4 | Discussion
The heterozygous deficit and high levels of inbreeding with little or no random mating deficit of heterozygotes, may be the result of the habitat where the Chilean Palm lives and the existence of small and isolated populations, which are maintained as a result of the form of reproduction and seed dispersal.
The sclerophyllous forest inhabited by J. chilensis has been highly exploited, leading to the species reduction over the years. Currently, approximately only 121,284 specimens are left (or 2.5% of the original population of the 19th century), being distributed among highly fragmented populations (Bascuñán, 1889; González et al., 2017; Rubinstein, 1969). These remaining populations are in an advanced stage of aging, with little or no appearance of natural shoots, and under a high anthropic impact due to the commercialization of their fruits and sap (González et al., 2017). In addition, J. chilensispopulations present a clustered arrangement, which can both be related to their inherent low long-distance capacity of seed dispersal as to their relatively small effective sizes (González et al., 2017; Trénel et al., 2008).
In the Pleistocene, seed dispersal was the product of endozoocoria by the extinct megafauna species belonging to the following families: Gomphotheriidae, Camelidae, Equidae, Notohippidae, Homalodotheriidae, Toxodontidae, Astrapotheriidae, Macraucheniidae, Mylodontidae and Megatheriidae (Carrasco, 2013; Gonzáles et al., 2017). Currently, the seeds are dispersed in territories close to the mother plant as result of gravity, floods and runoff. Although the main current dispersers are humans who transfer the seeds to the different commercialization sites, and the Octodont degus Molina and Spalacopus cyanus Molina rodents that hoard the seeds, the recently introduced domestic species, such as cattle and horses, also play an important effect, considering that they remove, consume and regurgitate the seeds, but leaving them susceptible to competition and desiccation (González et al., 2017; Vander Wall & Longland, 2004). The frequency of rodent-seed interaction is low (<25%) and transport usually occurs at short distances (<6m) (Fleury et al., In Prep; Vander Wall & Longland, 2004), indicating that rodent-dependent dispersion may be insufficient for genetic exchange between existing palm groves, which leads to a lack of gene flow and isolation between patches (González et al., 2017).
On the other hand, pollen can cover greater distance than seeds (González et al., 2017; Kremer et al., 2012; Montúfar et al., 2011; Sezen et al., 2005), but its movement is scarce once pollinators visit mainly contiguous flowers of the same individual (González et al., 2017). It has been described that in systems with restricted dispersal, interruption of genetic connectivity occurs even in continuous populations (Lowe et al., 2005; Nora et al., 2011; White et al., 1999). All these factors may promote genetic isolation, lack of diversity and inbreeding, leading to a reduced rate of populational change and increased probability of extinction (Nora et al., 2011; Picó & Quintana-Ascencio, 2005), as we observed here to Chilean palm. In addition, the geographic distribution of palm groves is highly fragmented, which implies that the populations are dissociated, forming small independent groups, in which the degree of inbreeding increases as a result of increased crosses between related individuals (Crawley, 1997; Picó & Quintana-Ascencio, 2005; Young &Clarke, 2000). When gene flow is disrupted, populations can start a local differentiation process that can lead to long-term speciation by genetic isolation (Herron & Freeman, 2014).
Other limitations for J. chilensis regeneration are the germination of seeds and establishment of the seedlings. Germination occurs in a very long period, ranging from six months to four years, occurring more frequently within approximately 18 months (González et al., 2017). The growth stage of the seedlings is crucial for the long-term survival of individuals (González, 2017) and can only be achieved with the existence of a nurse plant understory of sclerophyllous and/or spiny species, which provides the necessary environment for their development until stipe’s formation (30-40 years) (Del Fierro et al., 1998; González & Vita, 1987; González et al., 2017). Valiente-Banuet et al. (2006) have shown that this nurse effect prevented tertiary species from disappearing due to increased aridity in the Quaternary. Palm trees (Arecaceae) that emerged in the Cretaceous dispersed in the Early Tertiary Cenozoic and had significant extinction rates in the Quaternary due to the rainforest’s retraction (Fleury et al., 2015; Kissling et al., 2012). In Las Palmas, commune of Petorca, previous studies have demonstrated that natural regeneration only occurs in high-altitude areas with difficult access (Youlton et al., 2016).
