Conservation Genetics Of Przewalski’s Horse(Eguus Przewalskii) In China:Implications For Conservation

The Przewalski’s horse (Equus przewalskii) is a flagship species for conservation that once inhabited the Eurasian steppes, but was extirpated in the wild in the mid1960s. The present-day Przewalski’s horse population originated from individuals captured at the turn of the19th century. The captive population went through a severe bottleneck and suffered from inbreeding. Studies of genetic diversity within Przewalski’s horses have been sparse and limited to the captive population. Starting in2001, reintroduction programs were initiated in Xinjiang and Gansu provinces and proved to be one important practice in worldwide conservation biology. However, knowledge on genetic diversity in China’s horse populations is limited, but would help improving the genetic management and assess the success of the reintroduction.This aim of this study was to evaluate the genetic diversity in two captive (Wild Horse Breeding Center, WHBC; Gansu Endangered Species Research Center, GESRC) and one released population (Kalameili Nature Reserve, KNR) of Przewalski horse populations in China using mtDNA, microsatellite, pedigree data and computer simulations during2011-2013. Main results are as listed below:1. The mean PCR success rate of mtDNA control region was96.2%(93.8%-100%) in fecal DNA of Przewalski’s horse, which indicated a high feasibility of using non-invasive sampling approach in the genetic studies on the equids.2. Two mtDNA haplotypes were obtained (PR1, PR2) with a nucleotide difference of1.63%based on105Przewalski’s horses, but quite unequal in regards of haplotype frequency among populations. The PR1was dominant haplotype in three populations, averaging76.2%(60～1.9%), but PR2only accounted for8.1%in KNR population. The analysis of differentiation coefficient test revealed thatGESRC and KNR differentiated significantly (P=0.00267). Probability of Identity (PI) based on haplotypic information was higher than that from dam lines, indicating haplotypic information could be used to evaluate materinal diversity.3. A total of45alleles were identified for the10microsatellite loci in the126fecal DNA samples. Allelic richness (AR) in WHBC, GESRC and KNR was3.77,3.39,3.33, with mean number of3.49. AR in KNR population was lower than that of its founding WHBC population (the Wilcoxon’s signed rank test, P=0.01). The mean expected heterozygosity (HE) was0.49(ranging from0.45to0.52) and0.46(ranging from0.39to0.53) in the WHBC and GESRC respectively, as compared to0.44(ranging from0.32to0.54) in the KNR. When testing the relationship between fp and IR, fm, there was a positive relationship between fp and IR (r=0.50, R2=0.25, P=0.005) and fp was positively correlated with fm (r=0.34, R2=0.12, P=0.014).4. Based on FST, the highest genetic differentiation was estimated between populations in WHBC and KNR (FST=0.115, p<0.05), and the lowest between WHBC and GESRC (FST=0.063, p<0.05). The STRUCTURE Bayesian clustering yielded the most support for three, albeit admixed, genetic subpopulations within8simulated populations of126individuals (Ln P(D)=-2359.02, K=3).5. By means of simulation, a population size of100is required to retain90%of the genetic diversity in the reintroduced population (KNR) over the next100years; The number of immigrants needed to retain90%of rare alleles increased to20every5years, when the starting population was20.6. According to the results above, implications for conservation of Przewalski’s horse are listed below:(1) Managers should make complete and accurate studbook documentation, and timely upload local pedigree information to the International Studbook System of Przewalski’s horse. Molecular and pedigree approaches should be applied. Based on genetic analysis, the structure of the herd could be adjusted to avoid loss of genetic diversity.(2) When founding a released population, it is necessary to select the most distantly related individuals but with appropriate genetic structure. Another important issue to note is to maintain the genetic diversity of original captive population, and meanwhile, to ensure the genetic representation of the released population to minimize the genetic drift and avoid population subdividation.(3) Release sites with a larger carrying capacity should be selected in order to immigrate less individuals to retain rare alleles and save reintroduction cost. Upon release, temporal monitoring is crucial to ensure population maintainance and growth, which are beneficial to retain rare allels. Future reintroduction efforts should determine levels and directions of inbreeding of reintroduction projections and utilize multiple source populations, meanwhile avoiding hybridization with domestic horses.