidence of high survivorship of seedlings in areas where seedlings were protected at TS1, but a loss of seedlings was documented in exposed areas. The A1 and A2 stages had no observed mortality in the 8 years between surveys. It appears to take longer than 8 years for trees to grow from a trunk <2 m tall (A1) to 1 > 2 m tall (A2; Table 4). We found extreme variability among plants at TS1, TS2, and TS3 with high growth rates of some individual plants (Table 4). Based on the transition rate between the differing stages observed at the 8 year time interval, we estimate it takes approximately 73 years (±24 years) for trees to reproduce, but we expect a large variation in individual growth rates (Table 4).
We trialed several variations of demographic parameters in initial growth models that were run for TS1 based on observed growth parameters, all resulted in population increases over the time frame modelled (Figure 3a). However, when models added potential impacts of failed seed set (Catastrophe 1) the population remained stable with little increase (Figure 3b). The model that included the chance of seedling failure due to fire (Catastrophe 2) combined with reproductive failure (Catastrophe 1), maintained the population at similar sizes to present (Figure 3c), and no models predicted extinction of this population.
The average distance to nearest neighbor population is 1.9 km and the presence of single plants at several sites suggests successful seed dispersal within a 3 km range (Table 5). Our metapopulation model for T. spectablilis that includes all known wild plants, predicts the species overall population will slowly increase most noticeably after approximately 60 years (Figure 4). It is predicted to take at least 80 years for the sites with single plants to develop into multi-aged populations due to the time to reproductive maturity, slightly sooner for TS4 as it is composed of established seedlings

| Genetics
Of the nine loci tested only four were polymorphic within the species Pd15, Ob11, Aacu07, Pd32 (Table 6) (Tables   5 and 6). The newly discovered populations possess two polymorphic loci that were monomorphic in the original TS1, TS2, and TS3 populations (Table 6). When only the polymorphic loci are considered in diversity measures, the seedling population TS4 is remarkably genetically diverse, as is TS7 (Table 5). Pd32 and Aacu07 were the most variable loci with 5 alleles recorded in the species and TS7 containing all alleles of Aacu07 (Table 6; Figures 1 and 5). All populations were inbred with allelic fixation index (F) > 0 (Table 5). TS1 is monophorphic at all but one locus, Aacu07, where a few adult individuals contain an alternative allele 156 (Table 6). This allele is also shared by TS4, TS5, and TS7 (Table 6; Figure 1). Our sample of seedlings from TS1 found that they arose from one individual, and this individual was of the few plants that was heterozygous for the only polymorphic allele found in this population, thus the seed distributed around the world sampled the limited genetic diversity found in this population.
TS3 does not appear to have arisen from TS1 as TS3 is homozygous for a unique allele at locus Pd32, which is restricted to this population (Table 6; Figure 4). The seedling population TS4 has an   Figure 5). The diversity of the seedling population at TS4, particularly at locus Pd32 makes it clear that these seedlings arose from more than one mother plant, consistent with local observations that there were previously up to three possible parent plants at this site. The genetic composition of the single planta at TS5 and TS6 suggests they could have arisen from dispersal events from nearby TS7 as all the alleles present in TS5 and TS6 are present in TS7 (Table 6; Figures 1 and 5).
The population at TS7 contains a unique allele 267 at locus Ob11 and two unique alleles at locus Aacu07 (Table 6; Figure 1). Given

