Project

Conservation genetics of Boswellia papyrifera (Del.) Hochst: A commercially valuable resin producing wood-land tree species in Ethiopia

The value of genetic information in identifying populations that deserve priority for conservation make the study of genetic variation central to field of conservation genetics (Petit et al., 1998). Genetic variation is one of the most important components in maintaining population viability and resilience to environmental stress.

Project description

The value of genetic information in identifying populations that deserve priority for conservation make the study of genetic variation central to field of conservation genetics (Petit et al., 1998). Genetic variation is one of the most important components in maintaining population viability and resilience to environmental stress. Conservation genetics among other things aimed at preserving a considerable portion of a species' genetic variation (Frankham, 2009). However, the relationship between genetic diversity and population resilience might depend on the type of genetic variation, that is, whether it is neutral or adaptive type of genetic variation  (Kohn et al., 2006). Neutral genetic variation may not be indicative of the adaptive evolutionary potential, rather the adaptive genetic diversity which is contained in a limited set of genes in functional regions of the genome play roles in fitness (Booy et al., 2000; Tienderen et al., 2002; Ouborg and Angeloni, 2010). Empirical studies that relate neutral genetic diversity and fitness in natural populations are limited and the findings are variable (Ouborg and Angeloni, 2010). Few of them show a weak positive correlation between genetic diversity and fitness components (e.g.Leimu et al., 2006) while others failed to find such relationships (e.g Merila and Cronkrak, 2001). Review works by Booy et al. (2000) revealed that there is no general relationship between neutral genetic diversity and population fitness to environmental stress. In other words, high genetic diversity does not guarantee high adaptation potential unless the diversity constitutes specific genes that enable the population to stand against the test of the new environmental stress.

Complementing neutral genetic variation with data on adaptive genetic variation would enable a better understanding of the genetic health, historical and adaptive uniqueness of populations for conservation consideration. Nonetheless, determining fitness-related genetic variation in natural populations are complex (Booy et al. 2000; Tienderen et al., 2002), because assessing adaptive traits, identifying the genes that potentially affect such traits and developing the marker systems to detect the variation requires advanced technology (Trenderen et al., 2002; Kohn et al., 2006) and whether the expense in time and effort justifies the potential returns is also questionable (Kohn et al., 2006). Consequently, for practical conservation problems, characterizing the structure of neutral genetic variations that have been generated independently of selective forces as a result of different migration route, demographic processes and gene flow pattern at different spatial scale remain crucial to provide key information upon which planning conservation of  genetic resources can be based (Booy et al., 2000; Debout et al., 2011). Neutral genetic markers are valuable tool to 1) provide evidences of mutation events, recent and historical gene flow useful to evaluate spatial genetic structure and the historical divergence of populations, 2) to infer the influence of important population demographic processes such as expansion, fragmentation and bottlenecks on the level and spatial structure of genetic variation (Kohn et al., 2006; Ouborg and Angeloni, 2010), and 3) to diagnose the genetic viability of populations which is reflected as estimates of inbreeding, effective population size and rate of gene flow between individuals and population.

B.papyrifera is tree species ecologically confined to the Terminalia-Combretum deciduous broad-leaved woodlands in Ethiopia (Ogbazgh et al., 2006). Dry-lands contain highly resilient species adapted to the seasonal pattern of rainfall and recurrent drought that prevail in these ecosystems. However, powerful forces of disturbances such as habitat degradation and overexploitation of species overpower the resilience of dry-land ecosystems and constitute potentially serious threats to the genetic resources (Janzen, 1988; Mortimore et.al., 2009). The Terminalia-Combretum woodlands in Ethiopia have been facing several challenges that the potential range of forest communities with B.papyrifera is greatly reduced and degraded (Ogbazghi et al., 2006; Abiyu et al., 2010). The species is under increasing threat from decline in population size (Ogbazgh et al., 2006), decline in seed set of over-tapped trees, high seedling mortality (Abiyu et al., 2010), and high adult mortality (Groenendijk et al., submitted). Despite the degradation of B. papyrifera populations and ever increasing destruction of its habitat, the current management and conservation guidelines do not take genetic information into account as this information is still completely lacking for this tree species. This project aims at determining the level and spatial structure of neutral genetic diversity and how the genetic and demographic processes have influenced the pattern of genetic diversity. It specifically aims at:

  1. developing of markers for B. papyrifera using EST sequences
  2. investigating phylogeographic patterns of B. papyrifera
  3. characterizing genetic diversity within and among B. papyrifera populations in Ethiopia
  4. characterizing gene flow and fine-scale spatial genetic structure within a population

The study employs neutral genetic markers(SSRs) which will be developed based on EST sequences in leaf and bark tissues of the species. The set of ESTs also gives an overview of the genes being expressed in this species, and possibly list of putative markers (SNP). The phylogeography of B. papyrifera will be studied using SSRs developed from cpDNA (cpSSRs). The outcomes from the study will contribute to make reasoned decision on identifying and prioritizing units for conservation and provide information upon which conservation strategies can be identified.