Fig. 6. Effective migration patterns of Opisopappus
taihangensis and Opisopappus longilobus .
a: Posterior mean migration rates m (on the log10 scale); b: Posterior
mean diversity rates q (on the log10 scale)
3.3 The relationship between SNPs and landscape
factors
A total of 29 SNPs were identified under selection based on theF ST outlier approach implemented in BayeScan
software (q-value < 0.01)
(Support files 3).
Samßada results showed that, in the first 29 (AIC < 17)
effective models, seven landscape factors of Taihang Mountains, average
precipitation in August, average precipitation in November, built-up
land (residential and infrastructure), rain-fed cultivated land,
workability (restricted site management), solar radiation in August, and
soil PH, were closely related with the selected SNPs, which accounted
for 13.8% of total variation revealed by BAYESCAN. Average
precipitation in October in Taihang Mountains accounted for 3.4%, was
significantly correlated with 29 SNP loci (Support files 5).
LFMM analysis revealed that 27 of 29 SNP loci were associated with
average precipitation in August (8.66%), average precipitation in
November (15.75%), built-up land (residential and infrastructure)
(11.81%), rain-fed cultivated land (11.81%), workability (restricted
site management) (11.81%), solar radiation in August (12.6%), soil PH
(14.17%), average precipitation in October (13.39%) (Table 3).
In total, 29 selected SNPs were strongly associated with landscape
features of Taihang Mountains revealed by Samβada and LFMM analysis,
especially average precipitation in November.
The identified selected SNPs were mainly enriched in Carbohydrate
metabolism, Energy metabolism, Translation, Signal transduction and
Transport and catabolism. The genes related with these SNPs regulate
Glycolysis / Gluconeogenesis, Pentose and glucuronate interconversions,
Ribosome, MAPK signaling pathway. In particular, MAPK signaling and
plant hormone signal transduction pathway were found to be involved in
the three genes based on samβada analysis.
4. Discussion
4.1 Landscape features affect genetic characteristics of
Opisthopappus
species
The genetic diversity of O. longilobus was higher than that ofO. taihangensis , which is consistent with previous studies (Ye et
al., 2021). Being an ancestral species of Opisthopappus , more
genetic variation might be acculmated into this species than its
descendant O. taihangensis . Furthmore, the OLb group of O.
longilobus had the highest genetic diversity than other three groups.
It suggested that this group might be a diversity centre for O.
longilobus, even for the whole Opisthopappus genus, especially
the areas of HLT and THDXG populations, which had the highest genetic
diversity among all populations (Ren et al., 2022) (Table 1).
For the two groups of O. longilobus , the OLa group had a relative
lower genetic diversity than OLb group (Table 1). The populations of OLa
group are at the margins of geographic range. Generally, the marginal
populations are often thought to be poorly adapted to their environment
(Bontrager and Angert, 2019). Howover, a gene exchange/flow can provide
beneficial genetic variation and may facilitate adaptation to
environmental change (Li et al., 2021b; Wood et al., 2021). This is
because that gene flow is expected to increase heterozygosity and
reintroduce variation that can allow for masking or purging of fixed
deleterious alleles (Ferrer et al., 2021; Muola et al., 2021).
Unexpected, the OTc group (central populations) of O.
taihangensis presented a slightly lower genetic diversity than that of
OTd group (marginal populations) (Table 1). This might be related with
the relative higher gene flow from OTd to OTc (Fig. 3).
Multilocus analysis resulted in significantly negativeF IS values for the
inbreeding coefficient, indicating
the presence of heterozygote excess for Opisthopappus species.
The phenomenon of excess heterozygotes (e.g., Carapa procera ,Dioon edule , Prunusavium ) has widely been observed in
other species. In general, the main reasons for the excess of
heterozygotes are low number of individuals in the breeding population,
overdominance, stepwise selection for homozygotes and negative
assortative mating (Million, 2021; Stoeckel et al., 2006). The excess of
heterozygotes implied that the species possessed a rich genetic
diversity that favored the adaptation of the species to different
environments (Tay Fernandez et al., 2021; Theodoridis et al., 2021).
Because of the lack