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.