The Phylogeny And Geographical Distribution Pattern Of Discogobio Of Cyprinidae

The genus Discogobio is a member of the subfamily Labeoninae, family Cyprinidae. Due to having a disc and obvious horseshoe-shaped skin fold, it became a single genus. The fishes of Discogobio, having a little shape, adapt to living in the rush waters, and inhabit in the submarine rivers, streams and lakes. They mainly distribute to Nanpanjiang, Yuanjiang and Pearl River in Guizhou, Yunnan and Guangxi.There are 9 species in the past recorded, but with the specimens gathering spots increasing, many species boundaries of Discogobio changed blurred, Some specimens cann't be classified into recorded species. Furthermore, the researches of Discogobio in the past focused on exterior shape and characteristic contrast. The aim was discrimination species. Only in the recent time, the researches were refered to species differentiation and adapting, and only to the evolution of a or some organs, never refered to the origin and phylogeny of the whole genus. Based on these questiones, it was necessary to do a deep research and find new taxonomy evidences to make these species classification more credible. Now the aim of this work was to demonstrate the origin and evolution of Discogobio and the water system differentiation.This work including classification, phylogeny and geographic distribution pattern of Discogobio. 217 specimens were used for classification, and 18 specimens for muscle and bone observation. The taxonomic results showed that there were 13 species in all. Due to Discogobio polylepis having 45-46 laterial line scales, and Discogobio macrophysallidos having 41-44 laterial line scales, there being distinct interval between this two species, so the vality of Discogobio polylepis had been restored. After examined the specimens from Wenshan, the species classified originally into D. yunnanensis and D. brachyphysallidos, are really two new species, and with one another new species, there being three new species in all.Discogobio antethoracalis can be distinguished from all other species of Discogobio congeners by the following characters: oral sucking disc large with its posterior edge reaching vertical of anterior margin of eye (vs. small with its posterior edge not reaching vertical of anterior margin of eye in D. longibarbatus, D. macrophysallidos, D. polylepis and D. poneventralis n. sp); snout with small tubercles (vs. with a pair of large tubercles in D. bismargaritus, D. laticeps, D. multilineatus and D. tetrabarbatus); body depth more than 17.2% SL (vs. less than 16.7 in D. elongatus); mid-ventral region anterior to pelvic-fin insertion scaleless (vs. scaled in D. longibarbatus, D. macrophysallidos, D. bismargaritus, D. laticeps, D. multilineatus and D. tetrabarbatus or naked only restricted to belly in D. yunnanensis); snout rounded, not projected (vs. slightly pointed, projected in D. brachyphysallidos); prepectoral length 16.3-18.3% of SL (vs. 19.1-22.0 in D. brachyphysallidos); interorbital width 52.5-60.9% of HL (vs. 44.7-50.0 in D. brachyphysallidos); HL 17.5-20.6% of SL (vs. 20.8-22.8 in D. brachyphysallidos or 20.6-24.4 in D. propeanalis n. sp); head depth 13.2-14.2% of SL (vs. 14.4-16.6 in D. propeanalis n. sp); anus to anal-fin origin distance 25% posterior end of pelvic-fin base to anal-fin origin distance (vs. more than 25 in D. brachyphysallidos or less than 25 in D. propeanalis n. sp).Discogobio propeanalis can be distinguished from all other species of Discogobio congeners by the following characters: oral sucking disc large with its posterior edge beyond vertical of anterior margin of eye (vs. small with its posterior margin not reaching vertical of anterior margin of eye in D. longibarbatus, D. macrophysallidos, D. polylepis and D. poneventralis n. sp); snout with small tubercles (vs. with a pair of large tubercles in D. bismargaritus, D. laticeps, D. tetrabarbatus and D. multilineatus); body depth more than 17.2% of SL (vs. less than 16.7 in D. elongatus); mid-ventral region anterior to pelvic-fin insertion scaleless (vs. scaled in D. longibarbatus, D. macrophysallidos, D. bismargaritus, D. laticeps, D. multilineatus and D. tetrabarbatus or naked only restricted to belly in D. yunnanensis); central freshly pad of disc nearly oblong (vs. central freshly pad of disc nearly square in D. brachyphysallidos); interorbital width beyond half of HL (vs. less than half of HL in D. brachyphysallidos); pelvic-fin beyond anal-fin origin (vs. not reaching in D. brachyphysallidos); anus closer to anal-fin origin, anus to anal-fin origin distance less than 25% posterior end of pelvic-fin base to anal-fin origin distance (vs. more than 25 in D. brachyphysallidos or equal to 25 in D. antethoracalis); HL 20.6-24.4% of SL (vs. 17.5-20.6 in D. antethoracalis); head depth 14.4-16.6% of SL (vs. 13.2-14.2 in D. antethoracalis).Discogobio poneventralis can be distinguished from all other species of Discogobio congeners by the following