| D ISCUSS I ON
Tahina spectabilis was previously documented from a single location in northwestern Madagascar (Dransfield, Leroy, Metz, & Rakotoarinivo, 2008;, this area houses populations TS1, 2, and 3. The discovery of new locations of T. spectabilis, populations TS4, 5, 6, and 7, has considerably expanded its distribution range by orders of magnitude from the original IUCN Red List assessments, which gave both EOO and AOO as 4 km 2 . We estimated that the lifespan of a T. spectabilis is on average 73 years before it flowers and dies, longer than initially predicted , but this is expected to be highly variable and should be used as an approximate only. A broad age range has been found in other palm species (e.g., Martínez-Ramos et al., 2010) and high variation among growth rates of individuals has also been previously reported for palm species (Jansen, Anten, Bongers, Martínez-Ramos, & Zuidema, 2018). McPherson and Williams (1998) found that palms in fire prone environments can take at least two decades to attain an above- The SDM models found that the species distribution is correlated with substantial seasonal rainfall (400-480 mm) during the wettest month (February) when T.spectabilis seedlings would be establishing. The predicted range area of T. spectabilis represents a particular ecological niche as it is located in the western climatic domain but also benefits from the marginal high moisture rate from the Sambirano region. The importance of low variation in temperature seasonality (43% of the distribution range) throughout the year emphasizes the role played by the heat in the growth physiology of palms by the absence of dormancy during the dry season (Tomlinson, 2006). Precipitation regime in the area is governed by the seasonal Loci/allele   Population   TS1  TS2  TS3  TS4  TS5  TS6  TS7 Pd15 123 Summer rainfall is associated with heat and comes frequently with the intertropical convergence zone during which most of the annual precipitation is discharged in the area (Jury, 2016 to a higher rate of reproductive failure and seedling establishment then this would lead to reduced or slowed predicted population growth based on our current models. We reported evidence of palm weevil in the fallen trunks of palms that had aborted their seed crop (Gardiner, Rabehevitra, & Rajaonilaza, 2017). Palm weevils are known to impact many palm species boring into old or damaged trunks (Azmi et al., 2017;Murphy & Briscoe, 1999;Rugman-Jones, Hoddle, Hoddle, & Stouthamer, 2013). Their presence is concerning for this species though it is unknown if they caused the failure of the fruit set. While our population models indicate that reproductive failure could impact on T. spectabilis population growth, they also show that this seems unlikely to lead to its extinction. Previous demographic studies have shown that changes in individual palm growth rates and fecundity must be large and persistent to affect population growth rates (McPherson & Williams, 1998;Pinéro et al., 1984;Ratsirarson et al., 1996).
Extrinsic factors may have a major impact on the survival of the T. spectabilis population, as they can cause stochastic effects at the demographic level (Sodhi & Ehrlich, 2010)  Our models suggest that fire alone is unlikely to lead to extinction of T. spectabilis populations. McPherson and Williams (1998) study also predicted that fire was insufficient to cause large changes in population growth rates and did not explain the rarity of their study species.
Grazing by herbivores such as cattle and goats has been documented to potentially impact on many palm species, particularly affecting the seedling stages, subsequently leading to reduced population growth (Mandle & Ticktin, 2012;Nazareno & dos Reis, 2014;Shapcott, Dowe, & Ford, 2009). The two largest T. spectabilis populations are closely associated with rocky outcrops. Some studies have found such habitats provide advantage for palms by increasing survivorship and reducing herbivory (Berry, Gorchov, Endress, & Stevens, 2008), and this may be the case for T. spectabilis. Many palm species are utilized by humans for a variety of purposes, such as the consumption of the palm heart and harvesting of palm leaves for thatch and a variety of other purposes (Gamba-Trimiño et al., 2011;Gruca et al., 2016;Jansen et al., 2018;Martínez-Ballesté et al., 2005;Navarro et al., 2011;Reis et al., 2000). Previous studies of palm demography have demonstrated that loss of palm leaves can reduce palm survival, growth and reproduction (Mandle & Ticktin, 2012;Martínez-Ramos et al., 2010;Ratsirarson et al., 1996;). We found evidence that the leaves of T. spectabilis from TS7 are used locally for ceremonial mats, and this could impact viability and growth of individual plants in this very small population. Traditional harvesting may be sustainable in some instances, but there are varying estimates of sustainability from a variety of studies on a variety of harvested species (Jansen et al., 2018;Martínez-Ballesté et al., 2005;Navarro et al., 2011). Thus for the population at TS7, it will be important to work with the local people to ensure that leaf harvesting is sustainable. Our population models that accounted for both reproductive failure and seedling mortality mimic the potential impacts of fire, grazing, harvesting, and insect attack and show that T. spectabilis is potentially tolerant to the combined effects of these. Mandle et al. (2015) also found the Phoenix loureiroi palms in India were resilient to low levels of fire, grazing, and harvesting.
The consumption of heart of palm has been documented as a widespread practice in Madagascar that potentially impacts on Critically Endangered palm species (Gruca et al., 2016;Shapcott et al., 2012). Given the long generation time of T. spectabilis, the critically small population sizes and the hapaxanthic reproductive lifecycle, this species is particularly vulnerable to impacts of heart of palm consumption as it kills the plants before they can reproduce (Gamba-Trimiño et al., 2011;Shapcott et al., 2012).
Rare species are often found to have less genetic diversity than those species that are more abundant (Gitzendanner & Soltis, 2000;Leimu et al., 2006). While our study used a limited number of variable markers to assess genetic diversity, the low genetic variation found in T. spectabilis in this study is consistent with this expectation. Low genetic diversity has been found in other endangered Madagascan palm species (Gardiner, Rakotoarinivo, et al., 2017;Ratsirarson et al., 1996;Shapcott et al., 2012). However, the newly discovered population TS7 contained more genetic diversity than expected given the very small population size. Higher than expected genetic diversity has also been found in very small populations of the critically endangered Madagascan species Voanioala gerardii  and Beccariophoenix madagascariensis (Shapcott et al., 2007).