Other studies on different taxa of the Arecaceae family have been suggested that fragmentation considerably affects the permanence and perpetuation of palm groves. In the south of the Brazilian Amazon, forest fragmentation decreased Bactris Jacq . ex Scop. genus (peach palm) palm reproduction due to inbreeding depression, possibly leading to eventual extinction (Clement et al., 2009). For theAstrocaryum aculetassimum (Schott) Burret, an endemic species to the Brazilian Atlantic Forest, it has been reported that the species populations are highly affected by the loss of seed dispersers due to fragmentation and hunting (Galetti et al. 2006). Also, for theAstrocaryum mexicanum Liebm. ex Mart. species inhabiting the Los Tuxtlas (State of Veracruz / Mexico), has been shown that the abundance of coleopterans and pollinating beetles varies according to the size of the fragment (Aguirre & Dirzo, 2008). In Ecuador, the seedlings ofCeroxylon echinu latum Galeano and Attalea colenda (O.F. Cook) Balslev & A.J. Hend. have failed to survive as a result of deforestation (Anthelme et al., 2011; Borchsenius et al., 1998; Montúfar, 2011). An extensive review of literature of palms from Tropical America indicated that anthropic influences may cause changes in the genetic structure, increased inbreeding and genetic drift in fragmented populations (Montúfar, 2011). Similarly to this study, thePhoenix dactylifera L. populations occurring in natural oases in Tunisia also presented HE values higher thanHO values, with low genetic structure and a long period of isolation between sampled patches (Ben-Abdallah et al., 2020).
Some germination and establishment tests have been conducted forJ. chilensis seed (Cabello A., 1999; Infante L., 1989; Lewin L., 2003; Saiz et al., 1989) as of the in the context of implementation of the National Plan for the Conservation of Chilean Palm, carried out by Chilean government (National Forest Corporation, CONAF) in 2005. This Plan outlines a set of policy guidelines to restore/recover the species populations throughout its distribution. Furthermore, since 2017 (Resolution 106/2017, CONAF) seed harvesters are officially prohibited from harvesting in La Campana National Park, the largest palm grove (~ 60% of existing palms). The J. chilensisharvest and management techniques, however, have not considered genetic variability as a key factor in deciding which individuals or populations should be restored or which territories should be protected. It is essential that protective measures be based on multidisciplinary analyses including genetic, ecological, reproductive and physiological data. Currently, the Chilean palm is classified as Vulnerable (Benoit, 1989; Hechenleitner et al., 2005; IUCN / CMMC, 1994; Rodríguez et al., 2005), and as in Danger of Extinction from the Chilean region of Coquimbo (Squeo et al., 2001). We suggest that the current threat classification consider too short time horizon, that might cause underestimate the threats and underprotect the Chilean palm; and request the re asses the J. chilensis extinction risk both the Danger of Extinction and as a Natural Monument. Also, we underline that the genetic variation must be considered in artificial propagation. This can be specially useful for conserving species at risk, especially when translocations for restoration, genetic rescue, or assisted gene flow are fundamental aspects for the successful long-term population (Flanagan et al. 2018) as the J. chilensis . The fact thatJ. chilensis is a monospecific, relict and endemic, with a patchy distribution, no long-distance dispersal, no capacity for vegetative propagation or sprouting large and recalcitrant seeds, and under severe exploitation and anthropic impact may altogether argue in that sense. Moreover, the high inbreeding and low populational genetic diversity places the permanence of current and future populations at high risk due to the lack of adaptation to environmental changes that allow them to survive and evolve (Dawson et al., 2011; González et al., 2017; Jump et al., 2009) especially in face of scenarios of climate changes and negative anthropogenic effect.