Abstract
Sapindus emarginatus Vahl (Sapindaceae) also known as ‘Indian Soap nut’ is significantly important for saponin content in its fruits. However, its current population in India is heavily fragmented due to a lack of sustainable harvesting practices. Moreover, changing climatic regimes may further limit its distribution and possibly compromise the survival of the species in nature. The aim of the present study was to: predict the future distribution range of S. emarginatus; identify the bioclimatic variables limiting this distribution and to evaluate its adaptive fitness and genomic resilience towards these variables. To determine future species distribution range and identify limiting bioclimatic variables, we applied two different ecological niche models (ENMs; BioClim and MaxEnt) on real occurrence data (n = 88 locations). The adaptive fitness of the species was evaluated by quantifying the genetic variability with AFLP markers and marker-environmental associations, using AFLP-associated Bayesian statistics. We found 77% overlap between the baseline (2030) and predicted (2100) species distribution ranges, which were primarily determined by maximum temperature (TMAX) and mean annual precipitation (MAP). The TMAX and MAP contributed 43.1% and 27.1%, respectively to ENM model prediction. Furthermore, AFLP loci significantly associated with bioclimatic variables, and TMAX and MAP represent the lowest proportion (6.15%), confirming to the severe response of the species genome towards these variables. Nevertheless, the very low Linkage disequilibrium (LD) in these loci (4.54%) suggests that the current sensitivity to TMAX and MAP is subject to change during recombination. Moreover, a combination of high heterozygosity (0.40–0.43) and high within-population variability (91.63 ± 0.31%) confirmed high adaptive fitness to maintain reproductive success. Therefore, the current populations of S. emarginatus have substantial genomic resilience towards future climate change, albeit significant conservation efforts (including mass multiplication) are warranted to avoid future deleterious impacts of inbreeding depression on the fragmented populations.
Highlights
Sapindus emarginatus Vahl (Sapindaceae) known as ‘Indian Soap nut’ is significantly important for saponin content in its fruits
The present investigation was performed to address the major questions: How the future climatic regime is going to affect the species population distribution? What is the state of the genomic resilience of different populations of S. emarginatus to respond to the projected climatic regime? What are the bioclimatic variables contributing as limiting factor in population distribution? In order to resolve these questions, ecological niche models (ENMs) was performed with real occurrence data of the populations of S. emarginatus from three biogeographical regions in India (Fig. 1) with multi-modeling approach with two different models viz. BioClim and MaxEnt, comparing the predicted species distribution pattern between baseline and projected climatic regimes
We found that TMAX and mean annual precipitation (MAP) with maximum contribution to the model prediction
Summary
Sapindus emarginatus Vahl (Sapindaceae) known as ‘Indian Soap nut’ is significantly important for saponin content in its fruits. It has been suggested for covering the commercial forestry trials, botanical gardens, and biodiversity database along with the natural distribution of a tree species to measure its climatic or environmental requirements through SDM/ENM11 These model-based predictions are not practically successful until the species population itself is not adaptively fit[12]. The response of species to the predicted changing climatic condition with high genetic heterogeneity leading to the adaptive fitness is of significant importance for the sustainability of population in limited distribution[18]. In order to resolve these questions, ENM was performed with real occurrence data of the populations of S. emarginatus from three biogeographical regions in India (Fig. 1) with multi-modeling approach with two different models viz. BioClim and MaxEnt, comparing the predicted species distribution pattern between baseline (the year 2030) and projected (the year 2100) climatic regimes. The signature of adaptation in genome of the species was evaluated using genome-wide association (GWAS) between marker and bioclimatic variables
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