Evidence from the genetic identity of TS2 indicates that it is a founder and arose by colonization from TS1. Likewise, TS5 and TS6 appear to have arisen from TS7 which indicates that the species can disperse seed at least a few km. Whereas, based on their allelic composition, TS3 and TS4 appear to have arisen from as yet undiscovered populations. Sezen, Chazdon, and Holsinger (2007) also found evidence of palm seed dispersal over similar distances and evidence of founder populations. The fruit of palms are an important food source for many animals, including lemurs (Arroyo-Rodriguez, Aguirre, Benitez-Malvido, & Mandujano, 2007;Dransfield, Uhl, et al., 2008;Gaiotto, Grattapaglia, & Vencovsky, 2003;Shapcott et al., 2007). Frugivorous birds and fruit bats are also known to be important for seed dispersal of palm species (Shapcott, 1998a(Shapcott, , 1998b. Gaiotto et al. (2003) found that seeds of the heart of palm species Euterpe edulis had been dispersed by birds and become established up to 22 km away. Seed of T. spectabilis could potentially be dispersed across the landscape by fruit bats, parrots or lemurs which were observed or reported in the vicinity.
The main genetic consequences of fragmentation include reduced genetic diversity and increased population differentiation (Leimu, Vergeer, Angeloni, & Ouborg, 2010). Habitat fragmentation is expected to lead to random patterns of genetic differentiation and allele loss due to drift (Nistelberger, Coates, Llorens, Yates, & Byrne, 2015). Populations on the edge of the geographical species range are predicted to be less genetically diverse than those in the species center (Lawton, 1993). Cibrián-Jaramillo et al. (2009) found evidence of a pattern of palm expansion via stepping stone founder populations radiating out from around regional clusters. Our results appear to show a pattern of radiation by founder populations from a center of diversity associated with the northern region. Tahina spectabilis displays geographic clustering similar to the genetic patterns found in Lemurophoenix halleuxii  and Beccariophoenix madagascariensis (Shapcott et al., 2007).
Heywood (2019) identifies the urgent need for action to prevent further plant extinctions. Conservation in the form of reintroduction and translocation carries elements of risk, and there are relatively few reported cases of successful establishment of translocation species (Godefroid et al., 2011;Silcock et al., 2019;Weeks et al., 2011). Tahina spectabilis seeds were wild harvested and distributed nationally and internationally as part of a conservation program initiated shortly after the species' discovery (Gardiner, Rabehevitra, Letsara, et al., 2017;Gardiner, Rabehevitra, & Rajaonilaza, 2017). The maintenance of genetic diversity and identity of regions must be considered carefully, both when sourcing of germplasm and introducing new material (Byrne et al., 2011;Mckay, Christian, Harrison, & Rice, 2005;Weeks et al., 2011). The planted populations of T. spectablis were sourced from the closest known source but they have very low genetic diversity as the seed arose from only one or two parent plants. We report that there are now five new planted populations that have been established in Madagascar within the adjacent area previously modelled as suitable for T. spectabilis. These planted populations have the potential to contribute to expanding T. spectabilis distribution extent to the south of its current known range including into a protected area. These new populations have the potential to contribute to considerable population increase in around 50-100 years as the trees mature and produce seed and at that time they will alleviate pressure on wild populations for commercial seed supplies for horticulture.
This study has found that while the total number of T. spectabilis plants has increased and the Area of occupancy (AOO) and Extent of occurrence has expanded (EOO) since its discovery the number of plants of a size capable of reproduction has declined since 2008 and remains at a critically small size thus the species remains Critically Endangered according to the IUCN criteria (D). Our modelling shows that if the current known populations remain protected by local customs and new conservation practices (Gardiner, Rabehevitra, Letsara, et al., 2017;Gardiner, Rabehevitra, & Rajaonilaza, 2017), T. spectabilis populations are expected to maintain themselves and eventually expand and we expect to see a recovery in the next 100 years. If new populations are discovered as a result of recent searches this will assist to ensure the species long-term viability if new discoveries are accompanied by local conservation security actions. However, the species appears sensitive to seasonal rainfall with this predicting its distribution and potentially its reproductive events and thus may be impacted by climate change in the longer term.

ACK N OWLED G M ENTS
This paper is in memory of the late Xavier Metz who discovered T. spectablis, hosted some of us to visit it in the wild, and established mechanisms for its conservation. The field work for both trips was

CO N FLI C T O F I NTE R E S T
There are no competing interests.

AUTH O R CO NTR I B UTI O N S
AS lead the collection of field data in 2008 and 20,016, analyzed the final genetics, and demographic data undertook demographic modelling, supervised student HJ and was principal manuscript writer. HJ undertook initial genetic and demographic analysis and contributed to writing especially methods.LS undertook second genetic analysis and contributed to PVA model methods and critical review and editing manuscript. YS contributed to developing demographic models and PVA and critical review of the manuscript.
LG obtained funding and lead the 2016 field trip conceptual design as well as contributing to critical manuscript writing and revision. DR organized local field logistics and contributed to the field work in the 2016 trip as well as developing conservation priorities for the species and contributed to manuscript writing. RL participated in the 2016 field trip and liased with local authorities and Botanic Gardens to obtain permits as well as contributing to the critical manuscript revision.