3.7 | Demographic history of B. schroederi
To reconstruct the demographic history of B. schroederi , and explore the relationship with the giant panda, we used the pairwise sequentially Markovian coalescent (PSMC) model to estimate the changes of the effective population size of both B. schroederi and the giant panda within the last one million year (H. Li & Durbin, 2011). PSMC analysis showed that the effective population sizes (Ne ) ofB. schroederi and the host giant panda have almost exactly the same trend from 300 Kya (thousand years ago) to 10 Kya (Fig. 5a), but the change of effective population size of the roundworms showed a slight lag. The effective population size of the giant panda declined significantly during the last two Pleistocene glacial periods (300-130 Kya and 50-10 Kya), and the effective population size of the roundworm also reached a historical low level. The most obvious change occurred in the Greatest Lake Period (50-30 Kya), where the effective population size of the two species reached their pinnacle (Jinchu & Wei, 2004). In addition, we applied Multiple Sequentially Markovian Coalescent (MSMC) method (Schiffels & Durbin, 2014) to infer the recent demographic events ofB. schroederi and performed 5 repetitions (each repetition used 4 individuals per population). The effective population size of roundworms showed a sharp decline in the last 10,000 years, which also may be related to the host population dynamics. Studies have indicated that human activities may have caused the decline of the giant panda population in the past few thousand years, and the roundworm population may be affected by this.