Scale Genetic Structure of Dysoxylum Malabaricum, a Late-Successional Canopy Tree Species in Disturbed Forest Patches in the Western Ghats, India
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Conserv Genet DOI 10.1007/s10592-016-0877-7 RESEARCH ARTICLE Fine- and local- scale genetic structure of Dysoxylum malabaricum, a late-successional canopy tree species in disturbed forest patches in the Western Ghats, India 1 2,3 4 3 Sofia Bodare • Gudasalamani Ravikanth • Sascha A. Ismail • Mohana Kumara Patel • 5 6 2,3,7 Ilaria Spanu • Ramesh Vasudeva • Ramanan Uma Shaanker • 5 1 1,8 Giovanni Giuseppe Vendramin • Martin Lascoux • Yoshiaki Tsuda Received: 20 December 2015 / Accepted: 6 August 2016 Ó Springer Science+Business Media Dordrecht 2016 Abstract Dysoxylum malabaricum (white cedar) is an structure at the landscape level (\50 km), regardless of age economically important tree species, endemic to the Wes- class, due to limited gene flow between forest patches. A tern Ghats, India, which is the world’s most densely pop- comparison of the distributions of size classes in the four ulated biodiversity hotspot. In this study, we used variation locations with published data from a more southern area, at ten nuclear simple sequence repeat loci to investigate showed that large trees (diameter at breast height, DBH, genetic diversity and fine scale spatial genetic structure [130 cm) are present in the southern sacred forests but not (FSGS) in seedlings and adults of D. malabaricum from in the northern forest reserves. This pattern is likely due to four forest patches in the northern part of the Western stronger harvesting pressure in the north compared to the Ghats. When genetic variation was compared between south, because in the north there are no cultural taboos seedlings and adults across locations, significant differ- regulating the extraction of natural resources. The impli- ences were detected in allelic richness, observed cations for forest conservation in this biodiversity hotspot heterozygosity, fixation index (FIS), and relatedness are discussed. (P \ 0.05). Reduced genetic diversity and increased relatedness at the seedling stage might be due to frag- Keywords Dysoxylum malabaricum Á Fragmentation Á mentation and disturbance. There was no FSGS at the adult Disturbance Á Land use Á Spatial genetic structure Á Western stage and FSGS was limited to shorter distance classes at Ghats the seedling stage. However, there was clear spatial genetic Electronic supplementary material The online version of this article (doi:10.1007/s10592-016-0877-7) contains supplementary material, which is available to authorized users. & Yoshiaki Tsuda 5 Institute of Biosciences and Bioresources, National Research [email protected] Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy 1 Program in Plant Ecology and Evolution, Department of 6 Department of Forest Biology, College of Forestry, Ecology and Genetics, Evolutionary Biology Centre, Uppsala University of Agricultural Sciences, Dharwad, Sirsi, ¨ University, Norbyvagen 18D, 75236 Uppsala, Sweden Karnataka 581401, India 2 Ashoka Trust for Research in Ecology and the Environment, 7 Department of Crop Physiology, University of Agricultural Royal Enclave, Srirampura, Jakkur Post, Bangalore, Sciences, Bangalore, Karnataka 560065, India Karnataka 560064, India 8 3 Present Address: Sugadaira Montane Research Center, School of Ecology and Conservation, University of University of Tsukuba, 1278-294 Sugadairakogen, Ueda, Agricultural Sciences, Bangalore, Karnataka 560065, India Nagano 386-2204, Japan 4 Ecosystem Management, Department of Environmental Systems Science, ETH Zu¨rich, Universita¨tsstrasse 16, 8092 Zurich, Switzerland 123 Conserv Genet Introduction (Wang et al. 2011). Although SGS can be affected by several factors, including colonization events and micro- Tropical forests harbor large amounts of biodiversity, but environmental selection, its main determinants are believed human activities over the last few decades have caused to be mating system, dispersal mode and adult density severe deforestation, fragmentation and disturbance (Vekemans and Hardy 2004). Moreover, as SGS patterns (Wright and Muller-Landau 2006; Abdullah and Nakagoshi are scale dependent, it is important to evaluate genetic 2007). As a consequence, many forests that were once structure at several geographic levels, i.e., broad scale (e.g. continuous now exist as isolated and disturbed patches or several hundred to thousands of kilometers), fine scale (e.g. meta-populations (Sork and Smouse 2006). Natural and over tens to several hundred meters) and also at an inter- artificial habitat disturbances, such as forest fires, tsunamis, mediate landscape scale (Manel et al. 2003; Tsuda et al. and land use, and their effects on the genetic diversity of 2010), to understand how SGS is formed over a species