4.1 | Effects of geological changes on the evolution ofSinocyclocheilus in the central Yunnan Basin
The Yunnan-Guizhou Plateau in China has a high concentration of plateau
lakes, with most forming as a result of stratigraphic fault subsidence
in the late Cenozoic. Located in the hinterland of the Yunnan-Guizhou
Plateau, Dianchi Lake is the largest freshwater lake in Yunnan Province.
The basin of Dianchi Lake has experienced extensive geological and
climatic changes over the past 3.4 million years. Specifically, with the
uplift and subsidence of the lake basin and the associated expansion and
contraction of the lake area, Dianchi Lake which was previously a part
of the Nanpanjiang River system, has transformed into a tributary source
for the Jinsha River in a “river capture event” (Zhu et al., 1991).
Such changes in the landscape have made it possible for aquatic
organisms that were once restricted to the Nanpanjiang River to colonize
the Yangtze River Basin, thereby expanding their geographic ranges.The
structural evolution of Dianchi Lake is a notable feature of the
geomorphology and neotectonics of the Yunnan Plateau. The population
structure of Sinocyclocheilus fishes inhabiting the region also
reflects the complex geological development of Dianchi Lake.
Dianchi Lake is a fault subsidence lake of plateau limestone formed by
the Tertiary Himalayan Orogeny. During the Yanshan Movement, the Yunnan
Plateau experienced stratigraphic uplift, folding, and faulting. These
processes led to the formation of high mountains and basins and shaped
the present landform. As a result of strong neotectonic movement that
occurred up to the Himalayan movement in the late Cenozoic, a large
north-south trending fault spanning was formed in the Xishan Mountains.
When the fault collapsed, Dianchi Lake was formed by the accumulation of
water during the initial formation of the resulting graben. The
formation of Dianchi Lake comprised three main stages, which also
influenced the population structure of Sinocyclocheilus fishes in
the region.
The first stage of lake formation occurred approximately 3.4 Ma.
According to the divergence times of Sinocyclocheilus in the
Central Yunnan Basin, we speculate that the common ancestor ofSinocyclocheilus in the Central Yunnan Basin, the “Central
Yunnan Group,” colonized the lake during this period.
The second stage of lake formation saw the expansion of the lake basin
during the early and middle Pleistocene (2.59~0.13 Ma).
The early Pleistocene (2.59~0.78 Ma) saw a gradual
intensification of the uplifting and depression of the Dianchi Lake
Basin relative to the surrounding fault block mountains. As the northern
section of the basin continued to subside, the lake deepened and its
area expanded. During this time, the “Central Yunnan Group”
differentiated into the “Mile Group” and the other groups. During the
middle Pleistocene (0.78~0.13) Ma, the lake basin
accumulated water, forming the main lake. This period corresponded with
the differentiation of Sinocyclocheilus fish populations in
central Yunnan, a process that may have been driven by the specialized
ecology of Sinocyclocheilus and the distinct geological
conditions of Dianchi Lake. Notably, populations ofSinocyclocheilus (C and F) in Dianchi Lake and in Fuxian Lake
differentiated 0.84~0.49 Ma, which is related to the
original Nanpan River system in Dianchi Lake. This is further supported
by the fact that the capture of Tanglang River occurred after this
period.
The third stage of lake formation occurred during the period in which
the Tanglang River was captured (0.126~0.01 Ma), leading
to a transformation of the water system of the ancient Dianchi Lake. The
Dianchi Lake, originally belonging to the Nanpan River water system, was
transformed into a tributary source lake of the Jinsha River water
system. Bailong vauclusian spring (FM) and Long vauclusian spring (JW)
happened to be at the intersection of the Nanpan River water system and
the Jinsha River water system. Due to the contraction of lake with
decline of water level, differentiation (0.12~0.05 Ma)
occurred (Fig. 3) .