Danxia landform occurring sporadically in southern China is a unique type of petrographic geomorphology. It has nurtured about 400 rare or threatened plant and animal species, whose diversity, ...endemism, and conservation have called increasing scientific and public attentions. Among them,
Primulina danxiaensis
(W. B. Liao, S. S. Lin, and R. J. Shen) W. B. Liao and K. F. Chung is a tiny perennial grass species recorded only in Mount Danxia, a natural World Heritage Site as part of China’s Danxia. In this study, restriction site-associated DNA sequencing (RAD-seq) was performed to investigate genetic diversity among these 12 populations of
P. danxiaensis
. A total of 432,041 variant sites were detected in 84,779 loci across 94 samples. The expected heterozygosity (
H
E
) ranged from 0.017 to 0.139. Bottleneck signals were detected in most populations, Tajima’s D tests showed that most loci could be under recent positive selection, and one of the six positively selected loci identified by BayeScan was annotated as tRNA
Glu
, which may contribute to the species’ adaptation to shady environment. STRUCTURE analysis and phylogenetic tree showed that the 12 populations of
P. danxiaensis
could be divided into four gene pools (clades) corresponding to their geographic locations, and significant correlation was observed between genetic and geographic distances. Our study demonstrated that
P. danxiaensis
maintained a middle level of genetic diversity and strong population structure; geographic distance could be an important factor limiting gene flow among populations of
P. danxiaensis
, which were only sporadically recorded in Mount Danxia.
Background
The picturesque limestone karsts across the Sino-Vietnamese border are renowned biodiversity hotspot, distinguished for extremely high endemism of calciphilous plants restricted to caves ...and cave-like microhabitats that have functioned as biological refugia on the otherwise harsh habitats. To understand evolutionary mechanisms underlying the splendid limestone flora, dated phylogeny is reconstructed for Asian
Begonia
, a species-rich genus on limestone substrates represented by no less than 60 species in southern China, using DNA sequences of nrITS and chloroplast
rpL16
intron. The sampling includes 94
Begonia
species encompassing most major Asian clades with a special emphasized on Chinese species.
Results
Except for two tuberous deciduous species and a species with upright stems, a majority of Sino-Vietnamese limestone
Begonia
(
SVLB
), including sect.
Coelocentrum
(19 species sampled) and five species of sect.
Diploclinium
,
Leprosae
, and
Petermannia
, are rhizomatous and grouped in a strongly supported and yet internally poorly resolved clade (Clade
SVLB
), suggesting a single evolutionary origin of the adaptation to limestone substrates by rhizomatous species, subsequent species radiation, and a strong tendency to retain their ancestral niche. Divergence-time estimates indicate a late Miocene diversification of Clade
SVLB
, coinciding with the onset of the East Asian monsoon and the period of extensive karstification in the area.
Conclusions
Based on our phylogenetic study,
Begonia
sect.
Coelocentrum
is recircumscribed and expanded to include other members of the Clade
SVLB
(sect.
Diploclinium
:
B. cavaleriei
,
B. pulvinifera
, and
B. wangii
; sect.
Leprosae
:
B. cylindrica
and
B. leprosa
; sect.
Petermannia
:
B. sinofloribunda
). Because species of Clade
SVLB
have strong niche conservatism to retain in their ancestral habitats in cave-like microhabitats and
Begonia
are generally poor dispersers prone to diversify allopatrically, we propose that extensive and continuous karstification of the Sino-Vietnamese limestone region facilitated by the onset of East Asian monsoon since the late Miocene has been the major driving force for species accumulation via geographic isolation in Clade
SVLB
. Morphologically species of Clade
SVLB
differ mainly in vegetative traits without apparent adaptive value, suggesting that limestone
Begonia
radiation is better characterized as non-adaptive, an underappreciated speciation mode crucial for rapid species accumulations in organisms of low vagility and strong niche conservatism.
Microbial Life of Cave Systems Summers Engel, Annette; Jones, Daniel; Lavoie, Kathleen ...
2015, 2015-10-16, Letnik:
3
eBook
The earth's subsurface contains abundant and active microbial biomass, living in water, occupying pore space, and colonizing mineral and rock surfaces. Caves are one type of subsurface habitat, being ...natural, solutionally- or collapse-enlarged openings in rock. Within the past 30 years, there has been an increase in the number of microbiology studies from cave environments to understand cave ecology, cave geology, and even the origins of life. By emphasizing the microbial life of caves, and the ecological processes and geological consequences attributed to microbes, this book provides the first authoritative and comprehensive account of the microbial life of caves for students, professionals, and general readers.
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