species are important topics in ecology and conservation distribution range. biology (Banks et al. 2013; Iwaizumi et al. 2013). In many Dysoxylum malabaricum Bedd. Ex C.DC. (white cedar) cases of habitat disturbance, decreases in genetic diversity is an economically important and endangered species, and increases in population differentiation are expected, endemic to the Western Ghats region of India, one of the especially when disturbances induce genetic drift and world’s eight hottest hotspots of biodiversity (Myers et al. restrict gene flow among populations (Vellend 2004; 2000) and by far the most densely human populated of the Evanno et al. 2009; Struebig et al. 2011). Currently, one of biodiversity hotspots (Cicotta et al. 2000). Dysoxylum the most prevalent environmental changes, especially in malabaricum is considered a sacred tree and is harvested tropical forests, is anthropogenic disturbance, including for religious purposes, including the construction of tem- land use change and deforestation, which results in loss of ples (Manjunath 2003), as well as for commercial and continuous habitat and the creation of smaller, spatially personal uses (Kumar 2009). While the degradation of isolated, forest fragments. While habitat loss and overhar- forests in the present study area has been occurring for vesting is an immediate threat to many forest tree species, about 200 years, the most severe usage has occurred more disturbance may also be detrimental to forest ecosystems in recently, e.g. from the forest reserves in Northern Kar- the long term. In particular, following disturbance late- nataka in the Western Ghats (Gokhale 2004). Over the last successional canopy species, which constitute a large few decades, overharvesting and land use have reduced and portion of the biomass and provide shade and habitat to fragmented the remaining populations; most notably the other species, are replaced by pioneer species, which may stock of juvenile and young adult individuals has been undermine the integrity of the ecosystem. Furthermore, reduced in some locations, with potential long-term effects recent studies demonstrate that both genetic and species on the reproductive success and survival of populations diversities can decrease following fragmentation and dis- (Shivanna et al. 2003; Ismail et al. 2014). In particular, the turbance (Vellend and Geber 2005; Evanno et al. 2009; species density in sacred groves and forest reserves dis- Struebig et al. 2011). Because genetic diversity is an tributed throughout the Western Ghats region is at risk integral part of biodiversity and the basis of a species’ (Boraiah et al. 2003; Gunaga et al. 2013). Sacred groves adaptive potential, it is important to assess the genetic and forest reserves have traditionally been sustainably diversity of late-successional trees to ensure their long term managed by local communities (Chandrakanth et al. 2004; persistence in disturbed tropical forests. The present study Tambat et al. 2005). However, in recent years, due to aims to address this problem by combining genetic and changes in socio-economic conditions and decreasing demographic approaches for investigating genetic diversity social norms regulating the extraction of natural resources and genetic structure across age classes. from these forests, they are now largely a source of income Measuring spatial genetic structure provides a way to and are exposed to non-sustainable harvesting (Tambat assess how pollen and seed flow changes over time. Spatial et al. 2005; Gunaga et al. 2013). As an old-growth and genetic structure (SGS) measures the nonrandom geo- large canopy tree depending on large birds for dispersal, D. graphical distribution of genotypes, and results in increased malabaricum provides an ideal system for studying the relatedness among geographically close individuals com- ability of economically and ecologically important late- pared to more distant ones (Epperson 1992; Vekemans and successional tree species to survive in disturbed habitats. Hardy 2004). Fine scale SGS (FSGS) has been observed in Previous conservation genetics studies on D. malabar- plant species (Vekemans and Hardy 2004) and measures of icum have shown the presence of genetic structure on a FSGS have been suggested to be more sensitive than range-wide and local scale. In the range-wide study, clustering algorithms and standard inbreeding statistics to genetic clusters were found to stretch over large as well as detect the early genetic effects of environmental changes small geographic distances, with more clustering and a higher fixation index (FIS) in the northern part of the 123 Conserv Genet species distribution range (Bodare et al. 2013). One FSGS perceived level of disturbance, based on the intensity of study in a moderately disturbed southern location (Kodagu, human land use activities. The