characters: oral sucking disc small with its posterior margin not reaching vertical of anterior margin of eye (vs. large with its posterior margin reaching or beyond vertical of anterior margin of eye in D. yunnanensis, D. brachyphysallidos, D. elongatus, D. bismargaritus, D. laticeps, D. tetrabarbatus D. multilineatus D. antethoracalis n.sp and D. propeanalis n. sp); rostral pair equal to eye diameter (vs. twice as long as eye diameter in D. longibarbatus); maxillary pair of barbels not reaching posterior margin of oral sucking disc (vs. beyond in D. longibarbatus); mid-ventral region anterior to pelvic-fin insertion scaleless (vs. scaled in D. macrophysallidos); eye visible in ventral view (vs. not visible in D. macrophysallidos); prepelvic length 57.1-58.1% of SL (vs. 52.4-55.6 in D. macrophysallidos); pectoral-pelvic length 40.8-41% of SL (vs. 32.6-35.9 in D. macrophysallidos); HL 17.5-18.4% of SL (vs. 19.8-21.8 in D. macrophysallidos); snout length 44.9-47.2% of HL (vs. 48.9-55.4 in D. macrophysallidos).Compared with the macroscopical shape of Discogobio, P. bamaensis were choosen as outgroup. The research of external shape characters adopt normal measures, muscle comparisons adopt normal anatomise, and skelecton specimens adopt transparence skelecton facture. External measurable, countable, morphologic, muscle and skelecton characters were used to compare macroscopical characters, and 85 steady characters were choosen. The method of out-group analysis was used to decide the evolutionary polarity of character state. The character state of Discogobio being similar or same as ones of P. bamaensis was regard as plesiomorphy, different was apomorphy. A matrix of character states was constituted by this means. The most-parsimonious, strict-consensus and bootstrap 50% majority-rule consensus tree were produced, based on the matrix, with the PAUP and in the Order abd Unorder mode. In whatever mode, the structures of the most-parsimonious, strict-consensus tree were totally the same, and the bootstrap 50% majority-rule consensus tree was a little different. Contrast with the bootstrap 50% majority-rule consensus tree, the most-parsimonious tree showed the evolving sequences among the species and the relations between sister groups, so it could reflect the evolution among the species better. So discussions below were all besed on the most-parsimonious tree. The results were as follows: (1) all species of the genus Discogobio formed a monophyletic clade. (2) in-group was divided into A and B clades, and"D. macrophysallidos and D. longibarbatus"formed A clade, B clade was composed of the other large disc species. (4) B clade was divided into C and D clades, D. bismargaritus, D. laticeps, D. tetrabarbatus D. multilineatus formed C clade, due to they having a pair of large tubercles. (5)"D. yunnanensis, D. brachyphysallidos, D. elongatus, D. antethoracalis n.sp and D. propeanalis n. sp"formed A clade. (6) C and D clades constituted sister group, and then constituted sister group with A clade.The results of geographical distribution patterns were as follows, (1) Jinshajiang, Lvzhijiang, Shundianhe, Nanpanjiang, Panlonghe, Beipanjiang, Xiyangjiang and Hongshuihe were divided into A and B clades,"Jinshajiang, Lvzhijiang, Shundianhe, Nanpanjiang and Panlonghe"formed A clade."Beipanjiang, Xiyangjiang and Hongshuihe"formed B clade. (2)"Beipanjiang, Xiyangjiang and Hongshuihe"formed B clade. They belonged to the Pearl River, and this result matched the present Pearl River situation. (3) A clade was divided into C and D clades. (4)"Jinshajiang and Yuanjiang-Red River"formed C clade. This result showed that Jinshajiang and Yuanjiang-Red River had been connected in the history. (5)"Nanpanjiang and Yuanjiang-Red River"formed D clade. This result showed that Nanpanjiang and Yuanjiang-Red River had been connected in the history.According to the research of phylogeny and geographical distribution patterns, Discogobio appeared in the lake on Yungui plateau, which from the time after ancient Yungui plateau had formed to the time before Nanpanjiang formed. After Nanpanjiang formed, Discogobio fish inhabitated originally in the lake on Yungui plateau was captured by Nanpanjiang. After the uplift of Yungui plateau, large fall between the upriver and mid-lower of the Pearl River came into being. The ancestor of Discogobio evolved two groups, tubercles no differentiation and forming projected snout. The ancient Dianchi originally flowed southerly, into Nanpanjinag, and then flow backwards, into Jinshajiang. So, D. yunnanensis inhabitated originally in the Dianchi was captured by Jinshajiang. Discogobio fish only distributes to the left of Yuanjiang-Red River, which was related to ancient shallow lake or east rivers on the Yungui plateau were captured by the left tributaries of Yuanjiang-Red River. Ancient Discogobio fish inhabitated originally in the Nanpanjiang was captured by Panlonghe, and originally in the Jinshajiang was captured by Lvzhijiang.