Demographic history of Cycas bifida and C.
micholitzii and conservation implications
In the long course of history, plants would expand or shrink to cope
with environment (e.g., glacial cycles) and habitat changes (e.g.,
habitat destruction). What’s more, some plants become endangered or
extinct. According to our field survey, C. micholitzii has more
populations and larger distribution ranges than C. bifida(Supplementary Table S1). Our IMa simulation analysis also revealed that
the effective population size of C. micholitzii was larger than
that for C. bifida (Figure 5a), and the EBSP results further
revealed a larger effective population size in C. micholitziithan in C. bifida (Figure 7). In addition, the effective
population sizes of the both species were larger than that of the
ancestral species (Figure 5a), which indicated that they had been
experienced population expansion once. Based on the EBSP analysis both
species have experienced small-scale population expansion during the
Upper - Pleistocene (Figure 7). The Quaternary climatic oscillations
made deeper impacts on the population dynamics of C. bifida which
experienced constant small-scale expansion, then small-scale contraction
and a recent re-expansion, while little impacts on C.
micholitzii . According to previous researches (Y. C. Chiang et al.,
2009; Xiu Yan Feng et al., 2017; Xiu Yan Feng, Wang, & Gong, 2014; X.
Y. Feng et al., 2016; Y. Q. Gong et al., 2015; Jian Liu et al., 2015;
Zhan, Wang, Gong, & Peng, 2011; Y. Zheng et al., 2016), the glacial and
interglacial climatic fluctuations have had varying degrees of
influences on some Cycas species, and distinct demographics were
detected in them. Of those, Cycas revoluta (Y. C. Chiang et al.,
2009), Cycas taitungensis (Y. C. Chiang et al., 2009) andCycas guizhouensis (X. Y. Feng et al., 2016) have experienced
population expansions during the most recent glacial period, whileCycas debaoensis (Zhan et al., 2011), Cycas simplicipinna(Xiu Yan Feng et al., 2014), Cycas diannanensis (Jian Liu et al.,
2015), Cycas multipinnata (Y. Q. Gong et al., 2015), Cycas
dolichophylla (Y. Zheng et al., 2016) and Cycas segmentifida(Xiu Yan Feng et al., 2017) have experienced population contractions.
Improving knowledge about the demography of Cycas species will
help us to predict how they will react to environmental fluctuations in
the future and to draft conservation strategies for them. Considering
that C. micholitzii had higher genetic diversity and accumulated
more variation than C. bifida , it is capable to adapt to the
changeable climate and environment in the future (DeWoody, Harder,
Mathur, & Willoughby, 2021). On the other hand, massive illegal digging
of C. bifida for trading or ornaments was occurred, and its
habitat was destroyed more seriously for planting commercial or
medicinal crops, which reduced its number. Therefore, more attention
should be paid to protecting the genetic diversity of C. bifida .
Of course, C. micholitzii cannot be ignored.