The effects of population size on genetic parameters and mating system of sandalwood in Gunung Sewu, Indonesia

Abstract

We combined field observations with isoenzyme analysis to compare population demographic and its effects on genetic diversity and mating systems, among six populations of sandalwood in Gunung Sewu, Indonesia, during March to August 2015. This endangered economic-important species was originated from the southeastern parts of Indonesia, but is recently occured as new landraces in Gunung Sewu, Java island. The observed heterozygosity varied from H o 0.184 to 0.385 in parents, and from H o 0.083 to 0.348 in offspring levels, based on the degree of clonality and genetic base. Most of genetic variation is distributed within populations, and only 2.7% were presented among populations, that was indicated by the low D ST and F ST value (H T 0.30; H S 0.276; D ST 2.4%; F ST 7.98%). A dendrogram indicated a grouping of populations into three clusters. However, there were seemed to be no association between geographical and genetic distance. Genetic depletion occured due to (i) clonality events as result of heavy-exploitation and/or natural disturbance which induced root suckering, (ii) genetic drifts and bottleneck effects, (iii) the founder effects due to parental low diversity, and (iv) the alteration on mating systems to be more inbreeders. Some of the results confirmed a "reproductive assurance prediction" while some others were contradicting this. It seemed that genetic diversity and mating systems are not much affected by population size, but more by the parental heterozygosity and the degree of clonality. Our results emphasized the importance of populations' genetic base or parental genetic diversity to naturally maintain the genetic and evolutionary processes under equilibrium conditions.

The genetic diversity and reproductive dynamics of sandalwood in Gunung Sewu (Java, Indonesia) in 2012-2019: designing conservation strategies in a continuous versus fragmented landrace

“…Threatened and fragmented plant species can maintain their genetic diversity only if the genetic base is wide and the mating preference is outcrossing (Bradbury et al 2015). These conditions have significant implications in designing conservation efforts and are the main issues in sandalwood, which has been proven to have strong ability for clonal reproduction via root suckers (da Silva 2016; Ratnaningrum et al 2015Ratnaningrum et al , 2017, partial self-compatibility (Ratnaningrum et al 2017), and mating system alterations to accommodate more inbreeding under isolated conditions (Indrioko and Ratnaningrum 2015;Ratnaningrum et al 2015). Compared with non-fragmented populations, a fragmented sandalwood population is more likely to become extinct because of restricted gene flow, increased clonality, genetic base narrowing, genetic diversity reduction, and mating system alterations.…”

“…Some landraces in Gunung Sewu are naturally isolated because of the specific landscape types of the area, while others are fragmented and clonalized because of natural hazardous and anthropogenic disturbances. Some landraces included in conservation areas are derived from more diverse genotypes (Ratnaningrum et al 2015(Ratnaningrum et al , 2017.…”

“…Reproductive and genetic processes are strongly affected by parental clonality and genetic base, which, in turn, remarkably determine mating systems and affect reproductive outputs. Populations that are more clonalized and show lower diversity are more likely to become inbreeders than those that do not (Ratnaningrum et al 2015(Ratnaningrum et al , 2017. In such populations, most flowering trees share the same parent and, therefore, are genotypically identical.…”

“…Regenerated sandalwood in Bejiharjo is largely derived from root suckers, and its mating system has been altered to become more inbred, a condition that can cause extreme reductions in offspring genetic diversity. Limited seed sets after flowering and pollination result in less seedling recruitment because of inbreeding depression (Ratnaningrum et al 2015(Ratnaningrum et al , 2017Ratnaningrum and Kurniawan 2019). Most conservation efforts consider this landrace as a priority because sandals of the Karangmojo group (including Bejiharjo) are among those with higher levels of santalol (Haryjanto et al 2017).…”

“…In contrast to the Bejiharjo landrace, the Bleberan landrace shows a very wide genetic base and is highly outcrossed (Ratnaningrum et al 2015;; thus, it has been recommended as a seed source for planting programs (Fathin and Ratnaningrum 2018). Bleberan is considered a continuous population because it exists in the middle of other landraces and ex situ conservation sites, such as Wanagama, Watusipat, Banyusoco, and Mulo, all of which are within less than 5 km of each other.…”